AVS-48SI PICOBRIDGE - rockgateco.com · Cryogenic AC Resistance Bridge and Temperature Controller...

PICOWATTVeromiehentie 14FI-01510 VANTAA, Finlandphone 358 50 3375192Internet: www.picowatt.fie-mail: [email protected]

AVS-48SI PICOBRIDGE®

High-performanceCryogenic AC Resistance Bridge and Temperature Controller

User Guide for Operation viaUSB/RS232 Serial Interface

or LabView

Firmwareversion 1R1 User Guide

AVS-48SI PICOBRIDGE

Revised: 2017-03-27 avs48si_serial_operation_user_guide.indd RV-Elektroniikka Oy PICOWATT

CONTENTSWARRANTY 3

SPECIFICATIONS 4

STARTING TO USE THE AVS-48SI 7CONNECTIONS W version with wire connection 7 Fversionwithopticalfibrelink 8

SENSOR WIRING 9PHYSICAL FRONT PANEL 9PHYSICAL REAR PANEL 10

PART I - SERIAL OPERATIONAVS-48SI SERIAL COMMAND SUMMARY 15INTRODUCTION 18SHORT BRIDGE TUTORIAL 19SERIAL COMMANDS AND QUERIES 20CALIBRATION 29OTHER COMMANDS 33CABLE SPECIFICATIONS 35RE-PROGRAMMING ARDUINO 36TROUBLE SHOOTING 37

PART II - LABVIEW OPERATIONINTRODUCTION 41PROGRAM INSTALLATION 42SHORT TUTORIAL 43THE AVS48SI.VI PROGRAM Front tab 45 Settings tab 53 Service tab 59

CALIBRATION 61

TEMPERATURE READOUTR/Tconversionfiles 65Assigningtosensors 66

OPENING THE INSTRUMENT 68

INDEX 69


AVS-48SI PICOBRIDGE


WARRANTY

Picowatt warrants the AVS-48SI hardware to be freefromdefectsinmaterialsandworkmanship.Ourliability under this warranty is limited to repairing or replacing any instrument or part thereof which, within three (3) years after the shipment to the originalpurchaser,provesdefective.Thiswarrantyisvoid if the instrument has not been used according to the instruction manual, or if it has been used under exceptionalenvironmentalconditions(seebelow).

In need of warranty repair, the instrument must be returned to Picowatt, prepaid , and with a detailed description of the fault or misfunction following the instrument.

The instrument must always be returned complete withthepreamplifier,preamplifiercableandwiththemicroprocessorunit.Thisisbecausethenthecalibra-tionandperformanceoftheAVS-48SIcanbecheckedandguaranteed.

The name, address and e-mail address of a person who is able to give supplementary information should be includedwheneverpossible.Iftherepairwascoveredby warranty, Picowatt will return the instrument on ourcostusinganeconomicalshippingmethod.

If no fault is found, or if there is a strong indication that the warranty is void, the purchaser is charged for thereturnfreightandcostsinadditiontotherepair.Itis recommended that Picowatt be contacted prior to shipment.Wecanpossiblygiveinstructionsforaddi-tional tests or simple component replacements so that unnecessaryshipmentsmaybeavoided.

Caution: The AVS-48SI Picobridge is a delicate laboratory in-strument.Ithasbeendesignedonlyforthepurposeofmeasuringresistancesofpassiveresistivenetworks.Usingthisinstrumentforany other purpose will void the warranty and may cause permanent damagetotheinstrument.BynomeansshouldtheAVS-48SI be used to measure internal resistances of power supplies, batteries, capacitors oranyotherdeviceswhichcansupplyenergytothebridgeinput.TheAVS-48SI has been designed to operate in a laboratory environment, which means normal living room atmosphere, temperature, humidity andpurityofair.Theunitdoesnottoleratecontinuousvibration or hardshocks.

RV-ElektroniikkaOyPicowattVeromiehentie 14FI-01510 VANTAAFINLANDtelephone +358 50 337 5192email:[email protected]

LabView is a trade mark of National Instruments, USA.Picobridge is a registered trade mark of RV-Elektroniikka Oy


AVS-48SI PICOBRIDGE


Signal Inputs and Outputs

(rear panel BNC connectors)

ANALOG OUTPUT Calibrated voltage output 0...+3Vfromtheanalogcircuitry.

(ROUT=100Ω,Range=3Ω,30Ω..etc.)

Analog output can also be set to be the control error VCerr,filteredbytheanalogfilter.

CONTROL SET POINT DAC voltage output cali-bratedto±100µV.AvailablealsowhentheTCoptionisnotinstalled.VSetp=0.005...+2.99V.Step50µV.

CONTROL ERROR OUTPUT Voltage output VCerr=-3…+3Vfromtheanalogcircuitry.

Notfilteredinordertominimizedelaysinthetemperaturecontrolloop.Controlpolaritycanbechangedfromsoftware.Availablealsowhentemperaturecontrollerisnotinstalled.

ACMONITORAmplifiedACsignalfromthesensor.Fortrouble-shootingandforcheckinglow-frequency interference and noise levels withanoscilloscope.BNCwithgroundedjacket.

*HEATER OUTPUT Temperature controller’s heateroutputisanegativecurrentsource.Positive terminal is grounded to instrument caseandmainsearth.Maximumcompli-ance 12-13 Volts and maximum current about 250mA.Connectiontoheaterusingoneortwocoaxialcables.

*EXTERNAL HEATER DRIVE The con-troller’s heater can be driven by an external voltage0…+3V.Selectionbetweeninternal

( )/ Range *3O sensorV R V=

( ) ( )Cerr O setp setp OV V V or V V= − −

SPECIFICATIONS

(Specificationsmarkedwith*areapplicableonlywhentheoptionaltemperaturecontrollercardisinstalled).

RANGE 0-3Ω...0-30MΩ8ranges

EXCITATION 3µV…10mV RMS 8 excitation ranges, square wave current, 12.5/13.64/15Hz.Excitationcurrent=excita-tionvoltagedividedby1/3oftherange.

CHANNELS 4-wireconnectedchannels#1-7.2-wire mode for any sensor is selectable by software.Differencebetween2-and4-wirereadingscanbeusedfordiagnostics.Channel#0 is reserved for measuring internal reference resistors.

INPUTCONNECTOR DC37S(female).Mating(user’s)connectortypeDC37P.All7channels are pin-to-pin compatible with the wiringoftheAVS-47xsensors0-6.

SENSOR GROUNDING Floating inside the cryostat (recommended default) or I- lead groundedtothecryostat.

MAXIMUM CURRENT LEAD RESISTANCE 3Ωrangeand10mVexcitation:2*10Ω 3Ωrangeand1mVexcitation:2*100Ω 30Ωrangeand10mVexcitation:2*100Ω Higherrangesandanyexcitation:2*1kΩ

INPUTCAPACITANCE Max.1nFineachoranylead.Inputcapacitanceiscancelledbyashape-basedcapacitancecompensationcircuit.

INPUT NOISE VOLTAGE Typically 5nV/ at13.64Hz.

SPEED Time needed for the signal to reach a goodfinallevelwhenstepisfrom0to2/3ofthe range:-About6secondsfor10mVexcitation- About 12 seconds for 3µV excitation

ANALOG FILTER Residues of the carrier are removed from the analog output by a 3rd or-derBesselfilterwitha3dBroll-offfrequency

Hz

ofabout1.2Hz.Filteringisnotappliedtothecontrol error VCerr for avoiding delay in the controlloop.


AVS-48SI PICOBRIDGE


Analog PID Temperature Controller (option)

*HEATERRESISTANCE Nolimits,but100Ωistherecommendeddefault.Maximumpoweris obtained when RH = 50Ω.

*HEATER POWER 18 logarithmically spaced powerrangesfrom1µWto1.8Wintoa100Ωheaterandfrom0.5µWtoabout3Wintoa50Ωheater.Ratiobetweenpowerofadjacentranges is

*PID PARAMETERS 14 logarithmically spaced proportional gains GP from 1 to 1000012 logarithmically spaced integrator gains GI

11 logarithmically spaced derivator gains GD (modifiedresponse)

*TRANSFER FUNCTION

The heater power - not current - is a linear functionofthecontrolerror.Thiscanimprovestabilitywhenthepowerlevelvaries.

Other

POWER INPUT The AVS-48SI Picobridge features three options for supplying power:1) 90-250V50-60Hz0.1Amainsvoltage

(safety earth lead is mandatory)2) 18V50-60Hz1Asafelowvoltage(allows

yourownpowerwiringandfiltering).3) 12V1.5ADCbatteryinpute.g.forhunt-

ing interference due to ground loops or mainspowerline.

( )heater P Cerr I Cerr D Cerr sense

2heater heater heater

I G * V G V G * V / / 3R

P =I * R

dt d dt= + +∫

drive (analog PID circuitry) and external drive ismadebyashort-circuitpiece.

EXTERNAL CLOCK I/O This I/O can be used to operate the bridge at a non-standard frequency.Theexternalsignalmustbe0…+5V square wave signal

(Insteadof13.64,usethecurrentlyselectedexcitationfrequency12.5/13.64/15.0Hz)If not loaded, this I/O outputs a frequency of 600Hz(0…+5Vsquare).

USERDAC DACvoltageoutputfrom0.005Vto2.99Vcalibratedto±100µV.RearpanelBNCconnector.Settlingresolution50µV.

*13.64600

EXTPSD

FF HzHz

=

RESOLUTION AND CALIBRATION ACCU-RACY

TheRMSresolutionisheredefinedasthestandarddeviationofnon-filteredA/Dconver-sions.Digital filtering reduces these figures approximately by a factor of sqrt(N), where N is the filter length in samples.

The standard deviations are measured us-ing room temperature sensors, which means that resistor noise is dominating when resist-anceishigh.

Peak-to-peakresolutionisabout5timesworsethantheSTDresolution.

One volt corresponds to 1/3 of the measur-ingrange(e.g.1volton300kΩrangecorre-spondsto100kΩ).

When excitation is high and S/N ratio is good, accuracy of the calibration is deter-mined by the ohmmeter used for measuring thereferenceresistors.Whenexcitationislowand S/N ratio is poor, calibration accuracy be-comesmainlydependentonthepeak-to-peaknoiseoftheaveragedsignal.Onthelowest3μVexcitationrange,asmanyas800readingsareaveragedbythecalibrationprogram.

5 10


AVS-48SI PICOBRIDGE


Single-conversionSTDresolutions.Room-temperaturedecaderesistorsweremeasuredontheirrespectiverangesandallexcitations.Thelow-excitationbehaviourofthe30MΩrangeisduetoreducedgain.Readthegraphasfollows:1kΩsensorismeasuredon3kΩrangeand10µVexcitation.Thegraphgivesasingle-conversionSTDofabout6E-4V*3kΩ/3V=0.6Ω.Anaverageof100conversions(about20seconds)reducesnoisetoabout60mΩ.

1.00E‐05

1.00E‐04

1.00E‐03

1.00E‐02

3 30 300 3000 30000

Single‐sided

max. error

Excitation (uV)

Calibration Accuracy

3R

30R

300R

3K

30K

300K

3M

30M

RANGE

At high excitations, calibration accuracy is worse than the resolution because of the performance limits of thecalibratingohmmeter.Accuracyatlowexcitationsisbetterthanresolution,becauseverylongaveragesareusedforsuppressingnoise.Valuesoftheaboveexamplegiveaccuracyof±1.5E-4V*3kΩ/3V=±0.15Ω.


AVS-48SI PICOBRIDGE


STARTING TO USE THE AVS-48SI

Unpack the shipment

The shipment should contain the following (if no options):

1.AVS-48SIMainUnit(19”)2.AVS-48SIPreamplifierUnit3.AVS48SI-Serial/USB-Wor-FCPUunit(second

alternative,ifopticallinkwasordered)4.5-meterPreamplifierCable25-way

(PR25P25P25W5M)5.5-metercableAVS-48SI<=>CPUunit

(PB9P15P6W5M)6.1.5-metercableCPUunit<=>Computer

(RS9P9S7W1.5M)7.Powermainscord8.3-waymaleDINplug(PREH71430-030)

for the alternative 18V AC power supply9.4-waymaleDINplug(PREH71430-040)

for the alternative 12V DC power supply10.1Aslowblowsparefuse(rearpanel)5x20mm11.Pre-wiredMolexconnector(22-01-2045)for

measuring reference resistors12.TwomaleDC37Pplugswithmetalshellsfor

sensor connections13.37-wayshort-circuitplugforprotectingthepre-

amplifierinput(ispluggedintotheinput).14.+12VwalladapterforpoweringtheCPUunit

Only if included in the order:

15.TemperatureControllerOption,installed

16.National Instument’s USB-232 converter with its installation software (NI 778472-01)

17.AVS48SI-PicolinkopticalReceiver/transmitterunitifopticallinkwasordered.

18.5or10-meterOpticalcable

19.1.5metercablebetweenAVS-48SIMainUnitanditem17.Thisreplacesitem5,whichisomittedwhenAVS48SI-Picolinkisordered(PB9P15P6W1.5M).

Install the USB-232 Converter

Before obtaining a USB-232 converter, verify its compatibilitywithyourplatform.OurCPUboxwith ArduinoMega2560usesRS232 in its simplest andmostcommonconfiguration:onlyRXD,TXD andGroundwires,nohandshaking,9600bauds,8databits,noparityandonestopbit.

Follow the manufacturer’s instructions on how to installtheirconverteranditsdriver.UseWindowsControl Panel’s Device Manager or National Instu-ments’ Measurement and Automation Explorer for findingtheserialportnamethatyouwilluse,eitherdirectlyorviatheconverter.

CONNECTING THE AVS-48SI

WIRE CONNECTION, NO OPTICAL LINK

Connectthepreamplifierunittothemainunitusingthe 5 meter long 25-way cable with DB25P connec-torsatbothends(cabletypePR25P25P25W5M).Tighten the connectors properly, a good ground con-nectionisimportant.

Connect the AVS48-USB/Serial-W CPU unit to the AVS-48SI main unit by the 5 meter long cable that has 9-pin DE9P and 15-pin DA15P connectors (ca-bletypePB9P15P6W5M).

Connect the CPU unit to your computer or to the USB-232converterbythe1.5meterlongcablethathas male and female 9-pin DE9 connectors (cable typeRS9P9S7W1.5M).

Verify that there is the supplied 37-way short-circuit connectorpluggedintotheAVS-48SIpreamplifierinput.

ConnecttheAVS-48SImainunittomainspower.The instrument has a universal power supply for 90-250V.Switchonthemainunit.Greenpower-onlightwillturnon.

Connect the CPU unit to mains using the 12V mainsadapter.SomeactivityontheAVSfrontpanelLEDsshowsthattheCPUhasbooted.

CheckthevoltageontherearpanelANALOG OUTconnector.Itshouldbenearto1V.


AVS-48SI PICOBRIDGE


OPTICAL FIBRE CONNECTION

(If the AVS-48SI was shipped with the optional AVS48SI-Picolink).

Connectthepreamplifierunittothemainunitusingthe 5 meter long 25-way cable with DB25P connec-torsatbothends(cabletypePR25P25P25W5M).Tighten the connectors properly, a good ground con-nectionisimportant.

ConnecttheAVS48SI-PicolinkBoxtotheAVS-48SImainunitusingthe1.5meterlongcablewith9-way DE9P and 15-way DE15P connectors (cable typePB9P15P6W1.5M).Thisboxhasonlyopticalisolators,nodigitalintelligence.ThereforeitcanbeplacedinsidetheFaradayshield.Thisboxgetsitspowerfromthebridge.

ConnectthePicolinkBoxtotheAVS48-USB/Serial-F CPU unit by using the 5- or 10meterlongopticalfibrecable.Theall-plasticopticalcableconsistsoffourfibres,whichhavebeenmarkedwithcolorsblack,red,yellowandblue.Theopticaltransmitters(white)andreceivers(black)aremarkedwithnumbers1..4.Connectthefibrestocorrespondingnumbersontheboxes.Recommendeduseofthecolors:1=black,2=red,3=yellowand4=blue.

Pushtheendsofthefibresintothereceivers/transmittersasdeepastheygoandtightenthenuts.Be extremely careful not to tighten them too much: thesecomponentsaremechanicallyweakandtheybreakeasily.Useonlyfingers.However,thefibresmuststayfixed,andtheydo,ifyouavoidtensionandsharpbendingofthecable.

Thefibreendscanberenewedbycuttingamil-limeterortwousingsharpfull-flashendcutters,iftheydonotseemtobeingoodconditionafteryears.

Connect the CPU unit to your computer or to the USB-232converterbythe1.5meterlongcablethathas male and female 9-pin DE9 connectors (cable typeRS9P9S7W1.5M).

Verify that there is the supplied 37-way short-circuit connectorpluggedintotheAVS-48SIpreamplifierinput.

ConnecttheAVS-48SImainunittomainspower.The instrument has a universal power supply for 90-250V.Switchonthemainunit.Greenlightwillturnon.

Connect the CPU unit to mains using the 12V mainsadapter.SomeactivityontheAVS48SIfrontpanelLEDsshowsthattheCPUhasbooted.

CheckthevoltageontherearpanelANALOGOUTconnector.Itshouldbenearto1V.

TheoptionalopticallinkfortheAVS-48SIconsistsoftwoboxesconnectedbythefibreopticcable.BoxontheleftisconnectedtotheAVS-48SIandcontainsonlytheoptocard.Itgetspowerfromthebridge.TherightmostboxcontainsboththeoptocardandanArduinoMega2560processorunit(CPU),whichcontainsthefirmwareoftheAVS-48SI.Itispoweredbyawalladapter.


AVS-48SI PICOBRIDGE


SENSOR WIRING

Wiring of the AVS-48SI sensors is pin-to-pin com-patible with the 7 rst sensors of the AVS-47x series of bridges. e ground pins are for cable shieldsPin name CH0 CH1 CH2 CH3 CH4 CH5 CH6I+ 1 3 5 7 9 11 13V+ 20 22 24 26 28 30 32V- 2 4 6 8 10 12 14I- 21 23 25 27 29 31 33GROUND: 15, 34, 16, 35, 17, 36, 18, 37, 19 and the shielding braid. (GND is connected to the enclosures of the preamplier and main units). e braid is an important part of the ground-connection, so please tighten the connectors well.

Front panel of the AVS-48SI Picobridge Preamplier Unit

AVS-48SI PHYSICAL FRONT PANEL

e physical front panel of the AVS-48SI Picobridge contains only the power switch and seven indicator lights.

Power switch and Power indicator. This switch doesnotbreakthemainspowerbutaninternal15Vvoltage.Whileitbreaksallpowerfromtheinstrument’s circuitry, mains power continues to flowintothemainAC/DCconverter.Ifyouhaveto open the cover of the instrument, verify that the mainspowercordhasbeenpulledoff.Aredlighton the power supply board warns, if mains power is connected.Thegreenpowerindicatoronthefrontpanel lights when low DC voltages are connected toAVS-48SIcircuitry.

Power can be switched separately off from the bridge,orfromthemicroprocessorbox,orboth.In any case, you need to re-boot the CPU in order

torestorecorrectoperation.Re-starting brings the bridgeintheresetstate.Acompletelynewsessionhastobestarted.

Analog signal error lights. The two red lights show the most common analogerrors.

• OVL light. Analog overload occurs if the signal amplitude before phase-sensitive detection exceeds +/- 2 Volts. is is usually due to an external inter-ference (poor shielding of sensor leads, high resist-ance and low excitation together with mechanical vibration, or a severe ground current in the sensor leads).

• LRES light. Although a combination of exces-sive lead resistance measured on a low range and high excitation (refer to specications) can greatly reduce the measurement accuracy, a warning about high lead resistance is in practice caused only by a broken current path to the sensor. Check the lead


AVS-48SI PICOBRIDGE


resistances by measuring a sensor rst in two-wire mode and then in 4-wire mode. e dierence is the total resistance of the current leads.

Picobus status lights.Thefollowingfourlightsshow the line states of the low-noise synchronous, serial Picobus interface between the external mi-croprocessorboxandthebridge.

CP light. Clock Pulses from the box to the bridge.

DC light. Synchronous Data from the box to the bridge.

DI light. Synchronous Data from the bridge (In-strument) to the box.

AL light. ALarm tells about an analog error (OVL and/or LRES) to the program.

e CP, DC and DI lights blink when the AVS-48SI exchanges data with the microprocessor box.

AVS-48SI PHYSICAL REAR PANEL

Mains input. The mains input voltage range is 90-250V50-60Hz.Thepowercordmustcontaina ground lead connected to the safety ground, it isforbiddentocutit.IfyouneedtoisolatetheAVS-48SI from mains ground, use an approved 1:1isolationtransformer.TheAVS-48SIoffersalso some low-voltage power inputs, which are describedbelow.

Fuse.Theprimaryfusesizeis1Aslowblow,5x20mm

18V AC input. The bridge can be powered by a 50-50HzACvoltageofabout18Vrms.Currentdrainislessthan1A.Thislow-voltageinputdoesnotrequireagroundlead.Thevoltageisconnectedbetweenpins1and3ofthe3-wayDINsocket.Mating plug for the wires is 71430-030/0800,

manufacturedbyPrehkeytecGmbH.

12V DC input. The third alternative to power the bridge is a 12V DC source - a battery or a labora-torypowersupply,forexample.Currentdrainisasmuchas1.5A.Negativeterminalofthebatteryis connected to pins 1&2 and positive terminal to pins3&4orthe4-wayDINsocket.Matingplugis71430-040/0800,manufacturedbyPrehkeytecGmbH.Aseriesdiodeprotectstheinputfromreversepolarity.

Themainsinputcanremainconnected.Ifthemainsvoltageiswithinspecifications,theDCsourcewillactasabackupsourcewithnodrain.There is no charging circuitry for the battery, how-ever.

Picobus Serial Input. The AVS-48SI is connected to the microprocessor box via a synchronous, serial Picobus interface.Thisisaproprietarystandard.Itusesthefoursignallinesdescribedabove.Ifyou

Physicalrearpanelasseenfromthebackside.Insertingcablesetc.,whentheAVS-48SIismountedinarack,maybeeasierifone“looksthepanelfromthefrontside”.


AVS-48SI PICOBRIDGE


TheA

VS-48SIphysicalrearpanel.Thisp

hotohasbeenflippedhorizontallyandtexts

haveflippedonceagaininordertomakethem

morelegible.Thisv

iewcanbeuseful

whenpluggingcablesw

henthebridgeisfixedinarack.


AVS-48SI PICOBRIDGE


need to remove the 9-pin DE9P connector plug fromthecable,e.g.fortakingthecableviaasmallhole,refertothecablespecificationswhenrecon-nectingwires.Cabletype:PB9P15P6W5M.

Heater out. The heater output is a negative cur-rentsource.Maximumcurrentis-250mAonthehighest power range and the open-circuit voltage cannotexceedabout-13V.Theheater,whichmustbe isolated from ground, can be connected to the AVS-48SIintwoways.

1) Use one coaxial cable connected to the grounded BNC terminal on the rear panel. e shielding braid is in contact with the AVS-48SI enclosure. is simple solution requires, that the connector in the cryostat should be isolated from ground, and also the heater must be oating. en there is no path for a low-frequency ground current. A problem may be, that the cable can take high frequency interference into the cryostat. It may be possible to reduce this danger by connecting a capacitor from the braid to the cryostat.

2) Use two coaxial cables connected to the le (nega-tive) and right (ground) terminals. In this solu-tion, both shielding braids are isolated from the AVS-48SI enclosure but they must be connected to the body of the cryostat. e center wires of the cables carry the heating current. As the braids are now connected to the cryostat, they provide a bet-ter shield against high frequencies than solution #1. e price is that two connectors are needed.

Analog out. ANALOG OUT is the PSD integrator’s voltagefromtheself-balancingloop.Theresiduesofthe12.5/13.64/15.0Hzsquare-wavecarrieraresuppressed by an analog 3RDorderBesselfilterhav-inga3dBroll-offfrequencyofabout1.2Hz.Theanalog output is stepless and it provides a resolu-tionthatislimitedonlybynoise,notbythedigitiz-ingstep.Analogoutputextendsupto3Volts,andwith possibly reduced accuracy to some hundred millivoltsabove.

The ANALOG OUT signal can be switched to show the difference (analog out - set point volt-age).Thisdeviationsignalisalsofilteredbytheanalogfilter.

Control Error Out. The CONTROL ERROR OUT is also formed by subtracting the Set Point DAC’s outputvoltagefromtheAnalogOuputvoltage.Insteadofanormaldifferentialerroramplifier,theLinearTechnology’sLT1043buildingblockcreatesthe difference with practically no offset or gain error.CONTROLERRORgoesfrom-3Vto+3V.If

temperature control is enabled, this stepless voltage servesasinputtothecontroller.Inordertopreventunnecessary phase-shift in the closed control loop, theCONTROLERRORisnotfilteredasistheANALOGOUTPUT.

Control Set Point.Iftheuserhasanexternalcon-troller and wants to use it instead of the AVS-48SI’s controller option, there are two possibilities that dependonthecontroller’sstructure:eithertaketheCONTROL ERROR OUT -signal or use the CON-TROLSETPOINT.Thesetpoint,whichispro-grammedbycommandSDACV,goesfrom0.005Vto+2.99Voltsandhas50μVsettlingresolution.ThisvoltagecomesdirectlyfromtheLTC2600analog-to-digitalconverter.ItisnotbufferednorprotectedbytheAVS-48SI.

AC Monitor Out.Thisisthepreamplifier’soutputamplifiedbythemainamplifier’svariablegain.

The above gains are (analog out)/(voltage drop acrosssensor).A1Vpp50Hzsignalonscopescreenwhenexcitationis3μV,means3μVppmainsfrequencyinterferenceattheinput.

If the bridge is in balance, the AC amplitude is very small.Itcontainsnoisewhosesourceismainlythevoltagenoiseofthepreamplifierinput.Whenahigh resistance is measured at low excitation level, thenoiseisincreased.Thisoutputisveryusefulincheckingthatthereisnothingunwantedinthesignalthatisreceivedfromthesensor.

EXCITATION GAIN 10mV 1000 3mV 1700 1mV 4200300μV 12000100μV 3800030μV 12000010μV 3400003μV 340000


AVS-48SI PICOBRIDGE


Asoundtracelookslikethis:Excitationis3μVandthemeas-uredresistanceiszero.Thepreamplifierwassetonmaterialthatdampedvibrations.Theplacewasfreefromchangingmagneticfields.

Excitationis3μVandbridgewasmeasuring100Ω on 3MΩ range.A100nVpp40Hzsignalwasinjectedtothesensor.TheFFTtrace(averageof50sweeps)showsalsoalittle50Hz,butnootherunwantedinterferences.Thisisanidealcase!

ThisFFTwastakenfromaninternalwirewoundreferenceresistorwhenthepreampwasplacedassuchonthetable.Vi-brationfromthescope’sfanincreasedthe50Hzpeaktenfold.Themanyturnsofwirewoundresistorsmakethemsensitivetovibrationandchangingmagneticfields.

Connect a digital oscilloscope with FFT capability tothisoutputandmeasuretheFFTspectrum.Itshouldbequiteflatwiththeexceptionofasmallpeakattheoperatingfrequencyandasmallpeakatyourmainsfrequency.Makethesamemeasure-ment from one of the AVS-48SI’s internal referenc-es when the preamp is on the table, not connected toanythingelsethantothemainunit.Anidealmeasurementofarealcooledsensorshouldlookasgood.

If excitation is reduced by one step, the noise level willincreasebyafactorof3.However,onthetwolowest levels, noise does not increase so much becausetheamplifiergainisreduced.

User Dac. This is another outputfromtheLTC2600converter that is available for you, if you need an accuratelyadjustablevoltage.TheUserDACisavailable also while the Set Point DAC is needed fortemperaturecontrol.UserDACgoesfrom0.005Vto+2.99V.Theaccuracy is better than 100μV.This16-bitconverterhas50μVsettlingresolution.

The exceptionally good DAC accuracy has been achieved by measuring the DAC voltage by the LTC2400A/Dconverter.Thereadingisthenusedforgeneratingacorrectingsoftwarefeedback.Some commands and operations are slow because oftherequiredA/Dconversion.

Ext Heater Drive In.Theanalog“Externalheaterdrive”-signalisverysimilartothedigital“DirectHeaterDrive”.Externaldriveisavoltagefrom0upto+3Volts.Itmustbesuppliedtothisrearpanelterminal by some external voltage source, whereas direct heater drive is controlled by software (HTRDIR,HDACV).

Before using External Heater Drive, the top cover of the AVS-48SI must be opened and the short-circuit piece in jumper JP1, near to the left rear cornerofthe“B”controllerboard,mustbemovedfromINTtoEXT.Theheateroutputstageisnowavoltage-controlledcurrentsource.Itsheaterrangesandpowerdisplayswork,butthePIDcircuitandsetpointarebypassed.0inputresultsinnooutputand +3V gives the maximum output of the selected range..


AVS-48SI PICOBRIDGE


Move the short circuit piece from INT to EXT for driving the heater output stage by an external voltage.

Ext Clock In. You can change the AVS-48SI to oper-ate also on other frequencies than 12.5/13.64/15.0 Hz. is requires an external 0/+5V square-wave generator to be connected to the external clock input. If the generator has a low output impedance (typically 50Ω), it will override the bridge’s internal clock.

e equation for setting a new frequency FPSD is

Where FSOFTWARE is the operating frequency currently selected by soware. If “Ext Clock In” is not loaded, it outputs a 600Hz square signal.

To AVS-48SI Preamplier. e cable consists of 25 wires within a shielding braid. e braid is very important, as it is responsible for the low impedance of the 5-meter ground connection between pream-plier and main units. is 1:1 cable has two DB25P plugs, and the signals are:

*600

EXTPSD SOFTWARE

FF FHz

=

1 Ground14 +15V2 -15V15 Relay +15V3 Reference square 116 Reference square 24 Excitation preamplier output 117 Excitation preamplier output 25 Excitation feedback 118 Excitation feedback 26 Signal preamplier output 119 Signal preamplier output 27 Signal feedback 120 Signal feedback 28 Sensor bias voltage measure output 21 External sensor bias input9 Capacitance compensation square-wave22 Synchronous serial data to preamplier unit10 Synchronous serial clock to preamplier unit23 Synchronous serial strobe to preamplier unit11 Inverted power-on signal 24 Return current path for relays (see pin 15)12 -15V25 +15V13 Ground

Preamplifiercableandconnector


AVS-48SI PICOBRIDGE


AVS-48SI SERIAL COMMAND SUMMARY

INITIAL COMMANDS

IDN?and*IDN?Identificationquery(includesfirmwareversion)HW? Hardware query (only CPU hardware version)LINETERM[0..3|?]Lineterminatorcommand/query(1forLabView,2or3forhyperterminal)

CONFIGURATION OF MEASUREMENT

PSDF[0..2|?]Operatingfrequencycommand/query(12.5,13.64,15.0Hz)CH[0..7|?]Sensorchannelcommand/query(0=calibrationreferences)RAN[0..7|?]Rangecommand/query3Ω,30Ω,300Ω...30MΩEXC[0..7|?]Excitationcommand/query3μV,10μV,30μV...10mVGNDS[0..1|?]Sensorgroundingcommand/query(0=floating,default.1=I-leadgrounded)TW[0..1|?]2-or4-wiremeasurementcommand/query(0=4-wire,default)ARN[0..60|?]Autorangecommand/query(argument=autorangedelayinsec.,0=disabled)

CONFIGURATION OF TEMPERATURE CONTROL

HTRRAN[0..18|?]Heaterrangecommand/query(0=heaterdisabled,allparams.areresetto0)PROPG[0..13|?]Proportionalgaincommand/query(0=contr.errordoesnotaffectoutput)INTG[0..10|?]Integratorgaincommand/query(0=integratorisheldatreset)DERG[0..10|?]Derivatorgaincommand/queryINTHEATER[0..1|?]Internal/externalheatercommand/query(0=external,normalheater)HTRDIR[0..1|?]Heaterdriversourcecommand/query(0=PIDcircuitrydrivestheoutput)HDACV[0.005..2.99|?]HeaterDACvoltagecommand/query(DACdrivesheaterwhenHTRDIR=1)SDACV[0.005...2.99|?]SetPointDACvoltagecommand/querySETPOINT[0..30,000,000]Temperaturecontrolsetpointcommand(Setpointinohms)HTRI? Heater current query (current is measured, result in Amperes)HTRV? Heater voltage query (voltage is measured, result in Volts)HTRP? Heater power query (= HTRI? * HTRV? result in Watts)ERRSIGNAL? Error signal query (result in Volts)DRDT[0..3|?]Controlpolaritycommand/query(0forsensorwithdR/dT>0.1fornegative)HOLDMODE[0..1|?]Holdmodecommand/query.1=enterhold,0=releasehold,queryreturnsthe currentholdingstatus(0=normal,1=holding).

COMMANDS FOR SAVING INTO EEPROM

SAVEBRD Savesthecurrentlyeffectivebridgesettingsaspropertiesofthecurrentlyselectedchannel.SAVETCR SavesthecurrentlyeffectivePIDparametersaspropertiesofthecurrentlyselectedheaterrange.SAVECAL Savescalibrationcoefficientsforallrange-excitationpairs.


AVS-48SI PICOBRIDGE


SAVEADC SavescalibrationcoefficientsfortheA/Dconverter.Affectsalsoanalogoutputs.SAVEREF Savesstatedormeasured“true”valuesofthecalibratorresistors.SAVELINETERM Saves the selected line terminator to be the defaultPRESETMODE Enables entering properties of channels and heater ranges and saving them with SAVEBRD

andSAVETCRwithoutmakingthesettingseffective.

COMMANDS FOR RECALLING SAVED SETTINGS

RECALLBR[0..7]RecallsfromtheEEPROMachannel’spropertiesandmakesthemeffective.Argument=channeltoberecalled.

RECALLTC[1..18]RecallsfromtheEEPROMaheaterrange’sPIDparametersandmakesthemeffective.Argument=heaterrangetoberecalled.

COMMANDS FOR REAR PANEL OUTPUTS

BNC[0..1|?]AnalogOutCommand/query.Selectsoneoftwoanalogvoltagestotheoutput.0=voltagepro-portional to sensor resistance, 1 = voltage proportional to (VSENSOR - VSETPOINT )* 3V (Reversed by setting DRDT=1).

UDACV[0.005..2.99|?]UserDACvoltagecommand/query.CommandprogramstheDAC,querymeasurestheDACoutputvoltage.

SDACV[0.005..2.99|?]SetpointDACvoltagecommand/query.CommandprogramstheDAC,querymeas-urestheDACoutputvoltage.

CALIBRATION

CALIBRATE[0..2]MainCalibrationcommand.Startsoneofthreeautomaticcalibrationprocedures: 0:Slowfullcalibrationdeterminescorrectionsforallrange-excitationpairs.Longaveragesandsettling

timesformaximumaccuracy.Takesabout4hourstocomplete. 1:Fastfullcalibration.Shortaveragesandwaitingtimes.Fasterbutlessaccurate,especiallyonlowexci-

tations.Takesabout1hour. 2:Partialcalibration.Calibratesonlythecurrentlyselectedrange-excitationpair,butuseslongaverages

andsettlingtimes.Requiredtimedependsonexcitation. TheabovethreecalibrationprocedurescanbeterminatedbysendinganythingviatheRS232interface.CALADC Calibrates the A/D and D/A converters so that they comply with an external voltmeter that is

usedforthiscalibration.Requiredonly,ifsuchacomplianceisdesired.SeecommandsDVMHIandDVMLO.

CALREF[0..1] Enablesenteringormeasuringandenteringvaluesofthecalibratorresistors.TheaccuracyoftheAVS-48SIdependsonhowaccuratelyvaluesofthese7resistorsareknown.1startsthecalibra-tionsession,0endsit.Requiresahigh-end,calibrated4-wireohmmeter.SeecommandsREFIDandREFVALUE.

OTHER COMMANDS

DLY[0..30]Delaycommandinsecondsfortimeseparationbetweencommandsonasingleline.ItcanbeusedforlettingthebridgetostabilizebeforeRESxandADCxcommands.

REPEAT Repeats commands/queries on a single line in an endless loop until terminated by sending any-


AVS-48SI PICOBRIDGE


thingviatheRS232interface.REPEATmustbethelastitemontheline.TIMEandTIME?Intervalmeasurementcommandandquery.Theyareformeasuringthetimetakenbycom-

mandsandqueriesorgroupsofthem.Multilinegroupsarepossible,butthentheresultincludesalsodelaysthatareexternaltotheAVS-48SI.Resultisinmilliseconds.

TIMEisplacedbeforethesequencetobemeasured.TIME?isplacedafterthesequence.RESTARTTakesbridgetostart-upstate.Doesnotalternorsaveanypropertiesorcalibration.DEFAULTS SetsallpropertiestosafeinitialvaluesandsavesthemintoEEPROM.Doesnotchangecalibra-

tioninanyway.RESETALL ResetsallpropertiesandcalibrationfactorsandsavesthemintoEEPROM.Everythingmustbe

re-calibratedandre-programmed.EPRCAL Reads the offset and scale correction DAC voltages into RAMEPRADC Reads the offset and scale correction factors for the ADC into RAMEPRREF Readsthe“true”statedvaluesofthereferencesfromEEPROMintoRAMERR? Errorquery.Placeattheendofaline.Responseistext(string),exceptthat“0”meansnoerror.

Severalerrormessagesmayhavebeenconcatenatedintoalongstring.TheerrorregisterisemptiedbytheERR?query.

MAX?,MIN?Maximumandminimumreadingsamongthegroupofaverageddatapoints.STD?StandarddeviationoftheaveragedA/Dconversiondatapoints.QRATIO?Qualityratiois(max-min)/std.Isabout5forahealthymeasurement.Unreliableonthehighest

excitationsasthedigitizingstepoverridesrandomnoise.CP[0..1]TurnsofforontheCPindicatorlight(service)DC[0..1]TurnsofforontheDCindicatorlight(service)


AVS-48SI PICOBRIDGE


INTRODUCTION - Part I

This Part I is for operating AVS-48SI Picobridge® via its versatile USB or RS232 serial interface (the letters“SI”denote“SerialInterface”).Theoptionalfactory-installable Temperature Controller is in-cludedintheseinstructions.

The bridge alone is AVS-48SI.TogetherwithaAVS48-Serial/USB CPU box, connected by a wire cable, the bridge becomes AVS-48SI-W.Ifthewirecable is replaced by a 5-meter AVS48SI-Picolink opticallink,thebridgebecomesAVS-48SI-F5.Op-tionalincreaseofthefibrelengthto10metersmakesan AVS-48SI-F10.

The AVS-48SI is a very versatile and perhaps world’smostaccuratecryogenicresistancebridge.

The AVS-48SI bridge is divided in three parts:

1)asmallpreamplifierbox,whichcanbemountedneartothecryostatinordertokeepthesensitivecables to the sensors short

2)a19-inchwidemainunitforrackmountinginsidetheshieldedroom.Thepreamplifierandthe main unit are connected together by a 5-meter cable.

3)asmallexternalmicroprocessorunit.ThisCPU box should be located outside the shielded room inordertominimizetheelectromagneticinter-ferencethataprocessorunitcangenerate.Itisconnected to the main unit by a 5-meter shielded cable that is galvanically isolated in order to pre-vent groundcurrents.TheboxprovidesasimpleRS232 interface and a wide command set for full controlofthehardware.ThisnewversionoftheAVS-48 can be used with any computer, operat-

ing system and application software, including LabView,whichsupportRS232communication.If the computer does not offer a physical COM: port, a virtual port can be created by using a USB-232converter.

The AVS-48SI can be also equipped with a fibre-optical connection between the microprocessor unit andthemainunit.Inacasewheretheshieldingbraid of the wire cable cannot be grounded to the conducting wall of the cryostat room, the optical cable provides the EMI-safestsolution.Itisalsoeasytotaketheopticalcablethroughsmallholes,asitneedsnoconnectors.

The sensor input of the Picobridge is pin-to-pin compatible with that of our popular AVS-47x seriesbridges,makingupgradingeasy.Theanaloginstrumentitselfisa“blackbox”withoutadisplay,keyboardordigitalintelligenceofitsown.Thenec-essaryfirmwareisprovidedbyanexternalmicropro-cessorunit.

A factory-installable temperature controller option offers many improvements compared with our old TS-530A, such as more tightly spaced power ranges, smooth changing of heater power range, and a hold modeforvisitingothersensorstemporarily.

e 19” wide main unit of the AVS-48SI Picobridge

e 170x130x65mm preamplier can be located near to the cryostat, whereas the 103x123x55mm microprocessor unit should be located asfar from the cryostat as possible


AVS-48SI PICOBRIDGE


The“Hype!Terminal”(seetextforlink)iseasytouse:JustspecifytheComportnumber(SetUp)anditisready.Intheabovepicture:identificationandhardwarequeriestellthefirmwareversionandtheCPUhardwareversion.Thenthecurrentlyactivechannel,range,excitationandalsotheordinalnumberofthecalibrationreferenceresistorarequeried.TheresultoftenADCconversionsisavoltage,whereastheRES?querygivestheanswerinohms.ResponsetoERR?iszero,whichmeansnoerror.

BEGIN WITH A HYPERTERMINAL

A very good way to get acquianted with the serial commands is to use a hyperterminal program, which lets you send commands to the AVS-48SI and read theresponse.ForWindowsusers,wecansuggestaprogramcalled“Hype!Terminal”writtenbyCarlosMontoya.Itisdownloadablepresentlyfrom

https://sourceforge.net/projects/hypeterminal/

In the following text, we will use examples that have beentestedwithHype!Terminal.Whenwritingyourowncomputerapplication,keepahyperterminalprogram at hand so that you can test your command sequencesandmeasurethetimetheyneed.

A hyperterminal program is also useful for cali-brating the instrument, where a simple command starts a process that needs a long time to complete butdoesnotproduceoutput.

SHORT BRIDGE TUTORIAL

These instructions assume that you have a hyperter-minalprogramrunningonyourcomputer.Ifyourcomputer does not have a physical Com: serial port (which is also called an RS232 port), but you have a free USB port, you can convert it to a Com: port byusingaUSB-232converter.AconvertermadebyNational Instruments is available from us, but many other -and perhaps cheaper- converters are also com-merciallyavailable.

Maketheconnectionsbetweenpartsofthesystemasinstructedinthepreviousparagraph.Connectalsoa digital voltmeter to the ANALOG OUT rear panel BNC.Checkthattheshort-circuitplugisinsertedinthepreamplifier’s37-wayinputconnector.

Checktheserial port number that the hyperterminal programwilluse.Itmustcorrespondtothephysi-cal COM port or the port name that the USB-232 converterisusing.

SwitchontheAVS-48SI.Agreenlightinitsfrontpanelshowsthatpowerison.


AVS-48SI PICOBRIDGE


Switch on the CPU box by plugging its wall adapterintoamainssocket.Theuniversalpowersupplywillworkfrom90to250V,50-60Hz.Someactivity on the AVS-48SI’s front panel lights will showthattheCPUhasbootedandthatthefirmwareprogramisrunning.

Your DVM on the analog output should now show1.000Voltstoafew±100microvoltsaccuracy.

Startthehyperterminalprogramandchecktheserialportnumber-correctifnecessary.SendthequeryIDN?.Theresponsewillbe“PICOWATT,AVS-48SI,1R0”orsomenewerfirmwareversion.Sendquery HW?.Theresponse“PICOWATT,RS232PB_A1”,isthehardwareversionoftheCPUbox.Youmay need to change the line terminator character(s) depending on your hyperterminal program, if the re-sponsedidnotshowuporiftherearenolinebreaks.ThisismadebytheLINETERM(argument).Thearguments are

0: no termination1: LF (newline, 1\n, ASCII 10)2: CR (carriage return, 1\r, ASCII 13) 3: CRLF (initial factory default)

Checkthepresentstateofthebridgebywritingalineofqueries:“CH?;RAN?;EXC?”(quotesareforclarity,donotincludetheminthemessages).There-sponsewillbe“0;2;7”indicatingchannel0(calibra-tion references), 300Ωrangeand10mVexcitation.

Measurethecalibratoras“RES;RES?”.Theresponseisinohms.Ifyouissue“ADC;ADC?”,theresponseisinVolts.ComparetheresponsewithyourDVM’sdisplay.

Reduce the excitation to the 3µV minimum bysending“EXC0”.NowtheDVMdisplaywillbe quite noisy, as so is also the response, if you repeattheRES;RES?sequenceseveraltimes.Reducethefluctuationbyusinganaverage:send“RES100;RES?”.Thiswilltakeabout20secondstocomplete, but the noise will be much lower, which youseebyrepeatingthisafewtimes.

The AVS-48SI offers some statistics queries: MAX?, MIN?, STD? and QRATIO?.Thepeak-to-peaknoise(max-min)ofthose100conversionscouldbesomethinglike0.0035andthestandarddeviation0.0007.ThesereadingsareinVolts.Ifthe noise is pure random, the ratio (max-min)/std (=qratio)isabout5.Amuchhigherreadingsuggests

AVS-48SI SERIAL INTERFACE COM-MANDS AND QUERIES

The serial commands that will be described below cover the necessary functions for creating computer controlledapplications.Ifyoufeelthatsomefurthercommands would be necessary or useful, please let usknow.

The second part of this manual describes, how to use the AVS-48SI hardware together with the “avs48si.vi”virtualinstrumentLabViewprogram.Thehardwarespecifications,connectionofthein-struments, cabling and physical front and rear panels arethesameforbothapplications.TheLabViewprogram offers more software functionality and is ready to use without need to write a line of code, whereas use of the serial interface does not require LabView.Automaticcalibrationissupportedinbothcases.

All calibrationcoefficientsarestoredintheAr-duinoMega2560CPU,andtherefore:

- calibrations made using LabView are valid and available for serial operation

- calibrations made via the serial interface are valid andavailableforLabViewoperation.

aninterferingspike.QRATIO?isnotveryreliableonhighexcitationsbecauseofdigitizingsteps.

Measure the short-circuit input plug by sending “CH1;RAN0;EXC5”.Channel,rangeandexcita-tion will now change, and after a reasonable settling time,RES10;RES?willyieldaboutzero.

It is not necessary to write everything each time a channelismeasured.Saveachannel’ssettingsandenable autoranging for it:

CH0;RAN2;EXC7;ARN10;SAVEBRDCH1;RAN0;EXC5;ARN10;SAVEBRD

Now the channels are measured by

RECALLBR0;DLY10;RES5;RES?RECALLBR1;DLY10;RES5;RES?

The ten seconds delay (DLY) allows the bridge to settlebeforestartingtomeasure.Ifautorangeneedsto change the range, the 10 second autorange delay (10afterARN)isaddedtoDLY.


AVS-48SI PICOBRIDGE


COMMANDS, QUERIES AND RESPONSES

Communication between a computer and the AVS-48SIconsistsofsendingmessages,i.e.commands and queries, to the bridge and reading responses fromit.TheAVS-48SIdoesnotsendanythingbyitself,itcanonlyrespondtoqueries.Becauseofthisstrict rule one does not need to poll the computer’s serialinputaftercommands,butonlyafterqueries.Commands are performed in the order they were received and responses are received in the same orderastheywerequeried.Responseshavenohead-ers,whichmakesthemeasiertoreadintoaprogram.Someoperations,likechangingrangeorexcitation,needalotoftime,andonemustbepreparedtothat.

All commands and queries consist of two parts: a) twoormorelettersandb)anargument.

Theletterpartiscase-insensitive(RAN1=ran1)

Therecan,butneedsnot,beoneormorespacesbetween the two parts (RAN1 = RAN 1 = ran 1)

Inmostcases,commandsandquerieshaveidenti-cal letter parts (command EXC7, query EXC?)

Notallcommandshavecorrespondingqueriesandnot all queries have corresponding commands

Theargumentofaqueryisasingle“?”character(e.g.LINETERM?).Aquerywithoutthe“?”isas-sumedtobeacommandwhoseargumentis0.

Theargumentofacommandmustbenumeric.Some commands do not have an argument, which theprogramthenassumestobezero(e.g.RE-START).Similarly,ifonlyaletterpartofacom-mand or query is given, it is assumed to be a commandwhoseargumentiszero(RAN=RAN0,REFVALUE=REFVALUE0).

Mostnumericargumentsareintegers.Valuesof analog voltages and set point must be given as floatingpointnumbers(e.g.SETPOINT100.123).Do not give numbers in exponential form, they are notunderstoodbytheArduinoCPU.

Argumentshavetheirownminimumandmaxi-mumvalues.Ifagivenargumentexceedsitsmaximum or falls below its minimum, it is coerced to the maximum or minimum and the command is performed without any error message (CH9 will be coercedtoCH7).

COMMAND DELIMITER

Several commands and/or queries can be sent on onemessageline.Theitemsmustbeseparatedfromeach other by a commanddelimiter,whichis“;”(semicolon,ASCII59).ThisdelimiterisalsousedinIEEE-488.2standard.Adelimitermustnotbeusedintheendofamessageline.

The message line must be shorter than 255 char-acters,includingspacesanddelimiters.

MESSAGE LINE TERMINATOR

A message line must be terminated by a line termi-natorcharacterorcharacters.TheAVS-48SIacceptsthreecommonlyusedterminators(seeLINETERM).Instead, your computer program or the platform may expect only one of them, and therefore the line ter-minatorcanbespecifiedandsaved.WhentheAVS-48SIrespondstoqueries,itusesonlythespecifiedterminator.Trytheterminatorsandsavetheworkingone.

TIMING

Thesimpleinterfacewithouthandshakingandthefirmwareprogramthatdoesnotuseinterruptsre-quirealotofattentiontotiming.

ThefirstthingistomakeuseofthefactthattheAVS-48SIdoesnotsendanythingbyitself.Itneedsaquerytowhichitcanrespond.However,com-mandstakeverydifferenttimestocomplete,andifyou use timeoutsinyourprogram,makesurethatenough time is reserved for waiting for the response tocome.Itisbesttowriteonlysuchmessagelinesthat have all queries at the end, so that when re-sponding starts, responses to all queries come in quicksuccession.

You do not need to worry about timing between commands within one message line: they are per-formedintheorderthattheycameandtheyjusttakethetimethattheyneed.Responsesareinthesameorderasthequerieswereonthemessageline.

However, NOTHING must be sent to the AVS-48SI while it is processing previously given com-mandsorqueries.Thisisdifficulttoremember,buttherearefivewaystomakesurethatthenextmes-sage line is delayed until the CPU is ready to accept anewmessage.


AVS-48SI PICOBRIDGE


1.Addthe“OperationComplete”queryOPC?asthelastitemonaline,ifitcontainsonlycommands.Poll the computer’s serial input until character “1”(withoutthequotationmarks)isreceived.The AVS-48SI is then ready to receive a new messageline.

2.Addthe“ErrorQuery”ERR?asthelastitemonalinethatcontainsonlycommands.ThisworkslikeOPC?,exceptthatyoumustbepreparedtohandleatextstringreponse.Ifthereisnoerrorontheline,responseis0.Incaseofanerror,theresponseisamessagelike“analogoverload”.

3.Ifthelinehasqueriesorbothcommandsandque-ries, place at least one -but prefefably all- queries intheend.Youcanthentrustthatallresponsescomein,say,100millisecondsafterthefirstchar-acteroftheresponsestringwasdetected.

4.Polltheresponseforthespecifiedlinetermina-tor.Yourprogramcanstopreadingtheresponseassoonasthelineterminatorhasbeenreceived.Thenanewmessagelinecanbesent..

5.Usedelays.Thissimplemethodhastheseriousdrawback,thatcommandsneeddifferenttimestocomplete.ResponsetoasimplequerylikeRAN?comes in twenty milliseconds, whereas changing rangeorexcitationrequiresabouttwoseconds.Acompleteautomaticcalibrationtakesaboutfourhours.Thismustbetakenintoaccount,ifyourprogramcontainstimeouts.

For simplicity, these synchronisation methods are not shown explicitly in this manual’s examples, but usesomeoftheminyourprograms.Whentestingcommands with a hyperterminal program, the need forsynchronisationisdifficulttosee,asonecannotsendmessagelinesintooquicksuccession.Usethe hyperterminal program and the TIME/TIME? command/query for measuring how much time your commandsequencesneed.Mostcommands/que-riesneedlessthan60ms.Inthefollowing,therearesomeestimatesincurlybrackets:time1|time2,wheretime1isforcommandandtime2forquery.

Checkthetiming,ifyourprogramgivesstrangeresultsorifitdoesnotworkasexpected!

GENERAL INSTRUMENT COMMANDS

Inthefollowingtext,[CH]intheendofacommanddescription means, that this value is saved as a prop-ertyofthecurrentlyselectedchannel.[BRD]meansthat the value is saved as a general setting common toallchannelsandisreadfrommemoryatstart-up.[HTR]meansthatthesettingissavedasapropertyofaheaterrange.Otherwise,thesettingorparametermustbeenteredagainforanewsession.

IDN?and*IDN?Identificationquery(Re-sponsee.g.“PICOWATT,AVS-48SI,1R0”)

HW? Hardwarequery(onlytheCPUhardware,e.g.“PICOWATT,RS232PB_A1”)

LINETERM[0..3|?]Responselineterminatorcommand/query.0 = no terminator1 = LF (linefeed) ASCII 102 = CR (carriage return) ASCII 133 = CRLF A message line must be terminated by a line terminator.TheAVS-48SIacceptsalterna-tives 1-3, whereas an application program mayacceptonlyoneofthem.Forexample,LabView requires that serially received strings areterminatedbyLF.Theselectedtermina-tionshouldbesavedusingSAVELINETERM.[BRD]

RESTARTDEFAULTSRESETALL

Refertothedescriptionsofthesecommands.TheRESTART command does not destroy any proper-tiesthathavebeenpre-programmed,itonlytakestheAVS-48SItoitsstart-upstate.Itdoesnotsaveanything.

The DEFAULTS command sets all properties and other settings to safe initial values and also saves themintotheEEPROM.Usewithcare.

The RESETALL command resets all calibration factors and all properties of all channels and heater ranges.Usewithextremecare!Everythingmustbere-calibratedandre-programmed.


AVS-48SI PICOBRIDGE


RESTARTRestartcommand.Re-startstheCPU and sets it to default state: Reference channel #0, 300R range, 10mV excitation, 100Rreferenceresistor,4-wireandfloatingsensor, no autoranging and previously selected lineterminator.Iftheprogramhashanged,thiscommandwillnotwork.Insuchacase,plug off and on the mains power adapter in order to get a real power-on boot.

CONFIGURING THE BRIDGE

PSDF[0..2|?]Excitationfrequencyofthebridge(command/query)0=12.5Hz,1=13.64Hz,2=15.0Hz[BRD]

CH[0..7|?]Inputchannelcommand/query.Channel 0 is connected to one of seven inter-nal ultra-stable wire-wound reference resis-tors.Channels1-7areavailableforsensors.[CH]

RAN[0..7|?]Rangecommand/query.Rangesfrom 0 to 7 are: 3Ω, 30Ω, 300Ω,3kΩ,30kΩ, 300kΩ, 3MΩ and 30MΩ.TwoDACsarere-programmed,whichtakestime.[CH]1.4s|20ms

EXC[0..7|?]Excitationcommand/query.Ex-citations from 0 to 7 are: 3uV, 10uV, 30uV, 100uV,300uV,1mV,3mVand10mVrms.Excitation current is the nominal excitation voltage divided by one third of the selected range.TwoDACsarere-programmed,whichtakestime.[CH]1.4s|20ms

GNDS[0..1|?]Sensorgroundingcommand/query.0=floatingsensor.Noneofafloatingsensor’sleads must be in contact with the cryostat ground.Thispreferredconnectionpreventsgroundcurrents.1=groundedsensor.Agroundedsensor’scurrent return lead (-I lead) is grounded to the cryostat,e.g.forbetterthermalcontact.Thesoftware setting must correspond to the wiring oftheensor.Eachsensorcanhaveitsowngroundingsetting.[CH]

TW[0..1|?]2-or4-wiremeasurementcommand/query.0 = 4-wire connection with separate two wires for excitation current and two non-loaded wires for the voltage drop (default), 1 = only two leads for both voltage and cur-rent.Measuredvalueincludesleadresist-ances.[CH]

ARN[0..60|?] Autorangecommand/query.0=autorangingisnotused.1-60=autorangingisenabledforthecur-rentlyselectedchannel.Theargumentis“autorangingdelay”inseconds.Itspurposeistoallowasettlingtimeafteranautorangingoperation.Forexample,ARN5 means that there is a 5 seconds delay after an automatic change of range before any futheroperationcantakeplace(usuallyoneormoreA/Dconversions).Thesamedelayisused between subsequent autoranging opera-tions in a case, where range must be changed severaltimes. If autorange has to change range, the new range will be automatically saved into EEPROM.Ifthischannelislaterrecalled,theAVS-48SIwilltrythenewrange.[CH].

CONFIGURING THE TEMPERATURE CON-TROLLER

Any sensor can be used as the controlsensor.Setit for measurement and select the sensor’s DRDT polarity.Thecontrolsetpointcanbegivenonlyinohms, because the ArduinoMega2560CPUdoesnot offer enough storage space for R/T conversion tables.The“avs48si.vi”LabViewprogramfeaturestemperaturereadout.

A special feature of the AVS-48SI temperature controller is, that the output power, not the voltage orcurrent,islinearlydependentonerrorsignal.Out-put from the PID circuit is a linearly varying voltage, butthenanapproximatesquarerootistakenbeforesendingthedrivetotheoutputstage.Thedesiredresult of this is, that the closed-loop gain does not changewithpowerlevel.Withoutthesquareroot,loop gain at 1W level would be 10 times higher than at0.1Wlevel.

Connection to the heater is described in the


AVS-48SI PICOBRIDGE


PROPG[0..13|?]Proportionalgaincommand/query.Proportionalamplifier’soutputisheldatzerowhenPROPG=0.IfPROPGismadezeroduringtemperaturecontrol,theheateroutput will be solely dependent on the PID integrator’svoltage.[HTR]

INTG[0..10|?]Integratorgaincommand/query.INTG0resetstheintegratorandkeepsitsvoltageatzero.Ahighergainmeansstrongerintegrationaction.[HTR]

DERG[0..10|?]Derivatorgaincommand/query.DERG0meansnoderivation.Ahighergainmeansstrongerderivationaction.Thederiva-torhasamodifiedresponse,whichconcen-trates its effect to low frequencies and sup-pressesderivationathighfrequencies.[HTR]

INTHEATER[0..1|?]Internalheatercommand/query.TheAVS-48SIhasa100Ω 2W internal heatermainlyfortestpurposes.Itisinthermalcontactwithaforward-biasedsilicondiode.They can be used for testing the controller (seeDRDT).0 = Normal external heater (default), 1=Ext.htr.replacedbyinternal100Ωheater.

HTRDIR[0..1|?]HeaterDriverSourcecommand/query.Thetemperaturecontroller’soutputstage can be driven either by the PID circuit orbyaninternalD/Aconverter.0=PID,1=DAC.Theconverterisprogrammedasbelow.

HDACV[0.005..2.99|?]HeaterDirectDACvolt-agecommand/query.ThisistheD/Aconvert-er that can be used for driving the heater out-putstageinsteadoftheanalogPIDcircuitry.TheDACdoesnotgotoexactzero.Useoneof these two methods for nulling the heater output: 1) set the heater range to HTRRAN0, 2) direct the heater current to the internal heaterbyINTHEATER1.0.7s|0.3sThe query HDACV? measures the DAC out-put–itisnottheprogrammeddigitalvalue.

SDACV[0.005...2.99|?]SetPointDACvoltagecommand/query.Thesetpointcanbegivenin addition to resistance (SETPOINT), also in voltage.Avoltagesetpointisindependenton

paragraph“PhysicalRearPanel”undertitle“HeaterOutput”.

A typical “standard” resistance is 100Ω, but the current source heater output of the AVS-48SI accepts any value. e maximum power of 3W is achieved when heater is 50Ω. If heater resistance is higher than 50Ω, the output voltage compliance limits the achievable maximum power, if it is lower, the maxi-mum output current limits the power.

HTRRAN[0..18|?]Heaterrangecommand/query.HTRRAN0 disables the heater so, that no currentflowsintotheheater.Unlikewiththe LabView program, HTRRAN0 does not automaticallyresetothersettings.Ifyouneedtodoit:HTRRAN0;PROPG0;INTG0;DERG0(ITG0keepsthePIDintegrator’svoltageatzero).

A special feature of the AVS-48SI is that changing heater range during control has no practical effect on the output power if the systemwasinequilibriumbeforethechange.Thelongtime,about1s,thatHTRRANtakesisduetothisfeature.Pleaseobserve,thatthere must be enough power available also on thenewrangeafterachangedownwards.Theproportional gain may need to be increased in order to maintain response speed (see SAVETCRandRECALLTC).

Heater range can always be changed up-wards, but the P-gain may need to be reduced inordertoavoidinstability.Controllingatavery low percentage of the maximum range powershouldbeavoided.Maximum power with a 100Ω heater:

0. control o1. 1 µW2. 2.5 µW3. 6.2 µW4. 15.4 µW5. 38.1 µW6. 100 µW7. 249 µW8. 619 µW9. 1.54 mW

10. 3.81 mW11. 10.0 mW12. 24.9 mW13. 61.9 mW14. 154 mW15. 381 mW16. 1.00 W (0.5W@50Ω)17. 1.53 W (1.24W@50Ω)18. 1.53 W (3.06W @50Ω)


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thecontrolsensor’smeasuringrange.QuerymeasurestheDACoutputvoltage.0.7s|0.3s

SETPOINT[0...]Setpointcommand.Thiscom-mand is for giving the temperature control setpointinresistance(ohms).Theargumentmustbeafloatingpointnumber,noexpo-nentialrepresentation.Theenteredresistanceis converted to voltage on the basis of the currently selected control sensor’s measuring range.TheresultingvoltagecanbequeriedbySDACV?.If the measuring range is changed, the SETPOINT command must be repeated, because the resistance-to-voltage conversion takesplaceonlyafterthiscommand.0.1s

HTRI? Heateroutputcurrentquery.Responseisafloatingpointnumber(Amperes).Currentmeasurementworkswellevenonthelowestheaterranges.UsetheI2

HEATER * RHEATER equa-tion for calculating heating power more reli-ably.Theheateroutputisacurrentsource,andtherefore IHEATER does not reveal short circuits betweenheaterleads.0.5s

HTRV? Heateroutputvoltagequery.Responseisafloatingpointnumber(Volts).Themeas-ured voltage is low on low heater ranges and maycontainasignificantoffset.ThefullMain Calibration procedure measures this offset and saves the result, which is auto-matically subtracted from subsequent HTRV? responses.TheoffsetcanalsobedeterminedbymeasuringHTRV?whenHTRRAN=0.

HTRV? measures the voltage at the output oftheAVS-48SI.Itdoesnottakeintoaccountthepossiblevoltagedropintheheaterleads.HTRV? does react to shorts between heater leads.0.5s

HTRP? Heateroutputpowerquery.ItreturnstheproductHTRI?*HTRV?.Itisbettertocalculate the power as I2

HEATER * RHEATER on the lowest power ranges if more accuracy is needed.Ontheotherhand,HTRP?hasthebenefit,thatitreactstobothshortsandopen

circuitsintheheaterconnection.0.5s

ERRSIGNAL? Errorsignalquery.Thisisthemeasured difference between the control sen-sor’svalueandthesetpoint,bothasvoltages.Error signal’s polarity depends on DRDT as below.0.5s

DRDT[0..3|?]Controlpolaritycommand/query.0 = for sensor that has a positive dR/dT, 1 = fornegativedR/dT.DRDTdeterminesalsothe behaviour of the rear panel ERROR BNC output: 0: signal - setpoint voltage1 : setpoint voltage - signal2 : testvoltage - setpoint voltage3 : setpoint voltage – testvoltageTestvoltage is an internally generated voltage ofabout0.6-0.65Volts(forwardbiasedsilicondiode in thermal contact with the internal 100Ωheaterresistor“INTHEATER”).A simple test to the temperature controller can be done as follows: Connect a DVM to therearpanelCONTROLERRORoutput.Givecommands“INTHEATER1;DRDT3;SDACV0.64;PROPG10;HTRRAN16”.Theerrorsignalshouldnowstarttoapproachzero.When approaching becomes slow or stops, is-sue“INTG5”.Approachingshouldstartagainas integrator resets the remaining control error.Thefinalerrorshouldfluctuatearoundzero.Query the output:HTRI?=>70-80mAHTRV?=>7-8VHTRP?=>~0.5W

HOLDMODE[0..1|?]Holdmodecommand/query.Command: System goes into hold mode by issuingHOLDMODE1.Systemcomesoff from the hold mode by issuing HOLD-MODE0.Bothprocessestakesometime.

Query:0=normaloperation,1=holding.

In hold mode, the PID integrator’s output is replacedbyaD/Aconverter.Itisprogrammedto output the voltage that is measured by the Go-to-Holdprocess.Youcanvisitandmeas-ure other sensors in this mode, but you must


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SAVING SETTINGS FOR LATER USE

Settings and parameters are saved into an EEPROM, whose write count is guaranteed up to 100,000 times.Awornoutmemorycannotbereplaced.Inorder to prevent the write count from growing un-necessarily,thefirmwaredoesnotsaveanythingautomatically.Instead,theusermustexplicitlysaveitemsthatneedtobeinmemory.Thisisthelistofthe save commands, and what they do:

SAVEREF True values of the 7 reference resis-torsaresavedbythiscommand.Referto“CalibratingtheReferences”foradescriptionon how these values are entered and saved ormeasuredandsaved.Thiscalibrationisneededonlyinfewcases.

SAVEADCThissavesthescalefactorandthezerooffsetoftheA/Dconverter.Referto“Cali-bratingtheA/DandD/Aconverters”forhowto calibrate the converters so, that the analog outputscomplywithyourownDVM.Thiscalibration should not be done, unless such a compliancetoahighaccuracyisneeded.

SAVECAL 128 correcting factors for the scale and offset of the resistance bridge are saved by this command, which is to be used after the maincalibrationprocedure.Eachcombina-tion of range and excitation has its own pair of numbers, which correct the analog and digital outputsoftheself-balancingbridgecircuit.Referto“CalibratingtheBridge”.

SAVEBRD Saves the following properties of a channel for later RECALLing of that channel: Range, Excitation, 2/4-wire sensor connection, floatingorgroundedsensorandautorangingdelay(autorangingisenabledifdelayis>0).•Ifyouwanttosavethecurrentlyeffective

A/D CONVERSION

ADC[1..1000|?]Analog-to-DigitalConversioncommand/query Command:Makesoneormoreconversions,whosemeanvalueiscalculated.100conver-sionsaremadein20seconds.

Ifanyofthereadingsexceeds2.8Vorfallsbelow0.2V,autorangewillchangetherangeifautorangeisenabled.RefertotheARNcommand.

ADC0orwithoutargumentisADC1.Query:Outputsthecalculatedaverage.TheresultisafloatingpointnumberinVolts.TheA/Dconversionfunctionchecksforsomeerrors, so the ERR? query after ADC? can be useful.216ms

RES[1...1000|?]ResistanceCommandandQuery.Command:SameasADCwithanothername.Query: The voltage is converted to resist-ance on the basis of the currently effective measuringrange.OtherwisesameasADC?.216ms

STATISTICS

MAX?, MIN? These queries return the maximum and minimum ADC values (in Volts) of con-versionsaveragedforoneADCxcommand.

STD Standard deviation of the averaged ADC conversions.UsealongaverageforareliableSTD.Ifnoiseispurelyrandom,STDbehavesas noise: two times higher STD means two timeshighervoltagenoiseattheinput.Ifthemeasureddatahasatrend,STDisoflittleuse.

returnbacktothecontrolsensorbeforeexit-inghold.Somedriftduringholdisunavoid-able,asthereisnoactivecontrol.Theamountof drift depends on how near the system was initially to equilibrium and how stable is the heatload.Theprocedureitselfcausesalmostnochangeincontroltemperature.2.3sfor0=>1,60msfor1=>0.

QRATIOThisissimply(MAX-MIN)/STD.Forapurelyrandomnoise,QRATIOisabout5.Amuchhigherfiguremaytellaboutaninterfer-ingspikeinthedata,whereasamuchlowerfigurecantellaboutinsufficientnumberofsamples.Qratioisalsoaffectedbythedigitis-ingstepwhenexcitationishigh.Itisbestusedatlowexcitations.


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settings for a channel, give the command SAVEBRD.•Ifyouarenotsureaboutthecurrentset-tings,youcanfirstquerythem.•ForprogrammingallsettingsforchannelNo.x,constructalinelikethis:CHx;EXC2;RAN3;TW0;ARN5;OPC?Polltheresponseforcharacter“1”.Whenit shows that the whole line has been han-dled,issueSAVEBRD.Thedrawbackofthis method is, that the bridge actually goes to the programmed settings, which can lead to unwanted measuring of some sensors at a highexcitationcurrent.Refertodescriptionof“PRESETMODE”onhowtoprogramthechannelsquicklywithoutchangingbridgestate.

SAVETCR Each of the 18 heater ranges of the temperature controller can have its own PID parameters (proportional, integration and derivationgains).Theideais,thatdiffer-ent control temperatures often need different heating power and that thermal parameters of the system can change a lot at very low temperatures.MakingthePIDparametersde-pendent on power level is therefore somewhat equivalenttomakingthemdependentdirectlyontemperature.Justaswiththebridge,thePID parameters can be saved and recalled as propertiesofaheaterpowerrange.

Saving properties of the currently se-lected heater range is made by issuing the SAVETCR command after suitable parameters havebeenmadeeffective.Referto“PRE-SETMODE”forhowtoprogrammanyheaterrangesquickly.Example:HTRRAN5;PROPG10;ITG5;DERG0;SAVETCR;OPC?1.2s

SAVELINETERM Saves the line terminator, which has been previously set by command LINE-TERM[0..3].

PRESETMODE[0..1]PresetmodeisforsavingpropertiesintotheEEPROMwithoutmakingthem effective, in other words, without affect-ing the states of the bridge or the temperature controller.Programmingthechannelsand

heater ranges is much faster in the preset mode and there is no danger of accidental excessheatingofsensorsortheheater.Forexample, pre-program range and excitation of channels 1 and 2:PRESETMODE1 (starts the mode)CH1;RAN4;EXC3CH2;RAN5;EXC2SAVEBRD (saves both channels’ properties)PRESETMODE0 (ends the mode and sets the bridge to the last programmed channel)

Recall the pre-programmed Channel #1 byRECALLBR1.

Properties of a heater range are pre-pro-grammed in the same way:

PRESETMODE1HTRRAN5;PROPG7;INTG5;DERG0HTRRAN6;PROPG8;INTG6;DERG0SAVETCRPRESETMODE0 (controller is left to the last programmed heater range using its new PID parameters).

Forexample,takeheaterrange#5inuse:RECALLTC5.

The PRESETMODE1 command needs 20ms whereas return to normal with PRESET-MODE0needs1.3seconds.

RECALLING SAVED SETTINGS

RECALLBR[0..7]Thesavedpropertiesofachan-nelcanbemadeeffectivebyrecalling.Argument is the number of the channel to be recalled.Thebridgegoesimmediatelytotherecalledstate.1.6s

If you simply change the channel from CHx to CHy by sending only CHy, this new channel will be measured using settings that were effective for CHx, not those that are in thenon-volatilememoryforCHy.Theideais, that you can use the same settings for any channelbyjustselectingthechannel.Youcan alternatively use individual settings for eachchannelbyfirstsavingandthenrecallingthem.


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REAR PANEL ANALOG OUTPUTS

ANALOG OUTBNC[0..1|?]RearpanelAnalogOuputcommand/

query.TheAnalogOutBNCcanoutputtwoquantities:0: Voltage proportional to (RSENSOR/Range) * 3V1: Voltage proportional to (VSENSOR - VSETPOINT )* 3V

(Reversed, if DRDT=1)BNC0 is the voltage measured normally by theADCorREScommands.

Recalling is very handy and, with au-toranging, it requires a minimum number ofcommandsinascanningapplication.Ifautoranging changes range, the new range is automaticallysavedintotheEEPROM.Whenthis channel is recalled again, the bridge tries the new range and no further autoranging operationsareneeded.

A simple scanning application of pre-pro-grammed channels 1-3 would need only

RECALLBR1;DLY10;ADC20;RES?RECALLBR2;DLY10;ADC20;RES?RECALLBR3;DLY10;ADC20;RES?

Should one need to change the excitation of e.g.CH2:

RECALLBR2;EXC[newexc];SAVEBR;OPC?

RECALLBR2makesCH2activeandsoen-suresthatthenewexcitationissavedforCH2.

RECALLTC[1..18]Recallstheheaterrange(=theargument)withitssavedPIDparameters.Therecalled settings are made effective immedi-ately.RECALL0isnotincluded,becauseitdisablescontrols,setsallparameterstozeroandresetstheintegrator.Thiscoulddisruptthecontrolsession.0.3s

If you select a new heater range without recalling it, the currently effective PID param-eters, instead of the saved ones, are used for thenewrange.

USER DAC UDACV[0.005..2.99|?]UserDACvoltage

command/query.TheUserDACisalwaysavailable for you, if you need a very precise programmablevoltageinyourlaboratory.Thesettlingresolutionofthe16-bitDACis50μVandabsolutecalibrationaccuracy±100μV.The output is not protected, do not supply energyintoit.0.7sUDACV? query causes the output voltage to bemeasuredbytheA/Dconverter.Itisnotthedigital programmed value and therefore it can beslightlydifferent.1.1s

By building an external scaling/level shift-ing circuit, arbitrary unipolar or bipolar DAC outputscanberealized.ItisalsopossibletoplacesuchacircuitinsidetheAVS-48SIunit.A +/-15V power connector is available inside forsuchpurposes.Contactfactory.

CONTROL SET POINTSDACV[0.005..2.99|?]SetPointVoltagecom-

mand/query.TheSetPointDACisalsoavail-able for your own purposes, if temperature controlisnotinuse.Ithasthesamesettlingresolution and calibration accuracy as the UserDAC.Theoutputisnotprotected.0.7s|1.1s. The SDACV command is used for setting the set point voltage in applications, where the analog CONTROL SET POINT voltage isusedforsomeexternalpurpose.Itdoesnotdepend on measuring range and it does not needtobere-enteredifrangeischanged.

On the contrary, the SETPOINT com-mand is used in temperature control applica-tions.Thensetpointisgiveninohms,andthefirmwareconvertsittoDACvoltage,whichdependsonthecurrentmeasuringrange.ThisconversiontakesplaceonlyaftertheSET-POINTcommand.Therefore,thiscommandwith its previous argument must be repeated afterthemeasuringrangewaschanged.


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CALIBRATION

The AVS-48SI has three self-calibration processes for maintaining its accuracy, which is exceptionally goodamonglowtemperatureresistancebridges.

• The accuracy of the instrument’s digital output re-lies on Main Calibration.Althoughthisproceduretakesalotoftime,itcanbemadeinsituwithoutmoving the instrument, it is completely automatic andnoexternalinstrumentsareneeded.TheMainCalibration cancels most of the effects of tempera-turechangesandagingoftheinstrument.ThemoreoftenMainCalibrationisrun,thebetter.

• Calibration of the A/D and D/A converters changes the offset and scale factors of both the analog-to-digital and digital-to-analog convert-ers.TheideaofthiscalibrationisnottoachieveanabsoluteaccuracybuttomaketheAVS-48SItocomplywithyourownlaboratoryinstruments.This calibration is not necessary unless accuracy of suchacomplianceisrequired.AnexternalDVMisnecessary.

• The Main Calibration relies on seven wire-wound ultra-stableresistors.Their“true”valueshavebeenmeasured before delivery and saved into a non-volatilememory.Insomerarecases,e.g.ifthepreamplifierhasbeenreplaced,thosevaluesmustbeeitherenteredorfirstmeasuredandthenenteredandsavedagain.ThisismadewiththehelpoftheReference Resistor Calibration.Averyaccuratehigh-end4-wireohmmeterisrequired.

MAIN CALIBRATION

During a full Main Calibration, seven wire-wound ultra-stable reference resistors are measured, each using its best corresponding measuring range and all8excitations.Inaddition,eachrange-excitationpairisusedformeasuringazeroresistance.Thismakes128measurementsaltogether.Onthelowestexcitations, averages consist of 800 A/D conver-sions.Thereforethiscommandtakesalongtimetocomplete.Thefullcalibrationcanberuninthenighttime.

CALIBRATION PRINCIPLEThe idea of this procedure is to compare readings

fromthemeasuredreferenceswiththestated“true”

values of them and to calculate correction factors thatmakethemequal.Butunlikewithmostotherinstruments, the correction factors do not affect the digitaloutputalone.Instead,theyfine-adjusttheoffset of the phase-sensitive detector and the magni-tude of the excitation current so that measuring the analog output results in readings that correspond to thereferences.Thatiswhythemaincalibrationcor-rectsalsotheanalogoutput.

AFTER CALIBRATIONCompletion of the long calibration procedure is

indicated by lighting the CP and DC indicators on theAVS-48SI’sphysicalfrontpanel.Completioncan also be seen by adding the ERR? query after theCALIBRATEcommand.Iftherehasbeennoerror (response = 0), the calibration should be tested by measuring most relevant reference resistors at themostrelevantexcitations.Comparetheread-ingswiththestated“true”valuesofthereferences.Those values are obtained by REFIDx;REFVALUE? (x=0..7).Ifthevaluesagree,savethecalibrationintoEEPROM by SAVECAL.Afterthat,theoldcali-brationcannotberestored.Ifyoudonotsavethenew calibration, if will be in effect until the CPU is booted, the CPU is RESTARTed, or the old calibra-tionisreadfromtheEEPROMbyEPRCAL.

PRECAUTIONSAlthough calibration of low ranges and high

excitationsislikelytobesuccesfulwithoutanyprecautions, the situation is different when the high-estranges(100kΩ..30MΩ) are calibrated using the lowestexcitations(3μV..100μV).

The wire-wound resistors are -because of their construction- sensitive to vibration in a magnetic field(likethatoftheearth!).Alsothecircuitboardscangeneratetinyvoltagesiftheyvibrate.Asuc-cesful calibration of the lowest ranges/excitations requiresthatthepreamplifierisisolatedfromvibra-tionandrapidlychangingmagneticfields.Inad-dition,ifanythingisconnectedtothepreamplifierinput,itmustbewellshielded.CheckbeforestartingtocalibratethatthesignalisOK.Select3MΩ range, 3μVexcitationand1MΩreference(“REFID7”).Watch the red OVL and green AL lights on the AVS-48SIfrontpanel.Ifyouseeeitherofthemblinking,there is probably too much mains hum in the signal


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for successful calibration of the highest range(s) and lowestexcitation(s).Thesetwophotosshow,howthesignalbehaves.Forgettingmoreinformationabout the signal:

Connect an oscilloscope to the AC OUT monitor output.Becauseofour“groundeverythingevery-where”-principle,theoscilloscope can be connected normallywithonecoaxwithgroundedbraid.Thefirstphotoshowsasoundsignal.Ashort-circuitplugis connected to the input, and the trace never exceeds the±2Vlimitsofsignaloverload.Calibrationofthisrange/excitationpairshouldsucceedunlikeinthesecond photo, where a small amout of mains hum is fedintothebox.

If your sensors or the sensor wires are not per-fectly shielded, you may need to detach the input connectorbeforestartingtocalibrate.Inserttheshort-circuit plug into the input rather than letting it open.

Even if one cannot get a sound signal for the worst ran/exc combinations, the higher excitation ranges or lower resistance ranges may have no prob-lemsandthentheycalibratesuccesfully.

CALIBRATE[0..2]StartstheautomaticMainCali-brationProcedure.All8excitationsareusedfor measuring long averages on all 8 measur-ingranges.

0: Full calibration of all range-excitation pairs.Usedformaintainingmaximumac-curacyofthebridge.Takesabout3.5hoursto complete, and is therefore intended to be runinthenighttime.Whencalibrationiscomplete, the green CP and DC indicators on the AVS-48SI physical front panel light until the CPU receives any command via the serial interface.Thecalibrationcanbetestedbeforesavingitintothenon-volatilememory.Saveitby command SAVECAL.

This calibration calibrates the digital output and eliminates most of the drift of the analogoutput.

One can try to calculate the input noise from this sound trace as follows:peak-to-peaknoiseisabout2volts,asseenfromthephoto,andrmsnoiseis1/5ofit=0.4V.Theamplifiergain(see“ACMonitorOut”)is340000,whichmakes1.2μVrmsatthein-put.Thismuststillbedividedbysqrt(Δf),whereΔf=100istheapproximatenoisebandwidthfromanFFTmeasurement.Thiscalculationyieldstherefore120nV/sqrt(Hz).Thenoiseequationgives130nV/sqrt(Hz)for1MΩat300K. For comparison, the input noise of the bridge itself is 5nV/sqrt(Hz).

One10cmpieceofwirefeeds50Hzhumintothepreamplifier.Because of the high measured resistance (1MΩ reference), the hum couples capacitively to the input and generates an inter-ference,whichcausesoverload.Dependingonthefrequencyand severity of clipping, such a signal would lead to a bad or extremelybadcalibrationofthisrange/excitationpair.Scalesoftheoscilloscopearesameinbothphotos.Vibrationorfastchangingmagneticfieldscanalsodisturbcalibration.Anactualmeasurement,inturn,issensitivetovibra-tionoftheleadstothesensors.

Full calibration must be made, if the ADC and DAC calibration has been run, or if the values of the reference resistors have been changed.


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ENTERING VALUES OF CALIBRATION REF-ERENCES

Values of the 7 calibration references are saved in thenon-volatileEEPROMmemoryoftheCPU.Theaccuracy of the bridge depends on these ultra-stable resistors.Ifthepreamplifierunitischanged,valuesof the new unit’s references must be entered the firmwareandsaved.Thevalues, originally meas-uredbyPicowatt,arewrittenonastickerinsidethepreamplifier’sbottomcover.Thereferenceresis-tors are measured by the bridge as any other sensor (selectCH0andREFID[0..7]).IftheAVS-48SIhasbeen just calibrated, the measured values correspond tothesavedvaluestoahighaccuracy.

1: Same as above, but with much shorter averagesandshortersettlingtimes.CALI-BRATE1 needs less time, about 30 minutes, butatthecostofreducedaccuracy.Itismainlyintendedforproduction.Especiallyonlow excitation ranges, the short averages do notguaranteegoodcalibration.

2: CALIBRATE2 starts a slow partial calibration.Itcalibratesonlythecurrentlyselected range and excitation using long aver-agesjustlikethefullcalibrationofalterna-tive0.Usethismodebeforeanaccuratemeasurement that does not need many ranges orexcitations.Timerequiredisdependenton excitation, the maximum being about 5 minutesat3μV.

This procedure affects only the correction factorsofthecalibratedrange-excitationpair.SAVECAL after Calibrate2 updates factors for the calibrated properties, but it retains the calibrationofotherranges/excitations.

If the main calibration fails and it has not yet been saved, the old calibration can be restored by com-mand EPRCAL(EePromReadCALibration).

CALIBRATION OF THE A/D AND D/A CON-VERTERS

The offset and gain errors of the analog-to-digital converter are corrected by software, and the correc-tionfactorsarestoredinanEEPROM.Theywereinitially measured as a part of the manufacturing process.ItispossibletorecalibratetheADCso,thatitcorrespondstoyourownexternalDVM’sreading.Good compliance with your instruments, if that is required,isthemainreasontorunthisprocedure.The ADC itself is very stable and it will not need recalibrationotherwise.

The outputs of the digital-to-analog converters are corrected, in turn, by measuring them with the ADCandthenapplyingsoftwarefeedback.Calibra-tion of the ADC adjusts all the rear panel outputs so,thattheyagreewithyourDVM.Notethattheabsolute accuracy of this calibration cannot be better thanyourDVM.

PROCEDURE: 1) Connect your DVM to the CONTROL SET

POINT rear panel output 2) Send command CALADC.Thisstartsthemode.3) The DVM should show a voltage near to 0.1000Volts=VLOW

4) Enter this value by sending command DVMLO VLOW

5) The program proceeds, and your DVM shouldbenearto2.8000V=VHI

6)EnterthisvaluebysendingcommandDVMHI VHI

The procedure has now all the data it needs, andthemodeendsbyitself.ADCcalibrationis now complete, and your DVM should show 2.8000V.Youcantestthenewcalibrationbythe SDACV[0.005...2.99]command.

Save the new calibration into EEPROM by“SAVEADC”.Ifthenewcalibrationisnotsaved, it remains in effect only until the CPU isrestartedorrebooted.ThenoldcoefficientsarereadfromtheEEPROM.Alternatively,theoldADCcoefficientscanbereadbackintoRAMbyissuingcommand“EPRADC”.

Full calibration must be made, if the ADC andDACcalibrationhasbeenrun.


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The“true”valuesofthereferencescanbeenteredintotheprogrambyfirstgivingtheordinalnumberof each resistor (REFID) and then its stated value (REFVALUE[argument]).Whenalloranyofthe7valueshavebeenentered,theresultcanbecheckedagainst spelling errors by giving REFIDx and then queringREFVALUE?Thenew,checkedvaluesaresaved by sending command SAVEREF.

REFID[0..7|?]Referenceordernumbercommand/query.Thereferenceshavethefollowingnominal values from number 0 to 7: Zero, 1, 10 and 100Ω,1,10and100kΩ 1MΩ.REFID[x]selectsareferenceandRE-FID? query returns the ordinal number of the referencethatiscurrentlyselected.

REFVALUE[0..1100000|?]Referencevaluecom-mand/query.Thiscommandisusedforgivinga value to reference, whose number was previouslyspecifiedbytheREFIDcommand.Usefloatingpointrepresentation,exponentialformatisnotunderstoodbytheArduino2560CPU.

The REFVALUE? query returns the value of the reference, whose ordinal number was specifiedbyREFID[x].Usethiscommandcarefully:IfyoubymistaketypeREFVALUEwithoutthequestionmark,theprograminter-prets this as a command with argument = 0 andsetsthisresistor’svalueto0ohms.

Values given by the REFVALUE com-mand remain in RAM memory until the CPU isbooted(atpower-on).ThentheoldvaluesarereadfromtheEEPROM.Theoldvaluescan also be recalled by command EPRREF.

The new values are saved permanently by sending SAVEREFcommand(noargument).

MEASURING VALUES OF CALIBRATION REFERENCE RESISTORS

This procedure requires an external high-end ohm-meter and a special cable that must be built by the user.

The ohmmeter must be capable of measuring resistancesfrom1Ωto1MΩwitharesolutionof1E-5.Becauseofthelowestreferencevalues,4-wiremeasurement is necessary and so is also offset

compensation (the DVM alternates the polarity of themeasuringcurrent).Recalibration of the 7 refer-ence resistors should be done only, if one is sure that this does not degrade the calibration.Picowatthasrecordsofthevaluesatthetimeofshipping.Theyhavealsobeenwrittenonastickerinsidethebottomcoverofthepreamplifier.

1. Prepare the measuring cable. e shielded cable must have 4 wires for +I, +V, -V and -I. Make the connections to your ohmmeter as required.

The AVS-48SI accessories include a pre-wired Molex 22-01-2045 connector:

pin function wire color1 +I brown2 +V red3 -V orange4 -I yellowSolder this cable to your prepared DVM cable.

Photos on the next page show, how the cable is connected.

Measurement and entering the values is made using theCALREFprocedure.Afterthiscommandthebridge is in a mode, where the reference resistors are isolated from other circuitry so, that they can be measured.Duringthebridge’snormaloperation,thiswouldnotbepossible.

CALREF[0..1]Commandforstarting/endingcalibration mode for the references with theaidofanexternalohmmeter.Beforestarting to measure the reference values, query and write down the previous values (REFIDx;REFVALUE?).Theycannotberestoredafterthenewvalueshavebeensaved.This procedure is best used from a hyperter-minalprogram.

1) Send CALREF 1 for starting the mode 2)SendREFID1. 3) Read the resistance R1 from your ohmme-

ter.Writeitdownasafloatingpointnumberinohms.

4)SendREFVALUE[R1] 5)goto2andcommandREFID2andsoon.

When all 7 resistors has been measured and


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A 4-way cable is connected to the multiplexer board. e shield is gounded

Wires from right to le: +I, +V, -V, -I. e white current return lead (-I) is in contact with cirtuit ground and the box.

e bottom cover is shielding the multiplexer board against low-frequency interference. It should be in electrical contact with the chassis in order to be useful.

entered, remove the external ohmmeter and sendCALREF0forendingthismode.Checkthe new values for typing errors by using REFID[x]commandsandREFVALUE?queries.TheenteredvaluesremainineffectuntiltheCPUboxisre-started.CommandSAVEREF (without argument) saves them in theEEPROM.Ifthenewvaluesarenotsaved,oldvaluesarereadatstart-up.Theycanalsobe read from the EEPROM to RAM any time by sending command EPRREF(noargument).Thiscommanddoesnotrestoreanythingelse.

If you see a typing error or otherwise a suspectvalue,youcanstartthismodeagain.Itis not necessary to go through all values, you can measure and enter only the wrong value andthensaveagain.

OTHER COMMANDS

DLY[0..30]Thisdelayfunctioninsertsadelaybetween two commands or queries on the commandline.Argumentisseconds.Donotuse DLY as the last item on a row, because it doesnotpreventsendinganewlinetooearly.Use OPC?, ERR? or any other query as the lastitemandpollfortheresponse.

REPEAT This command repeats one command linecontinuously.Thecommandsandqueriesbehave excactly similarly as if only one the linewassent.Ifthelineincludesqueries,theCPU sends responses and your program can readthemastheycome.RepeatingisstoppedbysendinganythingviatheRS232line.Ex-amples with a hyperterminal program:

ADC5;ADC?;REPEATresponse:1.23451.23471.2343etc.

Full main calibration must be run after hav-ing changed any of the reference resistor values.


AVS-48SI PICOBRIDGE


UDACV1;DLY2;UDACV2;DLY2;REPEATResponse: The user DAC output toggles between1and2volts.TheDLY2givestheDACvoltagetimetostabilizesothatyoucanseebothfinalvalues.

TIME and TIME? These are used for measuring the timetakenbyacommand,queryoracom-pletecommandline.TheTIMEcommandisplaced before the sequence to be tested, and theTIME?issetafterit.Theresultsareinmilliseconds.Examples:

TIME;TIME?=>1010ms general overhead

TIME;ADC;TIME?=>215mssigma-delta ADC alone needs 180ms

TIME;ADC100;TIME?=>19537ms100conversionsatmax.speed,19.5s

TIME;RAN3;TIME?=>1371msCommand requires that two DACs are repro-grammed.Needs1.37s.

TIME;UDACV2.5;TIME?=>671ms(the UDACV and SDACV commands need only20msifargumentwasnotchanged).

RESTARTRestartcommand.Re-startstheCPU and sets it to default state: Reference channel #0, 300R range, 10mV excitation, 100Rreferenceresistor,4-wireandfloatingsensor, no autoranging and previously selected lineterminator.Doesnotchangepre-pro-grammedpropertiesnorsaveanything.Plugoff and on the mains power adapter in order to bootalsotheoperatingsystemoftheCPU.

DEFAULTS Sets all properties of the bridge and temperature controller to safe initial values and saves them into EEPROM:

Selected:Channel0,Ref.resistor100Ω, Range 300Ω,excitation10mV,noautorange.

Other channels: Range 30MΩ, excitations 3μV,sensorsfloating,4-wire,noautoranging,lineterminatorCRLF,allPIDparameterszero.

RESETALL This command resets all calibration coefficients:OffsetandscalecorrectionDACsarebothsetto1.5Volts,whichisinthemiddleoftheir0.005..2.99Voutputrange.

TheoffsetvoltagecorrectionfactoroftheADCissetto0.00andscalecorrectionfac-torto1.00.

The“true”valuesofthereferenceresistorsare set to 1Ω, 10Ω...1MΩ.

TheresetvaluesaresavedintoEEPROM.Theoldvalues,settingsorpropertiescan-notberestored.

Usethiscommandwithgreatcare!Aftersav-ing the reset values, everything must be calibratedagain.

ERROR MESSAGES

ERR? Error query should be placed in the end of a messageline.Outputisatextstring,whereaplain“0”meansnoerror.Severalerrormes-sagesmaybeconcatenatedintoonestring.

Commands: Because a command never produces a response, there is no way for the bridgetoinformaboutacommanderror.One must use the ERR? query routinely or ifanerrorissuspected.

Queries: Because a query always produces a response,theCPUsendsaquestionmark,if there was a query error or if the ADC? queryreportsaboutanerror.Inordertoknowmoreabouttheerror,issuetheERR?query.

ErrorregisterisemptiedbytheERR?query.Many commands and autoranging also reset the register, so it must be queried as close totheerrorsourceaspossible.

Errormessage,ifacommandorqueryisunknownor misspelled

Command[command]notrecognizedQuery[query]notrecognized

Error messages from A/D conversion:adcoverrangeV>3V


AVS-48SI PICOBRIDGE


CABLE SPECIFICATIONS

e AVS-48SI-W comes with two cables, Picobus Cable and Serial Cable. e 5 meter Picobus cable connects the converter to the AVS-48SI and the 1.5 meter Serial cable connects the box to the computer directly or via an USB-232 converter. e -F ver-sion has an additional 5- or 10- meter optical cable, whereas the 5-meter Picobus cable is shortened to 1.5m.

Picobus Cable (PB9P15P6W5M) for -W versionPicobus Cable (PB9P15P6W1.5M) for -F version

e male DE9P and male DA15P are connected by a braided (shielded) cable with 6 conductors (e.g. Tasker C6015). Length: 5 meters for -W, 1.5 meters for -F.

Note that the shielding braid must remain isolated from the 15-pin connector shell of the -W type cable. A 100nF ceramic capacitor with shortest possible leads connects the braid to the connector shell. e

DE9P DA15Ppin color Picobus name

1 9 brown +5V (oating)2 -- -- 3 -- -- 4 15 grey DC5 7 white GND (oating)6 6 lila AL7 4 yellow CP8 5 green DI9 -- --

DE9SDE9P RS232 Description1 - - -2 brown RXD RS232 output box=>PC3 lila TXD RS232 input PC=>box4 yellow DTR DC (for Picobus appl.)6 green DSR AL (for Picobus appl.)5 braid Computer ground = shielding braid7 white RTS CP (for Picobus appl.)8 gray CTS DI (for Picobus appl.)9 -

Serial Cable (RS9P9S7W1.5M)

e male DE9P and female DE9S are connected by a braided 1:1 cable of 6 conductors (e.g. Tasker C6015). is cable is for RS232 communication between the CPU box and the computer (or USB-232 converter). e DSR, RTS, CTS and DTR leads are reserved for other applications using Picobus, they are not used for RS232 communication. Length: 1.5 meters. Same for both the -W and -F versions.

Shielding braid is divided in two parts at both ends. One is connected to pin 5, and the other part to the connector’s metal shell.

adcunderrangeV<-3Vanalog error (AL=1 during A/D conversion) AC signal overload OVLHigh lead resistance LRES

Error messages from calibrationAny error message from A/D conversioncalibration aborted by useroffsetcorrection>2.9Voffsetcorrection<0.1Vscalecorrection>2.9Vscalecorrection<0.1V

braid is connected to the shell of the 9-way connec-tor at the AVS-48SI end. is arrangement reduces the antenna eect at high frequencies while not providing a path for ground currents at the mains frequency. Inside the AVS-48SI, Picobus signals and its power supply are galvanically isolated from the bridge ground . We recommend strongly that the braid is connected rmly to the conducting wall of the shielded room at the entering point. is completely prevents the cable from taking high frequences inside the Faraday shield.

With the 1.5M long cable (-F version), braid is connected directly to both connector shells. No capacitor is needed. is is because the AVS48SI-Pi-colink Box1 is located inside the shielded room near to the AVS-48SI main unit and it shares the common ground with the bridge


AVS-48SI PICOBRIDGE


RE-PROGRAMMING THE ARDUINO MEGA2560 CPU (Windows)e rmware can be updated by reprogramming the Arduino Mega2560 board. In order to do this, you need

a USB cable (type A/B) Arduino development soware for Mega2560. It is

best to download this from Arduino WEB site. e new rmware version. It is available from us.

1. Follow Arduino’s instructions to download and install their programming environment soware.

2. Open the four screws holding the “front” panel of the CPU box (the panel with the DA15S connector or opto connectors). e Picobus cable from this connector to the AVS-48SI must have been removed. Plug the “A” type connector into the USB connector of your computer and the “B” connector into the “hidden” USB connector inside the CPU box (refer to the photo). e box will now start, as it gets power from the computer’s USB.

3. StarttheArduinoprogrammingenvironment.SelecttheArduinoMega2560boardtypeandchecktheserialportnumber.

4. Open the downloaded new version of the “avs48232_xry.ino” soware (“sketch”, as they call it). From the Sketch menu, select UP-LOAD. If you do not get any error messages, updating has been done in a few seconds. You can now detach the USB cable, x the rear panel and connect the 25/15 Picobus cable to the resistance bridge. en test the new rmware using an RS232 terminal program or your own soware.

Before asking us to email an updated version, please check and tell us your old rmware version so, that we can send to you also the old version for backup. e version number is the last item in the response to IDN?

Re-programming does not alter any of the cali-bration factors nor saved channel or heater range properties.

The CPU unit is opened by removing the front plate of the DA15 con-nectorside.Thenthecoverplatecanbepulledoff.Ifitdoesnotcomeouteasily,unscrewalsothetwotopmostscrewsontheotherside.


AVS-48SI PICOBRIDGE


SERVICE MEASUREMENTS

The A/D converter has access to many internal nodes oftheAVS-48SIcircuitry.Manyofthemaremeas-uredbyvariouscommandslistedinthismanual.There are also nodes whose voltage levels can providevaluableinformationincaseoftroubles.Allpointsarelistedbelowwithoutmoreexplanations.Contactfactoryformoreinformation.

The voltage to be measured is selected by the ADCINP[0..25|?]command(servicetab).Allre-sponsesareinvolts.

0: Ground 0V1: ADCreferencevoltage(3.00V)2: DClevelofsignalpreamp.output3: DClevelofsignalmainamp.output4: BRIDGE OUTPUT (normally used, ADC?)5: DClevelofexc.preamp.output6: DClevelofexc.mainamp.output7: Exc.channelPSDintegratoroutput8: Sensor DC bias voltage (not in use)9: Integratorvolt.ofcapacit.compens.circuit10: PID control error11: PIDproportionalampl.output12: PID integrator voltage13: PID derivator output14: PID Square-root circuit’s output voltage15: PID heater drive voltage16: PIDheateroutputvoltage(HTRV?)17: PID heater current (HTRI?)18: Excitation adjust DAC voltage19: Offset adjust DAC voltage20: Excitation fast settle DAC voltage21: Signal fast settle DAC voltage22: Set Point DAC voltage (SDACV?)23: PID integrator fast settle DAC voltage24: User DAC voltage (UDACV?)25: PID heater direct DAC voltage (HDACV?)

TROUBLE SHOOTING IDEAS FOR THE SERIAL COMMUNICATION

Ifyouhavedifficultiesinestablishingserialcommu-nication between your computer and the AVS-48SI, you can try the following trouble-shooting proce-dure.Theproblemmightnotbefoundthisway,butitatleastgivesusvaluableknowledgeofwhereinthesystemtheproblempossiblyis.

Formakingthesetests,youneedahyperterminalprogram, or any other program that allows you to sendserialcommandstotheCPUbox.Typically,your modern computer has only USB ports and then you need a USB-232 adapter between the computer andtheCPU.

Communication between the AVS-48SI bridge and the CPU box uses four signals, two from the box tothebridgeandtwofromthebridgetothebox.They are AL:“alarm”lineindicatingapossibleanalogerror

(OVLorLRES).Bridge=>BoxDI:databitsBridge=>BoxDC:databitsBox=>BridgeCP:clockpulsesBox=>Bridge

Both the sent and received data bits are synchro-nizedtothesameclock.Communicationbetween the CPU and the bridge is based on our proprietary synchronous,serial“Picobus”protocol.Althoughthiscommunicationisserial,itisNOTRS232.Please do not mix synchronous and asynchronous serialformats.InsynchronousPicobuscommunica-tion, long strings, that are sent from the CPU to the bridge, contain the stateofthebridge.Theyarenotcommands.Somedata,liketheA/Dconver-sionresult,canbereadfromthebridgetotheCPU.Asynchronous serial communication between the CPU and the computer, on the other hand, uses short mnemonic commands and queries for controlling individual bridge settings and for reading conversion resultsandcurrentlyeffectivesettings.

The commandinterpreterrecognizesandinterpretsthemessagesthatithasreceived.Variousfunctions(subroutines) build the required Picobus strings and send them to the bridge, which does not have any digitalintelligenceofitsown.TheRFemissionsfromtheAVS-48SIarethereforeexceptionallylow.

Because of the slow speed of the AVS-48SI


AVS-48SI PICOBRIDGE


and tiny amounts of data, the simplest possible serial protocolcanbeused(9600bauds,8databits,noparityandonestopbit.Nohandshaking).Itisbasedon signals called TxD, RxDandGround.TxDtrans-fers data from the external computer to the box, and RxDfromtheboxbacktothecomputer.

PROCEDURE FOR THE -W VERSION

1) Remove the four cross-head screws that hold the front panel of the CPU box (the panel with the 15-wayconnector).Thenpulloffthetopcoverlid.Placethebox,sothatthefrontpanelistotheleft.YoucanseearowofseveralgreenandtworedLEDs.Theyarefortroubleshooting.LEDsontheleft(“bridgeside”)showsignalstoan from the primary interface of the AVS-48SI bridge.TheyaremarkedwithAL,DI,CPandDC.Atrightarethetwoasynchronoussignals,TxDandRxD.TheDI,AL,CPandDCsignalsontherighthavenomeaninginthisapplication.Theycanlightornot.

2) Connect a DVM to the ANALOG OUT rear panelBNCofthebridge.

3)Connecttheserialcable(RS9P9S7W1.5M)from the box to the USB-232 converter or to your computer, if it has a physical COM: port (RS232port).ConnecttheDE9/DA15cable(PB9P15P6W1.5M)fromtheAVS-48SIbridgetotheCPUbox.Switchonthebridge.

4)Connectthe+12VDCpowerplug.Thegreen“ON”light,andoneyellowLEDontheArduinoCPUboardshouldturnonaftersomeblinking.This tells that

theCPUgetspowerandthattheCPUhasbooted

5) Reduce the baudrate of the hyperterminal to 300 or600.SendthecommandRESTARTandatthesametimewatchtheTxDlight.Itshouldblink.This shows that the computer sends via TxD and thattheCPUboxisreceivingthetransmission.The CPU does not react to this command as it uses9600bauds.Increasebaudratebackto9600.

6)SendcommandsCP1andDC1.Thecorrespond-ing LEDs in the CPU box should light on and staylighted.ThesamewiththeLEDsonthe

bridgefrontpanel.Thisindicatesthat

thecommandshavebeeninterpretedcorrectly,thefirmwareprogramisrunning,and

theCPUsendsPicobusdatatothebridge,whichhasreceivedthedatasuccesfully.

7)SendcommandRESTARTagain.TheDI,DCand CP lights both in the CPU box and on the frontpanelshouldblink,whichshowsthatthebridgeissendingdata.Thebridgeshouldgotoitsdefaultstate:CH0,300Ωrangeand10mVexcita-tion.TheDVMshouldshowabout1Volt.

ThreeofthefourPicobuslinesareOK. Thisisabigmacrocommand.Correctresult

showsthatthebridgecanberemotelycontrolled.

8)SendcommandRAN1.Thiswillcauseoverloadasthebridgemeasures100Ωonthe30Ωrange.The green AL lights both on the front panel and in the CPU box turn on and the red OVL front panellightstartstoblink.ThisindicatesthatalsotheremainingALPicobuslineisOK.TheDVMwillshowabout4.2Volts.

9) Send query IDN? The response “PICOWATT,AVS-48SI,1R1”endswiththever-sionnumber(1R1oralaterversion)ofthefirm-ware.Acorrectresponsetellsthatserialdatasentby the CPU to the computer has been received succesfully.

Iftheteststopstoafailure,pleaseletusknowyourresultssothatwecantrytohelp.

PROCEDURE FOR THE -F VERSION

1) Connect the CPU box to the computer or to theUSB-232converterusingthe1.5mlongDE9P/DE9Scable(RS9P9S7W1.5M).Con-necttheAVS48SI-PicolinkBox1totheAVS-48SIbridgebythe1.5mDB9P/DA5Pcable(PB9P15P6W1.5M).

2) Connect a DVM to the ANALOG OUT rear panelBNCofthebridge.

3) The three most common reasons, why the system withoptolinkdoesnotstartare:thefibresarein


AVS-48SI PICOBRIDGE


wrongorderorsomeofthefibreshasnotbeeninsertedproperlyoranendofafibreisnotingoodcondition.thefibresaremarkedwithcolors.Theorder

in“Box1”(neartothebridge)is1,2,3,4fromlefttoright.TheorderintheCPUbox(theonewiththemainsadapter)is4,3,2,1.Use1=black,2=red,3=yellowand4=blue.Checkthattheendsofallfibresarecut

sharply.Ifsuspect,usesharpfull-flushendcutters to remove a millimeter or two from the fibres.thefibresmustbepushedasdeepastheygo.

Insertdepthis17mmfortheblackand16mmforthewhiteconnectors.Sometimesafibrewantstostopearlier.Thereceivers/transmittersandtheirthreads

aremechanicallyweakandvulnerable.Tightenonlybyfingersinordernottobreakthethings.

Insertfirstonlyfibres1and2andonlytotheCPUbox,leaveotherfibresintact.Asyounowstart the CPU by plugging in the +12V wall adapter,theblackandredfibresshouldblinkseveraltimeswiththesamebrightness.Ifthishappens,connectthesetwofibresalsotothePicolinkBox1.

4)GivecommandCP1fromthehyperterminal.ThefrontpanelCP(ClockPulses)ledshouldlightonthebridge’sphysicalfrontpanel.Givecom-mandDC1andtheDC(Datafrom“Computer”)ledshouldalsolight.Thisshowsthatthebridgereceivesbothsignals.

5)Insertfibres3and4toAVS48SI-PicolinkBox1,butnotyettotheCPUbox.GivecommandADC;ADC?Fibre3shouldblinktwotimeswhen the A/D converter sends the response from the bridge to the CPU using the DI (Data from Instrument)line.Fibre4canbelightedornot,it depends on the state of the AL (Alarm) signal, whichreactstoanalogerrors.Thebridgehasnotyetbeeninitialized,sothestatecanberandom.

6)Inserttheremainingfibreends.Disconnectandreconnect the +12V power plug or the wall adapter.Thebridgeshouldenterintostate,whereit measures an internal 100Ω resistor using 300Ω rangeand10mVexcitation.TheDVMconnectedtotheAnalogOutBNCshouldshow1.Ifyou

givecommandSDACV1.2(SetpointDACVolt-age=1.2V),thesetpointBNCshouldbeat1.2Volts.

7. Selectthe30Ωrange.Thiscausessignalover-load, which should be shown by the red OVL warning light and the green AL light on the physical front panel as well as the AL light inside theCPUunit.

If this test fails somewhere, please contact us so that wecantogethertrytofindout,why.

RV-Elektroniikka Oy PicowattVeromiehentie 14FI-01510 VANTAAFinland

e-mail: [email protected]: www.picowatt.


AVS-48SI PICOBRIDGE


Part IILabView Programs


AVS-48SI PICOBRIDGE


INTRODUCTION

Part II of this manual is for how to operate the AVS-48SI Picobridge® and its optional analog Tempera-tureControllerfromthe“avs48si.vi” LabView™ program.AlsocalibrationoftheinstrumentviaLabViewisdiscussed.

The LabView programs use the same serial interface between the computer and the Arduino CPU box as theserialoperationdescribedinPartI.Thesepro-gramsalsomakeuseofthesamecommands.Every-thinghasnotbeenwrittentwotimes.SomethingthatisnotheremaybefoundintPartIandviceversa.

All settings and calibration factors are stored in the EEPROM memory of the CPU.TheLabViewpro-grams read data from there and also save changed dataitintotheCPU.Thismeans,thatonecanchange over from using LabView to serial operation andviceversawithoutlosinganything.Therearetwo exceptions: The optional names of the seven channels and all Resistance-to-Temperature conver-sionfilesareheldinthecomputer’smemory.Sensornames and direct temperature readout are offered only by the “avs48si.vi”.

Direct temperature readout, smartfiltering,andveryinformative front panel are just examples of features and functionality that are impossible with the CPU withitslimitedprogramandstoringspace.Impor-tant is also the fact that the “avs48si.vi” is a com-plete virtual instrument, ready for use without need towritealineofprogramcode.Themeasurementresultsareavailableviaadiskfileforusebyotherprograms.Theyarealsoavailableviaafunctionalglobal variable for other simultaneously running LabViewprograms.

The exceptionally informative front panel of the “avs48si.vi”isdividedinthreesections:Theleft-most area shows all settings that are currently used formeasuringtheselectedsensor.Duringautomaticscanning, the displays change showing the settings ofthecurrentlyscannedchannel.

The area in the center shows the resistance, tem-perature and the name of the measured or scanned channel.Ifonlyonechannelismeasured,onlythischannelislighted.Ifsomechannelsarescanned,

all scanned channels are lighted so, that one can see resultsfromallsensorsatasingleglance.

The rightmost side is for the optional temperature controller.Thereyouchoosefrom18logarithmicallyspaced heater ranges, and either set or pre-program itsPIDparameters.Magnitudeofthecontrolerrorisindicatedbyastronglynon-linearizedanimatedpanel meter, which shows the trend even when the error is large but becomes very sensitive near to balance.InadditiontoshowingtheheatingpowerinWatts, an animated analog meter tells the percentage of the delivered power compared with the selected range’smaximum.

Justlikewithserialoperation,theAVS-48SIcanbeequipped with the optional AVS48SI-Picolink Opti-calFibreLink.

The AVS-48LVA version was the predecessor of this “SI”version.Thereareseveralimportantchangesbetween them:

LVAusedourproprietarysynchronized“Picobus”protocol for communication between the bridge and thecomputer,whereasSIusesthewell-knownasyn-chronousRS232protocol.

LVArequiredaWindowsPCrunningLabView.The SI version requires only an RS232 or USB port andcapabilitytouseRS232forcommunication.TheLVA could be used only via LabView, whereas the SI can be controlled either using its serial commands or viaLabView.

TheLVAsavedeverythingonPC’sdisk.TheSIkeepsallcalibrationandpre-programmedsettingsstored in the CPU so, that the same stored data can beusedbothinserialorLabViewoperation..

TheLVAdidnothaveanydigitalintelligenceofitsownbutreliedtotallyonthecomputer.TheSIhasanexternalsmallCPUunit.InordertominimizeRFinterference, this box is should be located outside the shieldedcryostatroom.

OpticalLinkwasnotavailablefortheLVA,butitisavailablefortheSIversion.

Thevirtualfrontpanelofthe“avs48si.vi”worksmorelogicallythanthatoftheold“avs48lva.vi”.


AVS-48SI PICOBRIDGE


SHORT TUTORIAL

MEASURING AND SCANNING

These instructions assume that you have at least the base version of LabView2012 or later running on yourcomputer.Ifyourcomputerdoesnothaveaphysical Com: serial port (which is also called an RS232 port), but you have a free USB port, you can getaCom:portbyusingaUSB-232converter.Aconverter made by National Instruments is avail-able from us (NI part 778472-01), but many other convertersarealsocommerciallyavailable.ConnectyourcomputertotheCPUboxbythe1.5-metercableRS9P9S7W1.5M.Alternatively,connecttheCPUboxtoyourUSB-232converterbythiscable.The CPU box is intended to be located far from the cryostat, preferably outside the shielded cryostat room.

Openthemeasurementprogrambyclicking“avs48si.vi”.

The front panel is divided in three parts: The most often needed controls for the AVS-48SI resistance bridge are on the left, while the measurement results ofthe1+7channelsareinthemiddle.Therightmostsideisfortheoptionaltemperaturecontroller.

On the bridge side, the visible values values are automatically saved for the currently selected sensor

channel when a resistance measurement or scanning isstarted.Theycan-buttheyneednot-berecalledfrom memory when this channel is selected for measurementnexttime.

On the controller side, the visible values can be saved for the currently selected heater range by clicking“ENTER”.

In addition to the front tab, the “avs48si.vi”hastwoothertabsforlessfrequentlyneeded controls and indicators: Settings tab and Servicetab.

Checkthattheshort-circuit plug is inserted in the preamplifier’s37-wayinputconnector.

Before running the program, go to the Settings Tab (makeLabViewhandtoolactive)andchecktheserialportnumber.Itmustcorrespondtothephysi-cal COM port or to the port name that the USB-232 converterisusing.

If this port number is correct, you need not do anything.Ifitisnot,selectthecorrectport,makeitdefault(DataOperations=>MakeCurrentValueDefault)andthensavethe“avs48si.vi”sothatyouneednotchecktheporteverytimeinthefuture.

StarttheVIfromLabView.The“STATE”boxshouldshow“Initialising”andthebridgesidetextsgodisabledandgrayedoutforamoment.Duringinitialisation, the program reads settings and other necessarydatafromtheCPUbox.Onceinitialisa-tionisready,thebridgeendsuptothe“IDLE”state.Youcannowstarttomeasure.

If the bridge has not yet been used, or if the CPU has just been booted, the default start-up state is chan-nel #0, where a 100Ω reference is measured on the 300Ωrangeand10mVexcitation.Ifthebridgehasalready been used, the last measured channel with itssettingsisautomaticallyrecalled.Selectnowthefollowing settings

Channel:0“Calibrators”Range: 300Ω

INSTALLATION OF THE AVS48SI.VI

Copy the“avs48si_1r0”(oranylaterversionnum-ber) directory with all its contents from the supplied memorysticktoyourharddisk.Youcanrenamethis directory, but include the version number in the name: Updated versions in the future will use many, butnotall,samesub-VIswithunchangednames.Keeping new and old versions in separate directories isalmostnecessary.Ifyouhaveanolderversiononyourdisk,renametheolddirectorybeforestartingthenewversionforthefirsttime.ThenLabViewissurenottouseautomaticallyanyofthoseolderfilesorVIs.

Donotrunprogramsfromthememorystick,butkeepitasaread-onlybackup.

Thereisnothingmoretoinstalltheprograms.Justnavigateintothenewdirectoryandclickavs48si.vi.

A measurement is stopped by selecting the IDLE state. e EXIT button is active only in the IDLE state.


AVS-48SI PICOBRIDGE


Excitation: 10mV2/4-wire: Four wireSensor grounding: Floating sensorAutorange: disabledFilter length: 20Filter mode: SMARTScan enable: disabled

The middle screen display should now show a resist-ance that is very near to 100Ω.Agreen light to the right of the FILTERMODEboxisblankeduntilthefilterhasreceived20readings.Soonafterthatitstartstoblinkasanindicationofavalidresultandthatreadingsaretaken.Stopthemeasurementbyclicking“IDLE”.

SelectCH1andre-startthemeasurement.Thisinputisshortedbytheprotectinginputplug.Itshouldshowonlyfewmilliohms.Stopthemeasurement.

While still on channel CH1, include it in a scan cyclebyselecting“SCANENABLE”=enabled.Enable also autoranging.Changerangeto3kΩ and excitationto1mV.StartthemeasurementinordertosavethesenewselectionsforCH1.

The Picobridge tries to measure the short circuit usingthe3kΩrange.Itgivesaverylowreading,and therefore the enabled autoranging changes range onestepdown.Itisnotenough,andautorangingcontinues until the lowest 3Ωrangeisreached.Thentheprogramwillhappilymeasuretheshort.YoucanstopthemeasurementnowwithIDLE.

SelectchannelCH0andclickRECALL for recall-ingitsprevioussettings.Includealsoitinthescancycle.Startandstopameasurement.ThissavesthechangedsettingsforCH0.

Now you have enabled scanning and saved good properties of two channels, which will use some dif-ferentsettings.Startscanningbyclicking“SCAN”.The scan-enabled channels are shown on the display byaslightlydifferentcolorofthechannelnumber.

The middle display will show results for both chan-nels.Achannel’sreadingisfrozenonthedisplayassoonasthefilterhasbeenfilledwithA/Dconver-sionsandthesmartfilterhasfoundthatalldatathatformtheaveragearevalid.Thecurrentlyscannedchannel’s settings are visible on the grayed panel andtheychangewhenthechannelchanges.

TEMPERATURE READOUT

Just for demonstrating temperature display, a very simpleresistance-to-temperaturecontrolfile(low_cost_pt100.txt)hasbeenassignedtochannelCH0.Ofcourse,asthereisafixedreferenceresistorinCH0 instead of a real PT-100, the temperature will showabout0.0°C.Youprobablywishtogetridofthisnon-existentsensor.Itisdescribedalittlelater.

Exitthe“avs48si.vi”,butleaveitinmemory.Fromtheoperatingdirectory,findandopenprogram“avs48si_create_r_t_information_file.vi”.Beforerunningthismulti-purposeVI,set“ProcessingMode=ReadandExit”,and“SaveMode=Save.cnfFile”.Youcannowstarttheprogram.

Ontheleftside,selectInputChannel=0.Youshouldsee“low_cost_pt100.txt”astheR/Tfile’sname,thatthefilehasthreecolumns(breakpointnumber, resistance, temperature), the sensor has positivedR/dT,thefileusesresistance(insteadofLog(R)), and that temperature is expressed in de-greesCelsius.

ThebreakpointsoftheassignedR/Tfilesareseenhighestontherightside.SelectCH0andviewthesixbreakpoints.

Inthemiddle,thefileinformationisvisibleintheformitwasreadfromthefile.

Thelowestfieldshowscommentsthatmayhavebeenwrittenonthe9firstlinesoftheR/Tfile.Theconversiondatabeginsonthetenthline(line9).

Theprogramisstillrunning.Inordertoget rid of thisdemoassignment,changethefilenamefrom“low_cost_pt100.txt”tosomethingnon-existentlike“noname.txt”orjustblank.Thenclick“ACCEPTEDITS”.Theassignmenthasbeenremovedandtheprogramends.

In order to later assignarealR/Tfile,followthesameprocedure.Placethefileintheoperatingdirec-tory.Thereisnosearchfacilityinthisprogram,soeithertypethefilenameorcopyitfromthecomput-er’sdirectoryandpasteittotheprogram.YoucanruntheVIonceagainforcheckingthatthefilewasfoundandunderstoodcorrectly.See“Resistance-TemperatureConversionFiles”.

Startthe“avs48si.vi”.TemperaturedisplayforCH0shouldhavebeendisappeared.


AVS-48SI PICOBRIDGE


CONTROLLING TEMPERATURE

(only if the -T option has been installed)

The AVS-48SI temperature controller’s heating current can be directed to a 100Ω internal resistor insteadoftheheaterinthecryostat.Thisresistoris in thermal contact with a forward-biased silicon diode.Thediode’svoltagecanbeusedtoreplacetheoutputfromtheactualbridge.Thisassemblyisforsuperficialandfasttestingofthecontroller.

Inserttheshort-circuitpluginthepreamplifierinputfor preventing signal overload that an open input willcause.ConnectaDVMtothe“ControlError”BNCoutput.Usethesettingssuggestedbelowforthistest.

Withthe“avs48si.vi”running,gotothe“Settings”tab.SelectCH1asthe“ControlChannel”(anyotherchannel than 0 can be named as the control channel), andsetDRDTto“SETPT-TESTV”.Verifythattheheater resistance has been set to 100Ω.Returntothefronttab.SelectCH1andthe300Ω range, 10mV excitationandautorangingdisabled.Startameasure-ment,whichalsomakesthesechangeseffective.

A green light should show that CH1 is the control sensor.Inthistest,itcouldbeanychannel,asthetestdoesnotusethebridgeatall.Thecontrollerdisplay is still disabled and grayed out, but as soon as you select heater range #1, the controller becomes enabled.Inordertooperate,thecontrollerrequiresthat

AchannelhasbeennamedascontrolchannelThischannelisselectedformeasurementHeaterrangeisotherthanzero

Select the following parameters: INTERNAL HEATERSETPOINT UNIT = RESISTANCESETPOINT=64Ω(0.64Vacrossdiode)PROPG = 1000HTRRAN=#16

The ENTERbuttonhasturneddarkgreyinordertoremind that there are pending changes, which need tobesaved.ClickENTER.ClickENTERafteranychanges,butwaituntilithasturneddark.Ifitturnsdarkagain,justclickitagain.

Heatingstarts.TheERRORpanelmetershouldslowlyapproachzerowithoutreachingitbecauseofthecontrolerrorofaP-controller.

As soon as approaching has become very slow, selectINTG=0.02andclickENTERwhenithasturneddark.HeatingcontinuesasthePIDintegratorworkstoresettheremainingcontrolerror.Theerrorshouldenduptozero,orveryneartoit.TheDVMconnectedtotheControlErrorBNCshouldfluctuatearoundzeroandtheAnalogOutBNCshouldshow0.64V.

Stop control by nulling the PID parameters, set the heaterrangetozero,changebacktoexternalheaterandclickENTERoncepromptedbyitschangedcolor.

Heating is stopped by setting Heater Range to zero. is also resets all PID parameters and keeps them at zero.

Turn o the “Control sensor” indicator light by setting the control channel to “NO CONTROL” (Settings tab).


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Resistance Bridge side of the avs48si.vi -pro-gram’s virtual front panel. Front tab.

FRONT TAB

BRIDGE SIDE

Input channel.Channels1..7arewiredtotheDC37S input connector and they are pin-to-pin compatiblewithchannels0..6oftheoldAVS-47,AVS-47AandAVS-47Bbridges.ChannelNo.0isreserved for measuring any one of the 7 ultra-stable calibrationreferenceresistors.ItisselectedontheSettingstab.

If you suspect that you are getting incorrect readings from a sensor, select the most suitable referencewhilekeepingtherangeandexcitationunchanged,andswitchtochannel0.Ifthereadingis near to the true resistance of the reference, the bridgeismostlikelytoworknormally.

Channel names. You can give short descriptive channel names to the channels, and these names areshownonthemaindisplay.Thebigandbrightlettersmaketheresultsmoreconvenienttoreadfromadistance.1)Selectachannel2)Recallitsparameters, if you have already used this channel,

3) enter or edit the name 4) Start a measurement for saving the edited name together with all other settingsvisibleontheleftsidedisplay.Itisnotrel-evant, whether this channel is currently connected toasensorornot.5)Stopthemeasurementbyclicking“IDLE”.Thenewnamefortheselectedsensorcomesineffect.Channelnamesaresavedoncomputerdiskinfile“avs48chnames.cfg”.

Range. Rangesfrom0-3Ωto0-30MΩareavail-able.Digitalresolutionofthedisplayis6digits,whichmeans10µΩonthelowestrangeand100Ωonthehighestrange.Resolutionofthereadingsthemselves depends on range, excitation, sensor temperature,filterlengthandpossibleexternaldis-turbancies.Startingameasurementsavestherangesetting for this channel automatically, if automatic savingofpropertiesisenabled(default).

Autorange. Autorange can be enabled or disabled individuallyforeachsensorchannel.Itchangesrangeupwards,iftheunfilteredreadingexceeds2.8/3oftherange,anddownwards,ifthereadingfallsbelow0.2/3oftherange.Autorangingactionre-startsthefilter.Itguaranteesthateachchannelismeasuredonavalidrange.Autorangingshouldbe used routinely with the exception of the pos-sibletemperaturecontrolchannel.Autorangingisextremely useful for unattended scanning on the background.Startingtomeasuresavesautorangingsetting for the selected channel automatically, if automaticsavingofpropertiesisenabled(default).

Excitation: The AVS-48SI features nominal ex-citationsfrom3µVto10mVrms.Excitationisasquare AC current, whose magnitude is the nominal excitationdividedbyonethirdoftherange.Forexample,1mVexcitationona3kΩrangecreatesacurrentof1mV/(3000ohm/3)=1µA.Thiscausesavoltagedropof1nVacrossa1kΩsensor.Excita-tionisinformofsymmetricalsquare-wave.

The exceptional insensitivity to input capacitance isauniquefeatureoftheAVS-48SIPicobridge.Itis the result of a shape-based compensation circuit, whichmakesuseofthesquarewaveform.Evensmallpassivefiltersareallowedinthesensorleadsfor preventing high frequencies from entering thecryostat.Startingtomeasuresavesthesettingautomatically for the selected channel, if automatic


AVS-48SI PICOBRIDGE


savingofpropertiesisenabled(default).

Filter length. Excitation power must be extremely lowinordernottoheatacryogenicsensor.Thismakesthesignal-to-noiseratiopoor,whichisseenaslargerandomnoiseinthereadings.Thepricethatnormalaveragingfiltershavetopayfortheirsmoothingaction,istheirslowresponse.A20-sec-ondfiltertakes20secondstosettle after a change inchannelorrange.

The AVS-48SI software addresses this problem withits“smartfilter”,thatoutputssinglerawread-ingsuntilthefilterhasbeenfilleduptoitslength.Thenitstartstooutputarunningaverage.Onecangetaroughestimateofthefinalvalueinsecondsevenifthefilterisverylong.Thesmartfilterhasalso an algorithm for eliminating readings that are not valid because of a settling transient, or if values inthefiltercontentshaveasignificantinterferencespike.Eightlengthsfrom5to1000A/Dconver-sionsareavailable(thelongestfiltertakesabout300secondstobecomefull).

Zero filter length: Raw readings are output at maximumspeed,whichisabout3/second.Thelightremainsblanked.Scanningrequiresanon-zerofilterlength,becauseitproceedstothenextenabled channel only after a valid average has been found.Seealso“Savingofproperties”

Filter mode.Inadditiontothedefault“smart”mode,thefilterhasan“always”modeforexcep-tionally noisy situations, where the data always contains some readings that render the contents invalid.Thesmartfilterwouldthenbecontinuous-lyresetwithoutgivinganyoutput.Inthe“always”mode,thefilterdoesnotmakeanyvaliditychecks.

Smart filter: The green light turns on when the averageisvalidandblinksathalfthespeedofA/Dconversions.Itturnsblanked,ifaspikeorincreasednoisemaketheaverageinvalidagainandremainsblankeduntilthedisturbancehastravelledoutfromtherunningaverage.Scanningproceedstothenextchannelwhenthelightturnson.

Always mode: Validity of the average is not tested.Thelightturnsonwhenthefilterisfilleduptoitslengthandthenitstartstoblink.Scanningworksalsointhe“always”modeifthefilterlength

is>0.Seealso“Savingofproperties”.

2/4-wire. Any sensor can be connected using either two current and two voltage leads, or using only two wires that carry both current and voltage

Four wire connection is the common standard and it should be preferred whenever the resistances ofthesensorwiresrepresentanysignificantpartcomparedwiththesensoritself.

Two-wire connection can be used with very high resistivity sensors or when one is desperately inshortofconnectorspace.Thetwowiresaresoldered to the appropriate current terminals of the inputconnector.Select“TWOWIRE”configura-tionfora2-wireconnectedchannel.

Also a 4-wire connected sensor can be measured usingonlythecurrentleads.Justswitchto“TWOWIRE”mode.Thedifferencebetween2-and4-wire readings is the total resistance of the current leads.Shortcircuitsbetweensensorleadsinsidethecryostatcanchangethisdifference.Keepingtrackof such differences provides a way to detect some faultswithoutaffectingtheexperiment.Seealso“Savingofproperties”.

Sensor grounding. Any sensor can be either isolated fromthecryostat(“Floatingsensor”),oritscur-rentreturnlead(“I-lead”)maybegroundedtothecryostat for improving thermal contact or for using ground as a common return, which saves wiring andconnectorspace.Thefrontpanelcontrolmustbe set in accordance with how the sensor has been wired.Floatingsensoristhepreferreddefault,becausethennogroundcurrentcanflowintheI-lead.Seealso“Savingofproperties”.

Scan enable. Any channel can be included in or excludedfromthescansequence.Scan-enabledchannelsaremarkedbyadifferentlycoloured“CH1”etc.Ifonewantstosave results from only one channel, it must be scan-enabled alone, so that itcanbemeasuredinscanmode.Resultsaresavedtoadiskfilewhenanaverageisconsideredvalidbythefilteralgorithm.Afilteredaveragewithtime stamp is available after each A/D conversion fromtheGlobalFunctionalVariable“avs48si_


AVS-48SI PICOBRIDGE


data_out_array_fg.vi”Seealso“Savingofproper-ties”.

Recall.The“avs48si.vi”remembersthebridgeset-tings that were used when the selected channel was measuredlasttime.Youmustbeintheidlestateforrecallingsettings.Selectachannelandclick“RE-CALL”.Thepreviouslysavedsettingsbecomevis-ible,buttheyarenotyetsenttothebridge.Inotherwords, the bridge state is not changed by recalling a new channel with its settings from Arduino’s memory.Youcannowcheckthesesettingsandmodifythem,ifdesired.Thenewsettingsaresenttothebridgeassoonasyouclick“MEASURE”,and this also saves the possibly edited settings for theselectedchannel.

Even if you are going to scan the channel, start ameasurementfirstfortestingthesettingsandforsavingthem.Scanningwillthenreadthealreadysavedvalues.Controlsonthebridgesidearedisa-bledandgrayedoutduringrecall.

Measure. You must be in the idle state before you canstartameasurementoftheselectedchannel.Inorder to prevent unnecessary heating of the sensor, theprogramsetsexcitationfirsttoitslowestvalue,then all other new settings are sent to the bridge hardware, and the process is ended by setting exci-tationtoitsrequestedvalue.

Thebridgemakesabout3A/Dconversions per second.Duringmeasurement,youcannotchangethesettings.Allcontrolsontheleftsidedisplayaredisabledandgrayedout.Stopthemeasurementbyclicking“IDLE”.Thecontrolsbecomeena-bled.Stoppingthemeasurementorscanningdoesnotstoptheanalogbridgefromworking.Alsotheanalogoutputsworkasbefore.ThisremainstrueevenifyoustoptheVIuntilitisre-started.

Resultscannotbesavedondiskinthemeasuremode.However,eachreadingisavailableinafunctionalglobalvariable“avs48si_data_out_ar-ray_fg.vi”forothersimultaneouslyrunningLab-Viewprograms.Referto“Savingtheresults”formoreabouttheFGvariable.

If you want results from one single channel to be savedondisk,enablethischannelaloneforscan-ning.Enablealsosavingandselectthefiletype.

An on-going measurement is indicated by the blinkingDATAVALIDlight.BlinkingrateisonehalfoftheA/Dconversionrate.AlsotheCP,DCand DI lights on the AVS-48SI’s physical front panelblink.

Scan. Intheidlestate,click“SCAN”forstart-ingcontinuousscanning.Thescan-enabledandpreviously saved channels are measured in numeri-calorder,eachusingitspersonalsettings.Cyclesstartfromthecurrentlyselectedchannel.Thescan-markedrowsonthemaindisplayarefilledorupdatedassoonmeasurementsbecomeready.Thishappenswhenthefilter,whoselengthmust be 5 orlonger,isfilledwithvaliddata.TheAVS-48SIshows resistances (and temperatures) of all scanned channelsconvenientlyatthesametime.

Enable autoranging for all scan-enabled chan-nels with the exception of the possible temperature controlsensor.Usealongfilterforbestresultsandespecially for channels that require a low excita-tion.

Scanning speed is determined by the sum ofallfilterlengthsplussomeoverheadneededtochangethechannel.Youcanmakescanningslowerbyusinglongerfilters.Youcanalsoincludechan-nel 0, the reference channel, in the scan sequence andselectalongfilterforit.

Scanresultscanbesavedintoadiskfileandthey are also available in the FG (functional global) variable“avs48si_data_out_array_fg.vi”.Thescansequence can include any number of channels start-ingfromone.Theyneednotformacontiguousset.

Continuousscanningisstoppedbyclicking“IDLE”.Nochangesarepossibleduringscanning

Idle.Click“IDLE”forstoppingtomeasureortoscan.Allcontrolsbecomeenabledandyoucanchangethechannelsandtheirproperties.

A measurement is stopped by selecting the IDLE state. e EXIT button that stops the whole VI is active only in the IDLE state.


AVS-48SI PICOBRIDGE


The idle mode of the software does not stop analogtemperaturecontrollerfromworking.

MAIN DISPLAY

Resistance display. The measured channel or the scannedchannel(s)areshowneachonitsownrow.Scan-enabledchannelsaremarkedbyadifferentlycolouredchannelnumber.

Each row has also a warning light for analog sig-nalerrors.Theyare:signaloverloadandhighleadresistance.TheAVS-48SIcombinesthem,butthephysical front panel of the instrument shows them separately.

Signal overloadmightbecausedbyabrokenV+sensor lead or a large mains frequency interference, forexample.Highleadresistancemightbecausedbyabrokensensorcurrentlead.Ifalowresistanceis measured using a low range and high excitation, leadresistanceexceedingthespecificationscanre-duce accuracy severely without necessarily turning onthewarninglight.

Please compare your wire resistance with the specifications.Thetotalcurrentleadresistancecanbe determinedbysettingthe“2/4WIRE”firstto“TwoWire”andthento“FourWire”andcalculat-ingthedifference.

Temperature display. Temperature is shown only for channels that have associated R/T conversion files.Theassociationprocessusing“avs48si_create_r_t_information_file.vi”andtheR/Tfilestructurearedescribedelsewhereinthisdocument.

Eachrowhasaredwarninglight.Itturnson,if the measured resistance is below the lowest or abovethehighestbreakpointintheR/Tfile.Thenthe minimum or maximum temperature of the calibration range is displayed and the temperature readingismeaningless.Usetheresistancereadinginsuchacase.

Channel name. Short descriptive channel names makethedisplayeasiertoreadfromadistance.Yougiveoreditthenamesinthe“CHANNELNAME”controlbox.Thenewnamebecomesvis-ibleonceLabViewconcludesthatyouaredone.Itsavedwhenyoustartameasurement.

A green light shows the channel that has possibly beendefinedasthetemperaturecontrolchannel.

TEMPERATURE CONTROLLER

The heater output power of the AVS-48SI, instead of current,isalinearfunctionoftheerrorsignal.

Control error meter. The scale of this animated analogmeterhasbeennonlinearizedstrongly.Itshows the trend of the error signal even if it is large, but the meter is very sensitive near to bal-ance.Sensitivitynearzeroisabout100µVwhilethe error signal’s maximum value is +/-3V (≈ 90dB dynamicrange).

Positivedeflectionmeansthatmorepowerisneeded in order to achieve the set point tempera-ture.Inaway,thiscorrespondstothenatureoftheexponentiallysettlingcontroltemperature.

The bright and informative main display shows resistances, temperatures and sensor names of all eight channels con-venientlyatthesametime.Shownarealsoscan-enabledsensors,thepossiblecontrolsensorandsomeerrors.


AVS-48SI PICOBRIDGE


Heater power % meter. This animated panel meter shows heating power as a percentage of the select-edrange’smaximum.Themaximumiscalculatedon basis of the given heater resistance, which can besetonthe“Settings”tab.Editit,ifneeded,andclick“ENTER”onthecontrollersideofthefrontpanelinordertosavethenewvalue.Theheaterresistor’s value RHcan be saved only when tempera-turecontrolisenabledbyclickingENTERwhentemperaturecontrolisenabled.

Heater power display (digital).Therightmostfieldunder the power meter shows the selected heater range’scalculatedmaximumpower.Itassumes12.4Vcompliance voltage for RHhigherthan100Ωand calculated maximum currents for RH lower than 100Ω.ThemaximumheatingpowerthattheAVS-48SIcandeliverisabout3Wintoa50Ωheater.

The leftmost indicator box shows the actual heat-ingpowerinWatts.Itistheproductofmeasuredtrueheatervoltageandcurrent.Thevoltageisverylowonthelowestheaterranges,whichmakestheproductthensomewhatunstable.

The true heater power indicates both shorts and open circuits in the heater wires: The V*I product willbezeroifashortnullsthevoltagedrop,orifanopencircuitpreventscurrentfromflowing.

Heater range. The AVS-48SI has 18 power ranges,

thepowerratiobetweenrangesis10^(1/5)=1.58.Closelyspacedrangesmakeiteasiertokeepheat-inginthemiddleregionoftherange.

The AVS-48SI features changing the heater range without appreciable effect on temperature pro-vided, that the system was in equilibrium before the change.Forreducingtherange:

1) Change the heater range downwards 2)Watchthepowerdisplayorthe%-meter.Ifthey

show that the intended lower range can give enough power for maintaining the control tem-perature, then

3)click“ENTER”,otherwisereturnbacktotheoriginalrangeandquitthisexperimentbyclick-ingENTER.

Youcanalwayschangeupwards.

If you increase power range, the loop gain is increased, and you may need to reduce the propor-tionalgaininordertomaintainsystemstability.Ifyou reduce heater range, the gain of the control loop is reduced and you may need to increase pro-portionalgaininordertomaintainsettlingspeed.

Temperature control is enabled, if the following threeprovisionsarefulfilled:

1)Measurementchannelisgreaterthanzero,2) the control channel is the same as the measure-

ment channel and 3)heaterrangeisgreaterthanzero.Thenthe

controlsbecomevisibleandenabled.Thepowerrange and all its personal settings become in ef-fectbyclicking“ENTER”.

In a sensitive application, when accidental high power can cause damage, the maximum power can be limited by disablingthehighestranges.EXIT the program before the following procedure:

1)clickthe“HEATERRANGE”controlboxwiththe pointing tool,

2)fromthecontextmenu,select“EditItems..”,3)selectrange#18andclick“DisableItem”,4) continue disabling all ranges that you consider too

high, 5)savethe“avs48si.vi”.Thedisabledrangescanbe

enabledbackbyareverseprocedure.

Heating can be stoppedquicklybysettingheaterrangeto“CONTROLOFF”.Thismakesallset-tingszeroanddisablescontrolandtheheater.As

Display of the avs48si.vi program’s temperature controller side. Front tab.


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an exception to the general rule, ENTER is not neededinthiscase.Seealso“Heaterconnection”.

Proportional gain. There are 13 logarithmically spacedproportionalgainsin1:2:5etc.sequencefrom1to10000.Ifproportionalgainissetto0when the system is in equilibrium, the heating power is solely determined by the voltage that has accumulatedinthePIDcontroller’sintegrator.

In many cases, you can set the proportional gain to a useful value as follows:

1)Settheintegratorandderivatorgainstozero,2) set the proportional gain to maximum value that

does not yet cause overshoot when the set point ischangedupanddown.

Different temperatures are best controlled on differentpowerranges.Thereforeeachpowerrange can have its own PID parameters which canbeRECALLedforthisrange.Ifparametersare not recalled, they remain the same for all ranges,justasontheresistancebridgeside.Seealso“Savingofproperties”.

Integrator gain. The AVS-48SI uses the expression “integrator gain” instead of the more common “integration time constant”.Theconceptofgainis more convenient to use: When you increase inte-gratorgain,youincreasetheintegratingeffect,i.e.youmakeintegrationfaster.Therearetenselecta-blelogarithmicallyspacedgainsfrom0.001to1ina1:2:5etc.sequence.

Toolittleintegrationmakesthesystemslow,whereas too much integration leads to unacceptable overshootorunstabilityofthecontrolsystem.Asuitable integrator gain can add a little overshoot totheproportional-onlymode.Zerointegratorgain(“None”)shortstheintegratortozero.

Do not resettheintegratorbymistake.Youmaybe able to speed up balancing after a change in set pointbysettingtheintegratorgainto0.001untiltheP(orPD)controllerisalmostsettled.Thenen-abletheoriginalintegratorgain.Seealso“Savingofproperties”.

Derivator gain. There are 10 selectable derivator gainsina1:2:5etc.sequence.Thehigheristhegain,themoresignificantisthederivationaction.Thederivatorhasamodifiedresponse,whichpreventsitfromamplifyinghigherfrequencies.Be-causeofthismodifiedresponse,thederivatorgainhas a maximum, which shifts lower when INTG is increased.

DerivationisthemostdifficultofthethreePIDparameterstoadjust.Asuitableamountofderiva-tioncanmakecontrolfasterso,thatitcanbetterreact to temperature changes or to a slope, whereas too much derivation leads to excessive overshoot, oritmakesthesystemunstable.Tooweakderiva-tionisofnouseatall.Alotoftemperature-de-pendenttrial-and-errorworkmaybeneeded,whichmeans that derivator is most useful for saving time inarepeatedoperation,wheretheextrasetupworkisjustified.Seealso“Savingofproperties”

Set point unit. Set point is given in Ohms by de-fault.

Set point can also be given in temperature, if an R/Tconversionfilehasbeenassociatedwiththecontrolsensor.Thenthemaindisplayshowsboththesensor’sresistanceandtemperature.Dependingontheconversionfile,temperaturesaregiveninKelvinsordegreesCelsius.SelecttheappropriateSET POINT UNIT, enter the desired resistance or temperature.Formakingthenewsetpointeffec-tive.andclick“ENTER”whenitturnsdarker.

IfthesensorhasanR/Tconversionfile,youarelikelytogivethesetpointintemperature.Howev-er, it may happen that a desired set point is outside thecalibrationrange.ThentheSETPOINTcontrolbox turns red and the resulting set point defaults to theminimumormaximumofthecalibrationrange.

In order to reach the desired far control point, changeoverfromtemperaturetoresistance.Change the SET POINT UNIT from temperature to resistance and the SET POINT indicator box starts toshowthesetpointinohms.ClickENTERwhenitturnsdarkgray.NowalsotheSCALEboxshowsOhms.Thecontrolsetpointhasnotchangedsofar.After this, you can edit the set point, if desired, and clickENTERagain.Youcanchangethesetpointfromresistancetotemperatureinthesameway.


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Set point. Setpointisgivenasafloatingpointnumberlike115.05orinexponentialformlike1.1505E2or1.1502e2.Itisinternallyconvertedtoa voltage, based on the selected resistance measur-ingrange.Ifthesetpointisgivenintemperature,the conversion accuracy depends on the number andlocationsofthebreakpoints.TheR/TandT/Rconversions (for set point) are based on linear interpolation.

Scale. This indicator shows the temperature scale (“K”or“C”)thatisusedbythecontrolsensor’sR/Tconversionfile.Ifnoconversionfileexistsforthecontrolsensor,Scaledefaultsto“Ohm”.ReferalsotodiscussionabouttheR/Tfiles.

Heater connection. The AVS-48SI has an inter-nal100Ωheater,whichisratedfor2Watts.Thisresistor is in thermal contact with a silicon diode, whoseforwardvoltagechangesabout-2.5mV/C.The“INTERNAL100R”positioncanbeusedforsimplifiedoperationaltestofthetemperaturecontroller.Thedefaultpositionofthiscontrolis“EXTERNAL”.

Previously was described a method for stopping controlquickly:Settheheaterrangeto“CON-TROLOFF”(referto“Heaterrange”).Thiswillnullallcontrolsettings.Restoringcontrolafterthatrequires recalling or re-programming the original settings and waiting for the system to reach bal-ance.

Output power can also be disconnected tempo-rarily from the heater without nulling any of the controlsettings.Thisresultsinfasterreturntobalance.Becausethereisnoactivecontrol,thefol-lowing method can be useful, if only a short pause incontrolissufficient.Thesystemshouldbeatequilibriumforbestresults.Doasfollows:

1)Select“INTERNAL100R”heaterconnection,2)click“GOTOHOLD”,3) once the yellow light shows that the system is in

hold state, do whatever you need the pause for, 4)select“EXTERNAL”heaterconnection

5)click“EXITHOLD”.

This operation must be done without using “EN-TER”

If you do not want to null the heating power, butneedtoe.g.disconnectthesensorcableforamoment, go to the HOLD mode for a while (see “Hold”).

Recall. Each heater range has its own set of the three PID parameters: proportional gain, integrator gainandderivatorgain.Theyaremadeactivebutalso saved automatically for the currently selected heaterrangewhenyouclickENTER.Settingsother than these three on the controller side are also saved,buttheyarecommontoallheaterranges.

SelectanewheaterrangeandclickRECALL.This brings visible the settings that were previously used with this new range and which were saved for it.Youhavenowtheopportunitytorecallanotherheater range or modify the settings before you makethemactivebyclickingENTER.

The philosophy is very similar to that on the bridgeside.Onbothsidesoneisabletoseetherecalled settings, possibly change them, recall another range, or recall the original heater range beforeactivatingthesettings.Onthebridgeside,the MEASURE and SCAN modes are started from the IDLE state, whereas on the controller side, new settingsaremadeactivebyclicking“ENTER”.

Enter. Changes made to the controller settings are activatedbyclickingENTER.Manychangestaketime because of required two-step D/A conversions, andyoushouldnotclickENTERuntilacommandhasbeenfullyhandled.Inordertoavoidthat,EN-TER button turnsdarkgreywhenitisreadytobeclicked.Thenewcolouralsoremindsyou,ifyouhavemadechangesorjustlookedatthealterna-tives,thatyouneedtoactivatethem.Ifyoudidnotdochangesbutreturnedbacktooldsettings,click-ing ENTER does not alter anything, it only changes itscolorback.SometimesachangeisleftpendingafteryourfirstpressofENTERandthebuttonturnsbacktodarkgray.JustclickENTERagain.

EvenifENTERhasturneddarkgrey,youcancontinuemakingchanges,itisnotnecessarytoactivateallchangesseparatelyastheyaredone.All

Exponential form is allowed only when using LabView. Give set points in oating point form when using serial commands.


AVS-48SI PICOBRIDGE


changescanbeenteredtogether.

Therearetwoexceptionstotheaboverule:zeroHEATER RANGE and GO TO HOLD:

IfheaterrangeissettoCONTROLOFF,controlis stopped immediately, all settings are nulled and theheaterisdisabled.Thisisforenablingrapidshutdown.

GOTOHOLDandEXITHOLDalsowork with-outentering.However,enteringwillbeneededforrestoringthelightgraycolorof“ENTER”(Holdhasrequiredinternalchanges).

Hold. The hold state is mainly for measuring sensors other than the control sensor without completely stoppingtemperaturecontrol.Once“GOTOHOLD”hasbeenclicked,theprogrammeasuresthe PID integrator’s output, which is then replaced bytheoutputofadigital-to-analogconverter.Theheating output remains constant in the hold state butthereisnoactivecontrol.Holdingworksbest,whenthePIDsystemisingoodequilibrium.Themagnitude of the unavoidable temperature drift depends on initial balance and on the stability of theheatload.

While holding, you can visit any sensor and you canevenscantheenabledsensors.Thescanresultsaresavedondisk,ifsavingisenabled,andtheyarealways available in the global functional variable forotherLabViewprograms.Afteryourmeasure-ments or scanning, BE SURE to select the control channel again and start measurement with MEAS-URE.Afterthebridgehassettled,clickEXITHOLD.

You can change the measuring range or exci-tation of the control channel during temperature control.Doasfollows:

1) Switch the bridge side to IDLE, 2) select GO TO HOLD, 3) once holding, select the new measuring range or

excitation, 4)clickMEASURE5) when the measured reading has been reasonably

settled,clickEXITHOLD.

Thisworksregardlessofwhetherthesetpointisinresistanceortemperature.Ifthesystemwasinequilibrium, the effect in controlled temperature wouldbeminimal.Pleasenote,thatlowering

measuring range by one step will increase the loop gainbyadecade.Increasingrangewillreducethegainbyadecade.Youmayneedtodecreaseorincrease the proportional gain for maintaining sys-tem stability or for maintaining its response speed, respectively.Controlaccuracywillbebetter,ifyoudo not control very near to the low end of the meas-uringrange.AspecialfeatureoftheAVS-48SIisthat the heating power, not current, is a linear func-tionofthecontrolerror.Thisreducestheneedtoadjustproportionalgainwhenpowerlevelchanges.

All controls on the right controller side are dimmedanddisabledwhenthesystemisholding.

Exit. UseEXITforstoppingthe“avs48si.vi”pro-gram, do not abort it from LabView if not neces-sary.The“legal”stoppingclosestheserialportsothatitcanbeusedbyotherprograms.

For security, the program can be exited only whenitisdoingnothing.ItisonlythenthattheEXIT button is enabled, and this happens only if:

ThebridgehasbeensetintoIDLEstateThecontrollerhasbeendisabledbysettingHeater

Range to CONTROL OFF for stopping the con-troller.

Ifthe“avs48si.vi”isaborted,orifremotecontrolstops in some other way, the analog bridge and controllercontinueworking.Re-startingtheVIdoes not alter operation of the bridge, whereas the controller is reset and it must be started from its defaultno-controlstate.Thisisforsafety.


AVS-48SI PICOBRIDGE


SETTINGS TAB

The Settings tab can be accessed regardless of the selectedLabViewtoolwhenthe“avs48si.vi”pro-gramisrunning.Whenitisnotrunning,usethehandtoolforselectingatab.ThesameappliestotheServicetab.

Serial port. This control shows the serial ports that areavailable.Selecttheonethatisorwillbecon-nectedtotheexternalCPUboxoftheAVS-48SI.Serial port is one of the few settings that require savingthe“avs48si.vi”.Oncesaved,youdonotneedtoadjustiteverytimetheprogramisstarted.

If your computer does not offer a physical RS232 (or Com: ) port, you need a USB-232 converter forcreatingsuchaport.Iftheconverteriscompat-ible with your platform, the name of the virtual Com: port that it has created should be listed in the“SERIALPORT”controlbox.Picowattoffersa converter from National Instruments (part num-ber778472-01),butworkingconvertersofotherbrands may be available from elsewhere at a lower cost.TheArduinoboxexpectstwo-wireRS232communicationwithouthandshakingwithserialparameters9600,8,N,1(baudrate9600,8databits,noparityand1stopbit).Thisisbelievedtoprovide the best possible compatibility, because it is the most common default of various programs andplatforms.

Filter delay.Ifthefilterisusedin“ALWAYS”mode, it calculates a running average without checkingthevalidityofthereadingsinanyway.The average can therefore contain transients after a changeinrangeorchannel.“FILTERDELAY”in-

sertsafixeddelaybetweensuchchangesandstart-ingofthefilter.Onthehighestexcitationranges,some 5 seconds is enough, whereas on the lowest excitationadelayof15secondscouldsuitable.FilterdelayisnotusedintheSMARTmode.

Thefilterdoesnotreacttosuddenchangesinthesensor value in the ALWAYS mode, whereas in the SMARTmodeitdoes.

DR/DT. The instrument’s control polarity must correspond to the sign of the control sensor’s slope dR/dT.Mostcryogenicsensorshavenegativeslopes,whilesensorsforhighertemperatures,likePlatinum wire resistors, have positive temperature coefficients.Clicking“MEASURE”savestheselectedpolarity.

If temperature control is NOT needed, you can use the set point voltage (see below) as a reference for the deviationoutput.UseDR/DT to determine the polarity of the difference between measured signal and the set point DAC voltage: Positive polarity means (signal - set point) and negative polaritymeans(setpoint-signal).Thisdeviationisavailableatarearpanel“CONTROLERROR”connector and it can be displayed on the front panel asanalternativetothenormalresistancedisplay.Seebelow.

Analog out BNC. Normally this rear panel BNC connector outputs a voltage proportional to the measured resistance as

VOUT = RSENSOR/RANGE*3V.

The calibration system of the AVS-48SI considers


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this output as the primary quantity to calibrate and therefore the accuracy of the analog output is very good.Inordertosuppressresiduesofthecarrierfrequency, the analog voltage from the phase-sensitive detector (PSD) is smoothed by a 3RD order Bessel filterofabout1.2Hz3dBfrequencybeforeoutputting.Ifthe“ANALOGOUTPUTBNC”rearpanel

controlischangedfrom“Analogout”to“Errorout”,therearpanelconnectorshowsthedifferencebetweentheanalogoutputandthe“SETPOINTDAC(V)”control.Thisselectorisavailableonthesettings tab but do not use it if temperature control isactive.Itwilloverwritethesetpointcomingfromthecontrollersection.Deviationvoltageisseenalsoon the front panel, where the display title changes to “DEVIATION(dR)”.

PSD Frequency. Select one of three crystal-con-trolledoperatingfrequencies12.5Hz,13.64Hz(de-fault)or15.0Hz.Thedefaultfrequencyisusuallysuitablebothin50and60Hzcountries.

Electric motors can generate mechanical or acoustic vibrations containing frequency compo-nents that are near to but not exact (sub-)multiples ofthemainsfrequency.Suchcomponents,iftheyproduce voltages in the input circuit, can cause veryslowbeatingespeciallyifthebridgeuses12.5or15Hzexcitation.Thenselectinganotheroperat-ingfrequencycanreducebeatingandmakeitfasterandeasiertofilteroff.Evenanarbitraryfrequencyis possible by feeding an external signal to the

“EXTCLOCK”input.

Filter output. The smartfiltermaintainsarunningaverageoftheindicatednumber(=filterlength)ofA/Dconversionresults.Inaddition,thefilter

fitsaleast squares line to the data points in the filter

calculatestheaverage,andstandarderrorofdatainthefilter

calculatestheMean Squared Error (MSE) outputsthelastpointofthefittedline

MSE is the sum of squared distances of the data pointsfromtheleastsquaresline,normalizedbydividingthesumbythenumberofdatapoints.Because of its quadratic nature, MSE is very sensi-tive to the curvature of the initial transient part of data.Inaddition,itgrowsrapidly,ifthedatainthefiltercontainsapeakduetosomeinterferenceorifthedatachangesrapidly.Thisbehaviourisusedforexcludinginvaliddatafromtheresults.

Thefilterisre-startedbymanychangesinthesysteminadditiontosignalcurvatureorpeaks.After re-start, new conversion results are col-lectedintothefilter.Aslongasthefilterisnotfull,it outputs rawnon-filteredreadingsassuch,nottheiraverage.Theyapproachthefinalvaluemuchsooner than the average, but of course they contain noisethatislatertobesmoothedbythefilter.Thepurpose is, that the user gets a rapid estimate of the finalvalue.

Assoonasthefilterisfull,fittingalinetothedata starts and MSE is calculated after each new A/Dconversion.TheMSEiscomparedwithlimitsthat have been tabulated for range and excitation, and if it is smaller than the limit, the average is consideredvalid.Thisisshownbyagreenindica-torlight,andthedisplaychangestoshowaverage.If the raw data has been noisy, you see a sudden decreaseinnoiselevel.

“MEAN”isthenormaloutput.Inadditiontothe mean, you can see the standard deviation of thedata(onServicetab).Itbecomesvisibleoncedatainthefilterhasbeenconsideredvalid.Youcan compare this STD with our room-temperature specifications.IftheSTDismuchlargereventhough your sensor is cooled, you have an interfer-enceproblem.Usealongfilterinordertomake

12.4Hz interfering signal of 200μVpp was induced to a 10Ω sensor measured with VEXC=300μV and fBRIDGE=12.5Hz .e interference beats with the excitation at fBRIDGE-fEXC=0.1Hz. e beating amplitude of 700mVpp (analog output) went down to 12mVpp when the bridge frequency was changed to 15Hz. A 60-fold improvement!


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STDrealiable.

“LASTPOINT”meansthemostrecentpointofthefittedline.Inacasewheretemperatureisdriftingrapidly,anormalaveragewilllagintime.Forexample,afilterwithL=100(about30sec-onds),theaveragewilllagby15seconds.The“lastpoint”outputwillbeclosertotheinstantane-oustemperaturethantheaverage.Asfarasnoiseis considered, this output is inferior to the normal average.Usethismodeonlyfordriftingdata.

Calibrator. Seven ultra-stable wire-wound resistors locatedinthepreamplifierunitserveascalibrationstandardsoftheAVS-48SI.They have excellent temperature(3-5ppm/°C)andlong-termstability(≈30ppm/yearduringfirstyears,laterusuallyevenless),buttheirinitialtoleranceisonly0.1%.There-fore the true values of these resistors are measured and saved into the non-volatile EEPROM memory oftheArduinoCPUcard.Thisisapartoftheinitialcalibration.Newcalibratorvaluesareeasilyenteredintomemoryifthepreamplifierischanged,oraftersomerepairstothepreamplifierormainunit.Theoriginalcalibratorvaluesarewrittenonastickerinsidethebottomcoverofthepreampli-fier.Thisisagreatimprovementcomparedwiththe older AVS-47x bridges, which required external standardsforrestoringitscalibration.

Sensor channel #0 is devoted to measuring these

standards.Inthe“CALIBRATOR”controlbox,se-lect one of the resistances 0, 1Ω, 10Ω, 100Ω,1kΩ, 10kΩ,100kΩ, or 1MΩ.Itstruevalueisshownimmediately.Returntofrontpanel,selectchannelCH0,andtheinterestingrangeandexcitation.Startameasurementforactivatingthesechanges.Ifthedisplay differs from the indicated true value by more than few hundreths of a percent, you should consider running the automatic Full Main Calibra-tion program (see Main Calibration, Calibrating the A/D and D/A Converters and Reference Resistor Calibration).

Despite its special nature, CH0 can be included in ascancycle.Thisprovidessomedegreeofqualitycontrol.Itcanalsobeusedforincreasingthetotalscancycletime,ifslowerscanningisdesired.

Control CH. Temperature control requires that one ofchannels1-7isassignedasthecontrolchannel.For clarity, the selected channel is shown also on thefrontpanelbyagreenLED.Thecontrollersec-tion becomes enabled when 1) the control channel has been selected, 2) the measuring channel is the same as the control channel and 3) heater range is notzero.Autorangingshouldbedisabledforthecontrolchannel.

If temperature control is not active, the control sensorcanbemeasuredorscannedlikeanyothersensors.Ifyouchangethecontrolchannelduringcontrol (Settings tab), control will be stopped and allparameterswillbenulled.

Heater resistance. Numeric value of the heater resistance is needed only for calculating the maxi-mumpoweroneachheaterrange.Atypicalresist-ance“standard”resistanceis100Ω,butthecurrentsource heater output of the AVS-48SI accepts any value.Themaximumpowerof3Wisachievedwhenheateris50Ω.IfRH is lower than 50Ω, the availablecurrentwilllimitthemaximumpower.IfRH is higher than 50Ω, the maximum output com-pliancevoltagewilllimitthepower.

Setpoint DAC (V) and User DAC (V).Thesetwo digital-to-analog converter outputs (from LTC2600)giveveryaccuratelycalibratedvoltagesintheregion0.005....2.99Volts.Theoutputscansupply over 10mA, but it is recommended to buffer them externally, if more than a few milliamps are needed.Theoutputsarenotprotected,sopleasebe

The seven wirewound calibrator references are located on themultiplexerboardinthepreamplifierunit.The4-wireconnectormakesitpossibletomeasuretheseresistorsus-inganexternalhigh-endohmmeter.


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carefulnottosupplyenergyintothem.

The user DAC is always available for you own applications, whereas the setpoint DAC is needed fortemperaturecontrolwhenitisactive.Voltagesof these two DACs can be changed without stop-pingthepossiblyon-goingmeasurement.Justenterthenewvalueandclickanemptyplaceonthepanelorhitenterofyourcomputerkeyboard.

The set point should be given in resistance or temperature from the SET POINT box when tem-peraturecontrolisactive.Ifnotcontrolling,orifnoTC option is installed, give the set point in voltage fromtheSetpointDAC(V)boxontheSettingstab.The user DAC voltage is always given as a voltage ontheSettingstab.

Heater Drv Source and Heater Direct DAC (V).In addition to normal use, where the PID circuit drives the heater output stage, the AVS-48SI features alternative direct numeric control of theoutputcurrent.Underthe“HEATERDRVSOURCE”select“DIRECTDAC”,gotothefrontpanelandclick“ENTER”afterithasturneddark.Now the heater output can be considered a voltage-controlledcurrentsource.Usethe“HTR DIRECT DAC(V)”controlboxforsettingtheoutputcur-rent.

This voltage determines the output current, not thepower.Threevoltscorrespondstothemaxi-mumcurrentoftheselectedpowerrange.TheDACdoesnotgotoexactzero,therewillbeasmall fraction of the maximum current left even if theDACissettozero.Above0.005Volts,responseislinear.Selectthe“CONTROLOFF”heaterrangefordisablingpoweroutputcompletely.

“ENTER”isrequiredafterchangingthedriversource,butnotforchangingtheDACvoltage.

Saving off/on.The“avs48si.vi”cansavemeasure-mentdataonadiskfile.Savingisavailableonlyin scanning mode, but because even one single

Do not use the Setpoint DAC(V) input while controlling. is input will override the set point coming from the controller.

channel can be measured in scan mode, this is not alimitation.Savingisalwaysoffbydefaultwhenthisprogramisstarted.Thepurposeistopreventthedatafilefromgrowinginfinitelywithoutany-bodynoticing.

Regardless of whether saving is enabled or not, measurement data is always available to other running LabView programs via a functional global variable(FG).

Data file name. Data is saved as comma-separatedvalues(CSV).Thedefaultnameis“avs48si_data.csv”,whichisalwaysofferedasde-faultwhenthisprogramisstarted.Youcanmodifythe default name only temporarily for your current session.

Data saving mode. In additon to offering data to othersimultaneouslyrunningVIs,the“avs48si.vi”cansavedatatodiskinoneoftwoselectablemodes.

To a disk file:

If“Single-linereplace”isselected,thefilewillconsist of only one row that contains data from the latestscannedchannel.Afterachannelhasbeensuccesfully scanned and new data is available, the existingfileisre-written.Thisfiletypeisintendedto be used by some external program, which con-tinuouslypollstheexistenceof“avs48si_data.csv”and once it appears, reads the single line and then deletesthefile.

If“Multi-lineappend”isselected,everycom-pleted scan measurement of a channel adds a newlinetothefile,whichisneverdeletedbythe“avs48si.vi”Thismodeismainlyintendedforcol-lectingdatathatistobeanalyzedlater.

For other LabView VIs:

Inadditiontosavingdatatodisk,the“avs48si.vi”offersdatatoothersimultaneouslyrunningVIsbymeansofa“FunctionalGlobal”variable“avs48si_data_out_array_fg.vi”.Thisvariable is a VI that consists basically from two non-initializedshiftregisters.Theyhavefixedloca-tions in the computer memory and they can be ac-cessedforwritingandreadingbyanyrunningVI.

Data can be read from this FG in two forms: 1) a CSV string containing the result of the last com-


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CSVdatafromatemperaturecontroltest.Anassemblyofa100Ω heater and a PT-100 sensor was inserted in an empty bottle foreliminatingairflowsattheroomtemperature.Channel#1wasmeasuredintheSCANmode,savingwasenabledandsavemodewasmulti-lineappend.Eachreadingisanaverageof1000A/Dconversions.Standarddeviationoftemperatureswas0.001°C.Thecolumnsarefromlefttoright:ChannelNo.,Resistance,Temperature,TemperatureUnit,SignalError,Rpastcalibr.range,Range,Excitation,Year,Month,Day,Hour,Minute,FractionalSeconds,DataValid.

Herechannels0,3and4arescanned.Allchannelshavefixed100Ω resistors, so the temperature readinghasnomeaninginthisphoto.ThisisanolderpicturewheretheDataValidcolumnwasstillmissing.


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pleted measurement of scan measurement, or 2) an 8-element arrayofclusters.Inthelattercase,eachelementcorrespondstooneofthe8channels.When sensors are measured or scanned, only the corresponding elements contains data, other ele-mentshaveemptyclusters.

Oftenitiseasiesttousetheclusteroutput.Oneneedsonlyto“UnbundlebyName”thedesireditems.IftheAVS-48SIisscanningandonereadsthe FG only occasionally, this arrangement guar-antees, that the information is as up-to-date as it canbe.TheFGcanbere-initiazedafterithasbeenread.Thiseliminatesthepossibilitythatsomedataisreadmultipletimes.

Reading every complete scan cycle as soon as ithasbeencompletedismorecomplicated.OnesolutionistopolltheCSVstring’sfirstcharacter(=channelnumber).Whenitequalstothelastchan-nel in the cycle, it is time to read the output array and re-initializetheFG.

Dataissavedondiskonlyifsavingisenabled,whereasdataiswrittentotheFGalways.

R/T file information. You can inspect the types oftheR/Tconversionfilesthathavebeenassoci-atedwithvariousinputchannels.Changethearrayindex selector (=channel number) for seeing the followingdataabouttheconversionfilethatwas

This is one of the eight elements in the output array of the “avs48si_data_out_array_fg.vi”.Everyelementisaclusterof15items.Inthisfigure,thecompleteclusterhasbeenunbundled.

associated with this channel:

Thefilename.Conversionfilesarenon-formattedplaintextfileswitha.txtextension

Thefilemayhavetwoorthreecolumns:a)resist-anceandtemperature,orb)numberofbreak-point,resistanceandtemperature.

SignofdR/dT

R/Tformat.Theresistancemaybeexpressedasresistanceorlog(R).Thelatteriscommonwithcryogenic sensors that are highly nonlinear within theiroperatingrange.

TemperaturescaleinthefilecanbeeitherCelsiusorKelvins.

Refer to description on how to create and assign R/Tfiles.

Comment area (9 first rows). NinefirstrowsofeachR/Tconversionfileareavailableforfree-formcomments,likesensortype,date,serialnumberandnumberofbreakpointsetc.Theactualconversiondatabeginsfromthetenthrow.

Refer to description on how to create and assign R/Tfiles.

Response to *IDN?.HereyoucancheckthefirmwareversionofthemicroprocessorprogramthatrunsontheArduinoMega2560micropro-cessormodule.Thefirmwareversionofthe“avs48si.vi”LabViewprogramisalsointhenameofthedirectorythatcontainsthenecessaryVIs.

Automatic Saving of Properties. If enabled (de-fault),theavs48si.viwillsavethecurrentlyvis-ible properties of the selected channel each time “MEASURE”isclicked.Whenthissamechannelis measured next time, its previous settings can be convenientlyrecalled.ThesameappliestoPIDparameters of the temperature controller - they are saved for each heater power range for later recall-ingwhen“ENTER”isclicked.

Automatic saving can also be disabled.Thennoproperties or PID parameters are saved by press-ing“MEASURE”or“ENTER”.Settingsthatweresaved before disabling automatic saving are avail-ableforrecalling.Thiscaneliminatethepossibilityofalteringthepropertiesbymistake.


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e “avs48si.vi” service panel provides access to various service measurements and to modifying the smart lter’s Mean Square Error criteria.

SERVICE TAB

The service tab contains some information that you willnotneedoften.

Adc input channel. The analog-to-digital converter oftheAVS-48SIcanbeconnectedto26variousinternal voltages, and most of them are for produc-tiontesting.Theyalsohelpinremote diagnosis, as many internal voltages can be measured without openingtheinstrument.

Input#4isthedefault-itisthebridgeoutput.Allotherinputschangethe“RESISTANCE”titleonthefrontpanelto“SERVICE”andtheunitchagestoVolts.Someotherinterestinginputsarelistedbelow.Thechannel,whereservicevoltagesareshown, depends on channel that happens to be se-lected.Filteringisusuallynotneededwithservicedisplays.

0=Ground.Thedisplayshouldbeverynearto0,onlyfewtensofμV.

1=ADCreference.Thevoltageshouldbeabout3Volts.Itsexactmagnitudeisnotveryimportant.

16=PIDheatervoltageand#17PIDheatercur-rent.Thesearenotshownonthetemperaturecontroller’sfrontpanel.However,theyaremeas-ured and the true heating power is calculated as theirproduct.

22=SetpointDACor#24UserDAC.Thesevoltages are measured from the DAC outputs by theA/Dconverter.Theirvaluesshouldbesameastheprogrammedvalues+/-100μV.

After having selected a display item, stop and restart measurementinordertomaketheselectioneffec-tive.

Standard deviation (V).Standarddeviationiscal-culatedfromreadingsinthefilter,whichmustbefilleduptoitslengthbyvaliddata.Thereisagreenlightontheservicetabthatshowswhenthefiltercontentsisvalid.

Iffilterlengthisshort,liketensofreadings,STDwillfluctuatealot.Usealongfilterforgettingstablereadings.STDmayhelpinfindingsomeproblems.Takereadingsbothfromyoursensorandfromtheappropriatereferenceresistor.ComparethesewiththeAVS-48SIspecifications.Ifyourcooled sensor gives much higher STD readings than those from a room-temperature reference, you mayhaveaninterferenceproblem.ButiftheSTDfromthereferenceismuchhigherthanspecified,somethingwiththebridgemaybeoutoforder.

Square error table.Thesmartfiltercomparesthecalculatedandnormalizedmeansquarederror(MSE)withtabulatedcriteria.Thetableshowsthe factory default criteria for all combinations of rangeandexcitation.Theyhavebeendeterminedso, that a valid average can be found even when measuringa10MΩroom-temperatureresistor(exceptonthelowestexcitations).Thistableservesas a reference if you have changed the criteria but thenwanttorestoretheoriginalvalues.


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Square error array. This two-dimensional array letsyouchangetheMSEcriteria.Doasfollows:

1.Usethearrayindexcontrolssothatthe“SquareErrorCriteria”boxshowstheMSEcriterionforthecurrentlyselectedrange-excitationpair.

2.Ifthecriterionissomethingelsethanwhatisshown on the orange table, write it down as a back-up.

3.Measureyoursensorwithalongfilter.4.WritedowntheMSEreadingtheshownin

“SquareError”boxwhenithasreacheditsfinalvalue(itmayfluctuatealot).

5.ReplacetheelementbyanewMSEvalue.

6.Followthegreenlightforsometime.Ifitturnsoff even seldom, then the new criterion is too low andyouhavetoincreaseit.

The new value should be ten to hundred times greaterthanthemeasuredMSE.Ifitistoosmall,thefiltermayneverbecomevalid,iftherehappenstobemorenoiseinthemeasurement.

This is the tradeoff: The higher is the limit, the faster and more surely validity is found, but the distancetothefinalvaluewillbelongerandthefirstvalidaverageswillcontainmorereadingsthatbelongtothesettlingtransient.ThecloserthelimitistothemeasuredMSE,thelongerittakestofindvalidity,butthefirstvalidaveragesareclosertothefinalvalue.


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CALIBRATION

TheLabViewprogrampackagecontainsthreeVIsfor calibration: Main Calibration, ADC and DAC CalibrationandReferenceResistorCalibration.The bridge can be calibrated using these programs, or it can be calibrated by using the serial com-mands as instructed in Part I of this manual (please referalsotothoseinstructions).Bothyieldequallygood results, and because the calibration data is stored in the CPU, both the serial operation and LabViewoperationusethesamestoreddata.

Using LabView is perhaps more convenient, it gives some more information and -this is very comfortable- a screen capture program can be used fordocumentingthecalibration.Thebenefitofserial operation is of course, that it does not require LabView.

MAIN CALIBRATION

The purpose of the Main Calibration procedure is tofindcorrection factors so, that when the bridge measures its internal calibration reference, the displayshowsthe“true”valueofthatreference.These“true”valueshavepreviouslybeenmeasuredat the factory and stored in the CPU’s non-volatile memory.Thismeasurementcanalsoberepeated,whichcanbeneededinsomerarecases.

In addition to the digital display and digital output, Main Calibration affects also the analog voltageoutput.

For each pair of range and excitation, two cor-rectionfactorsaredetermined:oneforzerooffsetandoneforthescalefactor.Botharedeterminedusing averages of several A/D conversions, as many as 800, when 1MΩ reference is measured at 3μVexcitation.Thereare8x8combinations,eachrequiring two averages, so 128 averages are need-ed.Thiswilltaketime,andthefullMain Calibra-tionneedsabout3.5hours,butitisfullyautomaticanditcanbelefttoruninthenighttime.

Main Calibration can be run as often or seldom asonewants.However,themoreoften,thebetter.

BEFORE STARTINGMain Calibration can, it it should, be run in situ when the AVS-48SI is in the place and at the tem-peraturewhereitisused.However,thecombina-

tion of a high calibrator resistance and a low exci-tation is quite sensitive to vibration and changing magneticfields.Iftheseorotherinterferencecauseclippingofthesignalfromthepreamplifier,calibra-tion results on these range-excitation pairs will be moreorlesserroneous.Itisthereforebesttoverifythesignalquality.

Select 3MΩrangeand3μVexitationandstarttomeasure.IfyouseetheredOVL and/or the green ALlightonthephysicalfrontpanelblinking,trythefollowing:

Replacetheconnectortothesensor(s)bytheshort-circuitplug.Nevercalibratewhenthereisnothing inserted in the input plug, because even then interferencecanenterthepreamplifierbox.

Trytodecouplethepreamplifierboxfrommechanical vibration by placing it on a piece of somesoftmaterial.

Movethepreamplifierfartherawayfrompumpsetc.andtryifitshouldstandsideways.

Even if these measures do not help and the high-est ranges/lowest excitations cannot be calibrated properly,otherrangeswillnotsufferfromthis.Referalsoto“MainCalibration/Precautions”inPartI.

FULL CALIBRATION

Full main calibration calibrates all range-excitation pairsusinglongaverages(serialcommand“CALI-BRATE0”).Loadthe“avs48si_main_calibration.vi”andproceedasfollows:

Checkthatyourcomputerdoesnotturnoffauto-maticallyaftercalibrationwhenitisnotused.

Selectthecorrectserialportbeforestartingtheprogram.

Starttheprogram.CP,DCandDIlightsonthephysicalfrontpanelblinkasreadingsaretaken.

Selectmethodas“allrangesslow”.Becausethis is a full calibration, range or excitation are notselectedmanually.The“ADCOUT”showsapproximate readings from a 100Ω reference and 10mVexcitation.

IfthiswasOK,click“PRESSTOCONTINUE”.After some initial operations, the calibration begings.Youcannowgohomeandhaveagoodnigth’ssleep.


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SuccesfulMainCalibration(full)hasbeencompleted.

Inthemorning,youshouldseeascreenlikethisscreencapture.Iftherewerenooverloadsduringcalibration,theERRORMSGfieldshouldshow“0”.Anoverloadcouldhavecausedamessagelike“60scalecorrection>2.9V”.Thismeans,thatcalibrationof the 3MΩrange(=RAN6)using3μVexcitation(=EXC0) has failed and the calibration can be more orlesserroneous.

There are also three useful tables: The new offset correction voltages are usually all almost in the mid-dleofthe0.1...2.9Vadjustmentrange.Thescalecor-rections have more spread, but also they should be withinthisrange.Thedifferencesbetweenoldand

new scale correction voltages tell, how much these voltages will be changed from the previous calibra-tion (usually some thousands at high excitations and sometenthswhenexcitationislow).Changesincorrection voltages have the following effects on the ADC readings:

offsetcorr.:+1Vincrease=>0.01Vincreasescalecorr.:+1Vincrease=>0.1Vdecrease

Ifeverythinglooksgood,select“SAVEANDEXIT”.Incaseoferrors,youmustdecidewhattodo.Youcancheckthesignalquality,aswasdis-cussed earlier, and try a new calibration at a suitable time.Youcanalsosavethecalibration,ifyoudonotneed those failed ran-exc combinations (but some-bodyelsemayneedtheminthefuture!!).

Takingaphotographorascreencaptureofthere-sult is a good way to remember, when the instrument

Full Main Calibration is best aborted by powering the CPU unit o and on.


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wascalibratedandhowthevaluescompare.

PARTIAL SLOW CALIBRATION

If only one or few ranges or excitations will be needed and you have no time, you can calibrate only those combinations in a much less time without compromisingaccuracy.Afterhavingstartedtheprogram as before, proceed as follows:

Selectmethod#2,“SELECTEDRAN&EXCSLOW”(serialcommand“CALIBRATE2”).

Selecttheinterestingfirstrange-excitationpair.

Checkthe“ADCOUT”voltage.

Click“PRESSTOCONTINUE”.Calibrationstarts.Thetimeneededdependsonselectedexci-tation.3μVrequireslessthan5minutes.Thenthescreenisupdated.

Bothcorrectionvoltage-fieldsseemjustlikeinthecaseoffullcalibration,butthedifferencefieldhasonlyonenon-zeroentrycorrespondingtothejustcalibratedrange-excitationpair.IfitseemsOK,select“SAVEANDEXIT”.Theremainingpartofthecalibrationwillnotbealtered.

FAST CALIBRATION

Thismethodisafirststepwhenstartinganewinstrumentafterafterassembly.Itusesshortaver-agesandsettlingtimes,anditskipssomephasesthat

PartialMainCalibrationofthe300kΩrangeand10μVexcitation.Thiscalibration,ifsaved,wouldchangethescalingofthisrange-excitationpairby0.0011*100kΩ = 110Ω(or0.1%)upwards.

CALIBRATION OF THE A/D AND D/A CON-VERTERS

The LTC2400 analog-to-digital converter itself is very stable and this calibration will not be needed unless:

AmajorpartoftheAVS-48SIhasbeenchangedor replaced,

Youwanttheanalogoutputs(analogordeviationout, set point DAC and user DAC) to comply withyourownDVMorsomeotherinstrument.

TheLTC26008-channeldigital-to-analogcon-verter has only moderate performance, which is notcomparablewiththeaccuracyoftheAVS-48SI.ThereforewehaveplacedtheLTC2600inacorrect-ingsoftwarefeedbackloop,whichworksasfollows:Suppose that one of the eight DAC output channels isinstructedtooutpute.g.1.0000Volt.Theactualoutput voltage is measured by the LTC2400 result-inginonly0.9972Volts(someoffset,somescalingerror).Thefirmwarecalculatesthedifferenceandsendsanewinstructionthatdemandsnow1.0028Volts.Thiscorrectstheoutputto1.0000V.Thesigma-deltaA/Dconversiontakestimeandthereforethe A/D converters in the AVS-48SI are slow but exceptionallyaccurate.Theirsettlingstepis50μV.

InordertomaketheanalogoutputsoftheAVS-48SI compatible with your DVM, do as follows:

Open“avs48si_adc_and_dac_calibration.vi”.Before starting it, verify that the serial port is correct.

ConnectyourDVMtothe“CONTROLSETPOINT”output.

StarttheVI.TheDVMshouldabout0.1Volts.Whentheprogramasks,entertheexactreadingofyourDVMtothefirstbox.PressCONTINUE.

TheDVMshowsthen≈2.8Volts.Entertheexactreadingtothesecondbox.PressCONTINUE.

arerequiredforafinalcalibration(serialcommand“CALIBRATE1”).

AFTER CALIBRATION

Loadthe“avs48si.vi”andmeasuresomeoftheinternal reference resistors using the interesting ran-excpairs.

Full main calibration is necessary aer the ADC and DAC Calibration and/or aer the Reference Resistor Calibration programs.


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REFERENCE RESISTOR CALIBRATION

This calibration will be needed only if the preampli-fierunit,mainunitortheCPUboxhasbeenre-placed.Therearetwoalternatelevels:

Onlyenterandsaveknownvaluesoftherefer-ences,

Measure,enterandsavethevalues

Theoriginallymeasured“true”valuesoftherefer-enceresistorsarewrittenonastickerinsidethebot-tomcoverofthepreamplifier.Theyarealsoavail-ablefromus.Ifthereisastrongreasontosuspect,that these values are not correct, those values can bemeasured,andthiscalibrationprogrammakesiteasy.

Wires from right to le: +I, +V, -V, -I. e current return lead (-I) is in contact with circuit ground and the box. See the text for actual colors.

One needs a 4-wire ohmmeter that can measure resistances with offset compensation from 1Ω to 1MΩ with a resolution of 1E-5 ohms and has an ac-curacybetterthan0.01%.Doasfollowsformeasur-ing and entering the references:

Preparea4-wiremeasuringcableforyourohm-meter.TheAVS-48SIaccessorypackageincludesa Molex 22-01-2045 connector pre-wired as follows:pin function wire color1 +I brown2 +V red3 -V orange4 -I yellow

Solder this cable to your prepared ohmmeter cable.Thefollowingphotoshows,howthecableisconnected.

TheADCandDACcalibrationprogrammakesiteasy to align the analog outputs of the AVS-48SI withyourownDVM.

Ifthenewoffsetandscalefactorsseemplausible,selectSAVEANDEXIT.Ifyoumadeatypingerror or the results seem strange, select EXIT W/OSAVINGandtryagain.

PleasereferalsotosimilarinstructionsinPartI.

Load“avs48si_reference_resistor_calibration.vi”.Beforestartingtheprogram,checkthattheserialportiscorrect.

StarttheVI.Yourohmmetershouldnowreadzeroohmstobetterthan±10μΩ.Thezeroread-ingcannotbechanged.Click“CONTINUE”.

The1Ωreferenceisnowmeasured.Whenasked,write your ohmmeter’s reading into the corre-spondingboxandclickContinue.

Repeattheaboveupto1MΩ.Theprogramwillthenwarn,ifithasseenanunexpectedvalue.Checkthenforpossibletypingerrors.Ifevery-thinglooksgood,select“SAVEANDEXIT”,

Full Main Calibration must be run aer having calibrated the A/D converter.


AVS-48SI PICOBRIDGE


otherwise,donotsavebuttrytofindthecauseoftheerror.

When this VI is running, the AVS-48VI is in a special mode, where the reference resistors are isolated from other circuitry but connected to theMolexheaderbyreedrelays.Duringnormaloperation,thereferencescannotbemeasured.

Full Main Calibration must be run aer having changed the reference resistor values

TEMPERATURE READOUT

TEMPERATURE CONVERSION FILES

TheAVS-48SIusessimpleconversionfilesforcon-vertingresistancestotemperaturesandviceversa.R/Tconversionfilesareplaintextfileswithtwoorthreecolumns.Conversionismadebysimplelinear interpolationbetweenbreakpoints.Whenmeasuring,intepolation is made from resistance to tempera-ture.Whengivingatemperaturecontrolsetpointindegrees, interpolation is from temperature to resist-ance.

Iftheresistanceexceedsthehighestbreakpointvalue, the interpolation algorithm gives the tempera-turecorrespondingtothehighestbreakpoint.Ifitfallsbelowthelowestbreakpoint,thetemperatureofthelowestbreakpointistheresult.Logicissimilarwhen converting the set point from temperature to resistance.Anerrorisindicatediftheargumentisoutsidetheinterpolationrange.

The columns are:Ordinal number of the breakpoint |

resistance | temperature OR

Resistance | temperature

Ninefirstrows0..8arereservedforyourfree-formcomments,likenameandtypeofthesensor.Thisuseful information is visible on the Settings Tab of the“avs48si.vi”program.

Numbersinadjacentcolumnsmustbeseparatedbyoneormorespacesortabcharacters.

Thefirstbreakpointmustbeonline#9(thetenthline).

Resistances must be in ascending order, from low tohighregardlessofthepolarityofdR/dT.

Aspecial“avs48si_create_r_t_information_file.vi”programexistsforwritinginformationabouttheR/Tconversionfilesandabouttheirtypesintothe“avs48si_rt_file_info.cnf”configurationfile.ThisVIalsoassociatestheR/Tfileswiththeinputchannels.


AVS-48SI PICOBRIDGE


Anturityyppi: PT-100 kaupallData: vastus vs. celsiusPisteita: 6L-tilakerroin: positiivinen

1 80.31 -502 100.00 03 119.4 504 138.5 1005 157.31 1506 175.84 200

Sensor Model: RU-1000-BF0.007Serial Number: U02889Data Format: 4 (Log Ohms/Kelvin)SetPoint Limit: 100.0 (Kelvin)Temperature coefficient: 1 (Negative)Number of Breakpoints: 198

No. Units Temperature (K)

1 3.02771 1022 3.02845 993 3.2913 96.54 3.02985 945 3.03062 91.56 3.03144 897 3.03232 86.58 3.03325 849 3.03424 81.5ETC...

If the sensor covers a large temperature range and is nonlinear, it may be advantageous to use logarithms of the resistance as argument:

Averysimpleconversionfileforaroom-tempera-turePT-100resistorcouldlooklikefollows(thisfileisincludedinthesoftwarepackageforusewiththetutorial):

R/Tconversionfilescanbecreatedusingaspread-sheetprogramandbysavingthefileasplaintaborspacelimitedtext(.TXT)withoutanyformatting.TexteditorslikeNotepadcanalsobeused.Thesensormanufacturermayprovideconversionfiles,whichneednoorlittleediting.

NumberofthebreakpointsislimitedonlybycapabilitiesofLabViewanditsrunningenviroment.

ASSIGNING TO SENSORS

TheexistingR/Tconversionfilesareassignedtosensorsbymeansof“avs48si_create_r_t_informa-tion_file.vi”.ManysimilarsensorscanusethesameR/TfileandanysensorcanhavemorethanoneR/Tfile,althoughonlyoneofthemcanbeassignedatatime.

ThisVIcreatesaninformationfile,whichthe“avs48si.vi”needsforinterpretingtheconversionfilesproperly.Itemsthatmustbetoldtothepro-gramforeachfiletobeassignedare:

Thenamesoftheconversiontextfiles.Spellingerrorscanbeavoidedbyfindingthefileintheoperatingdirectory.Thecopyandpasteitsnametotheprogram.

NumberofbreakpointsinthefileNumberofcolumns:theconversionfilecanhave

either two columns (resistance and temperature) orthreecolumns(breakpointnumber,resistanceandtemperature).

Polarityofthesensor’sdR/dT(monotonicityisassumed).

Temperatureunit(KelvinorCelsius)

With this information, the program creates an infor-mationfile“avs48si_rt_file_info.cnf”.Itcontainsrecords for all 8 channels, but records are empty forchannelsthathavenotbeenassigned.Thisisabinaryfile,whichcanbereadonlyusingthe“avs48si_create_r_t_information_file.vi”.

The assignments are made as follows:

Openthe“avs48si_create_r_t_information_file.vi”butdonotrunityet.

All conversion les must be located in the avs48si.vi’ s operating directory.


AVS-48SI PICOBRIDGE


AsimpleR/Tconversionfileforaroom-temperaturePT-100hasbeenassignedtochannel1.Thisfilehas6breakpoints(resistance),threecolumns,positiviedR/dTandtemperaturesareinCelsius.Attopright,onecanseethebreakpoints,atbottomrightareshownthepossible9commentrows.

Select“READANDEDIT”astheprocessingmodeand“SAVE.CNFFILE”asthesavemode.This is a multi-purpose VI, which has also other modesforuseasasub-VI.

Starttheprogram.Ifthe“avs48_rt_file_info.cnf”fileisnotfound,the“filereadinfo”fieldtellsthatadefaultfilewithoutanypriorassociationswillbecreated.Ifafileisfound,gothroughallchan-nels and verify that there are no unwanted prior associations.

Ifsuchunnecessaryassociationsarefound,youcanremovethembychangingthefilenametoblankortosomethingnon-existent.RemovinganassociationdoesnotremovetheR/Tfile.

Selectthedesiredsensorchannelandentertherequiredinformation.Youcanrepeatthisnowforothersensorsandthenclick“ACCEPTEDITS”.AnewinformationfileiscreatedandtheVIexits.Thepossiblyexistingassociations,iftheywerenotremovedorchanged,remainintact.

Ifyoujustwanttoseetheexistingassociationsand do not want to edit, add or remove anything, select“DISCARDEDITS”andthepresentfilewillnotbealtered.

Finally,starttheVIagainusingthesamemodes.On the right side, you can now view the informa-tionstoredinthefile,andcorrectanypossibleerrors.

Later,whenyourunthe“avs48si.vi”measuringprogram,theSettingsTabshowsthisinformation.Use this method for removing the demo

association of a PT-100 to the calibration channel CH0.


AVS-48SI PICOBRIDGE


OPENING THE INSTRUMENT

The main unit of the AVS-48SI (ELMA type 15) has been designed for good shielding against received andtransmittedRFinterference.Itstopandbottomcovers have special spring contacts for grounding the coverstothecaseatmanyplaces.Thesecontactsarequite tight if the covers have not been opened many timesalready.Thesephotographsshow,howtoopenthecoverswithoutbendingthempermanently.

Removethetwosidepanels.

Liftthecoverslightlyfromtheside.Theninsertaflatscrewdriverorsomeotherflattoollikeinthisphoto.Movethe tool to the right and lift the cover from the spring con-tacts.Donotlettheplatetobendsharply-youcanlightlypresstheliftedsidedownwardsforpreventingbending.

Startfromtherearside.Bothsidesaresimilar,buttracesontheblackfrontpanelaremorevisiblethananydamageontherear.Openallspringcontactswiththetoolbeforeliftingthecoverbyhands.

Liftthecoverfromthebackandalsothefrontcontactsopen.

Checkthatthe3+3contactsareingoodconditionbeforeclosingtheunit.Pressthecoverfirmlyatthepositionsofthecontactsinordertoclosethemproperly.Youmayhearaclickwhenthishappens.


AVS-48SI PICOBRIDGE


IndexSymbols

2/4-wire 4612V DC battery input 1018V AC low-voltage input 10

AAccuracy, curve 5AC monitor output 4, 30ADC a/d conversion c/q 26ADC and DAC Calibration 63Adc input channel 59A/D conversion speed, LabView 47ADC reference voltage 59AL alarm signal

indicator light 10, 61All ranges slow 61Analogfilter4, 54Analog out BNC 53Analog output 4, 7, 28

rear panel BNC 12Analog overload 9ArduinoMega25607, 20, 23, 36ARN autorange c/q 23Array of clusters 58ASSIGNING R/T FILES TO SENSORS 66Automatic saving of properties 45, 58Autorange 45Autoranging

enabling 43, 47AVS-47x compatibilityCompatibilityw.AVS-47x18

avs48chnames.cfgchannelnamesfile45AVS-48LVA 41AVS-48 main unit 18AVS-48preamplifier18Avs48si_adc_and_dac_calibration.vi63Avs48si_create_r_t_information_file.vi43, 66avs48si_data.csvfile56avs48si_data_out_array_fg.vi47, 56AVS-48SI-F5 18AVS-48SI-F10 18Avs48si_main_calibration61AVS48SI-Picolink8, 18, 35Avs48si_reference_resistor_calibration.vi64Avs48si_rt_file_info.cnf65, 66avs48si.vi(LabView)41

installing the program 42AVS-48SI-W 18

AVS48-USB/Serial-W CPU 7

BBooting the CPU 23Breakpointnumber43

CCables, included cable types 7Cablespecifications35CALADC calibrate ADC and DAC command 31CALIBRATE 1 63CALIBRATE 2 63CALIBRATE main calibration command 30Calibration 29, 61coefficients20precautions 29ReferenceResistorCalibration.vi32

CALIBRATION OF THE A/D AND D/A CONVERTERS 63

Calibrator 55stability of references 55

CALREFref.resistorcalibrationcommand32Capacitance, input 4Channel 4Channel name 48Channel names 45avs48chnames.cfgfile45

CH input channel c/q 23Clockinput,external5Coercing command’s argument 21Command arguments 21Command delimiter 21Command interpreter 37Command order 21Commands and queries 21Commentarea(9firstrows)58Compatibilityw.AVS-47x9, 18Compliance voltage, heater output 49COM: port 18Connectionsbetw.instruments7Connectorformeasuringref.resistors32Control CH 55Control channel 44Control error meter 48Control error output

rear panel BNC 12, 53Control sensor c/q 23Control set point 28

rear panel BNC 12Correction factors 29, 61CPClockPulse

indicator light 10CPU box, opening 38


AVS-48SI PICOBRIDGE


CPU unit 18CSV string 56CTS 35Current leads, resistance 4

DDAC outputs 5Datafilename56Data saving mode 56DC data from computer

indicator light 10DEFAULTS command 22, 34Delays 22DERG derivator gain c/q 24Derivator gain 50Deviation output, polarity 53DI data from instrument

indicator light 10DIRECT DAC 56

Direct DAC(V) control box 56Disabling automatic saving of properties 58DLY delay command 33DR/DT 53

deviation polarity 53DRDT control polarity c/q 23, 25DTR 35DVMHI command 31DVMLO command 31

EEEPROM 41EEPROM write count 26EMI 18Enter 51ENTER button 44turnsdark51

EPRADC,readADCcal.coefficients31EPRCALreadMaincal.coefficiensfromEEPROM31EPRREFreadref.resistorvaluesfromEEPROM32, 33ERR error query 34Error indicators lights 9Error messages 34Error output, temperature control 4ERRSIGNAL error signal query 25EXC excitation c/q 23Excitation 4, 45

magnitude of current 45Exit 52Externalclockinput5

frequency equation 14rear panel BNC 14

External heater 4

External heater driveINT/EXT jumper JP1 13rear panel BNC input 13

F

FAST CALIBRATION 63FFT fast Fourier transform 13fibre-opticalconnection18Filter

indicator light 43settling time 46zerolength46

Filter, analog 4Filter delay 53Filter length 46Filter mode 46

always 46smart 46

Filter mode control 43Filter output 54Four wire connection 46Front tab 42Full calibration 30FULL CALIBRATION 61Functiona global (FG) variable 47Fuse 10

GGalvanic isolation 18GNDS sensor grounding c/q 23Ground currents 18Grounding, sensor 4

H

HDACV heater drive voltage c/q 24Heater connection 51Heater Direct DAC 56HEATER DRV SOURCE 56Heater, external drive 4Heater output 4

maximum power 24rear panel BNC 12

Heater power 5Heater power display (digital) 49Heater power % meter 49Heater range 49

changing downwards 49table of ranges 24

Heater resistance 5, 24, 55Hold 52HOLDMODE command/query 25


AVS-48SI PICOBRIDGE


HTRDIR heater drive by voltage c/q 24HTRI heater output current query 25HTRP heater output power query 25HTRRAN heater range c/q 24HTRV heater output voltage query 25HW? hardware query 20, 22Hyperterminal program 19

I

Idle 47IDN? 58IDN?identificationquery20, 22InitializingtheFG58Input capacitance 4Input channel 45Input connector 4

wiring 9Installingtheavs48si.vi42Integrator gain 50Interference 61Internal resistances 3Interpolation,R/Tfiles65

limits 65INTG integrator gain c/q 24INTHEATER external/internal heater c/q 24, 25Introduction 18, 41

LLaboratory environment 3Lead resistanceschecking9measuring 46, 48warning light 9

Lead resistances, maximum 4, 48Least squares line 54LINETERM c/q 22Line terminator 20, 21Log(R)inanR/Tconversionfile43Loop gain, temperature control 49, 52Low_cost_pt100.txtdemoR/Tfile43

MMagneticfields61Main calibration 29MAIN CALIBRATION 61timetaken61

Mains adapter 7Mains hum 29, 30Mains input 10MAX? maximum query 20, 26Mean Squared Error (MSE) 54Measure 47

Message line terminator 21MIN? minimum query 20, 26Multi-line append 56

NNational Instruments USB-232 converter 7, 19, 42, 53Noise

oscilloscope view 13STD curves 6

Noise voltage 4Notepad 66

OOpening the CPU box 38Opening the instrument 9OPENING THE INSTRUMENT 68Optical cable 8

renewing ends 8Opticallinkoption8Oscilloscope, connection 30Outputs, analog 4Overload 48

warning light 9, 61Oversoot, temperature control 50

PPartial calibration 31PARTIAL CALIBRATION 63Peak-to-peakresolution5Physical front panel 9Physical rear panel 10

viewed from front side 11Picobridge 3, 18Picobus cable 35Picobus, proprietary protocol 41Picobus Serial Input 10Picobus status lights 10Picolink35PID parameters 5Power input 5, 7Power switch 9Preamplifierinputconnector14PRESETMODE command/query 27Primary interface, picobus 10PROPG proportional gain c/q 24Proportional gain 50PSDF operating frequency c/q 23PSD Frequency 54

Q

QRATIO? quality ratio query 20, 26Quickcalibration31


AVS-48SI PICOBRIDGE


R

Range 4, 45changingr.ofcontrolsensor52

RAN measuring range c/q 23Rawreadings,filteroutput54Recall 47, 51RECALLBR recall channel properties 27Recalling

channel properties 43RECALLTC recall heater range properties 28REFERENCE RESISTOR CALIBRATION 64ReferenceResistorCalibration.vi32Reference resistors 31REFID 32REFIDordinalnumberofcalib.referencec/q29, 32REFVALUE 32REFVALUE“true”valueofcalib.referencec/q29, 32,

64Remote diagnosis 59RemovingdemoR/Tfileassociation67REPEAT command for repreating mode 33Reprogramming the CPU 36RESETALL command 22, 34Resistance display 48Resolution, curve 5Response to *IDN? 58RES resistance c/q 26RESTART command 22, 34Re-starting the CPU 9RS232 18R/Tconversionfiles65

assigning to sensors 43R/Tfileinformation58RTS 35RXD 35, 38

S

SAVEADC save adc offset and scale factors 26, 31SAVEBRD save channel properties 26SAVECALsavecalibrationcoefficients26, 29, 30, 31SAVELINETERM save line terminator 27SAVEREFsaveref.valuescommand26, 32SAVETCR save heater range properties 27Saving data from one sensor 46, 47Saving measured data

for other LabView VIs 56toadiskfile56

Saving off/on 56Saving of properties 45, 58Scale 51Scan 47

Scan enable 46Scanning

enabling for a CH 43filterlength47order of channels 47SCAN command 43speed 47

SDACV 28SDACV set point DAC c/q 24, 31Sensor grounding 46Sensor, grounding 4Sensor heating, starting to measure 47Sensor wiring 9Serial cable 35Serial format 7Serial port 53serial port number 19, 42Service measurements 37Service tab 42Set point 51Setpoint DAC (V) 55SETPOINT resistance set point cmd 25Set point, temperature control 4Set point unit 50

changing between R and T 50exceeding limits 50

Settings tab 42Shielded room 18Shielding braid 35Short-circuit plug 7, 8, 30, 42Signal overload 48Single-line replace 56Smartfilter41, 46, 54

LAST POINT output mode 55MEAN output mode 54

SpecificationsOther 5Temperature controller 5

Speed of balance 4Spreadsheet program 66Square error array 60Square error table 59Standard deviation STD 5Standard deviation (V) 59Start-up state 42Statistics queries 20STD? standard deviation query 20, 26

TTemperature controller 18

disabling high ranges 49enabling control 49, 55internal test assembly 51


AVS-48SI PICOBRIDGE


resettingintegratorbymistake50stopping control 49, 51, 52testing with an internal load and sensor 44

Temperatureconversionfiles65examples 66

TEMPERATURE CONVERSION FILES 65Temperature display 48

warning lights 48Temperature readout 41Testingtemp.ctrlwithinternalheater25TIME command for measuring time interval 34Timeout 21Timing issues 21Trademarks3Transfer function, controller 5Transient part of settling data 54Trouble-shooting

serial operation 37TS-530A temperature controller 18Tutorial

LabView operation 42serial operation 19

TW 2/4-wire connection c/q 23Two-wire connection 46TXD 7, 38

U

UDACV 28Unbundle by Name 58Unpackingtheshipment7USB 18USB-232 converter 7, 35, 53USB-232 converter, installing 7USB cable 36User DAC 5

accuracy 13rear panel BNC 13

User DAC output 13, 28User DAC (V) 55

VVibration 3

sensitivity to 61Virtual instrument 41

WWall adapter 7Warranty 3Write count, EEPROM 26

DECLARATION OF CONFORMITY

Manufacturer: RV-Elektroniikka Oy PicowattAddress: Veromiehentie 14 01510 VANTAA Finland Telephone: +358 50 337 5192 E-Mail:[email protected]

declares that under our sole responsibility

Product Name: AVS-48 Picobridge

ProductDescription: CryogenicACResistanceBridgeincluding19”main unit,smallpreamplifierunitandaninterconnectioncable

is in conformity with the following Directives:

2004/108/EC: Electromagnetic Compatibility2006/95/EC: Low-voltageDirective(ElectricalSafety)2011/65/EU: ROHSDirective

and that the following harmonized standards have been applied:

EN 50 081-1: Generic emission standard, Part 1: Residential, commercial and light industryEN 50 082-1: Generic immunity standard, Part 1: Residential, commercial and light industryEN61010-1: Safetyrequirementsforelectricalequipmentformeasurement,control and laboratory useEN 50 581: ROHS

Additional information: This product has been designed for measuring low and ultralow temperaturesincryostatsusingresistivetemperaturesensors.Inordertoprevent the measuring current from heating the sensor, currents down to 1pA canbeused.Theenvironmentisthereforeexpectedtobeelectromagneticallybenign,freefromchangingstrongelectricandmagneticfieldsandfreefromsignificantchangesorinterferenceinthemainssupplyvoltage.

Vantaa,25June2013 RV-ElektroniikkaOyPicowatt

Reijo Voutilainen President

AVS-48SI PICOBRIDGE - rockgateco.com · Cryogenic AC Resistance Bridge and Temperature Controller...

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Transcript of AVS-48SI PICOBRIDGE - rockgateco.com · Cryogenic AC Resistance Bridge and Temperature Controller...