Siemens SIMATIC Manual page 341

Wiring: Voltage measurement
①
Voltage measurement: (± 5V, ± 10V, 1 ... 5V, 0...10V)
②
Voltage measurement (± 50 mV, ± 500 mV, ± 1 V) (note the input resistance defined in the technical data)
③
Equipotential bonding
④
Internal supply
⑤
+ 5 V from backplane bus
⑥
Logic and backplane bus interface
⑦
Electrical isolation
⑧
Multiplexer
⑨
Analog to Digital Converter (ADC)
⑩
Current source
Figure 6-10 Block diagram and terminal diagram
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
6.6 Analog input module SM 331; AI 8 x 13 Bit; (6ES7331-1KF02-0AB0)
Analog modules
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