Bimetallic thermometer thermometer factory group why working under high temperature disorder

In the practical application of the bimetallic thermometer measurement, often someone will ask, why bimetallic thermometer in high temperature, will work properly, the temperature measurement are not allowed to be? Aiming at this problem, I think I should first understand the working principle of the bimetallic thermometer and then combining principle, why bimetallic thermometer in high temperature work properly? Basic principle: the thermometer factory group, bimetallic thermometer temperature sensing element is composed of two layers of different linear expansion coefficient, made of sheet metal folding welding together, linear expansion coefficient of large pieces of metal is called the active layer, and the other one is called passive layer, one end of the element is fixed, the other end of the free end, when the measured temperature changes, as a result of the two layers of metal linear expansion coefficient is different, the free end by the combination of torque and bending ( Or deformation) , the change of curvature and physical properties of the bimetallic strip material, length of the thickness of each layer, temperature, and has nothing to do with the width. When temperature is designed, the bimetallic strip of material and geometry size, so the change of curvature is only related to temperature, if on the free end is equipped with drive mechanism, pointer and dial indication in temperature, so you can directly show the temperature value. Because the thermal expansion coefficient of metal can approximate thought only when in low temperature is constant, by high temperature, the thermal expansion coefficient of metal will not remain constant, then to metal heat bilges cold shrink principle of bimetallic thermometer to measure the temperature is not accurate. Through the above analysis, hope to help everyone to use bimetallic thermometer.