Gas detection device, gas detection system, and gas detection method

Abstract

To provide a gas detection device, a gas detection system, and a gas detection method capable of detecting gas leaks with high accuracy.SOLUTION: A gas detection device (1) includes a light source (11) that emits light in accordance with a drive signal, a light signal detection unit that detects a signal on the basis of the emitted light and outputs a first detection signal, a sound wave detection unit that detects sound waves generated by a leak of the gas to be detected and outputs a second detection signal, a gas cell (40) having a hole (43) through which gas passes and introducing gas from the hole into a gas detection space, and a control unit (50) that switches and executes multiple operating modes. The multiple operation modes include a first mode that outputs a drive signal and performs a concentration calculation of the gas to be detected in the gas on the basis of the first detection signal and a second mode that determines the leakage or possibility of leakage of the gas to be detected on the basis of the second detection signal.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a gas detection device, a gas detection system, and a gas detection method.

Background Art

[0002] In recent years, development of a gas sensor (gas measuring device) has been underway, which includes a light source that emits infrared rays, is configured such that the infrared rays pass through a gas containing a gas to be detected, and detects the concentration of the gas to be detected by utilizing the absorption characteristics of the infrared rays by the gas to be detected. The gas to be detected is, for example, alcohol or carbon dioxide. For example, Patent Document 1 discloses a photoacoustic gas sensor that measures the gas concentration by picking up the vibration of gas molecules that have absorbed light as sound using a high-performance microphone or the like.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, in general, for gas leak detection, an ultrasonic leak detector that detects ultrasonic waves having a frequency of 30 kHz or higher generated by a gas leak is used. A minute leak from a pipe generates ultrasonic waves that are not normally present in an environment such as a factory, so gas leaks can be detected by detecting ultrasonic waves having a frequency of 30 kHz or higher. Here, when a large amount of gas leak occurs, ultrasonic waves are often not generated. Therefore, it is difficult to detect all gas leaks only with an ultrasonic leak detector, and it cannot be said that the detection accuracy is sufficient. Additionally, it is conceivable to provide an additional gas sensor, but problems such as an increase in cost and securing an installation location may occur.

[0005] An object of the present disclosure made in view of such circumstances is to provide a gas detection device, a gas detection system, and a gas detection method capable of detecting gas leakage with high accuracy.

Means for Solving the Problems

[0006] (1) A gas detection device according to an embodiment of the present disclosure includes a light source that emits light according to a drive signal, an optical signal detection unit that detects a signal based on the emitted light and outputs a first detection signal, a sound wave detection unit that detects a sound wave generated by leakage of the gas to be detected and outputs a second detection signal, a gas cell having a hole through which a gas passes and introducing the gas from the hole into a gas detection space, and a control unit that switches and executes a plurality of operation modes. The plurality of operation modes include a first mode that outputs the drive signal and performs concentration calculation of the gas to be detected in the gas based on the first detection signal, and a second mode that determines leakage or the possibility of leakage of the gas to be detected based on the second detection signal.

[0007] (2) As an embodiment of the present disclosure, in (1), when at least one of the concentration of the gas to be detected being equal to or higher than a first threshold value and the magnitude of the second detection signal being equal to or higher than a second threshold value is satisfied, the control unit outputs a signal indicating that leakage of the gas to be detected has been detected.

[0008] (3) As an embodiment of the present disclosure, in (1) or (2), the control unit switches between the first mode and the second mode based on the second detection signal.

[0009] (4) As an embodiment of the present disclosure, in (3), when the second detection signal is equal to or higher than a third threshold value and less than a second threshold value, the control unit increases the number of measurement times in the second mode and then switches from the second mode to the first mode.

[0010] (5) As one embodiment of the present disclosure, in either (3) or (4), when the second detection signal is zero or more and less than the third threshold value, the control unit switches from the second mode to the first mode.

[0011] (6) As one embodiment of the present disclosure, in (1) or (2), the control unit switches between the first mode and the second mode at a predetermined time.

[0012] (7) As one embodiment of the present disclosure, in any one of (1) to (6), when the control unit determines the possibility of leakage of the detected gas, the control unit increases the number of measurements in the second mode.

[0013] (8) As one embodiment of the present disclosure, in any one of (1) to (7), in the first mode, the control unit outputs the drive signal so that the drive frequency of the light source becomes the resonance frequency.

[0014] (9) As one embodiment of the present disclosure, in any one of (1) to (8), the control unit corrects the first detection signal based on at least one piece of information among the temperature, humidity, and pressure of the gas.

[0015] (10) As one embodiment of the present disclosure, in any one of (1) to (9), in the second mode, the control unit outputs the drive signal so that the light source does not emit light.

[0016] (11) As one embodiment of the present disclosure, in any one of (1) to (9), in the second mode, the control unit outputs the drive signal so that the light source emits light.

[0017] (12) As one embodiment of the present disclosure, in any one of (1) to (11), The light source is a quantum infrared light emitting element.

[0018] (13) As one embodiment of the present disclosure, in any one of (1) to (12), The light source is provided with a built-in sensor on the same element substrate and is capable of measuring the light emission amount.

[0019] (14) As one embodiment of the present disclosure, in any one of (1) to (13), The light source, the optical signal detection unit, and the acoustic wave detection unit are mounted in the internal space of the gas cell.

[0020] (15) As one embodiment of the present disclosure, in any one of (1) to (14), The optical signal detection unit is a detection element that captures acoustic waves generated by the gas to be detected absorbing light, and the optical signal detection unit and the acoustic wave detection unit are the same detection element.

[0021] (16) The gas detection system according to one embodiment of the present disclosure is the gas detection device according to any one of (1) to (15), and a notification device that notifies the user of gas leakage.

[0022] (17) The gas detection method according to one embodiment of the present disclosure is a light source that emits light according to a drive signal, an optical signal detection unit that detects a signal based on the emitted light and outputs a first detection signal, an acoustic wave detection unit that detects acoustic waves generated by leakage of the gas to be detected and outputs a second detection signal, a gas cell that has a hole through which the gas passes and introduces the gas into a gas detection space from the hole, and a control unit that outputs the drive signal, and is a gas detection method executed by the gas detection device, wherein the control unit executes a first mode of performing concentration calculation of the gas to be detected in the gas based on the first detection signal, and executes a second mode of determining leakage or the possibility of leakage of the gas to be detected based on the second detection signal. [Advantages of the Invention]

[0023] According to the present disclosure, it is possible to provide a gas detection device, a gas detection system, and a gas detection method that can detect gas leakage with high accuracy.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0025] Hereinafter, a gas detection device 1 (see FIG. 1) according to an embodiment of the present disclosure will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals. In the description of the present embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0026] (Gas Detection Device, Gas Detection System) FIG. 1 is a diagram showing the configuration of the gas detection device 1 according to the present embodiment. The gas detection device 1 is a device that detects leakage (gas leak) of a gas to be detected in a factory or the like. In the present embodiment, the gas detection device 1 also has a function of a device (gas sensor) that measures the concentration of the gas to be detected in a gas. The gas detection device 1 includes a light source 11, a detection unit 41, a gas cell 40, and a control unit 50. Further, the gas detection device 1 may include a substrate 30. FIG. 1 is a cross-sectional view showing a cross-section of the gas detection device 1 including these components. Details of the components of the gas detection device 1 will be described later.

[0027] A gas detection system may be configured by a gas detection device 1 and a notification device including at least one of a display, a light, and a speaker. That is, the gas detection device 1 may configure a gas detection system together with a notification device that notifies a user of a gas leak by at least one of information display, light, and sound when a gas leak is detected.

[0028] Here, the gas cell 40 has a hole 43 through which a gas (for example, ambient air) passes, and the gas is introduced from the hole 43 into the gas detection space 42. The gas detection device 1 measures the concentration of the gas to be detected in the introduced gas. The gas to be detected is a specific gas to be detected, and may be, for example, carbon dioxide, water vapor, carbon monoxide, nitrogen monoxide, ammonia, sulfur dioxide, alcohol, formaldehyde, methane, propane, chlorofluorocarbon, alternative chlorofluorocarbon, R32, R1234y, or the like.

[0029] The gas detection device 1 detects ultrasonic waves generated by leakage or the like of the gas to be detected, and outputs a signal indicating that the leakage or the like of the gas to be detected has been detected when it is determined that there is a gas leak or the like. In the gas detection system, the notification device receives a signal indicating that the leakage or the like of the gas to be detected has been detected, and notifies the user of the gas leak or the like by at least one of information display, light, and sound.

[0030] In addition to detecting gas leaks, the gas detection device 1 can measure the concentration of the gas to be detected in the gas introduced into the gas detection space 42 by the NDIR (Non-Dispersive InfraRed) method or the photoacoustic method, and output an electrical signal indicating the measurement result. The NDIR method detects light absorption by gas molecules with an optical sensor to measure the gas concentration. The photoacoustic method measures the gas to be detected by picking up the vibration of gas molecules that have absorbed light as sound (acoustic waves) with a high-performance microphone or the like.

[0031] The gas detection device 1 is configured to include a gas cell 40 on the main surface 30a of the substrate 30. Here, the main surface 30a is one of the surfaces of the substrate 30 having the largest area. As shown in FIG. 1, orthogonal coordinates are set such that the xy plane is parallel to the main surface 30a of the substrate 30. The z-axis direction is the direction perpendicular to the main surface 30a of the substrate 30. The z-axis direction may be referred to as the height direction or the vertical direction. The positive z-axis direction corresponds to the upward direction. In the present embodiment, the light source 11 and the detection unit 41 are disposed inside the gas detection space 42 above the main surface 30a.

[0032] (Substrate) The substrate 30 has a function of holding the gas cell 40, the light source 11, and the detection unit 41. In the present embodiment, the substrate 30 also holds the control unit 50. In the present embodiment, the substrate 30 is a PCB (printed circuit board) on which the light source 11, the detection unit 41, and the control unit 50 are mounted, and electrical connections between them are also made. The material of the substrate 30 is, for example, paper, glass cloth, ceramics, polyimide, liquid crystal polymer, or the like.

[0033] (Gas cell) The gas cell 40 has a gas detection space 42 for detecting the gas to be detected. The gas cell 40 is provided on the main surface 30a of the substrate 30. That is, the gas detection space 42 is an internal space surrounded by the outer wall of the gas cell 40 and the substrate 30. The material of the outer wall of the gas cell 40 can be, for example, metal, glass, resin, composite materials thereof, etc. The resin can be, for example, phenolic resin, epoxy resin, polyimide resin, bismaleimide triazine resin, fluororesin, polyphenylene oxide resin, LCP (liquid crystal polymer), PP (polypropylene), PEEK (polyether ether ketone), PA (polyamide), PPE (polyphenylene ether), PC (polycarbonate) or PPS (polyphenylene sulfide), PMMA (polymethyl methacrylate resin), PAR (polyarylate resin), etc., and hard resins obtained by mixing two or more of these can be mentioned. Further, the gas cell 40 is preferably made of a material with a small light absorption coefficient and a high reflectivity in order to efficiently confine the light emitted from the light source 11 within the gas cell 40. Specifically, a resin housing coated with an alloy containing aluminum, gold, silver, a dielectric, or a laminate thereof is preferred. When the inner surface of the gas cell 40 is formed by vapor deposition or plating on the resin housing, it is possible to improve high productivity and weight reduction as compared with the case of forming with a metal material. Also, the gas cell 40 may be formed by cutting, but from the viewpoint of productivity, it is preferably formed by injection molding or press working. Further, the gas cell 40 and the substrate 30 may be mechanically joined by an adhesive, a screw, a claw, a fitting, a grommet, welding, solder, etc.

[0034] (Light source) The light source 11 emits light including wavelengths absorbed by the gas to be detected. The light source 11 is also referred to as a light emitting part. The light source 11 may be provided on the main surface 30a of the substrate 30 inside the gas detection space 42. In this embodiment, the light is infrared light. That is, the light source 11 is composed of an infrared light emitting element. The light emitting element emits light according to a drive signal (specific examples are voltage or current pulses). It is preferable that the light emitting element can be driven at high speed. For example, it is preferable that the drive signal is a pulse of 15 kHz or more. The light emitting element may be, for example, an LED (Light Emitting Diode), a laser (Light Amplification by Stimulated Emission of Radiation), a MEMS heater, a lamp, etc. In this embodiment, the light source 11 is an LED (infrared LED) that emits infrared light. Also, it is preferable that the light source 11 is a quantum type infrared light emitting element that emits infrared light using electrons or holes in a semiconductor so that it can be driven at a high frequency.

[0035] Here, the gas detection device 1 may further include a drive unit that outputs a drive signal to drive the light emitting element. In this embodiment, the drive unit is included in the control unit 50. That is, a part of the control unit 50 functions as a drive unit.

[0036] Also, the light source 11 may be provided with auxiliary members having auxiliary optical functions such as wavelength selection, condensing, scattering, and wavelength conversion. Specifically, the auxiliary members are a wavelength selection filter, a lens, a phosphor, a diffraction grating, etc.

[0037] Also, when the light source 11 is a quantum type light emitting element such as an LED, an optical sensor (built-in sensor) capable of measuring the light emission amount of the light source 11 may be provided on the same element substrate. Since the light source deteriorates according to use, by monitoring the light emission amount, correction of deterioration becomes possible, and the life of the device can be extended.

[0038] Here, the wavelength of the infrared ray may be 2 μm to 12 μm. The region of 2 μm to 12 μm has many absorption bands specific to various gases and is a wavelength band particularly suitable for use in the gas detection device 1. For example, there are absorption bands of methane at a wavelength of 3.3 μm, carbon dioxide at a wavelength of 4.3 μm, and alcohol (ethanol) at a wavelength of 9.5 μm.

[0039] (Detection unit) The detection unit 41 detects a change corresponding to the abundance of the gas to be detected in measuring the concentration of the gas to be detected present in the gas in the gas detection space 42. The detection unit 41 may be provided on the main surface 30a of the substrate 30 inside the gas detection space 42. The light emitted from the light source 11 passes through the gas detection space 42 and is absorbed according to the abundance of the gas to be detected. The detection unit 41 detects a signal based on the light emitted from the light source 11 and outputs a first detection signal which is one of the detection signals. The detection unit 41 is a microphone in this embodiment, but is not limited thereto and may be a barometric pressure sensor or a pressure sensor, etc. Also, in this embodiment, the signal based on light is an acoustic wave (vibrational sound) from the gas molecules of the gas to be detected that has absorbed the light. That is, the detection unit 41 detects the acoustic wave and outputs the first detection signal. The detection unit 41 preferably has a configuration covered by a metal housing in order to suppress the influence of electromagnetic noise generated when the light source 11 is driven.

[0040] Also, the detection unit 41 detects a sound wave generated by leakage of the gas to be detected or the like and outputs a second detection signal. The second detection signal is one of the detection signals different from the first detection signal. Due to leakage (gas leak) of the gas to be detected or the like, for example, ultrasonic waves with a frequency of 30 kHz or more are generated. The ultrasonic waves have a significantly different frequency from, for example, the sounds generated during operation in a factory and reach the detection unit 41 through holes 43 or the like described later. Thus, in this embodiment, the detection unit 41 is a detection element that captures the acoustic wave generated when the gas to be detected absorbs light, and realizes a light signal detection unit that outputs the first detection signal and a sound wave detection unit that outputs the second detection signal with one (the same) detection element. Another configuration example of the detection unit 41 will be described later as a modification.

[0041] (Gas detection space) The gas detection space 42 is separated by an outer wall to form a space, and has the function of containing a gas such as air in its internal space. The gas contained in the gas detection space 42 is replaced through the hole 43.

[0042] (Hole) The hole 43 is provided in a part of the outer wall (side wall and ceiling) that partitions the gas detection space 42 of the gas cell 40. Gas passes through the hole 43, and the gas in the gas detection space 42 is replaced. There may be a plurality of holes 43. Here, the hole 43 may be provided with a dust-proof filter (dust-proof filter). The dust-proof filter may be, for example, a non-woven fabric, a Teflon (registered trademark) sheet, or the like. For example, when detecting a gas leak in a pipe through which the gas to be detected passes, the gas detection device 1 may be installed such that the hole 43 is near the pipe.

[0043] (Control unit) The control unit 50 controls the entire gas detection device 1. In addition, the control unit 50 executes arithmetic processing to obtain the concentration of the gas to be detected. That is, the control unit 50 calculates the concentration of the gas to be detected in the gas introduced into the gas detection space 42 based on the first detection signal from the detection unit 41. In addition, the control unit 50 determines the leakage or the possibility of leakage of the gas to be detected based on the second detection signal. The control unit 50 may be configured to include one or more processors. The processor may be, for example, a general-purpose processor or a dedicated processor specialized for specific processing, but is not limited thereto and can be any processor. The control unit 50 may be provided outside the gas detection space 42 (see FIG. 1), or may be provided inside the gas detection space 42. Further, the control unit 50 may be provided on the main surface 30a of the substrate 30, but may be embedded in the substrate 30, for example, or provided on the back surface opposite to the main surface 30a. Details of the concentration calculation and leakage determination of the gas to be detected by the control unit 50 will be described later.

[0044] (Gas detection device design) In the gas detection device 1 according to the present embodiment, the gas detection space 42 is partitioned by an outer wall and provided as an internal space of a structure (gas cell 40) that is close to a rectangular parallelepiped, for example. Therefore, by utilizing the resonance mode of the gas cell 40, that is, the fact that sound waves of a specific frequency (natural frequency) are greatly amplified, the sound picked up by the microphone (detection unit 41) can be increased. If the sound picked up by the microphone is increased, the influence of noise can be reduced, so that the measurement accuracy of the gas detection device 1 can be improved. By setting the driving frequency of the light source 11 to a resonance frequency substantially equal to the natural frequency of the resonance mode of the gas cell 40, the output of the detection unit 41, which is a microphone, can be increased.

[0045] Here, regarding the light emission state of the light source 11, if the state of emitting light is set to ON and the state of not emitting light is set to OFF, the driving frequency of the light source 11 is determined by the ON interval. In the present embodiment, the light source 11, which is an infrared light emitting element, emits light so as to repeat ON and OFF according to a driving signal. For example, if the driving signal is a pulse that takes a high level and a low level, the light source 11 turns ON when the driving signal is at a high level and turns OFF when the driving signal is at a low level. Therefore, the driving frequency of the light source 11 can be determined by the driving signal. Here, the duty ratio (the time that is ON with respect to the period) of the driving signal is not limited, but may be set to 10% or more and 50% or less as an example.

[0046] FIG. 2 is a diagram illustrating the change in the output of the microphone (detection unit 41) when the driving frequency of the light source 11 is changed. The gas cell 40 used in the experiment of FIG. 2 has a size of 1.06×0.96×0.85 cm 3 and has a hole 43 with a diameter of 1 mm. A driving current of 350 mA is applied to the light source 11, which is an infrared LED, and the duty ratio is 30%. When the driving frequency of the light source 11 was changed by 1 kHz in the range of 16 to 23 kHz, the output of the microphone (detection unit 41) became larger at 21 kHz compared to others. In the example of FIG. 2, the resonance frequency is considered to be 21 kHz.

[0047] (Concentration calculation) Here, the natural frequency (f n : n = 1, 2, 3, …) of the resonance mode of the gas cell 40 can be calculated by the following formula (1). To simplify the explanation, it is assumed that the shape of the gas cell 40 is a cube, and L x , L y , L z are such that L x = L y = L z = L holds. If L is the volume of the gas detection space 42 as V, then it is the cube root of V.

[0048]

Equation

[0049] Here, λ n is the wavelength of the natural frequency. c is the speed of sound. k is the specific heat ratio of the gas. R is the gas constant. T is the temperature of the gas. M is the molar mass of the gas. FIG. 3 is a diagram showing the resonance modes (n = 1, 2, 3) in the gas cell 40. Here, as the resonance frequency, a driving frequency that is approximately equal to the natural frequency when n = 1 may be used, or a driving frequency that is approximately equal to the natural frequency in cases other than n = 1 may be used. For example, the value of n may be selected so as to avoid the influence of noise present in the environment where the gas detection device 1 is used.

[0050] Here, as the concentration calculation of the detected gas, the control unit 50 acquires the vibration of the gas molecules of the detected gas that has absorbed light as a first detection signal which is the microphone output, and calculates the concentration of the detected gas according to the amplitude (magnitude) thereof. The control unit 50 has a plurality of operation modes. The plurality of operation modes include a first mode and a second mode which will be described later. When the operation mode of the control unit 50 that performs the concentration calculation of the detected gas from the amplitude of the first detection signal is the first mode, the control unit 50 may output a drive signal so that the drive frequency of the light source 11 becomes the resonance frequency in the first mode. By using the resonance frequency, highly accurate measurement is possible. Also, the resonance frequency is preferably the same frequency as the ultrasonic wave (for example, 30 kHz or more). In this case, the concentration measurement of the detected gas and the ultrasonic detection can be executed without greatly expanding the sensitivity band of the detection unit 41 (microphone). Also, in the first mode, it becomes possible to avoid noise present in an environment such as a factory and measure the concentration of the detected gas with higher accuracy. Here, that the drive frequency of the light source 11 becomes the resonance frequency is not strictly limited to the case where the drive frequency of the light source 11 exactly matches the resonance frequency. For example, that the drive frequency of the light source 11 becomes the resonance frequency may include that the drive frequency is 0.9 times or more and 1.1 times or less of the resonance frequency. Also, for example, that the drive frequency of the light source 11 becomes the resonance frequency may include that there is a deviation of about -1 kHz to +1 kHz between the drive frequency and the resonance frequency.

[0051] Also, in the gas detection device 1, the magnitude of the ultrasonic wave can be detected from the amplitude of the second detection signal. The control unit 50 determines the leakage or the possibility of leakage of the detected gas based on the second detection signal. Here, when the determination of gas leakage based on the second detection signal is the second mode, in the second mode, for example, an ultrasonic wave with a frequency of 30 kHz or more can be detected, and a small amount of gas leakage can be detected. Also, when a large amount of gas leakage occurs, no ultrasonic wave is generated, but it is detected by the concentration measurement of the detected gas in the above-described first mode that a large amount of gas leakage has occurred. Therefore, by switching between the first mode and the second mode and executing by the control unit 50, leak-free and highly accurate gas detection becomes possible.

[0052] When at least one of the conditions that the concentration of the detected gas is equal to or higher than the first threshold value and the magnitude of the second detection signal is equal to or higher than the second threshold value is satisfied, the control unit 50 may output a signal indicating that leakage or the like of the detected gas has been detected. In the first mode, the control unit 50 may calculate the concentration of the detected gas, and if the concentration of the detected gas is equal to or higher than the first threshold value (for example, 30,000 ppm), it may be determined that there is gas leakage. In the second mode, the control unit 50 may determine that there is gas leakage if the magnitude (microphone output) of the second detection signal is equal to or higher than the second threshold value (for example, 5 mV). Here, in the second mode, if the magnitude of the second detection signal is greater than zero and less than the second threshold value, the control unit 50 may determine that there is a possibility of gas leakage. When the control unit 50 determines that there is gas leakage, a signal indicating the gas leakage determination may be output to the notification device, and the notification device may notify the user of the gas leakage by at least one of information display, light, and sound.

[0053] The control unit 50 may switch between the first mode and the second mode as follows. For example, when the second mode is being executed, the control unit 50 may switch between the first mode and the second mode based on the second detection signal. For example, when the second detection signal is equal to or higher than zero and less than a third threshold value described later, that is, when ultrasonic waves are not generated, the control unit 50 may switch from the second mode to the first mode. Also, for example, when the second detection signal is equal to or higher than the third threshold value and less than the second threshold value, that is, when it is determined that there is a possibility of gas leakage, the control unit 50 may increase the number of measurement times in the second mode and then switch from the second mode to the first mode. By this, when there is a risk of gas leakage, ultrasonic detection can be performed for a longer time.

[0054] The control unit 50 may switch between the first mode and the second mode at a predetermined time. The predetermined time may be, for example, when a certain state has elapsed for a certain period of time, or it may be a preset time. The set time may be, for example, a regular time such as every hour. By switching between the first mode and the second mode according to time, the concentration measurement of the detected gas and the ultrasonic detection will surely be executed. Here, as described above, when the control unit 50 determines that there is a possibility of gas leakage, it may increase the number of measurements in the second mode.

[0055] Here, FIG. 4 illustrates the change in the microphone output depending on whether the light source 11 is driven or not in the second mode. The upper diagram of FIG. 4 shows when the light source 11 is not driven, and the drive signal remains at a low level. Also, the lower diagram of FIG. 4 shows when the light source 11 is driven, and the drive signal is a pulse that takes high and low levels. The control unit 50 may output a drive signal so that the light source 11 does not emit light (so that the light source 11 is not driven) in the second mode. In this case, the control unit 50 can directly associate the microphone output with the ultrasonic detection level, and the processing load related to the determination of gas leakage is reduced. Also, the control unit 50 may output a drive signal so that the light source 11 emits light (so that the light source 11 is driven) in the second mode. In this case, the control unit 50 may continue to output the same drive signal, for example, in both the first mode and the second mode, and the processing load related to the control of the drive signal is reduced. However, as shown in the lower diagram of FIG. 4, the microphone output shows a waveform in which the drive signal and the ultrasonic detection level are superimposed. The control unit 50 needs to specify the ultrasonic detection level in consideration of the level variation according to the change in the drive signal from the microphone output.

[0056] Here, it is preferable that the temperature, humidity, and pressure of the gas are known in the measurement of the detected gas. For example, in the environment where the gas detection device 1 is used, it is preferable that information on the temperature, humidity, and pressure of the gas can be obtained from a temperature sensor, a humidity sensor, a pressure sensor, etc. At this time, the control unit 50 may correct the first detection signal based on at least one piece of information among the temperature, humidity, and pressure of the gas. By performing the correction, the measurement accuracy can be further improved. Here, a known method may be used for correcting the detection signal based on at least one piece of information among the temperature, humidity, and pressure.

[0057] The control unit 50 switches between the first mode and the second mode, and may further have a standby mode. The standby mode is a state in which neither the first mode nor the second mode is executed. The operation mode of the control unit 50 transitions among the first mode, the second mode, and the standby mode. For example, if it waits (measurement is not immediately performed) after the execution of the first mode, the operation mode of the control unit 50 transitions to the standby mode.

[0058] FIG. 5 is a flowchart exemplifying the gas detection method executed by the gas detection device 1 according to the present embodiment. In the example of FIG. 5, it is described that gas leakage is detected. In the example of FIG. 5, at the start of the process, the operation mode of the control unit 50 is the standby mode (step S1).

[0059] The control unit 50 sets the operation mode to the first mode and calculates the concentration of the detected gas in the gas (step S2). That is, the control unit 50 performs measurement in the first mode.

[0060] If the concentration of the detected gas is equal to or higher than the first threshold value (for example, 30,000 ppm) (Yes in step S3), the control unit 50 determines that there is gas leakage and outputs a signal for detecting gas leakage (step S9). If the concentration of the detected gas is less than the first threshold value (No in step S3), the control unit 50 proceeds to the process of step S4.

[0061] The control unit 50 determines gas leakage based on the second detection signal with the operation mode being the second mode (step S4). That is, the control unit 50 performs measurement in the second mode.

[0062] If the magnitude of the second detection signal is equal to or greater than a second threshold value (e.g., 5 mV) (Yes in step S5), the control unit 50 determines that there is a gas leak and outputs a signal for detecting gas leak (step S9).

[0063] If the magnitude of the second detection signal is less than the second threshold value (No in step S5), the control unit 50 compares it with a third threshold value which is less than the second threshold value and greater than zero. If the magnitude of the second detection signal is equal to or greater than the third threshold value (Yes in step S6), the control unit 50 determines that there may be a gas leak and increases the number of measurements in the second mode (step S7). That is, the control unit 50 increases the preset value of N times described later and sets it to perform more frequent determination of gas leakage in the second mode.

[0064] After step S7 or when it is determined that there is no possibility of gas leak (No in step S6), the control unit 50 checks the number of times of determining gas leakage based on the second detection signal in the second mode (step S8). That is, the control unit 50 performs a branch of processing based on the number of times of measurement in the second mode. If the number of measurements in the second mode is less than N times, the control unit 50 returns to the processing of step S4. If the number of measurements in the second mode is N times or more, the control unit 50 returns to the processing of step S2.

[0065] The flowchart of FIG. 5 is an example of the processing of the gas detection method. As another example, the execution of the first mode may be repeated in the first cycle, and the execution of the second mode may be repeated in a second cycle shorter than the first cycle. Also, in the second mode, only the presence or absence of gas leak may be determined, and the determination that there may be a gas leak may be omitted.

[0066] Also, in the example of FIG. 5, after the control unit 50 enters the standby mode (step S1), the operation mode is set to the first mode. Here, after the standby mode, the control unit 50 can adopt a gas detection method in which the operation mode is set to the second mode. In this case, the flowchart will be the one in which the processes of steps S2 to S3 and the processes of steps S4 to S8 in FIG. 5 are swapped.

[0067] As described above, the gas detection device 1, the gas detection system, and the gas detection method according to the present embodiment can correctly detect gas leakage even when, for example, ultrasonic waves are not generated, and can detect gas leakage with high accuracy due to the above configuration.

[0068] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications or corrections based on the present disclosure. Therefore, it should be noted that these modifications or corrections are included in the scope of the present disclosure.

[0069] In the above embodiment, the gas detection device 1 is realized with the configuration of a photoacoustic gas sensor. However, a configuration (hereinafter referred to as "configuration of the modification example") in which a microphone for detecting ultrasonic waves is combined with an NDIR type gas sensor is possible. That is, in the above embodiment, the detection unit 41 is composed only of a microphone that also serves as an optical signal detection unit that outputs a first detection signal and a sound wave detection unit that outputs a second detection signal. On the other hand, in the configuration of the modification example, the detection unit 41 may be composed of a separate element microphone (functioning as means for detecting ultrasonic waves) and an optical signal detection unit. In an NDIR type gas sensor, the wavelength of infrared rays absorbed varies depending on the type of gas, and the concentration of the gas to be detected is measured by detecting this absorption amount. Also in this modification example, the detection unit 41 detects a signal based on the light emitted from the light source 11 and outputs a first detection signal, but the signal based on the light is not an acoustic wave but infrared rays after being absorbed by the gas to be detected.

[0070] In the configuration of the modification, the detection unit 41 has a light receiving element as a light signal detection unit in addition to the microphone. The light receiving element may be provided with an optical filter for selecting the wavelength of the received light, or may have a configuration without an optical filter. The light receiving element is, for example, a quantum type infrared sensor. A quantum type infrared sensor is a sensor that detects infrared rays by using electrons or holes generated by the light quanta when the semiconductor is irradiated with infrared rays. The light receiving element is not limited to a quantum type infrared sensor, and may be other types of sensors such as a thermal type infrared sensor. However, since the quantum type infrared sensor has higher sensitivity and a faster response speed than the thermal type infrared sensor, it is preferable that the light receiving element is a quantum type infrared sensor. The light receiving element outputs a signal corresponding to the amount of received light (infrared ray amount) as a first detection signal. The material of the quantum type infrared sensor is not limited to a specific one. However, the quantum type infrared sensor preferably contains at least one of indium and gallium and at least one of arsenic and antimony as materials, and has a diode structure composed of at least two types of layers, a P-type semiconductor and an N-type semiconductor. Also, as a method for the control unit 50 to calculate the concentration of the gas to be detected in the gas based on the first detection signal, a known method may be used. In the configuration of the modification, the arrangement of the microphone has a high degree of freedom. For example, as shown in FIG. 6, the light source 11 and the light signal detection unit (light receiving element) may be mounted in the internal space of the gas cell 40, and the sound wave detection unit (microphone) may be mounted outside the gas cell 40. For example, as shown in FIG. 7, the light source 11, the light signal detection unit (light receiving element), and the sound wave detection unit (microphone) may be mounted in the internal space of the gas cell 40.

Explanation of Signs

[0071] 1 Gas detection device 11 Light source 30 Substrate 30a Main surface 40 Gas cell 41 Detection unit 42 Gas detection space 43 Hole 50 Control unit

Claims

1. A light source that emits light according to a drive signal, An optical signal detection unit that detects a signal based on the emitted light and outputs a first detection signal, and a sound wave detection unit that detects a sound wave generated by leakage of the gas to be detected and outputs a second detection signal, A gas cell having a hole through which the gas passes and introducing the gas from the hole into a gas detection space, A control unit that switches and executes a plurality of operation modes, The plurality of operation modes include a first mode that outputs the drive signal and performs concentration calculation of the gas to be detected in the gas based on the first detection signal, and a second mode that determines leakage or the possibility of leakage of the gas to be detected based on the second detection signal. A gas detection device.

2. When at least one of the concentration of the gas to be detected being equal to or higher than a first threshold value and the magnitude of the second detection signal being equal to or higher than a second threshold value is satisfied, the control unit outputs a signal indicating that leakage of the gas to be detected has been detected. The gas detection device according to claim 1.

3. The control unit switches between the first mode and the second mode based on the second detection signal. The gas detection device according to claim 1 or 2.

4. When the second detection signal is equal to or higher than a third threshold value and less than a second threshold value, the control unit increases the number of measurement times in the second mode and then switches from the second mode to the first mode. The gas detection device according to claim 3.

5. When the second detection signal is equal to or higher than zero and less than a third threshold value, the control unit switches from the second mode to the first mode. The gas detection device according to claim 3.

6. The control unit switches between the first mode and the second mode at a predetermined time. The gas detection device according to claim 1 or 2.

7. The gas detection device according to claim 1 or 2, wherein when the control unit determines the possibility of leakage of the detected gas, the control unit increases the number of measurement times in the second mode.

8. The gas detection device according to claim 1 or 2, wherein in the first mode, the control unit outputs the drive signal so that the drive frequency of the light source becomes the resonance frequency.

9. The gas detection device according to claim 1 or 2, wherein the control unit corrects the first detection signal based on at least one piece of information among the temperature, humidity, and pressure of the gas.

10. The gas detection device according to claim 1 or 2, wherein in the second mode, the control unit outputs the drive signal so that the light source does not emit light.

11. The gas detection device according to claim 1 or 2, wherein in the second mode, the control unit outputs the drive signal so that the light source emits light.

12. The gas detection device according to claim 1 or 2, wherein the light source is a quantum type infrared light emitting element.

13. The gas detection device according to claim 1 or 2, wherein the light source is provided with a built-in sensor on the same element substrate and can measure the light emission amount.

14. The gas detection device according to claim 1 or 2, wherein the light source, the optical signal detection unit, and the acoustic wave detection unit are mounted in the internal space of the gas cell.

15. The optical signal detection unit is a detection element that captures acoustic waves generated by the detected gas absorbing light, and the optical signal detection unit and the acoustic wave detection unit are the same detection element. The gas detection device according to claim 1 or 2.

16. The gas detection device according to claim 1 or 2, and An alarm device that notifies the user of gas leakage, a gas detection system comprising.

17. A gas detection method executed by a gas detection device, comprising: a light source that emits light according to a drive signal; an optical signal detection unit that detects a signal based on the emitted light and outputs a first detection signal; a sound wave detection unit that detects a sound wave generated by leakage of the gas to be detected and outputs a second detection signal; a gas cell having a hole through which the gas passes and introducing the gas from the hole into a gas detection space; and a control unit that outputs the drive signal. The control unit executes a first mode in which the concentration of the gas to be detected in the gas is calculated based on the first detection signal; and executes a second mode in which the leakage or the possibility of leakage of the gas to be detected is determined based on the second detection signal.

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