Siemens SIMATIC S7-400 Reference Manual page 289

Circuit for resistance and temperature measurement
The following conditions apply when measuring the resistance and temperature with the SM
431; AI 16 x 16 Bit:
Table 5-64 Channels for resistance and temperature measurement of the SM 431; AI 16 x 16 Bit
Measuring type parameter
Resistance
(4-conductor connection)
Resistance
(3-conductor connection)
Thermal resistance
(linear, 4-wire connection)
Thermal resistance
(linear, 3-wire connection)
Thermocouple (linear)
Circuit for reference junction compensation for thermocouples
If you select "RTD on Channel 0" as a reference junction for reference junction compensation
for thermocouples, the following applies:
Table 5-65 Reference junction compensation via RTD on channel 0 of the SM 431; AI 16 x 16 Bit
Reference junction parameters
RTD on Channel 0
Unused channels
Unused channels can be left open. Set the measuring range modules to position "A". You can
improve the noise immunity of the module in a measuring environment with serious
interference by short-circuiting the channels.
For unused channels, set the "measuring method" parameter to "deactivated". This reduces
the module's cycle time.
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
5.23 Analog input module SM 431; AI 16 x 16 Bit (6ES7431-7QH00-0AB0)
Permissible for
channel n
0, 2, 4, 6, 8, 10, 12 You must disable the "Measuring type" parameter for channels
or 14 n+1 (1, 3, 5, 7, 9, 11, 13, 15).
0, 2, 4, 6, 8, 10, 12 Reason: The connections of channel n+1 are used to supply the
resistance that is connected to channel n.
or 14
0, 2, 4, 6, 8, 10, 12
or 14
0, 2, 4, 6, 8, 10, 12
or 14
0 to 15 You can select the reference junction. It is only advisable to
specify a reference junction with thermocouples.
Permissible for channel n
2 to 15
Condition
Condition
You must connect and configure on channel 0 a
resistance thermometer with linearization, a 3- or
4-conductor connection in climatic range. This
means that channels 0 and 1 are assigned.
Reason: If channel 0 is to be used as the refer‐
ence junction, a resistance-type sensor must be
connected there to record absolute temperatures
in the climatic range.
Analog modules
289