Fundamentals Of Analog Value Processing; Wiring Thermocouples - Siemens SIMATIC ET 200iSP Operating Instructions Manual

Analog electronic modules

14.9 Fundamentals of analog value processing

14.9 Fundamentals of analog value processing
14.9.1

Wiring 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 14-29
No compensation
Use of a Pt100 Climat‐
ic Range resistance
thermometer to re‐
cord the reference
junction temperature
(best method)
Internal compensa‐
tion 4 AI TC
386
Compensation of the reference junction temperature
Option
You record not only the temperature of
the measurement point. The tempera‐
ture of the reference junction (transition
from Cu line to thermocouple line) also
affects the thermo-electromotive force.
The measured value then includes an er‐
ror.
You can record the reference junction
temperature using a resistance ther‐
mometer (Pt100 climatic range). This
temperature value is distributed to the
ET 200iSP modules in the 4 AI TC with
corresponding parameter assignment
and offset in the modules with the deter‐
mined temperature value of the measur‐
ing point.
Number of reference junctions: 2
The TC sensor module (temperature sen‐
sor) is mounted on the terminals of the
terminal module of the EM 4 AI TC. The
temperature sensor reports the terminal
temperature to the 4 AI TC. This value is
then calculated together with the meas‐
ured value from the channel of the elec‐
tronic module.
Explanation
Operating Instructions, 11/2022, A5E00247483-AK
Reference junction parameters
None
The parameter assignment of the in‐
terface module and the 4 AI TC must
be coordinated:
• 4 AI RTD parameterized to Pt100
climatic range at the correct slot;
• 4 AI TC: Reference junction: "yes";
reference junction number "1" or
"2"
• Interface module: Assignment of
the reference junction to a slot
with 4 AI RTD; selection of a chan‐
nel;
• 4 AI TC: Reference junction num‐
ber "internal"
ET 200iSP