Working principle of thermal resistance

The working principle of thermal resistance is very simple. Temperature measurement is based on the thermal effect of resistance. The resistance of resistance body changes with the change of temperature. Therefore, as long as the resistance change of the temperature sensing thermal resistance is measured, the temperature can be measured. The resistance value and temperature of metal thermal resistance can generally be r = R. [1+a(t—t。)] In which: RT is the resistance at temperature T; R 。 Is the temperature T. (usually T. 0 "C) corresponds to the resistance value; a is the temperature coefficient. The relationship between the resistance value and temperature of semiconductor thermistor is RT = AEB / T, where RT is the resistance value when the temperature is t; a and B depend on the structural constants of semiconductor materials. The temperature measurement of thermal resistance is based on the characteristic that the electrical resistance value of metal conductor increases with the increase of temperature.

Thermal resistance is the most commonly used temperature detector in medium and low temperature areas. Its main characteristics are high measurement accuracy and stable performance. Among them, the measurement accuracy of platinum thermistor is the highest. It is not only widely used in industrial temperature measurement, but also made into a reference instrument. At present, there are mainly metal thermistors and semiconductor thermistors. In comparison, thermistors have larger temperature coefficient, higher resistance value at room temperature (usually more than thousands of ohms), poor interchangeability and serious nonlinearity. The temperature measurement range is only 50 ℃ ~ 30 ℃, in our company, it is only used for indoor temperature detection of paperless recorder. Metal thermal resistance is generally suitable for temperature measurement in the range of - 20O ~ C ~ 500 ~ C. It is characterized by accurate measurement, good stability and reliable performance. It is widely used in our factory.

At present, the most widely used thermal resistance materials are platinum and copper: platinum resistance has high precision, is suitable for neutral and oxidizing media, has good stability and certain non linearity, and the higher the temperature, the smaller the resistance change rate; Within the temperature measurement range, the resistance value of copper resistance has a linear relationship with temperature. The number of temperature lines is large. It is suitable for non corrosive media. It is easy to be oxidized above 150 ℃. The most commonly used platinum resistor in China is r- 1OQ、R。- Loofl and r= 1000 ~ and their graduation numbers are ptl0, PTl00 and ptl000 respectively; Copper resistance has R= 50D, and r= There are two kinds of 1ooq, and their graduation numbers are cu50 and cul00. PTl00 and cu50 are the most widely used.