JPH07180844A - Reduced pressure high frequency heating apparatus - Google Patents

Abstract

PURPOSE:To prevent instruments from being damaged and the commodity value of an article to be heated from being lowered by judging the existence of electric discharge based upon a detection signal of pressure in a closed container under reduced pressure, and controlling a microwave generator based upon the judgement. CONSTITUTION:An article 3 to be heated is placed in a closed container 2, the container is exhausted by a vacuum pump 5 to reduce the pressure therein. A magnetron 7 irradiates the inside of the closed container 2 with microwaves to heat the article 3. A pressure detector 10 detects predetermined set pressure in the closed container 2 and also detects the rise of pressure upon electric discharge being produced. A pressure judgement device 20 judges the existence of electric discharge based upon a signal from the pressure detector 10, and a controller 21 controls the magnetron 7 based upon a judgement result on the production of the electric discharge from the pressure judgement device 20, whereby the electric discharge is prevented from being continued. Thereby, associated instruments are prevented from being damaged and the commodity value of the article is prevented from being deteriorated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decompression high-frequency heating device for performing microwave heating in a closed container under reduced pressure.

[0002]

2. Description of the Related Art Conventionally, there has been known a method of irradiating microwaves under vacuum to heat foods such as drying foods and thawing frozen products. An example of such a decompression high-frequency heating device will be described with reference to FIG.

The decompression high-frequency heating device 50 is provided with a hermetic container 52 for accommodating an object 51 to be heated and a vacuum pump 53 for exhausting air in the hermetic container 52. Further, a magnetron 55 that generates microwaves is connected to the hermetic container 52 via a waveguide 54, and the hermetic container 52 and the waveguide 54 are connected.
The space between and is sealed by a plate-shaped partition plate 56 (for example, synthetic resin) having high radio wave transmission. Also, the closed container 5
2 is provided with a pressure detection device 57 so that the degree of vacuum in the closed container 52 can be measured. Further, a vacuum release valve 58 for returning the inside of the closed container to atmospheric pressure is connected to the closed container 52.

Next, an example of a heating method of such a reduced pressure high frequency heating device will be described.

After the object 51 to be heated is placed in the closed container 52, the vacuum pump 53 is started to reduce the pressure in the closed container. Then, when the pressure detection device 57 detects that the pressure has reached a preset pressure, the vacuum pump 53 is stopped by the control of the control device (not shown), and the pressure reduction is stopped. afterwards,
The magnetron 55 is started by a controller (not shown) to heat the object 51 to be heated. When the predetermined heating time is completed, the magnetron 55 is stopped and the vacuum release valve 58 is opened. Therefore, the inside of the closed container is returned to the atmospheric pressure, and the heating is completed. After that, the object to be heated 51 is taken out.

The principle of such a reduced pressure high frequency heating device is as follows.
When water is heated under vacuum, it utilizes that the water boils at a saturation temperature according to its pressure. For example, the boiling point of water is 100 ° C. at atmospheric pressure, but it boils at a low temperature of 29 ° C. under a vacuum of 30 Torr. Using this principle, for example, when thawing frozen products such as tuna and meat, the pressure in the closed container is reduced to 30 Torr, and when microwaves are irradiated, the temperature of the heated object is the boiling point of water at 30 Torr. Maintained at 29 ° C. Therefore, it becomes possible to thaw frozen products such as tuna, meat, etc. in a raw state while preventing partial whitening and preventing whitening.

[0007]

However, when microwaves are radiated in a vacuum condition of the pressure in the closed container of 100 Torr or less, a discharge phenomenon may occur in the closed container if the microwave output is too high. is there. This discharge phenomenon is likely to occur in the vicinity of the power feed port of the waveguide, which guides the microwave into the closed container, and the microwave energy transmitting window material may damage the microwave transparent window material provided in the power feed port. Further, when a discharge phenomenon occurs, microwave energy is consumed in the discharge part, the microwave is not effectively absorbed in the object to be heated, and heating becomes uneven. In order to avoid this discharge, it is necessary to suppress the output of microwaves, but if the output of microwaves is suppressed, there are problems such as a longer heating time and a smaller amount of treatment per unit time.

The present invention has been made to solve the above-mentioned problems, and prevents the microwave transmitting window material provided in the microwave power feeding port from being damaged by electric discharge and heating unevenness of an object to be heated. It is an object of the present invention to provide a decompression high-frequency heating device capable of preventing the deterioration of commercial value by eliminating the above.

[0009]

In order to achieve this object, in a decompression high-frequency heating apparatus of the present invention, a hermetically sealed container in which an object to be heated can be stored and an object to be heated in the hermetically sealed container are irradiated with microwaves. Microwave generating means, a pressure reducing means for exhausting gas in the closed container, a pressure detecting means for detecting the pressure in the closed container, and a determining means for determining the presence or absence of discharge based on the signal of the pressure detecting means. And a control means for controlling the microwave generator based on the judgment of the judgment means.

[0010]

In the decompression high-frequency heating apparatus of the present invention having the above structure, the object to be heated is placed in the closed container, and the decompression means exhausts the gas in the closed container to reduce the pressure in the closed container. . The microwave generator heats an object to be heated by irradiating the sealed container with microwaves. The pressure detecting means detects a predetermined set pressure in the closed container and also detects a pressure increase when a discharge occurs. The determination means determines the presence or absence of the discharge phenomenon based on the signal of the pressure detection means, and the control means controls the microwave generator based on the determination result of the discharge occurrence of the determination means to prevent the discharge from continuing.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic block diagram of the present invention.

A closed container 2 is housed in a main body cover 1 of the decompression high-frequency heating apparatus of the present invention, and an object 3 to be heated is placed in the closed container 2. A door 4 for loading and unloading the object 3 to be heated is provided in the opening on the left side of the main body cover 1, and a vacuum pump 5 is connected to the right end of the closed container 2 by a pipe 13. The closed container 2 and the vacuum pump 5 are fixed to a base 6 provided at the bottom of the body cover 1. Further, a magnetron 7 is connected to the upper part of the closed container 2 via a waveguide 8. A space between the waveguide 8 and the closed container 2 is sealed by a plate-shaped partition plate 9 (for example, synthetic resin) having high radio wave transmission. A pressure detection device 10 is connected to the wall surface of the right end portion of the closed container 2 by a pipe 12, and a pipe 1 between the closed container 2 and the vacuum pump 5 is connected.
A vacuum exhaust valve 14 is connected to 3. A pipe 15 is connected to the wall surface of the right end portion of the closed container, and a vacuum release valve 16 is installed in the pipe 15.

Next, the configuration of this embodiment will be described with reference to the block diagram of FIG. The pressure detection device 10 is connected to the pressure determination device 20, and the pressure determination device 20 is connected to the control device 21. The control device 21 is also connected to control the magnetron 7, the vacuum exhaust valve 14, the vacuum release valve 16, and the vacuum pump 5 based on the pressure determination result.

Next, the method of cooking the frozen object 3 (food) and the control method when electric discharge occurs will be described with reference to the flow chart of FIG.

When a start key (not shown) is pressed after the object 3 to be heated is placed in the closed container 2, the vacuum release valve 16 is closed and the vacuum exhaust valve 14 is opened under the control of the control device 21 (S1). After that, the vacuum pump 5 is activated (S2), the magnetron 7 is activated (S3), and the closed container 2
Decompression of the inside and heating of the object to be heated 3 are started. Then, when the pressure reduction further progresses and the pressure detection device 10 detects that the pressure has reached a preset atmospheric pressure (for example, 30 Torr) (S4.
If YES, the vacuum exhaust valve 14 is closed (S5), and the pressure reduction to the predetermined pressure is completed.

If there is no discharge during the heating time (S6, Y
ES), the pressure detection device 10 for pressure rise due to steam generation
(S7), and when the pressure inside the closed container 2 rises to a predetermined upper limit pressure (for example, 35 Torr) (S7.
YES), the vacuum exhaust valve 14 is opened (S8), the pressure in the closed container 2 is reduced to the original pressure (30 Torr) again (S4, YES), and the vacuum exhaust valve 14 is closed (S).
5). By repeating this operation, the inside of the closed container 2 is controlled within a predetermined pressure range.

The method of detecting electric discharge during cooking is as follows: When the pressure in the closed container 2 is sampled by the pressure detecting device 10 at regular intervals and a sudden pressure increase due to electric discharge is judged by the pressure judging device 20 to be electric discharge ( (YES in S6), the magnetron 7 is immediately stopped by the control of the control device 21 (S9), and the microwave irradiation is stopped. Then, the vacuum release valve 16 is opened (S10) to return the atmospheric pressure in the closed container 2 to the atmospheric pressure. When the occurrence of discharge is not detected (S6 ・ NO, S7 ・ N
O), when the heating time ends (S11, YES), the magnetron 7 is stopped by the control device 21 (S9), the vacuum release valve 16 is opened (S10), and the atmospheric pressure in the closed container 2 is returned to the atmospheric pressure. The vacuum pump 5 is stopped (S
12) and the cooking is completed (S13).

From the cooking test results, the pressure rise due to the steam generation smoothly rises as shown by the curve in FIG.
However, when the discharge occurs, the pressure rises instantaneously as shown by the curve in FIG. 5, and when the magnetron 7 is stopped, the pressure falls. From the above results, it is possible to detect the occurrence of discharge by determining the pressure increase due to steam generation and the pressure increase due to discharge by measuring the pressure change at regular time intervals.

As described above, in the present embodiment, the generation of the discharge when the microwave is irradiated under the reduced pressure is detected, and the microwave is stopped so that the discharge does not continue. It is possible to prevent the partition plate 9 between the corrugated tube 8 and the corrugated tube 8 from being damaged by thermal energy due to electric discharge. In addition, the object to be heated 3 whose heating was stopped halfway due to the occurrence of discharge
Can be reused by changing the setting of the heating time, and the loss of the object to be heated due to the occurrence of discharge can be prevented.

Further, since the discharge phenomenon is likely to occur when heated in a no-load state, the detection method of the present invention makes it possible to detect no-load operation and prevent damage to equipment such as a magnetron. Is.

In the present embodiment, the control for stopping the magnetron is performed when it is determined that a discharge has occurred. However, a warning sound or a warning is displayed based on the determination of discharge. Is also possible.

Regarding the microwave control during discharge, the microwave output may be controlled without stopping the magnetron at the time of discharge generation, and the output may be suppressed to prevent the discharge from continuing. .

[0024]

As is apparent from the above description, according to the decompression high-frequency heating apparatus of the present invention, the pressure detecting means detects the occurrence of electric discharge, and the microwave generating apparatus is controlled by the signal from the pressure detecting means. Since the discharge is prevented from continuing, damage to the equipment is prevented and the commercial value of the heated object is prevented from being reduced.

[Brief description of drawings]

FIG. 1 is a schematic view of the structure of a reduced pressure high frequency heating apparatus of this embodiment.

FIG. 2 is a block diagram showing an electrical configuration of a reduced pressure high frequency heating apparatus of this embodiment.

FIG. 3 is a flow chart of the reduced pressure high frequency heating apparatus according to the present embodiment.

FIG. 4 is a pressure diagram when steam is generated in the decompression high-frequency heating device of this embodiment.

FIG. 5 is a pressure diagram when a discharge occurs in the reduced pressure high frequency heating apparatus according to the present embodiment.

FIG. 6 is a schematic structural view of a conventional reduced pressure high frequency heating device.

[Explanation of symbols]

 2 Airtight container 5 Vacuum pump 7 Magnetron 8 Waveguide 9 Partition plate 10 Pressure detection device 14 Vacuum exhaust valve 16 Vacuum release valve 20 Pressure determination device 21 Control device

Claims (1)

[Claims] 1. A hermetically sealed container capable of accommodating an object to be heated, a microwave generation unit for irradiating the object to be heated in the hermetically sealed container with microwaves, and a decompression unit for exhausting gas in the hermetically sealed container, Pressure detection means for detecting the pressure in the closed container, based on the signal of the pressure detection means, determination means for determining the presence or absence of the occurrence of a discharge phenomenon, based on the determination of the determination means,
A decompression high-frequency heating device comprising a control means for controlling a microwave generator.