Siemens Simatic S7-400 - Manual (Page 261)

Analog Modules
5-45
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
Non-Isolated Sensors
The non-isolated sensors are connected with the local ground potential (local
ground). When using non-isolated sensors, you must connect M
ANA
to chassis
ground.
Connecting Non-Isolated Sensors
Caused by local conditions or interference, potential differences U
CM
(static or
dynamic) can occur between the locally distributed individual measuring points. If
the potential difference U
CM
exceeds the permissible value, you must provide
equipotential bonding conductors between the measuring points.
M+
M–
U
ISO
M+
M–
M
ANA
Chassis ground
Non-isolated
sensors
U
CM
Equipotential
bonding conductor
Figure 5-8 Connecting Non-Isolated Sensors to an Isolated AI
Note
Do not use non-isolated two-wire transmitters and non-isolated resistance sensors!