JP6630757B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detector.

  Patent Literature 1 discloses a gas detector using infrared light absorption characteristics of gas molecules such as methane. The gas detector uses infrared laser light that has been frequency-modulated as detection light, receives the irregularly reflected light of the detection light that has passed through the gas to be detected by the light receiving element, and obtains an output signal equal to the modulation frequency from the output signal output by the light receiving element. A fundamental wave signal having a frequency and a second harmonic signal having a frequency equal to twice the modulation frequency are detected. Then, the concentration of the gas to be detected is calculated from the intensity of the second harmonic signal with respect to the fundamental signal.

JP 2001-235420 A

  According to the gas detector described in Patent Literature 1, it is possible to detect generation or leakage of gas at a location away from a gas generation source (leakage source). However, there is a limit to the detectable separation distance, and it has been desired to realize a high-sensitivity gas detector capable of detecting at a longer distance. Also, for example, when a gas detector is mounted on a drone or the like to detect the generation or leakage of gas from above, the weight that can be mounted on the drone is limited, and a lighter and more sensitive gas detector can be realized. Was desired.

  An object of the present invention is to provide a highly sensitive gas detector having a long detectable distance. Another object of the present invention is to provide a lightweight and highly sensitive gas detector.

  In order to solve the above-described problems, in a first aspect of the present invention, a detection light source unit that emits detection light, an optical system that converges the detection light reflected from an object, and the optical system that converges A light receiving unit that receives the reflected light, and outputs a signal corresponding to the intensity of the received light, and a concentration calculating unit that calculates the concentration of the gas to be detected based on the signal output by the light receiving unit. A detector, wherein the optical system includes a plurality of optical elements, and a first optical element located closest to the light receiving unit among the plurality of optical elements focuses substantially parallel light on the light receiving unit. Provided is a gas detector which is a light condensing element for causing the gas detector to emit light.

  The optical system may include, as one of the plurality of optical elements, a second optical element located farthest from the light receiving unit. In this case, the second optical element may include the first optical element. A condensing element having a larger aperture and converging the substantially parallel reflected light incident on the optical system, excluding the first optical element and the second optical element among the plurality of optical elements A single or a plurality of optical elements are located between the first optical element and the second optical element, and are light-scattering elements that diverge light converged by the second optical element into substantially parallel light, Is also good. At least one of the optical elements included in the optical system is disposed at a position that blocks an optical path of the detection light, and an optical element disposed at a position that blocks the optical path of the detection light includes a detection light that passes the detection light. A passage hole may be formed.

  In the second aspect of the present invention, a detection light source unit that emits detection light, an optical system that converges the detection light reflected from an object, and receives the reflected light converged by the optical system, A gas detector comprising: a light receiving unit that outputs a signal corresponding to the intensity of received light; and a concentration calculating unit that calculates a concentration of a gas to be detected based on the signal output by the light receiving unit. The system includes a single or a plurality of optical elements, and the substantially parallel reflected light incident on the optical system is converged on the light receiving unit by a single optical element or by a combination of a plurality of the optical elements. At least one of the optical elements included in the optical system is disposed at a position that blocks the optical path of the detection light, and the optical element disposed at a position that blocks the optical path of the detection light passes the detection light. A detection light passage hole is formed To provide a gas detector are.

  In the gas detector described above, the gas detector may further include a guide light source unit that emits a guide light indicating an irradiation position of the detection light. In this case, at least one of the optical elements included in the optical system includes the guide light. A guide light passage hole that allows the guide light to pass therethrough may be formed in the optical element that is disposed at a position that blocks the light path of the guide light and that is disposed at a position that blocks the light path of the guide light. At least one of the optical elements included in the optical system may be a Fresnel lens.

FIG. 1 is a configuration diagram illustrating an outline of a gas detector 100. FIG. 1 is a configuration diagram illustrating an outline of a gas detector 100. It is the schematic diagram which showed the gas detector 100 in three dimensions. FIG. 2 is a configuration diagram illustrating an outline of a gas detector 200. FIG. 2 is a configuration diagram illustrating an outline of a gas detector 200. 9 is a graph showing an example of an experiment of a reception level with respect to a distance.

(Embodiment)
FIG. 1 is a configuration diagram showing an outline of the gas detector 100. The gas detector 100 has a light source unit 102, a light receiving unit 104, a signal detecting unit 106, a concentration calculating unit 108, a display unit 110, and an optical system 130.

  The light source unit 102 includes a detection light source unit 102a and a guide light source unit 102b. The detection light source unit 102a emits the detection light 120a. The detection light 120a is applied to the object, and the measurement or detection of the concentration of the gas on the optical path is performed based on the information on the absorption of the gas to be detected contained in the reflected light from the object.

  The detection light source unit 102a emits, for example, frequency-modulated laser light as the detection light 120a. By modulating the frequency of the laser light, a second harmonic signal corresponding to the gas concentration is generated. The wavelength (frequency) of the detection light 120a is preferably a wavelength that is absorbed by the gas to be detected but not absorbed by the background gas. When the gas to be detected is methane, an infrared laser beam having an oscillation wavelength of 1.65 μm can be used as the detection light 120a. When the gas to be detected is hydrogen sulfide, an infrared laser beam having an oscillation wavelength of 1.57 μm can be used as the detection light 120a. In the case where a semiconductor laser is used for the detection light source unit 102a, a standard cell in which a gas to be detected is sealed is prepared, and the oscillation wavelength of the detection light 120a is determined by referring to the light absorption in the standard cell. It is preferable to adjust the operating temperature and the like of the semiconductor laser oscillator so as to coincide with the center of the absorption line.

  The guide light source unit 102b emits guide light 120b. Since the wavelength range of the detection light 120a is usually an invisible infrared range, a visible guide light 120b is used so that the irradiation position of the detection light 120a can be easily determined. Since the optical axis of the guide light 120b is set so as to substantially coincide with the optical axis of the detection light 120a, the irradiation position of the guide light 120b indicates the irradiation position of the detection light 120a. As the guide light 120b, for example, red or green semiconductor laser light can be used.

  The light receiving unit 104 receives the reflected light converged by the optical system 130 and outputs a signal (light receiving signal) corresponding to the intensity of the received light. Examples of the light receiving unit 104 include a photoelectric conversion element such as a photodiode and a photomultiplier and a drive detection circuit thereof. The light receiving unit 104 may include, for example, an optical filter such as a bandpass filter, a slit, a spectral mechanism, and the like.

  The concentration calculator 108 calculates the concentration of the gas to be detected based on the light reception signal output by the light receiver 104. For example, the signal detection unit 106 receives the light reception signal output by the light reception unit 104, and from the light reception signal, outputs a fundamental signal having a frequency equal to the modulation frequency of the detection light 120a and a frequency twice as high as the modulation frequency twice. Detect the wave signal. Synchronous detection can be used to detect the fundamental wave signal and the second harmonic signal. Then, the concentration calculation unit 108 can calculate the concentration (column density) of the detected gas in the atmosphere where the background gas exists, based on the ratio between the fundamental wave signal and the second harmonic signal.

  The display unit 110 displays the concentration of the detected gas calculated by the concentration calculation unit 108. Note that instead of providing the display unit 110, an output unit that outputs the density value by wire or wirelessly may be provided.

  The optical system 130 converges the detection light 120a reflected from the object. The optical system 130 includes a plurality of optical elements, and specifically includes a first optical element 130a, a third optical element 130b, and a second optical element 130c.

  The first optical element 130a is one of a plurality of optical elements of the optical system 130, and is located closest to the light receiving unit 104. The first optical element 130a is a condensing element that converges substantially parallel light to the light receiving unit 104.

  The second optical element 130c is one of a plurality of optical elements of the optical system 130, and is located farthest from the light receiving unit 104. The second optical element 130c has an opening larger than the first optical element 130a. The second optical element 130c is a light-collecting element that converges substantially parallel reflected light incident on the optical system 130.

  The third optical element 130b is one of a plurality of optical elements of the optical system 130, and is located between the first optical element 130a and the second optical element 130c. The third optical element 130b is a light diffusing element that diverges the light converged by the second optical element 130c into substantially parallel light. In addition, although the case where the third optical element 130b is configured by a single optical element is shown here, the third optical element 130b may be configured by a combination of a plurality of optical elements.

  In the gas detector 100 of the present embodiment, by making the opening of the second optical element 130c larger than the opening of the first optical element 130a, more reflected light is collected and the collected reflected light is converged by the optical system 130. As a result, more intense light can be incident on the light receiving unit 104, so that the sensitivity of the gas detector 100 for measuring gas concentration or detecting gas can be increased.

  In addition, since the opening of the second optical element 130c is enlarged, at least one of the optical elements included in the optical system 130, for example, the second optical element 130c may be arranged at a position that blocks the optical path of the detection light 120a. is there. In such a case, a detection light passage hole 140a that allows the detection light 120a to pass therethrough may be formed in the optical element (the second optical element 130c) disposed at a position that blocks the optical path of the detection light 120a. Thereby, reliable irradiation of the detection light 120a can be secured.

  In addition, as in the case of the detection light 120a, the optical path of the guide light 120b may be blocked by increasing the opening of the second optical element 130c. In such a case, a guide light passage hole 140b that allows the guide light 120b to pass therethrough may be formed in the optical element (for example, the second optical element 130c) disposed at a position that blocks the optical path of the guide light 120b. Thereby, as with the detection light 120a, reliable irradiation of the guide light 120b can be ensured.

  Also, at least one, and preferably all of the optical elements included in the optical system 130 can be Fresnel lenses. Accordingly, the weight of the optical system 130 can be reduced, and the weight of the gas detector 100 can be reduced.

  According to the gas detector 100 of the present embodiment, the sensitivity of gas concentration measurement or gas detection can be increased by increasing the opening diameter of the second optical element 130c. Further, by using a Fresnel lens as the optical element included in the optical system 130, the weight can be reduced.

  The gas detector 100 described above can be separated into a main body 100a and an optical attachment 100b, as shown in FIG. The main body 100a has a configuration in which the light source 102, the light receiving unit 104, the signal detecting unit 106, the density calculating unit 108, and the display unit 110 include the first optical element 130a. The optical attachment 100b includes a second optical element 130c and a third optical element 130b. By allowing the main body 100a and the optical attachment 100b to be separated from each other, for example, only the main body 100a is used for short-distance measurement, and the optical attachment 100b is attached to the main body 100a when performing long-distance measurement. Can be used.

  In addition, the optical attachment 100b can be configured such that the first optical element 130a and the second optical element 130c are fixed to the main body 100a by the support 150 as shown in FIG. Note that the illustration of the second optical element 130c is omitted in FIG. The support 150 is preferably as thin as possible and has mechanical strength to support the first optical element 130a and the second optical element 130c. By supporting the first optical element 130a and the second optical element 130c with the thin column 150, for example, when the gas detector 100 is mounted on a drone, the influence of wind pressure can be reduced.

  In the above-described embodiment, the case where the optical system 130 has the first optical element 130a, the third optical element 130b, and the second optical element 130c has been described, but the present invention is not limited to this. For example, as in the gas detector 200 shown in FIG. 4, the optical system may be a single optical element 230, and in this case, the single optical element 230 may be used to reduce substantially parallel reflected light incident on the optical system. The optical element 230 may be arranged at a position where the light converges on the light receiving unit 104 and blocks the optical path of the detection light 120a, and the optical element 230 may be formed with a detection light passage hole 140a through which the detection light 120a passes. Further, the optical element 230 may have a guide light passage hole 140b through which the guide light 120b passes.

  As shown in FIG. 5, the gas detector 200 can be separated into a main body 200a and an optical attachment 200b as in the case of the gas detector 100.

(Example)
In the gas detector 100, the reception level was examined when the optical attachment 100b was attached (Example) and when the optical attachment 100b was not attached (Comparative Example). The opening diameter of the optical attachment 100b (the opening diameter of the second optical element 130c) was 120 mmφ, and the opening diameter of the first optical element 130a built in the main body 100a was 33.5 mmφ. The second optical element 130c and the third optical element 130b are a convex lens made of glass and a concave lens made of glass, respectively. Light incident on the second optical element 130c is converged substantially parallel to the first optical element 130a. The focal length and arrangement were adjusted to emit light. The first optical element 130a was a Fresnel lens.

  In this example, the detection sensitivity (reception level) of the methane bag of 2.63% was measured by changing the distance. FIG. 6 is a graph showing the reception level of the gas detector 100 with respect to the installation distance of the methane bag, and shows a case where the optical attachment 100b is attached (Example) and a case where the optical attachment 100b is not attached (Comparative Example). Show.

  As shown in FIG. 6, in the embodiment in which the optical attachment 100b is attached, the reception level is 1 even at a distance of 45 m, whereas in the comparative example in which the optical attachment 100b is not attached, the reception level is 0 at a distance of 25 m. I have. It can be seen that the sensitivity is greatly improved in the gas detector 100 to which the optical attachment 100b is attached. Although not shown in FIG. 6, in the comparative example, detection was impossible at a distance of 35 m, and in the example, detection was not possible at a distance of 65 m. Even if the reception level is 0, it does not mean that gas is not detected. Therefore, it is practically possible to detect gas up to a distance of about 35 m in the comparative example, and to detect gas up to a distance of about 65 m in the example. I can say. That is, by attaching the optical attachment 100b of the present embodiment, it can be said that the gas detectable distance is extended about twice.

  As described above, the present invention has been described using the embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments. It is apparent to those skilled in the art that various changes or improvements can be made to the above-described embodiment. It is apparent from the description of the appended claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  100: gas detector, 100a: main body, 100b: optical attachment, 102: light source, 102a: detection light source, 102b: guide light source, 104: light receiver, 106: signal detector, 108: concentration calculator, 110 display unit, 120a detection light, 120b guide light, 130 optical system, 130a first optical element, 130b third optical element, 130c second optical element, 140a detection light passage hole, 140b Guide light passage hole, 150: support, 200: gas detector, 200a: main body, 200b: optical attachment, 230: optical element.

Claims (3)

A detection light source unit that emits detection light,
An optical system that converges the reflected light from the object of the detection light,
A light receiving unit that receives the reflected light converged by the optical system and outputs a signal corresponding to the intensity of the received light,
A gas detector having a concentration calculator that calculates the concentration of the gas to be detected based on the signal output by the light receiver,
The optical system includes a single or a plurality of optical elements,
By a single optical element, or by a combination of a plurality of the optical elements, the substantially parallel reflected light incident on the optical system, converge on the light receiving unit,
At least one of the optical elements included in the optical system is disposed at a position that blocks an optical path of the detection light,
An optical element arranged at a position that blocks an optical path of the detection light has a detection light passage hole that allows the detection light to pass therethrough,
The optical system is configured to be separable from the main body including the detection light source unit, the light receiving unit, and the concentration calculator ,
The gas detector, wherein the detection light source unit is disposed at a position where the reflected light is not blocked in an optical path from the optical system to the light receiving unit . Further having a guide light source unit that emits guide light indicating the irradiation position of the detection light,
At least one of the optical elements included in the optical system is disposed at a position that blocks an optical path of the guide light,
An optical element arranged at a position that blocks an optical path of the guide light has a guide light passage hole through which the guide light passes ,
The gas detector according to claim 1, wherein the detection light source unit and the guide light source unit are arranged at a position where the reflected light is not blocked in an optical path from the optical system to the light receiving unit . The gas detector according to claim 1, wherein at least one of the optical elements included in the optical system is a Fresnel lens.

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