JPH01167984A - Heating condition detecting device - Google Patents

Abstract

PURPOSE:To make the heating finishing time constant even though the same amount of substances to heat are heated repeatedly by using a temperature compensating element to detect the ambiance temperature of a piezo-electric element sensor, and converting the setting to determine the cooking finishing. CONSTITUTION:When the same amount of water of substances 12 to be heated are heated repeatedly, a control device 23 detects and records the temperature of an exhaust 8 at the time by using a temperature compensating diode 6 after a starting button 20 is pushed, and the voltage level of a setting device 21 is set. When steam is begun to generate from the substance to be heated 12, the differential signal pulse is generated from a piezo-electric sensor 1, and when it exceeds the set voltage, the current flowing to a magnetron 13 is stopped. When the same amount of water is heated continuously, the differential signal is generated in the same manner. In this case, although the signal level of the differential signal pulse is decreased with the temperature rise of the exhaust 8, the output voltage of the diode 6 is also varied, and the device 23 decreases the setting of the device 21 responding to the variation amount. Consequently, the heating time can be made constant even though the same amount of substances 12 to be heated is heated repeatedly.

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 a change in the resistance value of the humidity sensor 36 by dividing the voltage of a reference voltage power source 37 with a resistor 38 and comparing the voltage. (For example, Japanese Unexamined Patent Application Publication No. 53-77365) As shown in FIG. occurs, and there is a means to detect the polarization current. (For example, Japanese Patent Application Laid-Open No. 61-269890) Problems to be Solved by the Invention When using such a conventional humidity sensor a6,
Since the voltage across the resistor is used as the control signal, when producing a large number of components, variations in the resistance, resistance, and voltage of the power supply of each component of the humidity sensor 36 will lead to variations in the control voltage signal, making management difficult. It was difficult.

Furthermore, when the piezoelectric sensor 1 is used, due to the temperature characteristics of the piezoelectric sensor, if the object 12 to be heated is repeatedly heated in a microwave oven, the temperature of the exhaust section 8 to which the piezoelectric sensor 1 is attached will increase. As the temperature increases, the polarization current of the piezoelectric element sensor 1 detected by the atmospheric temperature condition of the exhaust section 8 and the degree of rise at room temperature also decreases, and when the same amount of heated object 12 is heated, the heating end time is not constant. There was a point.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention uses a temperature compensation element that detects the ambient temperature of the piezoelectric element sensor, and adjusts the temperature according to the signal of the piezoelectric element sensor and the signal of the compensation element. The configuration is such that the setting means can be changed.

According to the present invention, the decrease in polarization current due to the temperature characteristics of the piezoelectric sensor due to the temperature rise in the exhaust section 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.

FIGS. 1(a) and 1(b) are perspective views of a piezoelectric element cell 1 according to an embodiment of the present invention, and a diagram showing how the piezoelectric element sensor 1 and temperature correction element 6 are mounted. In FIG. 1(a), the piezoelectric ceramic element 1 made of lead titanate, etc.
Electrodes 2 and 3 are provided on both sides, and lead wires 4 and 5 are wired to each electrode 2 and 3. Furthermore, as shown in FIG. 1(b), the piezoelectric element sensor 1 and the temperature compensation element 6 (in one embodiment of the present invention, a temperature compensation diode) are connected to the sensor during the exhaust part of the heating chamber 7. The attachment is disposed adjacent to the hole 9 and is attached to the wall of the exhaust section 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 for cooling the magnetron 13, a duct 15 for blowing part of the air from the cooling fan 14 into the heating chamber, and a door switch 16. , a filter 17 (hereinafter referred to as a filter) that filters the output signal of the output of the piezoelectric sensor 1, an amplifier 18 that amplifies the signal of the filter 17, and detects changes in forward voltage with respect to temperature changes of the temperature compensation diode 6. and a converter 19 for analog-to-digital conversion;
Start button 20 to start cooking. Setting means 21 that determines the end of cooking of the object to be heated 12, a comparator 22 that compares the signal from the amplifier 18 and the signal from the setting means 21, and a control means 23 that detects the signal from the comparator 22 and controls the main body.
, and a biasing means 24 for biasing the magnetron 13. Further, an object to be heated 12 is disposed within the heating chamber 7 , and a portion of the cooling air from the magnetron 13 is guided into the heating chamber 7 via a duct 15 by a cooling fan 14 . A part of the cooling air is shown by a solid arrow line 25, and a gas such as moisture generated from the object to be heated 12 is shown by a dotted arrow line 26. cooling air and
Gas containing moisture and the like generated from the object to be heated 12 is 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 sensor 1 when 400 aa 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 50H2 band due to the hot air containing warm water vapor hitting the piezoelectric element sensor 1. 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, and the signal level is: The voltage is several mV. Furthermore, even if dirt adhered 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 changed from 0 to 50H.
A bandpass filter is created by a bypass filter 27 and a lowpass filter 28 to configure a filter having two passbands. 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 is a diagram showing the relationship between the output voltage of the piezoelectric element sensor 1 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 1 generates a polarization current according to the differential amount of thermal change in steam containing warm moisture. This is because if the ambient temperature around the piezoelectric element sensor 1 is high at this time, even if warm water vapor collides with the piezoelectric element sensor 1 and exchanges heat, the change in thermal temperature will be small. FIG. 7 is a system block diagram of an embodiment of the present invention. 19 is a converter that converts the voltage level of the temperature compensation diode 6 from analog to digital, and 20 is a cooking start button. 21 is
The control means is composed of a ladder resistor and an operational amplifier, and is a setting means that determines the end of the heating means. The voltage level of this setting means 21 and the signal of the piezoelectric element sensor 1 are compared to a comparator 22.
When the control means 23 detects that the voltage level exceeds the voltage level of the setting means 21, the contact point of the relay which is the energizing means 24 for energizing the magnetron 13, the cooling fan 14,
The contact point of the relay 32 of the lighting lamp 31 in the heating chamber 7 is opened to stop energizing the magnetron 13, cooling fan 14, etc. In addition, 33 is the control means 2
The power supply 34 is a storage means for storing a digital value converted by the converter 19 from the voltage level of the temperature compensation diode 6 at the time when the start button 20 is energized and cooking is started. is for controlling the setting of the setting means to be changed according to the value of the storage means. FIG. 8 is a diagram showing the relationship between the detection voltage of the piezoelectric sensor 1 amplified by the amplifier 18 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 20, the control means 23 detects and stores the temperature of the exhaust section 8 at that time using the temperature compensation diode 6, and sets the voltage level of the setting means 21.

When water vapor starts to be generated from the heated object 12, a differential signal pulse is generated from the piezoelectric element sensor 1, and when the set voltage is exceeded, the magnetron 13 is de-energized. Continue with water 4
When 00aa is heated, a differential signal pulse is first generated from the moisture remaining in the heating chamber 7, and later when water vapor from the heated object 12 is generated, a differential signal pulse is generated in the same way.

However, as the temperature of the exhaust section 8 rises, the signal level of the differential signal pulse decreases, but the temperature compensation diode 6
Since the output voltage changes, the control means 23 lowers the setting of the setting means 21 according to the change, so that even if the same amount of the object 12 is heated, it is heated in the same heating time T. is the one that ends. In one embodiment of the present invention, a microcomputer is used as the control means 23, and complex control sequences such as detection of differential signal pulses, arbitrary level setting of the setting means 21, and reheating time setting are configured. suitable for. Further, as shown in FIG. 9, an analog quantity is output from the control means 23,
A similar result can be obtained by adding the analog amount to the amplifier 18 according to the voltage level of the temperature compensation diode 6, and the present invention is not limited to this embodiment. In addition, as shown in FIG. 10, a piezoelectric element sensor 1, a correction element 6
By integrally molding with resin 35, the piezoelectric element sensor 1 and the correction element 6 are kept at the same temperature, which enables accurate correction by the correction element 6, and prevents deterioration of the element due to gas from the heated object 12. effective.

In one embodiment of the present invention, a temperature compensation diode is used as the temperature compensation element, but a temperature compensation thermistor,
Any temperature correction element such as a capacitor or varistor may be used, and the present invention is not limited to this embodiment.

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

(1) 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, and the setting means is changed depending on the ambient temperature of the exhaust section at that time. There is no difference in the heating completion time even if the microwave oven is used repeatedly due to the influence of room temperature, etc., and it is possible to always finish the heated object consistently.

(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, whereas piezoelectric sensors , such a special circuit is not required at all, and the end of the heating state can be automatically detected at low cost and with a simple configuration.

[Brief explanation of the drawing]

FIG. 1(a) is a sectional view of a piezoelectric element sensor of a heating state detection device according to an embodiment of the present invention, and FIG. Figure, 2nd
The figure is a block diagram of the main body configuration of a microwave oven using the same piezoelectric element sensor, Figure 3 is an output voltage waveform diagram of the same piezoelectric element sensor, Figure 4 is a circuit diagram of the same filter, and Figure 5 is the same temperature correction A characteristic diagram showing the relationship between the voltage of the element and the ambient temperature, Figure 6 is a characteristic diagram showing the relationship between the output voltage of the piezoelectric element sensor and the ambient temperature, Figure 7 is a block diagram of the same system, and Figure 8 is the same after repeated heating. Fig. 9 is a block diagram of another example of the same system, Fig. 10 is a piezoelectric element sensor of another embodiment of the present invention,
FIG. 11 is a block diagram of the temperature correction element, FIG. 11 is a block diagram of the main body using a conventional humidity sensor, and FIG. 12 is a block diagram of the main body using another 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, 19... converter, 20... Start button, 21...Setting means, 22...
Comparator, 23... Control means, 24...
Biasing means, 34... Storage means, 35...
·resin. Name of agent: Patent attorney Toshio Nakao and 1 other person/-
--Piezoelectric cable assembly 2.3--Iden 4 to 1st port 4. ．． 5
--- Sword sk (gradient 6 - temperature correction element tb) Fig. 2 Fig. 3 O/θθ O, m: i number (Hl) Fig. 4 Fig. 5 Ticket surface temperature 1jlt'c> High 6th ticket W5 Temperature - Hama (t) Figure 8 jJL thermal closure (AJLL) ◆ Figure 10 = 1 ] Figure 120

Claims (4)

[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 and an amplifier for appropriately filtering the signal of the piezoelectric element sensor; a converter for converting the signal of the correction element from analog to digital; a setting means for determining the end of cooking of the object to be heated; a comparator for comparing a signal from an amplifier with a signal from the setting means; a start button for operating the heating means; a storage means for storing an initial value of the converter when the start button is activated; and the heating means. and a control means for stopping the biasing of the biasing means in response to a signal from the comparator, and the control means controls the setting of the setting means according to the initial value of the storage means. A heating state detection device configured to change the temperature. (2) The heating state detection device according to claim 1, wherein the control means is constituted by a microcomputer. (3) The control means is configured to output a plurality of analog quantities, the amplifier is configured to add together the analog quantities output from the control means, and the analog quantity is determined according to the initial value of the storage means. 2. A heating state detection device according to claim 1 or 2, wherein the heating state detection device is configured to change the heating state by changing the temperature. (4) The heating state detection device according to claim 1, wherein the piezoelectric element sensor and the correction element are integrally molded with resin.