Compensating lead

When you try to extend the thermocouple to the instrument, if the distance is long, there are problems such as that the thermocouple wire becomes expensive, and that the measurement accuracy deteriorates due to disturbances such as noise. To solve these problems, a compensation lead wire is used.

Compensating lead wires are available in extension type and compensating type. The extension type can keep high accuracy over a wide temperature range because of using the same material as the thermocouple.
On the other hand, the compensating type uses a substitute alloy that is almost identical to the thermoelectromotive force characteristics of the thermocouple, so the price is low, but the operating temperature range is narrow.
The compensation junction temperature (connection point temperature) with the thermocouple, component materials, tolerance of the compensation lead wire itself, etc. are standardized, and the type of compensation lead wire can be identified by color.
It is necessary to select a thermocouple suitable for the type of thermocouple, operating temperature, and ambient conditions.

The sheathed thermocouple wire (duplex wire) is the wire used to make the thermocouple’s sensing point (probe part).
The compensating lead is the wire used to send the thermocouple signal from the probe to a device that reads that signal.

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