Connecting A Compensating Box For Thermal E.m.f. Measurement - Siemens S5-135U/155U System Manual

9.5.8 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
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
in temperature evaluation (20
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.
Terminal Box
Thermocouple
–
Compen-
sating
Box
+
Power
=
Supply
for Com-
pensat-
~
ing Box
Figure 9-23 Connecting a Compensating Box
System Manual
C79000-G8576-C199-06
Analog Input/Output Modules
o
C, this must be taken into account
o
C measuring point temperature = 0 mV).
Analog Input Module
M+
MUX
Range
Card for
M–
4 Inputs
6ES5 498-
-1AA11
22–
23+
o
C, it compensates for
A
#
D
0 V Bus
9-63