Pan detector for induction heating cooking unit

Claim 2

In an induction heating cooking unit of the type including a work coil which is adapted to be coupled electromagnetically to a cooking vessel placed in overlying relation to said coil; safety control means responsive to levels of magnetic flux above and below a given range of values of said flux for preventing and permitting, respectively, energization of said coil; permanent magnet means disposed relative to said safety control means, and to the location of the base wall of a cooking vessel when properly located over said coil, to direct a magnetic field with a flux level above said given values through said safety control means in the absence of a ferromagnetic mass at least comparable to the smallest cooking vessel to be used on said coil and in said proper location; said magnetic field being shunted sufficiently in the presence of said mass in said proper location to reduce the flux level of the field through said safety control means to a value below said given values, so that unless an adequate load for coupling is present above said coil, said coil is prevented from being energized.

Claim 3

In a unit according to claim 1 wherein: said safety controls means comprises switching means closely adjacent said coil; and said permanent magnetic means comprise a pair of permanent magnets on opposite sides of said switching means, said magnets being disposed relative to said switching means, and having their poles arranged, and being spaced apart such that in said absence of said mass the flux level passing through said switching means causes said switching means to assume one condition, and in the presence of said mass the field is shunted sufficiently from said switching means that the flux level through said switching means is reduced sufficiently that said switching means assumes another condition.

Claim 4

In a unit according to claim 1 wherein: said safety control means includes a magnetic reed switch.

Claim 5

In a unit according to claim 2 wherein: said permanent magnets have their poles oriented generally vertically, with the north pole of one magnet being upwardly facing and the north pole of the other magnet being downwardly facing, and with said magnets being spaced apart sufficiently that said reed switch is located in a fringe area of the magnetic lines of force.

Claim 6

In an induction heating cooking unit of the type including a work coil underlying a refractory material sheet forming a cooking surface upon which a cooking vessel is adapted to be supported and electromagnetically coupled to the coil when the coil is energized, an arrangement for controlling the energization of said work coil in accordance with the presence of a ferromagnetic mass at least comparable to the base wall of the smallest cooking vessel to be used with said cOil when in overlying relation to said coil comprising: safety switch means responsive to the presence of levels of magnetic flux above and below a given range of values to assume one and another condition, respectively; permanent magnet means disposed relative to said safety switch means and to the location of the base wall of the cooking vessel properly located over said coil, to place said safety switch means in a magnetic field providing a level of magnetic flux above said given range of values in the absence of said base wall of said cooking vessel, said permanent magnet means being so disposed that sufficient lines of force are shunted sufficiently in the presence of said base wall of a cooking vessel to reduce the levels of magnetic flux in which said safety switch means is present to a level below said given range of values; and electrical circuit means for controlling energization of said coil including said safety switch means in said one condition preventing energization of said coil and in said another condition permitting energization of said coil, so that unless an adequate load for coupling is present in the proper location overlying said coil, said coil is prevented from being energized.

Claim 7

In an induction heating cooking unit of the type including a work coil underlying a refractory material sheet forming a cooking surface upon which a cooking vessel is adapted to be supported and electromagnetically coupled to the coil when the coil is energized, an arrangement for controlling the energization of said work coil in accordance with the presence of a ferromagnetic mass at least comparable to the base wall of the smallest cooking vessel to be used with said cOil when in overlying relation to said coil comprising: safety switch means responsive to the presence of levels of magnetic flux above and below a given range of values to assume one and another condition, respectively; permanent magnet means disposed relative to said safety switch means and to the location of the base wall of the cooking vessel properly located over said coil, to place said safety switch means in a magnetic field providing a level of magnetic flux above said given range of values in the absence of said base wall of said cooking vessel, said permanent magnet means being so disposed that sufficient lines of force are shunted sufficiently in the presence of said base wall of a cooking vessel to reduce the levels of magnetic flux in which said safety switch means is present to a level below said given range of values; and electrical circuit means for controlling energization of said coil including said safety switch means in said one condition preventing energization of said coil and in said another condition permitting energization of said coil, so that unless an adequate load for coupling is present in the proper location overlying said coil, said coil is prevented from being energized.