JPH01267995A - Heating device - Google Patents

Abstract

PURPOSE:To provide a certain cooking finished condition and eliminate use of parts or elements for correction of temp. by reading the peak hole value of the output voltage from a piezo element sensor, and by controlling the apparatus concerned. CONSTITUTION:The output from a piezo element sensor 1 is connected with an amplifier 2 for voltage amplification, which is constructed so that the DC component is not impressed to the sensor and so that the DC component of the sensor voltage output is checked, and further a peak hold circuit 23, a comparator 3 for comparison of voltage, and a control device 4. The apparatus is controlled by reading the peak hold value of the output signal from the abovementioned piezo element sensor 1. This lessens variation of the output, facilitates the control, and accomplishes a stable finish condition in cooking without resorting to use of any parts or elements for correction of temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a heating device using a piezoelectric element sensor used in a high frequency heating device or the like.

BACKGROUND OF THE INVENTION The mechanism of a conventional heating device such as a high-frequency heating device will be explained with reference to the drawings.

FIG. 7 shows a conventionally used high-frequency heating device with a humidity sensor. In the case of a humidity sensor, the moisture in the food boils and the humidity rapidly changes from decreasing to increasing, so by detecting this point it is possible to determine the end of cooking. Based on this, as shown in FIG.
5 is detected by dividing the voltage of the reference voltage power supply 26 with the resistor 27 to control the equipment. (For example, Japanese Unexamined Patent Publication No. 53-77365) There is also a method of using a piezoelectric element sensor instead of the humidity sensor as shown in FIG. Heat is exchanged between the piezoelectric element sensor 1 and water vapor, and the thermal change generates a polarization current, which is detected to control the device. (
(For example, Japanese Patent Application Laid-Open No. 62-37624) Problems to be Solved by the Invention However, when a humidity sensor is used as described in L, gas or oil in the food adheres to the humidity sensor during cooking, reducing detection sensitivity. Therefore, it is necessary to evaporate the deposits on the humidity sensor using a heater for refresh heat treatment or the like after each cooking cycle, resulting in the problem of extra power and cost.

Another method is to use a piezoelectric element sensor instead of a humidity sensor, but if you directly amplify the output of the piezoelectric element sensor, the disadvantage is that the output changes little and is difficult to control, and the output increases as the temperature rises due to the influence of temperature characteristics. As the temperature decreases, the detection time gradually increases, leading to variations in the degree of doneness of cooking, which necessitates the need for special elements and parts for temperature correction.

The present invention has been made to solve such conventional problems, and aims to detect the heating state of food with a simple configuration and provide a constant cooking finish state.

Means for Solving the Problems In order to solve the above problems, the heating state detection device of the present invention first uses a piezoelectric element sensor in place of the conventional humidity sensor.

Furthermore, if the output of a piezoelectric element sensor is directly amplified and extracted, there are disadvantages in that the output changes little and is difficult to control, and the detection time gradually increases because the output decreases further as the temperature rises due to the influence of temperature characteristics. However, since this can cause variations in the finished state of cooking, there was an issue in which a special element or component for temperature correction was required, so a mechanism was adopted in which the output was read through a peak hold circuit. By using a peak hold circuit, the output changes sharply, making it easier to control, and also eliminates the need for temperature correction elements and components.

Operation With the above configuration, the present invention controls the equipment by reading the peak hold value of the output signal of the piezoelectric element sensor, so there is no need for temperature correction elements or parts, since the output changes are small and difficult to control. Stable cooking even without using it 1
It has the effect of providing a relaxed state.

Embodiment FIG. 1 shows an embodiment of a high-frequency heating device using a heating state detection device with a piezoelectric element sensor of the present invention. It has a configuration in which a peak hold circuit is added to the conventional heating state detection device with a piezoelectric element sensor.

In FIG. 1, the output of a piezoelectric sensor 1 is a voltage amplifying amplifier 2 (hereinafter referred to as a DC blocking amplifier) configured to prevent direct current components from being applied to the sensor and to block direct current components of the sensor voltage output. ), a peak hold circuit 23 , a comparator 3 for voltage comparison, and a controller 4 .

Food 6 is placed in the heating chamber 5 , and a portion of the cooling air from the radio wave emitter (magnetron in this case) 7 is guided into the heating chamber 5 via a duct 9 by a cooling fan 8 . A part of the cooling air is shown by a solid arrow line 10, and a part of the air containing water vapor, oil, etc. generated from the food is shown by a dotted arrow line 11. The cooling air and the air containing water vapor and oil generated from the food are removed from the exhaust section 1.
2 and sent out from the heating chamber 5 to the outside.

A piezoelectric element sensor 1 is attached to the exhaust section 12. In this embodiment, the core 1 of the motor that drives the cooling fan 8
3, a winding 17 is wound together with a winding 16 from the power plug 14 via a power switch 15, and this winding 17 is connected to a constant voltage power supply consisting of a rectifier bridge 18, a capacitor 19, a resistor 20, and a constant voltage diode 21. This eliminates the need for a transformer for the control circuit. Moreover, the buzzer 22 is
It is configured to operate according to a signal from the controller 4 when the amplified and peak-held signal voltage becomes larger than a threshold voltage ΔVt set as a reference for the end of cooking. At the same time, the power supply voltage of the radio wave emitting section 7 is opened by a signal from the controller 4.

In FIG. 2(a), the output of the piezoelectric sensor 1 is input to the amplifier 2.
The waveform amplified by , and peak-held by the peak-hold circuit 23 is shown.

FIG. 2(b) shows an output waveform obtained by simply amplifying the output of a similar piezoelectric sensor 1 with an amplifier 2. Figure 2(a)
Unlike the peak-held waveform, it has a gentle rise, so it is strongly influenced by the temperature characteristics of the piezoelectric sensor, and there is a variation Δ weight in the time it takes to exceed the threshold voltage ΔVt, which requires temperature correction. It turns out that it is.

FIG. 3 shows an example of a peak hold circuit.

D is a diode, C is a capacitor, and R1 and R2 are resistors. The steepness of the peak hold can be determined by selecting the charging time constant RIXC.

FIG. 4 shows an example of data regarding the signal and noise of the piezoelectric sensor. FIG. 4(a) shows an example of a signal waveform when the water in the refrigerator 5 boils. In Figure 4(b),
An example of the results of spectrum analysis of this waveform is shown below. 40
It can be seen that when the ultrasonic microphone for kHz is exposed to wind containing warm water vapor, a large signal is emitted in the 0 to 50 Hz band. 1. The difference between A and mouth is about 30 dB, and the signal level is a voltage of several mV. be. A is when the water in the refrigerator has boiled, water is before boiling, and c is when the high-frequency heating device is not energized.

FIGS. 5 and 6 show examples of waveforms of a bandpass filter that is a combination of a lowpass filter and a bypass filter.

Effects of the Invention As described above, the heating state detection device of the present invention provides the following effects.

(1) Since the device is controlled by reading the peak hold value of the output voltage of the piezoelectric element sensor, there is no variation in the cooking end time, a constant cooking finish state is achieved, and there is no need for temperature correction elements or parts.

(2) Since the output voltage of the piezoelectric element sensor is held at its peak, there is a large change in the signal before and after the food boils (because the rise is steep, it may malfunction or end without being detected) Never.

(3) Humidity sensors and gas sensors essentially utilize the grain boundary phenomenon of the sensing element, so to prevent clogging of grain boundaries, they must be kept warm with a heater or periodically heated. Piezoelectric sensors do not require many complicated maintenance efforts, such as burning off dirt.

Therefore, there is no need for electricity for heat retention or for baking, making it a power-saving type.

(4) For the same reason as (3), the heating state detection device of the present invention does not require any control parts for maintaining the accuracy of the heat-retaining heater power or a special transformer for the heater power, and is therefore inexpensive. When the heating state detection device of the present invention is used in a high frequency heating device or the like, the cost can be significantly reduced.

(5) As is clear from FIG. 2(b), stable control is possible because the signal is large compared to the noise level caused by electromagnetic noise within the high-frequency heating device and wind noise from the cooling fan.

(6) Furthermore, since a DC blocking amplifier is used, no DC voltage is applied to the piezoelectric element sensor, and changes in element characteristics due to ion conduction or the like can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a state in which a heating state detection device according to an embodiment of the present invention is used in a high-frequency heating device, and FIG. 2(a) is a characteristic diagram of a peak hold waveform of the heating state detection device of the present invention. Figure 2(b) is a characteristic diagram of a heating state detection device using a conventional piezoelectric element sensor, Figure 3 is a circuit diagram showing an example of a peak hold circuit, and Figures 4(a) and (b) are A characteristic diagram of the signal and noise of a piezoelectric element sensor, Figure 5 is a circuit diagram of an amplifier with band-pass filter characteristics, and Figure 6 is a diagram of the amplifier output voltage waveform when 400 oa of water is heated using the circuit in Figure 5. , FIG. 7 is a block diagram of a conventional example using a humidity sensor, and FIG. 8 is a block diagram of a conventional example using a piezoelectric element sensor. DESCRIPTION OF SYMBOLS 1...Piezoelectric element sensor, 3...Comparator, 4...Controller, 5...Heating chamber, 7.
... Radio wave emitting section, 23 ... Peak hold circuit, 24 ... Reference value setting means. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2 (α2 (b) θ Examination [5ecl Figure 3 Figure 4 ζυ) 50 1θO(?h) Figure 5? Figure 6 - Masama

Claims (1)

[Claims] a heating chamber for storing a food to be cooked; a heating means for supplying heating energy to the heating chamber; a piezoelectric element sensor for detecting the cooking state of the food to be cooked; and a peak hold for an output signal from the piezoelectric element sensor. a comparator that compares the peak-held signal with a reference value for the completion of cooking; and a controller that controls the operation of the heating means based on the signal from the comparator.