Eaton Analogue Input Modules with passive input for 4-wire transmitters

INTRODUCTION

Application and function

The Analogue Input module types MTLx541A/MTLx541AS (single channel) and MTLx544A/MTLx544AS

(dual channel) are intrinsic safety isolators that interface with process measurement transmitters located in

a hazardous area of a process plant. They are also designed and assessed according to IEC 61508 for use in

safety instrumented systems up to SIL 2.

The MTLx541A provides an input for a separately-powered 4/20mA transmitter located in a hazardous

area, and repeats the transmitter current into a load in the safe area. The MTLx544A supports two identical

channels for use with two separate transmitters. The MTLx541AS and MTLx544AS versions act as a current

sink for the safe area connection rather than driving the current into the load.

All the modules allow bi–directional transmission of HART communication signals superimposed on the

4/20mA loop current, so that the transmitter can be interrogated either from the operator station or by a hand

held communicator (HHC).

There are no configuration switches or operator controls to be set on the modules. These modules are

members of the MTL4500 and MTL5500 range of products.

Variant Description

Functionally the MTL4500 and MTL5500 range of modules are the same but differ in the following way:

- the MTL4500 modules are designed for backplane mounted applications

- the MTL5500 modules are designed for DIN-rail mounting.

In both models the hazardous area field-wiring connections (terminals 1.2. and optionally 4.5) are made through

the removable blue connectors, but the safe area and power connections for the MTL454xA/MTL454xAS

modules are made through the connector on the base, while the MTL554xA/MTL554xAS modules use the

removable grey connectors on the top and side of the module.

Note that the safe-area connection terminal numbers differ between the backplane and the DIN-rail

mounting models.

Note: To avoid repetition, further use of MTLx54xA and MTLx54xAS in this document can be understood to

include both DIN-rail and backplane models. Individual model numbers will be used only where there is a need

to distinguish between them.

All the module types described in this manual have the same connectivity for the field signals, supporting

4-wire process transmitters or currents sourced in the hazardous area. The connection of the repeated current

signals into the input measurement channels for the safety logic system follows the arrangement shown in the

following diagram. When the input channels of the Safety Instrumented System (SIS) are providing power for

the loop, the ‘S’ variants of the isolator modules are used to ‘sink’ the measuring current.

In the other cases the isolator modules ‘source’ the measuring current that flows into a load resistor inside the

input card of the Safety Instrumented System.