The analog-input multiplexer system

The MTL838C is an analog multiplexer receiver that is used with the MTL831C

hazardous area millivolt input multiplexer transmitter. The status of up to 32 analog

inputs may be communicated from the hazardous area to the safe area via a data

highway, comprised of a simple twisted pair – over distances up to 2km.

Each data highway must be protected by an MTL5553/5053 digital isolator when

the inputs are located in a Zone 0 or 1 hazardous area.  The MTL831C is typically

used with thermocouple and RTD inputs and is intrinsically safe.  It can be mounted

in a Zone 0 or 1 hazardous area and will accept 16 inputs.  For systems that do not

require Zone 0 or Zone 1 installation, the MTL5553/5053 can be eliminated.

Up to two MTL831C transmitters can be combined on a single MTL838C receiver

input – up to a total of 32 analog inputs – as shown in Figure 1.

The MTL838C acts as a Modbus slave . It may be connected into any standard

Modbus network, with up to 31 MTL838C slaves on each network.  If each unit has

its full complement of 32 analog inputs, the status of a total of 992 analog inputs

may be passed to a Modbus master using a single RS485 network.