Bimetal Thermostat Tetsing

Bimetal thermostatic control in photo, removed from an electric iron, il­ lustrates the principle shown in the series of three drawings.


  1. In the drawing at left, current flows through closed contacts of the bimetal switch and through heating element, which supplies heat to both appliance and to the switch itself.

  2. In center drawing, heat has caused bimetal arm to warp up­ wards, breaking electrical circuit. Appliance now cools until bimetal arm again makes contact. Cycle repeats and temperature of the iron stabilizes at a point that is dependent on the time of cycling.

  3. Drawing at right shows how heat range can be adjusted by varying position of second contact. By raising it on the threaded shaft, more heat is needed to lift bimetal contact. Shorter cool-down period is effected, resulting in higher overall temperature of the iron.