The conceptual sketch for a closed loop control for a toaster is shown below. The controller is a bimetallic switch. It works by combining two metals of different thermal expansion so that, when heated, it bends away from the more expansive metal and can then open a pair of contacts. The heat is interrupted when the contacts are opened and is reestablished when the bimetallic strip cools.

The heat source is “waste” heat generated in the resistor that also heats the toast. The stationary contact is adjustable so that the clearance between the two contacts determines the set point as to when the heater is on or off.

Draw a block diagram of the system, indicating on the diagram which parts of the conceptual sketch correspond to the blocks.

Resistor Bimetallic Switch Plug Radiant heat Toast