The present invention relates to a cooking utensil and, more particularly, to a control circuit responding to an output signal derived from a gas sensor in a cooking utensil, for example, a microwave oven.
Recently, a combined microwave and electric heating cooking oven has been developed. In such a cooking oven it is very difficult to determine a preferred cooking time period. The cooking time period must be determined in accordance with the kind of foodstuff to be cooked, the initial condition of the foodstuff, the amount of the foodstuff, the output energy level of the cooking apparatus, the environment condition, etc.
One approach is to detect the food temperature or the oven temperature to control the microwave generation or the heater energization. However, the temperature responsive control is not perfectly satisfactory.
Accordingly, an object of the present invention is to provide a novel control system for a cooking utensil.
Another object of the present invention is to provide a combined microwave and electric heating cooking oven including a gas sensor and a control circuit responding to an output signal derived from the gas sensor.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects pursuant to an embodiment of the present invention, a gas sensor is disposed in a path of the gas exhausted from an oven cavity. A control circuit is provided for terminating the microwave generation or the heater energization when an output voltage signal of the gas sensor reaches a preselected value.
A plurality of selection switches are provided for determining the above-mentioned preselected value, at which the control circuit responds, in accordance with the kind of foodstuff to be cooked. More specifically, the selection switches are associated with resistors for selecting the preselected value by dividing an output voltage level of the gas sensor in an initial condition.
The present control is based on the fact that the concentration of the gas developed from the foodstuff being cooked reaches a predetermined value when the foodstuff has been cooked. The predetermined value of the gas concentration varies in a fashion depending on the kind of foodstuff being cooked. The output voltage signal of the gas sensor represents the gas concentration and, therefore, the completion of the cooking can be detected by detecting whether the gas sensor output reaches the preselected value.