Connecting Sensors To Analog Inputs - Siemens SIMATIC S7-400 Reference Manual

Analog modules

5.9 Connecting sensors to analog inputs

5.9 Connecting sensors to analog inputs
Introduction
The analog input modules support various sensors, such as voltage/current sensors, and
resistors, depending on the set measuring method.
This section contains general information that is generally applicable to all the connection
options for sensors described in the sections that follow.
Cables for analog signals
Always use shielded twisted-pair cables to wire analog signals. This reduces interference.
Connect both ends of the analog cable shield to ground.
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. To avoid this
situation, you should ground the shield only at one end of the cable.
Non-isolated analog input modules
In the case of the non-isolated analog input modules there is an electrical connection between
the reference point of the measuring circuit M
You use non-isolated analog modules if there are few or no potential differences between the
measuring sensors and chassis ground.
Isolated analog input modules
With the isolated analog input modules there is no electrical connection between the reference
point of the measuring circuit M
You use isolated analog input modules if a potential difference U
reference point of the measuring circuit M
bonding conductor between the M
not exceed the permitted value.
Limited potential difference U
Only a limited potential difference U
measuring lines of the input channels and between the leads and the reference point of the
measuring circuit M
must take different actions, described below, depending on the potential connection of the
sensors.
Connecting electrically isolated sensors
The isolated sensors are not connected with the local ground potential (chassis ground). They
can be floating.
With isolated sensors, potential differences might arise between the different sensors. These
potential differences can arise as a result of interference or the local distribution of the sensors.
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and chassis ground.
ANA
ANA
CM
CM
. In order to prevent the permissible value from being exceeded, you
ANA
and chassis ground.
ANA
and chassis ground. By means of an equipotential
ANA
terminal and chassis ground, make sure that U
(common mode voltage) may occur amongst the M-
S7-400 Automation System Module Data
Reference Manual, Ausgabe 11/2016, A5E00850736-08
can occur between the
ISO
does
ISO