An energy regulator (or simmerstat) is an "infinite switch" that controls the temperature of a "burner" or ring on the hob of an electric stove or cooker. It can be considered as a very slow pulse-width modulation device. Although the device is similar in operation to a bimetallic switching thermostat, the device does not actually sense the temperature of the "burner" to be controlled, but uses the heating time of a very small electric heating element as an analog.
A rotary knob/cam arrangement is usually employed to switch-on the electric current to the "burner" and to also set the desired heating level.
Within the device, the very small electric heating element, mentioned above, heats up a bimetallic strip. After so many seconds, the bimetallic strip becomes sufficiently warped to trigger a set of spring-loaded switch contacts to open, thus interrupting the electric current to the heating element. At the same time, another (more robust) set of spring-loaded switch contacts, mounted in parallel with the former, also open, cutting off the heavy current to the "burner". Both the small heating element and the "burner" now begin to cool off. At some point the bimetallic strip will be sufficiently straight to trigger both sets of switch contacts to close, thus causing both the small heating element and the "burner" to recommence the above heating cycle.
Rotating the rotary knob/cam arrangement further increases the pre-load on the trigger mechanism. Consequently, it takes longer for the bimetallic strip to warp sufficiently to trigger the electric "cut-out" described above. Thus the "burner" becomes hotter.