Purpose: temperature measurement, is the earliest pyroelectric detection device.
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 components of infrared spectrophotometer or infrared spectrometer, etc.
Structural composition: The material that composes the thermocouple can be either metal or semiconductor. In terms of structure, it can be a line or 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 and compare the thermoelectric potential values of the standard and the thermocouple to be checked, and calculate the deviation or the corresponding thermoelectric potential value.
①Characteristics of bipolar method
a. Directly measure the electric potential of the thermocouple.
b. The standard and the inspected can be of different models.
c. The measuring ends of the thermocouple may not be bundled together, but they must be kept at the same temperature.
②Attention when checking the bipolar method
a. The furnace temperature must be strictly controlled in accordance with the regulations, otherwise it will bring about greater measurement errors.
b. When the temperature of the standard and the tested reference terminal is not 0℃, the reference terminal temperature should be corrected to 0℃ for data processing.
2. Jifa of the same name
At each verification point, 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, and then use the calculation method to obtain the deviation or Corresponding potential value.
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 of the unipolar thermoelectromotive force between the standard and the thermocouple under test.
②Attention when checking the polar law with the same name
a. The standard and inspected thermocouples must be the same model before they can be compared.
b. The binding requirements for standard and inspected thermocouples are strict, otherwise errors are likely to occur.
c, differential method
Using the differential method to verify the thermocouple is to place the standard and the thermocouple (same model) in the verification furnace, connect them in reverse series, and directly measure the difference of the thermoelectromotive force.
①Characteristics of differential method verification
a. Simple operation, rapid reading and convenient calculation.
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 verifying by millisecond method
a. The standard and inspected thermocouples must be the same model to compare.
b. The positive pole of the tested thermocouple must be connected to the positive terminal button of the potentiometer, otherwise the calculation result is wrong.
Thermocouples that have been verified to meet the requirements will be issued a verification certificate, and 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.