Thermocouple cold junction temperature compensation method - Database & Sql Blog Articles
To understand the temperature compensation problem of thermocouples, we must start with the principle of thermocouples. Now we only talk about the total thermoelectric potential and intermediate temperature rules of the thermocouple closed loops. The former illustrates that for a selected thermocouple, when the reference junction temperature is constant, the total thermoelectromotive force becomes a single-valued function of the temperature at the measuring end. That is, a certain thermoelectric potential corresponds to a certain temperature, and in the thermocouple index table, the reference end temperature is 0 degrees. However, at the application site, the reference junction temperature varies widely and cannot be constant at 0 degrees, which causes measurement errors, which is why the thermocouple is temperature compensated. In practical applications, the reference end of a thermocouple is often referred to as a cold end. Hfo Generating Set,Generator For House,Sound Proof Hfo Generating Set,Sound Proof Hfo Generator Shaoxing AnFu Energy Equipment Co.Ltd , https://www.sxanfu.com
Thermocouple cold junction temperature compensation methods are:
1. The ice bath method is commonly used in the laboratory, that is, the temperature of the reference end is constant at 0 degrees, but it is costly and difficult to do.
2. The cold junction temperature correction method is often used in places where the requirements are not high, that is, when the cold junction temperature cannot be constant at 0 degrees, the indication value of the meter needs to be corrected. It is easy to do but has a large error.
3. The compensation bridge method is less used alone, and the potential generated by the unbalanced bridge is used to compensate for the change in the thermoelectric potential caused by the temperature change of the cold junction of the thermocouple. The compensation bridge has separate products and is also installed in the instrument.
4. Compensation wire method This is the most common method, which is to extend the thermocouple, the cold end is led to a relatively stable temperature (usually the control room), and then the cold end temperature is manually adjusted, that is, the meter zero is adjusted to room temperature. , or automatically compensated by the circuit inside the meter. It is also impossible to extend the thermocouple for precious metal thermocouples. Because the price is too high to work, the base metal is used to make the extension wire with the similar thermoelectric characteristics. The intermediate temperature rule is the theoretical basis for applying the compensation wire. The compensation wire does not automatically compensate for the change in the temperature of the cold junction of the thermocouple. It only refers to the cold end of the thermocouple to a place where the temperature is relatively stable. The compensation is also performed by manual and instrument. Therefore, the compensation wire should be called a thermocouple extension cable so that it does not give a wrong understanding.