Bimetallic Disc Thermostats
How They Work:
As with cantilever type thermal controls, bimetal disc thermal controls rely on a specially formed bimetallic "disc" to provide the work force necessary to open and close a set of electrical contacts. The bimetal disc thermostat reacts to changes in temperature in an application and will provide the work energy to open and close the contacts. Since the bimetallic element of the thermal control does not carry the circuit current of the application, these devices are not subject to the self-heating effect caused by the electrical load passing through the bimetal element. This gives disc type devices the ability to handle higher current loads.
Like their cantilever counterparts, disc type devices are available with design options that provide for the controls to either open or close an electrical circuit upon increases in temperature. Many manufacturers of bimetallic disc thermostats also offer devices with a manual reset feature. This means that once the bimetallic element is activated in the device, the device must be manually reset by the end user in order to restore the flow of electricity to the application. This is the same principle as resetting a circuit breaker. Some manufacturers of disc type devices also offer devices which incorporate self-hold functionality. These devices incorporate the use of an internal heat source which generates enough heat to prevent the device from resetting until external power to the application is removed.