FAQ (Frequently Asked Questions)

Thermocouple/Compensating Cable

What will happen if a thermocouple (compensating cable) is connected with the wrong polarity?

The color code of the thermocouple / compensating cable differs greatly according to the standard of each country, and it may sometimes mistake the polarity at the wiring operation. What will happen to the temperature indication in that case?

The connection part of the thermocouple and extension lead wire is the terminal box or connection box (junction box) attached to the thermocouple and the connection part has an atmospheric temperature in many cases. If you mistakenly connect polarity from the terminal box etc to the terminal of the receiving instrument, the difference between the temperature of the terminal box part and the temperature of the receiving instrument terminal affects the error. If there is no temperature difference, the error is not generated; however, since the temperature difference is extremely large in summer and winter, an error of 10℃ or higher may be generated.
As an extreme example, if in summer the terminal box reaches 40℃ and the receiver reaches 20℃, for E of the thermocouple type, with correct polarity, an thermo-electromotive force of 1,228 μV which is the difference of the thermo-electromotive force of 2,420 μV at 40℃ and the thermo-electromotive force of 1,192 μV at 20℃ will be generated. However, with the wrong polarity, a completely inverse negative thermo-electromotive force of -1,228 μV which is -2,456 μV of original thermo-electromotive force will be generated. This value is -30℃ lower than the original one when converted with the measured temperature of approx. 500 C.
Also, if only the terminal box has the wrong polarity and the receiver has the correct polarity, a larger error will be generated since the thermocouple is inversely connected. If only the receiver has the wrong polarity in the same way, a larger error will be generated since the thermocouple including the extension lead wire is inversely connected.

Technical Data

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