Infrared gas sensor and stationary gas detection device

Abstract

An infrared gas sensor (110) includes: a light-emitting unit (120) that is disposed in a pressure-resistant explosion-proof container (111) having a light-transmitting window (115) and emits infrared light onto a measurement region (S) formed so that a test gas flows outside the pressure-resistant explosion-proof container (111); a light-receiving unit (130) including a measurement light-receiving sensor (131), which receives measurement light in a mid-infrared region via a measurement band-pass filter (132), and a reference light-receiving sensor (136), which receives reference light via a reference band-pass filter (137); and a long-pass filter (150) that is disposed on the optical path between the light-emitting unit (120) and the light-transmitting window (115) and reduces the transmittance of light, from the visible region to the near-infrared region, that passes through the light-transmitting window (115). A stationary gas detection device (100) includes the infrared gas sensor (110).

Description

Infrared gas sensor and fixed gas detection device

[0001] The present invention relates to an infrared gas sensor whose measurement region is open to the atmosphere and a fixed gas detection device equipped with the infrared gas sensor.

[0002] A non-dispersive infrared absorption gas sensor (hereinafter referred to as "infrared gas sensor") that detects the concentration of a target gas by detecting the amount of change in infrared radiation due to absorption of the target gas in the test gas is known, and is configured to enable high-speed response by opening the measurement area to the atmosphere (see, for example, Patent Document 1).

[0003] In the infrared gas sensor described in Patent Document 1, an infrared light source, a measurement light-receiving sensor that detects measurement light in a wavelength range that includes the absorption wavelength of the target gas, and a reference light-receiving sensor that detects reference light that has a lower absorption rate with the target gas than the measurement light are disposed within a housing having a light-transmitting window, and a reflective member that reflects light emitted through the light-transmitting window is disposed outside the housing so as to form a measurement region open to the atmosphere between the housing and the reflective member. A beam splitter is disposed on the optical path from the reflective member within the housing to the measurement light-receiving sensor, reflecting a portion of the light to be incident on the reference light-receiving sensor and transmitting the rest of the light to be incident on the measurement light-receiving sensor. In addition, the measurement light-receiving sensor and the reference light-receiving sensor usually have bandpass filters that filter the measurement light and the reference light, and the measurement light-receiving sensor and the reference light-receiving sensor detect the measurement light and the reference light, respectively.

[0004] In addition, in an infrared gas sensor having such a configuration, a band-pass filter that transmits light in a specific wavelength range is disposed on the optical path from the infrared light source to the reflecting member within the housing, and light in the specific wavelength range is selectively emitted to the measurement region (see, for example, Patent Document 2).

[0005] Therefore, gas detection devices equipped with infrared gas sensors used in explosive atmospheres are required to meet explosion-proof requirements such as intrinsic safety and pressure-resistant explosion-proof. In recent years, when devices using light sources that emit powerful energy are used, there is a risk that the light radiation characteristics of the light source may ignite the surrounding explosive atmosphere, so they are also required to meet requirements to prevent ignition by emitted light (optical radiation explosion-proof requirements). In infrared gas sensors with a measurement area open to the atmosphere as described above, the light from the infrared light source is emitted outside the housing, so they must meet the optical radiation explosion-proof requirements.

[0006] The optical radiation explosion-proof requirements may apply to any components equipped with a focusing optical system such as a lens or reflector for the light emitted outside the housing. Furthermore, the optical radiation explosion-proof requirements require that the product meet the requirements not at its normal driving voltage (or driving current or driving power), but at the driving voltage (or driving current or driving power) just before the product fails. Therefore, in order for an infrared gas sensor to meet the optical radiation explosion-proof requirements, it is necessary to consider the optical energy emitted from the infrared light source when the product fails.

[0007] US Patent Application Publication No. 2001 / 0015408 European Patent Application Publication No. 0457624

[0008] Infrared light sources, such as lamps and LEDs, typically used in infrared gas sensors are designed to prevent breakdowns, such as wire breakage. Therefore, just before a breakdown occurs, the voltage (or current or power) applied to the infrared light source increases, resulting in stronger light energy emitted from the infrared light source. While this can be addressed by incorporating overpower fault protection into the electrical circuit, such as a current and / or voltage limiter installed between the infrared light source and the power source, this increases the complexity of the circuit configuration, which is a significant disadvantage in product design. In particular, unlike battery-powered portable detectors, designing an overpower fault protection circuit for stationary detectors is difficult because the original power source (voltage) supplied to the product is a factor.

[0009] On the other hand, as in the infrared gas sensor described in Patent Document 2, if the light emitted from the infrared light source is filtered by a bandpass filter and then emitted outside the housing, it is believed that the optical radiation explosion-proof requirements can be met. However, because the bandpass filter selectively transmits light in a specific narrow wavelength range, the amount of light emitted into the measurement area is reduced. To achieve stable gas detection performance, it is necessary to increase the amount of light emitted to the light receiving sensor. However, if the light from the infrared light source is filtered by a bandpass filter before being emitted outside, problems arise, such as difficulty in aligning the light receiving sensor (optical adjustment) and high manufacturing costs. In order to increase the amount of light reaching the light receiving sensor, it is necessary to increase the size of the bandpass filter, but bandpass filters themselves are expensive compared to other optical filters, which increases manufacturing costs.

[0010] The present invention was completed in view of the above circumstances, and aims to provide an infrared gas sensor with a simple configuration that can satisfy the requirements for optical radiation explosion protection and that can reduce manufacturing costs, and to provide a fixed gas detection device that can satisfy the requirements for optical radiation explosion protection and that is capable of high-speed response.

[0011] The infrared gas sensor of the present invention is an infrared gas sensor that detects the concentration of a target gas by detecting, with a light-receiving unit, a change in infrared light emitted from a light-emitting unit due to absorption by the target gas in the test gas, and that includes a pressure-resistant explosion-proof container having a light-transmitting window, and the light-emitting unit is disposed within the pressure-resistant explosion-proof container. The light-emitting unit is configured to emit infrared light through the light-transmitting window toward a measurement region that is formed so that the test gas flows outside the pressure-resistant explosion-proof container and is open to the atmosphere. The light-receiving unit includes a measurement light-receiving sensor that receives light through a measurement bandpass filter that transmits measurement light in the mid-infrared region that includes the absorption wavelength of the target gas, and a reference light-receiving sensor that receives light through a reference bandpass filter that transmits reference light that is less absorbed by the target gas than the measurement light. The above-mentioned problem is solved by configuring the infrared gas sensor to include a long-pass filter that reduces the transmittance of light in the visible to near-infrared region that passes through the light-transmitting window on the optical path between the light-emitting unit and the light-transmitting window. Furthermore, the fixed gas detection device of the present invention is a fixed gas detection device comprising a device main body having an explosion-proof structure and a gas sensor that is detachably attached to the device main body, and solves the above-mentioned problems by configuring the gas sensor as the above-mentioned infrared gas sensor.

[0012] According to the first aspect of the present invention, the emission of light in the visible to near-infrared range outside the pressure-resistant explosion-proof enclosure is suppressed, thereby ensuring sufficient light intensity for gas detection for the measurement light in the wavelength range that absorbs the target gas and the reference light in the wavelength range where the absorption intensity by the target gas is lower than that of the measurement light, while minimizing the energy of the light emitted outside the pressure-resistant explosion-proof enclosure. Therefore, an infrared gas sensor that satisfies the desired optical radiation explosion-proof requirements can be constructed with a simple configuration of a long-pass filter, without providing overpower fault protection in the electrical circuit, such as a current and / or voltage limiter, between the infrared light source and the power supply. Furthermore, since long-pass filters are less expensive than band-pass filters, they can be manufactured cost-effectively.

[0013] According to the invention of claim 2, miniaturization can be achieved while ensuring a sufficient optical path length required for gas detection, making it suitable for application to, for example, a fixed gas detection device in which the gas sensor is detachably attached to the device body. According to the invention of claim 3, a sufficient amount of light can reach the measurement light-receiving sensor and the reference light-receiving sensor while satisfying the desired optical radiation explosion-proof requirements, thereby ensuring highly reliable gas detection. According to the invention of claim 4, the output of the measurement light-receiving sensor and the output of the reference light-receiving sensor can be used, enabling stable gas detection. According to the invention of claim 5, since the infrared gas sensor has a measurement region open to the atmosphere, high-speed gas detection is possible, and a pressure-resistant explosion-proof fixed gas detection device that satisfies the optical radiation explosion-proof requirements can be provided.

[0014] The present invention relates to an infrared gas sensor, a fixed gas detection device, and a method for detecting a gas emitted from an infrared gas sensor.

[0015] As shown in FIG. 1, the infrared gas sensor 110 according to this embodiment is a single-light-source, two-wavelength non-dispersive infrared absorption gas sensor, and includes a pressure-resistant explosion-proof container 111 having a light-transmitting window 115, a light-emitting unit 120 and a light-receiving unit 130 disposed within the pressure-resistant explosion-proof container 111, and a reflecting member 140 disposed outside the pressure-resistant explosion-proof container 111.

[0016] The pressure-resistant explosion-proof container 111 is made of, for example, stainless steel, and has an opening 112 that opens in one direction. A plate-shaped light-transmitting member 116 is provided at the opening 112 of the pressure-resistant explosion-proof container 111 to airtightly close the opening 112, thereby forming a light-transmitting window 115. In this embodiment, the light-transmitting member 116 is made of, for example, sapphire, but the material, thickness, and other specific configurations are not particularly limited as long as it can transmit light in the wavelength range required for gas detection and can satisfy the desired explosion-proof requirements.

[0017] The light-emitting unit 120 includes an infrared light source 121 and a reflector 122 provided to surround the infrared light source 121, and is configured to emit light emitted from the infrared light source 121 directly or after being reflected by the reflector 122 to the outside of the pressure-resistant explosion-proof container 111 through the light-transmitting window 115. The infrared light source 121 is not particularly limited as long as it is a light source that can output infrared light in a wavelength range that includes the absorption wavelength of the target gas, and for example, a filament lamp or an LED can be used.

[0018] The light receiving unit 130 includes a measurement light receiving sensor 131 disposed at a position capable of receiving light reflected by the reflecting member 140 on the wall surface facing the light transmitting window 115 of the pressure-resistant explosion-proof container 111, and a reference light receiving sensor 136 disposed on a wall surface different from the wall surface on which the measurement light receiving sensor 131 is disposed. In Fig. 1, 133 denotes a main board having, for example, a light source drive circuit for the infrared light source 121 and an output processing circuit for the measurement light receiving sensor 131, and 138 denotes a sub-board having an output processing circuit for the reference light receiving sensor 136.

[0019] In this embodiment, the measurement light-receiving sensor 131 is equipped with a measurement band-pass filter 132 that transmits measurement light in the mid-infrared region that includes the absorption wavelength of the target gas, and the measurement light is filtered by receiving light reflected by the reflecting member 140 through the measurement band-pass filter 132. Note that the measurement light-receiving sensor 131 does not need to be equipped with the measurement band-pass filter 132 itself, and the measurement band-pass filter 132 may be separately disposed on the optical path from the reflecting member 140 to the measurement light-receiving sensor 131 inside the pressure-resistant explosion-proof container 111.

[0020] The reference light-receiving sensor 136 also includes a reference bandpass filter 137 that transmits reference light in the mid-infrared range, which has a lower absorption intensity due to the target gas than the measurement light. Light reflected by the reflecting member 140 is received through the reference bandpass filter 137, filtering the reference light. Using a wavelength for the reference light that is absorbed less by the target gas than the measurement light increases the intensity difference between the measurement light and the reference light in the presence of the target gas. This allows the output of the reference light-receiving sensor 136 to easily detect changes in the output due to the target gas when reducing the influence of external disturbances from the output of the measurement light-receiving sensor 131. The reference light may have a wavelength that is not absorbed by the target gas. The reference light-receiving sensor 136 is similar to the measurement light-receiving sensor 131, and the reference bandpass filter 137 may be separately disposed on the optical path from the reflecting member 140 to the reference light-receiving sensor 136 within the pressure-resistant explosion-proof container 111.

[0021] In this way, by providing the measurement bandpass filter 132 and the reference bandpass filter 137 on the light-receiving unit 130 side rather than on the light-emitting unit 120 side, it is possible to increase the amount of light in the mid-infrared range that reaches the light-receiving unit 130. This eliminates the need for lenses or reflectors with complex shapes, making it possible to simplify the design of the optical paths to the measurement light-receiving sensor 131 and the reference light-receiving sensor 136. Furthermore, since the measurement bandpass filter 132 and the reference bandpass filter 137 may be small in size, it is possible to reduce manufacturing costs.

[0022] A beam splitter 135 is disposed on the optical path from the reflecting member 140 inside the pressure-resistant explosion-proof vessel 111 to the measurement light-receiving sensor 131. The beam splitter 135 reflects a portion of the light that has passed through the light-transmitting window 115 so that it is received by the reference light-receiving sensor 136, and transmits the rest of the light so that it is received by the measurement light-receiving sensor 131. In this manner, by configuring the measurement light-receiving sensor 131 and the reference light-receiving sensor 136 to receive light that is disposed on different wall surfaces, the outputs of the measurement light-receiving sensor 131 and the reference light-receiving sensor 136 can be used, enabling stable gas detection.

[0023] A pair of rod-shaped support members 114 are erected on the outer surface of the wall of the pressure-resistant explosion-proof container 111, on which the light-transmitting window 115 is provided, so as to extend in the same direction at positions facing each other with the light-transmitting window 115 in between. The reflecting member 140 is supported by the support members 114 at a position spaced a predetermined distance in one direction from the light-transmitting window 115. As a result, a measurement region S that is open to the atmosphere is formed between the pressure-resistant explosion-proof container 111 and the reflecting member 140, so that the test gas flows outside the pressure-resistant explosion-proof container 111. The maximum distance L between the outer surface of the light-transmitting window 115 and the reflecting surface of the reflecting member 140 is set within a range of, for example, 20 to 40 mm, thereby ensuring a sufficient optical path length required for gas detection while miniaturizing the infrared gas sensor 110.

[0024] In the infrared gas sensor 110, a long-pass filter 150 is disposed on the optical path from the infrared light source 121 to the reflecting member 140 within the pressure-resistant explosion-proof container 111. The long-pass filter 150 reduces the transmittance of light in the visible to near-infrared range, for example, light in the wavelength range of 0.38 μm to 3 μm, which passes through the light-transmitting window 115. This allows light in the mid-infrared wavelength range to be mainly emitted to the outside of the pressure-resistant explosion-proof container 111.

[0025] The long-pass filter 150 is, for example, a filter for light in the mid-infrared region, for example, a filter for measuring a combustible gas or CO ２It is preferable to use a long-pass filter 150 having a transmittance of 80% or more for light having wavelengths at which the infrared ray absorbs infrared light. This allows a sufficient amount of light to reach the measurement light-receiving sensor 131 and the reference light-receiving sensor 136 while satisfying the desired optical radiation explosion-proof requirements, thereby ensuring highly reliable gas detection. Specifically, the long-pass filter 150 preferably has a transmittance of 80% or more for light in the wavelength range of 2.7 to 14.0 μm, and more preferably has a transmittance of 80% or more for light in the wavelength range of 3.0 to 4.5 μm, or a transmittance of 80% or more for light in the wavelength range of 4.5 to 14.0 μm. Furthermore, it is preferable that the long-pass filter 150 has a transmittance of 20% or less for light in the visible to near-infrared range, for example, light in the range of 0.38 μm to 2.7 μm. Using a long-pass filter 150 with such optical characteristics, the infrared gas sensor 110 can be configured to satisfy the desired optical radiation explosion-proof requirements.

[0026] In the above, the gas to be detected by the infrared gas sensor 110 is a gas having an absorption wavelength in the mid-infrared range, such as hydrocarbon gases such as methane and isobutane and other flammable gases; toxic gases such as carbon monoxide gas; or carbon dioxide gas.

[0027] As shown in FIG. 2, the infrared light source 121 used in the infrared gas sensor 110 has wavelength characteristics that show a peak intensity within a wavelength range λa from the visible range to the near-infrared range, and the amount of light is greater than the amount of light within the wavelength range λb used for gas detection.

[0028] However, in the above-described infrared gas sensor 110, the long-pass filter 150 is disposed on the optical path from the infrared light source 121 to the reflecting member 140 within the pressure-resistant explosion-proof enclosure 111, thereby suppressing the emission of light in the visible to near-infrared range outside the pressure-resistant explosion-proof enclosure 111. This makes it possible to minimize the energy of light emitted outside the pressure-resistant explosion-proof enclosure 111 while ensuring sufficient light intensity necessary for gas detection for the measurement light in a wavelength range that absorbs the target gas and the reference light in a wavelength range where the absorption intensity by the target gas is lower than that of the measurement light. In fact, when a filament lamp was used as the infrared light source and a voltage just before the lamp failed was applied to the filament lamp, the irradiance (light energy) of the infrared gas sensor according to the present invention, which has a long-pass filter, was measured. It was confirmed that the irradiance of the infrared gas sensor according to the present invention, which has a long-pass filter, during lamp failure could be reduced to approximately 1 / 8 of that of a comparative infrared gas sensor without a long-pass filter. As described above, the infrared gas sensor 110 can suppress the optical energy emitted to the outside of the pressure-resistant explosion-proof container 111, and therefore the infrared gas sensor 110 can be configured to satisfy the desired optical radiation explosion-proof requirements with a simple configuration of disposing the long-pass filter 150, without providing excessive power failure protection in the electrical circuit, such as a current and / or voltage limiter, installed between the infrared light source 121 and the power source. Furthermore, long-pass filters are cheaper than band-pass filters, and can be manufactured cost-effectively without compromising sensor performance.

[0029] The infrared gas sensor 110 can be suitably used, for example, as a gas detection unit in an explosion-proof fixed gas detection device. As shown in FIG. 3 , the fixed gas detection device 100 is configured by detachably mounting the infrared gas sensor 110 to a device main body 101. The device main body 101 is configured by arranging, for example, a power supply unit 103, an operation unit 104, a display unit 105, an alarm unit 106, an external output unit 107, an operation control unit (CPU) 108, and other electrical components within an explosion-proof container 102. The explosion-proof container 102 is made of, for example, stainless steel. With this fixed gas detection device 100, the infrared gas sensor 110 has a measurement region open to the atmosphere, enabling high-speed gas detection.

[0030] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and various modifications can be made. For example, in the above embodiments, the infrared gas sensor is configured as a so-called "reflective" type. However, the infrared gas sensor may be configured as a so-called "direct-light" type in which the light-receiving unit faces the light-emitting unit. In such cases, the light-receiving unit may also be configured to satisfy pressure-resistant explosion-proof requirements, for example, by being disposed in an explosion-proof container having a light-transmitting window. Furthermore, in the reflective type, the design of the optical system, such as the positions of the light source unit and the light-receiving unit within the pressure-resistant explosion-proof container, is not limited to those described in the above embodiments, and the light-receiving unit may be positioned so as to be able to receive light from the reflective member.

[0031] DESCRIPTION OF SYMBOLS 100: Fixed gas detection device 101: Device main body 102: Explosion-proof container 103: Power supply unit 104: Operation unit 105: Display unit 106: Alarm unit 107: External output unit 108: Operation control unit (CPU) 110: Infrared gas sensor 111: Pressure-resistant explosion-proof container 112: Opening 114: Support member 115: Light-transmitting window 116: Light-transmitting member 120: Light-emitting unit 121: Infrared light source 122: Reflector 130: Light-receiving unit 131: Measurement light-receiving sensor 132: Measurement band-pass filter 133: Main board 135: Beam splitter 136: Reference light-receiving sensor 137: Reference bandpass filter 138: Sub-substrate 140: Reflecting member 150: Longpass filter S: Measurement area

Claims

1. An infrared gas sensor that detects the concentration of a target gas by detecting, with a light-receiving unit, a change in the amount of infrared light emitted from a light-emitting unit due to absorption by the target gas in the target gas, the infrared gas sensor comprising: a pressure-resistant explosion-proof container with a light-transmitting window; the light-emitting unit is disposed within the pressure-resistant explosion-proof container; the light-emitting unit is configured to emit infrared light through the light-transmitting window toward a measurement region that is formed so that the target gas flows outside the container and is open to the atmosphere; the light-receiving unit includes a measurement light-receiving sensor that receives light through a measurement band-pass filter that transmits measurement light in the mid-infrared region that includes the absorption wavelength of the target gas, and a reference light-receiving sensor that receives light through a reference band-pass filter that transmits reference light that is less absorbed by the target gas than the measurement light; and a long-pass filter that reduces the transmittance of light in the visible to near-infrared region that passes through the light-transmitting window is disposed on the optical path between the light-emitting unit and the light-transmitting window.

2. An infrared gas sensor as described in claim 1, characterized in that the light receiving unit is disposed within the pressure-resistant explosion-proof container, and a reflective member that reflects light from the light emitting unit toward the light receiving unit is disposed outside the pressure-resistant explosion-proof container so as to form the measurement area between the light transmitting window and the reflective member.

3. The infrared gas sensor according to claim 1, wherein the long-pass filter has a transmittance of 80% or more for light in the wavelength range of 2.7 to 14.0 μm.

4. An infrared gas sensor as described in claim 2, characterized in that a beam splitter is arranged on the optical path from the reflecting member inside the pressure-resistant explosion-proof container to the measurement light receiving sensor, which reflects a portion of the light that passes through the light-transmitting window so that it is received by the reference light receiving sensor, and transmits the rest of the light so that it is received by the measurement light receiving sensor.

5. A fixed gas detection device comprising a device body having an explosion-proof structure and a gas sensor detachably attached to said device body, wherein said gas sensor is an infrared gas sensor as defined in claim 2.

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