Siemens SIMATIC ET 200AL, System Manual

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Thermocouples
5.3 Compensation for the reference junction temperature
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
81
5.3 Compensation for the reference junction temperature
5.3.1 Overview
Introduction
You have several options for measuring the reference junction temperature in order to obtain
a correct temperature value as a function of the temperature difference between the
reference junction and the measuring point.
You have various compensation options to suit requirements at the location of the reference
junction.
The compensation options supported by the analog module used are specified in the manual
of the respective module.
Options of compensating for the reference junction temperature
Table 5- 1 Compensation options: Explanation and use case
Compensation options Explanation Use case / special feature
Internal reference junction Function principle
With this type of compensation, the temperature of
the reference junction is measured using an
integrated sensor in the analog module.
Procedure
Connect the thermocouple to the I/O module
directly, or with compensating lines; see chapter
Compensation with internal reference junction
(Page 84).
• For the connection, use
compensating lines that match the
thermocouple material.
•
If the reference junction
temperature and the module
temperature are identical in your
system, you may also use lines
made from a different material.
• Advantages:
–
Inexpensive
– No external reference junction
required
– No additional wiring required