intrinsically safe barriers mtl7700 series …...din rail mounting safety barriers mtl7700 series...

IINNTTRRIINNSSIICCAALLLLYY SSAAFFEE BBAARRRRIIEERRSS

MMTTLL77770000 SSeerriieess

MMTTLL770000 SSeerriieess

DIN rail mountingsafety barriers

MTL7700 SERIES

Since its introduction in 1984 the MTL700Series barrier has established itself as the worldwidestandard for safety barriers. Known for its qualityand reliability, the MTL700 Series is widely used inapplications all over the world.

The MTL7700 Series follows closely in thefootsteps of the MTL700 but as a DIN rail mountingbarrier providing quick and easy installation withoutthe need for special hardware.

Removable terminals are used for ease ofinstallation, maintenance and for providing a loopdisconnect by simply unplugging the terminals fromthe side of the module. Wire entry is also angled toassist wiring within limited space enclosures.

MTL7700 barriers clamp simply and securelyonto standard T-section DIN rail, simultaneouslymaking a reliable IS earth connection.

For applications where field power isrequired for switch inputs or 2-wire transmitters, theMTL7700 Series provides a bussed power feedfacility. When used in conjunction with the MTL7798power feed module the user has a fully protected,electronically fused supply to many barriers with noadditional wiring required.

MTL7700 active modules are protected with anelectronic fuse for the majority of applications. TheMTL7798 active fused, power feed module canprotect up to 40 other modules using the bussedpower facility and provides a clear indication of atrip condition via a red LED.

The MTL774X range of barriers offer a NAMURcompatible input and a choice of relay or solid stateoutput. The solid state outputs are floating soswitching to ground or from a power rail into aninput is also possible. The solid state interface alsoprovides a high frequency transfer for use in flow orrotation applications.

Dual channel relay or solid state modules offerthe highest packing density with only 6.3mm perchannel and when used in conjunction with thepower bus, offer users the minimum of wiring withthe maximum packing density and the lowest costper channel.

♦♦ Proximity detector inputs

♦♦ Electronic fusing

♦♦ Direct replacement for MTL700 Series barriers

♦♦ Compatible terminal numbering and safety descriptions

♦♦ Removable terminals

♦♦ Bussed power feed to other modules

♦♦ Relay and solid state switch modules

♦♦ Dual channel variants — 6.3mm per channel

June 2004

June 2004

MTL V ΩΩ mA

7706+ 28 300 93 √√ Transmitters 35 507707+ 28 300 93 √√ Switches – 35 50

28 diode 35 507707P+ 28 164 171 √√ Transmitters, switches, 35 50

28 diode – controller outputs IIB 35 50

7710+ 10 50 200 √√ 6V dc & 4V ac systems 75 6.0 7.0 507715+ 15 100 150 √√ 12V systems 119 12.0 13.1 1007715P+ 15 50 291 √√ 12V dc systems 64 12.6 13.7 1007722+ 22 150 147 √√ 18V dc systems 174 19.6 20.2 507728+ 28 300 93 √√ Controller outputs, solenoids 333 25.9 26.5 507728- 28 300 93 √√ Transmitters 333 25.9 26.5 507728ac 28 300 93 √√ 333 25.0 25.9 507728P+ 28 234 119 √√ Controller outputs, solenoid valves 252 24.9 25.9 1007729P+ 28 164 170 √√ Controller outputs, solenoid valves IIB 184 24.9 25.9 100

Prox sw input,774X 10 — 19 solid state output — — 30/35 50

and line fault detect

7755ac 3 10 300 √√ 2 or 3- Wire RTDs 19.0 (1) 3.4 2503 10 300 √√ (floating bridge) 19.0 (1) 3.4 250

7756ac 3 10 300 √√ 3 - Wire RTDs 19.0 (0.7) 2.7 2503 10 300 √√ (grounded bridge) 19.0 (0.7) 2.7 2503 10 300 √√ 19.0 (0.7) 2.7 250

7758+/- 7.5 10 750 √√ √√ Gas detectors 17 6.0 7.3 2007.5 10 750 17 6.0 7.3 200

7761ac 9 90 100 √√ 107 6.0 7.0 1009 90 100 107 6.0 7.0 100

7761Pac 9 350 26 √√ Strain-gauge bridges 378 6.8 7.5 509 350 26 378 6.8 7.5 50

7764+/ac 12 1k 12 √√ √√ Strain-gauge bridges 1050 10.0 10.9 5012 1k 12 1050 10.0 10.6 50

7766ac 12 150 80 √√ 174 10.0 10.6 5012 150 80 174 10.0 10.6 50

7766Pac 12 75 157 √√ Strain-gauge bridges 92 9.6 10.5 10012 75 157 Strain-gauge bridges 92 9.6 10.5 100

7767+ 15 100 150 √√ 12V dc systems 119 12.0 13.1 10015 100 150 12V dc systems 119 12.0 13.1 100

7779+ 28 300 93 √√ Controller outputs requires channels 333 25.9 26.5 5028 300 93 Controller outputs separate in IIC 333 25.9 26.5 50

7796+ 26 300 87 √√ Vibration probes 333 23.9 24.5 5020 390 51 428 18.3 18.9 50

7796- 26 300 87 √√ Vibration probes 333 23.9 24.5 5020 390 51 428 18.3 18.9 50

7760ac 10 50 200 √√ Active dc & ac sensors 75 6.0 6.7 5010 50 200 Thermocouples 75 6.0 6.7 50

7765ac 15 100 150 √√ 124 12.0 12.5 5015 100 150 124 12.0 12.5 50

7778ac 28 600 47 √√ 651 24.0 25.4 5028 600 47 651 24.0 25.4 50

7789+ 28 300 93a √√ Switch inputs / 651 26.6 27.2 50Signal returns 651 26.6 27.2 50

28 diode — 0.9V+26Ω 26.6 27.2 5028 diode — 0.9V+26Ω 26.6 27.2 50

7787+/- 28 300 93 √√ √√ Transmitters 333 26.6 27.2 5028 diode — Controller outputs, switches 0.9V+26ΩΩ 26.6 27.2 50

7787P+ 28 234 119 √√ 253 26.4 27.2 8028 diode — 0.9V+21Ω 26.4 27.2 80

7788+ 28 300 93 √√ 333 25.9 26.5 5010 50 200 √√ 75 6.0 7.0 50

7788R+ 28 300 93 √√ Transmitters 333 25.9 26.5 5010 50 200 √√ 75 6.0 7.0 50

Vmax

V

SPECIFICATIONS‘Key’ barriers shown in blue

For notes 1 to 7 see 'Terminology' (later in this section)

ModelNo.

Safety description Polaritiesavailable

+ – ac

Basic circuit

Hazardous Safe

Fuserating

mA

Vwkg at 10(1)µA

V

Max. end-to-end

resistanceΩΩ

Application1 2 3 4 5 6

a Terminals 3 & 7 connected together*Diagrams show positive versions. All diodes reversed on negative versions. Additional diodes fitted on ac versions.

See 'HOW THEY WORK'and

'ACTIVE / ELECTRONICALLYPROTECTED BARRIERS'

See 'ACTIVE / ELECTRONICALLYPROTECTED BARRIERS'

See additionalspecification

June 2004

GENERAL SPECIFICATION

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 MTL7755ac/7756ac it decreases by at leastone decade for a 0.4V reduction in applied voltage.

TerminationsRemovable terminals accommodate conductors up to 2.5mm2

(13AWG). Hazardous-area terminals are identified by bluelabels. Removal force >15N

Colour coding of barrier labelGrey: non-polarisedRed: positive polarity (MTL7706 negative to transmitter )Black: negative polarityWhite: dummy barrier, MTL7799

Weight140g approx

Mounting and earthingBy 35mm Top Hat DIN rail

DIMENSIONS (mm)

KEY MTL7700 SERIES BARRIERS SUMMARISED

HOW THEY WORKAll MTL7700 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 MTL7707P+and MTL7729P+, 'ia' 'IIB').

TERMINOLOGY1. 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.

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 MTL7700 Seriesbarriers is 250V ac/dc. APPLICATION KEY BARRIER

Resistance temperature detectorsThermocouples, ac sensors

Transmitters, 2-wire, 4/20mA

Controller outputs, one line earthedController outputs, neither line earthed

Switches

Solenoids, alarms, LEDs

7756ac7760ac

7706+7787+

7728+7787+

7787+7741/3

7728

TYPEAnalogueinput (low-level)

Analogueinput (high-level)

Analogueoutput

Digital (on/off)input

Digital (on/off)output

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June 2004

ACTIVE / ELECTRONICALLYPROTECTED BARRIERS

ACTIVE / ELECTRONICALLY PROTECTED BARRIERSThe following barriers have built-in overvolt protection, allowing theiruse with unregulated power supplies. In many applications, eg, sensorinputs or controller outputs, there is insufficient power available toblow the barrier fuse and this additional protection is not necessary.However, where the barrier is connected to a power supply, eg, forenergising transmitters, switches, solenoids or local alarms, overvoltprotection allows the barriers to be used with unregulated suppliesand also gives protection against faulty wiring during commissioning.

MTL7706+ for 'smart' 2-wire 4/20mA transmittersThe MTL7706+ 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 MTL7706+ will passincoming communication signals up to 10kHz from a ‘smart’transmitter, while in the outgoing direction it will pass signals of anyfrequency likely to be encountered.

Since the MTL7706+ has no return channel for energising the load,the entire 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. A separate circuit limits the current toprotect the fuse in the event of a short circuit in the hazardous area.With a 20V supply, the barrier will deliver 16.2V minimum at 20mAfor the transmitter and lines and consumes typically 45mA at 24Voperation.

BASIC CIRCUIT

ADDITIONAL SPECIFICATION

Safety description28V 300Ω 93mA

Supply voltage20 to 35V dc w.r.t earth

Output current4 to 20 mA

Voltage available to transmitter and lines16.2V @ 20mA with 250Ω load (negative w.r.t. earth)11.0V @ 20mA with 500Ω load (negative w.r.t. earth)

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HazardousArea

SafeArea

Accuracy±2µA under all conditions

Safe-area load resistance0 to 500Ω

Supply current45mA typical at 20mA and 24V supply60mA maximum at 20mA and 20V supply

MTL7707+ for switch inputs and switched outputsThe MTL7707+ is a 2-channel shunt-diode safety barrier similar to theMTL7787+ but with built-in electronic overvolt protection. It isintended primarily for safeguarding a hazardous-area switchcontrolling a relay, opto-coupler or other safe-area load from anunregulated dc supply 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.

BASIC CIRCUIT


Safety description28V 300Ω 93mA, terminals 1 to 328V Diode, terminals 2 -4

Supply voltage10 to 35V dc with respect to earth

Output currentUp to 35mA available

Maximum voltage drop (at 20ºC, current not limited)

Iout x 345Ω + 0.3V, terminals 1 to 3Iout x 25Ω + 0.9V, terminals 4 to 2

Supply currentIout + 1.6mA, supply <26VLimited to 50mA, supply >28V or low load resistance

MTL7707P+ for switch inputs and switchedoutputs, 2W Transmitters (IIB gases)The MTL7707P+ is a two-channel shunt-diode safety barrier similar tothe MTL7787P+, 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.

HazardousArea

SafeArea

1

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June 2004

MTL7742 proximity sensor or switch inputwith solid state outputThe MTL7742 is a single channel switch/prox input barrier with anopen collector solid state interface to the safe area equipment. Thesolid state switch is especially useful for high frequency switchingapparatus including pulse and rotational sensors. The power busterminal can be used to connect power to the module and the inputpower supply range makes the module suitable for use withunregulated supplies

BASIC CIRCUIT

ADDITIONAL SPECIFICATIONSafety description

10V 19mASupply voltage

20 to 35V dc with respect to earthInput characteristics

Output energised if input >2.1mA(<2kΩ)Output de-energised if input <1.2mA(>10kΩ)

Output characteristicsOperating frequency dc to 2.5kHzMax off-state voltage 35VMax off-state leakage 10µAMax on-state voltage drop <1.41V @ 50mA

<1.22V @ 2mAtypically <1V

Max on-state current 50mASupply current

20mA maximum @ 24V

MTL7743 2 channel proximity sensor or switchinput and relay outputsThe MTL7743 is a dual channel switch/prox sensor input barrier witha relay interface. This module is ideal for applications where highchannel packing densities are required for digital inputs. Power isconnected using the power bus terminal.BASIC CIRCUIT


10V 19mA10V 19mA

Supply voltage22.9 to 30V dc with respect to earth

Input characteristicsRelay energised if input >2.1mA(<2kΩ)Relay de-energised if input <1.2mA(>10kΩ)

Relay Contacts*125V ac 0.5A. Resistive30V dc, 1A. Resistive

Supply current45mA maximum @ 24V

Response time <10ms

BASIC CIRCUIT


Safety description28V 164Ω 171mA, terminals 1 to 328V Diode, terminals 4 to 2

Supply voltage 10 to 35V dc with respect to earth

Output currentUp to 35mA available

Maximum voltage drop(at 20ºC, current not limited)

Iout x 218Ω + 0.3V, terminals 1 to 3Iout x 20.1Ω + 0.9V, terminals 4 to 2

Supply currentIout + 1.6mA, supply <26VLimited to 50mA, supply >28V or low load resistance

MTL7741 proximity sensor or switch input andrelay outputThe MTL7741 is a single channel switch/prox input barrier withchangeover relay contacts acting as the safe area interface. Relaycontacts provide a universal interface capable of switching a widerange of signals including ac, low level and high level voltages.Phase reversal is achieved by connecting the normally open ornormally closed contacts as required. The power bus terminal may beused to connect the module to a power source.BASIC CIRCUIT



22.9 to 30V dc with respect to earthInput characteristics

Relay energised if input >2.1mA(<2kΩ)Relay de-energised if input <1.2mA(>10kΩ)

Relay Contacts*125V ac 0.5A. Resistive30V dc, 1A. Resistive


Response time <10ms

HazardousArea

SafeArea

HazardousArea

SafeArea

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* There are limitations for use above 50V. Please refer to theInstruction Manual INM7700.

HazardousArea

SafeArea

HazardousArea

SafeArea

June 2004

MTL7744 2 channel proximity sensor or switchinputs with solid state outputsA dual channel version of the MTL7742. This module provides twosolid state interfaces for prox/switch inputs. Power is connected viathe power bus.

BASIC CIRCUIT


10V 19mA10V 19mA

Supply voltage20 to 35V dc with respect to earth

Input characteristicsOutput energised if input >2.1mA(<2kΩ)Output de-energised if input <1.2mA(>10kΩ)

Output characteristicsOperating frequency dc to 2.5kHzMax off-state voltage 35VMax off-state leakage 10µAMax on-state voltage drop 1.41V @ 50mA

1.22V @ 2mAtypically <1V

Max on-state current 50mASupply current

29mA maximum @ 24V

MTL7745 proximity sensor or switch inputwith relay output and line fault detectThe MTL7745 is a single channel switch/prox input barrier providingline fault detection. Proximity detectors or switches fitted with end-of-line resistors may be connected. Short circuit or open ciruit conditionsin the field wiring will generate an alarm condition. The LFD relaycontacts close when a fault is detected allowing the contacts to beconnected in parallel to provide a common alarm. The power busterminal can be used to connect power to this module.

BASIC CIRCUIT



22.9 to 30V dc with respect to earthInput characteristics

Output energised if input >2.1mA(<2kΩ)Output de-energised if input <1.2mA(>10kΩ)

LFD relay + Red LEDEnergised if input <50µA or <100Ω

Relay contacts*125V ac 0.5A. Resistive30V dc, 1A. Resistive


Response time <10ms

MTL7798 Power feed and protection moduleThe MTL7798 power feed module incorporates both voltage andcurrent sense mechanisms to protect barrier circuits by activating asolid state trip mechanism when fault or overload conditions occur inthe power source circuit. Resetting the module after tripping isachieved by interupting the supply to the unit. A red LED indicates acircuit trip condition and a green LED the availability of power at theoutputs. Bussed power for other modules is sourced from the top ofthe unit using the Bus Power Link BPL7700 or via terminals 1 and 2.

BASIC CIRCUIT

ADDITIONAL SPECIFICATIONInput voltage range (terminals 5&6)

20 to 26.8VMaximum input voltage capability

45VPower source requirements

>1.8ATrip mechanism

Minimum trip 26.8V @ 20°C (+18mV/°C)Output current range

0 to 800mAMaximum voltage drop

20mV @ 0mA, 1.0V @ 800mA load

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* There are limitations for use above 50V. Please refer to theInstruction Manual INM7700.

HazardousArea

SafeArea

HazardousArea

SafeArea

HazardousArea

SafeArea

June 2004

MTL7700 Series barriers protect devices located in all normallyoccurring explosive atmospheres, including air/flammable gasmixtures, dusts and fibres. Applications covered include theprotection of installations incorporating uncertified devices (‘simpleapparatus’) such as thermocouples, switches and resistive sensors, orseparately certified ‘energy storing’ (or ‘voltage producing’)apparatus including ac sensors, transmitters and current-to-pneumatic(I/P) converters. Recommended choices for specific applications arediscussed briefly in the following pages.

MTL7700 SERIESBARRIER APPLICATIONS

ANALOGUE INPUTS (HIGH LEVEL)

2-wire transmitters, 4/20mA, conventional and smartThe recommended barrier for use with 'conventional' and 'smart'4/20mA transmitters (fed by a 26V regulated supply) is theMTL7787+. This provides up to 12.9V (14.6V for MTL7787P+) atVwkg and 20mA for a transmitter and its lines as well as 5V for thetypical 250Ω load. This application and this barrier is suitable for usewith the optional power bus facility.

The MTL7706+ is recommended for applications where anunregulated supply of up to 35V is used. It provides 16.0V forconventional and Smart transmitters at 20mA, as well as 5V for atypical 250Ω load. With the MTL7706+ terminal 3 is negative withrespect to earth, so the connections to terminals 3 and 4 should bereversed.

3

4

1

2MTL7760acMTL7765MTL7778

RecorderControllerData loggerComputer

Compensating cable

3

4

1

2MTL7760ac Earth freesignal

PhotocellMicrophoneTurbineFlowmeter

+6.0V3

4

1

2MTL7760acVout0V

3

4

1

2MTL7788R+

250Ω1-5V

Power +26V

Power Bus

3

4

1

2MTL7796-Power -24V

Vout

0V

Probedriver

Transducer

Monitor

3

4

1

2MTL7706+MTL7787+MTL7787P+ 250Ω4 -20mA

Power +26V

Signal

Power Bus

1-5V

ANALOGUE INPUTS (LOW-LEVEL)

Thermocouples and mV sourcesThe recommended barrier for thermocouples and mV sources is theMTL7760ac. This 2-channel non-polarised barrier retains the ‘earth-free’ nature of the signal and, providing the receiver’s input ‘floats’,rejects common-mode ac and dc interference up to at least 7V and isunaffected by earth faults on the primary element.

HazardousArea

SafeArea

Vibration probesThe 3-wire transmitters used with vibration monitoring equipment areinvariably supplied by a –24V dc power supply – hence therecommended barrier choice is the negatively-polarised MTL7796–.

Slidewire displacement transducersThe simplest choice is the MTL7760ac. This barrier supplies powerand brings back a unipolar signal.

ac sensors, photocells, microphones and turbine flowmetersThe MTL7760ac is the recommended choice for these devices. Whilemany of these are designated ‘simple apparatus’ and thus do notneed certification, note that some ac sensors may be subject to asignificant level of inductance and will therefore need to be designedand certified for hazardous-area locations.

June 2004

RTDsFor 3-wire RTDs, a single MTL7755ac barrier is the most economicalchoice. This is suitable for use with a floating bridge – the two leadsfrom the bridge arms are protected by the barrier with the third(supply) lead being earthed through the barrier. The barrier has a lowend-to-end resistance of only 19Ω/channel to minimise span changesand its channels track within 0.15Ω (between –20 to +60°C) tominimise zero shift with temperature.

STRAIN-GAUGE BRIDGES

Single strain-gauge bridgesThis shows an arrangement using two or three barriers, which is safein IIC gases. With the MTL7761ac, the circuit is powered from a 14V,230Ω source; if the bridge resistance is 230Ω, then the bridgevoltage is 7V. If the bridge resistance is 350Ω, then the bridgevoltage is 8.4V.An MTL7764ac can be used to sense the bridge supply voltage.An MTL7761ac is used here for the mV output.An MTL7766Pac provides 12.3V for a 350Ω bridge with a 20Vsupply. MTL7761Pac's can be used for the sense and pick-off circuits.

HazardousArea

SafeArea

3

4

1

2MTL7756ac

Receiver

7 5

3

4

1

2MTL7755ac

Receiver

3

4

1

2

Receiver

3

4

1

2MTL7755acMTL7761ac

MTL7755acMTL7761ac

4-wire constant-current circuits do not need matched barrierresistances and can be protected by two MTL7761ac barriers. If theincrease in loop resistance is too great, use two MTL7755ac barriersinstead.

If the bridge circuit is already earthed, the third barrier channelprovided by an MTL7756ac is needed. For extreme accuracy, 3channels and an earth-free bridge can be used, a configuration thatcancels out the small errors due to barrier leakage.Channels 1 and 2 (those between terminals 1 & 2, and 2 & 4respectively) track to within 0.15Ω between –20 and 60°C.

3

4

1

2

+7V3

4

1

2MTL7761ac

MTL7764ac

3

4

1

2MTL7761ac

--7V

0V

Output (mV)

Sense+

—

June 2004

STRAIN-GAUGE BRIDGES (cont)

Double strain-gauge bridgesQuite frequently there is a demand to monitor two load cells, and apossible circuit, safe in IIC, is shown.Here, the lower voltage drop of the MTL7766Pac is an advantage.The MTL7766Pac supplies power to the bridge(s) whilst twoMTL7761Pac barriers interface with the sense and pick-off circuits.Using 350Ω bridge systems, the following voltages are availablefrom an MTL7766Pac with a ±10V supply:

1 bridge: 13.11V2 bridges: 9.75V

ANALOGUE OUTPUTS

Controller outputs (I/P converters)The single-channel MTL7728+ with a voltage drop of 6.66V at 20mAis the recommended choice for most controller outputs. Higher-powerversions are available: the MTL7728P+ (5.1V drop) is suitable for IICapplications; the MTL7729P+ (3.68V drop) for IIB applications.

HazardousArea

SafeArea

3

4

1

2

+10V3

4

1

2MTL7766Pac

MTL7761Pac

3

4

1

2MTL7761Pac

--10V

0V

Sense+

—

Output (mV)

3

4

1

2MTL7728+2

.2

3

4

1

2MTL7787+MTL7787P+

2

.2

3

4

1

2MTL7787+MTL7787P+

2

9

.2

The MTL7787+ and MTL7787P+ are also suitable for controllerscontaining a resistor which enables the return current to be monitoredfor high-integrity operation.

For controllers with an output circuit separated from the 0V rail by thecontrol transistor, the 2-channel MTL7787+ is the preferred choice asthe return channel can handle up to 26.6V allowing the control signalto be turned off completely. The voltage drop is 8.1V at 20mA. Ahigher-power version of the latter, the MTL7787P+, is also available.The return channel of these barriers handle up to 26.4V and themaximum voltage drop is only 6.38V

June 2004

DIGITAL (ON/OFF) INPUTS

SwitchesThe normal choice is the MTL7787+/7787P+ with a regulatedsupply. The MTL774X modules are recommended for applicationswhere an unregulated supply of up to 30V for relay output modules,or 35V for solid state output modules, is used.

The MTL7789+ offers a dual channel passive barrier for switch inputswhere the input current for each channel is <10mA.

DIGITAL (ON/OFF) OUTPUTS

Alarms, LEDs, solenoids valves, etcFor these applications, the MTL7728+ is recommended. Higher-powered versions are available: the MTL7728P+ is suitable for IICapplications; the MTL7729P+ for IIB applications.

If the control switch is to earth, then the 2-channel MTL7787+ barriershould be used, or, alternatively, the MTL7787P+ higher-powerversion. If the supply is poorly regulated use the MTL7707+.

The MTL7707+ is recommended for applications where anunregulated supply of up to 35V is used.

HazardousArea

SafeArea

3

4

1

2MTL7787+MTL7787P+

Power +26.6V

Signal

Power Bus

34

1

2

MTL7789+78

56

Power +26.6V

Power +26.6VLogic signal

Logic signal

Power Bus

34

12MTL7743

MTL774478

56

3'!'

3'!'

-

34

1

2MTL7745 5

6

620Ω

10kΩ

+22.9 - 30V

LFDCOMCH 1

Power Bus

34

12

MTL7742 56 3'!'

3'!'

-%

.22

2

34

12

MTL7741 56

78 ;,

",9

-%

22;"

+26V3

4

1

2

0V

3678 MTL7707+

MTL7787+MTL7787P+

Switches / Proximity detectorsMTL’s range of new switch/prox input barriers provide the user witha choice of relay and solid state outputs in single and dual channelversions.

The MTL7741 is single channel with a changeover relay output.

The MTL7743 and MTL7744 are dual channel versions affordingvery high packing densities. Power must be provided to thesemodules using the power bus facility.

The MTL7745 is a single channel proximity input (or switch input if‘end of lines’ resistors are fitted) with relay contacts providing switchand line fault status. The LFD relay contacts close when a fault isdetected.

The MTL7742 has a single channel solid state switch that can beconfigured to switch from a power rail or down to ground. This is alsoideal for high switching frequency applications.

+24.9V3

4

1

2MTL7707+MTL7728+MTL7728P+MTL7729P+

0V

3678

June 2004

SPARE CABLE CORES AND SCREENS

The MTL7799 dummy barrier is used primarily for securing andearthing unused cables and screen connections. Hazardous areaterminals 3 and 4 are internally connected to the DIN-railmounting/earth connection. It also provides a power bus connectionfor direct connection of power for modules such as the MTL7743 andMTL7744 where no power supply screw terminal is provided.

POSITIVE DC SYSTEMS

Low-level to 12V dc systemsThe two channels of the MTL7764+ and MTL7767+ can be combinedsafely in IIC.

The MTL7764+ can be used for low-level logic return signals whilstthe MTL7767+ is used for 6V dc and 12V dc systems.

18V dc systemsThe single-channel MTL7722+ is recommended for 18V dc systems.

AC AND DC SYSTEMS

High-level ac and dc systemsThe versatile star-connected MTL7765ac and MTL7778ac allow Vwkgto be developed from each channel to ground but only allow Vwkg tobe developed between channels. This provides some common-modevoltage capability and can allow higher cable parameters to be used.

NEGATIVE AND FLOATING POWER SUPPLIES

Digital (on/off) outputsThe MTL7728– is used with a negative power supply and positiveearth. Typically used for digital inputs or outputs, as shown.

The MTL7728-- can also be used with floating power supplies, fortransmitters.

HazardousArea

SafeArea

3

4

1

2

0V

MTL7764+MTL7767+

!) +10V/+12V

+10V/+12V

3

4

1

20VMTL7722+

!)

+19.6V

3

4

1

2MTL7765acMTL7778ac!!

)12V/24V?0V

+26V

3

4

1

23678 MTL7728—

.

3

4

MTL7799

@ !!!

1

-%

June 2004

POWER BUS APPLICATIONS

The PB7700 power bus is invaluable for saving installation time andwiring when connecting a 24V dc power source to a number ofbarriers.

Typical applications include hazardous-area switches, 4/20mAtransmitters and proximity detectors. The diagram illustrates theconfiguration for 4 barriers but up to 40 barriers can be served bythis method.

The MTL7798 power feed module would normally be used withstandard barriers such as MTL7787+ and MTL7787P+ because the current/voltage trip protection mechanism of the MTL7798 protectsthe fuses in the barriers.

The MTL7799 dummy barrier can be used instead of the MTL7798for direct ‘feed-through’ connection of a 24V dc supply onto thepower bus. Looping the power feed to each end of the bussed powerallows the removal of individual barriers without loss of power toothers in the chain.

Other units which can use the power bus facility:MTL7706MTL7707+MTL7707P+MTL7741MTL7742MTL7743MTL7744MTL7745MTL7787+MTL7787P+MTL7788+MTL7788R+MTL7789+

HazardousArea

SafeArea

A

!

June 2004

MTL7700 SERIESACCESSORIES

MOUNTING/EARTHING ACCESSORIESMTL7700 Series barriers mount easily and quickly onto standard DINrail which also acts as the intrinsically safe earth.THR2 standard DIN railTHR7000 plated railSpecially nickel-plated T-section (35mm x 7.5mm) DIN rail for use inpotentially corrosive atmospheres. Supplied in 1meter lengths.ISP7000 insulating spacers

Attached to the base of a DIN rail at either end or at intervals(depending upon DIN rail length) to isolate the IS earth from astructural earth.

ERB57S Earth-rail bracket, straightNickel-plated; supplied with two push fasteners, one 14mm earth-railclamp and one 10mm earth clamp for cables ≤16mm2.ETM7 earth terminal

For terminating cable screens and 0V earth returns and securingspare cores to the earth rail. A maximum of two ETM7s per barriercan be accommodated.

TGL7700

ERB57O

TAG57

ERL7ETM7

14mm earth-railclamp

THR2/THR7000

ERB57Sin lower position

ISP7000

ETL7000

10mm earthclamp

IMB57

Snap off extensionwhen using IMB57as a central support

27

7.5

35

14.6

62

50

20

M6 x 16

Ø4.4 M4 x 16

IMB57 Insulating mounting blockOne required at each end of a tagging strip/earth rail. Suitable forlow-profile (7.5mm) and high-profile (15mm) symmetrical DIN rail.

ERB57O Earth-rail bracket, offsetNickel-plated; supplied with two push fasteners, one 14mm earth-rail clamp and one 10mm earth clamp for cables ≤16mm2.

ETL7000 earth terminalProvides connection for routing the IS earth from the DIN rail to anappropriate plant earth. Maximum cable cross-section is 10mm2. Tworecommended per discrete length of DIN rail. See instruction manualINM7700 for more details.

BPL7700 Power Bus linkWhen a number of barriers use a common power supply, the optionalpower link (BPL7700) can be used. Typical applications includehazardous area switches, solenoids and 4–20mA transmitters. Thebarriers it can be used with are the MTL7706, MTL7707+,MTL7787+, MTL7787P+, MTL7789P+ and MTL774X. See next pagefor further details.

82m

m

135m

m

28m

m

66mm 15mm

150mm 10mm

3mm

9mm 14mm

5mm

133.5mm

10mm

3mm

10mm

57mm

14mm

10

43.548 overDIN rail

June 2004

TAGGING ACCESSORIESTwo methods of tagging are available which can be used separatelyor together:1) Individual barrier identification

TH7700 barrier identifiersTH7700 barrier identifiers are supplied clipped on to the tops of individual barriers to provide transparent holders for identification labels.

2) Tagging strip methodTAG57 Tagging strip, 1m lengthCut to size. Supplied with reversible tagging strip label suitable for either MTL5000 or MTL7000 Series module spacing.TGL7700 Tagging strip labels, set of 10 x 0.5mFor use with TAG57 tagging strip. Tags are reversible - one side for MTL7700, the other for MTL700.

HOW TO ORDER

MTL7700 barriersSelect by barrier number and polarity, e.g. MTL7728+

Mounting accessoriesTHR2 Standard DIN-rail, 35 x 7.5mmTHR7000 T-section DIN-rail, specially-plated,

35 x 7.5mm, 1m lengthISP7000 Insulating spacer

Standard earthing/earth-rail accessoriesETL7000 Earth terminal, DIN-rail mountedIMB57 Insulating mounting blockERB57S Earth-rail bracket, straightERB57O Earth-rail bracket, offsetERL7 Earth rail, 1m lengthETM7 Earth terminal, pack of 50

Standard tagging accessoriesTAG57 Tagging strip, 1m lengthTGL7700 Tagging strip labels, set of 10 x

0.5m

Bussed power linksBPL7700 Pack of 100

EnclosuresDX070 Enclosure, for MTL7700 x 5DX170 Enclosure, for MTL7700 x 13DX430 Enclosure, for MTL7700 x 33

Spares (all in packs of 10)SAF7712 Safe-area terminals 1&2HAZ7734 Hazardous area terminals 3&4SAF7756 Safe-area terminals 5&6HAZ7778 Hazardous area terminals 7&8TH7700 Tag holder

LiteratureINM7700 Instruction manual, MTL7700 SeriesINM57ENC Instruction manual, MTL5000/7000

Series EnclosuresCD7700... Customer drawings

June 2004

Region UK UK USA Canada/USA Japan(Authority) (BASEEFA) (BASEEFA) (FM) (CSA) (TIIS)

Systems

Standard EN 50014 EN 50039 3600, 3610 entity CAN/CSA E60079 See CertificatesEN 50020 3611, 3810 UL698, UL913, UL1604

IEC60079, C22.2

Approved for [EEx ia] IIC EEx ia IIC AIS/I,II,III/1/Entity Class 1, Div 2, Gps A,B, Ex (ia) IIC[EEx ia] IIB ‡ EEx ia IIB ‡ ABCDEFG- SCI-942; C,D; Ex nA [iA] IIC T4 Ex (ia) IIB ‡

NI/I/2/ABCD/T4[I/0] AEx[ia]IIC – Class 1, Zone 2, AEx nASCI-942 Entity; IIC T4NI/1/2/IIC/T4 Ta=60ºC except †where Ta=65ºC

Model No. Certificate No.

MTL7706+ BAS01ATEX7217 Ex01E2219 3010737 1345550MTL7707+ BAS01ATEX7217 Ex01E2219 3010737 1345550MTL7707P+ BAS01ATEX7218‡ Ex01E2220‡ 3010737‡ 1345550MTL7710+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16433MTL7715+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16434MTL7715P+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16611MTL7722+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16435MTL7728+/–/ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16397MTL7728P+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16436MTL7729P+ BAS01ATEX7218‡ Ex01E2220‡ 3010737‡ 1345550 C16612‡MTL7741 BAS01ATEX7217 Ex01E2219 3010737 1345550 C16613MTL7742 BAS01ATEX7217 Ex01E2219 3010737 1345550 C16614MTL7743 BAS01ATEX7217 Ex01E2219 3010737 1345550 C16615MTL7744 BAS01ATEX7217 Ex01E2219 3010737 1345550 C16616MTL7745 BAS01ATEX7217 Ex01E2219 3010737 1345550 C16617MTL7755ac BAS01ATEX7217 Ex01E2219 3010737† 1345550 C16450MTL7756ac BAS01ATEX7217 Ex01E2219 3010737† 1345550 C16437MTL7758+/– BAS01ATEX7217 Ex01E2219 3010737 1345550 C16618MTL7760ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16619MTL7761ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16438MTL7761Pac BAS01ATEX7217 Ex01E2219 3010737 1345550MTL7764+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16440MTL7764ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16441MTL7765ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16620MTL7766ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16442MTL7766Pac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16443MTL7767+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16444MTL7778ac BAS01ATEX7217 Ex01E2219 3010737 1345550 C16621MTL7779+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16445MTL7787+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16447MTL7787P+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16448MTL7788+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16449MTL7788R+ BAS01ATEX7217 Ex01E2219 3010737 1345550MTL7789+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16622MTL7796+ BAS01ATEX7217 Ex01E2219 3010737 1345550 C16446MTL7796– BAS01ATEX7217 Ex01E2219 3010737 1345550MTL7798 NI only

Note : For FM compliance, the MTL7700 Series barriers shall be installed in compliance with the enclosure, mounting, spacing and segregation requirements of the ultimate application.

‡ Certified to CENELEC IIB/FM Grps C-G only.

APPROVALS - for the latest certification information visit www.mtl-inst.com/certs_1.nsf

June 2004

ac1/dc Note 3 BASEEFA Group IIC Matched FM (Grps A&B) Matchedref. C L 2 L/R Power C L 2 L/R Power

Model No. (µµF) (mH) (µµH/ΩΩ) (W) (µµF) (mH) (µµH/ΩΩ) (W)MTL7706 + a 0.083 3.05 (4.2) 56 0.65 0.083 4.2 56 0.65MTL7707 + a1/a2/b 0.083 3.05 (4.2) 56 0.65 0.083 4.2 56 0.65MTL7710 + a 3 0.91 74 0.50 3 0.91 74 0.50MTL7715 + a 0.58 1.45 66 0.56 0.58 1.45 66 0.56MTL7715P + a 0.580 0.33 28 1.09 0.580 0.33 28 1.09MTL7722 + a 0.165 1.45 45 0.81 0.165 1.45 45 0.81MTL7728 +/-/ac a 0.083 3.05 (4.2) 56 0.65 0.083 3.05 (4.2) 56 0.65MTL7728P + a 0.083 1.82 (2.51) 44 0.83 0.083 1.82 (2.51) 44 0.83MTL774X b3 2.86 96 742 — 2.86 96 742 0.039MTL7755 ac a1/a2 100 0.46 145 0.225 100 0.46 145 0.225

b 100 0.13 69 0.45 40 0.13 69 0.45c 40 0.41 73 0.45 40 0.13 69 0.45

MTL7756 ac a1/a2/a3 100 0.46 145 0.225 100 0.46 145 0.225b1 100 0.13 69 0.45 40 0.13 69 0.45b2 100 0.06 44 0.675 40 0.13 69 0.45c1 40 0.41 73 0.45 40 0.13 69 0.45c2 40 0.23 61 0.60 40 0.06 44 0.675

MTL7758 +/- a1/a2 11.1 0.07 26 1.40 11.1 0.07 26 1.4b 11.1 0.02 10 2.8 8.8 0.02 10 2.8

MTL7760 ac a1/a2 3 0.91 74 0.5 3 0.91 74 0.5b 3 0.20 27 1.00 3 0.20 35.6 1.00

MTL7761 ac a1/a2 4.9 3.72 163 0.225 4.9 3.72 163 0.225b 4.9 0.91 62 0.45 0.31 0.91 62 0.45c 0.31 3.72 81 0.45 0.31 0.91 62 0.45

MTL7761P ac a1/a2 4.9 56 613 0.058 4.9 56 613 0.058b 4.9 14 236 0.115 0.31 14.0 236 0.115c 0.31 56 306 0.115 0.31 14.0 236 0.115

MTL7764 + a1/a2 1.41 240 1000 0.036 1.41 240 1000 0.036b 1.41 61 360 0.072 1.0 61 360 0.072

MTL7764 ac a1/a2 1.41 240 1000 0.036 1.41 240 1000 0.036b 1.41 61 360 0.072 0.125 61 360 0.072c 0.125 240 500 0.072 0.125 61 360 0.072

MTL7765 ac a1/a2 0.580 1.45 66 0.56 0.580 1.45 66 0.56b 0.580 0.32 22 1.125 0.58 0.32 31.6 1.12

MTL7766 ac a1/a2 1.41 5.8 151 0.24 1.41 5.8 151 0.24b 1.41 1.47 58 0.48 0.125 1.47 58 0.48c 0.125 5.8 75 0.48 0.125 1.47 58 0.48

MTL7766P ac a1 1.41 1.47 78 0.471 1.41 1.47 78 0.471b 1.41 0.34 29 0.942 0.125 0.34 29 0.942c 0.125 1.15 39 0.942 0.125 0.34 29 0.942

MTL7767 + a1/a2 0.58 1.45 66 0.56 0.58 1.45 66 0.56b 0.58 0.32 22 1.125 0.58 0.32 22 1.125

MTL7778 ac a1/a2 0.083 16 107 0.33 0.083 16 107 0.33b 0.083 3.05 (4.2) 42 0.33 0.083 4.0 107 0.654

MTL7779 + a1/a2 0.083 3.05 (4.2) 56 0.65 0.083 3.05 (4.2) 56 0.65b NOT PERMITTED

MTL7787 +/- a1 0.083 3.05 (4.2) 56 0.65 0.083 3.05 (4.2) 56 0.65a2 0.083 — — — 0.083 — — —b 0.083 3.05 (4.2) 56 0.65 0.011 4.2 56 0.65

MTL7787P + a1 0.083 1.82 (2.51) 44 0.835 0.083 1.82 (2.51) 44 0.83a2 0.083 — — — 0.083 — — —b 0.083 1.82 (2.51) 44 0.835 0.78 2.51 44 0.835

MTL7788 + a1 0.083 3.05 (4.2) 56 0.65 0.083 3.05 (4.2) 56 0.65a2 3.0 0.91 74 0.5 3.0 0.91 74 0.5b 0.083 0.33 25 0.92 0.083 0.33 25 0.92

MTL7788R + a1 0.083 3.05 (4.2) 56 0.65 0.083 3.05 (4.2) 56 0.65a2 3.0 0.91 74 0.5 3.0 0.91 74 0.5b 0.083 0.33 25 0.92 0.083 0.33 25 0.92

MTL7789 + C 0.083 16 106 0.33 0.083 16 106 0.33MTL7796 +/- a1 0.1 4.91 64 0.56 0.1 4.91 64 0.56

a2 0.22 13 136 0.26 0.22 13 136 0.26b 0.1 1.94 34 0.81 0.096 1.94 34 0.81

Notes: 1 ac indicates a non-polarised star connected barrier configuration.2 When the external circuit contains no lumped inductance greater than 10mH, the cable inductance may be increased to the values within

parenthesis.

For further barrier channel configuration data, please refer to the relevant certificate.

MAXIMUM CABLE PARAMETERS

Model No. ac1/dc Note 3 BASEEFA GroupIIB Matched FM (Grps C-G) MatchedRef. C L L/R Power C L L/R Power

(µµF) (mH) (µµH/ΩΩ) (W) (µµF) (mH) (µµH/ΩΩ) (W)MTL7707P + a1 0.65 5.34 125 2.64 0.65 5.34 125 2.64

b 0.65 5.34 125 2.64 0.587 5.34 125 2.64MTL7729P + a1 0.65 5.65 127 2.64 0.65 5.65 127 1.19

June 2004

Module No. Bussed MTL7000 MTL7000 MTL7000 MTL700 MTL700 MTL700 TypicalPower Equivalent Original ATEX equivalent Original ATEX Application

Certificate Certificate Certificate Certificate Number(s) Number(s) Number(s) Number(s)

MTL7710+ No Half of Ex95C2261 BAS99ATEX7285 MTL710+ Ex832452 BAS01ATEX7202 4/6VMTL7162+ Systems

MTL7715+ No N/A N/A N/A MTL715+ Ex832452 BAS01ATEX7202 12V SystemsMTL7715P+ No N/A N/A N/A MTL715P+ Ex92C2373 BAS01ATEX7202 12V SystemsMTL7722+ No MTL7122+ Ex95C2261 BAS99ATEX7285 MTL722+ Ex832452 BAS01ATEX7202 General PurposeMTL7728+/- No MTL7028+/- Ex95C2261 BAS99ATEX7285 MTL728+/- Ex832452 BAS01ATEX7202 Analogue / Digital

MTL7128+/-MTL7728ac No N/A N/A N/A MTL728ac Ex832452 BAS01ATEX7202 General PurposeMTL7728P+ No MTL7128P+ Ex95C2261 BAS99ATEX7285 MTL728P+ Ex92C2373 BAS01ATEX7202 Analogue / DigitalMTL7755ac No MTL7055ac Ex95C2261 BAS99ATEX7285 MTL755ac Ex832452 BAS01ATEX7202 RTD, GroundedMTL7756ac No MTL7056ac Ex95C2261 BAS99ATEX7285 N/A N/A N/A RTD, GroundedMTL7758+/- No N/A N/A N/A MTL758 Ex83453 BAS01ATEX7217 Active sensors,

ThermocouplesMTL7760ac No N/A N/A N/A MTL760ac Ex832452 BAS01ATEX7202 Active sensors,

ThermocouplesMTL7761ac No MTL7261ac Ex95C2261 BAS99ATEX7285 MTL761ac Ex832452 BAS01ATEX7202 Strain GaugesMTL7761Pac No MTL7061Pac Ex95C2261 BAS99ATEX7285 MTL761Pac Ex92C2373 BAS01ATEX7202 Load cell

MTL7161PacMTL7764+ No MTL7164+ Ex95C2261 BAS99ATEX7285 MTL764+ Ex832452 BAS01ATEX7202 High resistanceMTL7764ac No MTL7264ac Ex95C2261 BAS99ATEX7285 MTL764ac Ex832452 BAS01ATEX7202 Strain / Level

GaugesMTL7765ac No N/A N/A N/A MTL765ac Ex832452 BAS01ATEX7202 General PurposeMTL7766ac No N/A N/A N/A MTL766ac Ex832452 BAS01ATEX7202 Strain GaugesMTL7766Pac No MTL7066Pac Ex95C2261 BAS99ATEX7285 MTL766Pac Ex92C2373 BAS01ATEX7202 Strain Gauges

MTL7166PacMTL7767+ No MTL7167+ Ex95C2261 BAS99ATEX7285 MTL767+ Ex832452 BAS01ATEX7202 Dual MTL715MTL7779+ No N/A N/A N/A MTL779+ Ex832452 BAS01ATEX7202 Dual MTL728MTL7787+/- Yes MTL7087+ Ex95C2261 BAS99ATEX7285 MTL787S+ Ex832452 BAS01ATEX7202 Analogue / Digital

MTL7187+MTL7787P+ Yes MTL7087P+ Ex95C2261 BAS99ATEX7285 MTL787SP+ Ex92C2373 BAS01ATEX7202 Analogue / Digital

MTL7187P+MTL7788+ Yes N/A N/A N/A MTL788+ Ex832452 BAS01ATEX7202 TransmittersMTL7788R+ Yes N/A N/A N/A MTL788R+ Ex832452 BAS01ATEX7202 1—5V systemsMTL7796+/- No MTL7096- Ex95C2261 BAS99ATEX7285 MTL796+/- Ex832452 BAS01ATEX7202 Vibration sensors

MTL7196-

CORRELATION BETWEEN MTL7700 — MTL7000 — MTL700 BARRIERS (IIC)

Note 3 : The circuit configuration for the output parameters givenin the table ‘Maximum Cable Parameters’ are as follows:-

a - Single channel barrier.a1 - First channel of a dual/triple channel barrier.a2 - Second channel of a dual/triple channel barrier.a3 - Third channel of a dual/triple channel barrier.b - Both channels of a dual channel barrier connected in

parallel, with respect to earth.b1 - Two channels of a triple channel barrier connected in

parallel, with respect to earth.b2 - Three channels of a triple channel barrier connected in

parallel, with respect to earth.b3 - Both channels of each switch input connected togetherc - Both channels of a dual channel barrier interconnected,

with no earth return.c1 - Two channels of a triple channel barrier interconnected,

with no earth return.c2 - Three channels of a triple channel barrier interconnected,

with no earth return. This assumes two of the channels arein parallel.

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

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 blue

ModelNo.

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

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

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<0.005% of maximum output per °C

Span temperature drift<0.005% of maximum output per °C

Supply current8 to 40mA + 10mA max. at 20V8 to 40mA + 20mA max. at 35V

ADDITIONAL SPECIFICATIONSupply voltage

20 to 35V dc, positive w.r.t. earthOutput current

4 to 20mAVoltage available for transmitter and lines

15V minimum at 20mA with 22V supply15.5V typical at 20mA with 24V supplyNote: voltages are negative w.r.t. earth

Load resistance250Ω ±5% (can be greater if reduced transmitter voltage is acceptable)

Accuracy±2µA under all conditions

Supply current35mA typical at 20mA with 24V supply40mA maximum at 20mA with 35V supply

MTL702+ for 2-wire 4/20mA transmitters(Discontinued April 2006)

The MTL702+ 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 highly accurate. Like all barriers, the MTL702+ willpass incoming communication signals of any frequency from a ‘smart’transmitter, but inherently it cannot pass any such signals in theoutgoing direction.

Since the MTL702+ has no return channel for energising the load, theentire output of the single ‘25V’ channel is available to power thetransmitter, providing high output capability. This channel is positivelypolarised, and the safe-area signal is derived from the current thatflows through it by means of a built-in ‘current-mirror’ amplifier, withunity current gain, which repeats the current in a separate circuit inthe safe area.

To prevent any leakage through the Zener diodes and maximise theoutput voltage available at 20mA, the voltage applied to the barriersection is held constant at a suitable reference value by a comparatoramplifier and regulator. A separate circuit limits the current to protectthe fuse in the event of a short circuit in the hazardous area.

With a 22V supply, the MTL702+ will deliver 14V at 20mA for thetransmitter and lines and a quite exceptional 17V for the load, bothvoltages being increased by 2V if the supply is at least 24V. Themaximum consumption in normal operation is 60mA.

BASIC CIRCUIT

OVERVOLT–PROTECTED BARRIERSThe MTL702+, 706+, 707+, 707P+ and 708+ have built-in overvoltprotection, allowing their use with unregulated power supplies. Inmany applications, eg, sensor inputs or controller outputs, there isinsufficient power available to blow the barrier fuse and thisadditional protection is not necessary. However, where the barrier isconnected to a power supply, eg, for energising transmitters, switches,solenoids or local alarms, overvolt protection allows the barriers to beused with unregulated supplies up to 35V dc and also gives protectionagainst faulty wiring during commissioning.

3

4

1

2

4/20mA 4/20mA

50mA

60mA max+35V max.

100mA

Regulate

Current

mirror

+V ref

50mA850Ωmax.

+

–Tx

0V

Hazardous area Safe area


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.


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 <26VLimited at 50mA, 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, Vs<25VLimited at 50mA, Vs>28V 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 <26VLimited at 50mA, Vs >28V or low load resistance


Currentlimit

50mA

50mA

1 mA maxI out

+35V max1

2

3

4


BASIC CIRCUIT


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

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.


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

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


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

+– Sense12V

12V

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

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


+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

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.


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


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

June 2004


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

*


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


*

+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


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)

June 2004

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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

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.

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.

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 (<16mm2, 6AWG)Small (<4mm2, 12AWG)Weight (without barriers) kg

MTL700 SERIESENCLOSURES(continued)

MT12 MT20N

Polycarbonate: glass-filled base, transparent lidDark-grey base Light-grey base Mid-grey painted

Sheet steel

Lift-off floppy hinges,4 captive screws,hasp for padlock

IEC529:IP65 IEC529:IP674x20mm holes pre-drilledthrough top and bottom

Top and bottom gland plates detachable for drilling by user

Zone 2BASEEFA certificate

No. Ex83453, Code: Ex N II T6,BS 4683: Part 3: 1972

Corner screws or plasticlugs screwed to base

2 lugs + attaching screws

Fixed mounting lugs

None

0 3 3 33 3 6 10

0.36 1.08 2.20 12.62

None

DIMENSIONS (mm)

Safe area

272

310

172

107

148

98 57

75

Ø6

60125

125*

25

157

198

198

157

175100175

150*

25*

Ø6MT5MT2

305

382

MT20N

475

HA

ZARD

OU

S AREA

WIRIN

G

SAFE A

REA W

IRING

407

ø10

170 150

173*

200 (MT12)

MT12

Fixing lugs for MT12On these models, the screw-on fixing lugs canbe positioned as shown.*Add 5mm to depth if fixing lugs are used.

MT12

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.

intrinsically safe barriers mtl7700 series …...din rail mounting safety barriers mtl7700 series...

Documents