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Reduce the cost of installing
hazardous-area cabling
Save installation time, space and
Highlight problems quickly with
status reporting systems
Protect the process with sensor

failure detection and safety drives

Connect directly to host systems
through serial-data outputs
Analogue inputs to controllers with
Modbus® communications
Redundant data highways

MTL830 Series multiplexers with Modbus®
outputs provide a cost-effective alternative to singleloop
isolation. The cost of installed wiring is reduced
by up to 50% by communicating the input of multiple
hazardous-area sensors over dual-redundant data
highways. Further savings are achieved by reducing
the number of inputs to the host, cabinet space and

A multiplexer transmitter, mounted in the
hazardous area, caters for thermocouple, RTD and
mV analogue inputs. A compatible safe-area receiver
provides serial Modbus® outputs for feeding to host
PLC, PC or DCS controllers.

Dual-redundant data highways between the
transmitter and the receiver allow continuous normal
operation with only one highway connected. The
highway cable, a simple twisted pair or a pair of
wires within an IS multi-core cable, carries both
power and data, over distances up to 2km. If the
multiplexer transmitter is located in the hazardous
area, each data highway must be protected by an
MTL3052 digital isolator.

Multiplexer systems can communicate the status
of up to 32 inputs, reducing the number of hazardous
area wiring pairs from 32 to two.

Reduce costs by eliminating long runs of expensive
thermocouple compensation cable from the hazardous
to the safe area. AIso, if 3- or 4-wire RTDs are used,
costs are reduced by terminating each RTD at the
transmitter or its enclosure.

Dual redundant highways increase system
reliability. Failure detectors and safety drives protect
against the consequences of sensor failure, while
built-in systems report failures to the host controller.
Accessories include steel and stainless-steel
enclosures, earth-leakage detectors and a PC-based
configuration software package.

For more information see AN9010, ‘A user’s guide
to multiplexers’ and TP1098, ‘Cut the cost of intrinsic
safety – by multiplexing!’






MTL831B multiplexer transmitters are normally sited in the hazardous

area. They are connected to sensors in the field and communicate

these inputs to the safe area via single-pair data highways. The data

highways support communication between the safe and hazardous

areas,and also provide power to the transmitters – no additional field

power is required.

The MTL831B would typically be mounted close to the field instruments

in an enclosure such as the ENC8 or ENC83 (see ‘MTL800 Series



Monitors inputs from up to 16 THC or millivolt sources (max ±۶۰mV)

or up to 15 2-, 3- or 4-wire RTDs within a hazardous area.

Intrinsically safe; Zone 0 location

Communication and power pass over twin data highways

Powered by the data highway

Thermocouples and RTDs may be mixed on one transmitter


Two MTL831B multiplexer transmitters can share the same singlepair

highway to a single safe-area isolator/receiver combination,

providing up to 32 multiplexed inputs.


Cabling with low capacitance and resistance is recommended to

achieve greater distances between transmitters and receivers. See

cable parameters in ‘Basic Specifications’ for specific requirements,

and contact MTL for latest cable recommendations. The system is

designed to use both data highways, although it can be used with

only one data highway in place. However, use of a single highway

will increase response time.

Data highway lengths of up to 2km in hazardous areas and 3km in

safe areas have been achieved.


A range of steel and stainless steel enclosures is available for

mounting MTL831B units in the field (see ‘MTL800 Series Enclosures’).

ENC8 and ENC8SS (stainless steel) enclosures provide protection for

a single MTL831B. The enclosures are dust-tight and waterproof to


When using 4-wire RTDs, ENC83 and ENC83SS (stainless steel)

enclosures provide additional terminals to accommodate the third

and fourth RTD wires, which are not connected to the MTL831B


MTL838B-MBF receivers translate the information transmitted from

the MTL831B via the data highway. The MTL838B-MBF provides a

Modbus® serial-data output representation of the inputs together with

status information.


Translates data received from the MTL831B in the hazardous

area and makes it available as twin RS485 Modbus® serial data

outputs. The MTL838B-MBF is configured by personal computer for

thermocouple and RTD type, safety drive, high and low alarm and

any other operational parameters.


An MTL3052 isolator is required for each data highway, when the

transmitter is located in a hazardous area. It is not required for safearea



Up to 31 Modbus receivers can be multi-dropped on a single RS485

link to the host system. Modbus® receivers can be controlled by any

suitable Modbus® master. The receivers may be used with other

Modbus® slaves on the same RS485 link.

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