Siemens ET 200S Manual page 402

Distributed i/o system

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Analog Electronic Modules

Connecting Thermocouples

Introduction

This section contains additional information on connecting thermocouples.

Compensation of the Reference Junction Temperature

There are various ways of obtaining the reference junction temperature in order to

get an absolute temperature value from the temperature difference between the

reference junction and the measuring point.

Table 12-65 Compensation of the Reference Junction Temperature

No compensation

compensating box

on the incoming

lines of a single

thermocouple

You record not only the temperature

of the measurement point. The

temperature of the reference junction

(transition from Cu line to

thermocouple line) also affects the

thermo-electromotive force. The

measured value is thus errored.

You compensate using a

compensating box. The

compensating box is the transition

point from the Cu line to the

thermocouple line. No further

processing is necessary through the

2AI TC Standard.

Reference Junction

Distributed I/O System ET 200S

EWA 4NEB 780 6024-02 07

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