Analog electronic modules
4.3 Basics of Analog Value Processing
ET 200S
4-18
Manual, Edition 10/2005, A5E00514527-01
4.3.2
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 4-25 Compensation of the reference junction temperature
Option
Description
Reference junction parameters
No compensation
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.
None
Use of a compensating
box on the incoming lines
of a single thermocouple
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.
None
Use of a Pt 100 Climatic
Range resistance
thermometer to record the
reference junction
temperature (best method)
You can record the reference junction
temperature using a resistance thermometer
(Pt 100 Climatic Range). Given appropriate
parameter assignment, this temperature value in
the ET 200S is distributed to the 2AI TC Standard
modules and calculated in the modules together
with the temperature value obtained for the
measurement point.
Number of reference junctions: 1
The parameter assignment of the IM151-1
and the 2AI TC must be coordinated:
•
2AI RTD Standard assigned
parameters to the Pt 100 climatic
range at the correct slot;
•
2AI TC Standard: Reference junction :
RTD; select reference junction number
1
•
IM : Assignment of the reference
junction to a slot with the 2AI RTD
Standard; selection of a channel;
Internal compensation in
the case of the 2AI TC
High Feature
There is a temperature sensor in the
TM-E15S24-AT and TM-E15C24-AT terminal
modules. The temperature sensor reports the
temperature of the terminals to the 2AI TC High
Feature. This value is then calculated together
with the measured value from the channel of the
electronic module.
•
2AI TC High Feature:
Reference junction: Yes