Hotplate switched on by presence of cooking utensil - measures voltage across AC-supplied capacitors and operates heating-circuit switch

摘要

The hotplate is such that the presence of a cooking utensils closes its heating circuit. A detector (2) is located beneath the ceramic plate (1). The detector is connected to an oscillator (3). The voltage measured at the detector's output is used to control a switch in the hotplate's heating circuit. The detector consists of two capacitors. The voltage across these capacitors is rectified and filtered (4) and passed to a digital amplifier or transistor switch (5). Alternatively, a comparator may be used to evaluate the output voltage. The detector is located between the turns, or in the centre of, the spiral heating element.