Siemens SIMATIC Manual page 319

Wiring: Voltage and current measurement
Connection possible at both sides to channels 0 to 7
①
Connection for voltage measurement
②
Equipotential bonding
Figure 6-3 Wiring and block diagram
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
6.4 Analog input module SM 331; AI 8 x 16 Bit; (6ES7331-7NF10-0AB0)
Analog modules
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