JPH01132090A - Device for detecting heating condition - Google Patents

Abstract

PURPOSE:To enable the cooking condition of material to be heated to be detected in a simple manner by compensating drop in polarization current owing to temperature properties of a piezo-electric element sensor sensing an increase in temperature of an exhaust path by the sue of signals from a compensating element. CONSTITUTION:The voltage level of a setting means 21 determining the end of a heating means 13 is compared with the signal level of a mixer 20 by a comparator 22. And when the signal level is detected by a control means 23 to have exceeded the voltage level of the setting means 21, the contact of a relay acting as an energizing means 24 energizing a magnetron 13, and the contact of a relay 32 for a cooling fan 14 and a lighting lamp 31 for a heating chamber are released so as to let electrical continuity to the magnetron 13, the cooling fan 14 and the like be suspended. This constitution thereby allows the end of a heating condition to be automatically detected in a simple manner.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a microwave oven, which detects and controls the state of gas generated from food as the food is heated, and uses a piezoelectric sensor as a detection element. The present invention relates to the heating state detection device used.

Conventional technology As a conventional sensor for detecting the cooking status of a microwave oven,
As shown in FIG. 11, the microwave oven is controlled by detecting changes in the resistance value of the humidity sensor 36 by dividing the voltage of the reference voltage power source 37 with a resistor 38 and comparing the voltage. (For example, Japanese Unexamined Patent Publication No. 53-77385) As shown in FIG. 12, as a simple means of detecting a heating state, a polarization current is generated by thermally converting the water vapor of the voltage element sensor b. However, there is a means to detect the polarization current. (For example, Japanese Unexamined Patent Publication No. 61-269890) The invention attempts to solve the problem! Problems when using such a conventional humidity sensor 36,
Since the voltage across the resistor is used as the control signal, when a large number of units are produced, variations in the resistance of each component, the humidity sensor 36, and the voltage of the power supply will lead to variations in the control voltage signal, making management difficult. It was difficult.

Furthermore, when the piezoelectric element sensor 1 is used, due to the temperature characteristics of the voltage element sensor, if the object to be heated 12 is repeatedly heated in a microwave oven, the temperature of the exhaust section 8 to which the piezoelectric element sensor 1 is attached will rise. Since the detected polarization current of the piezoelectric element sensor 1 also decreases, the same amount of heated object 12
When heated, there was a problem that the heating end time was not constant.

Means for Solving the Problems In order to solve the above problems, the present invention uses a temperature compensation element that detects the ambient temperature of the piezoelectric element sensor, and mixes the signal of the piezoelectric element sensor with the signal of the compensation element. This configuration uses a mixer.

According to the present invention, the reduction in polarization current caused by the temperature characteristics of the piezoelectric element sensor due to the temperature rise in the exhaust path is corrected by the signal of the compensation element, and the cooking state of the heated object can be detected with a simple configuration. .

EXAMPLE Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIG. 1 is a perspective view of a piezoelectric sensor 1 according to an embodiment of the present invention, and a diagram showing a state in which the piezoelectric sensor 1 and a temperature correction element 6 are attached. The piezoelectric ceramic element 1 made of lead etc.
Electrodes 2.3 are provided on both sides, and a lead wire 4.5 is wired to each electrode 2.3. Furthermore, as shown in FIG. is located adjacent to the
It is attached to the exhaust wall with screws 10 and 11.

FIG. 2 is a block diagram of the main body of a microwave oven having the piezoelectric element sensor 1 of the present invention. A heating chamber 7 into which the object to be heated 12 is taken in and taken out, and a magnetron 1 which heats the object to be heated 12 at high frequency.
3. A piezoelectric element sensor 1 provided in the heating chamber exhaust section 8, a temperature compensation diode 6, a cooling fan 14 that cools the magnetron 13, a duct 15 that partially blows the air from the cooling fan 14 into the heating chamber, a door switch 16, a piezoelectric A filter 17 (hereinafter referred to as a filter) that filters the output signal of the element sensor 1, an amplifier 18 that amplifies the signal of the filter 17, and a detection that detects a change in forward voltage with respect to a temperature change of the temperature compensation diode 6. a mixer 20 that mixes the amplified signal of the piezoelectric element sensor 1 and the detected voltage of the temperature compensation diode 6, and a setting means 21 that determines the end of cooking of the object to be heated 12.
, a comparator 22 that compares the signal of the mixer 20 and the signal of the setting means 21, a control means 23 that detects the signal of the comparator 22 and controls the main body, and an energizing means 24 that energizes the magnetron 13. has been done. Further, an object to be heated 12 is disposed within the heating chamber γ, and a portion of the cooling waste of the magnetron 13 is melted into the heating chamber 7 via a duct 15 by a cooling fan 14.

A part of the cooling lice is shown by a solid arrow 25, and gas such as moisture generated from the heated object 12 is shown by a dotted arrow 1a26.

The cooling air and the gas containing moisture generated from the object to be heated 12 are discharged to the outside of the heating chamber 7 through the exhaust section 8 . Here, FIG. 3 shows an example of the output voltage waveform of the signal and noise of the piezoelectric element sensor 1 when 400 cc of water is heated. A shows an example of a signal waveform when the water in the heating chamber 7 boils.

Panel b shows the results of spectrum analysis of this waveform.

It can be seen that a large signal is generated in the 0 to 50 Hz band each time the piezoelectric element sensor 1 is hit by warm air containing warm water vapor. A is when the water in the heating chamber 7 has boiled, B is before boiling, C is when the microwave oven is not energized, and the difference between A and B is about 30 dB, signal level) V
is a voltage of several mV. Further, even when dirt was attached to the piezoelectric element sensor 1, the output waveform shown in FIG. 3 did not change.

This is because the piezoelectric element sensor 1 generates a signal in response to thermal changes. Therefore, as shown in FIG. 4, the output signal of the piezoelectric element sensor 1 is filtered by a filter having a pass band from 0 to 50 Hz. I am creating it. FIG. 5 is a diagram showing the relationship between the forward voltage of the temperature compensation diode 6 and the ambient temperature. Due to the nature of semiconductors, as the ambient temperature rises, the forward voltage decreases. FIG. 6 shows the circuit of the detector 19 and mixer 20. A portion 290 is a detector that detects a voltage change in the forward direction of the temperature compensation diode 6, and the differential amplifier has a characteristic that the output voltage of the amplifier increases when the ambient temperature rises. A portion 30 is a circuit that adds a signal obtained by amplifying the output of the piezoelectric sensor 1 through the filter 17 by the amplifier 18 and a signal from the temperature compensation diode 6 by the differential amplifier. 7th
The figure is a diagram showing the relationship between the output voltage of the mixer 20 and the ambient temperature, and the output voltage of the piezoelectric element sensor 1 decreases as the ambient temperature rises. This is explained as follows. The piezoelectric element sensor generates a polarized current in response to the differential amount of the thermal changes described above involving warm moisture. At this time, if the ambient temperature around the piezoelectric element sensor 1 is high, even if warm water vapor collides with the piezoelectric element sensor 1 and exchanges heat, the change in thermal temperature will be small. On the other hand, since the output signal of the temperature compensation diode 6 increases as the ambient temperature rises, the mixer 20 can output a stable output regardless of the ambient temperature of the exhaust section.

FIG. 8 is a system block diagram of one embodiment of the present invention. Reference numeral 21 denotes a setting means consisting of a control means, a ladder resistor and an operational amplifier, and determining the termination of the heating means. The voltage level of the setting means 21 and the signal level of the mixer 20 are compared by the comparator 22, and when the control means 23 detects that the voltage level exceeds the voltage level of the setting means 21, the magnetron 13
contacts of the relay which is the energizing means 24 that energizes the cooling fan 14 and the relay 3 of the lamp 31 for illumination in the heating chamber 7.
Open the contacts of 2, Magnelon 13, cooling fan 1
This is to stop the power supply to 4, etc.

Note that 33 is a power supply that supplies the control means 23 and the like;
is the cooking start button. FIG. 9 is a diagram showing the relationship between the detection voltage of the mixing section 20 and the heating time when the same amount of water (400 cc) of the object to be heated 12 is repeatedly heated. After pressing the start button 34, when steam starts to be generated from the object to be heated 12, a differential signal pulse of the piezoelectric element sensor 1 is generated, and when the set voltage is exceeded, the energization of the magnetron 13 is stopped. It is assumed that the output voltage of the temperature compensating element diode 6 at this time is Δv1.When 400 cc of water is subsequently heated, a differential signal pulse of the water remaining in the heating chamber 7 is generated, and soon the temperature of the heated object 12 is When water vapor is generated, a differential signal pulse is generated as well. However, as the temperature of the exhaust section 8 rises, the signal level of the differential signal pulse decreases, but the output voltage of the temperature compensation diode 6 changes to ΔV 1', so even if the same amount of the heated object 12 is repeatedly heated, The heating ends after the same heating time T. In addition, in the embodiment of the present invention, a microcomputer is used as the control means 23, and it configures a complicated control sequence such as detecting differential signal pulses, setting an arbitrary level of the setting means 21, and setting the reheating time. suitable for.

Furthermore, as shown in FIG. 10, by integrally molding the piezoelectric sensor 1 and the correction element 6 with resin 35, the temperatures of the piezoelectric sensor 1 and the correction element 6 become the same, and the correction element 6
In addition to making accurate correction possible, this also has the effect of preventing deterioration of the element due to the gas of the heated object 12.

In one embodiment of the present invention, a temperature compensating diode is used as the temperature compensating element, but the temperature compensating element is not limited to the above embodiment and may be any other temperature compensating element such as a temperature compensating thermistor, capacitor, or varistor.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) Since the reduction in the detection ability of the differential signal pulse at the end of heating due to the ambient temperature of the piezoelectric element sensor is corrected by the temperature correction element, there is no difference in the heating end time even if the microwave oven is used repeatedly. , it is possible to always achieve a stable finish on the heated object.

(2) Humidity sensors require a heater to refresh the oil or gas from the heated object adhering to the sensor, and a power source for the heater, making maintenance of the sensor complicated. The sensor does not require any such special circuitry and can automatically detect the end of the heating state with a low cost and simple configuration.

[Brief explanation of the drawing]

Figure 1+al is a cross-sectional view of a piezoelectric element sensor according to an embodiment of the present invention, Figure 1 (bl is a cross-sectional view showing the installation state of the same piezoelectric element sensor and a temperature correction element, and Figure 2 is a cross-sectional view of the same piezoelectric element sensor and a temperature correction element). Figure 3 is a block diagram of the main body configuration of a microwave oven that uses a piezoelectric element sensor, Figure 4 is a diagram of the output voltage waveform of the piezoelectric element sensor, Figure 4 is a circuit diagram of the filter, and Figure 5 is a diagram of the voltage of the temperature correction element. A characteristic diagram showing the relationship between ambient temperature, Figure 6 is a circuit diagram of the detector and mixer, Figure 7 is a characteristic diagram showing the relationship between the output voltage of the mixer and ambient temperature, and Figure 8 is the system block. 9 is a characteristic diagram showing the relationship between output voltage of the mixer and heating time when heating is repeated, and FIG. 10 is a sectional view of a piezoelectric element sensor and a temperature correction element according to another embodiment of the present invention. , 11th
The figure is a block diagram of the main body configuration using a conventional humidity sensor, and FIG. 12 is a block diagram of the main body configuration using another example of the conventional piezoelectric element sensor. 1...Piezoelectric element sensor, 6...Temperature correction element, 7...Heating chamber, 8...Exhaust section, 12...Temperature compensation element Heating object 13...Heating means, 17...Filter, 18...Amplifier,
20... Mixer, 21... Setting means,
22... Comparator, 23... Control means,
24...Biasing means, 35...Resin. Name of agent: Patent attorney Toshio Nakao and 1 other person! −
・-Piezoelectric Yonago-Dayoi 2 Figure 4 Figure 5 Atmosphere temperature (°C) Figure 7 o so
g. Atmosphere temperature [”CJ vkg diagram Fig. 10

Claims (3)

[Claims] (1) A heating chamber into which a heated object is taken in and taken out, a heating means for heating the heated object, a piezoelectric element sensor that detects the cooking state of the heated object, and a correction element for temperature compensation of the piezoelectric element sensor. a filter for appropriately filtering the signal of the piezoelectric element sensor, an amplifier, a mixer for mixing the signal of the amplifier and the correction element, a setting means for determining the end of cooking of the object to be heated; A heating state comprising: a comparator that compares a signal from the mixer with a signal from the setting means; an energizing means for the heating means; and a control means for stopping energizing the energizing means based on the signal from the comparator. Detection device. (2) The heating state detection device according to claim 1, wherein the control means is constituted by a microcomputer. (3) The heating state detection device according to claim 1, wherein the piezoelectric element sensor and the correction element are integrally molded with resin.