Siemens SIMATIC ET 200S - Operating 4-wire measuring transducers (MU) at external power supply

Analog Electronic Modules
12-20
ET 200S Distributed I/O System
EWA-4NEB 780602402-12
Non -isolated sensors
The non-isolated sensors are locally connected to the ground potential. M
ANA
must
be connected to the ground potential. Depending on local conditions or
interference potential differences U
CM
(static or dynamic) may be encountered
between the locally distributed measuring points.
If the permitted value for U
CM
is exceeded, equipotential bonding lines must be
installed between the sensor locations.
Figure 12-2 shows the general connection of non-isolated sensors to an
equipotentially bonded analog input module.
Non-isolated
sensors
M+
:
M
L+
M--
M
ANA
M+
:
M--
Backplane bus
U
CM
ADC
Grounding busbar
U
ISO
Equipotential
bonding
cable
Logic
Figure 12-2 Connection of non-isolated sensors to an equipotentially bonded analog input
module.
Operating 4-wire measuring transducers (MU) at external power supply
If the MU output and power supply is isolated, the MU can be connected to the 2AI
I 4WIRE without any additional connections.
If the MU output and power supply is not isolated, the MU can be connected to the
2AI I 4WIRE only if the power supply voltages have the same reference potentials
connections.
If the interference is increased, we recommend a connection between M-- and
M
ana
to the terminal module of the 2AI I 4WIRE.