JPH0634385B2 - Microwave oven with piezoelectric element sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven with a piezoelectric element sensor for detecting and controlling the state of gas generated from food in response to heating of the food.

2. Description of the Related Art A conventional heating device of this type, for example, a microwave oven with a sensor detects a change in the resistance value of a humidity sensor 28 by dividing the voltage of a reference voltage power supply 29 with a resistor 30 as shown in FIG. Controls the device. (For example, JP-A-5
Problems to be Solved by the Invention In such a conventional method, the voltage across the resistor 30 is used as a control signal. The resistance value and the resistance value of the resistor 30 cause variations in the voltage of the power supply 29 to be associated with variations in the control voltage signal, which makes management difficult. The present invention has been made in view of the above point, and an object thereof 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 uses a piezoelectric element sensor as a sensor, widens the sensor voltage generated with the progress of heating with an amplifier, and via an integrated voltage. The control output is obtained.

Operation According to the present invention, it is possible to prevent malfunctions when the power is turned on or when there is a disturbance noise signal, with a simple structure that does not require the ones corresponding to the reference voltage and the voltage dividing resistance of the conventional example.

Embodiment FIG. 1 shows an embodiment of a microwave oven with a piezoelectric element sensor according to the present invention. In FIG. 1, the output of the piezoelectric element sensor 1 is processed by a controller including a voltage amplification amplifier 2 and an integrator 3, and a comparator 4 that operates by comparison with a threshold voltage ΔV _T. Food 7 is arranged in the heating chamber 6, and a part of the cooling air of the magnetron 5 is introduced into the heating chamber 6 by the fan 8 through the duct 9.

A part of the cooling air is shown by a solid arrow line 10 and a warm gas such as moisture generated from food is shown by a dotted line 11. A warm gas containing water generated by heating the food by the cooling air is sent from the heating chamber 6 to the outside through the exhaust unit 12. The voltage element sensor 1 is attached to the exhaust unit 12. The controller also has a sounding buzzer 13, a DC power supply 14, and a switch 15.
Is attached.

2 and 3 show configuration examples. FIG. 2 shows the structure of the microwave oven used in the experiment. With a radio wave output of 500 W, the radio wave of the magnetron 5 is supplied to the heating chamber 6 via the waveguide 16, and the food tray 17 is rotated by the motor 18. FIG. 3 shows a state in which the piezoelectric element sensor 1 is attached to the exhaust section 12.

FIG. 4 shows a result example in which the piezoelectric element sensor is mounted on a microwave oven and the output signal of the sensor is shown in the relationship between the time axis (a) and the frequency axis (b). (a), (b), and (c) in Fig. (b) correspond to the background noise state of the microwave oven before the power is turned on, the state after the power is turned on but before the generation of water, and the state where water boiled at 100 ° C. .

FIG. 5 shows the time variation of the amplifier output voltage when 400 cc of water is heated. FIG. 6 is a circuit example of the controller of the present invention. A circuit is configured by a combination of operational amplifiers A _{1 to} A _{3, a} resistor, and a capacitor.
The amplifier 2 selectively widens the frequency component of about 10 Hz by the HPF and LPF. The integrator 3 is composed of a combination of a resistor and a capacitor. The buzzer 13 is driven by the output voltage of the comparator 4. FIG. 7 shows a time chart for explaining the control sequence. Although the sensor system of this embodiment has many advantages, it can be configured to apply a DC voltage only during microwave oven operation for energy saving. Occurs as the output of. Figure (b) shows the output voltage waveform of the integrator, and (c)
The figure shows the voltage applied to the buzzer 13.

As can be understood from the above figures, the noise when the power is turned on is absorbed by the integration by the integrator, and only the time when the switch 15 is manually opened until the switch 15 is manually opened is the sounding period of the operation. A microwave oven control circuit with good performance can be realized.

Further, in the embodiment, the integrator configuration is shown in which the capacitor is charged through the resistor. However, since the signal changes in a pulse shape as shown in FIG. 6, the comparator exceeding the preset threshold value is used. The present invention also includes a digital integrator that integrates the output frequency (adds the number of times).

Effects of the Invention It is possible to prevent malfunction due to amplifier noise when the power is turned on.
In addition, the effect of smoothing the output of the amplifier, which changes after the generation of water, produces a hold effect that keeps the buzzer running.
Further, since the buzzer 13 starts sounding a little later than the time when steam is generated, there is also an effect that it can be confirmed that the whole food has reached about 100 ° C.

Since the one that uses a humidity sensor or gas sensor essentially utilizes the crystal grain boundary phenomenon of the detection element, in order to prevent clogging of the grain boundary, keep it warm with a heater or periodically burn out dirt with a heater. However, many complicated measures are required in terms of maintenance, but such a thing is unnecessary in the present invention. Therefore, it is a power-saving type that does not require power for heat retention or power for burning out.

Further, it is inexpensive because it does not require a control part for maintaining the accuracy of the heater power for heat retention or a special transformer for heater power. Further, as is clear from FIG. 4 (b), since the signal is large with respect to the noise level due to electromagnetic noise in the microwave oven, wind noise of the cooling fan, etc., stable control can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of a microwave oven with a piezoelectric element sensor according to an embodiment of the present invention, FIGS. 2 and 3 are sectional views of the microwave oven and its exhaust portion, and FIGS. 4 (a) and 4 (b). ) Are output characteristic diagrams of the same sensor, FIG. 5 is a sensor output voltage characteristic diagram, FIG. 6 is a concrete control circuit diagram, FIG. 7 is a control time chart, and FIG. 8 is a block diagram of a conventional example. is there. 1 ... Pressure element sensor, 2 ... Amplifier, 3 ... Integrator,
4 ... Comparator, 5 ... Heating means (magnetron), 6 ...
… Heating chamber, 7 …… Heating object, 12 …… Exhaust section.

Claims (2)

[Claims] 1. A heating chamber for containing an object to be heated, heating means for heating the object to be heated in the heating chamber, an exhaust unit for exhausting gas inside the heating chamber to the outside of the heating chamber, and an exhaust unit for the exhaust unit. The piezoelectric element sensor is arranged so as to be in contact with the exhaust gas flow, and a controller, and the controller has an amplifier and an integrator that at least input a signal from the piezoelectric element sensor, amplify and integrate it, and output it. Microwave oven with a piezoelectric element sensor consisting of a structure. 2. A microwave oven with a piezoelectric element sensor according to claim 1, wherein a microwave generating means is used as the heating means.