Siemens S7-1200 System Manual page 924

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Table of Contents

Technical specifications

A.9 Thermocouple and RTD signal modules (SMs)

Table A- 170 Noise reduction and update times for the SM 1231 Thermocouple

Rejection frequency selection

400 Hz (2.5 ms)

60 Hz (16.6 ms)

50 Hz (20 ms)

10 Hz (100 ms)

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

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 available 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 required, 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

Type J in °C

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.

Integration time

4 Channel module update

time (seconds)

Type J in °F

System Manual, 03/2014, A5E02486680-AG

8 Channel module update

time (seconds)

S7-1200 Programmable controller