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Dry Boil Algorithm Disclosure Number: IPCOM000020192D
Publication Date: 2003-Oct-31
Document File: 3 page(s) / 92K

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Dry Boil Algorithm

This proposal is related to kettles with the sensor mounted on the base plate where also the heating element is mounted. The sensor has a bad thermal connection with the base plate. It is obvious that the temperature of the water is not measured when the system is operating. The measured temperature depends very much of the values of the different thermal impedances in different layers and mountings. One major problem is the influence of the ambient. In this case the heat radiation has a lot of effect on the sensor. Also in other constructions as known from, for instance certain fryers, this is a major problem. Having a bad thermal connection of the sensor with the base plate it is in principle not possible to measure the correct temperature. This proposal consists of temporarily switching of the power to measure the water temperature. What happens is the following: if the thermal impedance of the sensor to the ambient is large enough, then the water capacity will heat up the sensor. So the sensor measures the water temperature when the temperature has stabilized. This measurement is done at the start of the process. The power is switched on, 3 seconds later the power is switched of, then the temperature must be watched for several seconds to see where the temperature ends. This will be an indication of how much water is placed in the kettle.

This proposal describes a method to measure temperature accurately. With help of this temperature measurement it is possible to determine the amount of water, or no water on an accurate way. This method is useful for these systems where the sensor is not directly put in the water. Problems with electronic boil detections are ambient temperatures, heating elements, heat flows over the bottom. Water behavior during almost boiling, locally boiling and the moment all water is boiling. With help of determining the amount of water or the determining of no water at all an extra input variable is without additional cost available. This results in a much better performance of the boil detection.

Measuring temperature in an accurate way and in a cheap way is always a problem. Nowadays more and more microcontrollers are used because they become very cheap. When a microcontroller is already used in an application it is very easy and without any additional cost to implement this method.

Further regarding the measurement of the amount of water it is known that the dynamic behavior of the water and the temperature of the heating element is very much determined by how much water is tried to boil. The major problems occur when no water is tried to boil or very less water up to for instance 0,5 liter water, this is determined by measurements of the kettle and the applied power. With help of the temperature measurement it is possible to determine more accurate the amo...