BT-77 Bearing Tester with Non-Contact Tacho

Operating Instruction Manual

KOHTECT BT-77

CONTENT

PageINTRODUCTION................................................................................1

1.0BT-77INSTRUMENTDISCRIPTIONANDFUNCTION............11.1Specification1.1.1StandardConditionforOperation1.1.2SystemSpecification1.2OverviewonRollingBearingConditionMonitoring1.3UnderstandingShockInduced“Carpetvalue”and“Maximumvalue”1.4Tachometer1.5DesignofBT-771.5.1OperationKeys

2.0TAKINGMEASUREMENTWITHTHEINSTRUMENT..............72.1.Instrumentdisplayandmeasuringmodes2.1.1Settingthesystemrealtimeanddate2.2TakingBearingDiagnosisMeasurements2.2.1Selectionandsettingupthemeasuringpoints2.2.2Setupinitialparameter&takingbearingmeasurements2.2.3Takingbearingdiagnosismeasurementandsave2.2.4Fileformatandopenmeasuredfile2.3EvaluationoftheMeasuringResults2.4MeasuringRPMbyTachometer2.4.1SetupinstrumentandmeasuringRPM2.4.2MeasuringRPMbytheTachometer

3.0ROLLERBEARINGCONDITIONMONITORINGBYTHE SHOCKPULSEMETHOD(MEASUREMENTMETHOD)......14

3.1WhatisShockPulseMethod(SPM)anditbasis3.2HowShockPulseMeasuredandEvaluatedforRollingBearing3.3EvaluationofBearingConditionwithBT773.4Methodandmeasurementlocationofthebearing

4.0DELIVERY.................................................................................19

KOHTECT BT-77

KOHTECT BT-77

INTRODUCTION

ThismanualisintendedforthestudyoftheBT-77bearingconditiontester.Themanual

containsdescriptionof theBT-77bearing checkeroperatingprinciple, operating

proceduresoftheintendeduseandbearingshockpulseevaluationconcept.

1.0 BT-77INSTRUMENTDISCRIPTIONANDFUNCTION

1.1 Specification

1.1.1StandardConditionsforOperation:

Operatingtemperature(device&sensor),-10to55°С,(±5)°С;

Relativehumidity80%attemperature30°С;

Atmosphericpressure,84to106.7KPa(630-800mmHg);

Resonancefrequency,32kHz;

Measurementunit,dBi,dBc,dBm;

Range,max.99dB;

Resolution,1dB;

Accuracy,±5%;

Operatingtemperature(tacho),10to55°С,(±5)°С;

Tachometerrange,50-30,000rpm;

Tachometerresolution,1rpm;

Tachometersensingdistance,upto1m;

Memorycapacity,2MB;

PCcommunicationport,USB;

1.1.2SystemSpecification

Power supply, 3.6�� �iMH rechargeable battery.Powersupply,3.6���iMHrechargeablebattery.

Continuous operation on batteries, not less than 10 hours.Continuousoperationonbatteries,notlessthan10hours.

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

1

KOHTECT BT-77

Current consumption 220��, 50 Hz AC, not more than 5��A.Currentconsumption220��,50HzAC,notmorethan5��A.

The limits of complementary error of the instrument at voltage changing fromThelimitsofcomplementaryerroroftheinstrumentatvoltagechangingfrom

3.6��oltsto2.8��olts.

Probabilityofno-failureoperation,notlessthan0.92per2000hrs.

Theaverageinstrumentlife,notlessthan10years.

Failuretime,1000hours.Theaveragefailuretimeissetforstan-dardconditions

foroperation.

Dimensions,notmorethan60х110х30(mm).

Weight,notmorethan210gram.

1.2 OverviewonRollingBearingConditionMonitoring

Ideally, rollingbearingelementsareseparatedbyaprotective lubricantfilm,which

impedes their collision. However,manufacturingdefects, damages,whichappear

duringoperation,dirtinthebearing,insufficientorincorrectlubrication–allthese

factorscause thecollisionof thebearingelementsand,asa result, acoustic

oscillationsofawidespectrumaregeneratedinthebearingbody.

Aspeciallydesignedtransducer(patent№18652)isusedtofilteroutthepartofthis

spectrumthatcarriesinformationonthebearingfaultsdetection.Thetransducerfilters

thoseacousticoscillationswhicharegeneratedbythebearingdefects,andconverts

themintoelectronicsignalproportionaltothemagnitudeofshockpulsesignal,thatis

amplifiedandmeasuredby theBT-77electronicunit in therelativeunitsofdecibels

(dB).

Arealnewbearingisjustfromthebeginningofitsuse,asourceofinducedvibration,

theamplitudeoftheshockpulseofwhichisdBi.

ThedBi,initialvaluedependsonthelargenumberoffactors;however,inpracticeitis

possibletolimitthemtodiameterD(mm)oftheneckanditsrotatingspeed�(rpm).The

•

•

•

•

•

•

•

2

KOHTECT BT-77

valueofdBifeaturestheconditionofanewcorrectlyinstalledandlubricatedbearing.

The shockpulseamplitude increasesasa result ofwear and improper use.Shock

accelerationamplitudeoverrunningthevalueofdBi -dBsvfeaturesadamage,andis

usedfortheevaluationofbearingcondition.

ThisenableBT-77totellthedifferenceofshockpulsevaluesinduceislowshockand

highshock,anormalizedmeasurementscalecalldBnisuses,seebeneathTable-1.0.

dBn = 0-25 Goodcondition

dBn = 25-40 Satisfactorycondition

dBn > 40 Poorcondition,breakdownrisk

Table-1.0

Fig-1.0

3

KOHTECT BT-77

50 -

-dBa-absolutevalueatmeasuringpoint

40 -

- dBsv-valuefeaturesbearingfailure(dBa-dBi)

30 -

20 -

-dBi-originalvalueoftheshockaccelerationamplitude

10 -

-

0 -responsethresholdofthebearingchecker

-5 -

-10 -

Figure-1.1-Anexampleofthesevaluesratio.

Patternoftheinducedoscillations,whichareregisteredbyBT-77,changesaccording

tothebearingfaults.

1.3 UnderstandingShockInduced“Carpetvalue”and“Maximumvalue”

Atthemeasurements,thebearingcheckerallowstofilteroutandmeasuretwospecified

valuesoftheshockaccelerationamplitude:theCarpetvalue(dBc)andtheMax.value

(dBm).

ThedBcbackgroundvalue (theCarpetvalue) refers to the frequentcollisionsof the

bearingsurfaceroughness,dBcitgivesimportantinformationregardtothelubrication

ofthebearings,howwellthebearinghavebeenmountedandthewayinwhichthey

arebeenloaded,andisindicatedbythecontinuouslightofLED.ThedBmMax��alue

referstotheseparateshocks,characterizingthefaultslevel,andisindicatedbyseparate

LEDflashes.

4

KOHTECT BT-77

Forinstance,attheshockaccelerationamplitudemeasuringofawelllubricatedand

correctly installed bearing, the dBm is only slightly higher than dBc. But when one

measuresshockaccelerationamplitudeofabearinghaving faults, these faultsare

detectedbydBmmaximumvalues,atthat,thebackgrounddBcvaluedependsonthe

lubrication condition, and can grow increase substantially when there is insufficient

lubricationfollowedbyfrequentmetal-to-metalcontacts.

IncreaseofdBcbackgroundvaluemaybecausedbyotherreasonsaswell,e.g.atthe

drivecouplingmisalignment.Itiseasytodistinguishbetweenthesecases–withthe

couplingmisalignmenttherewillbethesamepictureforthebearingsonthebothsides

ofthecoupling.

Resultsoftheshockaccelerationamplitudemeasurementfordrivesbearingscanbe

influencedbyshocksproducedduring the running inofagearmesh,whichcanbe

transferredontothebearings.However,mostlythegearteethhumissolowthatdoes

notimpedethemeasurement.

Withtheshocks,originatedbythegearwheelsdefects,thedBmMax��alueincreases

sharplyforthetwobearingssimultaneously(onbothsidesofgear).

Thegreatesteffect from the technicalstatemonitoringofbearings is reachedwhen

measuringresultsarebeingputongraphagainstthetimefactor.Atthis,aforecastof

thetechnicalstatebecomespossible.Exampleofthemeasurementsresultsprocessing

isgiveninTable-1.0.

1.4 Tachometer

TheTI-7tachometeroperationisbasedonthemeasurementoffrequencyofinfrared

rayreturnfromthereflectivetape(oranothermarker)fixedontheturningshaft.Awhite

markerpenisprovidesinthepackagesothatusercanmarktherotortogetgood

5

KOHTECT BT-77

contrastwhentakingRPMmeasurement.

ThemeasuredRPMreadingcanalsobesavedwithinthedevicewithfilenameendby

“tac”extension.

1.5 DesignofBT77

ConstructivelyBT-77BearingTester is designed ina light andstrongalloy casing

protectedbysiliconsleevewiththerechargeableinternalbatterypowersupply,socket

forthemeasuringprobeandUSBportfortachometersensorsorfileuploadtoPCfor

datamanagement.ThecontrolsandconnectorslocationisshownontheFig.1.2a&

Fig.1.2b.

Fig.1.2a Fig-1.2bTopviewofBT-77

1.BT-77device

2.Bearingshockpulsemeasuringprobe

3.Tachometersensorandmagneticstand

4.Socketformeasuringprobe

5.USBportforTachometersensor/PCcom

6.SocketforACcharger

7.Softmembranepushpadforoperation

8.Back-litemonochromeLCDdisplay

456

6

12

8

3

KOHTECT BT-77

1.5.1OperationKeys

TurnO� Entersetupmenu

OK/Start Return/backtoearlierstep Adjustuporincrease Adjustdownordecrease/OFF(pressandhold)

2.0 TAKINGMEAUSREMENTWITHTHEINSTRUEMNT

Beforeusingtheinstrument,itisagoodpracticestocheckpropermechanicalfunctioning

ofthecontrols,connectorsandpowerstatewhenswitchon.

Note the device automatically switches off after 150 seconds when no further

operation.

2.1 InstrumentDisplayandMeasuringModes

Toswitch“O�”theBT-77bearingtester,press .Thedeviceperformselftest

asshowninFig-2.1andautomaticallyenterthefirstdefaultoperationmode-USB

interface,Fig-2.2.

ToconnectdevicetoPCforreportprintandview,makesuredeviceissetinUSB

interfacemodeandpress to ready for interface.Connect theUSBcable

betweendeviceandPCviatheUSBport.

Togo toothermode,presseither or to scroll through the fouroperating

modeoption.

Fig-2.1Fig-2.2

B e a r i n g Te s t e r

K o H T E C T B T - 7 7

( c ) 0 7 0 1 0 8 v 3 . 0 1 c

N o . 1 2 3 4 4 5 5

w w w . k o h t e c t . c o m

U S B i n t e r f a c e

* 3 . 0 2 v2 5 m a r 0 7 1 4 : 3 0 : 5 0

7

KOHTECT BT-77

2.1.1Settingthesystemrealtimeanddate

Atanyoperationmodedisplay,press toenterdate/timemenufollowby

toseesetitems.

Press and tosettheminutesandfollow toconfirmcorrectinput

setting.Thescreenproceedsandshowsubsequencesettingforhours,day,date,

monthandyeartobesetinsameway.

Whenalldateandtimesettingsarecorrectlyinput,press twicetoreturn

operationmodedisplaytobeginnewtask.

2.2 TakingBearingDiagnosisMeasurements

2.2.1Selectionandsettingupthemeasuringpoints

Whileselectingthemeasuringpoints,takeintoaccountthefollowingandseeFig3-3:

Metalcolumnbetweentheprobetipandbearingmustbe,ifpossible,straight

(don’ttakereadingsfromthecapthatcoversthebearinghousing).

Itiscriticalthatthemeasuringpointtobeselectedascloseaspossibleto

thebearing.

Whilemonitoringthebearing,usethesamemeasuringpoint.

Settingupmeasuringpoint:

Measuringpointsshouldbefreeofpaintanddirt;

Mount thestationaryextenders (pinsorbolts6-8mm)ofdesired lengthor

provideholes formeasuringprobeaccess in thebearinghousings located

behindthemachineprotectivegearsorcaps.

ATTENTION! Keep the probe location and the force the same during the measuring

cycle!

TheBT-77Tester automatically switches off after 150 secondswhen no further

operation.

•

•

•

P

P

P

P

P

8

KOHTECT BT-77

2.2.2Setupinitialparameter&takebearingmeasurements

Press toturnonBT-77,press keytoswitchdisplaytobearingdiagnosis

measurementmodeshowsinFig-2.3.

Press tobeginnewmeasurementshowninFig-2.4andpress again

tostarttakingreading.

Fig-2.3Fig-2.4

Ifparametersonscreenare�OTcorrectsetandneedtobechange,press

twicetodisplaychangeofdBi setting(see note below for dBi setting).

IfdBiisunknown,press againtochangeD(diameterofshaftorbearingI/Ddia)

byusing or keytosetandpress toconfirmtheDinputvalueand

gotonextsettingparameters.

ScreenwilldisplayRPM(shaftrotatingspeed)setting,sameusing or

keytosetandpress toconfirm.

Thedisplaynowshows“Single”“Average”or“Contin”,setting.Tochangethe

calculationmethodbyusing or keytoset.

�owpress twicetoviewthenewlycalculateddBivaluewithchangedinput

parameters.

Ifallparameterhavesetcorrectly,press toreturnreadyformeasurement

screen,Fig-2.4.

Tobeginnewmeasurement,press tostarttakingreading.Waitformeasured

todisplaywithevaluationasshowninFig-2.5b

Note: dBi can be input manually or calculate by device after input of the bearing inner

B e a r i n g s 7 7 D 1 1

* 2 . 7 7 v2 5 m a r 0 7 1 7 : 3 0 : 5 9

= = = = = = = = = = = = = = = =D = 2 5 N = 3 0 0 0d b i = 3 0 A v e r a g e

•

•

•

•

•

•

•

•

•

9

KOHTECT BT-77

diameter or shaft diameter “D” and RPM, “N” speed for the machine.

ATTENTION!

Measurement calculation method:

single reading with dBi taken into account. Result – normalized value of

dBm, dBc for condition evaluation based on the technology developed

by the Central Research & Design Institute of Navy.

continuous reading with dBi taken into account. Result updates every

seconds. Press “STOP” button to end the procedure.

five readings are taken with dBi taken into account; the result is their

arithmetic mean value.

2.2.3Takingbearingdiagnosismeasurementandsave

After identified themeasuringpointonmachine,place theprobefirmlyagainst the

machineatthedesiredmeasurementlocationandreadytotakereading.

Press andwaituntilbearingreadingisdisplayed.Whiletakingthereading,

displayshow“busy…”message,Fig.2.5a,andthemeasuringcycleis

approximately30-40secondif“Average”methodisselected.

Oncemeasurementfinish,thedisplayshowsFig-5b,themeasuringresults:the

Maxvalue,Carpetvalue(dBmanddBc)andconditionofthebearingevaluated

ondBnchartasfinalresult.

Fig-2.5aFig-2.5b

Tosavethereading,Press follow OKkeytoentermaindirectory.

Press again tomakenewdirectory, save, read or delete folder or press

Single-

Cont.-

Average-

•

•

d B m = 2 9 S a t i s f .d B c = 1 8

= = = = = = = = = = = = = = = =D = 2 5 N = 3 0 0 0d b i = 3 0 A v e r a g e

Max. valueBearing evaluationCarpet value

Input info

B u s y . .

•

•

10

KOHTECT BT-77

or toselectdesireddirectory(directorylineareshowswith)series of

numeric without “xxx.b77”or “xxx.tac” extension)tobesaved,seeFig-2.6in

section2.2.4savemeasuredfile.

Press toconfirmdatasaved.

2.2.4Fileformatandopenmeasuredfile

ForBT-77,anymeasured readingondisplay reading is savedwithin thedevice in

standardformatwithselfdevicegenerateddirectoryorfilenamesintermofdateand

time(“0325”mean25Marchand“165301”mean16hrs,53mins,01sec) followby

“b77”extensionformatfordatafile,seeFig-2.6.

Fig-2.6

Toopendatafileforreview,press or togotomydocumentsscreen

andpress toseefileanddirectoryasFig-2.6.

Press or tomovecursortodatafile(withb77extension)andpress

toopenforview.

2.3 EvaluationoftheMeasuringResults

BearingconditionisdefinedbytheshockaccelerationmagnitudedBn.

0...25dBn -goodcondition,optimaloperatingconditions;

25...40dBn -satisfactorycondition,themeasurementsaretakeninshort

timeintervaltoevaluatethetypeofcoming;

>40dBn -poorcondition,visiblefailuresappear,operatingconditionsbe

cameworse,accidentmayhappen.

/ 0 3 2 4 _ 1 7 0 4 0 5. .0 3 2 5 _ 1 6 5 2 1 10 3 2 5 _ 1 6 5 3 0 1 . b 7 7

1 6 bD a t a s a v e d

Main directory nameBack to earlier directorySub-dir nameData file name saved

File size

•

•

•

11

KOHTECT BT-77

Themeasuring results are recorded into the report. While continuouslymonitoring the

equipmentcondition,itisrecommendedtousetherecordsasgraphicaldatarepresentation

toshowclearlythetendencyofconditionchangeatthemeasuringpoints.

Table-2

DiagramsintheTable-2showasfollows:

Bearing№1isingoodtechnicalcondition

Afterthemeasurementdated15.02.90thelubricationwasreplacedinthebearing

№2,presentlythisbearingisingoodconditionandneedsclosemonitoring(more

frequentmeasurements).

Bearing№3isingoodtechnicalcondition.

Conditionofbearing№4isgettingworse,afterthemeasurementdated15.03.90

the lubricationwas replaced,nopositive resultswereshown, it isadvisable to

replace the bearing to avoid any serious faults (bending of the shaft, impeller

break-away,etc.).

2.4 MeasuringRPMbytheTachometer

2.4.1SetupinstrumentandmeasuringRPM

Applyreflectingtapeormarkontheshaftwhichrotationfrequencyshouldbemeasured.

Themarkshouldbecontrastagainsttheshaftmaterial(a lightmark-onthedark

Pump inventory numbe1121r Bearing № 1 Bearing № 2 Bearing № 3 Bearing № 4Date 10 30 50 10 30 50 10 30 50 10 30 50

18.01.9031.02.9015.02.9022.02.9001.03.9015.03.9022.03.9028.03.90

1.

2.

3.

4.

12

KOHTECT BT-77

background,adarkmark–onalightbackground).

Reflectivemarkingshouldnotlessthan20mmlengthonshaftfortachosensortotake

speedreading.

Placethetachometersothatyoufollowtherecommendationsonpositioningawayfrom

themeasuredobject.Selectthelocationofthetachometerthatwillprovidethereliable

andstableresponsefromthemark.Itisrecommendedtoplacethetachometeratthe

angledifferentfrom90degreesand10-20cmawaytothemarksurface–thiswill

decreasefaultresponsefromthesurfaceoftheshaftsurface.Useretro-reflecting

tapeasamark.(Itispossibletousethecorrectionfluid“Stroke”toapplythemark).

2.4.2MeasuringRPMbytheTachometer

Press to turnonBT-77,press key toswitchdisplay toTachometer

measurementmodeshowsinFig-2.7a.

Fig-2.7aFig-2.7b

Press twotimestostartrpmmeasurement.

Press torecordmachinerotatingspeedanddisplayRPMreading,Fig-2.7b.

When finishmeasuring, press save result or press to return to

programmodeoptionwhenRPMnoted.

•

Ta c h o m e t e r

* 2 . 7 7 v2 4 m a r 0 7 1 7 : 3 0 : 4 7

Ta c h o E P C = 1

R P M 3 0 0 4 . 8 1

•

•

•

13

KOHTECT BT-77

3.0 ROLLER BEARING CONDITION MONITORING BY THE SHOCK PULSE

METHOD(MEAUREMENTMETHOD)

3.1 WhatisShockPulseMethod(SPM)anditbasis

DesignationoftheShockPulseMethod(SPM)isasignalprocessingtechniqueused

tomeasure rollingbearingconditionand thequalityof their lubrication in themotor,

pumps,separators,turbocompressorsfordieselboost,etc.Usingtheinstrumentsto

measureshockpulses,onecandetermine theairorgas leaksvia looseness in the

high-pressurevesselsorpipes.TheresearchworkconductedatCentralResearch&

Design Institute of �avy allowed expanding the performance capabilities of the

instruments.Shockpulsecheckershavesettobeusedfortheevaluationofcondition

ofhigh-pressurefuelpumps,dieselinjectors,valvesofpistoncompressors.

TheShockPulseMethod (SPM)wasdevelopedbyaSwedish instrumentcompany

andbasedonmonitoringandanalyzingofhighfrequencycompression(shock)waves

causedbymechanicalimpact.Accelerationofmaterialparticlesgeneratespressureor

shockwavethatpropagatesasultra-sonicfrequencybandthroughtheobject.Inthe

initialphaseofimpact,theaccelerationofmaterialparticlesdependsonimpactvelocity

andisindependentofthemassofcollidingobjects.Withinshortperiodandthereisno

evidentdeformation.Thevaluewaveshockistheimpactvelocityofcollidingobjects.

In the secondphaseof the collision, the surfacesof twoobjectsaredeformed; the

energymovementdeclinestheobjectandgeneratesvibrationsthatarediagnosedby

thevibrationanalysis.

Piezoelectrictransducerisusedtomeasureshockpulse;vibrationandnoisebackground

donoteffectonit.Thetransducerselectricallyandmechanicallytuneto28…32kHz.

Shockwavecausedbythemechanicalimpactgeneratesthedecayingshockvibrations

intransducer.Themaximummagnitudeofthisdecayingvibrationisrelativetothevelocityof

theimpact(v).Sincethedecayingtransientiswelldefinedandhasconstantdecayvalue,it

14

KOHTECT BT-77

canbeeasilyfilteredoutallothervibrations,i.e.vibrationfrequencies.Theshockpulse

methodinvolvesmonitoringandanalyzingthedecayingtransientprocess.

3.2 HowShockPulseMeasuredandEvaluatedforRollingBearing

Theouterracewaysofthebearingalwaysfeatureroughness.Thereforeabearingunder

normaloperatingundergoesthemechanicalimpactsandcreatesshockpulses.Shock

pulsevalueisdependentonthebearingsurfaceconditionandtheperipheralcondition

ofthebearing.Shockpulsevalueoftheregularbearingfeatures1000timesincrease

sincethetimeabearingisnewuptothemomentwhenabearingneedsreplacement.

Becauseof the very largedynamic rangeshockpulsesaremeasuredonadecibel

scale.

Empirical tests showed that even the newand lubricatedbearing generates shock

pulses.ThevalueofthisinitialimpactissetasdBi(dB,initialvalue).Asthebearing

wears,thevaluedBa(averageshockpulsevalue)increases.�ormalizedvaluedBnfor

thebearingcanbeshownasfollowsdBn=dBa-dBi

(BearingLife)

Fig-3.1.depictsdBnandbearingliferatio.

Inorderfortheshockpulsesreadingtobequicklyandeasytoevalutatedonthebearing

condition,insimpleunderstandingscaledBnhasbeenderived.Itcategoriesthebearing

condition into threedifferent zonesby indicating theextentofbearingdamage from

goodtopoorcondition,Fig-3.1:

100%0 50

20

40

60dBn

100%0 50

20

40

60dBn

15

KOHTECT BT-77

dBn < 20 Goodcondition

dBn = 20-40 Satisfactorycondition

dBn > 40 Poorcondition(i.e.bearingneedreplacement)

Table-3

3.3 EvaluationofBearingConditionwithBT-77

Technicalconditionofthebearingismainlydeterminedbythelevelandrelationoftwo

measuringvaluesdBmanddBc.

dBm-maximumvalueofnormalizedsignalindecibel.

dBc-carpetvalueofnormalizedsignalindecibel(backgroundofthebearing).

However, under thework of the bearing the peak strikes have not only varying

magnitudes, but frequencies aswell. Fig-3.2 shows the typical examples of the

evaluationofbearingconditionandoperatingconditions(installation,rollerbearing

fit,alignment,lubrication)basedontherelationofshockmagnitudevalue(reading

ofscaledBc)andfrequencyvalue(numberofshocksperminute):

Fig-3.2

dBm

60

40

20

0 TimedBc

dBndBn

60

40

20

0Time

dBm

dBc

dBn60

40

20

0Time

dBm

dBc

dBm

dBc

60

40

20

0Time

dBn

dBc

60

40

20

0Time

dBm

dBdBn

dBm

dBc

60

40

20

0 Time

dBdBn

16

KOHTECT BT-77

1.Goodbearinggeneratesmainlyshocksintheinterfacebetweentheloadedrolling

element and the raceway.These shocks create normal background levelwith low

carpetvalue(dBc<10)andrandomstrikeswithmaximumvaluedBm<20dB.

2.Whenthedefectsoccurontheouterracewayofabearingorabearingelement,the

generalbackgroundfeaturespeaksignalswithMax��aluedBm>40dB.Thecollisions

happensrandomly,quiteoftentheircarpetvaluesstandwithinthelimitsdBc<20dB.

Thoughwhenthebearingfailureoccurs,thecarpetvaluecanbedecreased.Asarule,

agreatdifferencebetweendBmanddBcvaluesoccurs.

3.Whenthereisnolubricationsupplyortight(loose)rollerbearingfit,theCarpet��alue

willreflectthisbyincreasing(dBc>10),eventherearenotanydefectsontheouter

racewayofathebearing.TheMax��alueandtheCarpet��aluearerelativelyclose(dBm

=30,dBc=20).

4. Under pump cavitation both backgrounds feature highmagnitude value. Shock

pulsestandardsonpumpcavitationarepublished.Themeasurementsare takenon

thepumpcase.Beawarethatthecurvedsurfacesdampshockpulsesoutofcavitation.

ThedifferencebetweentheMax��alueandtheCarpet��alueisquitesmall(forexample,

dBm=38dB,dBc=30dB).

5.Mechanicalcontactbetweentherotatingandstationarypartsofthemechanismnext

tothebearingcreaterhythmic(periodic)ahighamplitudeburstofShockPulsewaves.

6.Ifthebearingundergoestheshockload,forexample,astheresultofpistonstroke

inthecompressionpump,theshockpulseswillberhythmic(periodic)withrespectto

theoperatingmodeofthemachine,sotheCarpet��alue(dBc)andtheMax��alue(dBm)

areeasilydefined.

17

KOHTECT BT-77

Drivinggearfailureinthegearboxalsocancausetheperiodicstrikes.Thesestrikes

willberhythmicinrespecttotheshaftspeed(onallbearingsinstalledinthegearbox).

Don’ttakemeasurementswhenyoustartthemotororyoujustappliedthelubrication

(completeitin15minutes).

Table-3.2 showsmentionedaboveandother possible cases of increased values of

shock impulses. Itmayhappen thatanewbearingmayhave theCarpet��aluedBc

morethan20dB.Ifthesevaluesarestablewithinsometimeinterval,bearingcondition

isacceptable.

3.4 Methodandmeasurementlocationofthebearings

Shockpulsemeasurementsshouldbecompletedonthebearinghousing.Whenfree

accesstothebearinghousing,usethemeasuringprobeasshowninFig-3.3a,3.3b

3.3candFig-3.3d.

Beforeshockpulsemeasurementitmaybenecessarytoconsultdesigndrawingsto

seehowthemachineisconstructedandcheckthemeasuringpointsbasedonsignal

path.Thesurfaceatthemeasurementpointshouldbeplane.Ifthepaintlayeristhick,

clearoffpaintonmeasuringspot.Fittheproberadicallytothecheckedsurface.

Fig-3.3aBearingloademissionFig.-3.3b.Shockpulsezones.

window(loadZone)

18

KOHTECT BT-77

Fig-3.3cShockpulsezones.1-��ibrationmeasuringprobe

2-Bearinghousing

3-Stresswavepropagation

4-Defectiverollingbearing

5-Shockpulsemeasuring

zones(Bearingloadzone)

Fig-3.3d

4.0DeliverySet

№ Description Qty �ote

1. BT-77w/rechargeablebatteryinserted 1

2. Bearing��ibrationmeasuringprobe 1

3. IRTachometerw/mountingstand 1

4. ACCharger,220-230��olts 1

5.Liquidmaker 1

6. CarryingCasewithFoam-insert 1

7. OperatingInstructionsManualinCD-ROM 1

8. CD-ROMPCsoftware 1

9. USBPCcommunicationcable 1

10. Makercalibrationcertificate 1

Table4.0

19