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Choosing a barrier

The MTL7700 range, with their advanced features, should be regarded as your first choice for all new designs or installations. The recommendations below are based therefore on the MTL7700 range.

Users of MTL700, 4700 or 7000 range can also use the guide because of our consistent numbering policy. Products, in any barrier range, that have the same two last digits (ignoring letters and ‘+’ symbols) will have very similar characteristics, e.g. MTL7787 and MTL787.

Click for alternatives to earlier barrier models
Analogue Inputs (high level)
  • 2-wire transmitters, 4-20mA conventional and ‘smart’
  • vibration probes
  • gas detectors
    		•
    Analogue Inputs (low level)
  • thermocouples and mV sources
  • ac sensors, photocells, microphones & flowmeters
  • slidewire displacement transducers
  • 2, 3 and 4-wire RTDs
  • strain-gauge bridges - single
  • strain-gauge bridges - double
    		•
    Analogue Outputs
  • controller outputs (I/P converters)
    		•
    Digital (ON/OFF) Inputs
  • switches
  • proximity detectors/switches
    		•
    Digital (ON/OFF) Outputs
  • alarms, LEDs, solenoid valves, etc.
    		•
    Digital (ON/OFF) Input/Output
  • -ve/floating supply
    		•
    AC/DC systems
  • 2-wire dc/ac systems and signal returns
    		•

    Analogue Input - 2-wire transmitters, 4-20mA conventional and ‘smart’
    Power Supply Barrier
    Loops
    Voltage for Tx
    and lines
    		 Main features
    Regulated MTL7787+

    1
    12.4V
    		 Compatible with most smart Tx’s
    MTL7787P+ 1 13.1V Higher power, IIC gases
    MTL7788R+ 1 13.7V 1-5V safe area ouput
    Unregulated
    20 to 35V    		 MTL7706+
    1
    15.5V
    (250ohm load)
    		 High accuracy; compatible with most smart transmitters; full output voltage
    available independently of supply voltage
    MTL7707P+ 1 13.0V Higher power, IIB gases

    Analogue Input - vibration probes
    Power Supply Barrier
    Loops
    		Main features
    Regulated MTL7796– 1 For –24V systems

    Analogue Input - gas detectors
    Power Supply Barrier
    Loops
    		Main features
    Nominal 6V supplies MTL7758+ 1 For high current/low voltage
    MTL7758+ Vwkg = 6.0V

    Analogue Input - thermocouple & mV sources
    Power Supply Barrier
    Loops
    		Max end to enc
    resistance
    per loop    		 Main features
    Earth-free signal, receiver
    input floating    		 MTL7760ac 1 150 ohm –
    Moving coil or low resistance receivers MTL7755ac 1 38 ohm –

    Analogue Input - ac sensors, photocells, microphones & flowmeters
    Power Supply Barrier
    Loops
    		Max end to enc
    resistance
    per loop    		 Main features
    Earth-free signals up to
    a few kHz    		 MTL7760ac 1 150 ohm –

    Analogue Input - slidewire displacement transducers
    Power Supply Barrier
    Loops
    		Vwkg Main features
    For nominal
    6V supplies    		 MTL7760ac 1 6.0V –

    Analogue Input - 2, 3 and 4-wire RTDs
    Power Supply Barrier
    Loops
    		Main features
    2-wire MTL7755ac

    1

    		 2 channels track to 0.15 ohm
    3-wire MTL7755ac 2/3 End-to-end resistance 19 ohm/channel
    MTL7756ac 1 End-to-end resistance 19 ohm/channel
    4-wire MTL7755ac
    1/2
    		 Needs 2 barriers
    MTL7760ac 1/2 Vwkg = 6V; needs 2 barriers
    MTL7761ac 1/2 Vwkg = 6V; needs 2 barriers

    Analogue Input - strain-gauge bridges (single)
    Power Supply Barrier
    Loops
    		Volts for 350 ohm bridge
    IIC gases MTL7761ac (2) +
    MTL7764ac (1)    		 1 9.75V from MTL7766Pac with 20V supply

    Analogue Input - strain-gauge bridges (multiple)
    Power Supply Barrier
    Loops
    		Volts for 350 ohm bridge (20V in)
    Number of bridges
    1…..........2….......3….........4
    IIC gases MTL7761ac (2) +
    MTL7766ac (1)    		 1 13.0….....9.2…....7.7…......6,2

    Analogue Output - controller outputs (I/P converters)
    Power Supply Barrier
    Loops
    		Volt drop
    at 20mA    		 Main features
    Output goes to 0V (earth return); regulated supplies MTL7728+

    1

    		 6.8V –
    MTL7728P+ 1 5.1V Higher power, IIC gases
    MTL7729P+ 1 3.7V Higher power, IIB gases
    Transistor between controller output and 0V; (diode return); regulated supplies MTL7787+ 1 8.1V –
    MTL7787P+ 1 6.4V Higher power, IIC gases
    Transistor between controller output and 0V; (diode return); unregulated supplies (20 to 35V) MTL7707+
    1
    		 8.6V –
    MTL7707P 1 6.0V Higher power, IIC gases

    Digital Input - switches
    Power Supply Barrier
    Loops
    		Main features
    Regulated MTL7787+ 1 Diode return
    MTL7787P+ 1
    MTL7789+ 2

    Digital Input - switches / proximity detectors
    Power Supply Barrier
    Loops
    		Main features
    Unregulated 22-35V MTL7741 1 Changeover relay output
    MTL7742 1 Transistor output, fast switching
    MTL7743 2 2 x relay contacts
    MTL7744 2 2 x transistor output
    MTL7745 1 Single channel relay + LFD

    Digital Output - alarms, LEDs, solenoid valves, etc
    Power Supply Barrier
    Loops
    		Usable power per loop Main features
    Switch in power leg, (earth return); regulated supplies MTL7728+

    1

    		 0.48W –
    MTL7728P+ 1 0.59W Higher power, IIC gases
    Voltage drop = 5.1V at 20mA
    MTL7729P+ 1 0.82W Higher power, IIB gases
    Control switch on earth (diode return); regulated supplies MTL7787+ 1 0.42W –
    MTL7787P+ 1 0.51W Higher power, IIC gases
    Transistor between controller output and 0V; (diode return); unregulated supplies (20 to 35V) MTL7707+
    1
    		 0.29W Up to 35mA available
    MTL7707P+ 1 0.68W Optimised for IIB gases

    Digital Input/Output - –ve and floating supplies
    Power Supply Barrier
    Loops
    		Volts for 350 ohm bridge
    Regulated negative/floating
    power supply    		 MTL7728– 1 –

    2-wire DC/AC systems - signal returns
    System or Function Barrier
    Loops
    		Vwkg Main features
    6V dc systems MTL7710+

    1

    		 6.0V –
    Low-level logic returns MTL7764+ 2 10.0V End-to-end resistance 1050 ohms
    12V dc systems MTL7715+ 1 12.0V –
    MTL7715P+ 1 12.6V –
    18V dc systems MTL7722+ 1 19.6V –
    2-wire dc/ac systems MTL7778ac 1 24.0V –
    Signal returns MTL7789+
    2
    		 26.6V 2 diode return channels + power
    Securing cables to earth for future use; terminating cable screens MTL7799 – – Bussed power feed - not certified