Yokogawa PC-Based MX100 - Manual (Page 83)

3-11
IM MX100-01E
Troubleshooting and Maintenance
3
2
1
4
5
Index
Calibration of Temperature Measurements using Thermocouples
Required Instruments
• DC voltage/current standard
Must meet the following specifications (5520A by FLUKE or equivalent)
Output accuracy: ±(0.005% + 1 µV) or less
• 0°C standard temperature device
Must meet the following specifications (ZC-114/ZA-10 by Coper Electronics or
equivalent)
Standard temperature stability accuracy: ±0.05°C or less
Reference Junction Compensation of Thermocouple Input
The input terminal section of the input modules is normally near room temperature, so
that the actual thermocouple output differs from the 0°C reference thermoelectromotive
table value. 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 a 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
30CH, Medium Speed DCV/TV/DI
Input Module in the same manner
as well.
Note
• Unlike the range calibration of DC voltage or RTD, the input section cannot be adjusted
for calibration of temperature measurement on the MX100 using a thermocouple. If
accuracy specifications are not upheld after calibration of temperature measurement using
thermocouples (see sections 4.4 through 4.6), check for input error and other factors, then
contact your Yokogawa dealer.
• If errors exist in the thermocouple wires and extension wires, correct calibration is not
possible. Be sure to use a calibrated thermocouple.
3.3 Calibration