Siemens SIMATIC S7-400 Reference Manual page 250

Analog modules
5.20 Analog input module SM 431; AI 8 x 14 Bit (6ES7431-1KF10-0AB0)
Circuit variants for the channels
Two channels are set in each case with the measuring range module. There are therefore
restrictions as regards the measuring method for the adjacent channels 0/1, 2/3, 4/5 and 6/7,
as shown in the following table:
Table 5-49 Selection of the measuring method for channel n and channel n+1 of the SM 431; AI 8 x 14 Bit
(6ES7431-1KF10-0AB0)
Measuring method, Measuring method, channel n + 1
channel n
Disabled x
Voltage x
Current 4-wire trans‐ x
ducer
Current 2-wire trans‐ x
ducer
4-wire x
resistor
3-wire x
resistor
Four-wire thermal re‐ x
sistor
3-wire thermal x
resistor
Thermocouples x
Example
If you select "current (2-wire transducer)" for channel 6, you can only disable the measuring
method or set "current (2-wire transducer)" for channel 7.
250
Deacti‐ Voltage Current
vated 4-DMU
x x
x
x
x
Current R-4L R-3L
2-DMU
x
x
Reference Manual, Ausgabe 11/2016, A5E00850736-08
RTD-4L RTD-3L
S7-400 Automation System Module Data
TC-L
x
x
x