Heater On Off Temperature Control using Bimetallic Switch. This device utilize a bimetallic switch to control heater temperature. The bimetallic switch consists of two different metals with different coefficients of expansion fixed together in a strip. These metals will expand or contract at different rates when heated or cooled. The bimetallic strip is used to convert a temperature change into mechanical displacement. The self-heating effect created by passing current through the bimetallic element, or a combination of both.
The heater will be on if about 30V is applied between its terminals. When the temperature is low the switch is closed and 30V applied to the heater and make it ON. So the temperature start increasing. Until a certain temperature the strip will bend downward and open the switch and the heater becomes OFF. So the temperature start