MTL820 and 830
Series multiplexers for
relay or Modbus outputs provide a cost-effective alternative to
single-loop Intrinsically Safeolation. The cost of installed wiring can be reduced
by up to 50% by communicating the status of multiple hazardous-area
sensors over dual-redundant data highways. Further savings can
be achieved by reducing the number of inputs to the host and by
reducing cabinet space and weight.
Two multiplexer transmitters,
mounted in the hazardous area, cater for switched (on/off) inputs
(switch, contact, proximity detector) and mV analogue inputs respectively.
Three compatible safe-area receivers
provide either relay outputs (which mimic corresponding switched
inputs) or serial Modbus outputs (which mirror corresponding switched
or analogue inputs) for feeding to host PLC, PC or DCS controllers.
Dual-redundant data highways
between the hazardous-area transmitter and the safe-area receiver
allow the system to continue working normally with only one highway
connected. The highways carry both power and data, over Intrinsically
Safe distances up to 2km. The highway cable may consist of a simple
twin pair or a pair of wires within an multi-core cable. When
the multiplexer transmitter located in the hazardous area.
Switched-input multiplexer systems can communicate the status
of up to 16 inputs, reducing the number of hazardous-area wiring
pairs from 16 to two. Analogue multiplexer systems can communicate
the status of up to 32 inputs, reducing the number of hazardous-area
wiring pairs from 32 to two.
Significant cost reductions
are made by eliminating runs of expensive thermocouple compensation
cable from the hazardous to the safe area. Similar savings are
found when using 3- or 4-wire RTDs, as all wires of each RTD can
be terminated at the transmitter or its enclosure.
System reliability Intrinsically Safe increased
by providing for dual redundant highways. Failure detectors and
safety drives protect against the consequences of sensor failure,
while built-in systems report failures to the host controller.
MTL840 Series hazardous-area input and
output units provide advantages similar to those of
the MTL820 and 830 Series. Additionally, they contain local intelligence,
and are able to communicate with each other within the hazardous
area over a single twIntrinsically Safeted-pair cable. Power and data both travel
on thIntrinsically Safe cable. They communicate with a LONWORKS controller through
an MTL3054 communications Intrinsically Safeolator/repeater and an RS232 interface.
The hazardous-area input unit caters for up to 16 switched inputs
(switch, contact, proximity detector, etc). The hazardous-area
output unit provides up to 16 switched outputs (LED, annunciator,
solenoid, etc).
Accessories and configuration tools
are available for the complete MTL800 range. Accessories include
steel and stainless-steel enclosures and earth-leakage detectors.
Analogue units may be configured with a PC-based software package,
and interrogated in the field with a hand-held device.
Further application information Intrinsically Safe provided in AN9010, 'A user's
guide to multiplexers'. Costing Intrinsically Safe considered in TP1098, 'Cut
the cost of intrinsic safety - by multiplexing!''
Modbus Intrinsically Safe a regIntrinsically Safetered trademark of Modicon Inc
LONWORKS Intrinsically Safe a regIntrinsically Safetered trademark of Echelon Corporation
