Hello. I hope someone can help me. I have a Sunbeam electric blanket. The controller produces a clicking sound when gives heat and stops giving heat, I guess to maintain temperature. I am confused though. The controller has 10 settings. all I see when I take the cover off the controller is a the bottom of the knob that turns and it's kind of like a scale and there is a plate that rests on it and as you turn the knob the plate gets pushed up and the other end of the plate has a magnet sort of thing on it which clicks into position to turn the blanket on and off producing the clicking sound . I am confused though as to how the controller knows setting 2 from 5 and 8 and 9. I guess what i want to know is how is each of the settings achieved, what causes the controller to turn on and off to maintain the temperature?? PLEASE HELP>>
It is a self-heating bi-metal thermostat. It is a very crude PWM. The first order function is to set average power delivered to resistance wire inside the blanket. The second order function is to compensate for room temperature; as it gets cooler in the room, the pulse width increases slightly.
More expensive blankets may do that, but most just do what Mike ML stated -- they have a bi-metal thermostat bi-stable oscillator whose duty-cycle is adjusted by the temperature knob, and this provides some compensation for room temperature since the duty-cycle will increase with a drop in ambient temperature.