Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1998-03-13
1999-08-31
Paschall, Mark
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219497, 219486, 219508, 99327, 99333, H05B 102
Patent
active
059450185
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an oven for food products with means for controlling the supply of heat in accordance with the progress of the cooking effected.
Ovens are known in which a temperature sensor is pushed into the food to be cooked which monitors the temperature development. Long experience with manual adjustment has built up a body of data which enables a feedback loop to be established around a temperature sensor and a power controller. This enables a very precise cooking and consistent results, provided the sensor is fitted absolutely correctly into the food. However, the need for an invasive sensor is percieved as impractical, as it requires frequent cleaning, and the need for high temperature plugs and sockets which are exposed to the humid, perhaps smoky and fatty atmosphere in the oven makes this solution less attractive. On the other hand, non-invasive techniques generally require a knowledge of the weight of the food.
In EP 0 239 290 B1 there is described a partial solution to the above problems in conjunction with a microwave oven where, after a cooling-down period to a specific temperature, the temperature rise due to application of heat is determined and used in conjunction with stored information for deciding on remaining cooking time and a maximum temperature of the oven during this time. However, the need for recalibration by means of cooling is complex and time-consuming, and the precision in the determination of the temperature rise is not sufficient to consistently provide a high quality result, in particular with an extended range of foodstuffs, including as cakes and pastry. There is hence scope for improving such methods for cooking and baking with minimal involvement of the user, in other terms there is a need for an expert-system type solution to the general problem of cooking food to a preferred quality.
BRIEF SUMMARY OF THE INVENTION
It has now been recognized that the food product itself constitutes a load on the supply of heat, and the changes in the product as cooking progresses express themselves as changes in the load. The oven as well as the food product possesses a thermal mass, but in particular the water content of the food product changes the heating function from a simple exponential relationship. Also the heat absorbing properties of the surface of the food product change with cooking which further removes the heating function from a simple relationship. It has, however, now been recognized that a great simplification in the use of an oven may be obtained by judicious use of the concept of thermal load. It is the purpose of the invention to provide an oven of the kind identified above in which the only necessary informational input from the user is the type or category of food to be cooked. Optional input may relate to the degree of cooking or baking and the initial status, e.g. frozen or "to be re-heated".
An oven which fulfils this purpose is peculiar in that during a heating-up phase it heats the food by alternating between at least two types of heat source while the relationship between oven temperature and time is logged and used for controlling the type of heat source and the supply of power during the remainder of the cooking time in accordance with the type of food being cooked.
In order to control the process an embodiment of the invention is particular in that the oven temperature is determined by means of at least one thermometric device fixed in the oven. Another advantageous embodiment is particular in that several thermometric devices are used, at least one of which being placed where heat is transported by convection. A further advantageous embodiment is particular in that at least another thermometric device is shielded from convection. These embodiments all serve to create as relevant an input to the control circuit as possible, and the ability to distinguish between air flow temperature and cavity temperature is very indicative of the processes taking place in the oven.
A functional relationship between the heat sou
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patent: 4647746 (1987-03-01), Eke
patent: 4812606 (1989-03-01), Eke
patent: 4831227 (1989-05-01), Eke
patent: 5177333 (1993-01-01), Ogasawara
patent: 5408075 (1995-04-01), De Matteis et al.
Aktiebolaget Electrolux
Paschall Mark
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