WO2006070948A1

WO2006070948A1 - Gas detection system

Info

Publication number: WO2006070948A1
Application number: PCT/JP2005/024289
Authority: WO
Inventors: Fujio Kurokawa; Toshiyuki Tanaka; Osamu Hirose
Original assignee: Sumitomo Chemical Co; Fujio Kurokawa; Toshiyuki Tanaka; Osamu Hirose
Priority date: 2004-12-28
Filing date: 2005-12-28
Publication date: 2006-07-06
Also published as: JPWO2006070948A1

Abstract

A gas detection system includes: a gas detection radio wave transmission/reception unit (11) having at least one gas detection radio wave transmission means (111) and gas detection radio wave reception means (112); a reference radio wave transmission /reception unit (12) having at lest one reference radio wave transmission means (121) for emitting a reference radio wave and the same number of reference radio wave reception means (121) as the number of reference radio wave transmission means (121), for receiving the reference radio wave without passing through the gas detection object region; radio wave phase detection means (13) for detecting a phase difference between the gas detection radio wave received by the gas detection radio wave reception means and the reference radio wave received by the reference radio wave reception means; and gas-in-object region detection means (14) for detecting whether gas exists in the gas detection object region according to the phase difference detected by the radio wave phase detection means.

Description

Gas detection system

TECHNICAL FIELD The present invention relates to invisible hydrogen gas, carbon dioxide gas, helium gas, etc.

The present invention relates to a gas detection system capable of accurately detecting a gas, and a gas detection system capable of detecting a gas characteristic (even if the relative permittivity for air is a mixture ratio of multiple gases).

Background Art In recent years, chemical plants have proposed various automatic monitoring technologies for gas leaks and fires using image processing in order to reduce costs, reduce personnel, or improve safety. Gas leaks can also be detected using chemical reaction detection type gas sensors, but there is a risk of accidents due to electrical circuit sparks, etc., because a gas sensor with a built-in electric circuit must be used inside the plant. For this reason, the area where the chemical blunt CP is detected is photographed with a CCD camera, and the occurrence of gas smoke and water vapor and changes in movement are detected by the motion detection means to detect gas leaks and fires. It is displayed on the display by the display means.

Disclosure of the invention In chemical plants, gases and flames to be detected are colorless. Since many of them are difficult to capture, it is often impossible to capture them as images with a CCD camera.

In addition, technologies that detect thermal changes using an infrared camera have also been proposed. For example, detection ¾ ^ is limited to flammable gases, and for flammable gases that are normally transparent (hydrogen gas, etc.) It cannot be detected before combustion (ie before an accident).

The present invention provides a gas detection sensor that can accurately detect even colorless hydrogen gas, carbon dioxide, and the like, a gas monitoring system, and an image processing device that visualizes information detected by the gas detection sensor. With the goal. Means to achieve the objective

In order to achieve the above object, the present invention is summarized as follows.

1. At least one gas detection radio wave transmission means that emits a gas detection radio wave; and the same number or more as the gas detection radio wave transmission means that receives the gas detection radio wave that has passed through the gas detection target area. Radio wave receiving means for gas detection;

Radio wave phase detection means for detecting a phase difference on the time axis of the gas detection radio wave received by the gas detection radio wave reception means;

Based on the phase difference detected by the radio wave phase detection means, gas detection means in the target area for detecting whether or not gas is present in the gas detection target area;

A gas detection system comprising:

2. The gas detection system according to claim 1, wherein at least one of the gas detection radio wave transmission means and the gas detection radio wave reception means has directivity. 3. Further, when the radio wave phase detection means detects the presence of gas in the gas detection target region, the radio wave phase detection means further comprises a gas type detection means for detecting the gas type. The gas detection system described in 1.

4. provided with a photographing means for photographing an area including the gas detection target area and a display means for displaying an image photographed by the photographing means;

When the radio wave phase detection means detects the presence of gas in the gas detection target area, the display means displays the gas detection result on a display superimposed on an image taken by the imaging means. The gas detection system according to any one of claims 1 to 3.

5. At least one gas detection radio wave transmission means that emits a gas detection radio wave and the same number of gas detection radio wave transmission means as the gas detection radio wave transmission means that receive the gas detection radio wave that has passed through the gas detection target area. A radio wave receiving / receiving unit for gas detection comprising a radio wave receiving means for

From at least one reference radio wave transmitting means for emitting a reference radio wave, and the same number of reference radio wave receiving means as the reference radio wave transmitting means for receiving the reference radio wave without passing through the gas detection target area A reference radio transmission / reception unit,

Radio wave phase detection means for detecting a phase difference between the gas detection radio wave received by the gas detection radio wave reception means and the reference radio wave received by the reference radio wave reception means;

A gas detection system with a special feature.

6. At least one of the gas detection radio wave transmission means, the gas detection radio wave reception means, the reference radio wave transmission means, and the reference radio wave reception means has directivity. The gas detection system according to claim 5.

7. The method according to claim 5, further comprising gas type detection means for detecting the gas type when the radio wave phase detection means detects the presence of gas in the gas detection target region. 6. The gas detection system according to 6.

8. a display means for displaying an image photographed by the photographing means for photographing an area including the gas detection target area;

When the radio wave phase detection means detects the presence of gas in the gas detection target area, the display means displays the gas detection result on a display superimposed on an image taken by the imaging means. The gas detection system according to any one of claims 5 and 7.

9. at least one omnidirectional gas detection means for emitting gas detection radio waves;

At least one gas detection radio wave receiving means for receiving the gas detection radio wave passing through the gas detection target area;

Radio wave phase detection means for detecting a difference between phases of the gas detection radio waves received by the gas detection radio wave reception means;

Based on the difference between the phases detected by the radio wave phase detection means, the gas detection target area gas detection means for detecting whether or not gas exists in the gas detection target area,

A gas detection system comprising:

10. Further, when the radio wave phase detection means detects the presence of gas in the gas detection target region, the radio wave phase detection means includes gas type detection means for detecting the gas type. The gas detection system described in 1. 1 1. It is provided with a display means for displaying an image photographed by the photographing means and the photographing means for ilfing the area including the gas detection target area,

When the radio wave phase detection means detects the presence of gas in the gas detection target area, the display means displays the gas detection result on a display superimposed on an image taken by the imaging means. The gas detection system according to claim 9 or 10.

12. The gas detection system according to any one of claims 9 to 11, wherein the gas detection radio wave transmission means and the gas detection radio wave reception means have directivity.

1 3. Gas detection system used in equipment that uses flammable gas or harmful gas,

Thermal noise receiving means for receiving thermal noise generated by gas;

A thermal noise detecting means for detecting whether the thermal noise received by the thermal noise receiving means exceeds a predetermined threshold;

An alarm means for issuing an alarm when the thermal noise received by the thermal noise detection means exceeds a predetermined threshold;

A gas detection system comprising:

14. The gas detection system according to claim 13, wherein the thermal noise detection means detects a gas type according to the frequency of the received thermal noise.

1 5. A set of radio wave transmission means and radio wave reception means, and radio wave phase difference detection means for detecting a phase difference on the time axis of the radio wave received by the radio wave reception means,

A gas detection system for measuring characteristics of a gas present in a propagation path of a radio wave based on the phase difference detected by the radio wave phase difference detection means. 16. The gas detection system according to claim 15, wherein the characteristic of the gas is a relative dielectric constant of gas existing in a propagation path of the radio wave with respect to air.

17. The gas detection system according to claim 15, wherein the special life of the gas is a mixing ratio of a plurality of gases existing in a propagation path of the radio wave. Brief Description of Drawings

FIG. 1 is a block diagram showing a gas detection system of the present invention.

FIG. 2 is a diagram illustrating a state in which the gas detection result is displayed on the display of the display unit so as to be superimposed on the image captured by the imaging unit.

FIG. 3 is an explanatory diagram of the first embodiment of the present invention, in which (A) is a perspective view of the plant and (B) is a plan view of the plant.

Fig. 4 is a diagram showing a point of zero amplitude in a healthy state received by the receiving antenna. FIG. 5 is an explanatory diagram of a second embodiment of the present invention, where (A) is a perspective view of a blunt, and (B) is a plan view of the plant.

FIG. 6 is an explanatory diagram of a third embodiment of the present invention, where (A) is a perspective view of the plant and (B) is a plan view of the plant.

FIG. 7 is a block diagram showing the gas detection system of the present invention. FIG. 8 is an explanatory view of a fourth embodiment of the present invention, where (A) is a perspective view of the plant and (B) is a plan view of the plant.

9A and 9B are diagrams showing an example of radio waves generated by the gas detection radio wave transmitting means of the present invention.

FIG. 10 is a diagram showing a configuration of a gas detection system for detecting a relative dielectric constant.

Figure 11 shows the measured phase difference of the received wave.

Figure 12 shows a plot of the theoretical curve for the phase difference.

Fig. 13 shows the case where the measurement gas occupying the radio wave propagation path has a constant length d, and a mixed gas of helium and oxygen is injected into the resin sample container. It is a figure which shows the result of having measured the phase difference about each when decreasing a helium density | concentration. BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram showing a gas detection system 1 of the present invention.

In FIG. 1, the gas detection system 1 includes a gas detection radio wave transmission / reception unit 1 1, a reference radio wave transmission / reception unit 1 2, a radio wave phase detection means 1 3, an in-target gas detection means 1 4, and a gas type detection. Means 15, photographing means 16, and display means 17 are provided.

The gas detection radio wave transmission / reception unit 1 1 passes through at least one (1 in this embodiment) gas detection radio wave transmission means 1 1 1 that emits the gas detection radio wave D and the gas detection target area A. Gas detection radio wave transmission means 1 1 2 for receiving the gas detection radio wave D 1 1 1 1 is provided. The reference radio wave transmission / reception unit 1 2 is used for reference without passing through the gas detection target region A and at least one reference radio wave transmission means 1 2 1 that emits the reference radio wave R (one in this embodiment). It consists of reference radio wave receiving means 1 2 2 for receiving radio wave R.

In this embodiment, the gas detection radio wave transmission means 1 1 1, the gas detection radio wave reception means 1 1 2, the reference radio wave transmission means 1 2 1 and the reference radio wave reception means 1 2 2 have directivity. . In the present embodiment and the following embodiments, the radio wave uses a frequency in the submillimeter wave band.

The radio wave phase detection means 13 detects the phase difference between the gas detection radio wave D received by the gas detection radio wave reception means 1 1 2 and the reference radio wave R received by the reference radio wave reception means 1 2 2. The gas detection means 14 in the target area 14 detects whether or not the gas G exists in the gas detection target area A based on the phase difference Φ detected by the radio wave phase detection means 13.

When the radio wave phase detection means 13 detects that the gas G exists in the gas detection target area A, the gas type detection means 15 detects the gas type.

The imaging means 16 images an area including the gas detection target area A. Further, the display means 17 can display the image photographed by the photographing means 16. When the radio wave phase detection means 13 detects that gas G is present in the gas detection target area A, the display means 17 is superimposed on the image taken by the photographing means 16 as shown in FIG. The gas detection result can be displayed on the display 1 7 1. In addition, gas leaks and fire alarms may be automatically generated by image recognition. In addition to gas or gas flame information, sound information collected from a microphone can be embedded in the image from the camera and displayed with sound.

A first embodiment of the present invention will be described with reference to FIGS. 3 (A), (B) and FIG. In Fig. 3 (A) and (B) ((A) is a perspective view and (B) is a plan view), a radio wave for gas detection outside the plant P (for example, a space of 5 Om in length, width, and height). Transmitting antennas al to a 6 that function as transmitting means (indicated by reference numeral “11 1” in FIG. 1) and receiving antennas bl to function as radio wave receiving means for gas detection (indicated by reference numeral “112” in FIG. 1) b 6 and are installed. In this example, it is assumed that one section of the plant is about 5 Om.

In this embodiment, the transmitting antenna a X and the receiving antenna bx (χ = 1, 2, 3, 4, 5, 6) are paired. For example, the pair of the transmitting antenna a 1 and the receiving antenna b 1 is a gas. When functioning as an antenna for a detection radio wave transmission / reception unit (indicated by reference numeral “11” in FIG. 1), for a pair of transmission antenna a 1 and reception antenna b 1, another transmission antenna ax, reception antenna bx (x = 2, 3, 4, 5, 6) are the antennas of the reference radio wave transmitting / receiving unit (see symbol “12” in Fig. 1).

In the present embodiment, the transmission antennas a 1 to a 6 and the reception antennas b 1 to b 6 have directivity. The gas detection radio waves D transmitted from the transmitting antennas a 1 to a 6 (the radio waves simultaneously function as reference radio waves R) are synchronized. The points of zero amplitude when received by the receiving antennas b 1 to b 6 are shown in Fig. 4 as (1) to (6).

Transmitting antenna a 1 to a 6 Radio wave for gas detection transmitted from D 6 When the gas passes through, the phase changes. Therefore, when the phase of the gas detection radio wave D received by any of the receiving antennas b1 to b6 fluctuates, gas is generated between the transmitting antenna and the corresponding transmitting antenna.

A second embodiment of the present invention will be described with reference to FIGS. 5 (A) and 5 (B) ((A) is a perspective view and (B) is a plan view). In Figs. 5 (A) and (B), radio wave transmission means for gas detection outside plant P Transmitting antennas a 1 and a 2 that function as (indicated by reference numeral “1 1 1” in FIG. 1) and receiving antennas that function as radio wave detection means for gas detection (indicated by reference numeral “1 1 2” in FIG. 1) b 1 to b 10 are installed.

In this embodiment, the transmitting antennas a 1 and a 2 are omnidirectional, but the receiving antennas b :! to b 10 have directivity.

Also in this case, the gas detection radio waves D transmitted from the transmitting antennas a 1 and a 2 are synchronized. As in the first embodiment, when the gas detection radio wave D transmitted from the transmission antennas a 1 and a 2 passes through the gas, the phase fluctuates. Therefore, when the phase of the gas detection radio wave D received by one of the receiving antennas b 1 to “b 10” fluctuates, gas is generated between the transmitting antenna and the corresponding transmitting antenna.

A third embodiment of the present invention will be described with reference to FIGS. 6 (A) and 6 (B) ((A) is a perspective view and (B) is a plan view). 6 (A) and 6 (B), the transmitting antenna a 1 functioning as a gas detection radio wave transmission means (indicated by reference numeral “1 1 1” in FIG. 1) outside the plant P, and a gas detection radio reception means Receiving antenna b 1 that functions as (indicated by “1 1 2” in Fig. 1) is installed, and relay antennas c 1 and c 2 are installed inside plant P. Although not shown, in this embodiment, as in the first and second embodiments, other transmission antennas functioning as antennas for the reference radio wave transmission / reception unit (indicated by reference numeral “1 2” in FIG. 1). Assume that there is a pair of a tena and a receiving antenna. In the third embodiment, for example, when monitoring gas leakage from a gas pipe installed between buildings, a relay antenna can be arranged at an appropriate place.

FIG. 7 and FIG. 8 (A), (B) ((A) is a perspective view, (B) is a plan view) A fourth embodiment will be described.

As shown in FIG. 8, the portable terminal 21 includes a thermal noise receiving unit 2 11, a thermal noise detecting unit 2 1 2, and an alarm unit 2 1 3. In the present embodiment, the mobile terminal 21 is applied to a device using hydrogen gas as a fuel (in FIG. 7, a plant), but is used in other types of gas devices (including equipment such as tanks and piping). It can also be applied. In FIG. 7, hydrogen gas is detected, but it can also be detected by a stationary receiver. The thermal noise receiving means 2 1 1 is provided with a thermal noise receiving antenna d, and can receive thermal noise N generated by gas.

The thermal noise detection means 2 112 can detect whether or not the thermal noise N received by the thermal noise reception means 2 11 1 exceeds a predetermined threshold value.

The alarm means 2 1 3 can issue an alarm when the thermal noise received by the thermal noise detection means 2 1 2 exceeds a predetermined threshold value. Since this alarm is usually a mobile terminal 21, the warning sound on the display is accompanied by a warning sound. '

8 (A) and 8 (B) show a case where the mobile terminal 21 transmits a radio wave to the plant side and detects the response.

Figures 9 (A) and 9 (B) show examples of radio waves emitted by Ryoaki's gas detection radio transmission means (indicated by the symbol “1 1 2” in Fig. 1). As shown in Fig. 9 (A), the radio wave transmitting means for gas detection can be transmitted by sweeping the frequency in a sawtooth shape. By using such a frequency-swept radio wave, various gases can be detected. Also, as shown in Fig. 9 (B), various types of gases can be detected by emitting radio waves containing harmonic components such as square waves and obtaining the phase for each frequency on the receiving side. Hereinafter, an image display procedure on the display unit 17 will be described below.

Imager 16 (CCD camera, etc.) Reads an image from force (S101), and gas detection means 14 (see Fig. 1) in the target area detects a gas leak ("YES" in S102). The gas generated by the seed detection means 15 is specified (S 103).

When the gas is identified, the display means 16 refers to the gas color and movement database (not shown in FIG. 1) prepared in advance and detects the gas from the sensor detecting the gas. A gas-like graphic is displayed on the monitor screen of the location of occurrence based on the information, such as an expression expressing transparency or an expression with a predetermined color (S104).

At the time of combustion, hydrogen gas is not visible to the human eye even in this situation, so it is expressed like a flame so that the person can judge that it is burning (S105).

Based on the information from the gas sensor, the movement of the gas due to the wind is detected, and the situation is activated graphically (S106). The information is also useful for recognition by gas moving image processing. Since the weight varies depending on the type of gas, the moving image processing can be used to identify the type of gas. For moving image processing, methods using differences between screens, methods using optical flow, etc. are effective.

These pieces of information are recorded and displayed as 3D graphics based on them (S107).

It also responds to changes in brightness due to changes in the screen, such as turning the CCD camera and zooming, daytime, night, and rain (S108).

Although the person finally judges gas leaks, etc., the type of gas is also identified from the viewpoint of image processing technology based on the displayed screen to improve the accuracy of gas detection (S109). An embodiment of the fifth invention will be described with reference to FIG. 10 and FIG.

FIG. 10 shows the configuration of a gas detection system for detecting the relative permittivity. The network analyzer 1 0 1 generates radio waves to be transmitted, radiates radio waves via the transmit antenna 1 0 2 and the derivative lens (lens made of PTFE) 1 0 3, and PTFE lenses 1 0 4 and 1 0 5 It has the function of receiving radio waves via the receiving antenna and analyzing the phase difference on the time axis of the received radio waves. Place the measurement target gas sealed in a plastic sample container 10 6 in the radio wave propagation path. In this embodiment, the length d of the measurement target gas region in the radio wave propagation path is a container that can be measured.

Fig. 11 shows the reception when the effective frequency range is changed from 50 GHz to 75 GHz using a gas mixture of helium 80% and oxygen 20% as the measurement target gas. Wave phase difference is measured and plotted. First, the same atmosphere as the laboratory atmosphere is sealed in a 10-resin sample container, radio waves of each frequency are transmitted and received, and the network analyzer is calibrated based on the phase difference at each frequency.

When the same atmosphere is measured after calibration, a measured value that shifts in the vicinity of zero phase difference is obtained, as shown in the plot of “ex 30 calibration” in the figure. In this state, if the measurement target gas is sealed in the plastic sample container 10 6 and the same measurement is performed, the frequency of the radio wave increases as shown in the plot other than “e X 3 0 calibration” shown in the figure. As you go up, you get a plot that goes up to the right where the phase difference increases. The amount of increase in the phase difference increases as the length d (see Fig. 10) of the measurement target gas region occupying the radio wave propagation path increases.

Next, a method for obtaining the characteristics of the measurement target gas from the plot shown in Fig. 11 will be described. The frequency of the transmitted and received radio waves is f [H z], and the measurement target gas region in the radio wave propagation path The length is d [m], the velocity of radio waves in the air is c [m / s], the relative permittivity of the gas to be measured is s _ag , the wavelength of the radio waves in the air is λ [m], and the gas to be measured If the wavelength of the radio wave is λ _3ε Cm] and the phase difference that occurs when the radio wave passes through the measurement target gas is Θ [radian], the phase difference Θ can be calculated by the following equation.

Alternatively, by rewriting the equation (1), s _ag dielectric constant to air of the measurement target gas is given by the following equation.

Using these equations, for example, in Fig. 11, the phase difference Θ at f = 60 GHz and d = 325 mm can be read as approximately 4.8 [degree] (□ 0. 084 [radian]). By substituting the value into Equation (2), it can be seen that the relative dielectric constant of the measurement target gas with respect to air is about £ _ag = _l.0004 . Furthermore, by substituting s _ag = l. 0004 into equation (1) and changing the frequency f [Hz] and the length of the measurement target gas region d [m], the theoretical values of the plot in Fig. 11 are obtained. Can be requested. The value of d is changed in six ways of 80 mm 1 1 Omm, 16 Omm, 2 O 0 mm, 25 Omm, and 325 mm used in the experiment, and the frequency f is changed from 40 GHz to about 75 GHz. Figure 12 shows the theoretical curve for the phase difference Θ. These are in good agreement with the experimental values shown in Fig. 11.

In addition, according to the present embodiment, the approximate concentration (gas mixture ratio) of the target measurement gas is calculated. Can be measured.

Figure 13 shows that the length d of the gas region to be measured in the radio wave propagation path is constant, and the resin sample container contains 80% helium and 20 ° oxygen. The results of measuring the phase difference Θ for each of (e X 0 3) and (e X 0 4) from which helium concentration was reduced by natural diffusion are shown. According to this, it can be seen that the phase difference is smaller in e X 04 with obviously small helium concentration. Using this, it is possible to know the approximate mixing ratio of the measurement target gas by measuring the phase difference in advance by changing the gas mixing ratio and comparing it with the phase difference obtained from the measurement target gas. it can. Industrial applicability

The present invention can detect all kinds of gases, and the first, second, and third inventions can detect from a long distance (for example, a distance of 50 m or more).

Further, in the first to fourth inventions, the gas leakage status or the like can be graphically displayed on the display by the image processing technology, or the gas leakage status or the like can be automatically and accurately recognized by the image processing.

Furthermore, in the first to fourth inventions, not only gas leakage in the blunt, but also gas leakage in automobiles such as hydrogen fuel cells can be observed from the road side (highway toll booth etc.). In the fifth invention, it is possible to measure the characteristics of the gas in the radio wave propagation path, mainly the relative permittivity with respect to the air, and a plurality of expected mixing ratios.

Claims

The scope of the claims

A gas detection system comprising:

2. The gas detection system according to any one of claims 1 to 4, wherein at least one of the gas detection radio wave transmission means and the gas detection radio wave reception means has directivity.

3. Further, when the radio wave phase detection means detects the presence of gas in the gas detection target region, the radio wave phase detection means further comprises a gas type detection means for detecting the gas type. The gas detection system described in 1.

4. An imaging unit that captures an area including the gas detection target region and a display unit that displays an image captured by the imaging unit,

5. At least one gas detection radio wave transmission means for emitting a gas detection radio wave, A gas detection radio wave transmission / reception unit comprising the same number of gas detection radio wave reception means as the gas detection radio wave transmission means for receiving the gas detection radio wave passing through the emission target area;

From at least one reference radio wave transmitting means for emitting a reference radio wave, and the same number of reference radio wave receiving means as the reference radio wave transmitting means for receiving the reference radio wave without passing through the gas detection target area A radio wave transmission / reception unit for reference

A gas detection system comprising:

6. At least one of the gas detection radio wave transmission unit, the gas detection radio wave reception unit, the reference radio wave transmission unit, and the reference radio wave reception unit has directivity. Gas detection system.

7. Further, when the radio wave phase detection means detects the presence of gas in the gas detection target region, the radio wave phase detection means includes a gas type detection means for detecting the gas type. The gas detection system described in 1.

8. an imaging unit that captures an area including the gas detection target region, and a display unit that displays an image captured by the imaging unit;

Based on the difference between the phases detected by the radio wave phase detection means, gas detection means in the target area for detecting whether or not the gas exists in the gas detection target area,

A gas detection system comprising:

10. Further, when the radio wave phase detection means detects the presence of gas in the gas detection target region, it further comprises gas type detection means for detecting the gas type. The gas detection system described in 1.

1. An imaging means for imaging an area including the gas detection target area, and a display means for displaying an image captured by the imaging means,

12. The gas detection system according to claim 9, wherein the gas detection radio wave transmission means and the gas detection radio wave reception means have directivity.

1 3. Gas detection system used in equipment that uses flammable gas or harmful gas, Thermal noise receiving means for receiving thermal noise generated by gas;

Thermal noise detecting means for detecting whether the thermal noise received by the thermal noise receiving means exceeds a predetermined threshold;

A gas detection system comprising:

14. The gas detection system according to claim 13, wherein the thermal noise detection means detects the type of gas according to the frequency of the received thermal noise.

A gas detection system for measuring characteristics of a gas present in a propagation path of a radio wave based on the phase difference detected by the radio wave phase difference detection means.

16. The gas detection system according to claim 15, wherein the characteristic of the gas is a relative dielectric constant of gas existing in a propagation path of the radio wave with respect to air.

17. The gas detection system according to claim 15, wherein the characteristic of the gas is a mixing ratio of a plurality of gases existing in a propagation path of the radio wave.