Siemens S7-400PLC Spécifications Page 221

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Analog modules
5.9 Connecting sensors to analog inputs
S7-400 Automation System Module Data
Reference Manual, Edition 09/2009, A5E00850736-06
221
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.
To ensure that the permissible value for U
CM
is not exceeded during use in heavily EMC-
affected environments, connect M- to MANA in modules with an M
ANA
connection.
1
2
3
M+
M-
U
ISO
M+
M-
M
ANA
(1) Electrically isolated sensors
(2) Chassis ground
(3) Connection required for modules with M
ANA
M +: Measuring line (positive)
M -: Measuring line (negative)
M
ANA
: Reference potential of the analog measuring circuit
U
ISO
: Potential difference between M
ANA
and chassis ground
Figure 5-5 Connecting isolated sensors to an electrically isolated AI
NOTICE
Do not connect M- to MANA when connecting 2-wire transducers for current measurement
and when connecting resistance-type sensors. This also applies to inputs which are
programmed accordingly, but remain unused.
Non-isolated sensors
The isolated sensors are not connected with the local ground potential (chassis ground).
When using non-isolated sensors, you must connect M
ANA
to chassis ground.
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