JPH0523334B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oven equipped with a piezoelectric element sensor that detects and controls the state of gas generated from food as the food is heated.

Prior Art As shown in FIG. 10, a conventional microwave oven with a sensor detects a change in the resistance value of a humidity sensor 41 by dividing the voltage of a reference voltage power source 42 with a resistor 43 to control the device. . (For example, Japanese Patent Publication No. 53
-77365 Publication) Problems to be Solved by the Invention This conventional system uses the voltage across the resistor 43 as a control signal. 43. Variations in the voltage of the power supply 42 lead to variations in the control voltage signal, making management difficult. The present invention has been made in view of this problem, and an object of the present invention is to provide a means for detecting the heating state of food with a simple configuration.

Means for Solving the Problems In order to solve the above problems, the present invention utilizes a piezoelectric element sensor different from the conventional sensor as a sensor and further attaches the sensor to the wall of the heating chamber via an insulator. be.

Effects According to the present invention, since a new sensor is used, in principle, there is no need for anything equivalent to the reference voltage or voltage dividing resistor of the conventional example, and control can be performed with a simple configuration.

Embodiment FIG. 1 shows a sensor mounting part of a microwave oven equipped with a piezoelectric element sensor according to the present invention. In FIG. 1, a piezoelectric element sensor 1 has terminals 2 on a sensor mounting plate 3 made of electrically and thermally insulating material such as a printed circuit board.
It is further attached to the wall 4 of the heating chamber via screws 5.

FIG. 2 shows an embodiment of a microwave oven equipped with a piezoelectric sensor according to the present invention. In FIG. 2, the output of the piezoelectric sensor 1 is connected to a voltage amplification amplifier 6 (hereinafter referred to as DC blocking) configured to prevent DC components from being applied to the sensor and to block the DC components of the sensor voltage output. (referred to as an amplifier), a comparator 7 for voltage comparison, and a controller 8.

A food product 11 is placed in the heating chamber 10 , and a portion of the cooling air from the magnetron 9 is guided into the heating chamber 10 through a duct 13 by a fan 12 . A portion of the cooling air is indicated by a solid arrow line 14, and a gas such as moisture generated from the food is indicated by a dotted arrow line 15. The cooling air and the gas containing moisture generated from the food are removed from the exhaust section 16.
It is sent out from the heating chamber 10 through.

A piezoelectric sensor is attached to the exhaust section 16 in the manner shown in FIG. In this example, fan 1
A winding 21 is wound around the core 17 of the motor that drives the motor 2 along with the winding 20 from the power plug via the power switch 19. The voltage diode 25 constitutes a constant voltage power supply section, eliminating the need for a transformer for the control circuit. Further, the buzzer 26 is configured to operate according to a signal from the controller 8 when the amplified signal voltage becomes larger than a set threshold voltage ΔV _T . Examples of actually measured configurations are shown using FIGS. 3 to 5. Figure 3 shows the configuration of the microwave oven used in the experiment. With a radio wave output of 500 W, the radio waves from the magnetron 9 are supplied to the heating chamber 10 via a waveguide, and the food plate 28 is rotated by a motor 29. FIG. 4 shows a state in which the piezoelectric element sensor 1 is attached to the exhaust section 16. FIG. 5 shows the configuration of a drip-proof ultrasonic microphone used in the experiment as a piezoelectric element sensor. Inner link 36, terminal board 3
7. Made of silicone rubber 38.

(National Technical Report P504~P514
vol29 No3 JAN 1983) Figure 6 shows an example of data regarding the signal and noise of the piezoelectric sensor mentioned above. a shows an example of a signal waveform when the water in the refrigerator 10 boils. Figure b shows an example of the results of spectrum analysis of this waveform. It can be seen that when the 40KHz ultrasonic microphone is exposed to wind containing warm water vapor, a large signal is emitted in the 0-50Hz band. The difference between A and B is about
30dB, signal level is several mV voltage. A is when the water in the refrigerator has boiled, B is before it has boiled, and C is when the microwave oven is not energized.

Figures 7 and 8 show a circuit example of an amplifier 6 with band-pass filter characteristics that combines a low-pass filter and a high-pass filter, and an example of the amplifier output voltage waveform when this circuit is used to heat 400 c.c. of water. It shows. As can be understood from the above results, by comparing the threshold voltage ΔV _T and the signal voltage in the comparator 7 of FIG. 2, the controller 4 issues a buzzer alarm when the signal voltage becomes larger than ΔV _T. This will tell you when your food has reached the boiling point. It is also possible to have a configuration in which heating is stopped by turning off the power supply voltage using a controller.

In the sensor used in the present invention, steam containing warm moisture transfers heat to the piezoelectric element 30 via the case 34, and a signal voltage is generated in accordance with the differential amount of this thermal change.

For this reason, as shown in Fig. 1, the structure of the present invention, in which the sensor is attached via a thermally insulated material from the heating chamber wall, where the temperature rises during radio wave heating or electric heating, allows the sensor to be attached to the heating chamber wall even during continuous heating. Since the temperature rise of the sensor due to heat conduction from the sensor is small, it is possible to extract a signal without reducing the output of the sensor.

Furthermore, as shown in FIG. 9, if the vibration isolating rubber 39 is attached via a metal washer 40,
It is also possible to prevent the generation of signals due to mechanical vibrations caused by opening and closing of the microwave oven door, etc.

Effects of the Invention As described above, according to the present invention, a microwave oven with a food heating state detection function can be realized with an extremely simple configuration.

Humidity sensors and gas sensors essentially utilize the grain boundary phenomenon of the sensing element, so to prevent clogging of the grain boundaries, they must be kept warm with a heater or periodically burned to remove dirt. Many complicated measures are required in terms of maintenance, such as
The present invention does not require such a thing. Therefore, there is no need for electricity for heat retention or for roasting, making it a power-saving type.

Furthermore, there is no need for control parts for maintaining the accuracy of the heat-retaining heater power or a special transformer for the heater power, and the cost is low. Furthermore, as is clear from FIG. 6b, since the signal is large, stable control can be achieved with respect to the noise level caused by electromagnetic noise within the microwave oven and wind noise from the cooling fan.

Furthermore, since a DC blocking amplifier is used, no DC voltage is applied to the sensor, and changes in element characteristics due to ion conduction or the like can be prevented.

Since the sensor has a structure in which the temperature does not easily rise due to heat conduction from the walls of the heating chamber, there is no reduction in signal output even if the sensor is repeatedly heated. In addition, although the embodiment has been described with one exhaust section provided in the heating chamber, the present invention also includes a case where two or more sections are provided for exhaust from the heating chamber and a piezoelectric element sensor is provided in one of them. It is something.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a sensor mounting part of a microwave oven equipped with a piezoelectric element sensor according to an embodiment of the present invention, FIG. 2 is a configuration diagram of the same microwave oven equipped with a piezoelectric element sensor, and FIG.
Figures 5 to 5 are cross-sectional views of the microwave oven and sensor, Figures 6a and b are sensor output waveform diagrams, Figure 7 is a circuit diagram of the bandpass amplifier, and Figure 8 is the output of the circuit in Figure 7. FIG. 9 is a block diagram of another embodiment of the present invention, and FIG. 10 is a block diagram of a conventional example. 1...Piezoelectric element sensor, 3...Sensor mounting plate,
4... Heating chamber wall, 16... Exhaust section, 30... Piezoelectric element, 34... Case.

Claims (1)

[Claims] 1. A microwave oven equipped with a piezoelectric element sensor, in which a piezoelectric element sensor is provided in the exhaust part of the heating chamber, and the piezoelectric element sensor is attached to be thermally insulated from the wall of the heating chamber.