Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1999-09-02
2000-11-21
Paschall, Mark
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219413, 219492, 99334, 99325, H05B 102
Patent
active
061506370
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for controlling the duration of reheating and/or of cooking of an indeterminate quantity Z of a food product of a given type placed in the chamber of an oven comprising a heating source and a detector of a signal characteristic of the state of reheating and/or cooking of the food product.
Numerous methods of automatic control have already been proposed with different types of detectors adapted to measure a particular signal characteristic of the state of reheating and/or cooking of food.
It has particularly been proposed to use a probe insertable directly within the food to measure the internal temperature of this food. In view of the difficulties encountered in certain situations, in particular in the case of frozen foods in which it is impossible to insert the probe, other methods have been developed involving the use of a detector measuring a characteristic signal without requiring physical contact with the food, this detector being for example a detector measuring the atmosphere (temperature or humidity) escaping from the cooking chamber, or else an infrared detector measuring the surface temperature of the food.
French patent FR-2 437 577 discloses an oven in which an infrared detector measures the surface temperature of the food and operates either according to a first control mode in which the heating is stopped as soon as a reference temperature is reached, or according to a second control mode in which the power of the oven is modulated as a function of the measured surface temperature. The modulation of the power consists either in providing successive supply cycles at a fixed power according to interrupted supply, or carrying out a progressive decrease by reducing the power.
The preceding method permits applying energy to the food gently. It is however not ideal when the energy source used is a hyperfrequency source, because it works against the result generally sought in microwave ovens, namely rapidity of cooking.
Moreover, the previous method supposes that the temperature of the food in the course of a reheating and/or cooking operation follows an even upward curve, with little or even no fluctuations, as shown by curve C.sub.1 in FIG. 1 showing the theoretical variation of temperature T of a food of a given type as a function of time t. This hypothesis has been found to be wrong in practice, as can be seen from the curve C.sub.2 of FIG. 1 representing a real case of variation of temperature T of said food as a function of time t. The observation of this curve shows that an instantaneous measure of temperature is of little significance, particularly in the portion of the curve comprised within the time interval t.sub.a to t.sub.b. Thus, within this interval, the time t.sub.a can be recorded as representing the instant at which the reference temperature has been reached, whilst in the absence of fluctuations of the signal (curve C.sub.1), the time t.sub.b would be recorded as the time necessary to reach the reference temperature.
There is also known from U.S. Pat. No. 4,812,606 another process for controlling the duration of cooking of a food in a microwave oven in which the temperature of the air in the cooking chamber is measured at a predetermined instance after the beginning of cooking, the residual temperature time is determined from a pre-established polynomial equation in an empirical manner relating the measured time to the residual time, then the supply is stopped when the residual time has passed.
There again, this process is not effective unless it is considered that the temperature undergoes little fluctuation with time, which is not generally the case in practice.
It will thus be easily seen that all the methods relying on the use of an instantaneous measurement of temperature to determine whether the supply from a source of energy should be altered, are hardly reliable.
SUMMARY OF INVENTION
The present invention has for its object a new process for controlling the duration of reheating and/or cooking of an indeterminate quantity Z of
REFERENCES:
patent: 4370546 (1983-01-01), Warner
patent: 4918276 (1990-04-01), Oh
patent: 4962299 (1990-10-01), Duborper et al.
patent: 5352866 (1994-10-01), Cartwright et al.
patent: 5530229 (1996-06-01), Gong et al.
Arroubi Mustapha
Durand Lionel
Moulinex (S.A.)
Paschall Mark
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