MTL700 SERIES...710 10 50 200 √√√ 6V dc & 4V ac systems 85 6.0 6.9 c 50 710P 10 33 300 √√...
Transcript of MTL700 SERIES...710 10 50 200 √√√ 6V dc & 4V ac systems 85 6.0 6.9 c 50 710P 10 33 300 √√...
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April 2006
for safe measurement andcontrol in hazardous areas
MTL700 SERIES
MTL700 Series shunt-diode safety barriersare 1- or 2-channel devices which pass an electricalsignal in either direction without shunting it, but limitthe transfer of energy to a level that cannot igniteexplosive atmospheres. Connected in series with thesignal transmission lines on a process plant, theyprotect hazardous-area wiring and equipmentagainst faults occurring in the safe area, and enablea wide range of measurement and controloperations to be carried out simply andinexpensively by intrinsically safe techniques.
Applications include the protection of installationscontaining ‘simple’ uncertified devices such asthermocouples, switches, and resistive sensors, orseparately certified ‘energy storing’ or ‘voltageproducing’ apparatus, for example ac sensors,transmitters, and current-to-pneumatic (I/P)converters.
Essential features of the MTL700 Series are theself checking ‘as-you-mount-it’ earthing via two studsdirectly to nickel-plated brass or copper busbar. Theearth connection is on top of the unit, allowing easyinspection, installation and removal. The shape ofthe barrier has been designed for easy wiring, whilethe common (14.5 mm) space requirement of both1- and 2-channel units simplifies planning oralteration of installations of all sizes. The busbar isinsulated for separate earthing, to eliminate thedanger of invasion by fault currents.
MTL700P shunt-diode safety barriers delivermore power into hazardous areas. Because of thehigher power levels available, it is important whenconsidering the use of MTL700P barriers to check thecompatibility of the electrical safety parameters ofthe field equipment (such as transmitters andsolenoid valves) with those of the barriers to makesure the combination is safe. In addition, with thebarriers designed for IIB gas group applications, theoverall gas classification of the system also needschecking
References. The following documents areavailable for further information on MTL700 Seriesbarriers:
AN9007 A user’s guide to shunt-diode safety barriersINM700 The MTL700 Series Instruction Manual
◆ All models short-circuit proof
◆ Fixed tagging & cable-screen earthing accessories
◆ Certified to worldwide standards
◆ 1 or 2 channels in same package
◆ Electronic protection prevents blown fuses
◆◆ Higher-power barriers for groupIIC and IIB gases
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June 2004
MTL V ΩΩ mA
702 25 200 125 √ Transmitters – – 35 See706 28 300 93 √√ Transmitters – – 35 'How707 28 300 93 √√ Switches – – 35 they
28 diode – – – – 50 work’707P† 28 164 170 √ Transmitters, switches, 35 50
15 diode – controller outputs – –708 28 300 93 √√ Solenoids, alarms, LEDs, – – 35 –
710 10 50 200 √ √ √ 6V dc & 4V ac systems 85 6.0 6.9 c 50710P 10 33 300 √ √ 8V dc systems 42 8.0 9.2 200715 15 100 150 √ √ 12V systems 155 12.0 13.0 100715P 15 50 291 √ 12V dc systems 60 12.5 13.8 200722 22 150 147 √ √ 18V dc systems 185 19.0 20.2 50722P 22 101 213 √ 18V dc systems 121 18.5 20.0 100728 28 300 93 √√ Controller outputs, solenoids 340 25.5 26.6 50
28 300 93 √ √ Transmitters 340 25.5b 26.6d 50728P 28 234 119 √ Controller outputs, solenoid valves 253 24.5 26.0 100729P† 28 164 170 √ Controller outputs, solenoid valves 184 24.5 26.0 100
751 1 10 100 √ Active dc & ac sensors 20 0.3 2.0 2501 10 100 (low impedance receivers) 20 0.3 2.0 250
755 3 10 300 √√ Resistance temperature 18.0a (0.6) 3.6 2503 10 300 detectors 18.0a (0.6) 3.6 250
758 7.5 10 750 √ √ Gas detectors 18 6.0 7.0 2007.5 10 750 18 6.0 7.0 200
761 9 90 100 √ 145 6.0 7.5 1009 90 100 145 6.0 7.5 100
761P 9 350 25 √ Strain-gauge 384 7.0 8.1 509 350 25 bridges 384 7.0 8.1 50
764 12 1k 12 √ √ √ Strain-gauge bridges 1075 10.0 10.7 e 5012 1k 12 1075 10.0 10.7 e 50
766 12 150 80 √ 185 10.0 11.2 5012 150 80 185 10.0 11.2 50
766P 12 75 157 √ Strain-gauge 93 9.8 11.3 10012 75 157 bridges 93 9.8 11.3 100
767 15 100 150 √ √ 12V dc systems 155 12.0 13.0 10015 100 150 155 12.0 13.0 100
768 22 150 147 √ √ 18V dc systems 185 19.0 20.2 5022 150 147 185 19.0 20.2 50
779 28 300 93 √ √ Controller outputs 340 25.5 26.6 5028 300 93 340 25.5 26.6 50
796 26 300 87 √ √ Vibration probes 340 23.5 24.6 5020 390 51 (MTL796 negative) 435 17.5 18.7 50
760 10 50 200 √√ Active dc & ac sensors 85 6.0 7.4 5010 50 200 Thermocouples 85 6.0 7.4 50
765 15 100 150 √ 135 12.0 13.2 5015 100 150 135 12.0 13.2 50
772 22 300 73 √ 2-wire dc & ac systems 340 18.0 19.7 5022 300 73 340 18.0 19.7 50
778 28 600 47 √ 665 24.0 25.7 5028 600 47 665 24.0 25.7 50
786 28 diode – √ √ Signal returns 2.2V+30Ω 25.5 26.6 5028 diode – 2.2V+30Ω 25.5 26.6 50
787 28 300 93 √ √ Controller outputs, 340 25.5 26.6 5028 diode – switches 2.2V+30Ω 25.5 26.6 50
787S 28 300 93 √√ Transmitters 340 25.5 26.6 5028 diode – Controller outputs, switches 0.9V+20ΩΩ 25.5 26.6 50
787SP 28 234 119 √ Transmitters, controller outputs 258 24.5 26.5 8028 diode – switches 0.9V+16Ω 24.5 26.5 80
788 28 300 93 √ √ 340 25.5 26.6 5010 50 200 85 6.0 6.9 50
Transmitters 340 25.5 26.6 50788R 28 300 93 √ √ 85 6.0 6.9 50
10 50 200
791 11 51 216 √ 31.25kbit/s fieldbus 62.6 10V (at 50µA) 10.5 10011 51 216 √ installations 62.6 –10V (at 50µA) –10.5 100
799 Dummy barrier for securing cables for future installations – takes hazardous-area circuits to earth.
}
3
4
1
2
Internalterminator
Vmax
V
SPECIFICATIONS ‘Key’ barriers shown in blueModelNo.
Safety description Polaritiesavailable
+ – ac
Basic circuit
Hazardous Safe
Fuserating
mA
Vwkg at10(1)µA
V
Max. end-to-end
resistanceΩΩ
Application
}
3
4
1
*2
(768 & 779 require channelsseparate in IIC)}
3
4
1
2
ac
3 (26V:796)
4 (20V:796)
1
*
2
3
4
1
ac
2Star connected
3
4
1
23
4
1
2
787S
3 (28V)
4 (10V)
1
2
250Ω
a: Tolerance ±0.15Ω at 20°C, channels track within 0.15Ω from –20 to +60°C. d: ac version 26.1V.b: ac version 24.5V. e: ac version 11.2V.c: ac version 7.4V. †: Gas group IIB (CENELEC), C (N America).*Diagrams show positive versions. All diodes reversed on negative versions. Additional diodes fitted on ac versions.Patents for MTL787S: UK Patent No. 2210522, USA Patent No. 4860151; Patents for MTL707P: UK Patent Nos. 2210521, 2210522; USA Patent No. 4860151; Patents for MTL787SP: UK Patent No. 2210522; USA Patent No. 4860151
3
4
1
2
Terminal 1 & 2open circuit
3
4
1
2
See 'HOW THEY WORK'and
'OVERVOLT-PROTECTED
BARRIERS'
See additionalspecification
switches
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June 2004
Ambient temperature and humidity limits–20 to +60°C continuous working–40 to +80°C storage5–95% RH
Leakage currentFor ‘basic’ barriers with a working voltage of 5V or more, theleakage current decreases by at least one decade per voltreduction in applied voltage below the working voltage, over twodecades. For the MTL755 it decreases by at least one decade fora 0.4V reduction in applied voltage.
TerminationsTerminals accommodate conductors up to 4mm2 (12AWG)Hazardous-area terminals are identified by blue labels.
Colour coding of barrier topGrey: non-polarisedRed: positive polarityBlack: negative polarityBlack (red label for safe-area terminals):
positive supply, negative to transmitter (MTL706) White: dummy barrier, MTL799
Weight125g approx
Mounting and earthingBy two integral M4 x 9 tin-lead plated steel fixing studs andstainless steel self-locking nuts (provided).
EMC complianceEN 50 081-2/EN 50 082-2, generic emission/immunitystandards. These rtefer to appropriate IEC/CISPR standards.(MTL707P+ and MTL702+ are not CE marked)
GENERAL SPECIFICATIONHOW THEY WORKAll MTL700 Series barriers are based on the same simple principle.Each channel contains two stages of pulse-tested Zener or forward-connected diodes and an ‘infallible’ terminating resistor. In the eventof an electrical fault in the safe area, the diodes limit the voltage thatcan reach the hazardous area and the resistor limits the current. Afuse protects the diodes, and the two stages of voltage limitationensure continued safety if either stage should fail. No active output-current limiting circuits are employed. All models are certified ‘ia’ forall zones and ‘IIC’ for all explosive atmospheres (except MTL707P+and MTL729P+, 'ia' 'IIB').
1. Safety descriptionThe safety description of a barrier, eg ‘10V 50Ω 200mA’, refers tothe maximum voltage of the terminating Zener or forward diode whilethe fuse is blowing, the minimum value of the terminating resistor, andthe corresponding maximum short-circuit current. It is an indication ofthe fault energy that can be developed in the hazardous area, andnot of the working voltage or end-to-end resistance.
2. PolarityBarriers may be polarised + or –, or non-polarised (‘ac’). Polarisedbarriers accept and/or deliver safe-area voltages of the specifiedpolarity only. Non-polarised barriers support voltages of eitherpolarity applied at either end. An exception to this is the MTL791Fieldbus barrier which has one positive and one negative channel.
3. End-to-end resistanceThe resistance between the two ends of a barrier channel at 20°C, ieof the resistors and the fuse. If diodes or transistors are present, theirvoltage drop (transistors ON) is quoted in addition.
4. Working voltage (Vwkg)The greatest steady voltage, of appropriate polarity, that can beapplied between the safe-area terminal of a ‘basic’ barrier channeland earth at 20°C for the specified leakage current, with thehazardous-area terminal open circuit.
5. Maximum voltage (Vmax)The greatest steady voltage, of appropriate polarity, that can beapplied continuously between the safe-area terminal of any barrierchannel and earth at 20°C without blowing the fuse. For ‘basic’barriers, it is specified with the hazardous-area terminal open circuit;if current is drawn in the hazardous area, the maximum voltage forthese barriers is reduced. The ‘ac’ channels of ‘basic’ barriers andmost channels of overvolt-protected barriers withstand voltages of theopposite polarity also – see circuit diagrams.
6. Fuse ratingThe greatest current that can be passed continuously (for 1000 hoursat 35°C) through the fuse.
7. Star connectionIn star-connected barriers, the two channels are interlocked such thatthe voltage between them cannot exceed the working voltage, Vwkg:this allows for higher cable capacitance or inductance.
8. Maximum safe-area voltage (Um)The maximum permissible safe-area voltage (Um) for MTL700 Seriesbarriers is 250V ac/dc.
TERMINOLOGY
APPLICATION KEY BARRIERResistance temperature detectorsThermocouples, ac sensorsController outputs, one line earthedController outputs, neither line earthed
Transmitters, 2-wire, 4/20mA
Switches
Solenoids, alarms, LEDs
755ac760ac728+787S+
dc power supply26.0V 20–35V
787S+
787S+
728+
706+
707+
708+
Patents for MTL706+, 707+, 708+, 787S+
KEY MTL700 SERIES BARRIERS SUMMARISED
TYPEAnalogueinput (low-level)Analogueoutput
Analogueinput (high-level)Digital (on/off)inputDigital (on/off)output
49.2
85.093.5
9.0
25.0 11.57.5 7.5
14.2
61.5
3 4 2
12 1
Hazardous-areaterminals
DIMENSIONS (mm)
Safe-area terminals
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April 2006
3
4
4/20mA
50mA
40mA max+35V max.
50mA
50mA250Ω±5%
Current limit
RegulateNegative
4/20mA
0V
1
2–
+Tx
MTL706+ for 'smart' 2-wire 4/20mA transmittersUK Patent No. 2205699USA Patent No. 4967302European Patent (Germany, France, Italy) No. EP 0 294 139 B1The MTL706+ is a 1-channel shunt-diode safety barrier, with built-inelectronic overvolt protection, for energising a 2-wire 4/20mAtransmitter in a hazardous area. It is powered from a positive supplyof 20–35V dc and delivers a 4/20mA signal into an earthed load inthe safe area. It is proof against short circuits in the field and in thesafe area and is extremely accurate. The MTL706+ will pass incomingcommunication signals up to 10kHz from a ‘smart’ transmitter, whilein the outgoing direction it will pass signals of any frequency likely tobe encountered.
Since the MTL706+ has no return channel for energising the load, theentire output of the single ‘28V’ channel is available to power thetransmitter, providing high output capability. This channel is negativelypolarised, and the safe-area signal is in fact the very current thatreturns through it from the hazardous area, the novel circuit beingenergised by a built-in floating dc supply derived from the external dcsource of power.
To prevent any leakage through the Zener diodes and maximise theoutput voltage available at 20mA, the floating supply is given a risingvoltage/current characteristic. This is achieved by monitoring the4/20mA current, an arrangement which allows all-frequencycommunication in both directions. A separate circuit limits the currentto protect the fuse in the event of a short circuit in the hazardous area.
With a 22V supply, the barrier will deliver 15V minimum at 20mA forthe transmitter and lines and consumes less than 40mA in normaloperation.
Note: the MTL706+ supercedes the MTL705+, which was similar in basicperformance but did not pass outgoing communication signals below about1kHz.
BASIC CIRCUIT
OVERVOLT-PROTECTEDBARRIERS
ADDITIONAL SPECIFICATIONSupply voltage
20 to 35V dc, positive w.r.t. earthVoltage available for transmitter and lines (at 20mA)
(Vsupply – 8V), limited at 16VVoltage available for load (at 20mA)
Vsupply – 5VLoad resistance
850Ω maximumOutput impedance to load
>1MΩCalibrated accuracy (at 20°C with 250ΩΩ load)
0.05% of maximum output, including non-linearity and hysteresis
Zero temperature drift
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June 2004
OVERVOLT-PROTECTEDBARRIERS(continued)
MTL707+ for switch inputsUK Patent Nos. 2245439, 2210521European Patent No. EP 0 310 280 B1
The MTL707+ is a 2-channel shunt-diode safety barrier similar to theMTL787+ but with built-in electronic overvolt protection. It is intendedprimarily for safeguarding a hazardous-area switch controlling arelay, opto-coupler or other safe-area load from an unregulated dcsupply in the safe area.
The outgoing channel accepts supply voltages up to +35V and isprotected against reverse voltages: the return channel is unaffected byvoltages up to +250V.
In normal operation the protection circuit introduces only a smallvoltage drop and shunts less than 1mA to earth, so its overall effect isminimal. If the supply voltage exceeds about 27V, however, causingthe Zener diodes to conduct – or if the safe-area load has a very lowresistance – the supply current is limited automatically to 50mA,protecting the fuse and power supply and enabling the loop tocontinue working.
ADDITIONAL SPECIFICATION
Supply voltage (Vs)10 to 35V dc, positive w.r.t. earth
Output current (Iout)Up to 35mA available
Maximum voltage drop (at 20°C, current not limited)Iout x 370Ω + 1.5V, terminal 1 to 3Iout x 50Ω + 2.1V, terminal 4 to 2
Supply currentIout + 1mA max, Vs 28V or low load resistance
MTL707P+ for switch inputs, IIB gasesThe MTL707P+ is a two-channel shunt-diode safety barrier similar tothe MTL787SP+, but is designed for use with group IIB gases andfeatures built-in electronic overvolt protection allowing use withunregulated power supplies up to 35V dc. It is intended primarily asa low cost solution for driving IIB certified 2-wire 4/20mAtransmitters, but can also be used with controller outputs with currentmonitoring, solenoid valves and switches. To protect the fuse andenable the loop to continue working, the supply current is limitedautomatically at 50mA should the output be short-circuited or excessvoltage applied.
ADDITIONAL SPECIFICATIONSupply voltage – channel 1 (Vs)
10 to 35V dc positive with respect to earthOutput current – channel 1 (I out)
Up to 35mA availableMaximum voltage drop (at 20°C, current not limited)
Iout x 200Ω + 0.2V, terminals 1 to 3Iout x 18Ω + 1.3V, terminals 4 to 2
Supply currentIout + 2mA max, Vs28V or low load resistance
MTL708+ for switched outputsUK Patent No. 2210521European Patent No. EP 0 310 280 B1
The MTL708+ is a 1-channel shunt-diode safety barrier similar to theMTL728+ but with built-in electronic overvolt protection. It is intendedprimarily for safeguarding solenoids, alarms, light-emitting diodes orother hazardous-area loads controlled by a safe-area switch from anunregulated dc supply in the safe area.
The barrier accepts supply voltages up to +35V and is protectedagainst reverse voltages.
In normal operation the protection circuit introduces only a smallvoltage drop and shunts less than 1mA to earth, so its overall effect isminimal. If the supply voltage exceeds about 27V, however, causingthe Zener diodes to conduct – or if the hazardous-area load has avery low resistance – the supply current is limited automatically to50mA, protecting the fuse and power supply and enabling the loopto continue working.
BASIC CIRCUIT
ADDITIONAL SPECIFICATIONSupply voltage (Vs)
10 to 35V dc, positive w.r.t. earthOutput current (Iout)
Up to 35mA availableMaximum voltage drop (at 20°C, current not limited)
Iout x 370Ω + 1.5V, terminal 1 to 3Supply current
Iout + 1mA max, Vs 28V or low load resistance
Hazardous area Safe area
Currentlimit
50mA
50mA
1 mA maxI out
+35V max1
2
3
4
Hazardous area Safe area
BASIC CIRCUIT
Hazardous area Safe area
BASIC CIRCUIT
Currentlimit
50mA
1 mA maxI out
3
2
+35V max1
LED,alarm,
solenoid,etc
4
Currentlimit
50mA
50mA
1 mA maxI out
+35V max1
2
3
4
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June 2004
BARRIERS FOR SENSORS
Note: voltage figures shown on busbar are safety description values.
ANALOGUE INPUTS, LOW LEVELThermocouplesThe preferred barrier for thermocouples is the MTL760ac, whose 2-channel non-polarised design retains the ‘earth-free’ nature of thesignal. Provided that the receiver’s input circuit floats, the combinationrejects common-mode ac and dc interference up to at least 6V and isunaffected by earth faults on the primary element. Even if thereceiver’s circuit is tied to its ‘0V’ rail, the use of a 2-channel barriertakes the worry out of earthing. To eliminate errors due to thermalemfs, the compensating cable should be continued from the barrier tothe receiver. For moving coil or other low resistance receivers, use theMTL751 (40Ω) or the MTL755ac (36Ω) if the resistance of theMTL760 (170Ω) is unacceptable.
USA regulations permit the thermocouple to be earthed on theassumption that the barrier will not conduct, but Europe and other‘IEC countries’ assume that it may do so. In these countries either thethermocouple and its cables must be insulated to withstand 500V, Fig.1; or the earth loop must be broken by an isolating transmitter, Fig.2, or by one of the isolating interface devices in the MTL2000, 3000,4000 or 5000 Series.
Resistance temperature detectorsFor 3-wire circuits with a floating bridge, the most economical solutionis provided by the MTL755ac 2-channel barrier, Fig.4. The two leads from the bridge arms are protected by thebarrier, while the third (supply) lead is earthed at the busbar. TheMTL755ac has a low end-to-end resistance of only 18.0Ω perchannel to minimise span changes, and its channels track within0.15Ω (from –20 to +60°C) to minimise zero shift with temperature.Close tolerancing of each channel to ±0.15Ω at 20°C facilitatesbarrier substitution.
If the bridge circuit is already earthed, a third barrier channel isneeded; in practice this can be one half of another MTL755ac, Fig.5. For extreme accuracy use three channels and an earth-free bridge,since the small errors due to barrier leakage tend to cancel.
4-wire constant-current circuits do not require matched barrierresistances, and can be protected more economically by twoMTL761ac 2-channel barriers, Fig.6. If the increase in loop resistanceis too great, use two MTL755acs.
Slidewire displacement transducersThere are many solutions. Perhaps the simplest is that shown in Fig.7, where an MTL760ac supplies power and brings back a unipolarsignal. Other barriers that could be used include the MTL761ac,765ac, 772ac, 778ac. Where polarity reversal or very highaccuracy are required, use the techniques designed for strain-gaugebridges, overleaf.
Photocells, ac sensors, flowmetersSimilar arguments apply, and the MTL760ac is recommended, Fig. 3.Any other 2-channel non-polarised barrier that will handle the voltagewould be suitable. All MTL barriers of this type transmit signals up toa few kHz. At higher frequencies the self capacitance of the Zenerdiodes – around 1000pF – may attenuate the signal. No certificationis required for sensors generating less than 1.2V, 0.1A, 20µJ and25mW. In practice this includes all photocells, but some ac sensorsmay have significant inductance and require to be designed andcertified for use in hazardous areas.
Hazardous area Safe area
MTL760ac
0VVout+7V max.
Fig. 7
34
12
10V10V
MTL760ac
3 4 2 110V
10V
Compensating cable
Insulatedfrom earth
Fig. 1
Recorder,controller,
data logger,computer
Fig. 2
Temperature transmitter
3 4 2 1
10V10V
Fig. 3
MTL760acEarth-freesignal
Photocell,microphone,
turbineflowmeter, etc
3 4 2 1
Receiver
LNE
3V3V
Fig. 4
MTL755ac
3 4 2 1
Receiver
LNE
3V3V
3V3V
Fig. 5
MTL755ac
1/2 MTL755ac
3 4 2 1
3 4 2 1
Receiver
LNE
MTL761acMTL755ac
MTL761acMTL755ac
Fig. 6
3 4 2 1
3 4 2 1
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June 2004
BARRIERS FOR SENSORS(continued)
ANALOGUE INPUTS, LOW LEVEL (continued)Strain-gauge bridgesFig. 8 shows an arrangement using two or three barriers, which issafe in IIC gases (system certificate no. Ex842125). With theMTL761ac, the circuit is powered from a 12V, 290Ω source; if thebridge resistance is 290Ω, then the bridge voltage is 6V. If theMTL766ac is used, the source is 20V, 370Ω, and provides a bridgevoltage of 10V when the bridge resistance is 370Ω.
Quite frequently there is a demand to monitor three load cells, and apossible circuit is shown in Fig. 9 (system certificate no. Ex842128).The two channels of each MTL766ac barrier are connected in parallelto reduce the source resistance, and provide 8V across the three350Ω bridges. However, the higher energy present means that thesystem is safe in IIA and IIB gases only.
Weighing by load-cell is an application where the lower voltage dropof the MTL766Pac, compared to the MTL766ac, is a great advantage.In such applications, the MTL766Pac supplies power to the bridgewhile an MTL761Pac interfaces with the sensing and pick-off circuits.Using the two barriers in combination (see Fig. 10), the minimumvoltages available in 350Ω bridge systems with a ±10V supply are asfollows:-
1 bridge: 13.0V2 bridges: 9.7V3 bridges: 7.7V4 bridges: 6.4V
Hazardous area Safe area
Gas detectors, logic systemsSome devices require a high current at a low voltage, for example,300mA at 2.3V for a typical gas detector. The low end-to-endresistance (18Ω) of the 2-channel MTL758+, and its working voltageof 6V, make this barrier ideal for energising gas detectors, 5V logicsystems, certain displays and similar equipment. The two channelscan be used separately or in parallel as required, and the systemremains safe in IIC gases if an MTL761ac is added to bring back themeasurement.
Fig. 11Gas detector
MTL758+
MTL761ac0V
9V9V
7.5V7.5V +6V
Output
34
12
34
12
MTL766Pac
MTL761Pac
350ΩBridge
Fig. 10
12V12V
+– Sense
MTL761Pac
Output, mV
9V9V
9V9V
+10V
0V
–10V
350ΩBridge
350ΩBridge
supply34
12
34
12
34
12
Fig. 8
Bridge
MTL761acMTL766ac
MTL764ac
MTL761ac
0V
+– Sense
12V12V
9V9V
+10V (MTL766)+6V (MTL761)
–6V (MTL761)–10V (MTL766)
Optional
Output, mV
34
12
34
12
34
12
MTL764ac
MTL766ac
MTL766ac
Bridge
Bridge
Bridge
Fig. 9
12V12V
+– Sense
MTL764ac
Output, mV
12V12V
12V12V
12V12V
+10V
–10V0V
34
12
34
12
34
12
34
12
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June 2004
BARRIERS FORTRANSMITTERS ANDSWITCHES
ANALOGUE INPUTS, HIGH LEVEL2-wire 4/20mA transmittersIf several transmitters are to be operated from a common dc supply,and this can be closely regulated (at 26V max), the MTL787S+ nowbeats the previously recommended MTL788+ by nearly half a volt,providing up to 12.9V at 20mA for a transmitter and its lines, as wellas the usual 5V for the load, Fig. 12. Its return channel is moretolerant of errors during installation and fault finding, and it is safewith cables of much higher inductance. If the load requirement canbe reduced, the voltage available for the transmitter will be greater.
If the supply can be closely regulated, and the transmitter iscompatible with the higher power levels available from this barrier inIIC gas groups, the 2-channel MTL787SP+ is recommended. With a26V supply it provides 14.6V at 20mA for a transmitter and lines aswell as the usual 5V for the load, beating the MTL787S+ by 1.7V, Fig.12.
The voltage available for the transmitter and its lines can be increasedby converting the return current into a 1–5V signal before it passesthrough an MTL788+ barrier. The MTL788R+ contains a 250Ωprecision resistor for this purpose and makes 14.2V available, Fig.13.
If greater voltage capability is required for the transmitter or the load,or the supply is not closely regulated, then the MTL702+ is a provengood solution, Fig. 14. This overvolt-protected barrier delivers 14V at20mA for the transmitter and lines from a 22–35V supply, plus a quiteexceptional 17V for the load, both voltages being increased by 2V ifthe supply is at least 24V. It will pass incoming communication signalsof any frequency from a ‘smart’ transmitter but inherently cannot passsignals in the outgoing direction. Accuracy is high and currentconsumption is less than 60mA.
Where 2-way communication with ‘smart’ transmitters is required,there are two solutions. If the supply is closely regulated, choose theMTL787S+ (above). If it cannot be closely regulated, choose theMTL706+, Fig. 15. This overvolt-protected barrier – derived from thepreviously recommended MTL705+ – provides 15V at 20mA for thetransmitter and lines from a 22–35V supply, plus 5V for the load. It islower in cost than the MTL702+, is extremely accurate, has a standardsafety description and consumes only 35mA. Note that the loadresistor must be 250Ω ±5% and that terminal 3 is negative.
If the supply is poorly regulated, the 2-channel MTL707P+ provides alow cost solution for IIB applications, where its low end-to-endresistance makes 13V available for the transmitter and field cablingplus 5V for the load when powered from 24V dc, and its overvoltprotection allows supply variations up to 35V dc, Fig. 16.
Fire and gas detectionDesigned primarily for fire and gas detection systems, the lowermaximum end-to-end resistance of the MTL722P+ (121Ω) comparedto the MTL722+ (185Ω) can be an advantage (see Fig. 17). Inaddition, it may prove useful in other 18V dc systems.
MTL707P+*28VDiode15V
+35V max.1–5V
0VFig. 16
4/20mA
34
12
* CENELEC gas group IIB (C & D N. America)
IIB
Hazardous area Safe area
+18V0V
MTL722P+22VEarth
18V dcsystems
Fig. 17
34
12
MTL787S+ MTL787SP+
28VDiode
Fig. 12
4/20mA 250Ω
+26V max.1–5V
0V
34
12
MTL788R+28V10V
Fig. 13
4/20mA
+26V max.1–5V
0V
34
12
MTL702+25V
E+35V max.1–5V
0VFig. 144/20/mA 250Ω
34
12
MTL706+28V
E+35V max.1–5V
0VFig. 15
Negative
4/20/mA 250Ω
34
12
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June 2004
DIGITAL (ON/OFF) INPUTSSwitchesFor switch-status transfer, Fig. 18, the MTL707+ is preferred for tworeasons. First, the circuit fails safe if there is an earth fault on either line– ie the safe-area load de-energises. Second, the MTL707+ accepts upto 35V from poorly regulated power supplies without blowing its fuse:if the supply is well regulated, the MTL787S+ can be used, see Fig. 19.
In both cases, optimum power transfer with relays is achieved if theresistance of the load is made about equal to the combined resistanceof the two channels. The relay coil should then be rated at about halfthe supply voltage.
Switches, data-loggers, logic systemsThe MTL710P+ can be used for supplying power to low-voltageequipment in hazardous areas, such as data-loggers, switches andlogic systems. Its low maximum end-to-end resistance of 42Ω,compared to 85Ω for the MTL710+, means it can typically supplymore than 65mA current at 5V from an 8V supply (see Fig. 20). It alsohas the advantage of a higher working voltage (8V compared to 6Vfor the MTL710+).
The MTL715P+ functions similarly for 12V dc systems and can also beapplied to multiple-switch and logic circuits where the additionalpower proves useful, Fig. 21.
Hazardous area Safe area
28VDiode
+35V max.Logic signal
0VFig. 18
MTL707+34
12
28VDiode
+26V max.Logic signal
0VFig. 19
MTL787S+34
12
+8V0V
MTL710P+10VEarth
8V dcsystems
Fig. 20
34
12
+12V0V
MTL715P+15VEarth
12V dcsystems
Fig. 21
34
12
ANALOGUE OUTPUTSController outputs – 4 to 20mAIn most cases the output current of a controller flows directly to its ‘0V’rail and the rail can be earthed at the busbar, Fig.22. Occasionally theoutput circuit may be fully floating. In either event the 1-channelMTL728+ or half an MTL779+ provides the solution. Overvoltprotection is not required, since current limiting in the controller protectsthe fuse in the barrier. The voltage drop introduced by the barrier is6.8V at 20mA.
The maximum voltage drop introduced by the MTL728P+ is only 5.1Vat 20mA (compared to 6.8V for the MTL728+).
For IIB applications, the MTL728P+ can be replaced with the similarlydesigned 1-channel MTL729P+.
If the output circuit of the controller is separated from the ‘0V’ rail by thecontrol transistor, Fig.23, a 2-channel barrier is necessary. TheMTL787S+ is recommended, since its return channel can handle up to25.5V, allowing the control signal to be turned off completely. Thevoltage drop introduced by the barrier is 8.1V at 20mA.
The maximum voltage drop introduced by the MTL787SP+ is only6.4V at 20mA (compared to 8.1V for the MTL787S+). The barrierreturn channel can handle up to 24.5V, allowing the control signal tobe turned off completely.
BARRIERS FOR CONTROL ELEMENTS
Hazardous area Safe area
MTL728+MTL728P+MTL729P+
+
0V rail28V
EI/P
Fig. 22
4/20mA34
12
+4/20mA
0V rail
MTL787S+MTL787SP+
28VDiodeI/P
Fig. 23
34
12
Controller
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June 2004
Hazardous area Safe area
MTL787S+ MTL787SP+
Monitor
0V rail
+
28VDiode
I/P4/20mA
Fig. 24
34
12
Controller
The MTL787S+ and MTL787SP+ are also suitable for controllerscontaining a resistor which enables the return current to be monitoredfor high-integrity operation, Fig.24.
For IIB applications where a 2-channel barrier is needed (see above),the MTL707P+ can be used as, although the overvolt protectionprovided by this barrier is not necessary, the diode return channel andlow voltage drop makes this an ideal replacement for the MTL787S+or MTL787SP+ for IIB gas groups, Fig.25.
DIGITAL (ON/OFF) OUTPUTSSolenoids, alarms, LEDsIf the supply is well regulated, an MTL728+ (or half an MTL779+) canbe used.
For IIC applications, the lower end-to-end resistance of the MTL728P+can make a big difference to the overall loop design when drivinghigher-power solenoid valves, provided the power supply is wellregulated, Fig.26.
Should greater power be required for heavy-duty solenoids in IIB or IIAgases only (‘IEC countries’; C & D in USA and Canada), use the twochannels of the MTL779+ connected in parallel or consider theMTL3022 or MTL5022.
Similarly the MTL729P+ is ideal for powering high-power heavy-dutysolenoid valves, in IIB gas group applications, providing a maximumusable output power of 0.78W at 24V, Fig.26.
Most solenoid valves, alarms, light-emitting diodes (LEDs) and otheron/off hazardous-area loads are best driven via an MTL708+ 1-channel barrier, with built-in overvolt protection, Fig.27. The circuit failssafe with an earth fault on the live line and is unaffected by an earthfault on the earth return, while the barrier will accept up to 35V withoutblowing its fuse.
If the control switch is on earth, then a 2-channel barrier has to be used,Fig.28, but be aware that an earth fault on the return line will energisethe solenoid, whereas one on the live line does the opposite. If thesupply is poorly regulated use the MTL707+ (or MTL707P+ for IIBgases). If it is well regulated use the MTL787S+ (or MTL787SP+).
Alternatively, for operational safety, use an MTL2000, 3000, 4000 or5000 Series isolating interface unit.
Fieldbus applicationsThe MTL791 (Fig.29) is a 2-channel barrier designed specifically for31.25kbit/s fieldbus applications. Used with a suitable floatingfieldbus power supply of up to 20V (such as that provided by theMTL5995 unit) it extends the range of fieldbus applications intohazardous areas. It is provided with an internal integral safe-areaterminator*.
* ‘Terminators’ are used to terminate a fieldbus.
MTL707P+
0V rail
+
28VDiode
I/P4/20mA
Fig. 25Controller
34
12
*
* CENELEC gas group IIB (C & D N. America)
MTL708+28VEarth
+35V max
0V
Fig. 27
34
12
28VDiode
+26.6Vmax (MTL787S+)+26.5Vmax (MTL787SP+)+35V max (MTL707+)+35Vmax (MTL707P+)
0VFig. 28
MTL787S+MTL787SP+MTL707+MTL707P+
34
12
* CENELEC gas group IIB (C & D N. America)
*
+11V–11V
T
Fig. 29
MTL791+
–
*FBT1Fieldbusterminator
Fieldbus devices Fieldbus devicesFieldbuspowersupply
34
12
MTL728+MTL728P+MTL729P+*
28VEarth
+26.6Vmax (MTL728+)+26V max (MTL728P+)+26Vmax (MTL729P+)
0V
Fig. 26
34
12
* CENELEC gas group IIB (C & D N. America)
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June 2004
702+ 1 Yes 0.110 2.39 47 0.17 2.2 0.782706+ 1 Yes 0.083 3.05 56 0.12 4.0 0.65707+ Both Yes 0.083 3.05 56 0.12 4.0 0.65708+ 1 Yes 0.083 3.05 56 0.12 4.0 0.65710 1 Yes 3.0 0.91 74 3.0 1.0 0.50710P 1 Yes 3.0 0.38 44 4.89 0.22 0.75715 1 Yes 0.580 1.45 66 0.7 1.4 0.56715P 1 Yes 0.580 0.33 28 1.04 0.23 1.09722 1 Yes 0.165 1.45 45 0.2 1.4 0.81722P 1 Yes 0.165 0.30 32 0.33 0.53 1.18728 1 Yes 0.083 3.05 56 0.12 4.0 0.65728P 1 Yes 0.083 1.82 44 0.16 2.86 0.83751ac 1 Yes 100 3.72 1464 1000 4.5 0.025
2 Yes 100 0.96 558 1000 1.2 0.05No 100 3.72 732 1000 4.5 0.05
755ac 1 Yes 100 0.46 145 1000 0.4 0.2252 Yes 100 0.13 69 150 0.1 0.45
No 40 0.41 73 150 0.1 0.453 No 40 0.125 48 – – 0.684 Yes 40 0.035 31.25 – – 0.92
No 40 0.06 42 – – 0.92758 1 Yes 11.1 0.070 26 6.0 0.05 1.40
2 Yes 11.1 0.02 10 6.0 0.02 2.80760ac 1 Yes 3.0 0.91 74 3.0 0.9 0.50
2 Yes 3.0 0.20 27 3.0 0.2 1.00761ac 1 Yes 4.9 3.72 163 3.1 3.5 0.225
2 Yes 4.9 0.91 62 0.4 1.0 0.45No 0.31 3.72 81 0.4 1.0 0.45
4 Yes 0.42 0.20 26.39 – – 0.90No 0.42 0.37 37.78 – – 0.90
6 Yes 0.42 0.085 14.39 – – 1.35No 0.42 0.13 18.67 – – 1.35
761Pac 2 Yes 0.31 56 306 0.43 14.4 0.115764± 1 Yes 1.41 240 1000 1.5 200 0.036
2 Yes 1.41 61 360 1.0 60 0.072764ac 1 Yes 1.41 240 1000 1.5 200 0.036
2 Yes 1.41 61 360 0.18 60 0.072No 0.125 240 500 0.18 60 0.072
765ac 1 Yes 0.58 1.45 66 0.7 1.3 0.562 Yes 0.58 0.32 22 0.7 1.4 1.125
766ac 1 Yes 1.41 5.8 151 1.5 5.6 0.242 Yes 1.41 1.47 58 0.18 1.5 0.48
No 0.125 5.8 75 0.18 1.5 0.48766Pac 2 Yes 1.41 0.34 29 0.22 0.20 0.942
767 1 Yes 0.58 1.45 66 0.7 1.7 0.562 Yes 0.58 0.32 22 0.5 0.4 1.125
768 1 Yes 0.165 1.45 45 0.2 1.7 0.81772ac 1 Yes 0.165 6.77 89 0.2 6.0 0.404
2 Yes 0.165 1.45 34 0.2 1.8 0.808778ac 1 Yes 0.083 16 107 0.12 14 0.327
2 Yes 0.083 3.05 42 0.12 4.2 0.654779 1 Yes 0.083 3.05 56 0.12 4.0 0.65786 1 or 2 Yes 0.083 – – 0.11 500 –
787 & 787S Both Yes 0.083 3.05 56 0.11 4.0 0.65787SP 2 Yes 0.083 1.82 44 0.13 2.70 0.835
788 & 788R Both Yes 0.083 0.33 25 0.11 0.5 0.92791 Both No 0.165 0.30 32 0.24 0.31* 1.18796 Both Yes 0.10 1.94 34 0.13 2.0 0.81
707P 2 Yes 0.65 5.65 127 0.45 6.21 1.19729P 1 Yes 0.65 5.65 127 0.49 6.25 1.19
Number ofsingle channelsinterconnected
withinhazardous area
CABLE PARAMETERS AND PERMITTED COMBINATIONSBarriermodel
numberMTL
Earth 1
return used?
Maximum permissible cable parameters
CapacitanceµF
InductancemH
L/R ratioµH/ΩΩ
CapacitanceµF
Matched 2
powerW
(BASEEFA)Inductance
mHor
* L/R = 31µH/Ω
BASEEFA (ATEX) (group IIC) FM (groups A&B)
BASEEFA (group IIB) FM (group C)
1x715P Ex92C2425 Yes 0.135 0.23 39.3 0.914x764ac2 x 761ac channels Ex842125 Yes 0.2 0.24 11.6 1.012 x 764ac channels2 x 766ac channels4 x 761ac channels Ex842125 Yes 0.2 0.2 12.7 0.982 x 764ac channels4x761Pac channels2x766Pac channels Ex92C2424 Yes 0.18 0.17 18.4 1.172 x 764ac channels Ex842128 Yes 0.2 0.28 11 1.044 x 766ac channels758 + 761ac Ex872392 Yes 0.42 0.013 10.5 3.27
4 x 764ac channels Ex842128 Yes 0.6 1.1 32.6 1.124 x 766ac channels2 x 768 channels Ex842114 Yes 0.78 1.8 70 1.622 x 768 channels Ex842114 Yes 0.39 1.8 46.6 1.62Any number of 786 channels2 x 779 channels Ex842114 Yes 0.39 4.3 83 1.32 x 779 channels Ex842114 Yes 0.39 4.3 55.6 1.3Any number of 786 channels
The tables give the maximum permitted cable parameters (including cable and load) for hazardous-area circuits in group IIC and IIB gases. However, the tables are by no means exhaustive and for fulldetails of other safe combinations, consult either BASEEFA system certificates Ex832469, Ex92C2374 or Ex92C2376 or MTL. The MTL702 is covered by BASEEFA system certificate Ex842308, andthe MTL706 by Ex872513.In practice cable parameters rarely present a problem, as all cables normally used for instrument interconnection have L/R ratios below 25µH/Ω and capacitance below 200pF per metre.Note 1 If values are not quoted for when an earth return is not used, those for an earth return (‘Yes’ in the table) can be used.Note 2 The maximum power that can be drawn from the barrier combination under fault conditions. Used for assessing the temperature classification of ‘simple’ hazardous-area apparatus.Note 3 The values of the parameters for Groups IIA and IIB can be found in certificate numbers BAS01ATEX7202 and BAS01ATEX7203.For FM permitted combinations, refer to MTL document SCI-88 (via FM ref 1H8A1.AX).
BASEEFAMaximum permissible cable parameters for group IIC (hydrogen)System
combinationBASEEFAsystem
Cert. No.Capacitance
µF
Earth 1
return used?
InductancemH
L/R ratioµH/ΩΩ
Matched 2power
W(BASEEFA)
or
BASEEFAMaximum permissible cable parameters for group IIB (not safe for group IIC)
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June 2004
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APPRO
VA
LS-
for
the
late
st c
ertifi
cation info
rmation v
isit w
ww
.mtl-i
nst
.com
/cer
ts_1
.nsf
-
EUROPE (EMEA) Tel: +44 (0)1582 723633 Fax: +44 (0)1582 422283AMERICAS Tel: +1 603 926 0090 Fax: +1 603 926 1899ASIA PACIFIC Tel: +65 487 7887 Fax: +65 487 7997E-mail: [email protected] Web site: www.mtl-inst.com
June 200413
Reg
ion
Pola
nd
Rom
ani
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KU
KU
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Syst
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EUROPE (EMEA) Tel: +44 (0)1582 723633 Fax: +44 (0)1582 422283AMERICAS Tel: +1 603 926 0090 Fax: +1 603 926 1899ASIA PACIFIC Tel: +65 487 7887 Fax: +65 487 7997E-mail: [email protected] Web site: www.mtl-inst.com
June 2004
MK05, MK12, MK20 Assembly diagramNote: MK5 has no earth rail/but does have terminal clamps on earth rail mounting brackets
Taggingstrip seal
Tagging stripwith label
Earth railclamp
Terminal clamps
Terminalclamps
Earth busbar
Earthrail
Earth railmountingbrackets
Insulatingmountingblock
MTL700 SERIESACCESSORIES
DO-IT-YOURSELF MOUNTING ARRANGEMENTBarriers are carried on lightweight plated busbar, which can bemounted on ‘top hat’ or G-profile rail or any flat surface with thebusbar insulated for separate earthing. It is recommended that twinearth cables should be used for maximum security and easy testing.Each barrier is clamped to the busbar and thereby earthed in a singleoperation, making it virtually impossible to forget the earthconnection, so easily left untightened or untested if there are scores ofindividual earth wires. Robust soft-plated double fixing studs on thetop of each barrier ensure permanent ‘gas-tight’ joints, which areimmune to vibration and corrosion yet allow barriers to be installed,inspected and removed easily.
The accessories system also provides a convenient row of terminals forterminating earth returns and cable screens, which remains in placeto keep these safely earthed should any barrier be extracted: adummy barrier is available as an alternative for the same purpose.With similar attention to users’ needs, a unique lift-up tagging facilityprovides permanent identification of circuits and barrier types to guideinstallation, fault-finding and inspection, and to ensure correctreplacement of any barrier for long-term safety.
ACCESSORIESEBB7 earth busbar, nickel-plated brass and ready drilled in onemetre lengths.IMB7 & SMB7 insulating mounting blocks are a convenientmethod of supporting the busbar. They are supplied complete withfixing screws and are ready for mounting on any flat surface. IMB7will also mount on top hat or G-profile DIN-rail. T-section DIN-railTHR2 is available in 1 metre lengths.TAG7 tagging strips clip onto the mounting blocks to positivelyidentify each location and provide space for the user to note detailsof barrier type, loop identification etc. Access to barrier mountingstuds is not impaired; just unclip one edge and swing the strip ‘open’or, if the optional plastic seal (TGS7) has not been fitted, unclip bothedges and lift it right off. TGL7 replacement labels for the taggingstrips are also available.ERL7 earth rail is a nickel-plated 3 x 10mm rail that attaches to themounting blocks via an ERB7 earth rail mounting bracket. It willaccommodate up to 2.5 ETM7 earth terminals per barrier location forterminating earth returns and cable screens from the hazardous area.ERB7 earth rail mounting bracket mounts directly over eithertype of mounting block; for a rigid earth rail an ERB7 on eachmounting block is recommended. One end carries a bolt-down fittingfor the rail – enabling easy removal for adding extra ETM7 terminals– the other end carries a 16mm2 terminal. When installed these16mm2 terminals provide connections for the high-integrity IS earth,for linking between sections of busbar, and for a common earth returnfrom the safe area.Other accessories available are the TQS7 torque spanner forsafe tightening of the vibration-proof self-locking nuts on the barrierearthing studs; SMC7 surface mounting clips for mounting a singlebarrier on a flat surface; and ISL3 or ISL7 self adhesive ‘Take Care’intrinsic safety warning labels.
MOUNTING KITSMounting kits provide all the necessary parts for installing up to aspecific number of MTL700 or MTL700P Series barriers. The kitsavailable are the MK02 (2 barriers), MK05 (5 barriers), MK12 (12barriers), and MK20 (20 barriers). Each kit provides facilities formounting and earthing the barriers, connecting the IS earth cable,terminating cable screens and noting tagging information (exceptthe MK02 kit which does not provide tagging facilities). InstructionSheet INS701 includes full assembly instructions.
DIN rail
◆ Mounting kits for up to 20 barriers
◆ Busbar, earth terminals and insulating mountingblocks for separate connection to IS earth
◆ Earth terminal rail for cable screens and earthreturns
◆ Integral tagging system to display barrier loopdata
End elevations with recommended spacing. Shaded portions show areas swept by barrier during installation and removal.
MK02 Assembly diagram
1076
45
Terminal clamp
Insulating block
Mounting bracket
85
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EUROPE (EMEA) Tel: +44 (0)1582 723633 Fax: +44 (0)1582 422283AMERICAS Tel: +1 603 926 0090 Fax: +1 603 926 1899ASIA PACIFIC Tel: +65 487 7887 Fax: +65 487 7997E-mail: [email protected] Web site: www.mtl-inst.com
June 2004
14.5
95
4.2
DIMENSIONS (mm)
TGS7 tagging strip seal –sold in bags of 10
SMC7 surface mounting clip – sold in bags of 10. Twoclips needed per barrier
ETM7 earth terminal – sold inbags of 50. For cable 4mm2. Also available as ‘ZB4’ from Klippon Electricals Ltd.
TQS7 torque spanner – set to 2.3Nm torque. Complete with 7mm A/F socket.
ISL3 or ISL7 ‘Take Care’ intrinsic safety label –ISL3 adhesive back, metal *ISL7 adhesive front, plastic
TGL7 tagging strip label only – packs of 10 x 0.5 metrelengths
ERL7 earth rail – sold in 1 metre lengths. Unplated rail available as ‘SSch 10 x 3mm brass busbar', from Klippon Electricals Ltd
IMB7 insulating mounting block mounts on a flat surface ortop hat rail (to EN 50 022 – 35 x 7.5; BS 5584; 35 x 27 x 7.3DIN 46277) or G-profile rail (to EN 50 035 – G32; BS 5825; 32DIN 46277). Recommended maximum number of barriers betweenblocks is 25.
SMB7 insulating mounting block mounts on a flat surface andprovides minimum overall installation height. Recommendedmaximum number of barriers between blocks is 25.
126
70
85 21.1
M4 x 20fixing screw
M4
97
70
85 14.1
M4
M4 x 25fixing screw
TAG7 tagging strip with label and 6 ‘clic’ rivets – 1 metre lengths
64
ERB7 earth rail mounting bracket – with earth rail bolt-downfitting and terminal for cable 16mm2
EBB7 earth busbar – 1 metre lengths. Mounts up to 64 barriers.
3
10
58 72 10
11.5 253
14.5ø4.4 3
11.5 25
25
175
140 (65*)
100 (40*)
DRK700 adaptor kit allows MTL700 Series barriers tobe mounted directly on DIN-Rail.
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EUROPE (EMEA) Tel: +44 (0)1582 723633 Fax: +44 (0)1582 422283AMERICAS Tel: +1 603 926 0090 Fax: +1 603 926 1899ASIA PACIFIC Tel: +65 487 7887 Fax: +65 487 7997E-mail: [email protected] Web site: www.mtl-inst.com
June 2004
The MT Series of enclosures provides a simple, effective meansof mounting and protecting MTL700 Series barriers in safe areas orlow-risk hazardous areas. Three lightweight polycarbonate enclosureswith see-through lids accommodate up to 2, 5 or 12 barriers in a safearea, and a Type N approved steel enclosure holds up to 20 barriersin Zone 2. All the enclosures are supplied ready fitted with a nickel-plated brass busbar mount, so barriers can be installed and wired upimmediately without special tools; the 20-barrier enclosure is alsoprovided with cable trunking to segregate the safe- and hazardous-area wiring neatly. The polycarbonate enclosures are impact resistant,flame retardant, and dustproof to IEC529:IP65, and the steelenclosure is dustproof and waterproof to IEC529:IP67.
Tagging. All the enclosures, except the 2-barrier model, are fittedwith removable tagging strips for positive identification of barrier typeand loop number. The tagging strips are mounted above the barriersand can be hinged in either direction to give access to the barriers.Each carries a label, protected by a slide-in transparent plastic cover,upon which the user can write his barrier and loop details. Inaddition, all the enclosures carry a ‘Take Care’ intrinsic safetywarning label on the lid.
Earthing. All the enclosures except the 2-barrier model are fittedwith three large terminals: two for making a high-integrity connectionto the essential IS earth, and one to accept a cable from the ‘earthy’end of a common power supply, or system 0V rail, in the safe area.
In addition each enclosure is provided with one or two rows of smallerterminals for terminating and earthing hazardous-area earth returnsand cable screens. Except in the 2 and 5 barrier models, theseterminals are mounted on earth rail running conveniently parallel tothe busbar and attached to it by brackets. Further terminals can beadded easily by the user if needed, up to 2.5 terminals per barrierspace.
The entire earth system is insulated from any nearby metal, and theearth cable itself should also be insulated, mechanically protected andidentified so as to eliminate all danger of invasion by fault currentsfrom high-power electrical equipment.
MTL700 SERIESENCLOSURESFor marshalling barriers in safeareas or Zone 2
◆ Three polycarbonate enclosures hold up to 12barriers in safe area
◆ Type N approved steel enclosure holds up to20 barriers in Zone 2
Although it is not mandatory, MTL recommends using two cablesconnected to the busbar via two terminals on separate brackets, sothat the resistance of the whole earth loop can be checkedperiodically without breaking the connection to earth. Severalenclosures can be included in the loop if necessary.
Mounting of the three larger polycarbonate enclosures is normallyby rear-fixing screws or screw-on plastic fixing lugs, using the pre-tapped brass bushes moulded into the enclosure’s base. The lugs canbe set horizontally, vertically, or at 45°, and are supplied as standardwith each enclosure together with the necessary screws. Alternatively,if the enclosures are to be front mounted and close packed, a plasticmembrane covering the inside of each tapped hole can be knockedout, allowing the passage of other screws. Plastic plugs are suppliedto seal the knockout apertures and preserve the IP65 integrity of theenclosures if this method of fixing is used. The 2- and 5-barrierenclosures are mounted by horizontal or vertical plastic fixing lugsheld on by screws self tapped into blind holes in the base, or by otherscrews passed through holes in the base moulding walls outside thelid gasket. The steel enclosure for 20 barriers has permanent fixinglugs, and provides the additional facility that its lid can be padlockedto prevent unauthorised interference.
Glanding. All the enclosures except the 2- and 5-barrier modelshave detachable top and bottom gland plates for convenient drillingby the user, while the 2- and 5-barrier enclosures each have four20mm holes pre-drilled through the top and bottom sides of the base.All cables entering or leaving any enclosure must be suitably glandedto preserve its IP integrity.
Note: to ensure safe carriage, MTL despatches the enclosures with barriers notmounted.
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EUROPE (EMEA) Tel: +44 (0)1582 723633 Fax: +44 (0)1582 422283AMERICAS Tel: +1 603 926 0090 Fax: +1 603 926 1899ASIA PACIFIC Tel: +65 487 7887 Fax: +65 487 7997E-mail: [email protected] Web site: www.mtl-inst.com
June 2004
No No Yes
Plastic lugs screwed to base, pluggedknockout holes, or rear-fixing screws
4 lugs + attaching screws4 plugs
Adhesive back, on lid
Tagging strip(s) with label(s) and seal(s)
Adhesive front, inside lid
Safe area
4 captive screws
2 5 12 20MT5MT2SPECIFICATION
Maximum barrier capacityConstructionFinishLid fixing
Protection: dust-tight/waterproofGland fixing
Permitted locationCertification
Mounting (see illustration)
Mounting Kit provided
Tagging facility providedCable trunking provided?'Take care ' IS label providedEarth terminals provided:Large (
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EUROPE (EMEA) Tel: +44 (0)1582 723633 Fax: +44 (0)1582 422283AMERICAS Tel: +1 603 926 0090 Fax: +1 603 926 1899ASIA PACIFIC Tel: +65 487 7887 Fax: +65 487 7997E-mail: [email protected] Web site: www.mtl-inst.com
June 2004
EnclosuresMT2 Enclosure for 2 barriersMT5 Enclosure for 5 barriersMT12 Enclosure for 12 barriersMT20N Type ‘N’ enclosure for 20 barriers
LiteratureINM700 MTL700 Series instruction manualAN9007 MTL700 Series application noteCD70... MTL700 Series customer drawings
Shunt-diode safety barriersEnter barrier product code plus polarity, e.g. MTL728+
Barrier accessoriesEBB7 Earth busbar, 1m lengthERL7 Earth rail, plated, 1m lengthETM7 Earth terminal, bag of 50ERB7 Earth rail mounting bracketTHR2 DIN rail 35 x 7.5mm, 1m lengthIMB7 Insulating mounting blockSMB7 Short insulating mounting blockSMC7 Surface-mounting clip, pack of 10
TAG7 Tagging strip + label, 1m lengthTGL7 Tagging strip label, ten 0.5m lengthsTGS7 Tagging strip seal, bag of 10
TQS7 Torque spannerISL3 'Take care' intrinsic safety label, adhesive back,
metalISL7 ‘Take care’ intrinsic safety label, adhesive front,
plasticDRK700 DIN Rail mounting kit
MK2 Mounting kit for 2 barriersMK5 Mounting kit for 5 barriersMK12 Mounting kit for 12 barriersMK20 Mounting kit for 20 barriers
MTL700 SERIES ORDERING INFORMATION
TO ORDER,State the part number (bold) and any part description shown below.