II - DCE FEL ČVUT v Praze

SIMATIC S7 Ex Analog Modules
Thermocouples
with compensation
box
3-28
Equalizing conductor
(same material as
thermocouple)
Thermocouple
UISO: Difference in potential between channels and M- terminal of
CPU
UCM: Differences in potential between channels
Necessary when all thermocouples which are connected to the inputs of a
module and which have the same reference junction compensate as follows.
The thermocouples which use a compensation box must be of the same type.
Each of the thermocouples can be grounded at any arbitrary point.
Supply
conductor
(copper)
Reference junction
+
-
U v
CH0
.
.
.
CH6
CH7
M+
M-
M+
M-
M+
M-
ADU
Compensation box with
reference junction temperature of 0 o C
P5V
M
Logic
Backplane
bus
Fig. 3-4 Connection of thermocouples with external compensation box to the isolated analog input module SM
331; AI 8 x TC/4 x RTD
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04