YOKOGAWA VZ20X, User Manual

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8-4
IM 77V01B01-01EN 5th Edition: 2023.03.07-00
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Thermocouple
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Reference junction compensation of thermocouple input
As the temperature of the input terminal section on the VZ20X is close to regular room
temperature, the actual output of the thermocouple differs from the value in the thermo-
electromotive force table at the reference temperature of 0°C. The VZ20X compensates
for this difference by measuring the temperature of the input terminals and adding the
thermo-electromotive force of that amount to the actual output of the thermocouple.
Accordingly, when the measurement terminal is short-circuited (equivalent to an
instance where the temperature of the probe is 0°C), the temperature of the input
terminal is indicated as the measured value.
When calibrating the VZ20X, input obtained by subtracting this compensation voltage
(thermo-electromotive force of reference temperature 0°C that is equivalent to the
temperature of the input terminal) must be applied from a standard temperature
generator. As shown in the figure, when reference contact compensation is performed at
0°C by using the 0°C reference temperature unit, calibration can be performed by
inputting the thermo-electromotive force of reference temperature 0°C from the DC
voltage generator.
1
2
3
4
－
＋
DC voltage
generator
(0°C reference temperature unit made by Coper Electronics Co., Ltd., model: ZC-114/ZA-10)
DC V
Output
VZ20X
input terminal
HI
LO
Thermocouple element
Copper wire