Technical specifications
A.11 Thermocouple and RTD signal modules (SMs)
S7-1200 Programmable controller
1478 System Manual, V4.2, 09/2016, A5E02486680-AK
Table A- 170 Noise reduction and update times for the SM 1231 Thermocouple
Rejection frequency selection
4 Channel module update
time (seconds)
8 Channel module update
time (seconds)
1
60 Hz (16.6 ms) 16.67 ms 0.223 0.445
To maintain module resolution and accuracy when 400 Hz rejection is selected, the integration time is 10 ms. This
selection also rejects 100 Hz and 200 Hz noise.
It is recommended for measuring thermocouples that a 100 ms integration time be used. The
use of smaller integration times will increase the repeatability error of the temperature
readings.
Note
After power is applied, the module performs internal calibration for the analog
-to-digital
converter. During this time the module reports a value of 32767 on each channel until valid
data is av
ailable on that channel. Your user program may need to allow for this initialization
time. Because the configuration of the module can vary the length of the initialization time,
you should verify the behavior of the module in your configuration. If requir
ed, you can
include logic in your user program to accommodate the initialization time of the module.
Representation of analog values for Thermocouple Type J
A representation of the analog values of thermocouples type J is shown in the table below.
Table A- 171 Representation of analog values of thermocouples type J
1450.0
:
14500
:
38A4
:
2642.0
:
26420
:
6734
:
Overrange
1200.0
:
12000
:
2EE0
:
2192.0
:
21920
:
55A0
:
Rated range
< -150.0 -32768 8000 < -238.0 -32768 8000 Underflow
1
1
Faulty wiring (for example, polarity reversal, or open inputs) or sensor error in the negative
range (for example, wrong type of thermocouple) may cause the thermocouple module to
signal underflow.
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