Siemens S5-135U/155U - Manual (Page 399)

9-17
System Manual
C79000-G8576-C199-06
9.3.8 Connection of Sensors
Observe the following information when connecting the sensors.
With isolated sensors, it is possible for the measuring circuit to develop a
potential with respect to ground which exceeds the permissible potential
difference U
<M>CM
(see maximum values of the individual modules). To
prevent this, you must connect the negative potential of the sensor to the
reference potential of the module (0 V bus).
Example:
Temperature measurement on a busbar with insulated thermocouples
In the worst case, the measuring circuit can develop an excessively high
potential on account of a static charge or contact resistances. This must be
prevented with an equipotential bonding conductor.
The permissible potential difference (U
CM
) between the inputs and the 0 V
bus must not be exceeded.
Depending on the system or type of sensor, the potential difference must be
kept in the permissible region with epuipotential bonding.
Equipotential Bonding Conductor
0 V Bus
+
–
U
E
A
D
Analog Input Module
Sensor, Isolated
MUX
M+
M–
#
Range
Card for
4 Inputs
Figure 9-6 Measuring Circuit with Equipotential Bonding Conductor for the 460 Analog Input Module
Connection of
Current or Voltage
Sensors
Equipotential
Bonding
Analog Input/Output Modules