Siemens SIMATIC S7-400 Reference Manual page 304

Analog modules
5.25 Analog input module SM 431; AI 8 x 16 Bit (6ES7431-7KF00-0AB0)
Circuit diagram for SM 431; AI 8 x 16 bit
M0+
M0+
R0
M0-
Figure 5-38
Note
An external protective network for the signal lines is required in accordance with IEC 61000-4-5
(12 V Blitzductor, model CT919-506, connected in series with all inputs as recommended by
the manufacturer).
304
A/Dconverter
Internal
supply
CH0
CH1
CH2
CH3
CH4
CH5
CH6
CH7
Circuit diagram for SM 431; AI 8 x 16 bit
Backplane
bus interface
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
Bus S7-400