Siemens SIMATIC ET 200AL System Manual page 2114

Compensation options
Dynamic reference
temperature
No/external compensation
RTD (0)
Analog value processing
Function Manual, 06/2014, A5E03461439-AC
Explanation
Properties
With this type of compensation, the reference
junction temperature is determined using a
module. Transfer this temperature value to other
modules in the user program by means of a data
record.
Procedure
Wire the thermal resistor (RTD) for the reference
junction to any channel.
The reference junction temperature is transferred
with a function block by means of data records
from the CPU or IM to the module, see section
Compensation by means of dynamic reference
temperature (Page 94).
Properties
With this type of compensation, the reference
junction temperature is measured outside the
analog input module. You can, for example,
connect a compensating box to the thermocouple
for this purpose.
Procedure
Connect the compensating box with the
connection module of the analog input module
with copper cables, see section "None" or external
compensation (Page 98).
Properties
This compensation is based on a measurement of
the resistance value of a Pt1000 at the clamping
unit of a compensation connector or of an external
resistance value Pt1000.
Procedure
Additional information about the connection
options with and without compensation connector
is available in the section Type of compensation
RTD (0) (Page 100).
5.3 Compensation for the reference junction temperature
Use case / special feature
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Thermocouples
You are using multiple modules at
the reference junction and can
therefore compensate for all
channels using a common
temperature value.
You only need a thermal resistor
(RTD) or a thermocouple to
measure the temperature value.
The temperature of the reference
junction for this type of
compensation is specified as 0 °C.
This can be achieved by using a
compensating box. A separate
compensating box is required for
each thermocouple.
Thermocouples of type B do not
require a compensating box.
The reference junction temperature
is determined with resistance value
of the Pt1000.
All channels of the analog input
module that you select for this type
of compensation receive the same
reference junction temperature.
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