Siemens SIMATIC ET 200S Manual page 500

Analog Electronic Modules
Compensation of thermocouples with a compensation unit
In addition to the error limits of the 2AI TC Standard electronic module (see
"Technical Specifications" table in this chapter), you must also consider the
precision of the compensation unit.
Compensation of thermocouples with a Pt100 on the 2AI RTD Standard
Factors that influence the precision of the temperature measurement
Rules for wiring
Supplementary technical
specifications for the error
li it limits of the 2A TC f th 2A TC
* This error can result in a greater measurement deviation when using thermocouples with
a very low rise of the thermocouple characteristic.
With the following thermocouples this results in a restriction of the input range of the
thermocouple for which the precision specifications of the manual apply:
Type N: --100 °C
Type K: --230 °C
Type E: --230 °C
12-94
Make sure that there is a good thermal contact between
the reference junction and the Pt100 used for
compensation.
We recommend wiring the Pt100 with a 4-wire connection.
The precision of the thermal resistor (Pt100) used for
compensation must be considered.*
The errors of the measuring input (2AI RTD Standard)
used for compensation must be considered*
ET 200S Distributed I/O System
EWA-4NEB 780602402-12