Siemens SIMATIC ET 200S Manual page 424

Analog Electronic Modules
Analog Output Modules
The analog output modules are generally isolated
• Between logic and backplane bus
• Between load voltage and M
Note
Make sure that the potential difference U
If there is a possibility of exceeding the approved value connect the M
and the central ground point.
Connecting sensors to analog inputs
Only a limited potential difference U
permitted between measurement cables M-- of the input channels and the
reference point of the measuring circuit M
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
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 +:
M --:
M
ANA
M:
L +:
U :
CM
U :
ISO
12-18
measuring line (positive)
measuring line (negative)
: reference potential of the analog measuring circuit
ground connection
24 VDC rated load voltage
potential difference between inputs and reference potential
of the M measuring circuit
ANA
potential difference between M
ANA.
does not exceed the approved value.
ISO
(common mode voltage/common mode) is
CM
. To ensure that the approved value is
ANA
and the central ground point
ANA
terminal
ANA
ANA
ET 200S Distributed I/O System
EWA-4NEB 780602402-12