Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-12-06
2001-05-01
Paik, Sang (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S446100, C374S131000
Reexamination Certificate
active
06225607
ABSTRACT:
BACKGROUND OF INVENTION
FIELD OF THE INVENTION
The present invention relates to a sensor-controlled cooktop with a cooktop plate, in particular made of glass ceramic or glass, with at least one cooking zone that is heatable by means of a heating element arranged below the cooktop plate, and with a heat radiation sensor unit arranged below the cooktop plate and directed toward the underside of the latter in the region of a measuring spot of limited area and which is connected to a control unit for regulating the heat output of the heating element.
A cooktop of this type is known from published British patent application GB 2 072 334 A. There, a parabolic reflector arrangement is provided below the cooktop plate. The reflector arrangement collects the heat radiation radiated from the underside of the bottom of a pan put down on the cooktop plate and heated by means of the heating element and conducts this heat radiation via a connected optical connecting line to an infrared-sensitive photodiode. The heat radiation detected in this way is used as a signal for regulating the heat output of the heating element.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a sensor-controlled cooktop, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which ensures that the heat output is regulated with sufficient accuracy independently of the pot.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sensor-controlled cooktop, comprising:
a cooktop plate, particularly a glass-ceramic plate, having an underside and a top surface with at least one cooking zone;
a heating element for heating the cooking zone disposed below the cooktop plate;
a heat radiation sensor unit disposed below the cooktop plate and directed towards a measuring spot of limited area defined on the underside of the cooktop plate, the heat radiation sensor unit having a defined spectral measuring range;
a control unit connected to the radiation sensor for regulating a heat output of the heating element; and
the cooktop plate, in a region of the measuring spot, having a transmittance in the spectral measuring range of the heat radiation sensor unit of less than 30%, or less than 10%, or, preferably, 0%.
In other words, the objects of the invention are satisfied in that the value of the transmittance of the cooktop plate, at least in the region of the measuring spot, amounts, at least in the spectral measuring range of the heat radiation sensor unit, to a substantially reduced amount. Selecting a low value for the transmittance of the material of the cooktop plate ensures that the unknown and therefore disturbing influence of the heat radiation radiated from the pot bottom in the direction of the cooktop plate and therefore onto the heat radiation sensor is minimal. This is important particularly because the value of the emittance of the underside of the pot bottom may shift typically between 20 and 90%, depending on the type of cooking pot. The invention therefore ensures that the heat radiation sensor receives essentially to exclusively the heat radiation radiated from the underside of the cooktop plate.
In accordance with an added feature of the invention, an emittance of the cooktop plate, at least in the region of the measuring spot and at least within the spectral measuring range of the heat radiation sensor unit, amounts to at least 60% and, in a preferred embodiment, to at least 90%.
This helps achieve sufficient measuring sensitivity of the sensor-controlled cooktop. The measuring accuracy according to the invention is at least sufficient to make it possible to carry out roasting or frying operations with satisfactory cooking results. In order to increase the accuracy of the sensor-controlled system, it is expedient to use pots or pans which have a bottom which is as flat as possible and therefore rests over a large area on the top side of the cooktop plate.
In accordance with an additional feature of the invention, a dark emission layer is formed on the underside of the cooktop plate in the region of the measuring spot. A measuring spot having suitable transmission and emission properties can be implemented at low outlay by providing the cooktop plate with the dark emission layer. The layer is preferably black. The transmission and emission values are then, on the one hand, independent of manufacturing spreads and, on the other hand, essentially constant over the lifetime of the cooktop plate in spite of the aging of the latter. Furthermore, the values are then also independent of the properties of the material of the cooktop plate or independent of the manufacturer or color shade.
In accordance with another feature of the invention, the measuring spot has a surface extent of about 1 to 4 cm
2
. This is a particularly suitable size of the measuring spot. It ensures, on the one hand, that the measuring spot is not too large, which would be detrimental to achieving a uniform cooking result in the pan or pot. On the other hand, the measuring spot also should not be too small, so that the influence of the heat radiation of the pot bottom on the glass ceramic remains sufficiently high. If the surface extent of the measuring spot is too small, its sensed temperature, despite the low thermal conductivity of, for example, glass or glass ceramic, essentially depends solely on the temperature of the glass ceramic in the vicinity of the measuring spot. The purpose of the cooktop according to the invention, however, is to deduce the temperature of the cooking vessel put down on the cooktop plate and heated or to regulate this temperature.
In accordance with a further feature of the invention, the heat radiation sensor unit includes a spectral filter having a spectral passband of approximately 4 to 8 &mgr;m. In this range, both the value of the transmittance and that of the average reflectance of the material of the cooktop plate in the case of typical glass-ceramic cooktop plates are sufficiently low. The result of this, in this wavelength range, is a high emittance of the underside of the cooktop plate and consequently high measuring sensitivity and accuracy. Alternatively, the spectral passband may typically also be between 10 and 20 &mgr;m. In this range, too, the value of the transmittance in the case of typical glass-ceramic material is about 0% and that of the reflectance is markedly lower than in the wavelength ranges adjacent on both sides. The choice of a suitable spectral filter depends, in particular, on its price and on the sensitivity or measuring and regulating accuracy of the sensor-controlled cooktop which can be achieved in the respective wavelength range.
In accordance with again an added feature of the invention, a measuring well is disposed at the underside of the cooktop plate in the region of the measuring spot. The heat radiation sensor unit is directed onto the measuring spot of the cooktop plate. This measure ensures that the influence exerted on the temperature of the measuring spot by the heating element radiating the heat radiation is greatly reduced or is ruled out. In this case, it is particularly favorable if the measuring well bears as closely as possible against the underside of the cooktop plate, and if the radiation channel in the measuring well is insulated as effectively as possible from the space outside the measuring well.
In accordance with a corresponding feature of the invention, the heating element surrounds the measuring well and the measuring spot substantially on all sides. This feature helps achieve as uniform a distribution of heat as possible in the pot bottom and in the cooktop plate and consequently high measuring accuracy.
In accordance with a concomitant feature of the invention, a computing unit receives a signal of the heat radiation sensor unit. The computing unit then computes, from the signal and from characteristic data of the cooktop stored in s memory unit, a temperature of a bottom of a heated pot placed on the cooktop plate
Has Uwe
Horn Katrin
Neuhauser Maximilian
BSH Bosch und Siemens Haus-geraete GmbH
Greenberg Laurence A.
Lerner Herbert L.
Paik Sang
Stemer Werner H.
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