JPH01219423A - Heated condition sensing device - Google Patents

Abstract

PURPOSE:To enable a uniform finished cooking to be attained with a simple configuration by a method wherein a minimum value of an output signal of a piezoelectric element sensor is read for every one cooking operation and the cooking is completed in response to an increasing degree of an output signal from its minimum value. CONSTITUTION:A piezoelectric element sensor 1 is connected to a voltage amplifying amplifier 2, a voltage comparing comparator 3 and a control unit 4. A food 6 is placed within a heating chamber 5, a part of cold air of an electromagnetic radiation part 7 is guided by a cooling fan 8 into a heating chamber 5 through a duct 9. The cold air 10 and air 11 containing water vapor or oil generated from the food are passed through a discharging part 12 and fed out from the heating chamber 5 to an external part. The piezoelectric element sensor 1 is fixed to the discharging part 12 and a buzzer 22 may operate with a signal of a controller 4 when an amplified signal voltage is larger than a set value of alphaVsmin in reference to an increasing degree from a minimum value Vsmin. As a countermeasure for a temperature characteristic, a minimum value of Vsmin of an output signal Vs is calculated for every one cooking operation. The cooking is terminated if a relation of Vs>alphaVsmin is attained. However, a value of alpha is determined for its most appropriate value in examinations.

Description

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

2. Description of the Related Art The mechanism of a conventional heating state detection device such as a high-frequency heating device will be explained with reference to the drawings.

FIG. 8 shows a conventionally used high frequency heating device with a humidity sensor. In the case of a humidity sensor, when the moisture in the food boils and the humidity rapidly changes from decreasing to increasing, it is possible to determine the end of cooking by detecting this point. Based on this, as shown in FIG. 8, the change in the resistance value of the humidity sensor 25 is determined by the reference voltage 11! The voltage of the source 26 is detected by dividing it 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 Unexamined Patent Publication No. 62-37624) Problems to be Solved by the Invention However, when using a humidity sensor as described above, gas or oil in the food adheres to the humidity sensor during cooking, reducing detection sensitivity. It is necessary to evaporate the deposits on the humidity sensor using a heater for refreshing heat treatment every time you cook, which creates the problem of extra electricity and cost. child.

There is also a method of using a piezoelectric element sensor instead of a humidity sensor, but the piezoelectric element sensor itself has temperature characteristics, and as the temperature rises, the output signal decreases and the heating end time becomes longer. The drawback is that the cooking condition is not consistent.

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

DESCRIPTION OF THE MEANS FOR SOLVING THE PROBLEMS To solve the problems, the heating state detection device of the present invention uses a piezoelectric sensor instead of a conventional humidity sensor. Furthermore, piezoelectric sensors have the disadvantage that when cooking is repeated, the temperature rises, and the output signal decreases due to the temperature characteristics, resulting in a longer heating completion time. is read and the cooking is terminated depending on the degree of increase from the minimum value of the output signal.

Operation With the above configuration, the present invention reads the minimum value of the output signal of the piezoelectric element sensor every - time of cooking, and finishes cooking according to the degree of increase from the minimum value of the output signal, so even when cooking is repeated. The cooking condition is always the same.

Embodiment FIG. 1 is a schematic flowchart for measures against temperature characteristics of a high-frequency heating apparatus using a heating state detection device with a piezoelectric sensor according to an embodiment of the present invention.

Before explaining the measures against temperature characteristics, we will discuss the actual boiling detection mechanism.

In FIG. 2, the output of the piezoelectric element sensor 1 is configured so that no DC component is applied to the sensor, and to block the DC component of the sensor voltage output. (hereinafter referred to as a DC blocking amplifier), a comparator 3 for voltage comparison, and a controller 4.

Food 6 is placed in a heating chamber 5, and a portion of the cooling air from a radio wave emitting unit (in this case, a magnetron) 7 is guided to the heating chamber 5 through 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.

1. 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 the wl source switch 15, and this winding 17 has a constant voltage composed of a rectifier bridge 18, a capacitor 19, a resistor 20, and a constant voltage diode 21. It forms the power supply section, eliminating the need for a transformer for the control circuit. Further, the buzzer 22 is configured to operate according to the signal from the controller 4 when the amplified signal voltage becomes larger than αVsmIn, which is set as a reference for the degree of increase from the minimum value Vsmln.
I'm here.

1 of the controller 4 simultaneously opens the power supply voltage of the radio wave emitting section 7.

FIG. 1 shows a schematic flowchart in which the minimum value Vsmln of the output signal v3 is determined for each cooking as a measure against temperature characteristics, and the cooking is terminated when Vs>αVsmjn. However, the optimum value of α must be determined through experiments.

Details will be explained below with reference to FIG.

FIG. 3 shows the correction results obtained when the microcomputer is programmed according to the schematic flowchart shown in FIG. It can be seen that cooking can be completed within a substantially constant time tawtb regardless of the decrease in the piezoelectric element sensor output caused by the temperature rise.

For comparison with FIG. 3, FIG. 4 shows how the cooking completion time increases as the temperature rises according to the conventional method. In the conventional method, cooking ends when the sensor output exceeds a certain set voltage. Therefore, as the temperature rises (Ta→Tb), the sensor output decreases and the cooking completion time is extended (ta→tb). .

The reason why the sensor output decreases as the temperature increases is because the temperature of the piezoelectric element sensor and its atmosphere increases with each cooking cycle, so even if the same amount of warm water vapor collides each time and exchanges heat, The changes gradually become smaller. Since the polarization current of the piezoelectric element sensor is generated in response to temperature changes, the cooking completion time becomes longer.

FIG. 5 shows an example of data regarding the signal and noise of the piezoelectric sensor. (,) shows an example of a signal waveform when the water in the refrigerator 5 boils. (b) shows an example of the results of spectrum analysis of this waveform. When the wind containing warm water vapor hits the ultrasonic microphone for 40kHz, O
It can be seen that a large signal is output in the ~50Hz band. The difference between the A and the mouth is about 30 dB.

The signal level is a voltage of several mV. A is a case when the water in the refrigerator has boiled, a case is before the water has boiled, and a is a case when the high-frequency heating device is not energized.

Figures 6 and 7 show a circuit example of amplifier 2 that combines a low-pass filter and a bypass filter and has band-pass filter characteristics, and the amplifier output voltage when this circuit is used to heat 400 cc of water. An example waveform is shown.

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

(1) Read the minimum value of the output signal for each cooking time,
The configuration is such that cooking is terminated according to the degree of increase from the minimum value of the output signal.With this, even when heating is repeated, the cooking completion time does not vary due to the temperature characteristics of the piezoelectric element sensor, and the cooking is in a constant state of completion. Become.

(2) Temperature correction can be achieved with simple modifications to the microcomputer program.There is no need to use special parts (for example, a fan for sensor cooling, a diode for temperature correction, etc.) just for temperature correction. , is extremely reasonable.

(3) Use a degree sensor or gas sensor to detect small objects,
Since it essentially utilizes the grain boundary phenomenon of the sensing element, there are many maintenance issues such as keeping warm with a heater to prevent clogging of grain boundaries, and periodically burning off dirt with a heater. Complicated measures are required, but piezoelectric sensors do not require such measures.

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

(4) For the same reason as (2), the heating state detection device of the present invention is inexpensive because it does not require any control parts for maintaining the accuracy of the heat retention heater power or a special transformer for the heater power. . 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), since the signal is large compared to the noise level due to electromagnetic noise in the high-frequency heating device and wind noise from the cooling fan, stable control can be performed.

(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 flowchart of a heating state detection device showing an embodiment of the present invention, Fig. 2 is a block diagram of the state in which the same device is used in a high-frequency heating device, and Fig. 3 shows the cooking end time of the device. Fig. 4 is a characteristic diagram showing that the cooking completion time is extended with the conventional device; Fig. 5a,
b is a characteristic diagram of the signal and noise of a piezoelectric element sensor, Fig. 6 is a circuit diagram of an amplifier with band-pass filter characteristics, and Fig. 7 is a diagram of heating 400 cc of water using the circuit shown in Fig. 6. Amplifier output voltage waveform diagram, Figure 8 shows f
This is a block diagram of a conventional example. 1...Piezoelectric element sensor, 4...Controller, 5...Heating chamber, 7...Radio wave emitting section,
8... Cooling fan, 12... Exhaust section. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure ΔVr 31st! ! t α saki tb Fig. 4 between yr t t < tb Fig. 5 (A) (b) Fig. 6? Figure 7 - Ginma

Claims (2)

[Claims] (1) A heating chamber in which a food to be cooked is stored for cooking, a radio wave radiating section that radiates electromagnetic waves to the food to be cooked to cook the food, a cooling fan that cools the radio wave radiator, and a heating chamber for storing the food to be cooked. an exhaust section that releases water vapor from the object to the outside of the heating chamber;
a piezoelectric element sensor that detects the boiling state of the food to be cooked and provides an output signal; and a minimum value of the output signal that reads the minimum value of the output signal for each cooking to prevent the influence of the temperature characteristics of the piezoelectric element sensor. A heating state detection device comprising: a controller for terminating cooking depending on the degree of increase in temperature; (2) The heating state detection device according to claim 1, wherein the degree of increase of the output signal from the minimum value is defined by a ratio to the minimum value.