Analog Electronic Modules
12-18
ET 200S Distributed I/O System
EWA-4NEB 780602402-12
Analog Output Modules
The analog output modules are generally isolated
• Between logic and backplane bus
• Between load voltage and M
ANA.
Note
Make sure that the potential difference U
ISO
does not exceed the approved value.
If there is a possibility of exceeding the approved value connect the M
ANA
terminal
and the central ground point.
Connecting sensors to analog inputs
Only a limited potential difference U
CM
(common mode voltage/common mode) is
permitted between measurement cables M-- of the input channels and the
reference point of the measuring circuit M
ANA
. To ensure that the approved value is
not exceeded, various actions must be implemented depending in the sensor
potential connection (isolated, non-isolated). The actions required are explained in
this chapter.
However , the general rule is that there must not be a connection from M-- to M
ANA
when connecting 2-wire measurement transducers and resistor sensors. This
applies for correspondingly configured but unused inputs.
Note
Unused analog inputs on the 2AI U, 2AI RTD and 2AI TC analog input modules
must be short-circuited.
Abbreviations used
The abbreviations used in the following diagrams have the following meanings:
M +: measuring line (positive)
M --: measuring line (negative)
M
ANA
: reference potential of the analog measuring circuit
M: ground connection
L +: 24 VDC rated load voltage
U
CM
: potential difference between inputs and reference potential
of the M
ANA
measuring circuit
U
ISO
: potential difference between M
ANA
and the central ground point
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