Why do bimetallic thermometers work abnormally at high temperatures
2022-12-05
In the actual measurement of bimetallic thermometers, people often ask why bimetallic thermometers work abnormally when encountering high temperatures, and the temperature measurement is inaccurate?
In response to this problem, I think we should first figure out the working principle of the bimetal thermometer, and then combine the principle to see why the bimetal thermometer malfunctions when it encounters high temperature?
Basic principle: The temperature sensing element of the NingDian bimetallic thermometer is made of two layers of metal sheets with different linear expansion coefficients, which are welded together. The metal sheet with a large linear expansion coefficient is called the active layer, and the other is called the passive layer. , one end of the element is fixed, and the other end is a free end. When the measured temperature changes, due to the different linear expansion coefficients of the two layers of metal sheets, the free end will be bent (or called deformation) by the combined torque. The physical properties of the materials that make up the bimetal sheet, the length is the thickness of each layer, and the temperature is related, but has nothing to do with the width. When the temperature is designed, the material and geometric dimensions of the bimetal sheet are determined, so the curvature is only related to the temperature, if The free end is equipped with an upper transmission mechanism, a pointer and a dial marked with temperature, so that the indicated value of temperature can be directly displayed.
Because the thermal expansion coefficient of metal can only be considered as a constant at medium and low temperatures, when it reaches high temperature, the thermal expansion coefficient of metal will not remain constant. At this time, it is measured by a bimetallic thermometer made of the principle of metal thermal expansion and cold contraction. The temperature is not accurate.
In response to this problem, I think we should first figure out the working principle of the bimetal thermometer, and then combine the principle to see why the bimetal thermometer malfunctions when it encounters high temperature?
Basic principle: The temperature sensing element of the NingDian bimetallic thermometer is made of two layers of metal sheets with different linear expansion coefficients, which are welded together. The metal sheet with a large linear expansion coefficient is called the active layer, and the other is called the passive layer. , one end of the element is fixed, and the other end is a free end. When the measured temperature changes, due to the different linear expansion coefficients of the two layers of metal sheets, the free end will be bent (or called deformation) by the combined torque. The physical properties of the materials that make up the bimetal sheet, the length is the thickness of each layer, and the temperature is related, but has nothing to do with the width. When the temperature is designed, the material and geometric dimensions of the bimetal sheet are determined, so the curvature is only related to the temperature, if The free end is equipped with an upper transmission mechanism, a pointer and a dial marked with temperature, so that the indicated value of temperature can be directly displayed.
Because the thermal expansion coefficient of metal can only be considered as a constant at medium and low temperatures, when it reaches high temperature, the thermal expansion coefficient of metal will not remain constant. At this time, it is measured by a bimetallic thermometer made of the principle of metal thermal expansion and cold contraction. The temperature is not accurate.
Through the above analysis, I hope it will be helpful for everyone to use the bimetallic thermometer in practice.
