Thermocouple verification method

Thermocouple introduction
Purpose: Temperature measurement is a kind of pyroelectric detection device that appeared early.
Classification: physical thermocouples are mostly used for temperature measurement; thin-film thermocouples (consisting of many thermocouples in series) are mostly used to measure radiation, for example, to calibrate various light sources and measure various radiation levels. Radiation receiving element of infrared spectrophotometer or infrared spectrometer, etc.
Structural composition: The material constituting the thermocouple can be either metal or semiconductor. The structure can be either a line or a strip-shaped entity, or a thin film made by vacuum deposition technology or photolithography technology.
Working principle: Its working principle is thermoelectric effect. For example, a junction composed of two different conductor materials can generate electromotive force at the junction. The magnitude and direction of this electromotive force are related to the properties of the two different conductor materials at the junction and the temperature difference between the two junctions. If these two different conductor materials are connected into a loop, when the temperature at the two joints is different, current will be generated in the loop.
Thermocouple verification method
1, bipolar method
At each verification point, measure the thermoelectric potential value of the standard and the thermocouple to be checked and compare them, and calculate the deviation or the corresponding thermoelectric potential value. Figure 1 shows the connection circuit of the bipolar method.



Figure 1 Connection circuit diagram of bipolar method
①Characteristics of bipolar method
A, directly measure the electric potential of the thermocouple.
B, the standard and the tested can be of different models.
C. The thermocouple measuring terminals can be unbundled together, but they must be kept at the same temperature.
②Attention during bipolar verification
A. The furnace temperature must be strictly controlled in accordance with the regulations, otherwise it will bring about large measurement errors.
B. When the temperature of the standard and the tested reference terminal is not 0℃, the temperature of the reference terminal should be corrected to 0℃ for data processing.
2, Jifa of the same name
Measure the differential thermoelectric potential between the positive pole of the tested thermocouple and the positive pole of the standard thermocouple and the negative pole of the tested thermocouple and the negative pole of the standard thermocouple at each verification point, and then use the calculation method to obtain the deviation or Corresponding potential value. The connection circuit of the pole method with the same name is shown in Figure 2.

Figure 2 The connection circuit diagram of the pole method verification with the same name
①Characteristics of homonymous polar law verification
A. Large changes in furnace temperature are allowed during the reading process (usually ±10°C).
B. It can directly measure the difference between the standard and the unipolar thermoelectromotive force of the thermocouple under test.
②Attention when checking the polar law with the same name
A. The standard and tested thermocouples must be of the same model before they can be compared.
B. There are strict requirements on the binding of standard and inspected thermocouples, otherwise errors will easily occur.
C, differential method
Verification of thermocouples by the differential method is to put the standard and the tested thermocouples (same model) in the verification furnace, connect them in reverse series, and directly measure the difference of the thermoelectromotive force. Figure 3 shows the verification circuit of the millisecond method.

Figure 3 The connection circuit diagram of the millisecond method
①Characteristics of the micro-difference method
A, the operation is simple, the reading is fast, and the calculation is convenient.
B, the difference can be read directly.
C. Lax requirements for furnace temperature during verification.
D. The measuring end of the thermocouple does not need to be bundled, as long as it is at the same temperature.
②Pay attention to when the micro-difference method is used for verification
A. The standard and tested thermocouples must be the same model to compare.
B. The positive pole of the tested thermocouple must be connected to the positive pole button of the potentiometer, otherwise the calculation result is wrong.
The thermocouples that meet the requirements will be issued a verification certificate, and the unqualified thermocouples will be issued a verification result notice. The verification period of thermocouple is generally half a year, and special circumstances can be determined according to the conditions of use.