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S5-115U Manual
Certain precautionary measures must be taken in order to make sure that potential difference
V
is not exceeded. Different measures are required for isolated and non-isolated transducers.
CM
When isolated transducers are used, the measuring circuit can assume a potential to earth that
exceeds the permissible potential difference U
modules).
To prevent this, the transducer's negative potential must be connected to the module's reference
potential (reference bus).
Example: Measuring temperature on a busbar with an isolated thermocouple.
In a worst-case situation, the measuring circuit can assume a potential that would
destroy the module; this must be prevented through the use of an equipotential
bonding conductor (see Figure 10-3).
Possible causes:
•
Static charge
•
Contact resistors through which the measuring circuit assumes the potential of the
busbar (e.g. 220 V AC).
When using non-isolated transducers, the permissible potential difference U
inputs and the reference bus must not be exceeded.
Example: Measuring the temperature of the busbar of an electroplating bath with a non-iso-
lated thermocouple. The difference between the potential of the busbar and the
reference potential of the module is max. 24 V DC. A 460 analog input module with
floating input (permissible U
Isolated
transducer
+
U
E
-
Equi-
potential
bonding
conductor
EWA 4NEB 811 6130-02b
CM
is 60 V AC/75 V DC) is to be used.
CM
Module
M+
Range
M -
card for
four
inputs
Reference bus
Figure 10-3. Connecting Transducers
Analog Value Processing
(refer to the maximum values for the various
Non-isolated
transducer
M+
+
U
E
M -
-
+
U
CM
-
U
CM
between the
CM
Module
Range
card for
four
inputs
Reference bus
10-5
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