Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2000-09-21
2001-07-10
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S518000
Reexamination Certificate
active
06259069
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns an apparatus for detecting the presence and/or the size of a cooking vessel on an electrically heated hotplate or hob, which includes a resistance heating element which is disposed under the hotplate or hob and which is connected to an electrical heating voltage supply.
2. Discussion of the Prior Art
Pot detection apparatuses of that kind are widely known. Thus, EP 0 788 293 A1 describes an electrical radiant heating body with a pot detection means, which uses an inductive sensor in the form of a loop of thick wire, which is disposed in the air space between the heating conductor and the hotplate and serves as an inductive element of a resonant circuit whose resonance frequency is displaced when a pot is placed on the hotplate by virtue of a change in the inductance of the wire loop.
DE 196 46 826 A1 discloses a pot detection arrangement using capacitive sensors which are formed by a plurality of electrodes, which are also disposed between the heating conductor and the hotplate, and with which an electrical resonance circuit is driven. When a pot is placed on the hotplate, the capacitance of those sensors changes, and therewith also the resonance frequency of the resonant circuit.
DE 39 34 157 A1 describes a cooking tray or hob in which a plurality of sensors are disposed therein for the purposes of detecting the surface area occupied by cooking vessels of different sizes. The sensors used are ultrasonic sensors or capacitive sensors, for measuring the heat flux or for measuring the radiation issuing from the heating means and the hotplate.
The pot detection apparatus disclosed in EP 0 553 425 B1 uses a sensor in the form of an electrical conductor which forms an open loop and which is disposed between the heating element and the hotplate. When a pot is put onto the hotplate, the conductivity of that sensor changes.
The described state of the art, for pot detection purposes, always requires special sensors which are arranged in the cooking tray or between the heating conductor and the hotplate. Those sensors must be designed in such a way that they can withstand the high temperatures of the cooking zone. In addition, steps must be taken to ensure that those sensors do not interfere with the electrical insulation system of heating means-cooking pot. In addition, a pot detection apparatus with such sensors is not suitable for use in relation to hotplates, against the underside of which the electrical resistance heating bears directly (by way of an insulating layer), without the presence there of an intermediate air gap in which those sensors could be disposed.
SUMMARY OF THE INVENTION
Based on that state of the art, the object of the present invention is to implement a pot detection apparatus of a simple structure, which does not suffer from the above-indicated disadvantages.
That object is attained by an apparatus for pot detection, in which the resistance heating element is utilized as a capacitive sensor for pot detection.
Using the resistance heating element itself as a capacitive sensor for pot detection means that there is no need for an additional sensor which would have to be disposed in the hotplate-resistance heating system. This therefore excludes from the outset any adverse effect in relation to the electrical insulating system consisting of the heating arrangement and the cooking pot. In addition, there is also no need for an air gap between the heating element and the hotplate, and the heating element can be brought into direct contact with the hotplate. In addition, the expenditure involved in securing an additional pot detection sensor in position and wiring it into circuit is eliminated.
Preferably, the invention is such that the capacitance of the resistance heating element, in relation to a reference potential, preferably earth, is connected into an electrical resonant circuit, that the resonance frequency of that resonant circuit can be detected by an evaluation unit, and that in that way the presence and/or the size of a cooking vessel on the hotplate can be ascertained.
The resistance heating element is preferably connected to the heating voltage supply by way of electrical switching means, preferably inductors, and is connected into the resonant circuit by way of a further electrical switching means, preferably a separating capacitor. In an advantageous embodiment the resonant circuit contains the resistance heating element, the separating capacitor, an inductive element, preferably a coil, and the reference potential. In addition it is preferably provided that a capacitor is connected between the electrical terminals of the resistance heating element.
In the case of multi-circuit hotplates, a development of the invention provides that it is possible to use a plurality of resonant circuits, wherein the respective heating element forming the corresponding heating circuit is used as a capacitive sensor for pot detection.
It is further provided that the hotplate comprises ceramic or glass ceramic, that the resistance heating element is a radiant heating body, a foil heating element or a heating path or layer disposed on a support, and that the resistance heating element has line windings or a flat ribbon or band.
The use of a flat ribbon or band heating body, a foil heating element, a heating layer or a heating path is particularly desirable for the invention as such a flat heating element is particularly well suited as a capacitive element.
In a preferred embodiment of the invention, by virtue of the value of or by virtue of the change in the resonance frequency of the resonant circuit, the size of a cooking vessel which is standing on the hotplate or the degree to which the hotplate is covered by a cooking vessel, can be detected by the evaluation unit.
It should be noted here that the invention concerns an apparatus for pot detection, with which it is not only possible to ascertain whether a cooking vessel is or is not standing on the hotplate, but also how much of the surface area of the hotplate is covered by a cooking vessel, whether a large or a small cooking vessel is standing on the hotplate, and whether it is standing thereon at a central position or in a laterally displaced position.
REFERENCES:
patent: 4334135 (1982-06-01), Smith
patent: 5296684 (1994-03-01), Essig et al.
patent: 5424512 (1995-06-01), Turetta et al.
patent: 5491423 (1996-02-01), Turetta
patent: 5893996 (1999-04-01), Gross et al.
patent: 5977523 (1999-11-01), Scott
patent: 3734157 A1 (1991-04-01), None
patent: 196 46 826 A1 (1997-08-01), None
patent: 0 553 425 B1 (1993-08-01), None
patent: 0 788 293 A2 (1997-08-01), None
Meyer Jorg
Morsch Norbert
Schotten Henno
Diehl AKO Stiftung & Co. KG
Paik Sang
Scully Scott Murphy & Presser
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