Two kinds of metal sheets with different thermal expansion coefficients are bonded together to make a bimetallic sheet The thermal expansion coefficient of the upper metal of the bimetallic sheet is greater than that of the lower metal. When the temperature rises, the upper metal sheet bends downward due to large elongation to disconnect the contact, so as to disconnect the circuit. The function of the bimetallic sheet temperature sensor is to control the on-off of the electrical metal base plate circuit.

For example, the installation position and insertion depth of the thermocouple cannot reflect the real temperature of the furnace. In other words, the thermocouple should not be installed too close to the door and heating place, and the insertion depth should be at least 8 ~ 10 times the diameter of the protective tube; The gap between the protective sleeve and the thermocouple wall is not filled with insulating material, resulting in heat overflow or cold air intrusion into the furnace. Therefore, the gap between the thermocouple protection tube and the furnace wall hole should be sealed with insulating materials such as refractory mud or asbestos rope to avoid the influence of cold and hot air convection on the temperature measurement accuracy; The cold end of the thermocouple is too close to the furnace body, so that the temperature exceeds 100; The installation of thermocouples shall avoid strong magnetic field and electric field as far as possible. Therefore, thermocouples and power cables shall not be installed in the same conduit to avoid errors caused by interference; Thermocouples cannot be installed in areas where the measured medium rarely flows. When using thermocouple to measure the temperature of gas in the pipe, the thermocouple must be installed against the flow direction and in full contact with the gas.

In recent years, with the in-depth research and progress of micro electro mechanical system (MEMS), the traditional flow sensor in industrial and hydrodynamics research is developing towards high integration, miniaturization, high precision and high reliability. Micro flow sensor has become an important research direction of MEMS.