Siemens SIMATIC Manual page 342

Analog modules
6.6 Analog input module SM 331; AI 8 x 13 Bit; (6ES7331-1KF02-0AB0)
Wiring: 2-wire and 4-wire transducers for current measurement
①
②
③
④
⑤
⑥
⑦
⑧
⑨
⑩
Figure 6-11
342
4-wire transducer (0/4 mA to 20 mA or ± 20 mA)
2-wire transducer (4 mA to 20 mA)
Equipotential bonding
Internal supply
+ 5 V from backplane bus
Logic and backplane bus interface
Electrical isolation
Multiplexer
Analog to Digital Converter (ADC)
Current source
Block diagram and wiring diagram
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ