Siemens Simatic S7-400 - Manual (Page 275)

Analog Modules
5-59
S7-400, M7-400 Programmable Controllers Module Specifications
A5E00069467-07
5.13 Connecting Loads/Actuators to Analog Outputs
Introduction
You can use the analog output modules to supply loads and actuators with current
and voltage.
This section contains general information that is generally applicable to all the
connection options for loads and actuators described in the sections that follow.
Cables for Analog Signals
For the analog signals
,
you should use shielded and twisted pair cables. The cables
Q
V
and S+ and M and S–, respectively, are to be twisted together. This reduces the
interference . Ground the screen of the analog cables at both ends of the cables.
If there are potential differences between the cable ends, an equipotential
bonding current, which can flow over the shield, can cause interference of the
analog signals. In such a case, you should ground the shield at one end of the
cable only.
Isolated Analog Output Modules
With the isolated analog output modules there is no electrical connection between
the reference point of the measuring circuit M
ANA
and chassis ground.
You must use isolated analog output modules if a potential difference U
ISO
can
occur between the reference point of the measuring circuit M
ANA
and chassis
ground. By means of an equipotential bonding conductor between the M
ANA
terminal and chassis ground, make sure that U
ISO
does not exceed the permitted
value.