Patent ID: 8405411

Claim:
A control method for an induction apparatus having at least one induction coil, at least one capacitor connected in parallel with the induction coil, the induction coil and the capacitor forming a parallel resonant circuit, and at least one switch connected in series with the parallel resonant circuit, between the parallel resonant circuit and a reference voltage, the method comprising: generating a digital test signal dependent on the voltage present in an intermediate node disposed between the switch and the parallel resonant circuit, the test signal comprising a first digital logic level when the voltage in the intermediate node is greater than a predetermined reference value and a second digital logic level when the voltage is smaller than the predetermined reference value, closing the switch for a first closure time, opening the switch at the end of the first closure time, evaluating the test signal for a waiting time when the switch is open to determine the presence or absence of a vessel on the induction coil, determining the presence of a vessel on the induction coil if during the waiting time the test signal maintains its digital logic level or determining the absence of a vessel on the induction coil if during the waiting time the test signal does not maintain its digital logic level, and closing the switch for a second closure time greater than the first closure time upon determining the presence of a vessel on the induction coil, reopening the switch and evaluating the test signal to determine if the test signal digital logic level changes during a waiting time, and repeating the switch closing, switch opening, and test signal evaluation steps using incrementally greater closure times until a change in the digital logic level of the test signal is detected and using the closure time that results in the change in the digital logic level of the test signal to determine the resistance of the vessel disposed on the induction coil.