JPS61269890A - Electronic range with piezoelectric element sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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.

BACKGROUND ART A conventional microwave oven with a sensor, as shown in FIG.
A change in the resistance value of the humidity sensor 35' is detected by dividing the voltage of the reference voltage power source 36 with a resistor 37 to control the device. (For example, Japanese Unexamined Patent Publication No. 53-77365) Problems to be Solved by the Invention This conventional method uses the voltage across the resistor 37 as a control signal, so when producing a large number of Variations in the resistance of the humidity sensor 35, resistance 37, and power source 36 lead to variations in the control voltage signal, making management difficult. The present invention has been made in view of the above, and has an object to provide a means for detecting the heating state of food, with a simple structure, and a measure against contamination of the vibration case during long-term use of the sensor.

Means for Solving the Problems In order to solve the above problems, the present invention uses a piezoelectric element as a sensor and amplifies the sensor voltage generated as heating progresses with a filter having low-pass filter characteristics. The control output is obtained through comparison.

Function According to the present invention, there is no need for a reference voltage or a resistor for voltage division in the conventional example, and control can be performed with a simple configuration.

Embodiment FIG. 1 shows an embodiment of a microwave oven equipped with a piezoelectric sensor according to the present invention. In FIG. 1, the output of the piezoelectric element sensor 1 includes an amplifier 2 including a voltage amplification amplifier (hereinafter referred to as a low-pass amplifier) that amplifies a frequency component lower than the commercial frequency component of the output signal, and an amplifier 2 for voltage comparison. It is connected to a comparator 3 and further to a controller 4.

Food 7 is placed in the heating chamber 6, and a part of the cooling air from the magnetron 5 is sent to the heating chamber 6 through a duct 9 by a fan 8.
guided within. A portion of the cooling air is shown by a solid arrow line 10, and a gas such as moisture generated from the food is shown by a dotted arrow line 11. The cooling air and the gas containing moisture generated from the food are removed from the exhaust section 1.
2 and is sent out from the heating chamber 6 to the outside. A piezoelectric sensor is attached to the exhaust section 12. In this embodiment, a winding 17 is wound around the core 13 of the motor that drives the fan 8 along with the winding 16 from the power plug via the power switch 15. 20. A constant voltage power supply section is constituted by a constant voltage diode 21, eliminating the need for a transformer for the control circuit. Further, the buzzer 21 is configured to operate according to a signal from the controller 4 when the amplified signal voltage becomes larger than a set threshold voltage ΔvT. Examples of actually measured configurations are shown using FIGS. 2 to 4.

Figure 2 shows the configuration of the microwave oven used in the experiment. The radio wave output from the magnetron 5 is so high that the radio waves from the magnetron 5 are supplied to the heating chamber 6 via a waveguide, and the food plate 24 is rotated by a motor 25. FIG. 3 shows a state in which a piezoelectric element sensor is attached to the exhaust section 12. FIG. 4 shows the configuration of a drip-proof ultrasonic microphone used in the experiment as a piezoelectric element sensor.
It consists of a lead wire 31, an inner link 32, a terminal plate 33, and silicone rubber 24.

(National Technical Report
t P504~P514vol 29 NO31A
N1983) In Figure 5, an ultrasonic microphone for 40 KHz reception is used as a piezoelectric element sensor and attached to a microwave oven.
An example of the results of spectrum analysis of the sensor output signal is shown.

(,) is the initial state of the sensor, (b) is the background noise state before the microwave oven is powered on, with silicone grease applied to the entire surface of the vibration case 30 of the sensor at a thickness of 0.5 to 1°, respectively. After turning on the power and before moisture is generated, water is 10
This is the result at 0°C. The results show that at frequencies below 5 Hz, the outputs are similar, but at frequencies above that, (b) has a smaller output value.

This indicates that it is necessary to take measures to reduce changes in the output signal due to dirt adhering to the vibrating case, which is the surface of the sensor, when the cell is used for a long period of time.

As a solution to this problem, the present invention uses an amplifier having a low-pass filter amplification section as shown in FIG. When the frequency gain characteristics of the amplifier shown in Figure 6 are maximized by adjusting the volume VR (MAX)
FIG. 7 shows the case (MEN) where it is minimized. FIG. 8 shows the result of amplifying the output of this sensor during boiling using the above amplifier. As is clear from Figure 8, by using a low-pass amplifier, it is possible to obtain an output with almost no difference between the initial state of the sensor and when silicone grease is applied, and it is possible to prevent the sensor from becoming dirty after long-term use. It can be understood that this is an effective measure to prevent stable output.

As is clear from the above results, the above amplifier output is
By comparing the signal voltage with the threshold voltage ΔvT in the comparator 3 shown in the figure, if the controller 4 issues a buzzer notification when the signal voltage becomes larger than ΔVT, it is possible to know when the food has reached the boiling point. .

It is also possible to have a configuration in which heating is automatically stopped by turning on the power supply using a controller. Figure 9 shows an example of sensor output at 42d.
The results are shown when the low-pass filter of B/○CT is used all around and the cutoff frequencies are set to 31.5 Hz, 40 Hz, and 50 Hz.

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 off to remove dirt. Although many complicated measures are required in terms of maintenance, the present invention does not require such measures. Therefore, there is no need for electricity for heat retention or for baking, making it a power-saving type.

Furthermore, there is no need for control parts to maintain 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. 5(b), the signal is large, so 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 low-pass amplifier is used, the signal output of the sensor can be obtained without change over a long period of time.In addition, when a low-pass amplifier is used, as shown in Figure 9, it is less susceptible to inductive noise from the commercial power supply. 40
When the frequency is set to Hz or less, a practically sufficient S/N ratio can be obtained.

In addition, conventional humidity sensors use shielded wires to connect the humidity sensor and amplifier to make them less susceptible to induced noise, but the present invention uses a low-pass amplifier, which makes it possible to use ordinary lead wires, making it less expensive. Can be configured.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a microwave oven equipped with a piezoelectric element according to an embodiment of the present invention, Figs. 2 to 4 are sectional views of the same microwave oven and a sensor, respectively, and Fig. 5 (,) and (b) are respectively the same. Characteristic diagram of a sensor output example, Figure 6 is a circuit diagram of the same amplifier, Figure 7 is a characteristic diagram of the amplifier in Figure 6, and Figure 8 is the output of the same sensor output via an amplifier.) Characteristics of an output example 9 is an output waveform diagram when the cutoff frequency of the same amplifier is changed, and FIG. 10 is a block diagram of a conventional example. 1...Pressure element sensor, 2...Amplifier including low-pass amplifier, 3...Comparator, 4...
...Controller, 6...Heating chamber, 12...
...Exhaust section, ΔVT...Threshold voltage, 29...Piezoelectric element, 30...Vibration case (thin plate). Name of agent: Patent attorney Toshio Nakao 1 person 7-
--Nodama Den Miko Nansa? ---Naozu L blocking amplifier 3---A Otsu I further, Jin, Fig. 1 4-Return l7B 6-j) D valve (1- /2-11 arrow Δv7 Fig. 2 Z5 3rd Figure 4 Figure 5

Claims (1)

[Claims] A piezoelectric element sensor was provided in the exhaust section of the heating chamber, and the output of the piezoelectric element sensor was amplified by an amplifier including a low-pass amplifier having an amplification section for voltage amplification having a low-pass characteristic with a cutoff frequency lower than the commercial frequency. A microwave oven with a piezoelectric sensor that is controlled by a controller based on the output of a comparator that compares the voltage with a preset threshold voltage.