What Is a Thermostatic Bimetal?
A thermostatic bimetal is a laminate of two metals with different thermal expansion coefficients. When a temperature change is applied to the thermostatic bimetal, the metal with the lower thermal expansion coefficient tries to maintain its original shape, while the metal with the higher thermal expansion coefficient tries to expand or contract. Therefore, as the temperature rises, the metal bends toward the side of the metal with the lower thermal expansion coefficient, and as the temperature decreases, the direction of bending is reversed.
Thermostatic bimetals are made by physically and electrically utilizing this curvature caused by temperature change.
Uses of Thermostatic Bimetals
The main application of thermostatic bimetals are as temperature sensors such as thermometers and thermostats that utilize the curvature of metals.
In particular, its use as a thermocouple using the Seebeck effect is well known. The use of thermostatic bimetals as thermocouples can be adapted to different applications because the range of temperatures that can be measured can be varied depending on the type of metal to which they are attached.
Its use as a thermostat is to open and close electrical contacts using the curvature of the metal. Since no power is required to turn the sensor on and off, it has a variety of uses, including temperature control functions for air conditioning and heating.
Principle of Thermostatic Bimetals
Thermostatic bimetals are made by laminating two types of metals with different thermal expansion ratios. As the temperature rises, the metal expands according to its thermal expansion coefficient, but because metals with different thermal expansion coefficients are bonded together, free expansion is restricted and the metal becomes curved. By physically and electrically utilizing this curvature of the metal, it can be used as a sensor for temperature change.
Thermostatic bimetals tip joined together can be used as a thermometer by converting the voltage generated by the Seebeck effect due to the change in temperature. Since the direction of curvature can be changed by temperature rise and fall, it can be used to open and close contacts to provide a temperature control function as well as a protection circuit for equipment by opening the contacts (turning off the power) when heated. In addition to the use of ambient temperature, the contact can also be used as a protective function for circuits due to overcurrent by opening and closing contacts due to the temperature rise caused by the energization of circuits.