1. Field of the Invention
The present invention relates to a method for detecting the presence of a cooking utensil on an induction heating element placed below an insulating surface, as well as an induction cooking hob using such method.
2. Description of the Related Art
Nowadays all induction cooktops execute pan detection routines immediately after the user has activated a single induction heating element. The object of the pan detection routine is to assure that a ferromagnetic pan is placed onto the hob in order to prevent potential hazardous situations.
Running pan detection routines implies that power is supplied to the heating element and therefore to the pot. Even though the power is supplied at the minimum level possible, nevertheless the induction hob cannot avoid heating up the pot. Furthermore, whenever the induction power converter is activated, it generates disturbing noise at start. These facts wouldn't be a problem if the user has placed an actual ferromagnetic pot on the hob but, in case a pan or pot not good enough or other metallic objects are placed onto the hob, the above known routine can heat up uselessly and dangerously the metallic object interrupting the normal functioning of the other heating elements of the hob.
Summing up, the drawbacks of this pan known pan detection routine are:                energy is spent uselessly;        there is a noisy audible “click” at start of the routine;        power supply to the other induction heating elements of the hob that are connected to the same induction power converter is interrupted.        
Furthermore, pan detection routines might become more and more complicated in case of induction hobs with “mixed” areas as the bridge, multiple-coil expandable or so called “cook anywhere” configuration where the pan can be placed in whatsoever location on the hob. These complex configurations might require the pan detection routine to be executed on each different coil and then it might require an unacceptable time before detecting the pan.