Siemens S5-135U, System Manual

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9-19
System Manual
C79000-G8576-C199-06
9.3.9 Connecting a Compensating Box for Thermal E.M.F.
Measurement
If the room temperature fluctuations at the reference point (e.g. in the
terminal box) affect the measurement result and you do not wish to use a
thermostat, you can compensate for the effect of temperature on the reference
point with a compensating box. Between - 10 and + 70
o
C, it compensates for
the change in thermal e.m.f. cause by temperature deviation (compensating
box, see Catalog MP 11). Ensure that the compensating box has thermal
contact with the terminals.
If the compensating box is aligned at 20
o
C, this must be taken into account
in temperature evaluation (20
o
C measuring point temperature = 0 mV).
Pins 22 and 23 are extended on analog input modules as an input for the
compensating voltage. You must select a common input loop for all inputs on
mode switch 2.
The compensating box must be connected in a floating circuit. The power
supply unit of the compensating box must have a grounded shield winding to
avoid AC system interference being picked up. A separate compensating box
with its special power supply unit is required for each analog input module.
22–
A
D
Analog Input Module
MUX
M–
23+
0 V Bus
M+
–
+
Power
Supply
for Com-
pensat-
ing Box
Thermocouple
Terminal Box
~
=
#
Range
Card for
4 Inputs
6ES5 498-
-1AA11
Compen-
sating
Box
Figure 9-8 Connecting a Compensating Box
Analog Input/Output Modules