An exemplary embodiment of the present invention is shown in the drawings in a purely schematic way and will be described in more detail below. In the drawings,
The present invention provides a reduction in the complexity of the circuitry and in the amount of computing power required of the electric controller of the baking oven, and also the possibility of using the method during pyrolytic cleaning processes in baking ovens. Moreover, the measurement and evaluation of the oxygen concentration in the cooking chamber allows high accuracy and reproducibility of the values measured using the method according to the present invention, and thus of the inventive method, since the amount of oxygen present in the cooking chamber is large enough during the entire cooking process or pyrolytic cleaning process to ensure a reliable measurement.
The specified range of values for the oxygen concentration limit ensures rapid and early detection of a dangerous situation prior to the actual occurrence of a fire in the cooking chamber. Laboratory tests performed showed that it is advantageous to use a limit of 18 percent by volume (abbreviated “vol. percent”) in one embodiment. Additionally, the limit for the rate of change of the oxygen concentration provides protection against false alarms and erroneous shutdown of the cooking chamber heating element or of the air circulation through the cooking chamber. Such malfunctions could occur if the limit selected for the rate of change of the oxygen concentration is too low. Unavoidable variance in the measured values, and unavoidable changes caused, for example, by steam released from the food, or, during the pyrolysis cycle, by the pyrolysis of the soils which have accumulated on the walls of the cooking chamber, could then lead to unwanted and false detection of a fire condition.
Food 16 placed on a food-supporting member is inserted in cooking chamber 4. Further, the baking oven has an electronic controller 18, which contains an evaluation circuit 18.1 with a timer and a memory 18.2 and is in signal communication with an oxygen sensor 14 located in a vapor duct 24 and with a cooking chamber heating element 20 in the form of a resistance heater.
When the baking oven is in operation, the vapors are removed from cooking chamber 4 through a catalyst 22 and vapor duct 24 in a manner known to those skilled in the art. This is symbolized by arrows 26. Thus, oxygen sensor 14 detects an instantaneous oxygen concentration, since the gases formed during the cooking process, or by pyrolysis during a pyrolytic cleaning process, are continuously removed from cooking chamber 4. These gases do not concentrate in cooking chamber 4.
The method according to the present invention is not limited to baking ovens having a catalyst 22.
If the baking oven is provided with a catalyst 22, as explained earlier for the present exemplary embodiment, it is generally advantageous to place oxygen sensor 14 downstream of the catalyst 22 in the direction of flow since the output signal of oxygen sensor 14 transmitted to the evaluation circuit is thereby amplified. This is the case because the oxidizable gas molecules escaping from food 16 are oxidized by the action of catalyst 22, and the number of gas molecules that displace the oxygen is thereby increased downstream of catalyst 22. In the process, oxygen is consumed. Thus, the oxygen concentration is reduced to a greater extent than when the sensor 14 is installed upstream of catalyst 22 in the direction of flow, for example, when installed in cooking chamber 4. Because of this, it is possible to use an oxygen sensor 14 that is less sensitive and therefore less expensive.
At the beginning of the pyrolytic cycle described earlier, the profile of the oxygen concentration measured by oxygen sensor 14 starts at the value of the ambient air; i.e., at about 21vol. percent. The oxygen concentration varies during the pyrolytic cleaning process. In the profile shown here by way of example, quantity (1−O2) increases sharply after a while, and then decreases until the initial oxygen concentration of about 21 vol. percent is reached at the end of the pyrolytic cleaning process.
Analogous to
Unlike the profile of (1−O2) in
Alternatively, it would also be possible to only cause a visual and/or audible alarm to be issued to the user. Alternatively or additionally, it is also conceivable either to shut down the cooking chamber heating element, or reduce the heat output thereof, or to shut down or reduce the air circulation through the cooking chamber, for example by means of a fan, or in another manner known to those skilled in the art.
In addition, other values in the range from about 15 vol. percent to about 20 vol. percent could also be used as the limit.
The method of the present invention is not limited to the exemplary embodiment described herein. For example, it would also be possible to use it in baking ovens which do not have a pyrolytic cleaning function, or to use it during a cooking process, and thus at low cooking chamber temperatures.
Number | Date | Country | Kind |
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10 2006 041 767.4 | Sep 2006 | DE | national |