Optical gas sensor device

Abstract

Provided is an optical gas sensor device with which the amount of light reaching a light receiving part is increased as compared to the prior art, and gas detection accuracy can be improved.　The optical gas sensor device comprises: a light source 2 that emits infrared rays into a gas to be detected; a light receiving part 4 that detects the infrared rays and generates a detection signal; and a cover member 1 having a light guide part 13 that forms a pipe shape with a circular or elliptical cross section in a direction orthogonal to a central axis. The optical gas sensor device is configured such that the light source 2 is disposed in one opening of the light guide part 13, the light receiving part 4 is disposed in another opening of the light guide part 13, and the infrared rays emitted from the light source 2 repeatedly reflect off an inner surface of the light guide part 13 before reaching the light receiving part 4. The cover member 1 is provided with a ventilation hole 11 for introducing the gas to be detected into the light guide part 13, the ventilation hole having openings respectively in a surface of the cover member 1 and at a location of the light guide part 13 where the amount of passing infrared rays is relatively small.

Description

Optical gas sensor device

[0001] The present invention relates to an optical gas sensor device, and more particularly to a technique useful for an optical gas sensor device having a light guide path with a curved portion, for example.

[0002] Conventionally, gas sensors using NDIR (Non-Dispersive Infrared) have been known. NDIR gas sensors are devices that utilize the property of each gas to be detected to absorb specific infrared wavelengths. By detecting which wavelengths are absorbed and to what extent when infrared light is emitted, the NDIR gas sensor measures the concentration of the target gas. The gas sensor includes, for example, an infrared light emitter and an infrared light receiver, and is configured to detect the concentration of the target gas located on the optical path between the light emitter and the light receiver.

[0003] In principle, a gas sensor detects infrared light absorbed by the gas to be detected with a light receiving part and calculates the gas concentration from the difference in the amount of light received before and after detection, so the longer the optical path length, the greater the difference due to the amount of absorbed light, improving the detection accuracy (measurement accuracy) of the gas concentration. Also, the more gas is taken into the optical path, the greater the difference due to the amount of absorbed light, and the better the detection performance.

[0004] Conventional inventions relating to NDIR gas sensor devices are described, for example, in Patent Document 1 and Patent Document 2. Patent Document 1 describes a reflector-type optical gas sensor device having a box-shaped space filled with a gas to be detected. The optical gas sensor device of Patent Document 1 can only reflect light at a fixed angle to any desired location, resulting in loss of infrared light due to misalignment of the light source or light receiving unit. Patent Document 2 describes an optical absorption gas sensor that includes a light-emitting diode, an annular radiation guide with a rectangular cross section that includes a curved portion that can be bent around the axis of one of its sides, and that guides infrared light emitted from the light-emitting diode, and an infrared photodiode that detects the infrared light emitted from the annular radiation guide.

[0005] The optical absorption gas sensor described in Patent Document 2 has a problem in that the direction (angle) of curvature of the annular radiation guide as an optical path is limited to a two-dimensional plane, making it difficult to miniaturize. Furthermore, the optical absorption gas sensor described in Patent Document 2 has a rectangular cross section perpendicular to the axial direction of the annular radiation guide. Therefore, there is a risk that the reflection angle of infrared light in the optical path is biased, and that misalignment of the light source and light receiving unit causes a loss of infrared light intensity, resulting in a decrease in the detection accuracy of the target gas. Therefore, the present applicant developed an optical gas sensor device having a configuration as shown in FIGS. 7A and 7B that has a three-dimensionally curved optical path and is intended to improve the detection accuracy of the target gas, and previously filed a patent application (Patent Document 3).

[0006] Japanese Patent Application Laid-Open No. 2018-136154 Japanese Patent Application Laid-Open No. 2013-517467 Japanese Patent Application Laid-Open No. 2023-162821

[0007] The optical absorption gas sensor described in Patent Document 3 has a cavity 13 in the cover 1 that forms an optical path, as shown in FIG. 7B . Also, as shown in FIG. 7A , gas intakes 111 and 112, which serve as two ventilation holes 11 that communicate with the cavity 13 from above, are provided in the upper part of the cover 1. It has been found that with the above-described configuration, a portion of the light traveling in the optical path leaks out of the ventilation holes 11, reducing the amount of light reaching the light receiving unit and degrading the gas detection accuracy. Furthermore, when the cover 1 having the cavity 13 is formed from resin, burrs and weld lines can occur near the boundary between the ventilation holes 11 and the cavity 13 due to resin flow during molding or resin injection, reducing the light reflectance and the amount of light reaching the light receiving unit.

[0008] The present invention has been made in light of the above-mentioned problems, and its object is to provide an optical gas sensor device that can increase the amount of light that reaches the light receiving element compared to conventional devices, thereby improving the accuracy of gas detection.

[0009] In order to solve the above problems, the present invention provides an optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; a light receiving unit that detects the infrared rays and generates a detection signal; and a cover member having a pipe-shaped light guiding unit whose cross section in a direction perpendicular to the central axis is circular or elliptical, wherein the light source is disposed at one opening of the light guiding unit and the light receiving unit is disposed at the other opening of the light guiding unit, and the infrared rays emitted from the light source are repeatedly reflected on the inner surface of the light guiding unit to reach the light receiving unit, and the cover member is configured to have ventilation holes that have openings at locations on the light guiding unit where a relatively small amount of infrared rays passes and on the surface of the cover member, for introducing the gas to be detected into the light guiding unit.

[0010] The optical gas sensor device of the present invention has the effect of increasing the amount of light that reaches the light receiving portion and improving the gas detection accuracy compared to the conventional device.

[0011] 5A . FIG. 5B is a schematic diagram of an NDIR-type optical gas sensor device according to the present invention. FIG. 5C is a perspective view showing the appearance of the optical gas sensor device of an embodiment. FIG. 5D is an exploded perspective view showing an example of upper and lower parts constituting the cover of the optical gas sensor device of FIG. 2. FIG. 5E is a partially see-through perspective view of the optical gas sensor device of FIG. 5A. FIG. 5F is a partially see-through plan view of the optical gas sensor device of FIG. 5A. FIG. 5G is a perspective view showing an example of a light source used in the optical gas sensor device of an embodiment. FIG. 5H is a perspective view showing an example of a conventional optical gas sensor device. FIG. 5I is a partially see-through perspective view showing the reflection of infrared rays in the light guide of the optical gas sensor device of FIG. 7A. FIG. 5I is a schematic view explaining the phenomenon of sink marks occurring in an injection-molded product having an uneven thickness. FIG. 5I is a cross-sectional view showing the occurrence of recesses on the surface of an injection-molded product having an uneven thickness. FIG. 5I is a cross-sectional view showing the reflection of light when recesses are formed on the inner surface of the light guide of the optical gas sensor device. FIG. 5I is a cross-sectional view showing the occurrence of sink marks when the thickness of the cover constituting the optical gas sensor device of an embodiment is made uneven. The optical gas sensor device according to the present invention is provided with a cover having a uniform thickness, a substrate for forming the optical gas sensor device, and a base plate for forming the optical gas sensor device.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical gas sensor device according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings. Fig. 1 shows a schematic configuration of an optical gas sensor device 100 according to the present embodiment.

[0013] 1 , the optical gas sensor device 100 of this embodiment includes a cover 1, a light source 2, an optical filter 3, a light receiving unit 4, and a signal processing unit 5. The optical gas sensor device 100 radiates (emits or emits) infrared rays from the light source 2, and emits the infrared rays through an optical path within the cover 1 toward a gas G to be detected (measured) within the cover 1. The infrared rays that are partially absorbed by the gas G to be detected are incident on the light receiving unit 4 via the optical filter 3 and detected, and the detection signal is processed by the signal processing unit to detect (measure) the concentration of the gas G to be detected, and generates and outputs a concentration signal. This is an NDIR type gas detection device.

[0014] Molecules of the gas G to be detected present in the optical path absorb infrared light, thereby reducing the amount of light reaching the light-receiving unit 4. However, the greater the amount of gas G, the greater the amount of infrared light absorbed, so the concentration of the gas G to be detected can be detected based on the detection signal from the light-receiving unit 4. The cover 1 has a ventilation hole 11 as a gas inlet, which is an inlet / outlet for the gas G to be detected. A gas filter 12 (e.g., a metal mesh filter or a resin porous film) is disposed in the ventilation hole 11 to prevent foreign matter from entering from the outside.

[0015] In particular, the optical gas sensor device 100 filters infrared light emitted from the light source 2 toward the gas G to be detected by the optical filter 3 and receives the filtered infrared light by the light receiving unit 4. The optical filter 3 is disposed in a position upstream of the light receiving unit 4 on the optical path near the light receiving unit 4. Compared to a configuration in which the infrared light emitted from the light source 2 is filtered by an optical filter before being emitted toward the gas G to be detected, this configuration only requires filtering on the light receiving surface of the light receiving unit 4, thereby making it possible to reduce the area of ​​the optical filter 3 and reducing costs. Furthermore, the optical gas sensor device 100 does not receive unfiltered infrared light emitted from sources other than the light source 2, thereby improving the signal-to-noise ratio of the sensor. However, the optical gas sensor device 100 may also be configured such that the optical filter 3 is disposed in front of the light source 2 and the infrared light emitted from the light source 2 is filtered by the optical filter 3 and emitted toward the gas G to be detected.

[0016] In the optical gas sensor device 100 of this embodiment, the optical path is designed so that the infrared light received by the light receiving unit 4 via the optical filter 3 does not arrive directly from the light source 2, but arrives after being repeatedly reflected on the inner surface of the cover 1. Since the higher the reflectivity of the inner surface of the cover 1, the higher the efficiency of light (infrared light) utilization. Therefore, it is desirable to form a reflective film on the inner surface of the cover 1.

[0017] The optical gas sensor device 100 of this embodiment is configured to select a detection wavelength so as to detect the gas G to be detected, which is a chlorofluorocarbon (CFC) substitute refrigerant used in air conditioners. The chlorofluorocarbon substitute refrigerant is a synthetic compound (gas) refrigerant used industrially as a substitute for specific chlorofluorocarbons (CFCs). Because CFC refrigerants have a high ozone depletion potential (ODP), which contributes to the destruction of the Earth's ozone layer, their replacement with hydrochlorofluorocarbon (HCFC) refrigerants, which have a low ODP, has begun. Furthermore, developed countries are increasingly switching from HCFC refrigerants to HFC refrigerants (R410A), which have an ODP of zero. CFC refrigerants, HCFC refrigerants, and HFC refrigerants have high GWPs and are known to contribute to global warming as greenhouse gases. For this reason, consideration is being given to replacing the HFC refrigerant (R410A) with an HFC refrigerant (R32) that has a lower global warming potential, and the optical gas sensor device 100 of this embodiment is intended to detect R32, a fluorocarbon refrigerant, as the gas G to be detected.

[0018] However, the gas G to be detected is not limited to R32. Therefore, the gas G to be detected may also be carbon monoxide, propane, methane, butane, ammonia, oxygen disulfide, nitrogen dioxide, nitric oxide, ozone, sulfur hexafluoride, difluoromethane, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), ethylene, etc. The light-receiving unit 4 is preferably configured to detect infrared rays at the wavelength with the greatest absorption among the multiple absorption wavelengths of the gas to be detected. For example, when detecting carbon dioxide (CO2) as the gas G to be detected for concentration detection, infrared rays at the wavelength of 4.26 μm, which has the greatest absorption among the multiple absorption wavelengths, are detected.

[0019] The optical gas sensor device 100 outputs various status signals based on the detected gas concentration of gas G and signals indicating the detected concentration of gas G or a value corresponding to the concentration to a device that performs processing based on the status signals and the detected concentration of gas G or a value corresponding to the concentration. The various status signals include, for example, a fault signal indicating a fault in the optical gas sensor device 100, an alarm signal indicating that the detected concentration of gas G is in an abnormal state (alarm state) at an alarm level, and a monitoring signal (normal signal) indicating that the detected concentration of gas G is normal. If the device is an alarm device, the alarm device issues various alarms (e.g., an alarm of a fault in the optical gas sensor device 100 based on the fault signal, an alarm of an abnormality in the detected concentration of gas G based on the alarm signal) in response to the various signals received from the optical gas sensor device 100. The device may be configured to include the optical gas sensor device 100.

[0020] Examples of the above devices include household air conditioners, household water heaters, industrial air conditioners, automotive air conditioners, freezers, refrigeration equipment, refrigerated showcases, air purifiers, household flammable gas leak alarms, household toxic gas alarms, household environmental monitoring equipment, industrial flammable gas leak alarms, industrial toxic gas alarms, industrial gas process monitoring devices, CO2 concentration measuring devices for greenhouse horticulture, CO2 measuring devices for plant factories, CO2 injection devices for food packaging, ethylene gas concentration measuring devices for food warehouses, etc. For example, the present invention can be applied to an ammonia monitoring device or gas leak alarm device in an ammonia tank that stores ammonia as a carrier for hydrogen, a decarbonization fuel, or as a fuel itself.

[0021] Furthermore, for devices that manage the concentration of the detected gas G itself, such as household environmental monitoring devices, CO2 concentration measuring devices for greenhouse horticulture, CO2 measuring devices for plant factories, and ethylene gas concentration measuring devices for food warehouses, the optical gas sensor device 100 is configured to output a signal indicating the concentration of the detected gas G or a value corresponding to the concentration to the device.

[0022] Next, a specific configuration of an embodiment of the optical gas sensor device 100 of the present invention will be described with reference to FIGS. 2 to 6. FIG. 2 is a perspective view of the exterior of the optical gas sensor device 100 of this embodiment, and FIG. 3 is an exploded perspective view of a cover constituting the optical gas sensor device 100 of FIG. 2. FIG. 4 is a partially see-through perspective view of the optical gas sensor device 100 of FIG. 2. FIG. 5A is a partially see-through plan view of the optical gas sensor device of FIG. 2. FIG. 5B is a plan view illustrating the reflection of infrared light within the light guide of the optical gas sensor device of FIG. 5A. FIG. 6 is a perspective view illustrating an example configuration of the light source 2. Note that to facilitate understanding of the orientation of this device, x-, y-, and z-axes are defined for the device, and these common x-, y-, and z-axes are illustrated in FIGS. 2 to 6. In the following description, the +z-axis direction is defined as upward, and the −z-axis direction is defined as downward.

[0023] As shown in FIG. 2 , the optical gas sensor device 100 of this embodiment includes a substrate 6 and a cover 1 attached to the upper surface (+z side surface) of the substrate 6. Elements and components constituting the signal processing circuit 5 and the like are mounted on the upper surface of the substrate 6, and the cover 1 is attached to the upper surface of the substrate 6 so as to cover the elements and components. The cover 1 is provided with a plurality of positioning pins 14 (see FIG. 3 ) that protrude downward, and pinholes (not shown) into which the positioning pins 14 of the cover 1 can be inserted are formed at predetermined positions on the substrate 6. The positioning pins 14 are inserted into the pinholes on the substrate 6, thereby attaching the cover 1 to a predetermined position on the substrate 6. The substrate 6 is made of a PCB (Printed Circuit Board) in which conductive wiring is printed on the surface of a plate material such as glass epoxy resin.

[0024] The cover 1 has a pipe-shaped hollow portion formed therein, with both ends facing downward (in the -z direction), into which the gas to be detected can be introduced. The light source 2 is positioned in the opening at one end of the hollow portion, and the optical filter 3 and the light receiving unit 4 are positioned in the opening at the other end. The cover 1 is attached to the substrate 6 so as to cover (enclose) the light source 2, the optical filter 3, and the light receiving unit 4. The hollow portion formed in the cover 1 is configured so that the gas to be detected can be introduced through ventilation holes 11 provided in the cover 1. The base of the cover 1 is made of, for example, resin. As shown in FIG. 3 , the cover 1 is composed of an upper part 110A (on the +z direction side) and a lower part 110B (on the -z direction side), and the upper part 110A and the lower part 110B are joined together to form an integrated unit.

[0025] 3, lower part 110B of cover 1 has coupling pins 123 and 124 on its upper surface. Coupling pins 123 and 124 are convex portions extending in the +z direction, and recesses 121 and 122 having the same diameter as the convex portions are formed in opposing locations on the lower surface of upper part 110A. By fitting coupling pins 123 and 124 of lower part 110B into recesses 121 and 122 of upper part 110A, upper part 110A and lower part 110B are integrated while being positioned relative to each other.

[0026] As shown in FIG. 4 , the cover 1 also includes a light guide 13 as a hollow portion into which the gas to be detected is introduced. The light guide 13 has a three-dimensionally winding shape, with a circular cross section perpendicular to the central axis, and each portion along the central axis has the same diameter. As shown in FIG. 3 , the upper part 110A includes an upper half-pipe 118A formed by a recess that constitutes the light guide 13, and the lower part 110B includes a lower half-pipe 118B formed by a recess that constitutes the light guide 13. The half-pipe 118A and 118B are joined together to form the pipe-shaped light guide 13. Thus, the cover 1 is composed of the upper part 110A and the lower part 110B, which are formed so as to divide the light guide 13 into two halves, upper and lower, by a plane along the axial direction. The upper part 110A and the lower part 110B are configured to have spaces for removing weight (removing excess weight) so as to reduce the weight of the cover 1.

[0027] The light guide 13 has openings at both ends. As shown in FIG. 4 , the light source 2 is disposed facing one opening, and the optical filter 3 and the light receiving unit 4 are disposed facing the other opening. Furthermore, as shown in FIG. 5A , the light guide 13 has a generally U-shape when viewed from above. An infrared reflective film is applied to the inner surface of the light guide 13. In this embodiment, gold is used as the infrared reflective film, but this is not limited thereto. Silver, aluminum, or a dielectric multilayer film may also be used. Furthermore, if necessary, a protective film such as silicon oxide or silicon nitride may be formed on the infrared reflective film to prevent corrosion of the metal film of the infrared reflective film. The infrared reflective film and the protective film can be formed by plating, sputtering, vacuum deposition, or the like.

[0028] 5B , the light guide 13 repeatedly reflects the infrared rays incident into the light guide 13 from the light source 2 with an infrared reflective film on the inner surface and emits the infrared rays to the light receiving unit 4, which has the optical filter 3 attached to its light receiving surface. In this way, the light guide 13 of the cover 1 repeatedly reflects the infrared rays emitted from the light source 2 with the infrared reflective film, and functions as an optical path so that part of the reflected light reaches the light receiving unit 4 via the optical filter 3, thereby efficiently guiding the infrared rays from the light source 2 to the light receiving unit 4.

[0029] As mentioned above, in the conventional reflector-type optical gas sensor device (Patent Document 1), only light at a fixed angle can be reflected to any desired location, and infrared radiation is lost due to misalignment of the light source or light-receiving unit. In contrast, in the optical gas sensor device 100 of this embodiment, the optical path inside the cover 1 is formed by the light-guiding unit 13, which is a pipe-shaped light-guiding unit with a circular cross section. As a result, the optical path inside the cover 1 is not affected by the size of the cross-sectional diameter of the light-guiding unit 13 or by misalignment of the light source or light-receiving unit, and infrared radiation emitted from the light source 2 is repeatedly reflected on the inner surface of the light-guiding unit 13, allowing almost all of it to reach the light-receiving unit 4.

[0030] The optical path length of the infrared light from the light source 2 to the light receiving unit 4 can be changed relatively easily not only by changing the size of the cover 1 but also by changing the diameter of the cross section of the light guiding unit 13. Furthermore, in the optical gas sensor device 100 of this embodiment, the area (diameter) of the cross section perpendicular to the axial direction of the light guiding unit 13 is constant in the axial direction. Therefore, the gas concentration per unit volume of the gas to be detected that has entered the light guiding unit 13 is easily uniform, making it easy to respond to changes in gas concentration.

[0031] The cover 1 is formed by resin injection molding, with the upper part 110A and the lower part 110B each using separate molds. The inner surfaces of the half pipe section 118A of the upper part 110A and the half pipe section 118B of the lower part 110B are smooth due to injection molding, eliminating the need for polishing. An infrared-reflecting film is formed on the inner surfaces of the half pipe sections 118A, 118B of the upper part 110A and the lower part 110B by plating (resin plating), sputtering, vacuum deposition, or other methods.

[0032] 2, gas intake ports 111 and 112 are formed in upper part 110A of cover 1 as inlets to ventilation holes 11. As shown in Fig. 4, gas inlets 131 and 132 are formed in the inner wall of the curved portion of light guiding section 13 as outlets to ventilation holes 11, and gas taken in through gas inlets 111 and 112 temporarily enters the inner space of cover 1 and is then introduced into light guiding section 13 through gas inlets 131 and 132. Gas inlets 131 and 132 are positioned so that a line connecting the centers of gas inlets 111 and 112 and the centers of gas inlets 131 and 132 (dotted chain line C in Fig. 5A) forms an angle of 45 degrees with respect to the x-axis when viewed from above.

[0033] The ventilation holes 11 have gas inlets 111 and 112 located inside the curved portion of the light guide 13 when viewed from above. The holes extend in the -z direction from the top surface of the upper part 110A of the cover 1 to the center height of the light guide 13, and then change direction at the bottom end to a 45-degree angle relative to the X axis in the horizontal plane. In other words, the ventilation holes 11 may be formed as a continuous, L-shaped passage that penetrates all the way to the light guide 13. In addition, the larger the area of ​​the gas inlets 131 and 132, the greater the amount of gas introduced into the light guide 13 and the higher the gas detection performance. However, the larger the area, the greater the amount of infrared light leaking to the outside, reducing the infrared light utilization efficiency. Therefore, it is advisable to determine the size of the gas inlets 131 and 132 based on a trade-off between the amount of gas introduced into the light guide 13 and the amount of infrared light leaking from the light guide 13 to the outside.

[0034] When light guide 13, which forms the optical path through which the gas to be detected is introduced, is curved, infrared rays incident from light source 2 into light guide 13 often pass through the outside of the curved portion of light guide 13 rather than the inside, as shown in Fig. 5B . Therefore, by providing gas inlets 131 and 132 as ventilation hole outlets on the inside of the curved portion as described above, the amount of infrared rays leaking out of light guide 13 can be reduced compared to when gas inlets 111 and 112 are provided on the outside of the curved portion of light guide 13 or on a straight portion as shown in Fig. 7A . This increases the efficiency of infrared utilization.

[0035] Furthermore, assuming that the amount of infrared light reaching the light receiving unit 4 is the same as when the vent holes are provided on the straight portion of the light guide 13, the area of ​​the gas inlets 131 and 132 can be made larger by providing them inside the curved portion than when the gas inlets 111 and 112 are provided on the straight portion of the light guide 13 as shown in FIG. 7A . This allows more gas to be taken into the light guide 13, thereby improving gas detection performance. Specifically, for example, when a vent hole that allows 10% of light to escape is located at a position where 80% of the light passes through (condition A), the amount of light that reaches the light receiving unit 4 is 80-80×0.1+20=92%. On the other hand, when a vent hole that allows 10% of light to escape is located at a position where 20% of the light passes through (condition B), the amount of light that reaches the light receiving unit 4 is 20-20×0.1+80=98%. In other words, condition B is more advantageous than condition A until the vent hole area is large enough to allow 40% of light to escape.

[0036] Furthermore, in the optical gas sensor device of this embodiment, the gas inlets 131 and 132 are provided at curved portions of the light guide 13, not at straight portions of the light guide 13 where a relatively large amount of light is reflected. Also, the portions of the mold corresponding to the straight portions of the light guide 13 are easier to polish than the curved portions. Therefore, the surface of the portions where a relatively large amount of light is reflected can be smoothed to improve reflectivity, thereby increasing the amount of infrared light that reaches the light receiving unit 4.

[0037] Furthermore, when the cover 1 is formed by resin injection molding, burrs and weld lines occur on the edges of the gas inlets 131 and 132 on the light guide 13 side, which serve as the outlets of the ventilation holes, and on the inner surface of the light guide 13 in the vicinity thereof. In this embodiment, the gas inlets 131 and 132 are provided in locations where the amount of infrared light passing through is relatively small (inside the curved portion). Therefore, even if burrs and weld lines occur on the edges of the gas inlets 131 and 132 or in their vicinity, the amount of infrared light obstructed by the burrs and weld lines can be reduced. This increases the amount of infrared light reaching the light receiving unit 4 compared to when a gas inlet is provided in a straight portion, thereby improving gas detection performance compared to conventional methods.

[0038] 4 is merely an example and is not intended to be limiting. For example, in this embodiment, the gas inlets 131 and 132 are formed to be located inside the curved portion of the light guiding unit 13 in a top view. However, they may be formed in a location that is inside the curved portion of the light guiding unit 13 in a side view (inside the portion that transitions from horizontal to vertical). Furthermore, in addition to the gas inlets 131 and 132, further gas inlets may be provided in different locations, for example, near the openings at both ends of the light guiding unit 13 (in the space surrounding the light source 2 and the light receiving unit 4).

[0039] Next, specific examples of the light source 2, optical filter 3, and light receiving unit 4 will be described. As shown in FIG. 6 , the light source 2 is a MEMS (Micro Electro Mechanical Systems) type light source mounted on the upper surface (+z side surface) of the substrate 6, and includes, for example, a membrane M having a membrane structure. The light source 2 includes a silicon chip 21, a thin-film heater 22, and a wire bonding pad 23. The silicon chip 21 is a semiconductor chip mainly made of silicon, and includes the membrane M in the center of its plane (xy plane). The thin-film heater 22 is a light source that emits infrared rays when heated by passing current through it, and is formed approximately in the center of the plane of the membrane M. The wire bonding pad 23 is wire-bonded to wiring on the substrate 6.

[0040] The light source 2 as a MEMS-type light source is small and low-profile, enabling miniaturization of the sensor module, particularly a lower profile compared to conventional incandescent light sources and LEDs (Light Emitting Diodes). Furthermore, the light source 2 as a MEMS-type light source has features (characteristics) such as a long life, low power consumption, and a short response time compared to conventional light sources. Therefore, by reducing the power consumption of the light source, which is dominant in the current consumption of the entire sensor module, it is possible to achieve low power consumption as a sensor module. The short response time of the MEMS-type light source makes it possible to shorten the standby time after power-on when performing intermittent driving, thereby reducing average power consumption.

[0041] Furthermore, compared to conventional light sources, the light source 2 as a MEMS-type light source can directly utilize the light emitted from the surface of a high-temperature part, making it possible to apply it to the detection of gases with long-wavelength absorption bands. The infrared radiation area of ​​the light source 2 is patterned with high precision on the plane of the Si substrate of the membrane M. Unlike conventional incandescent light sources with coiled filaments, the individual variation in radiation direction is very small. This reduces the variation in the amount of received light when a sensor module is constructed using the light source 2, contributing to improved product yield. Furthermore, the light source 2 is mass-produced using MEMS technology based on silicon wafers, making it easy to mass-produce. While the light source 2 is a surface-mounted component in this embodiment, this is not limited thereto and may be housed in a DIP (Dual Inline Package) component (e.g., a CAN package) or an SMD (Surface Mount Device) component (e.g., a surface-mount package made of ceramic, etc.).

[0042] The optical filter 3 is a filter that is provided to cover the light receiving surface of the light receiving unit 4 and transmits light (infrared light) in a wavelength range (band) corresponding to the absorption wavelength specific to the gas G to be detected. In this way, the transmission wavelength of the optical filter 3 is designed to match the absorption wavelength specific to the gas G to be detected. This suppresses changes in the amount of light caused by gases other than the gas G to be detected, improving the signal-to-noise ratio of the detection signal from the light receiving unit 4. More specifically, the optical filter 3 filters out infrared light with a wide wavelength range that is incident from the light source 2 and passes through the gas G (e.g., carbon dioxide), and transmits infrared light in a wavelength range that corresponds to the absorption wavelength of the gas G (4.26 μm in the case of carbon dioxide).

[0043] The optical filter 3 includes, for example, a silicon substrate as a substrate and a dielectric multilayer film. The silicon substrate is a planar silicon substrate. The material of the substrate is not limited to silicon, and Ge (germanium), quartz, alumina, BaF2 (barium fluoride), CaF2 (calcium fluoride), etc. can also be used. The dielectric multilayer film is a layered film made of multiple dielectric materials provided on both sides of the silicon substrate. The planar shape of the optical filter 3 is rectangular, but is not limited thereto and may be other shapes such as circular.

[0044] The light receiving unit 4 is mounted on the +z side of the substrate 6 and is a thermopile-type optical sensor (infrared sensor) having multiple thermocouples, which detects the amount of incident infrared light and outputs a detection signal as an analog electrical signal. Note that the light receiving unit 4 is not limited to a thermopile-type infrared sensor, and various types of infrared sensors such as quantum-type and thermal-type may also be used.

[0045] In addition, although the light receiving unit 4 is a surface-mounted component in this embodiment, the present invention is not limited to this and may be housed in a DIP component (such as a CAN package) or an SMD component (such as a surface-mounted package made of ceramic, etc.) In the gas sensor device of this embodiment, the light source 2 and the light receiving unit 4 are surface-mounted components, but regardless of whether they are DIP components or not, the amount of light that reaches the light receiving unit 4 through the light guide 13 can be increased compared to conventional devices.

[0046] As described above, the optical gas sensor device 100 includes the light source 2 that emits infrared rays toward a gas to be detected, the light receiving unit 4 that detects the infrared rays and generates a detection signal, and the cover 1 that has the light guiding unit 13 that is shaped like a pipe and has a circular or elliptical cross section perpendicular to the central axis. Furthermore, the light source 2 is disposed at one opening of the light guiding unit 13, and the light receiving unit 4 is disposed at the other opening of the light guiding unit 13, so that the infrared rays emitted from the light source 2 reach the light receiving unit 4 after repeatedly reflecting on the inner surface of the light guiding unit 13. The cover 1 is provided with ventilation holes 11 that have openings at a location of the light guiding unit 13 where a relatively small amount of infrared rays passes and on the surface of the cover 1, for introducing the gas to be detected into the light guiding unit 13.

[0047] More specifically, the light guide 13 is formed so that it has a curved central axis, and the area of ​​the light guide 13 where the amount of infrared light passing through is relatively small is inside the curved portion. This reduces the amount of infrared light leaking through the opening of the ventilation hole 11, thereby increasing the amount of light passing through the light guide 13 and reaching the light receiving unit 4 compared to conventional designs. Furthermore, because the cross section of the light guide 13 is a circular pipe shape, an infrared light path can be formed in any of three dimensions (x-axis, y-axis, and z-axis), thereby lengthening the light path length even in a small space and improving the detection accuracy of the target gas. Furthermore, because the light guide 13 can freely change the light path in any of three dimensions, space can be used efficiently and the substrate 6 can be made smaller. Furthermore, the light path length can be relatively easily changed by changing the diameter of the circular cross section of the light guide 13.

[0048] Furthermore, light guiding section 13 is formed with two curved sections due to its U-shaped central axis, and two ventilation holes 11 are provided in cover 1, with openings on the inside of the two curved sections and on the surface of cover member 1, for introducing the target gas into the light guiding section. Therefore, two ventilation holes 11 allow a larger amount of target gas to be introduced into light guiding section 13, thereby improving gas detection accuracy. Furthermore, since the cross-sectional area of ​​light guiding section 13 is constant along the central axis, the concentration of the target gas within light guiding section 13 can be made uniform.

[0049] The cover 1 is composed of multiple parts 110A, 110B divided by a cross section along the central axis of the light guiding section 13, and the multiple parts 110A, 110B are configured to have an infrared reflective film on the inner surface of the recess that forms the light guiding section 13. Therefore, by forming the multiple parts 110A, 110B by resin injection molding, polishing of the inner surface of the light guiding section 13 (half pipe sections 118A, 118B) is not necessary. This makes it easy to manufacture the cover 1 and reduces the cost of the optical gas sensor device 100.

[0050] The optical gas sensor device 100 of the above embodiment includes a substrate 6 on which the light source 2 and the light receiving unit 4 are mounted, and the cover 1 is attached to the mounting surface of the substrate 6 so that the light source 2 is located at one opening of the light guide unit 13 and the light receiving unit 4 is located at the other opening of the light guide unit 13. This allows for efficient assembly of the device. Furthermore, the cover 1 can be placed in the space above the light source 2, the light receiving unit 4, and the elements that make up the signal processing unit, thereby achieving a compact device.

[0051] Next, other ingenious configurations of the optical gas sensor device 100 of the above embodiment and their advantages will be described with reference to Figures 8 to 10 and 11. In injection molding, if the thickness of the molded product M is not uniform, for example, as shown in Figure 8A, a phenomenon called sink occurs due to differences in the amount of thermal contraction during cooling, and a recess R is generated on the surface of the molded product M, as shown in Figure 8B. On the other hand, in the cover 1 of the optical gas sensor device 100 of the above embodiment, as shown in Figure 9, if a recess R exists on the inner surface of the light guide 13 that forms the optical path from the light source 2 to the light receiving unit 4, part of the light emitted from the light source 2 will hit the inner surface of the recess R and be reflected, reducing the amount of light that reaches the light receiving unit 4 and reducing the accuracy of gas concentration detection.

[0052] Therefore, in the optical gas sensor device 100 of this embodiment, the shape of the upper part 110A constituting the cover 1 is devised to prevent unevenness from occurring on the inner surface of the light guide 13. Specifically, considering ease of mold formation (low cost), a flat surface shape for the upper part 110A, as shown in FIG. 10A, is desirable. However, in this embodiment, as shown in FIG. 10B, the cover 1 is designed to have as uniform a thickness as possible overall by making the upper wall portion of the light guide 13, which has a circular cross section, arc-shaped. As a result, in the case of the cover 1 shown in FIG. 10A, which has a partially thick wall, the portion marked with the symbol S may thermally shrink due to sink marks, which could cause depressions on the inner surface of the light guide 13. However, by adopting the shape shown in FIG. 10B, depressions are less likely to occur on the inner surface of the light guide 13. As a result, a decrease in the amount of light reaching the light receiving unit 4 is suppressed, thereby improving the accuracy of gas concentration detection.

[0053] 11A, the optical gas sensor device 100 of this embodiment is configured such that the cover 1 is fixed to the substrate by using a plurality of (six in the figure) positioning pins 14 that penetrate the substrate 6 as thermally caulkable caulking pins. The positioning pins 14 are driven into predetermined positions on the bottom surface of the upper part 110A of the cover 1, as shown in FIG. 3. However, when driving a plurality of caulking pins 14 into the upper part 110A, if the pins are randomly arranged, they must be driven in one by one, which has the disadvantage of lengthening the takt time in the manufacturing process.

[0054] 11B, the optical gas sensor device 100 of this embodiment is configured such that six crimping pins (14) are arranged in pairs at equal intervals in the Y direction, and each pair of two crimping pins (14) surrounded by dotted line D is arranged at equal intervals in the X direction. By arranging them in this manner, it becomes possible to simultaneously drive the two crimping pins (14) surrounded by dotted line D, or the three crimping pins (14) surrounded by chain line C. As a result, there is an advantage in that the time required to drive the positioning pins 14 can be shortened, thereby shortening the takt time.

[0055] Although the invention made by the inventor has been specifically described above based on the embodiments, the present invention is not limited to the above embodiments. For example, in the above embodiments, the gas intakes 111 and 112 and the gas introduction ports 131 and 132 are arranged on a line that forms a 45-degree angle with respect to the X-axis in a top view, but the angle with respect to the X-axis is not limited to 45 degrees. For example, the angle with respect to the X-axis may be set to an angle smaller than 45 degrees or larger than 45 degrees depending on the angle between the central axis of the light guide 13 and the optical axis of the light source 2, etc.

[0056] In the above embodiment, the light guide 13 is described as having a pipe shape with a circular cross section, but may be a pipe shape with an elliptical cross section. Furthermore, in the above embodiment, the optical gas sensor device 100 is described as including one set of the light source 2, the optical filter 3, the light receiving unit 4, and the light guide 13, but may be configured as including multiple sets of the light source 2, the optical filter 3, the light receiving unit 4, and the light guide 13.

[0057] The present invention can be applied to an optical gas sensor device including a light source, a light receiving section, and a pipe-shaped light guiding section.

[0058] REFERENCE SIGNS LIST 100 Optical gas sensor device 1 Cover 2 Light source 3 Optical filter 4 Light receiving section 6 Substrate 110A Upper part of cover 110B Lower part of cover 11 Ventilation hole 111, 112 Gas intake port (ventilation hole inlet) 131, 132 Gas introduction port (ventilation hole outlet) 13 Light guiding section 118A, 118B Half pipe section 121, 122 Recess 123, 124 Fixing pin 12 Gas filter 14 Positioning pin (crimped pin)

Claims

1. An optical gas sensor device comprising: a light source that emits infrared rays to a gas to be detected; a light receiving unit that detects the infrared rays and generates a detection signal; and a cover member having a pipe-shaped light guiding unit whose cross section in a direction perpendicular to the central axis is circular or elliptical, wherein the light source is disposed at one opening of the light guiding unit and the light receiving unit is disposed at the other opening of the light guiding unit, and the infrared rays emitted from the light source are repeatedly reflected on the inner surface of the light guiding unit before reaching the light receiving unit, and the cover member has openings at locations on the light guiding unit where a relatively small amount of infrared rays passes, and on the surface of the cover member, and is provided with ventilation holes for introducing the gas to be detected into the light guiding unit.

2. The optical gas sensor device according to claim 1, wherein the light guide section is formed so as to have a curved portion at its central axis, and the portion of the light guide section through which a relatively small amount of infrared light passes is located inside the curved portion.

3. The optical gas sensor device according to claim 2, wherein the light guide section is formed with two curved sections with a U-shaped central axis, and the cover member is provided with two ventilation holes, each with an opening on the inside of the two curved sections and on the surface of the cover member, for introducing the gas to be detected into the light guide section.

4. The optical gas sensor device according to claim 3, wherein the light guide section is formed so that its central axis forms a U-shape when viewed from above, one opening of the ventilation hole is provided on the upper surface of the cover member, and the other opening of the ventilation hole is provided inside the curved portion.

5. An optical gas sensor device as described in claim 4, wherein the cover member is composed of a plurality of parts divided by a cross section along the central axis of the light-guiding section, and the plurality of parts are configured to have an infrared reflective film on the inner surface of a recess forming the light-guiding section.

6. An optical gas sensor device as described in claim 5, further comprising an optical filter that transmits infrared light of a wavelength corresponding to the absorption wavelength of the gas to be detected, and the light receiving unit is configured to detect the infrared light incident through the optical filter and generate a detection signal.

7. An optical gas sensor device according to any one of claims 1 to 6, comprising a substrate on which the light source and the light receiving unit are mounted, and the cover member is attached to the mounting surface of the substrate so that the light source is located at one opening of the light guiding unit and the light receiving unit is located at the other opening of the light guiding unit.

Images