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.
Card for
22 +
A
D
Analog Input Module
MUX
M -
23 -
0 V Bus
M +
+
-
Power
Supply
for Com-
pensating
Box
Thermocouple
Terminal Box
Compen-
sating
Box
~
=
#
Range
4 Inputs
6ES5 498-
-1AA11
Figure 9-8
Connecting a Compensating Box
9
The 460 Analog Input Module
System Manual
C79000-B8576-C109-03
9 - 21
