Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-11-03
2001-04-17
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S449100, C219S448110, C219S492000, C219S494000, C219S459100
Reexamination Certificate
active
06218646
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of adjusting a limiting value of an operating temperature of a cooking unit, which has a glass or glass-ceramic cooking surface with at least one heated cooking zone. The invention also relates to a device for performing the method.
2. Prior Art
The glass-ceramic material for a modern cooking unit with a glass-ceramic cooking surface is made by a temperature/time treatment of a special glass. Among other things, the thermal expansion behavior is adjusted for the application. If impermissibly high temperature/time loads occur in usage, among other things, the reduced thermal expansion behavior is lost and, in extreme cases, the glass-ceramic material can fail or break.
Analogously this is also true for a cooking unit, which uses thermally or chemically pre-stressed glass. At a high operating temperature this leads to a loss of the pre-stressing, which can lead to destruction of the product.
In cooking units of the above-described kind according to the state of the art temperature monitoring of the glass/glass-ceramic cooking surface is provided by means of an operating temperature limiting device, which is adjusted so that the permissible temperature/time load on the glass/glass-ceramic cooking surface during the required operating life at a nominal operating frequency is not exceeded. A guideline or directive for the operating frequency has been published in German Standard DIN VDE 0700, Part 6, Appendix 8.
A mechanical operating temperature limiting device with a solid expansion controller is known. Also an electronic operating temperature limiting device is known. A conductor strip directly mounted on the cooking surface (as in DE 40 22 846 C2) or a discrete platinum temperature-measuring resistor (as in DE 37 36 005 A1) can be used as a sensor for this electronic operating temperature limiting device. However these electronic operating temperature limiting devices according to the state of the art—just as the corresponding mechanical operating temperature limiting devices—are always calibrated or adjusted to a fixed temperature limiting value and shut off the heating of the respective cooking zone, as soon as the set boundary or limiting value of the operating temperature, also the so-called shut-off temperature, has been reached.
These operating temperature limiting devices thus monitor the temperatures occurring in the cooking unit so that no impermissible change of the glass/glass-ceramic material occurs within the predetermined lifetime.
The usage frequency of the cooking unit differs from household to household according to different lifestyles. The above-mentioned standard for the operating frequency for safety of the user produces a comparatively high load with frequent cooking. In the current state of the art the given value for the operating frequency and the limiting value of the operating temperature determined from that lead to the disadvantage that the user who operates the cooking unit with reduced operating time cannot use the available permissible temperature/time load, i.e. the full potential of the cooking unit in regard to the ability of the glass/glass-ceramic cooking surface to withstand a load. It would be permissible for an operator who runs the cooking unit with reduced operating time to use a higher operating temperature for individual cooking events so that the cooking time for those individual events can be reduced.
If the user only uses an easy-to-use cooking utensil or if the utensil is empty, the given temperature/time load cannot be utilized. Also here the full potential of the glass-ceramic cooking surface cannot be used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of adjusting a limiting or boundary value of the operating temperature of a cooking unit, whereby the full potential of the cooking unit to withstand a load on its glass/glass-ceramic cooking surface is better utilized, while still guaranteeing that the service life of the cooking unit is not reduced.
It is another object of the present invention to provide a device for performing the method of adjusting the limiting or boundary value of the operating temperature of the cooking unit, whereby the full potential of the cooking unit to withstand a load on its glass/glass-ceramic cooking surface is better utilized, while still guaranteeing that the service life of the cooking unit is not reduced.
The method according to the invention comprises the steps of:
a) measuring a cooking surface temperature and turned-on time of the cooking unit to obtain temperature and time value pairs during a respective usage time interval and calculating a cumulative actual temperature/time load value from these temperature and time value pairs and also a cumulative operating time value from the respective turned-on time of the cooking unit during the respective usage time interval of the cooking unit;
b) storing the respective cumulative temperature/time load value and the cumulative operating time value during operation of the cooking unit;
c) storing a predetermined sequence of temperature and time value pairs as a permissible temperature/time load for a predetermined usage frequency over a standard service life of the cooking surface;
d) comparing the cumulative temperature/time load value stored in step b) with the permissible temperature/time load stored in step c) for the respective cumulative operating time values during a predetermined time interval (comparison interval); and
e) determining a limiting value for the operating temperature according to the comparing of step d) in order to obtain a permissible temperature/time load for the glass/glass-ceramic cooking surface for the given service life of the cooking unit.
The apparatus according to the invention comprises an operating temperature limiting means with adjustable operating temperature boundary or limiting value and at least one temperature sensor associated with it which measures the temperature in the heated cooking zone and a control unit for switching off the heating of the cooking zone when the limiting value of the operating temperature is reached, in which the operating temperature limiting means for adjusting the operating temperature limiting or boundary value includes a clock and a measurement and evaluation means for measuring, storing and comparing the temperature and time value pairs during respective usage time intervals and the turned-on time for each use required in the above-described method according to the invention.
The method and apparatus according to the invention have the advantage that they adjust the shut-off temperature for the operating temperature limiting means according to the usage frequency of the cooking unit. If the usage frequency is reduced in comparison to a standard guideline for the permissible load, a higher operating temperature can be permitted until the permissible standard load curve is reached. However the reverse is also true, namely that when the cooking unit is used very frequently, then the limiting value of the operating temperature must be reduced.
The energy or heat transferred to the cooking utensil on the cooking unit is increased by a higher operating temperature of the cooking surface, so that the cooking duration is advantageously shortened, without exceeding the permissible temperature/time load and thus guaranteeing that the service life of the cooking unit is not impaired.
In practice phases of frequent usage alternate with phases of reduced usage. After a phase of reduced usage the actual cumulative load is below that for the permissible maximum load at this time point. According to the method of the invention then in that situation the permissible limiting value for the operating temperature is increased. According to the usage frequency the permissible load curve is again reached sooner or later with this new temperature limit adjustment.
In rare or unusual cooking situations then as the need requires the method according to the invention
Dudek Roland
Engelmann Harry
Nass Peter
Schaupert Kurt
Pwu Jeffrey C
Schott Glas
Striker Michael J.
Walberg Teresa
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