Yokogawa Standalone MW100 - Manual (Page 209)

4-17 IM MW100-01E
Troubleshooting and Maintenance
1
2
3
4
5
App
Index
Reference Junction Compensation of Thermocouple Input
Normally, the input terminal of the input module is nearly at room temperature,
therefore the actual thermocouple output differs from the value in the table for the
thermoelectromotive force with the 0°C standard. Modules able to measure temperature
with thermocouples can be compensated by measuring the temperature of the input
terminal and adding the corresponding thermoelectromotive force to the actual
thermocouple output. Therefore with the measurement terminal shorted (equivalent to
an edge detection of 0°C), the measured value indicates the temperature of the input
terminal.
When calibrating modules capable of temperature measurements using thermocouples,
it is necessary to apply input from a DC standard voltage current generator with this
compensation voltage subtracted (the electromotive force of the 0°C standard that is
equivalent to the temperature of the input terminal). As in the figure, when performing
reference junction compensation at 0°C using a 0°C standard temperature device, you
can perform the calibration by inputting the 0°C standard electromotive force from DC
standard voltage/current generator.
Wiring Diagram
+
-
100Vpk MAX TO
250V MAX CH TO CH 600V MAX TO
Thermocouple wires or
TC extension wires
Thermocouple
wires
Copper
wires
Copper wires
DC voltage standard
Input terminal
–
+
Cold junction
0°C standard temperature
device
4-CH, High-Speed Universal
Input Module*
* Connect the 10-CH, Medium Speed
Universal Input Module and the
30-CH, Medium Speed DCV/TC/DI
Input Module in the same manner
as well.
Note
• Calibration of temperature measurements of the MW100 Data Acquisition Unit using
thermocouples differs from calibration of DC voltage and RTD ranges in that the input
cannot be adjusted. If the temperature measurement calibration using thermocouples does
not meet the accuracy specifications, check thoroughly for input error and other problems,
then contact your Yokogawa dealer or representative.
• If errors exist in the thermocouple wires and TC extension wires, correct calibration is not
possible. Be sure to use a calibrated thermocouple.
4.4 Calibration