Infrared gas sensor and fixed gas detection device

Abstract

To provide an infrared gas sensor and a stationary gas detection device, each of which has simple constitution, satisfies light radiation explosion-proof requirement, can detect gas quickly and enables the manufacturing cost thereof to be reduced.SOLUTION: An infrared gas sensor 110 has: a pressure-resistant and explosion-proof container 111 having a light transmission window 115; and a light-emitting unit 120 which is disposed in the container 111 and emits an infrared ray to a measurement region S formed in such a manner that detection-target gas flows in the outside of the pressure-resistant explosion-proof container 111. A light reception unit 130 includes: a light reception sensor 131 for measurement which receives light for measurement of a mid-infrared region via a band-pass filter 132 for measurement; and a light reception sensor 136 for reference which receives reference light via a band-pass filter 137 for reference. On an optical path between the light-emitting unit 120 and the light transmission window 115, a long-pass filter 150 is disposed which lowers the transmissivity of light in a visible region to a near-infrared region that passes through the light transmission window 115. A stationary gas detection device 100 is provided with the above-mentioned infrared gas sensor 110.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[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. [Background technology]

[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 light 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. 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 the reference light-receiving sensor and transmitting the rest of the light to the measurement light-receiving sensor. In addition, the measurement light-receiving sensor and the reference light-receiving sensor typically 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 bandpass filter that transmits light in a specific wavelength range is arranged on the optical path from the infrared light source to the reflective member inside the housing, and a configuration in which light in the specific wavelength range is selectively emitted to the measurement area is also known (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 using equipment that uses a light source that emits powerful energy, there is a risk that the light radiation characteristics of the light source may ignite the surrounding explosive atmosphere, so it has become necessary to meet requirements to prevent ignition by emitted light (light radiation explosion-proof requirements). In an infrared gas sensor having a measurement area open to the atmosphere as described above, light from the infrared light source is emitted outside the housing, so it is necessary to meet the requirements for explosion-proofing against light radiation.

[0006] The optical radiation explosion-proof requirements may apply to any configuration equipped with a focusing optical system such as a lens or reflector for the light emitted outside the housing. Also, the optical radiation explosion-proof requirements require that the product meet the requirements not at the normal driving voltage (or driving current or driving power), but at the driving voltage (or driving current or driving power) just before the product breaks down. Therefore, in order for an infrared gas sensor to meet the requirements for optical radiation explosion prevention, it is necessary to consider the optical energy emitted from the infrared light source in the event of a product malfunction. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2001 / 0015408 [Patent Document 2] European Patent Application Publication No. 0457624 Summary of the Invention [Problem to be solved by the invention]

[0008] Infrared light sources such as lamps and LEDs generally used in infrared gas sensors are designed to prevent breakdowns such as wire breakage, so just before the infrared light source breaks down, the voltage (or current or power) applied to the infrared light source increases, and the energy of the light emitted from the infrared light source becomes stronger. Although it is possible to address this issue by providing overpower fault protection to the electrical circuit, such as a current and / or voltage limiter installed between the infrared light source and the power supply, this complicates the circuit configuration and is a significant disadvantage in product design.In particular, unlike battery-powered portable detection devices, it is difficult to design an overpower fault protection circuit for stationary detection devices, as the original power supply (voltage) supplied to the product is involved.

[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 emitted outside the housing, it is thought that it will be possible to meet the optical radiation explosion-proof requirements. However, because bandpass filters selectively transmit 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. If light from an infrared light source is filtered by a bandpass filter before being emitted to the outside, problems arise, such as difficulty in aligning the light-receiving sensor (optical adjustment) and high manufacturing costs. Increasing the amount of light reaching the light-receiving sensor requires increasing 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. [Means for solving the problem]

[0011] The infrared gas sensor of the present invention detects the gas to be detected by absorbing the infrared rays emitted from the light emitting element. Change in light intensity and a reference light receiving sensor that receives light through a reference bandpass filter that transmits reference light whose absorption intensity by the target gas is smaller than that of the measurement light. The above-mentioned problem is solved by a configuration in which a long-pass filter that reduces the transmittance of light from the visible range to the near-infrared range that passes through the light-transmitting window is disposed 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. [Effects of the Invention]

[0012] According to the invention of claim 1, the emission of light in the visible to near-infrared range outside the pressure-resistant explosion-proof enclosure is suppressed, thereby making it possible to minimize the energy of light emitted outside the pressure-resistant explosion-proof enclosure while ensuring sufficient light intensity 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. Therefore, an infrared gas sensor that satisfies the desired optical radiation explosion-proof requirements can be configured with a simple configuration of a long-pass filter, without providing overpower failure protection in the electrical circuit, such as a current and / or voltage limiter, installed between the infrared light source and the power source. 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, it is possible to achieve miniaturization while ensuring a sufficient optical path length required for gas detection, and this is suitable for application to, for example, a fixed gas detection device in which the gas sensor is configured to be detachable from the device body. According to the invention of claim 3, the desired requirements for optical radiation explosion prevention are satisfied while a sufficient amount of light can reach the measurement light receiving sensor and the reference light receiving sensor, 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, so that stable gas detection can be performed. According to the invention of claim 5, the infrared gas sensor has a measurement area that is open to the atmosphere, making it possible to provide a stationary gas detection device that is pressure-resistant and explosion-proof and satisfies the requirements for optical radiation explosion-proofing, thereby enabling high-speed gas detection. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view schematically showing the configuration of an example of an infrared gas sensor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the spectral radiance characteristics of blackbody radiation. [Figure 3] 1 is a block diagram showing an outline of the configuration of an example of a fixed gas detection device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[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 so as 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 arranged to surround the infrared light source 121, and is configured to emit light emitted from the infrared light source 121 directly or by reflection 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 gas to be detected, 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 a 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. 133 in Fig. 1 is 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 is 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 bandpass 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 via the measurement bandpass filter 132. Note that the measurement light receiving sensor 131 does not need to be equipped with the measurement bandpass filter 132 itself, and the measurement bandpass 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 that is set in the mid-infrared range and has a smaller absorption intensity due to the gas to be detected than the measurement light, and the light reflected by the reflecting member 140 is received through the reference bandpass filter 137, thereby filtering the reference light. By using as the reference light a wavelength at which the absorption intensity by the target gas is smaller than that of the measurement light, the difference in intensity between the measurement light and the reference light in the presence of the target gas becomes large, and it becomes possible to easily detect changes in output due to the target gas when the output of the reference light-receiving sensor 136 reduces 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 configured to be separately arranged on the optical path from the reflective member 140 inside the pressure-resistant explosion-proof container 111 to the reference light receiving sensor 136.

[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 container 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 way, by having the measurement light receiving sensor 131 and the reference light receiving sensor 136, which are arranged on different wall surfaces, receive light, the output of the measurement light receiving sensor 131 and the output of the reference light receiving sensor 136 can be used, making it possible to perform 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, facing each other across the light-transmitting window 115 and extending in the same direction. The reflecting member 140 is supported by a support member 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 gas to be measured 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 20 to 40 mm, for example, 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 inside 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] It is preferable to use a long-pass filter 150 that has a transmittance of 80% or more for light in the mid-infrared region, for example, light of a wavelength that is absorbed by the combustible gas or CO2 to be measured. This satisfies the desired requirements for optical radiation explosion protection while allowing a sufficient amount of light to reach the measurement light-receiving sensor 131 and the reference light-receiving sensor 136, thereby ensuring highly reliable gas detection. Specifically, it is preferable to use a long-pass filter 150 having a transmittance of 80% or more for light in the wavelength range of 2.7 to 14.0 μm, and it is more preferable to use a long-pass filter having a transmittance of 80% or more for light in the wavelength range of 3.0 to 4.5 μm, or a long-pass filter having 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, for example, 20% or less for light in the visible to near-infrared range, for example, light of 0.38 μm to 2.7 μm. The long-pass filter 150 having such optical characteristics allows the infrared gas sensor 110 to be configured to satisfy the desired requirements for preventing optical radiation explosions.

[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 in the wavelength range λb used for gas detection.

[0028] However, according to the above-described infrared gas sensor 110, by disposing the long-pass filter 150 on the optical path from the infrared light source 121 to the reflecting member 140 inside the pressure-resistant explosion-proof container 111, light in the visible to near-infrared range is prevented from being emitted to the outside of the pressure-resistant explosion-proof container 111. Therefore, it is possible to reduce the energy of light emitted to the outside of the pressure-resistant explosion-proof container 111 while ensuring a sufficient amount of light 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 an infrared light source and a voltage of the magnitude immediately before failure was applied to the filament lamp, the irradiance (light energy) was measured. It was confirmed that the irradiance of the infrared gas sensor of the present invention, which has a long-pass filter, when the lamp fails can be suppressed to about 1 / 8 of that of a comparative infrared gas sensor which does not have 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, so that 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 electric 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 section of an explosion-proof fixed gas detection device. As shown in FIG. 3, fixed gas detection device 100 is constructed by detachably mounting infrared gas sensor 110 described above on device 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 inside an explosion-proof container 102. The explosion-proof container 102 is made of, for example, stainless steel. According to such fixed gas detection device 100, since infrared gas sensor 110 has a measurement region that is open to the atmosphere, high speed gas detection is possible.

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

[0031] 100 Fixed gas detection device 101 Device body 102... Explosion-proof container 103... Power supply section 104...Operation unit 105... Display section 106... Alarm section 107 External output section 108 ··· Operation control unit (CPU) 110 Infrared gas sensor 111 Explosion-proof container 112 Opening 114 Support member 115 ··· Light-transmitting window 116 Light-transmitting member 120 ··· Light-emitting part 121 Infrared light source 122 Reflector 130... Light receiving section 131 ··· Measuring light receiving sensor 132 Measurement bandpass filter 133 Main board 135 ··· Beam Splitter 136 Reference light receiving sensor 137 Reference bandpass filter 138 Sub-board 140 Reflective member 150 Long-pass 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 detection gas, A pressure-resistant explosion-proof container having a light-transmitting window is provided. the light-emitting unit is disposed within the pressure-resistant explosion-proof container, and the light-emitting unit is configured to radiate 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 via a measurement band pass filter that transmits measurement light in a mid-infrared region that includes an absorption wavelength of the detection target gas, and a reference light receiving sensor that receives light via a reference band pass filter that transmits reference light whose absorption intensity by the detection target gas is smaller than that of the measurement light, an infrared gas sensor, characterized in that a long-pass filter is disposed on an optical path between the light-emitting part and the light-transmitting window, the long-pass filter reducing the transmittance of light in the visible to near-infrared range that passes through the light-transmitting window.

2. the light receiving unit is disposed within the pressure-resistant explosion-proof container, 2. The infrared gas sensor according to claim 1, wherein a reflective member that reflects light from the light-emitting portion toward the light-receiving portion is disposed outside the pressure-resistant explosion-proof container so as to form the measurement region between the reflective member and the light-transmitting window.

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

4. 3. The infrared gas sensor according to claim 2, wherein a beam splitter is disposed on an optical path from the reflecting member to the measurement light-receiving sensor within the pressure-resistant explosion-proof container, the beam splitter reflecting a portion of the light transmitted through the light-transmitting window to be received by the reference light-receiving sensor and transmitting the rest of the light to be 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 the device body, 3. A fixed gas detection device comprising the infrared gas sensor according to claim 2.

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