JPH0665151B2 - Microwave oven with piezoelectric element sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave oven with a piezoelectric element sensor that detects and controls 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 29 by dividing the voltage of a reference voltage power supply 30 with a resistor 31 as shown in FIG. Control equipment. (For example, JP-A-5
Problems to be Solved by the Invention In such a conventional method, the voltage across the resistor 31 is used as a control signal. The resistance value, the resistance value of the resistor 31, and the variation of the power supply 30 lead to the variation of the control voltage signal, which makes management difficult. The present invention has been made in view of the above points, 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, increases the sensor voltage generated with the progress of heating with an amplifier, and through a voltage comparator. The control output is obtained. In particular, the present invention relates to a heating device which is provided with a timer circuit to prevent a malfunction when the power is turned on.

Operation According to the present invention, the reference voltage power source and the one corresponding to the voltage dividing resistor of the conventional example are not required, so that the configuration is simple.

Further, by using the timer circuit, the controller can be operated after a fixed period of time after the power is turned on, so that the malfunction due to noise at the time of turning on the power can be prevented.

Embodiment FIG. 1 shows an embodiment of a microwave oven with a piezoelectric element sensor of the present invention. In FIG. 1, the output of the piezoelectric element sensor 1 is based on an amplifier 2 for voltage amplification, a comparator 3 for comparison with a reference threshold voltage ΔV _T1, and a comparison with another reference threshold voltage ΔV _T2. It is processed by a control circuit including a hold circuit 4 for holding. Food 7 is placed in the heating chamber 6, and a part of the cooling wind of the magnetron 5 is guided into the heating chamber 6 by a fan 8 via a 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. The gas containing water or the like generated from the food heated by the cooling air is discharged from the exhaust unit 12
Through the heating chamber 6 to the outside.

The piezoelectric element sensor 1 is attached to the exhaust portion 12. The controller is composed of the amplifier 2, the comparator 3 and the timer 13 within 30 seconds, and the controller is additionally provided with a notification buzzer 14, a DC power supply 15 and a switch 16.

2 and 3 show configuration examples. FIG. 2 shows the structure of the microwave oven used in the experiment. With the radio wave output of 500 w, the radio wave of the magnetron 5 is supplied to the heating chamber 6 via the waveguide section 17, and the food tray 18 is rotated by the motor 19. 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 relation to the time axis (a) or the frequency axis (b). (a), (b), and (c) of 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, before the generation of water, and the state where water is boiled at 100 ° C. . FIG. 5 shows the time variation of the amplifier output signal voltage when 400 cc of water is heated.

FIG. 6 shows an example of the control circuit of the present invention. The circuit is composed of a combination of SCRs, operational amplifiers A _{1 to} A ₅ and resistance capacitors. The amplifier is a high pass filter HP
Circuitry for selective enrichment width the frequency component of about 10H _z by F and a low-pass filter LPF, the timer T _d = about 30 second timer, the hold circuit is the threshold voltage of the sum of the output of the comparator and a timer △ V _T2 The SCR has a hold function. FIG. 7 shows a time chart for explaining the control sequence. As shown in (a), when the microwave oven is started, noise is generated due to switching due to a sudden rising current to the magnetron 5. (b)
The figure shows the output of the comparator 3. The output of the timer 13 is shown in (c) and the combined sum of the outputs of (b) and (c) is shown in (d).
This corresponds to the input signal A ₄ in FIG. The output of the hold circuit is shown in (e). As can be understood from the above figures, the noise at power-on can be reduced by using the timer circuit.
Without being affected by switching noise at the time of starting, the buzzer 14 produces a sounding period from the time when water is generated by boiling due to boiling to the time when the switch 16 is manually opened, thereby forming a microwave oven controller with good operability. it can.

Effects of the Invention As described above, according to the microwave oven with the piezoelectric element sensor of the present invention, the following effects can be obtained.

That is, the controller has a built-in timer circuit so that the controller starts to operate after a fixed period of time after the power is turned on.
It is possible to prevent malfunction due to amplifier noise when the power is turned on.

In addition, since the one using 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, it is kept warm by a heater or regularly burns dirt with a heater. Although many complicated measures are required in terms of maintenance, such as being able to do so, such a thing is not necessary in the present invention. Therefore, it is a power-saving type that does not require power for heat retention or power for burnout.

Furthermore, 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 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 voltage characteristic diagram of the same amplifier output, 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 ... Comparator,
5 ... Heating means (magnetron), 6 ... Heating chamber, 7 ...
... Heated object (food), 12 ... Exhaust part, 13 ... Timer

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. It consists of a piezoelectric element sensor arranged so as to be in contact with the exhaust flow, and a controller that inputs a signal from this piezoelectric element sensor and outputs a control signal.The controller starts the control operation after a certain period of time after turning on the power. A microwave oven with a piezoelectric element sensor having a timer circuit as described above. 2. A microwave oven with a piezoelectric element sensor according to claim 1, wherein a microwave generating means is used as the heating means.