An Analysis of Tian Kang's Role of Compensating Wires for Fast Thermocouples

March 20, 2023

To understand the problem of temperature compensation of thermocouples, it is necessary to work from the principle of thermocouples. Tian Kang here talks about the total thermoelectric potential and intermediate temperature rule of the thermocouple closed loop related to it. The former explains: For the selected thermocouple, when the reference junction temperature is constant, the total thermoelectromotive force becomes a single-valued function of the measuring tip temperature, that is, a certain thermoelectric potential corresponds to a certain temperature, while in the thermocouple index table, the The end temperature is 0 degrees. However, in the application site, the reference junction temperature varies widely and cannot be constant at 0 degrees. This results in measurement error. This is the reason why the thermocouple has to be temperature compensated. In actual applications, the reference junction of the thermocouple is often referred to as Cold end.
The compensation conductor is a pair of conductors with insulating layers that have the same nominal value as the matched thermocouple thermoelectromotive in a certain temperature range (0~100°C). They are used to connect thermocouples and measuring devices to compensate them and thermoelectricity. The error caused by the temperature change at the joint.
Thermocouple cold junction temperature compensation methods are:
1. The ice bath method is often used in the laboratory, that is, the reference junction temperature is constant at 0 degrees, but it is expensive and difficult to do.
2. The cold end temperature correction method is often used in a less demanding scene, ie, when the cold end temperature cannot be constant at 0 degrees, the indicator value of the meter needs to be corrected, which is easy but has a large error.
3. The compensation bridge method is used less independently. It is to use the potential generated by the unbalanced bridge to compensate for the change in the thermoelectric potential caused by the temperature change at the cold junction of the thermocouple. The compensation bridge has a separate product and is also built into the meter.
4. Compensation wire method This is the most common method, that is to extend the thermocouple to the cold end lead to a more stable temperature (usually the control room), and then manually adjust the cold end temperature, that is, the instrument zero point to room temperature, Or by the meter within the circuit for automatic compensation. It is not possible to extend the thermocouple for a noble metal thermocouple. Because the price is too high, the extension wire is made of a metal with similar thermoelectric characteristics. The intermediate temperature rule is the theoretical basis for applying the compensation wire .
The compensating wire does not automatically compensate for the change in the temperature of the cold junction of the thermocouple. It merely directs the cold junction of the thermocouple to a place where the temperature is relatively stable. The compensation must be performed manually and with the instrument. Therefore, the compensation wire should be called a thermocouple extension wire. It will not give people a wrong understanding.
Anhui Tiankang will always adhere to the "TaiKang spirit of transcending excellence," and on the basis of creating a harmonious enterprise, it will continue to grasp the pulse of market development, actively seek economic strategic alliances, and continue to work for the revitalization of national industries. Welcome customers to negotiate.

Связаться с нами

Author:

Ms. Amy

Электронная почта:

amy@ucoax.com

Phone/WhatsApp:

+8613913156783