JPH01248490A - High frequency heating device with thawing sensor - Google Patents

Abstract

PURPOSE:To make real time detection of thawing and boiling of food possible by detecting the high frequency wave of a frequency band of a high frequency wave emitting means by means of an antenna disposed in a heating chamber. CONSTITUTION:A detection means 6 for detecting the wave of the frequency band of a high frequency wave emitting means 3 for heating food 1 is arranged via an antenna 4 shorter than the 1/4 wave length of the oscillation frequency of the high frequency wave emitting means 3. Namely, the change in the signal voltage when the wave is detected with the wave detection means 6 when the food 1 is thawed and further boiled in a heating room 2 is due to the temperature dependence of dielectric loss in the physical property changes of the food 1. As a result, thawing can be detected at the minimum point of the signal change while the boiling can be detected at its maximum point. This makes it possible to detect the thawing and boiling of the food on the real time basis.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a microwave oven, and more particularly to a high-frequency heating device that automatically detects thawing and boiling of a heated object.

2. Description of the Related Art Conventionally, in order to automatically detect the thawing state of a microwave oven, as shown in Japanese Patent Application Laid-Open No. 59-207595, the frequency of high-frequency radiation means for heating the object to be heated (hereinafter referred to as food) and detects the transmitted waves from oscillation sources in different and separate frequency bands with a receiving means, and changes in the signal (detects the minimum point)
It was used to detect thawing of food.

Problems to be Solved by the Invention In such conventional methods, the frequency band (
Since a different high-frequency oscillation source is provided separately from the 2450 MHz band, filters and the like are required, and there is a limit to how compact and low-cost it can be realized. Furthermore, boiling could not be detected.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides detection means for detecting the frequency band of the high-frequency radiation means for heating food through an antenna, and detects the signal change of the detection means. The structure is such that thawing is detected at the minimum point and boiling is detected at the maximum point.

Function According to the present invention, the detection circuit of the frequency band (2450 MHz band) of the high-frequency radiation means for heating the food has the effect of detecting defrosting and boiling of the food in real time.

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

FIG. 1 is a block diagram of the main body of a high-frequency heating device with a defrosting sensor according to an embodiment of the present invention.

1 is food, 2 is a heating chamber, 3 is a high frequency radiation means (hereinafter referred to as magnetron), and 4 is an antenna shorter than 1/4 wavelength of the oscillation frequency of magnetron 3 (in the present invention, 3 to 5
mm). 5 is an attenuator, 6 is a detection means, 7 is an amplifier for amplifying the detected signal, 8 is a cooling fan, 9 is a magnetron 3, based on the detected signal after amplification.
It is a control means (a microcomputer in one embodiment of the present invention) that controls the cooling fan 8.

FIG. 2 shows a detection means 6 for detecting the signal of the magnetron 3.
FIG. 10 is a 50 ohm resistor, 11 is a detection diode (for example, a Schottky barrier diode) 1
2.13 is a resistor, 14 is a bypass capacitor, and the signal from the magnetron 3 is detected as a voltage vS by these. In addition, 5 is an attenuator, the power radiated by the magnetron 3 into the heating chamber 2 is several hundred watts, and the detection means 6
This is to prevent excessive input from being required.

FIG. 3 is a diagram in which the detection means 6 is composed of a microstrip line.

Copper foil patterns 16 and 17 are etched on a dielectric substrate 15 having a certain dielectric constant Er.

The copper foil section 16 has a characteristic impedance of 50 ohms, and the section 17 is grounded. By configuring the detection means 11 on the microstrip line, it is easy to optimally design the length of the line according to the frequency band to be detected, and since this is done by etching, the detection accuracy is improved. .

FIG. 4 is a characteristic diagram showing changes in the signal voltage detected by the detection means 11 when the food 1 is thawed in the heating chamber 2 and further boiled.

In this way, the change in signal from thawing to boiling is caused by food 1
This is due to the temperature dependence of dielectric loss in physical property changes.

For example, there is an 80 times difference between ice at O'C and water at 0 °C, and high frequencies (especially in the microwave band) are
Since the dielectric loss is small, it is hardly absorbed, and when it enters a liquid state, the dielectric loss rapidly increases, becomes easily absorbed, and then decreases again.

Therefore, in ice conditions, the power of the high frequency wave detected by the antenna 4 is large, so the detected voltage VS is also large. When the high frequency power begins to be absorbed into the food 1, the power detected by the antenna 4 decreases and the detected voltage VS also decreases. As a result, food defrosts at the minimum point P (rate of change is zero)
, and thawing detection can be performed in real time.

We have found that the detected voltage gradually increases from the liquid state to near the boiling point as the dielectric loss decreases, but when boiling continues for a while, the detected voltage VS decreases again. This phenomenon cannot be explained by dielectric loss, but after the boiling point is passed, the heating chamber 2 is filled with water vapor, which disturbs the high frequencies, and as a result, the high frequencies input to the detection means decrease. Therefore, it is thought that the detected voltage VS decreases. Therefore, boiling can be detected in real time at the maximum point Q (rate of change is zero). In addition, a microcomputer is used as the control means 9, and it can detect the minimum point and maximum point, measure the elapsed time t until the detection of the minimum point and maximum point, and determine the on/off interval of duty control of the magnetron 3. Suitable for complex control such as control.

Further, although a diode is used as the detection means, any semiconductor element such as a transistor may be used, but 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) Since the high frequency in the frequency band of the high frequency radiation means is detected by the antenna placed inside the heating chamber, defrosting of the food is detected at the minimum point, boiling is detected at the maximum point in real time, and the initial thawing temperature of the food, With a simple configuration, thawing and boiling can be reliably detected regardless of the type of food.

(2) The control means detects the thawing point at the minimum point and the boiling point at the maximum point, and detects the relative change. Compared to detecting the signal at the absolute level, the components and main body of the detection means are It is possible to absorb variations in component parts.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main body of a high-frequency heating device with a defrosting sensor according to an embodiment of the present invention, FIG. 2 is a circuit diagram of the detection means, and FIG.
The figure shows the detection means configured on a microstrip line, and FIG. 4 is a characteristic diagram showing changes in the signal of the detection means during thawing and boiling. 1...Object to be heated, 2...Heating chamber, 3...
...High frequency radiation means, 4...Antenna, 5.
...Attenuator, 6...Detection means, 9...
Control means (microcomputer), 16... microstrip line. Figure 1 8--Ichiga ff
p means Figure 2

Claims (1)

[Claims] A heating chamber into which a heated object is taken in and taken out, a high-frequency radiating means for feeding high-frequency power into the heating chamber, an antenna having a wavelength shorter than 1/4 of the oscillation frequency of the high-frequency radiating means, and attenuating the power input from the antenna. an attenuator, a detection means for detecting the heating progress state of the object to be heated through the antenna, and detecting defrosting at the minimum point and boiling at the maximum point among the signal changes of the detection means, and detecting the boiling at the maximum point, A high-frequency heating device with a thawing sensor, which comprises a control means for controlling.