JPH0157478B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-frequency heating device that controls a heating operation by detecting changes in the amount of gas emitted from heated food, that is, changes in gas concentration. Recently, in a microwave oven known as this type of high-frequency heating device, a gas sensor detects the increase in the amount of gas emitted from food as cooking progresses, and the change in gas concentration, which is the detected amount. A device that stops the heating operation when the number of minutes reaches a set level has been developed and is being put into practical use. By the way, such microwave ovens are covered in the magazine "Electronic Technology" (August 1979 issue) published by Nikkan Kogyo Shimbun.
As disclosed in the Practical Gas Sensor (described on pages 50 to 56) published by the company Figaro Giken in the "Special Feature: Practical Humidity and Gas Sensors and How to Use Them", for example, semiconductor gas sensors made of ZnO-based elements. This semiconductor gas sensor has the following characteristics. FIG. 1 shows changes in the output level of the gas sensor in response to changes in ambient temperature using ambient humidity as a parameter, and it can be seen that the detection output varies depending on the surrounding situation. Further, FIG. 2 shows the change in the output level with respect to the change in the resistance value of the gas sensor, and it can be seen that even if the resistance value change r is the same, the output level change e will be greatly different if the operating point is different. Furthermore, FIG. 3 shows changes in the output level of the gas sensor over time, and it can be seen that the output level differs between the start of operation and during normal operation. That is, such variations in the detection output of the gas sensor often occur, for example, due to residual gas during several successive cooking sessions, which naturally results in a significant decrease in the reliability of the microwave oven. This invention was made in view of the above-mentioned circumstances, and provides an excellent high-frequency heating device that can always perform stable heating operations regardless of variations in the detection output of gas sensors, and that can improve reliability. Our goal is to provide the following. That is, the gas sensor detects changes in gas concentration and is greatly affected by temperature changes in the sensor resistance.In order to prevent this as much as possible, the output level of the gas sensor is initialized immediately before heating starts.
In this way, the signal level is accurately detected according to the sensor signal that changes over time, and when the signal level reaches the set level, it is determined that the predetermined temperature has been reached, and the heating output is controlled. An embodiment of the present invention will be described below with reference to the drawings. In Fig. 4, 1 is a microwave oven, and a magnetron 2 is installed on the ceiling of the oven, and the object to be heated, that is, food 3, is heated and cooked by the high frequency waves emitted from the magnetron 2. . The magnetron 2 is connected to a power supply circuit 4 consisting of a high voltage transformer, a rectifier circuit, etc., and this power supply circuit 4 is connected to an AC power supply 6 via a switch 5. Further, on the ceiling surface of the oven 1, a gas sensor 7 for detecting the amount of gas G emitted from the food 3 is provided, for example, a semiconductor gas sensor 7 made of a ZnO-based element. Thus, the output of the gas sensor 7 is supplied to the control section 8, and the output signal of the cooking switch 9 is also supplied to the control section 8. The control unit 8 corrects the output level of the gas sensor 7 before starting cooking under predetermined conditions, and controls the opening and closing of the switch 5 according to the corrected output of the gas sensor 7 or the output signal of the cooking switch 9. It is something to do. FIG. 5 shows the gas sensor 7 and the control section 8 in detail. That is, the gas sensor 7 includes a detection element 7a and a heater 7b for maintaining the detection element 7a at an appropriate operating temperature. Then, a DC voltage V ₁ is applied to the detection element 7a of the gas sensor 7 via the output correction circuit 10. Further, a DC voltage V ₂ is applied to the heater 7b. The output correction circuit 10 includes resistors R ₁ , R ₂ ,
R ₃ , R ₄ , R ₅ and a switching element such as an NPN transistor connected in series with each resistor.
It consists of Q ₁ , Q ₂ , Q ₃ , Q ₄ , and Q ₅ . In this case, the resistance values of resistors R ₁ , R ₂ , R ₃ , R ₄ , and R ₅ are R ₂ < R ₃
The relationship is ＜R ₁ ＜R ₄ ＜R ₅ . However,
The signal voltage at the connection point A between the gas sensor 7 and the output correction circuit 10 is converted into a digital signal by the analog/digital conversion circuit 11 and supplied to the microcomputer 12. Based on a pre-stored program, the microcomputer 12 closes the switch 5 to start cooking after a certain period of time, for example, about 16 seconds after the cooking switch 9 is turned on. Blower motor (not shown) for approximately 16 seconds
It has a function of operating the oven 1 and purifying the inside of the oven 1 by its air blowing action. Furthermore, the microcomputer 12 controls approximately
The output level of gas sensor 7 (connection point A
The output correction circuit 10 is actuated in order to make the output level of the gas sensor 7 match a pre-stored reference level in accordance with the result of this judgment. Further, the microcomputer 12 calculates and stores a setting level based on a heating cooking program (type of food, type of cooking, etc.) set by an operation unit (not shown), etc., and after starting heating cooking, the gas sensor 7 When the output level reaches a set level, the switch 5 is opened to end the heating cooking. Next, the operation of the above configuration will be explained with reference to FIG. First, the food 3 is set in the oven 1, and a cooking program for the food 3 is set. When the cooking switch 9 is turned on, the inside of the oven 1 is purified for about 16 seconds, after which the switch 5 is closed and the magnetron 2 starts to oscillate, thereby starting cooking. By the way, during approximately 16 seconds until heating cooking starts, the microcomputer 12 first turns on the transistor Q ₁ of the output correction circuit 10 and inserts the resistor R ₁ into the gas sensor 7, thereby adjusting the output of the gas sensor 7. Determine the level. Therefore, the microcomputer 12
The output level is at the reference level D as shown at point A in the diagram.
(2~3V), transistor Q ₁
remains on. Further, the microcomputer 12 is configured so that the output level of the gas sensor 7 is B as shown in the figure.
When the voltage is off the reference level D, such as at point or point C, the transistors Q ₂ , Q ₃ ,
Q ₄ and Q ₅ are selectively turned on to make the output level of the gas sensor 7 match the reference level D. here,
The table below shows the operating states of the transistors Q ₁ , Q ₂ , Q ₃ , Q ₄ , and Q ₅ according to the output level of the gas sensor 7, and the transistors marked with ○ are turned on.

[Table] That is, the output level of the gas sensor 7 always matches the reference level D during cooking. Then, when heating and cooking is started, gas G is emitted from the food 3, and the amount thereof increases as the heating time elapses. Then, when the amount of gas G increases and the output level of the gas sensor 7 reaches the set level E calculated and stored based on the cooking program,
The switch 5 is opened to cut off the power supply to the magnetron 2, and heating cooking ends. Therefore, when cooking, the output level of the gas sensor 7 is automatically made to match the reference level, so that even if the temperature or humidity inside the oven 1 changes, the aging of the gas sensor itself will not change. Even if this occurs, desired cooking can be carried out reliably. In particular, when heating is repeated many times, it is not affected by the remaining atmosphere in the oven 1 from the previous heating.
Very effective. Moreover, since the output level of the gas sensor 7 is directly corrected, the control configuration is extremely simple, the productivity is excellent, and furthermore, there are no cost problems. In the above embodiment, the output level of the gas sensor 7 is corrected in five stages, but the number of resistors and transistors in the correction circuit 10 is increased, and the control operation of the microcomputer 12 is adjusted accordingly. If appropriate settings are made, it is also possible to perform correction in more stages. Furthermore, although one resistor is selected from among the resistors of the correction circuit 10, it is also possible to select a plurality of resistors as one set by appropriately setting the control operation of the microcomputer 12. Furthermore, in the above embodiment, the heating operation is stopped when the set level is reached, but the subject matter is not limited to this. It may also be used as a dividing line for output in the case of continuous heating cooking that is performed at one time. In short, any correction may be made to make the output level of the gas sensor 7 match the reference level. As described above, according to the present invention, when performing a heating operation, the output level of the gas sensor is automatically corrected to match the reference level, so that stable heating is always achieved regardless of variations in the detection output of the gas sensor. Accordingly, it is possible to provide a high-frequency heating device that can operate and improve reliability.

[Brief explanation of drawings]

Figures 1, 2 and 3 are characteristic diagrams of a semiconductor gas sensor, Figure 4 is an overall schematic configuration diagram showing an embodiment of the present invention, and Figure 5 shows the main parts of Figure 4 in detail. The configuration diagram shown in FIG. 6 is a diagram for explaining the operation of the same embodiment. 1... Oven, 2... Magnetron, 3...
Object to be heated (food), 5... switch, 7... gas sensor, 8... control section.

Claims (1)

[Claims] 1. One semiconductor gas sensor that detects a signal level that changes depending on the amount of gas emitted from the heated object, an output correction circuit connected to this semiconductor gas sensor, and an output level of the gas sensor that detects the output level of the gas sensor immediately before the start of heating operation. means for making a determination, means for adjusting the output level of the gas sensor to a reference level immediately before the start of the heating operation based on the determination result, and activating the output correction circuit to compensate for variations in the detection output of the sensor, and starting the heating operation. A high-frequency heating device characterized by comprising means for controlling heating output when the output level of the gas sensor reaches a set level later.