Electric heating – Heating devices – With power supply and voltage or current regulation or...
Patent
1995-12-21
1998-05-12
Paschall, Mark H.
Electric heating
Heating devices
With power supply and voltage or current regulation or...
219501, 219441, 219508, 32420717, 324223, 324239, 324204, H05B 102
Patent
active
057509638
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an apparatus for controlling the electrical power supply to the cooking pot on a cooking device.
2. Description of the Prior Art
Constructions are known which are based on measuring the temperature of the cooking bottom by means of a sensor plate which is pressed against the bottom by means of a spring, whereupon the sensor in a way which is selected from many possibilities controls the Supply of energy until the preselected temperature has been reached, whereupon there is a switching between energy supply and disconnection in order that the temperature is kept constant. This may e.g. be in the neighborhood of the boiling point of the contents of the pot. This construction has the advantage for in particular cooking plates of the traditional type, i.e. solid and spiral, that it may be positioned in the center of the cooking plate and is hence out of the way. The disadvantage is that the temperature measured may be influenced by the cooking plate itself, but in practice there is a greater resistance to heat conduction between cooking plate and sensor than there is between the sensor and the pot bottom against which it rests through spring pressure, which all diminishes the harmful influence. For cooking plates of modern types, e.g. ceramic, halogen or induction which have a plane surface it is disadvantages that wells have to be formed into which the sensors are to be fitted, and in practice such constructions are not used with these types of cooking devices.
Furthermore components are known which in conjunction with the direct energy control constitute a model for the heat transmission between the cooking plate and the content in a pot. In its simplest form these have been known as a "Simmerstat" (reg. trade mark) which have a thermostatic wire with a well-defined heat transfer in conjunction with a knob which intermittently switches the full power on and off. However, this must be manually adjusted for each pot and cooking plate, and hence it of no consequence that the electromechanical construction has been replaced by electronic solutions.
Furthermore thermometric solutions are known in which a remote thermometer is connected to the cooking device by means of a cable for transmitting the signals from the thermometer to the electronic control unit. This provides a control of energy supply which is ideal from a temperature point of view, since it is only the thermal time constant because of the heat supply and the pot which influence the speed of control, but in practical use on a cooking device it is a construction which is not suitable. This is in particular caused by the fact that it is impossible to use a tight fitting lid, that the thermometer sensor may transfer a taste from pot to pot, and that it may be difficult to keep track of a number of remote thermometers, if there is one thermometer per cooking plate.
SUMMARY OF THE INVENTION
It is the purpose of the invention to provide a construction for control of the electric power supply to heat the contents in a pot which avoids the described disadvantages and which permits great flexibility with respect to which cooking plates are to be activated.
This is obtained in a construction according to the invention which is particular in that the measurement of the temperature is performed by creating a magnetic d.c. field in proximity to the contents of the pot, switching off the current which creates this field, and detecting temperature dependent decay of the magnetic field in a subsequent measuring period, and using the result is to control the heat energy supply to the pot in dependence of the difference between the desired temperature.
A desirable embodiment of the invention utilizes the same coil to create the magnetic field and to detect the decay of the magnetic field in a subsequent measuring phase.
A further desirable embodiment utilizes highly conductive parts of a pot such as a coil, the energy dispersion of which as a result of the decay of the magnetic field is
REFERENCES:
patent: 3781506 (1973-12-01), Ketchum et al.
patent: 4620083 (1986-10-01), Andre
patent: 4843319 (1989-06-01), Lara
patent: 5059902 (1991-10-01), Linder
Christensen Keld
Jensen Torben
Aktiebolaget Electrolux
Paschall Mark H.
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