Gas detection device

Abstract

By adjusting the wavelength of light used to detect the target gas, compared to adjusting the wavelength only before starting the detection of the target gas, the decrease in detection accuracy of the target gas is suppressed. [Solution] The gas detection device comprises an irradiation unit that irradiates light into the space to be detected, a detection unit that detects the presence of the target gas in the space based on the light reception results of the light irradiated from the irradiation unit and passing through the space, and a wavelength adjustment unit that adjusts the wavelength of the light irradiated from the irradiation unit to a predetermined wavelength range based on the light reception results of the light irradiated from the irradiation unit and passing through a sealing unit containing a reference gas with a known absorption wavelength during the detection period in which the detection unit detects the presence of the target gas.

Description

Technical Field

[0001] The present invention relates to a gas detection device.

Background Art

[0002] Patent Document 1 discloses a gas detection device including a light source that emits laser light having a wavelength with a high absorption rate by a detection target gas, and a light receiving unit that receives reflected light obtained by reflecting the laser light emitted from the light source. In this gas detection device, leakage of the detected external gas is detected based on the intensity of the received reflected light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] There is a technique for irradiating a space with light having a wavelength absorbed by a detection target gas and detecting the presence of the detection target gas in the space based on the light reception result of the light that has passed through the space. In such a technique, before starting the detection of the detection target gas, the wavelength of the light irradiated into the space may be adjusted to a wavelength range absorbed by the detection target gas. However, for example, when detecting the detection target gas over a long period of time, it may be difficult to maintain a high detection accuracy of the detection target gas only by adjusting the wavelength before starting the detection of the detection target gas. An object of the present invention is to suppress a decrease in the detection accuracy of a detection target gas as compared with a case where adjustment of the wavelength of light used for detecting the detection target gas is performed only before starting the detection of the detection target gas.

Means for Solving the Problems

[0005] The invention described in claim 1 is a gas detection device comprising: an irradiation unit that irradiates light into a space to be detected; a detection unit that detects the presence of a target gas in the space based on the light reception result of the light irradiated from the irradiation unit and passing through the space; and a wavelength adjustment unit that adjusts the wavelength of the light irradiated from the irradiation unit to a predetermined wavelength range based on the light reception result of the light irradiated from the irradiation unit and passing through a sealing unit containing a reference gas with a known absorption wavelength during the detection period in which the detection unit detects the presence of the target gas. The invention described in claim 2 is a gas detection device according to claim 1, wherein the irradiation unit includes an element that changes the wavelength of the irradiated light according to the temperature and the supplied current value, and the wavelength adjustment unit controls the temperature of the element so that the wavelength of the light irradiated from the irradiation unit falls within the wavelength range. The invention described in claim 3 is a gas detection device according to claim 2, wherein the wavelength adjustment unit controls the light-emitting element to a predetermined reference temperature, changes the value of the current supplied to the light-emitting element, recognizes the wavelength of the light irradiated from the irradiation unit based on the light reception result of the light irradiated from the irradiation unit and passed through the sealing unit, and changes the temperature of the light-emitting element from the reference temperature so that the wavelength of the light irradiated from the irradiation unit falls within the wavelength range. The invention described in claim 4 is a gas detection device according to claim 3, wherein the wavelength adjustment unit adjusts the wavelength of light irradiated from the irradiation unit using the first temperature as the reference temperature after the detection period has been performed in which the detection unit detects the presence of the target gas while the light-emitting element is controlled to a first temperature. The invention described in claim 5 is a gas detection device according to claim 4, wherein the wavelength adjustment unit changes the current supplied to the light-emitting element to at least a predetermined reference current, a first current greater than the reference current, and a second current less than the reference current, in order to recognize the wavelength of light emitted from the irradiation unit. The invention described in claim 6 is a gas detection device according to claim 1, wherein the wavelength adjustment unit recognizes the wavelength of light irradiated from the irradiation unit based on the light reception result of the light irradiated from the irradiation unit and passed through the sealing unit, and if the difference between the recognized wavelength and the wavelength range is greater than a predetermined threshold, an error notification is given. The invention described in claim 7 is a gas detection device according to claim 1, wherein the wavelength adjustment period during which the wavelength adjustment unit adjusts the wavelength of light irradiated from the irradiation unit is shorter than the detection period performed by the detection unit before and after the wavelength adjustment period. [Effects of the Invention]

[0006] According to the present invention, compared to the case where the wavelength of light used to detect the target gas is adjusted only before the detection of the target gas is started, it is possible to suppress a decrease in the detection accuracy of the target gas. [Brief explanation of the drawing]

[0007] [Figure 1] This diagram shows the overall configuration of the leak detection system to which this embodiment is applied. [Figure 2] This figure illustrates how the leak detection system to which this embodiment is applied is used. [Figure 3] This is a block diagram showing an example of the functional configuration of the control device to which this embodiment is applied. [Figure 4] This figure shows a portion of the optical absorption spectrum of methane, an example of a gas being detected. [Figure 5] This figure shows an overview of the operation of the gas detection device to which this embodiment is applied. [Figure 6] This diagram illustrates the adjustment operation performed by the wavelength adjustment unit when the target gas is methane. [Figure 7] This diagram illustrates the adjustment operation performed by the wavelength adjustment unit when the target gas is methane. [Figure 8] This diagram illustrates the adjustment operation performed by the wavelength adjustment unit when the target gas is methane. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the attached drawings. Figure 1 shows the overall configuration of the gas detection device 1 to which this embodiment is applied. Figure 2 shows how the gas detection device 1 to which this embodiment is used is used. Figure 2 is a view of the space S in which the gas detection device 1 performs gas detection, viewed from vertically above. In this embodiment, the gas detection device 1 irradiates the space S to be detected with light within a predetermined wavelength range. The gas detection device 1 also receives a portion of the reflected light reflected from the space S. Based on the intensity of the received reflected light, the gas detection device 1 determines whether or not the gas to be detected by the gas detection device 1 is present in the space S. Hereinafter, the gas to be detected by the gas detection device 1 may be referred to as the "detection target gas." In this embodiment, the space S to be detected by the detection target gas is the space along the optical path of the infrared light emitted from the gas detection device 1.

[0009] As will be explained in more detail later, if the target gas is present in the space S to be detected, a portion of the light emitted by the gas detection device 1 is absorbed by the target gas. The gas detection device 1 recognizes that there is light absorption by the target gas from the light received from the light reflected in the target space S, and detects a leak of the target gas in the target space S.

[0010] The gases to be detected by the gas detection device 1 are not particularly limited, but examples include fluorocarbons, carbon monoxide, carbon dioxide, ethylene, methane, ethane, propane, isobutane, butane, propylene, ammonia, hydrogen sulfide, and hydrogen fluoride. Specific examples of fluorocarbons include difluoromethane (refrigerant code: R32), pentafluoroethane (refrigerant code: R125), 1,1,1-trifluoroethane (refrigerant code: R143a), 1,1,1,2-tetrafluoroethane (refrigerant code: R134a), 1,1-difluoroethane (refrigerant code: R152a), 2,3,3,3-tetrafluoro-1-propene (refrigerant code: R1234yf), 1,3,3,3-tetrafluoropropene (refrigerant code: R1234ze), trans-1,2-difluoroethylene (refrigerant code: HFO1132(E)), trifluoroethylene (refrigerant code: HFO1123), and others.

[0011] An example of a space S that is the target of detection of the gas to be detected by the gas detection device 1 is an outdoor or indoor space in which a pipe 90 through which a gas containing the target gas is circulated is installed. In this case, the gas detection device 1 detects the target gas leaking from the pipe 90. In this example, the target space S is the space enclosed by the floor surface 91 on which the piping 90 is installed and the fence 92 provided around the piping 90. When viewed from above, the target space S has a rectangular shape with a long side and a short side. The fence 92 is provided so as to follow the long side and the short side of this rectangle.

[0012] Furthermore, the target space S is provided with a reflector 50 that reflects light emitted from the light emission unit 11 of the gas detection device 1, which will be described later. In this example, the reflector 50 is attached to the fences 92 located on the lower and right sides of Figure 2, which are among the fences 92 provided on the four sides of the target space S. As the reflector 50, for example, a retroreflective sheet having the property that incident light is reflected back in the incident direction can be used. Note that the reflector 50 is not particularly limited as long as the required reflectance can be obtained. Also, in this embodiment, the sheet-like reflector 50 is attached to the fence 92, but the fence 92 itself may have the function of the reflector 50. Further, when the target space S is outdoors, from the viewpoint of reducing the resistance due to wind, holes may be provided in the reflector 50, or the reflector 50 may be in a louver state.

[0013] The gas detection device 1 includes a detection unit 10 that detects gas leakage, a turntable 20 that rotates the detection unit 10, and a control device 30 that controls the operations of the detection unit 10 and the turntable 20. In the gas detection device 1, the detection unit 10 is placed on the turntable 20.

[0014] The detection unit 10 includes a light emitting unit 11 that emits light toward the space S. The detection unit 10 also includes a light receiving unit 12 that receives the light emitted from the light emitting unit 11 and reflected in the space S. The detection unit 10 also includes a lens 13 that condenses the light reflected in the space S onto the light receiving unit 12. The detection unit 10 also includes a test unit 15 that performs a test for adjusting the wavelength of the light emitted from the light emitting unit 11.

[0015] In the gas detection device 1 of this embodiment, the light emitting unit 11 that emits light and the light receiving unit 12 that receives the light reflected in the space S after being emitted from the light emitting unit 11 are integrated. Thereby, the target gas to be detected can be detected remotely. Note that the light emitting unit 11 and the light receiving unit 12 of the gas detection device 1 may be separate bodies. In this case, the target gas to be detected can be detected by arranging the light emitting unit 11 and the light receiving unit 12 so as to face each other with the space S to be detected therebetween.

[0016] The light-emitting unit 11 is an example of an irradiation unit that irradiates light into the space S to be detected. The light-emitting unit 11 is equipped with a laser diode (LD) chip that emits light within a predetermined wavelength range. The light-emitting unit 11 also includes a temperature detection unit that detects the temperature of the LD chip and a temperature adjustment unit that adjusts the temperature of the LD chip. The LD chip is an example of a light-emitting element in which the wavelength of the emitted light changes according to the temperature and the applied current value. The light-emitting unit 11 may be a so-called space output type that emits light from the LD chip without using an optical fiber, or it may be a so-called fiber output type that emits light from the LD chip via an optical fiber. Here, we will explain using the case of a so-called space output type light-emitting unit 11 as an example. The LD chip in the light emission unit 11 emits light within a predetermined wavelength range. In this embodiment, the light emission unit 11 emits parallel light from the LD chip using a collimator (not shown). As will be described in detail later, the wavelength of the light emitted from the LD chip changes depending on the temperature of the LD chip and the current supplied to the LD chip.

[0017] A portion of the light emitted from the LD chip of the light emission unit 11 passes through the half mirror 151 of the test unit 15 (described later) and is irradiated to the outside of the gas detection device 1. In addition, a portion of the infrared light emitted from the light emission unit 11 is reflected by the half mirror 151, passes through the test cell 152 of the test unit 15 (described later), and is received by the test light receiving unit 153 (described later).

[0018] The temperature detection unit of the light emission unit 11 is composed of, for example, a thermistor whose resistance value changes depending on the temperature of the LD chip. The temperature detection unit outputs information related to the temperature of the LD chip, such as the resistance value, to the control device 30. The temperature control unit of the light emission unit 11 is composed of, for example, a Peltier element that heats or cools the LD chip according to the direction and magnitude of the supplied current. Based on the control by the control device 30, the temperature control unit heats or cools the LD chip so that its temperature reaches a target temperature, which will be described later.

[0019] The light-receiving unit 12 is composed of, for example, a photodiode. The light-receiving unit 12 receives a portion of the light (reflected light) emitted from the light-emitting unit 11 and reflected by reflective surfaces such as walls and the ground in space S, via the lens 13. The light-receiving unit 12 also outputs an electrical signal corresponding to the intensity of the received light to the acquisition unit 32 of the control device 30, which will be described later. The electrical signal corresponding to the intensity of the light output from the light-receiving unit 12 will be explained in detail later.

[0020] The lens 13 is composed of, for example, a Fresnel lens, and focuses the light emitted from the light emitting section 11 and reflected in space S (reflected light) onto the light-receiving surface of the light-receiving section 12.

[0021] The test unit 15 is used to adjust the wavelength of the light emitted from the light emission unit 11. The test unit 15 is equipped with a half-mirror 151 that transmits a portion of the light emitted from the light emission unit 11 and reflects a portion of it. The test unit 15 is also equipped with a test cell 152 through which the gas to be detected is sealed and the light reflected by the half-mirror 151 passes. The test unit 15 is also equipped with a test light receiving unit 153 that receives the light that has passed through the test cell 152. The test light receiving unit 153 is made up of, for example, a photodiode and outputs an electrical signal corresponding to the intensity of the received light to the wavelength adjustment unit 34 of the control device 30, which will be described later.

[0022] The rotating platform 20 rotates the detection unit 10 horizontally at a predetermined rotational speed around a rotation axis that extends vertically. For example, the rotating platform 20 performs a forward movement in which it rotates the detection unit 10 350° clockwise from a predetermined starting point to an end point. Following the forward movement, the rotating platform 20 performs a return movement in which it rotates the detection unit 10 350° counterclockwise from the end point to the starting point. In the gas detection device 1, the detection unit 10 is rotated by the rotating platform 20, so that the light emitted from the light emission unit 11 of the detection unit 10 is sequentially irradiated over the entire space S. In addition, as the light emitted from the light emission unit 11 is sequentially irradiated over the space S, the light receiving unit 12 sequentially receives the light reflected in the space S and outputs a light reception signal. As a result, the gas detection device 1 can detect the target gas over the entire space S.

[0023] The control device 30 is a computer device composed of, for example, a CPU (Central Processing Unit) 30A, a ROM (Read Only Memory) 30B, and a RAM (Random Access Memory) 30C. The CPU loads various programs stored in the ROM 30B and other storage devices (not shown) into the RAM 30C and executes them, thereby realizing the various functions of the control device 30 described later. The RAM 30C is a memory used as the CPU's working memory, and the ROM 30B is a memory that stores various programs executed by the CPU 30A.

[0024] Figure 3 is a block diagram showing an example of the functional configuration of the control device 30 to which this embodiment is applied. The control device 30 includes an emission control unit 31 that controls the emission of light from the light emission unit 11. The control device 30 also includes an acquisition unit 32 that acquires a measured value representing the concentration of the target gas in space S based on the light receiving signal output from the light receiving unit 12. The control device 30 also includes a leak determination unit 33 that determines whether or not the target gas is leaking in space S based on the measured value acquired by the acquisition unit 32. The control device 30 also includes a wavelength adjustment unit 34 that adjusts the wavelength of the light emitted from the light emission unit 11 based on an electrical signal output from the test light receiving unit 153 of the test unit 15. The control device 30 also includes an output unit 35 that outputs information such as whether the target gas has leaked in space S based on the determination result from the leak determination unit 33. The control device 30 also includes a storage unit 36 ​​that stores various information such as information on a predetermined reference current and initial setting temperature for the LD chip of the light emission unit 11, and information on the target temperature calculated by the wavelength adjustment unit 34.

[0025] The emission control unit 31 controls the light emission unit 11 to emit light within a predetermined wavelength range into space S using the LD chip of the light emission unit 11. The emission control unit 31 controls the light emission unit 11 to emit light from the LD chip that is modulated by a predetermined wavelength at a predetermined frequency, centered around a predetermined wavelength (hereinafter sometimes referred to as the center wavelength). The predetermined frequency can be, for example, 10 kHz. The predetermined wavelength to be modulated can be, for example, around ± tens of pm.

[0026] In this way, under the control of the emission control unit 31, light in a wavelength range having a predetermined width above and below the central wavelength is emitted from the LD chip of the light emission unit 11. In this embodiment, the peak wavelength of the absorption peak in the optical absorption spectrum of the gas to be detected can be set as the central wavelength of the light emitted from the LD chip of the light emission unit 11. An absorption peak is the point where the slope of the optical absorption spectrum changes from positive to negative as the wavelength increases, and the absorption intensity reaches its maximum value. Hereinafter, the peak wavelength of the absorption peak in the optical absorption spectrum of the gas to be detected may be simply referred to as the peak wavelength.

[0027] Here, the wavelength of the light emitted from the LD chip of the light emission unit 11 changes depending on the temperature of the LD chip and the magnitude of the current supplied to the LD chip. More specifically, the wavelength of the light emitted from the LD chip becomes longer as the temperature of the LD chip increases, and shorter as the temperature of the LD chip decreases. Also, the wavelength of the light emitted from the LD chip becomes longer as the current supplied to the LD chip increases, and shorter as the current supplied to the LD chip decreases.

[0028] In the gas detection device 1 of this embodiment, the wavelength adjustment unit 34 calculates the target temperature of the LD chip so that the central wavelength of the light emitted from the LD chip of the light emission unit 11 becomes the peak wavelength. The emission control unit 31 controls the light emission unit 11 based on the target temperature obtained from the wavelength adjustment unit 34. Specifically, the emission control unit 31 controls a Peltier element, which is an example of a temperature adjustment unit for the light emission unit 11, so that the temperature of the LD chip reaches the target temperature. The emission control unit 31 also supplies a reference current, which is a current of a predetermined magnitude, to the LD chip. As a result, light in a wavelength range centered on the peak wavelength is emitted from the LD chip of the light emission unit 11.

[0029] As mentioned above, the wavelength of light emitted from the LD chip also changes depending on the magnitude of the current supplied to the LD chip. Therefore, the emission control unit 31 can also control the central wavelength of light emitted from the LD chip by changing the magnitude of the current supplied to the LD chip along with the temperature of the LD chip. On the other hand, when the magnitude of the current supplied to the LD chip is changed, not only the wavelength of the light emitted from the LD chip but also the intensity of the light emitted from the LD chip changes. For example, the intensity of the light emitted from the LD chip increases with a larger current supplied to the LD chip, and decreases with a smaller current supplied to the LD chip. And, for example, if the current supplied to the LD chip is increased in order to lengthen the central wavelength, the intensity of the light emitted from the LD chip may become excessively high, which may cause safety problems. Therefore, from a safety standpoint, it is preferable that the emission control unit 31 controls the central wavelength of the light emitted from the LD chip by adjusting the temperature of the LD chip.

[0030] The acquisition unit 32 acquires the received light signal from the light receiving unit 12, which is the light that has been irradiated into the space S by the light emitting unit 11 and has passed through the space S. Then, the acquisition unit 32 obtains a measured value representing the concentration of the target gas in the space S from the acquired received light signal. In this embodiment, the acquisition unit 32 acquires the column density (ppm·m), which is the product of the concentration of the target gas (ppm) and the thickness D (m) of the target gas present in space S, as a measured value.

[0031] Specifically, as described above, the light emission unit 11 emits light (first harmonic) modulated at a predetermined frequency (e.g., 10 kHz) centered around a predetermined central wavelength, based on control by the emission control unit 31. If the target gas is present in space S, a portion of the light emitted from the light emission unit 11 is absorbed by the target gas. This generates light (second harmonic) with twice the frequency (e.g., 20 kHz) of the light emitted from the light emission unit 11. The light receiving unit 12 receives the first and second harmonics reflected in space S. The acquisition unit 32 then receives the received signals corresponding to the first and second harmonics received by the light receiving unit 12. The acquisition unit 32 acquires the column density of the target gas in space S based on the ratio of the first harmonic component to the second harmonic component in the light received signal acquired from the light receiving unit 12.

[0032] The leak detection unit 33 determines whether or not the target gas has leaked in space S based on the measurement values ​​obtained by the acquisition unit 32. In the following description, the determination made by the leak detection unit 33 as whether or not the target gas has leaked in space S may be referred to as leak detection. The leak detection unit 33 performs a leak detection based, for example, on a comparison between the measured value obtained from the acquisition unit 32 and a predetermined reference value. In addition, the leak detection unit 33 determines that the target gas has leaked in space S if the measured value obtained from the acquisition unit 32 exceeds the reference value.

[0033] The wavelength adjustment unit 34 performs an adjustment operation to adjust the wavelength of light emitted from the LD chip of the light emission unit 11 during the detection period in which the acquisition unit 32 and the leak determination unit 33 detect a leak of the target gas in space S. In the adjustment operation, the wavelength adjustment unit 34 adjusts the wavelength of light emitted from the LD chip of the light emission unit 11 to a wavelength range centered on the peak wavelength in the optical absorption spectrum of the target gas.

[0034] The wavelength adjustment unit 34 adjusts the wavelength of the light emitted from the LD chip of the light emission unit 11 based on the light reception results of the light emitted from the LD chip and passed through the test cell 152, which contains a target gas, an example of a reference gas. Specifically, the wavelength adjustment unit 34 changes the magnitude of the current supplied to the LD chip of the light emission unit 11 to irradiate it with light. The wavelength adjustment unit 34 then acquires an electrical signal from the test light receiving unit 153 of the test unit 15, which is the result of receiving light that has passed through the test cell 152. Furthermore, based on the acquired electrical signal, the wavelength adjustment unit 34 calculates the light absorption intensity by the target gas sealed in the test cell 152.

[0035] Here, if the central wavelength of the light emitted from the LD chip of the light emission unit 11 does not deviate from the peak wavelength, the light emitted from the LD chip is absorbed by the target gas sealed in the test cell 152. In this case, the absorption intensity of the light calculated based on the electrical signal acquired from the test light receiving unit 153 will be high. On the other hand, if the central wavelength of the light emitted from the LD chip of the light emission unit 11 is deviated from the peak wavelength, the absorption intensity of the light calculated based on the electrical signal acquired from the test light receiving unit 153 will be lower.

[0036] Then, the wavelength adjustment unit 34 determines the target temperature of the LD chip based on the calculated light absorption intensity, such that the central wavelength of the light emitted from the LD chip in the light emission unit 11 becomes the peak wavelength. The wavelength adjustment unit 34 then outputs the target temperature of the LD chip to the emission control unit 31. The adjustment operation performed by the wavelength adjustment unit 34 to adjust the wavelength of the light emitted from the light emission unit 11 will be explained in detail with specific examples later.

[0037] The output unit 35 outputs information indicating that the target gas has leaked in space S, according to the leak determination result from the leak determination unit 33. The output mode of the output unit 35 is not particularly limited. For example, the output unit 35 outputs information indicating that the target gas has leaked in space S to a computer device such as a PC or tablet terminal, as an example of an output device (not shown). The output unit 35 then displays a message indicating that the target gas has leaked on these display screens. Alternatively, the output unit 35 may indicate that the target gas has leaked by illuminating the gas detection device 1 or a warning lamp located outside the gas detection device 1, as an example of an output device. Furthermore, the output unit 35 may also indicate that the target gas has leaked by voice through the gas detection device 1 or a speaker located outside the gas detection device 1, as an example of an output device.

[0038] Furthermore, the output unit 35 outputs an error notification, which indicates that it is difficult to adjust the wavelength of the LD chip if the deviation from the peak wavelength of the gas to be detected is excessively large during the adjustment operation by the wavelength adjustment unit 34. The output method of the error notification by the output unit 35 is not particularly limited, similar to the information indicating that the target gas leaked in the space S described above.

[0039] Next, the operation of the gas detection device 1 of this embodiment will be described. In a gas detection device 1 that irradiates a space S with light emitted from a light emission unit 11 and detects a target gas based on the reception result of the light that has passed through the space S, the wavelength range of the light emitted from the light emission unit 11 may be adjusted to the wavelength range absorbed by the target gas before starting the detection of the target gas. However, in cases like the gas detection device 1 of this embodiment, where light is continuously irradiated into the space S and the detection of the target gas is performed over a long period of time, it may be difficult to maintain a high detection accuracy of the target gas by simply adjusting the wavelength before starting the detection of the target gas. Furthermore, in the gas detection device 1, when the detection of the target gas is performed over a long period of time, the wavelength of the light emitted from the light emission unit 11 may deviate from the wavelength range absorbed by the target gas over time. In this case, it is difficult to detect the target gas with high accuracy.

[0040] In contrast, the gas detection device 1 of this embodiment performs an adjustment operation to adjust the wavelength of light emitted from the light emission unit 11 during the detection period in which the target gas is detected. This suppresses a decrease in the detection accuracy of the target gas compared to the case where the adjustment of the wavelength of light emitted from the light emission unit 11 is performed only before the detection of the target gas begins. In the gas detection device 1, the period during which the wavelength of light emitted from the light emission unit 11 is adjusted is sometimes referred to as the wavelength adjustment period. In other words, in the gas detection device 1 of this embodiment, a wavelength adjustment period is provided between detection periods.

[0041] The following explanation will use the case where gas detection device 1 detects methane as the target gas as an example. Figure 4 shows a portion of the optical absorption spectrum of methane, an example of a gas being detected. In Figure 4, the horizontal axis represents the wavelength of light, and the vertical axis represents the absorption intensity of light. As shown in Figure 4, the optical absorption spectrum of methane has an absorption peak with a peak wavelength of 1650.957 nm.

[0042] Figure 5 is a diagram illustrating the overview of the operation of the gas detection device 1 to which this embodiment is applied. Figure 5 shows the operation performed by the gas detection device 1 as time progresses. In Figure 5, time progresses from left to right. When the gas detection device 1 starts detecting the target gas in space S, first, the power to the gas detection device 1 is turned on, and a startup operation is performed to activate the gas detection device 1.

[0043] During startup, the output control unit 31 of the control device 30 adjusts the temperature of the LD chip in the light emission unit 11 in the detection unit 10 to a predetermined initial temperature. Specifically, the output control unit 31 obtains the temperature detection result of the LD chip from a thermistor, which is an example of a temperature detection unit in the light emission unit 11. Based on the temperature detection result of the LD chip, the output control unit 31 controls a Peltier element, which is an example of a temperature adjustment unit in the light emission unit 11, to adjust the temperature of the LD chip to the initial temperature.

[0044] Here, the initial temperature is the temperature at which, when a predetermined reference current (rated bias current) is supplied to the LD chip, it is estimated that light with a wavelength equal to the peak wavelength of the gas to be detected will be emitted from the LD chip. The initial temperature and the magnitude of the reference current vary depending on the characteristics of the LD chip and are determined according to the LD chip. In this example, the reference current of the LD chip is assumed to be 85mA and the initial temperature is assumed to be 34.56℃. Therefore, during startup, the light emission control unit 31 controls the Peltier element of the light emission unit 11 to adjust the temperature of the LD chip to the initial setting temperature of 34.56°C.

[0045] After the temperature of the LD chip in the light emission unit 11 is adjusted to the initial temperature, the gas detection device 1 then performs an adjustment operation to adjust the wavelength of the light emitted from the LD chip. In the light emission unit 11, the thermistor detects the temperature near the LD chip. Therefore, depending on changes in ambient temperature, a discrepancy may occur between the temperature of the LD chip detected by the thermistor and the actual temperature of the LD chip. In this case, even if a reference current is supplied to the LD chip, the central wavelength of the light emitted from the LD chip may deviate from the peak wavelength of the gas being detected. In the gas detection device 1, adjustment operations are performed to suppress the deviation of the central wavelength of the light emitted from the LD chip from the peak wavelength of the gas to be detected.

[0046] During the adjustment operation, the wavelength adjustment unit 34 of the control device 30 maintains the temperature of the LD chip in the light emission unit 11 at the initial setting temperature, and changes the magnitude of the current supplied to the LD chip from the reference current, causing light to be emitted from the LD chip. In addition, the wavelength adjustment unit 34 changes the current supplied to the LD chip to a predetermined reference current, a first current that is larger than the reference current, and a second current that is smaller than the reference current, causing light to be emitted from the LD chip. In this example, the initial temperature is an example of a predetermined reference temperature.

[0047] Furthermore, the wavelength adjustment unit 34 acquires an electrical signal from the test light receiving unit 153 of the test unit 15, which is the result of receiving light that has passed through the test cell 152. In addition, the wavelength adjustment unit 34 acquires the electrical signal, which is the result of receiving light by the test cell 152, for each of the cases in which a reference current, a first current, and a second current are supplied to the LD chip. Furthermore, the wavelength adjustment unit 34 calculates the light absorption intensity due to the target gas sealed in the test cell 152 based on the acquired electrical signal. In addition, the wavelength adjustment unit 34 calculates the light absorption intensity due to the target gas sealed in the test cell 152 for each of the cases in which a reference current, a first current, and a second current are supplied to the LD chip.

[0048] The wavelength adjustment unit 34 estimates the wavelength difference between the center wavelength of the light emitted from the LD chip when the reference current is supplied and the peak wavelength of the gas to be detected, based on the relative magnitudes of the light absorption intensities when the reference current, the first current, and the second current are supplied to the LD chip. Then, the wavelength adjustment unit 34 calculates the target temperature of the LD chip based on the estimated wavelength shift, so that the central wavelength of the light emitted from the LD chip when a reference current is supplied matches the peak wavelength.

[0049] Figures 6 to 8 illustrate the adjustment operation performed by the wavelength adjustment unit 34 when the target gas for detection is methane. Figures 6 to 8 show the relationship between the absorption peak of the methane optical absorption spectrum and the light absorption intensity due to methane calculated based on the light reception results from the test light receiving unit 153. In Figures 6 to 8, the horizontal axis represents the wavelength of light, and the vertical axis represents the light absorption intensity. In addition, in Figures 6 to 8, the absorption peak with a peak wavelength of 1650.957 nm in the methane optical absorption spectrum is shown by a dashed line.

[0050] As mentioned above, the magnitude of the reference current is 85mA. In this example, the wavelength adjustment unit 34 maintains the temperature of the light emission unit 11 at the initial setting temperature of 34.56℃ and supplies currents of 85mA, 85±1mA, and 85±2mA to the LD chip. The wavelength adjustment unit 34 then calculates the light absorption intensity by the methane sealed in the test cell 152 for each of the cases in which a current of 85mA, 85±1mA, and 85±2mA is supplied to the LD chip. In other words, the wavelength adjustment unit 34 calculates the light absorption intensity by methane at a total of five points when currents of 83mA, 84mA, 85mA, 86mA, and 87mA are supplied to the LD chip. In this example, 86mA and 87mA are examples of the first current, which is greater than the reference current of 85mA. Also, 83mA and 84mA are examples of the second current, which is smaller than the reference current of 85mA. Furthermore, when the magnitude of the current supplied to the LD chip is changed by ±1mA and ±2mA, the wavelength of the light emitted from the LD chip changes by approximately ±9pm and ±18pm, respectively.

[0051] In Figures 6 to 8, point C indicates the light absorption intensity by methane when a reference current of 85 mA is supplied to the LD chip. Points B and A indicate the light absorption intensities by methane when currents smaller than the reference current of 85 mA, 83 mA and 84 mA, are supplied to the LD chip. Points A and B indicate the light absorption intensities by methane when currents larger than the reference current of 85 mA, 86 mA and 87 mA, are supplied to the LD chip. Hereafter, the absorption intensity shown at point C in Figures 6 to 8 will be denoted as absorption intensity C. The same applies to the absorption intensities shown at points B, A, A, and B.

[0052] As shown in Figure 4, in the optical absorption spectrum of methane, the absorption peak with a peak wavelength of 1650.957 nm has a shape that is approximately symmetrical on the long-wavelength and short-wavelength sides. Therefore, in this embodiment, based on the relative magnitudes of the absorption intensities C, ±A, and ±B, it is possible to estimate the wavelength difference between the center wavelength of the light emitted from the LD chip when a reference current is supplied and the peak wavelength of the gas to be detected.

[0053] In the example shown in Figure 6, absorption intensity C is the largest. Also, absorption intensity A and absorption intensity -A are equal (A=-A), and absorption intensity B and absorption intensity -B are equal (B=-B). In this case, it can be inferred that when a reference current of 85mA is supplied to the LD chip, the central wavelength of the light emitted from the LD chip coincides with the peak wavelength of methane. Therefore, the wavelength adjustment unit 34 calculates the initial temperature (34.56°C), which is the current temperature of the LD chip, as the target temperature for the LD chip.

[0054] In the example shown in Figure 7, absorption intensity C is the largest. Also, absorption intensity A is greater than absorption intensity -A (A>-A), and absorption intensity B is greater than absorption intensity -B (B>-B). In this case, it can be inferred that when a reference current of 85mA is supplied to the LD chip, the central wavelength of the light emitted from the LD chip is shifted slightly to a shorter wavelength compared to the peak wavelength of methane. Therefore, the wavelength adjustment unit 34 calculates a target temperature for the LD chip by adding a correction value α to the initial temperature (34.56°C), which is the current temperature of the LD chip, to make the wavelength of the light emitted from the LD chip longer. This result is 34.56 + α°C.

[0055] In the example shown in Figure 8, absorption intensity -A is the largest, and absorption intensity C is smaller than absorption intensity -A (C < -A). Also, absorption intensity C is larger than absorption intensity -B (C > B). In this case, it can be inferred that when a reference current of 85mA is supplied to the LD chip, the central wavelength of the light emitted from the LD chip is shifted to a longer wavelength compared to the peak wavelength of methane. Furthermore, it can be inferred that the amount of shift between the central wavelength of the light emitted from the LD chip and the peak wavelength of methane when a reference current of 85mA is supplied to the LD chip is larger than in the example shown in Figure 7. Therefore, the wavelength adjustment unit 34 calculates a target temperature for the LD chip by subtracting a correction value β from the initial temperature (34.56°C), which is the current temperature of the LD chip, to shorten the wavelength of the light emitted from the LD chip. This correction value β is greater than the correction value α mentioned above (β > α).

[0056] The wavelength adjustment unit 34 then outputs the calculated target temperature of the LD chip to the emission control unit 31. With this, the adjustment operation by the wavelength adjustment unit 34 is completed. In the gas detection device 1 of this embodiment, the wavelength adjustment period during which the wavelength adjustment unit 34 performs adjustment operations is shorter than the detection period described later. The wavelength adjustment period is, for example, about 20 ms. As described above, in this embodiment, during the adjustment operation, the magnitude of the current supplied to the LD chip is changed by ±1mA and ±2mA from the reference current, and the absorption intensity at a total of five points is calculated. In this case, the amount of change in the wavelength of the light emitted from the LD chip is approximately ±9pm and ±18pm. This makes it possible to shorten the wavelength adjustment period compared to when the wavelength of the light emitted from the LD chip is changed by approximately ±several hundred pm to adjust the wavelength.

[0057] Furthermore, in this embodiment, the magnitude of the current supplied to the LD chip is changed during the adjustment operation without changing the temperature of the LD chip. When the wavelength of light emitted from the LD chip is changed by changing the temperature of the LD chip, the wavelength adjustment period may be long because it takes time for the LD chip to be heated or cooled by the Peltier element. In contrast, in this embodiment, by changing the magnitude of the current supplied to the LD chip without changing the temperature of the LD chip, the wavelength adjustment period can be shortened compared to the case where the temperature of the LD chip is changed.

[0058] In the gas detection device 1, if the deviation from the peak wavelength of the gas to be detected is excessively large, it may be difficult to adjust the central wavelength of the light emitted from the LD chip to the peak wavelength simply by adjusting the temperature of the LD chip. Thus, when a reference current is supplied to the LD chip, if the difference between the center wavelength of the light emitted from the LD chip and the peak wavelength of the gas to be detected is greater than a predetermined threshold, the control device 30 may output an error notification via the output unit 25. Examples of error notifications include information indicating that it is difficult to adjust the wavelength of the LD chip.

[0059] Although not shown in the diagram, consider the case in the above example where absorption intensity B is the largest and absorption intensity C is smaller than both absorption intensity A and absorption intensity B (B>A>C). In this case, it can be inferred that the wavelength of light emitted from the LD chip when a reference current of 85mA is supplied to the LD chip is shifted to a shorter wavelength compared to the peak wavelength of methane. Furthermore, it can be inferred that the amount of shift between the wavelength of light emitted from the LD chip and the peak wavelength of methane when a reference current of 85mA is supplied to the LD chip is larger than in the examples shown in Figures 7 and 8. Similarly, consider the case where absorption intensity -B is the largest and absorption intensity C is smaller than absorption intensity -A and absorption intensity -B (-B>-A>C). In this case, it can be inferred that the wavelength of light emitted from the LD chip when a reference current of 85mA is supplied to the LD chip is shifted to a longer wavelength compared to the peak wavelength of methane. Furthermore, it can be inferred that the amount of shift between the wavelength of light emitted from the LD chip and the peak wavelength of methane when a reference current of 85mA is supplied to the LD chip is larger than in the examples shown in Figures 7 and 8. In such cases, the control device 30 issues an error notification indicating that it is difficult to adjust the wavelength of the LD chip using the output unit 25.

[0060] In this embodiment, the wavelength adjustment unit 34 calculates the absorption intensity at a total of five points by changing the magnitude of the current supplied to the LD chip by ±1mA and ±2mA from the reference current during the adjustment operation. However, the wavelength adjustment unit 34 only needs to calculate the absorption intensity at at least three points by changing the magnitude of the current supplied to the LD chip to the reference current, a first current that is larger than the reference current, and a second current that is smaller than the reference current during the adjustment operation.

[0061] After the wavelength adjustment unit 34 performs the adjustment operation, the gas detection device 1 starts a detection period to detect leakage of the target gas in the space S, following the wavelength adjustment period. First, the emission control unit 31 of the control device 30 controls the temperature of the LD chip in the light emission unit 11 to a target temperature obtained from the wavelength adjustment unit 34 during the wavelength adjustment period. The emission control unit 31 then supplies a reference current to the LD chip. As a result, light in the wavelength range centered on the peak wavelength is emitted from the LD chip into space S. During the detection period, the acquisition unit 32 obtains a measured value representing the concentration of the target gas in space S based on the received signal output from the light receiving unit 12. The leak determination unit 33 then performs a leak determination to determine whether or not the target gas is leaking into space S based on the measured value obtained by the acquisition unit 32.

[0062] Subsequently, the gas detection device 1 performs the operation to detect leakage of the target gas for a predetermined period, and then, following the detection period, starts a wavelength adjustment period in which the wavelength adjustment unit 34 performs adjustment operations again. This suppresses a decrease in the detection accuracy of the target gas compared to the case where the wavelength of the light emitted from the light emission unit 11 is adjusted only before the detection of the target gas begins. In this embodiment, the detection period is longer than the wavelength adjustment period. The detection period is, for example, about 80 ms. That is, in the gas detection device 1 of this embodiment, a detection operation to detect leakage of the target gas in space S and an adjustment operation by the wavelength adjustment unit 34 are performed every 100 ms.

[0063] During the wavelength adjustment period that follows the detection period, the wavelength adjustment unit 34 performs the adjustment operation while maintaining the temperature of the LD chip in the light emission unit 11 at the target temperature used for the detection operation during the detection period. Furthermore, the wavelength adjustment unit 34 changes the magnitude of the current supplied to the LD chip from the reference current while maintaining the target temperature of the LD chip at the target temperature used for the detection operation during the detection period, causing light to be emitted from the LD chip. Moreover, during the wavelength adjustment period that follows the detection period, the wavelength adjustment unit 34 performs the adjustment operation without changing the temperature of the LD chip. In this example, the target temperature used for the detection operation during the detection period is an example of the first temperature or reference temperature. As a result, the time required to heat or cool the LD chip can be shortened compared to the case where the wavelength adjustment unit 34 changes the temperature of the LD chip to an initial temperature during the wavelength adjustment period that follows the detection period. This allows the wavelength adjustment period to be shortened compared to the case where the temperature of the LD chip is changed.

[0064] The adjustment operation performed by the wavelength adjustment unit 34 is the same as the adjustment operation during the wavelength adjustment period described above, except for the temperature used to control the LD chip. That is, the wavelength adjustment unit 34 calculates a new target temperature so that the central wavelength of the light emitted from the LD chip matches the peak wavelength when a reference current is supplied, and outputs this to the emission control unit 31.

[0065] Subsequently, the gas detection device 1 repeatedly alternates between a detection period and a wavelength adjustment period until it finishes detecting the target gas in space S. As a result, in the gas detection device 1 of this embodiment, even when light is continuously irradiated into space S and the target gas is detected over a long period of time, the wavelength range of the light emitted from the light emission unit 11 is periodically calibrated. As a result, deviation of the wavelength range of the light emitted from the light emission unit 11 from the wavelength range centered on the peak wavelength of the target gas is suppressed.

[0066] Incidentally, in general, gas detection devices that detect a target gas by irradiating a space to be detected with an LD chip or the like, and detecting the target gas based on the reception results of the light that has passed through the space, often perform an adjustment operation of the wavelength of light emitted from the LD chip when the gas detection device is started up. In this adjustment operation, the temperature of the LD chip is continuously changed over a wide range, and the absorption intensity of the light by the target gas sealed in a test cell is obtained. For example, if the target gas is methane, the gas detection device acquires the absorption intensity at a total of 120 points in a range of 34.56 ± 0.6 °C at 0.01 °C intervals, so that the wavelength emitted from the LD chip changes by ±540 pm. In this case, it takes several seconds to control the LD chip to each temperature, so it takes several minutes to acquire the absorption intensity at all points and calculate the target temperature of the LD chip. In gas detection devices, it is difficult to perform such lengthy adjustment operations during the detection period in which the target gas is being detected.

[0067] In contrast, in the gas detection device 1 of this embodiment, during the adjustment operation, the temperature of the LD chip is maintained at a predetermined reference temperature without changing it, and the magnitude of the current supplied to the LD chip is changed. As a result, the time required for adjusting the wavelength of light emitted from the LD chip can be shortened compared to the case where the temperature of the LD chip is changed, and the adjustment operation can be performed during the detection period in which the target gas is detected. In other words, the gas detection device 1 can continuously perform the detection operation of the target gas in space S without being stopped for a long period of time due to the adjustment operation. Furthermore, in the gas detection device 1 of this embodiment, adjustment operations are performed periodically during the detection period, which suppresses a large deviation in the wavelength range of light emitted from the LD chip from the wavelength range centered on the peak wavelength of the gas to be detected. As a result, a large deviation of the LD chip temperature from the target temperature is suppressed, and the time required to heat or cool the LD chip when adjusting it to the target temperature can be shortened.

[0068] In this embodiment, the detection unit 10 uses a so-called spatial output type light emission unit 11 that emits light from the LD chip without using an optical fiber. Furthermore, in the detection unit 10 described above, a portion of the light emitted from the spatial output type light emission unit 11 and passing through the collimator is received by the test light receiving unit 153 using the half mirror 151 of the test unit 15. However, the test section 15 and light emission section 11 of the detection section 10 are not limited to these. When using a spatial output type light emission unit 11, for example, a portion of the light emitted from the LD chip without passing through an optical fiber and before passing through the collimator may be guided to the test light receiving unit 153 via an optical fiber.

[0069] Furthermore, the detection unit 10 may also use a so-called fiber output type optical emission unit 11 that emits light from the LD chip via an optical fiber. When using a fiber output type optical emission unit 11, the light emitted from the LD chip via the optical fiber may be split by a beam splitter, and a portion of it (for example, 1% of the light emitted from the LD chip) may be guided to the test light receiving unit 153 via the optical fiber. In this case, the detection unit 10 guides the remaining portion (for example, 99% of the light emitted from the LD chip) via the optical fiber and emits it into space S as parallel light using a collimator. Furthermore, when using a fiber output type light emission unit 11, the detection unit 10 may be configured, similar to the example shown in Figure 1, so that a portion of the light emitted from the LD chip and passing through the optical fiber and collimator is received by the test light receiving unit 153 via the half mirror 151.

[0070] Although embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Various modifications and combinations are permitted as long as they do not contradict the spirit of the present invention. [Explanation of Symbols]

[0071] 1...Gas detection device, 10...Detection unit, 11...Light emission unit, 12...Light receiving unit, 13...Lens, 15...Test unit, 20...Rotating platform, 30...Control device, 31...Emission control unit, 32...Acquisition unit, 33...Leakage determination unit, 34...Wavelength adjustment unit, 35...Output unit, 36...Storage unit, 151...Half mirror, 152...Test cell, 153...Test light receiving unit

Claims

1. An illumination unit that irradiates light into the space to be detected, A detection unit detects the presence of a target gas in the space based on the light reception result of light irradiated from the irradiation unit and passing through the space, During the detection period in which the detection unit detects the presence of the target gas, a wavelength adjustment unit adjusts the wavelength of the light irradiated from the irradiation unit to a predetermined wavelength range based on the light reception result of the light irradiated from the irradiation unit and passing through the sealing unit containing a reference gas with a known absorption wavelength. A gas detection device equipped with the following features.

2. The irradiation unit includes a light-emitting element whose wavelength of light changes according to the temperature and the supplied current value. The wavelength adjustment unit controls the temperature of the light-emitting element so that the wavelength of the light emitted from the irradiation unit falls within the specified wavelength range. The gas detection device according to claim 1.

3. The wavelength adjustment unit controls the light-emitting element to a predetermined reference temperature and changes the current value supplied to the light-emitting element to recognize the wavelength of the light irradiated from the irradiation unit and passed through the encapsulation unit based on the light reception result, and changes the temperature of the light-emitting element from the reference temperature so that the wavelength of the light irradiated from the irradiation unit falls within the wavelength range. The gas detection device according to claim 2.

4. The wavelength adjustment unit adjusts the wavelength of the light emitted from the irradiation unit, using the first temperature as the reference temperature, after the detection period has been performed in which the detection unit detects the presence of the target gas while the light-emitting element is controlled to the first temperature. The gas detection device according to claim 3.

5. The wavelength adjustment unit changes the current supplied to the light-emitting element to at least a predetermined reference current, a first current greater than the reference current, and a second current less than the reference current, thereby recognizing the wavelength of the light emitted from the irradiation unit. The gas detection device according to claim 4.

6. The wavelength adjustment unit recognizes the wavelength of the light emitted from the irradiation unit based on the light reception result of the light emitted from the irradiation unit and passed through the sealing unit, and issues an error notification if the difference between the recognized wavelength and the wavelength range is greater than a predetermined threshold. The gas detection device according to claim 1.

7. The wavelength adjustment period during which the wavelength adjustment unit adjusts the wavelength of the light emitted from the irradiation unit is shorter than the detection period performed by the detection unit before and after the wavelength adjustment period. The gas detection device according to claim 1.

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