JPH0272585A - Heating condition detecting device - Google Patents

Abstract

PURPOSE:To remove the dispersion of heating finish time and to prevent the pollution of an element by installing a cooling fan which sucks the steam from inside a heating chamber through a suction air guide and a piezoelectric element which, being installed at the suction air guide, detects the boiling of a cooking substance and is cooled by the cooling fan. CONSTITUTION:A piezoelectric element 21 installed at an suction air guide 33 is cooled by external cold blast which is directly hitting against it by the positive pressure of the cooling fan 28, and further a part of the steam from inside a heating chamber 28 is taken in through a suction air guide 33 by the negative pressure by the suction of the cooling fan 28, and the piezoelectric element 21 detects the thermal change of the steam. Accordingly, the temperature rise of the piezoelectric element 21 is restrained, and the condition to give temperature change to the piezoelectric element 21 becomes constant at all times. Hereby, even if the same amount of load is added repeatedly, the dispersion of cooking time disappears, and since the flow of cooling blast 30 and a separate air flow 31' which includes the steam, oil, etc., arising from food 26 are sent out to the outside from the heating chamber 25 through an exhaust part 32, the dirt of the piezoelectric element by gas, oil, etc., becomes small.

Description

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

2. Description of the Related Art A conventional heating state detection device such as a high frequency heating device will be described with reference to FIGS. 7 and 8.

FIG. 7 is a configuration diagram of a conventionally used high frequency heating device with a humidity sensor. When using the humidity sensor shown in FIG. 7, the moisture in the food 2 in the heating chamber 1 boils and the humidity changes rapidly from decreasing to increasing, so by detecting this point it is possible to determine the end of cooking. be able to. Based on this, the voltage of the reference voltage power source 4 is set to the humidity sensor 3.
The device is controlled by detecting the voltage by dividing the voltage between the variable resistance value of the resistor 5 and the fixed resistance value of the resistor 5 (for example, the
3-77365).

The eighth factor is a configuration diagram of a high frequency heating device using a piezoelectric element instead of a humidity sensor. In FIG. 8, heating chamber 6
The water in the food 7 boils and becomes water vapor 8, and heat is exchanged between the piezoelectric element 9 and the water vapor 8. This thermal change generates a polarization current, which is detected and the device is activated. (for example, Japanese Patent Laid-Open No. 62-37624).

Problem to be Solved by the Invention However, when using a humidity sensor as described above, gas or oil in the food 2 adheres to the humidity sensor 3 during cooking, reducing detection sensitivity. It is necessary to evaporate deposits on the humidity sensor 3 using a heater for refresh heat treatment each time, resulting in the problem of extra power and cost.

Furthermore, if the piezoelectric element 9 is used instead of the humidity sensor, the piezoelectric element 9 itself has temperature characteristics, and as the temperature rises, the heating end time becomes longer. Therefore, there was a problem that the finished product of the food was not good.

The present invention solves the above-mentioned conventional problems, and aims to provide a heating state detection device that can suppress the influence of the temperature characteristics of a piezoelectric element to eliminate variations in heating completion time, and can also suppress contamination of the element. This is the purpose.

Means for Solving the Problems In order to solve the above problems, the heating state detection device of the present invention includes: a high-frequency radiator that emits high-frequency waves to a heating chamber; an intake guide that guides steam in the heating chamber; and the intake guide. The device is equipped with a cooling fan capable of sucking in a portion of the steam in the heating chamber, and a piezoelectric element attached to the intake guide to detect boiling of the food and cooled by the cooling fan.

Effect With the above configuration, the piezoelectric element attached to the intake guide is directly cooled by the external cold air generated by the positive pressure of the cooling fan, and furthermore, the negative pressure generated by the cooling fan draws some of the steam from the heating chamber into the intake guide. Since the structure is such that the piezoelectric element detects thermal changes in the steam, the temperature rise of the piezoelectric element is suppressed, and the conditions that cause temperature changes to the piezoelectric element are always constant. Even if it is added repeatedly, the cooking time will not vary, and the finished product will be good. In addition, since it detects a portion of the steam taken in through an intake guide provided separately from the exhaust section, compared to the conventional piezoelectric element installed in the exhaust section, it is possible to detect a piezoelectric element caused by gas or oil. There is little dirt (and stable signal output can be obtained over a long period of time.

Example Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a configuration diagram of a high-frequency heating device using a heating state detection device with a piezoelectric element, showing one embodiment of the present invention. In FIG. 1, the piezoelectric element 21 is attached to an intake guide 33 capable of inducing steam within the heating chamber 25. The output of this piezoelectric element 9 is passed through a voltage amplification amplifier 22 (hereinafter referred to as a DC blocking amplifier) configured to prevent DC components from being applied to the element and to block DC components of the voltage output. It is connected to a comparator 23 for voltage comparison, and further connected to a controller 24.

Food 26 is arranged in the heating chamber 25, and the radio wave emitting part 27 (
A part of the cooling air that cools the magnetron is guided into the heating chamber 25 through a duct 29 by a cooling fan 28. A part of the flow of the cooling air is shown by a solid line arrow 3o, and a part of the flow of air containing water vapor, oil, etc. generated from the food 26 is shown by a broken line arrow 31. In addition, the cooling air flow 30 and the food 2
Another air flow 31' containing water vapor, oil, etc. generated from the heating chamber 25 is sent out from the heating chamber 25 through the exhaust section 32.

Further, by utilizing the suction force of external cold air due to the positive pressure of the cooling fan 28, a portion of the steam in the heating chamber 25 is guided into the intake guide 33 by the negative pressure generated at that time.

34 is a motor core, 35 is a winding wound around the motor core, and this winding 35 constitutes a constant voltage power supply section consisting of a rectifier bridge 36, a capacitor 37, a resistor 38, and a constant voltage diode 39, and a transformer for the control circuit. is no longer necessary. Further, the buzzer 40 is configured to operate according to a signal from the controller 24 when the signal voltage amplified by the DC blocking amplifier 22 becomes larger than a threshold voltage ΔVt set by the comparator 23. .

In addition, the signal from the controller 24 simultaneously causes the radio wave emitting unit 27 to
The power supply voltage is closed, and during cooking, the cooling fan 28 continues to rotate, cooling the piezoelectric element 21 along the path indicated by the solid arrow 30, and suppressing the temperature rise caused by food vapor and the magnetron heater. 41 is a power plug, and 42 is a power switch.

FIG. 2 is a diagram showing the intake guide and the piezoelectric element mounting position. In FIG. 2, the piezoelectric element 21 is glued onto a metal plate 43 and attached to a resin-molded intake guide 33 so that the cold air (positive pressure air) of the cooling fan 28 directly hits the piezoelectric element 21. There is. This metal plate 41
The metal surface allows the steam in the intake guide 33 to come into direct contact with the piezoelectric element 21 and easily transfer heat to and from the piezoelectric element 21.
An air intake guide 33 made of resin thermally insulates the heating chamber 6 and the duct 29 to suppress a rise in temperature of the piezoelectric element 21. The suction of steam utilizes the negative pressure (suction power) of the cooling fan 28.

FIGS. 3(a) and 3(b) show data examples of signals and noise of the piezoelectric element, and FIG. 3(a) shows an example of a signal waveform when water in the heating chamber 25 boils. Figure 3 (b
) is a diagram showing an example of the result of spectrum analysis of this waveform. In Figure 3(b), the ultrasonic microphone for 40i is exposed to θ~5 due to the wind containing warm water vapor hitting the 40i ultrasonic microphone.
It can be seen that a large signal is output in the 0Hz band. The difference between signal (a) and signal (b) is about 3 odB, and the signal level is several mV.
voltage. The signal (a) is when the water in the heating chamber 25 is boiling, the signal (b) is when the water is boiling, and the signal (c) is when the high frequency heating device is not energized.

FIGS. 4 and 5 show an example of the u-path of the DC blocking amplifier 22 having band-pass filter characteristics, which is a combination of a low-pass filter and a bypass filter.
00 ct- is an amplifier output voltage waveform diagram when heated.

As shown in FIG. 4, the signal voltage output from the piezoelectric element 21 is input to the input terminal 22a of the DC blocking amplifier 22, and is amplified and output from the output terminal 22b as an output signal voltage A as shown in FIG. be done. As shown in Figure 5,
As time passes and the water in the food in the heating chamber reaches Sat, the signal voltage output from the piezoelectric element 21 rises rapidly, and the output signal voltage A from the DC blocking amplifier 22 also shows a sudden rise.

Therefore, in the comparison type 23 shown in FIG. 1, by comparing the set threshold voltage ΔVt and the output signal voltage A, the controller 24 issues a buzzer alarm when the signal voltage becomes larger than the threshold voltage ΔVt. In this way, you can know when the food has reached the boiling point.

FIGS. 6(a) and 6(b) are diagrams showing the difference between the case where the piezoelectric element is not cooled and the case where it is cooled in terms of the relationship between the cooking completion time and the degree of temperature rise. In FIG. 6(a), since the piezoelectric element 21 generates a polarized current according to the differential value of temperature change, when cooking is repeated without cooling as in the conventional case, -
The temperature of the piezoelectric element 21 and its atmosphere rises each time cooking is performed, so even if the same amount of warm water vapor collides and exchanges heat each time, the temperature change gradually becomes smaller. For this reason, each time cooking is repeated, the degree of temperature rise Δ1' becomes smaller, and the cooking completion time t becomes longer ().

On the other hand, when the piezoelectric element 21 is cooled by external cooling air for each cooking, the piezoelectric element 21 is cooled as shown in FIG. 6(b).
Since the temperature rise is suppressed, the degree of temperature rise Δ1' remains constant no matter how many times the cooking is repeated, and the cooking end time t remains the same.

Effects of the Invention As described above, according to the present invention, there is provided an air intake guide that guides the steam inside the heating chamber, a cooling fan that can draw in a part of the steam inside the heating chamber from the air intake guide, and a cooling fan that is attached to the air intake guide and that controls the cooking process. By having a piezoelectric element that detects the boiling of food and is cooled by a cooling fan, the piezoelectric element is cooled by the cooling fan, and it is possible to eliminate variations in the heating completion time due to the temperature characteristics of the piezoelectric element, thereby reducing the time of cooking. The finish is good, and because the piezoelectric element is installed not in the exhaust section but in the intake guide that guides a portion of the steam,
The piezoelectric element is less likely to be contaminated by gas or oil, and a stable signal output can be obtained over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a high-frequency heating device using a heating state detection device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the positions of the air intake guide and piezoelectric element mounting of the heating state detection device.
FIGS. 3(a) and 3(b) are diagrams showing an example of a signal waveform when water in the heating chamber of the high-frequency heating device using the same heating state detection device boils, and diagrams showing an example of the result of spectrum analysis of this signal waveform. , Figures 4 and 5 are the circuit diagram and amplifier output voltage waveform diagram of the DC blocking amplifier of the same heating state detection device, and Figures 6 (a) and 6 (b) are cooking diagrams when the piezoelectric element is not cooled and when it is cooled. FIGS. 7 and 8, which show the relationship between the end time and the degree of temperature rise, are configuration diagrams of a high-frequency heating device using a conventional heating state detection device, respectively. 21... Piezoelectric element, 25... Heating chamber, 26... Food, 27... High frequency radiation section, 28... Cooling fan,
32...Exhaust part, 33...Intake guide.

Claims (1)

[Claims] 1. A high-frequency radiator that radiates high-frequency waves to the heating chamber, an intake guide that guides the steam in the heating chamber, a cooling fan that can draw in a part of the steam in the heating chamber from the intake guide, and A heating state detection device comprising a piezoelectric element attached to the piezoelectric element to detect boiling of the food to be cooked and cooled by the cooling fan.