An instrument for measuring temperature. It is made of the change of the material property with the temperature, according to the corresponding laws of physics. There are a wide variety of thermometers, which are suitable for different temperature range and precision requirements. The most common glass liquid thermometer uses the changes in the volume of liquid (mercury, alcohol, toluene, etc.), indicating the temperature at the height of the liquid in the capillary. The measuring range of the glass mercury thermometer is - 30~600 degrees C, and the temperature limit of some organic liquids can be as low as - 150. Double metal thermometer two linear expansion coefficients of different metal combinations together, one end is fixed, when the temperature changes, due to the elongation of two kinds of metal, the other end displacement, deflection drives the pointer to indicate the temperature, temperature range of 80 to 600 DEG C, the disadvantage is that the accuracy is not high. A pressure meter type thermometer, which is used as a temperature indicator, is used as an industrial pressure gauge. The thermometer is filled with some medium in the sealed bubble. The pressure increased by the connecting capillary to the pressure gauge spring. The deformation of the spring causes the pointer to deflect to indicate the temperature. The working medium has gas (such as nitrogen, hydrogen), steam (chloroethane, chloromethane, ether), and liquid (mercury). The disadvantage is that the precision is not high.
The thermocouple thermometer consists of two kinds of metal wires, which are made up of metal wires. One end of the thermocouple is welded at one end, the working end is placed at the measured temperature, the other end is a free end, the temperature is fixed, and it is connected with the measuring instrument to form a closed loop. When the temperature is different at both ends, the electromotive force of the temperature difference appears in the loop, and its size is determined by the temperature to be measured. A variety of thermocouples, some can be measured at 3000 degrees C high temperature, some can be measured near the absolute zero degree of low temperature.
The resistance thermometer is used to measure the temperature according to the variation of the conductor resistance with the temperature. Platinum resistance thermometer accuracy up to 1 / 10000 degrees, and wide application scope, is the realization of international practical temperature reference thermometer. The semiconductor thermometer thermometer uses the resistance of semiconductor device to measure temperature with the change of temperature. It is characterized by high sensitivity and is used for low precision measurement.
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