JPS5973776A - Detection of discharge in applying microwave - Google Patents

Abstract

PURPOSE:To certainly detect discharge generation, by measuring the intensity level of the reflected wave of the microwave from a microwave applying part. CONSTITUTION:An incident wave detector 3 and a reflected wave detector 4 provided to a waveguide 2 are connected to power monitor 6 and an incident wave and the intensity of a reflected wave are displayed by a display meter 7. The power monitor 6 is connected to a reflected wave level signal detector 8 and inputs the detection signal due to the reflected wave detector 4. When discharge is generated in a microwave heating furnace and the intensity of the reflected wave exceeds a reference value, the reflected wave level signal detector 8 generates a relay operating signal to a microwave oscillator circuit 1 to operate a magnet control circuit 10 through a high voltage relay 9 and the oscillation of the microwave is stopped until the intensity of the reflected wave reaches the reference value or less.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for detecting discharge when microwaves are applied.

When high-power microwaves are transmitted using a waveguide and used for industrial purposes such as heating, the presence of substances such as dust in the air, evaporated matter from heated objects, or carbon may sometimes absorb the microwaves. However, as a result, a sudden heat generation phenomenon occurs, which leads to gas discharge. In other words, the discharge phenomenon is an ionization effect of gas (= ionization phenomenon of gas: accompanied by the generation of plasma flame), and when a discharge occurs, part of the microwave is reflected by this plasma flame, and part of it is absorbed. Not only will the object to be processed not be heated, but the waveguide or heater will be damaged by the plasma flame.

Furthermore, once the discharge state has occurred, it will continue unless the microwave is cut off or the plasma flame is cooled.

Therefore, it is necessary to immediately detect the occurrence of discharge and extinguish the discharge.

As mentioned above, the generation of electric discharge is the ionization phenomenon of gas, that is, the generation of plasma flame, and is accompanied by the generation of light and sound. For this reason, conventionally, plasma flame (light) was used to detect the occurrence of discharge.
Optical detection methods, which detect the ionization of air, and sound detection methods, which detect the audible sounds emitted when air ionizes, are used.

However, optical detection methods cannot distinguish the plasma flame from other light sources that have the same luminous intensity as the plasma flame. For example, when a substance with a high melting point such as incineration ash is melted, there is a large amount of radiant light from the molten slag, so it is difficult to distinguish this radiant light from light from a plasma flame (discharge light).

In addition, the sound detection method has had problems such as erroneous detection because it is not possible to distinguish an impact sound, such as when a waveguide or a heater is struck from the outside, from noise caused by electric discharge.

The present invention has been made in view of the above-mentioned conventional problems.
The present invention aims to provide a method for detecting discharge when microwaves are applied, which makes it possible to reliably detect the occurrence of discharge by measuring the intensity level of microwave reflected waves from a microwave application section.

Next, the present invention will be explained with reference to the drawings, which are one embodiment.

FIG. 1 shows a discharge detection system for detecting microwave reflected wave level fluctuations in a microwave heating furnace to which the method according to the present invention is applied.

In the figure, reference numeral 1 denotes a microwave oscillator, which applies microwaves to a microwave heating furnace (not shown) through a waveguide 2. The waveguide 2 includes an incident wave detector 3 that detects the incident wave applied to the microwave heating furnace, and a reflected wave detector 4 that detects the reflected wave that is reflected back from the microwave heating furnace. A directional coupler 5 is provided. The incident wave detector 3 and the reflected wave detector 4 are connected to a power monitor 6. The power monitor 6 is provided with a display 7 that displays the intensities of the incident wave and the reflected wave.

Further, the power monitor 6 is connected to a reflected wave level signal detector 8, so that the intensity of the reflected wave is minimized according to the intensity of the incident wave so that appropriate heating can be performed. A detection signal from 4 is inputted to -C.

As shown in FIG. 2, when electric discharge occurs in the microwave heating furnace, the intensity of the reflected wave increases instantaneously. Therefore, the state of this intensity variation is investigated in advance, and a reference value of the reflected wave intensity is appropriately set within a range smaller than the intensity of the reflected wave at the time of discharge occurrence, and the reflected wave level signal detector 8 The intensity of the reflected wave inputted by the reference value is compared in magnitude with a reference value. The reflected wave level signal detector 8 is connected to the microwave oscillator 1, and when the intensity of the reflected wave exceeds a reference value, it issues a relay activation signal to the microwave oscillator 1 and sends the signal to the microwave oscillator 1 via the high voltage relay 9. The magnet control circuit 10 is activated to stop the oscillation of the microwave until the intensity of the reflected wave becomes equal to or less than a reference value.

Next, the operation of the discharge detector having the above configuration will be explained.

As shown in FIGS. 3 and 4, the reflected wave power detected by the reflected wave detector 4 is displayed on the power monitor 6, while being filtered by the reflected wave level signal detector 8. After removing minute noise components, the signal is amplified, integrated, and compared in magnitude with a reference voltage, which is a reference value generated from a constant voltage power supply.

Then, when a discharge occurs in the microwave heating furnace (fourth
In the figure, at time to), the detected value of the reflected wave increases rapidly, and as a result, the above integrated value eventually exceeds the reference value (voltage) (same as above, time t1y), and the comparison is made with a slight time delay. It is detected in the circuit that the intensity of the reflected wave exceeds the reference value (same as above, time L2). Similarly, with a slight time delay, the high voltage relay 9 of the microwave oscillator 1 is activated by the reflected wave level signal detector 8 and turned off (time t3, as above), and the high voltage circuit that oscillates the microwave is turned off. The OFF state becomes confusing (Ibid., time (4).

As a result of the microwave being cut off, the discharge stops (ibid., time [8).

Regarding discharge extinction, as above, with a slight time delay, the above integrated value becomes smaller than the reference value (same as above, time (
6) When the comparator circuit detects the extinction of the discharge (same as above, time t'7), the high voltage relay 9 is activated and turns ON (same as above, time [8), and the high voltage circuit is reactivated. At time t9), microwave oscillation starts (same as above,
Time '10).

As is clear from the above description, according to the present invention, the discharge generated in the microwave application section is detected by measuring the intensity level of the microwave reflected wave from the microwave application section. Therefore, it is possible to reliably detect the discharge generated in the microwave application section, and it is also possible to mistake radiated light or noise caused by causes other than discharge as discharge.
It has the advantage of not being detected.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a discharge detector for a microwave heating furnace to which the method according to the present invention is applied, Fig. 2 is an explanatory graph showing changes in reflected wave intensity due to discharge generation, and Fig. 3 is a diagram of the discharge detector of a microwave heating furnace. A block diagram showing the operation, FIG. 4 is a timing diagram of the operation of FIG. 3. 1... Microwave oscillator, 5... Directional coupler, 8
...Reflected wave level signal detector.

Claims (1)

[Claims] (1) Detect the microwave reflected wave from the microwave application part, compare the intensity of this reflected wave with a reference value determined from the microwave reflection window caused by plasma, and check that the intensity of the reflected wave exceeds the above reference value. A method for detecting discharge when microwaves are applied, characterized by detecting occurrence of discharge by exceeding the threshold.