Siemens SIMATIC S7-300 Manual page 252

Analog modules
6.4 Analog input module SM 331; AI 8 x 16 Bit; (6ES7331-7NF10-0AB0)
Wiring: Voltage and current measurement
Connection possible at both ends at channels 0 to channel 7
Figure 6-3 Wiring and block diagrams
①
②
Wiring: 2 and 4-wire measuring transducer
Wiring possible at both ends at channel 0 to channel 7
6-18
Connection for voltage measurement
Potential compensation
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04