All kinds of working principle of the thermometer

Gas thermometers: Use hydrogen or helium as a temperature-measuring material, because the liquefaction temperature of hydrogen and helium is very low, close to absolute zero, so it has a wide range of temperature measurement. This thermometer is highly accurate and is often used for precise measurements.
Resistance thermometers: divided into metal resistance thermometers and semiconductor resistance thermometers, are based on the resistance value changes with the temperature of this property made. Metal thermometers are mainly used platinum, gold, copper, nickel and other pure metals and rhodium-iron, phosphor bronze alloy; Semiconductor thermometers mainly use carbon, germanium and so on. Resistance thermometers are widely used for their convenience and reliability. It can be measured from -260℃ to about 600℃.
Thermoelectric couple thermometer: it is a widely used temperature measuring instrument in industry. Made of thermoelectricity. Two different metal wires are welded together to form a working end, and the other two ends are connected with the measuring instrument to form a circuit. When the working end is placed at the measured temperature, the temperature of the working end is different from that of the free end, an electromotive force will appear, and a current will flow through the loop. By means of electrical measurements, we can determine the temperature at one place by taking advantage of the temperature at one place. It is suitable for the temperature difference between two substances, mostly used for high temperature and low turbidity measurement. Some thermocouples measure temperatures as high as 3000 ° C, while others measure temperatures close to absolute zero.
High temperature thermometers: refer to thermometers specially used to measure the temperature above 500℃, there are light thermometers, colorimetric thermometers and radiation thermometers. The principle and construction of high temperature thermometers are complex and will not be discussed here. Its measurement range is 500℃ to above 3000℃, not suitable for low temperature measurement.
Pointer thermometer: is shaped like a thermometer dashboard, also known as the thermometer, used to measure room temperature, is made of metal expansion and contraction principle. It is a bimetallic element as a temperature sensor for the control of the pointer. The bimetallic sheet is usually riveted together with copper sheet and iron sheet, with the copper sheet on the left and the iron sheet on the right. Since copper's thermal expansion and cold contraction effect is much more obvious than iron's, when the temperature rises, the copper sheet pulls the iron sheet to bend to the right, and the pointer will turn to the right under the drive of the bimetal sheet (pointing to high temperature). On the contrary, when the temperature becomes low, the pointer is driven to the left by the bimetal plate (pointing to the low temperature).
Glass tube thermometer: glass tube thermometer is the use of thermal expansion and contraction of the principle to achieve the measurement of temperature. Because the expansion coefficient of temperature measuring medium and boiling point and freezing point are different, so our common glass tube thermometer mainly have: kerosene thermometer, mercury thermometer, red pen water thermometer. Its advantages are simple structure, easy to use, relatively high measurement accuracy and low price. The disadvantage is that the upper and lower limits and precision of measurement are limited by the quality of glass and the nature of temperature measuring medium. And can not be far away, fragile.