Siemens SIMATIC S7-300 Module data - Connecting Non-Isolated Sensors to a Non-Isolated AI

Analog Modules
4-49
Programmable Logic Controllers S7-300 Module Data
A5E00105505-03
When connecting non-isolated sensors to non-isolated modules, you can operate
the CPU only in Grounded mode.
Non-isolated
sensors
M+
M
L+
M–
M
ANA
M+
M–
Backplane
bus
M
internal
L+
M
Ground bus
CPU
ADC
U
CM
Equipotential
bonding
conductor
Logic
Figure 4-10 Connecting non-isolated sensors to a non-isolated AI
Note
You must not use non-isolated two-wire transmitters and non-isolated
resistance-type sensors with a non-isolated AI!