Protective cover for optical gas sensor and optical gas sensor device
A box-shaped protective cover with locking pieces and filters retrofits existing optical gas sensors, addressing compatibility and installation challenges, enhancing protection and longevity by preventing dust and droplet ingress.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- MITSUMI ELECTRIC CO LTD
- Filing Date
- 2024-12-24
- Publication Date
- 2026-07-06
Smart Images
Figure 2026111873000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a protective cover for protecting an optical gas sensor from dust and droplets, and is useful as a protective cover for an optical gas sensor mounted on a substrate, for example.
Background Art
[0002] Depending on the installation environment, gas sensors may need to be protected from droplets such as dust and water droplets. Conventionally, as an invention related to a gas sensor with a protective cover, for example, there is one described in Patent Document 1. The protective cover of the gas sensor described in Patent Document 1 is composed of an inner protective cover and an outer protective cover attached so as to cover the tip of a long plate-shaped sensor element attached to the wall of a pipe through which the gas to be measured flows so that the tip protrudes inside the pipe. Further, the gas sensor described in Patent Document 1 is a sensor for detecting the gas concentration of NOx or the like in the exhaust gas of an automobile, and uses a sensor element having a structure in which a plurality of oxygen ion conductive solid electrolyte layers such as zirconia (ZrO2) are laminated, and may be installed in an environment where the temperature is relatively high.
[0003] On the other hand, conventionally, a gas sensor using NDIR (Non Dispersive Infrared) is known. The NDIR type gas sensor is a device having a function of measuring the concentration of a gas to be detected by detecting how much each wavelength is absorbed when infrared rays are emitted, utilizing the property that the gas to be detected has the property of absorbing each specific infrared wavelength. The gas sensor includes, for example, a light emitting part and a light receiving part for infrared rays, and is configured to detect the concentration of the gas to be detected on the optical path between the light emitting part and the light receiving part. In addition, an optical gas sensor is a method of taking in the gas to be detected inside, and may be mounted on a substrate on which electronic components are mounted. As an invention related to such a gas sensor, for example, there is one described in Patent Document 2.
Prior Art Documents
[0004] [Patent Document 1] Japanese Patent Publication No. 2021-60217 [Patent Document 2] Japanese Patent Publication No. 2023-162821 [Overview of the Initiative] [Problems that the invention aims to solve]
[0005] The protective cover described in Patent Document 1 comprises an inner protective cover and an outer protective cover, resulting in a large number of parts. Furthermore, the gas sensor described in Patent Document 1 and the light-absorbing gas sensor described in Patent Document 2 have different detection methods and structures, so the protective cover of Patent Document 1 cannot be directly applied to the light-absorbing gas sensor of Patent Document 2. Furthermore, in the case of light-absorbing gas sensors, there are times when it is desirable to attach a protective cover to a sensor that has already been installed and is in operation. However, since the gas sensor described in Patent Document 1 is attached to a pipe through which engine exhaust gas flows, it is difficult to attach a protective cover to a sensor that has already been installed and is in operation, and Patent Document 1 does not mention such a problem.
[0006] This invention was made in view of the above-mentioned problems, and its objective is to provide a protective cover suitable for an optical gas sensor mounted on a substrate. Another object of the present invention is to provide a protective cover that can be retrofitted to an existing optical gas sensor to protect it from dust, droplets, and the like. [Means for solving the problem]
[0007] To solve the above problems, the present invention provides A protective cover having a box-shaped wall with one side open is provided to cover an optical gas sensor, which is mounted on a substrate and detects the gas concentration in the cavity based on the detection signal obtained by receiving light emitted from the light source with the light receiving unit, the case having a cavity into which the gas to be detected is introduced and a gas intake port communicating with the cavity, and a light source and a light receiving unit arranged opposite each other on either side of the cavity, wherein the protective cover has a box-shaped wall with one side open, The device is configured such that an opening is formed in at least a part of the wall, a filter is provided in the opening, and at least one pair of locking pieces are provided on the opening edge of one surface, which are locked into a locking portion provided on the substrate. [Effects of the Invention]
[0008] The protective cover of the present invention can protect an optical gas sensor mounted on a substrate from dust, liquid droplets, and the like. Furthermore, it has the advantage of being able to be retrofitted to an existing optical gas sensor that has already been installed. [Brief explanation of the drawing]
[0009] [Figure 1] This is a perspective view showing the external appearance and internal structure of an NDIR optical gas sensor, which is an example of a sensor to be protected by the protective cover according to the present invention. [Figure 2] Figure 1 is an exploded perspective view showing an example of the upper and lower parts that make up the housing (case) of the optical gas sensor. [Figure 3] (A) is a bottom view of the upper part of the housing of the optical gas sensor shown in Figure 1, viewed from below, and (B) is an explanatory diagram showing the reflection of infrared light within the light guide section. [Figure 4] This is a perspective view showing one embodiment of a protective cover and an example of an optical gas sensor according to the present invention. [Figure 5] This is a perspective view showing the protective cover of the embodiment mounted on the substrate so as to cover the optical gas sensor mounted on the substrate. [Figure 6]This is a perspective view showing another example of the configuration of the protective cover of the embodiment. [Figure 7] This is a plan view of the protective cover of the embodiment. [Modes for carrying out the invention]
[0010] Hereinafter, embodiments of the protective cover for the optical gas sensor and the optical gas sensor device using the same according to the present invention will be described in detail with reference to the attached drawings. Figure 1 shows a schematic configuration of an NDIR optical gas sensor as an example of a sensor to be protected by the protective cover according to the present invention, and Figure 2 shows an exploded perspective view showing an example of the upper and lower parts that make up the housing body of the optical gas sensor in Figure 1.
[0011] The optical gas sensor (hereinafter referred to as the gas sensor) 10 comprises a housing body 11 consisting of an upper part 110A and a lower part 110B, as shown in Figure 2. The upper part 110A and the lower part 110B are formed from synthetic resin or the like and are joined together to form a single unit, as shown in Figure 1. The housing body 11 has a pipe-shaped cavity formed inside into which the gas to be detected can be introduced, with both ends facing downward (-z direction). The light source 2 is positioned at the opening at one end of the cavity, and the optical filter 3 and light receiving unit 4 are positioned at the opening at the other end, so that the housing body 11 covers (encompasses) the light source 2, the optical filter 3 and the light receiving unit 4, and is mounted on the substrate 6. The cavity formed in the housing body 1 is configured so that the gas to be detected can be introduced through the gas intake ports 1111 and 112 provided in the housing body 11.
[0012] More specifically, as shown in FIG. 2, pins 123 and 124 for joining are provided on the lower part 110B of the housing body 1 on its upper surface. The pins 123 and 124 for joining are convex parts extending in the +z direction, and recesses 121 and 122 having the same diameter as the convex parts are formed in opposing parts on the lower surface of the upper part 110A. By fitting the pins 123 and 124 for joining into the recesses 121 and 122 of the upper part 110A, the upper part 110A and the lower part 110B of the housing body 1I are integrated in a relatively positioned state.
[0013] Also, as shown in FIG. 1, the housing body 1I has a light guide part 13 as a cavity into which the gas to be detected is introduced. The light guide part 13 has a three-dimensionally bent and twisted shape, the cross-section in a direction orthogonal to the central axis is circular, and each part along the central axis has the same diameter. Further, as shown in FIG. 2, the upper part 110A has an upper semi-pipe part 118A which is a recess forming the light guide part 13, and the lower part 110B has a lower semi-pipe part 118B which is a recess forming the light guide part 13. Then, by joining the semi-pipe parts 118A and 118B, a pipe-shaped light guide part 13 is formed. Thus, the housing body 11 is composed of an upper part 110A and a lower part 110B which are formed so as to divide the light guide part 13 vertically by a plane along its axial direction. Also, a plurality of positioning pins 14 are provided on the housing body 11 so as to protrude downward.
[0014] Both ends of the light guide part 13 are open, and as shown in FIG. 1, a light source 2 is disposed so as to face one opening, and an optical filter 3 and a light receiving part 4 are disposed so as to face the other opening. Also, as shown in FIG. 3(A), when viewed from above, the light guide part 13 has a substantially U shape. An infrared reflection film is adhered to the inner surface of the light guide part 13. As the infrared reflection film, gold, silver, aluminum or a dielectric multilayer film can be used. Further, in order to prevent corrosion of the metal film of the infrared reflection film as required, a protective film such as silicon oxide or silicon nitride is formed on the infrared reflection film.
[0015] Also, as shown by the thick arrows in FIG. 3(B), the light guide portion 13 repeats the reflection of the infrared rays incident from the light source 2 into the light guide portion 13 with the infrared reflection film on the inner surface, and emits the infrared rays to the light receiving portion 4 to which the optical filter 3 is attached on the light receiving surface. Thus, the light guide portion 13 of the housing main body 11 functions as an optical path by repeatedly reflecting the infrared rays emitted from the light source 2 with the infrared reflection film, so that a part of the reflected light reaches the light receiving portion 4 through the optical filter 3, and guides the infrared rays from the light source 2 to the light receiving portion 4 to detect the gas. Also, the upper part 110A and the lower part 110B of the housing main body 1 are formed with infrared reflection films on the inner surfaces of the semi-pipe portions 118A and 118B by a plating method (resin plating), a sputtering method, a vacuum evaporation method, etc., so that the reflectance is improved and the amount of light reaching the light receiving portion 4 increases.
[0016] Also, as shown in FIG. 1, gas inlets 111 and 112 as the inlets of the ventilation holes are formed in the upper part 110A of the housing main body 11. Further, as shown in FIG. 3(A), gas inlets 131 and 132 as the outlets of the ventilation holes are formed in the inner wall of the curved portion of the light guide portion 13, and the gas taken in from the gas inlets 111 and 112 once enters the inner space of the housing main body 11 and is configured to be introduced into the light guide portion 13 from the gas inlets 131 and 132. Here, the gas inlets 131 and 132 are provided at positions such that a line (dashed-dotted line C in FIG. 3(A)) connecting the centers of the gas inlets 111 and 112 and the centers of the gas inlets 131 and 132 forms an angle of 45 degrees with respect to the x-axis in a top view.
[0017] Next, an embodiment of a protective cover for protecting the gas sensor 10 having the above configuration from dust, droplets, etc. will be described with reference to FIGS. 4 to 7. The protective cover 20 of this embodiment is box-shaped with one side (bottom side) open, and is mounted so as to cover the gas sensor 10 mounted on the substrate 6, as shown in Figure 4. Specifically, two locking pieces 22 are provided at diagonally opposite corners of the opening edge of the box-shaped body 21 of the protective cover 20, so as to protrude downward. These locking pieces 22 (one of the two is hidden and not visible in Figure 4) are inserted into engagement holes 6a, which are, for example, through holes formed in advance near the mounting area of the gas sensor 10 on the substrate 6, and the parts that protrude from the back surface of the substrate 6 are crimped. As a result, the protective cover 20 is coupled to the substrate 6 while covering the gas sensor 10, as shown in Figure 5. In this specification, a gas sensor 10 covered with the protective cover 20 is referred to as an optical gas sensor device. Furthermore, the structure for locking the locking piece 22 to the substrate is not limited to the engagement hole 6a which is a through hole; for example, a groove or recess may be provided in the substrate, and the end of the locking piece 22 may be inserted and fixed with adhesive.
[0018] Furthermore, electronic components (including elements) that constitute signal processing circuits, etc., are mounted on the upper surface of the substrate 6, and the gas sensor 10 is mounted on the upper surface of the substrate 6 so as to cover some of the electronic components. In addition, a pin hole (not shown) is formed in a predetermined part of the substrate 6 through which a positioning pin 14 provided on the lower surface of the housing body 11 of the gas sensor 10 can be inserted, and the gas sensor 10 is mounted in the predetermined position on the substrate 6 by inserting the positioning pin 14 into the pin hole on the substrate 6. The circuit board 6 is composed of a PCB (Printed Circuit Board) in which conductive wiring is printed on the surface of a plate material such as glass epoxy resin.
[0019] The protective cover 20 may be made of synthetic resin or metal. If the protective cover 20 is made of synthetic resin, the tip of the locking piece 22 is deformed by heat crimping, and if it is made of metal, it is deformed by 90 degrees by bending. In the embodiment shown in Figure 4, the locking pieces 22 are provided at two diagonally opposite corners of the box-shaped body 21, but locking pieces 22 may be provided at all four corners. Furthermore, the protective cover 20 is not particularly limited, but is formed to a size such that there is a gap of 1 mm or less between the four side walls of the box-shaped body 21 (excluding the top wall) and the four sides of the gas sensor 10.
[0020] Furthermore, at least the side of the protective cover 20 where the gas inlets 111 and 112 of the housing body 11 of the gas sensor 10 are located (the top surface of the box-shaped body 21 in Figure 4) is provided with an opening 21A that is larger than the area of the gas inlets 111 and 112. In addition, in this embodiment, an opening 21B is also provided on the front surface of the box-shaped body 21 (the side where the light source 2 and light receiving unit 4 are located) to improve the flow of the gas to be detected. These openings 21A and 21B are each provided with a dustproof and waterproof filter 23 to prevent the intrusion of dust, liquid droplets, etc. The filter 23 is made of, for example, a metal mesh, and in this embodiment, its peripheral edge is bonded and fixed to the inner wall surface of the box-shaped body 21 with adhesive.
[0021] The shape of the openings 21A and 21B in the protective cover 20 is not limited to a circular shape as shown in Figure 4, but can be any shape such as a rectangle or an ellipse. Furthermore, the surfaces on which the openings 21A and 21B are provided are not limited to the top and front surfaces, but may be provided on all three or even all five surfaces as shown in Figure 6. The means of fixing the filter 23 to the protective cover 20 are not limited to adhesive; other means such as screw fastening or snap fastening can be used. Furthermore, the shape of the filter 23 is not limited to a shape corresponding to the shape of the protective cover 20 or the shapes of the openings 21A and 21B, but can be any shape. For example, if the filter is rectangular, the waste of scrap material during cutting can be reduced compared to if it is circular.
[0022] Furthermore, depending on the IP rating required by the customer, dustproof and waterproof properties may be enhanced by, for example, applying adhesive between the opening edge at the lower end of the side wall of the box-shaped body 21 and the substrate 6, or by inserting a rectangular, annular, thin-film sealing member between the lower end surface of the side wall of the box-shaped body 21 and the upper surface of the substrate 6. This sealing member may be pre-attached to the opening edge of the box-shaped body 21 with adhesive or the like.
[0023] Furthermore, in the protective cover 20 of this embodiment, as shown in Figure 7, bulging portions 21a are provided along the vertical direction (perpendicular to the plane of the paper in Figure 7) by bulging the side walls of the box-shaped body 21 outward at two diagonally opposite corners of the four corners of the box-shaped body 21, and a locking piece 22 is provided on the lower surface of these bulging portions 21a. This structure was provided because there were constraints on the position of forming the engagement holes 6a provided on the substrate 6 due to the relationship with the electronic components mounted on the substrate 6, and the design is not limited to this structure; it is also possible to adopt a housing that does not have bulging portions 21a.
[0024] Furthermore, the protective cover 20 may be constructed by actively utilizing the above structure that includes the bulge portion 21a. For example, if there are multiple gas sensors 10 of slightly different sizes to be protected, the position of the engagement hole 6a to be formed on the substrate 6 can be determined to correspond to the largest gas sensor. For the protective cover of the largest gas sensor, the box-shaped body 21 may not have a bulge portion 21a on its side wall, or may have a small bulge portion 21a, with a locking piece 22 formed on its lower surface. On the other hand, for the protective cover of the smaller gas sensor, the box-shaped body 21 may have a bulge portion 21a with a relatively large protrusion on its side wall, with a locking piece 22 formed on its lower tip. In this way, when attaching protective covers suitable for multiple gas sensors of different sizes, the drilling device that forms engagement holes 6a in the substrate 6 and the device that performs crimping on the tip of the locking piece 22 can be used in common for multiple gas sensors of different sizes, thereby reducing manufacturing costs.
[0025] Furthermore, as shown in Figure 4, the substrate 6 on which the gas sensor 10, which is the object of protection of the protective cover 20 of this embodiment, is mounted has electronic components 7 mounted near the gas sensor 10. If the box-shaped body 21 is made without any irregularities or notches on its surface, when the protective cover 20 is attached to the substrate 6 on which the gas sensor 10 is mounted, the lower part of the box-shaped body 21 may interfere with the electronic components 7 located near the sensor. Therefore, in the protective cover 20 of this embodiment, a recess 21b is provided at the lower end of the front wall of the box-shaped body 21 to avoid interference with the electronic components 7. This structure allows the protective cover 20 to be attached to a gas sensor 10 that is already installed and operational, even if an electronic component 7 is mounted nearby on the circuit board 6, without creating any unnecessary gaps. Furthermore, since there is no need to avoid the electronic component, the outer dimensions of the protective cover can be reduced.
[0026] As described above, the protective cover of this embodiment has an opening 22A with a filter 23 and is mounted so as to cover the gas sensor 10 mounted on the substrate 6. Therefore, it can prevent foreign matter such as dust and droplets from entering the sensor without obstructing the inflow of the gas to be detected. This suppresses corrosion of the reflective film formed on the inner surface of the light guide portion 13 of the gas sensor 10, thereby extending the product life. It also prevents accidents in which the housing body of the gas sensor 10 is physically damaged by external force. Furthermore, it can protect not only the sensor but also other electronic components from foreign matter such as droplets. Furthermore, instead of adding a dust and droplet prevention function to the gas sensor 10 itself, a protective cover 20 is attached to cover the gas sensor 10 to protect it from dust and droplets. Therefore, measures against dust and droplets can be implemented without redesigning the main housing 11 of the gas sensor 10.
[0027] Furthermore, the protective cover of this embodiment can easily achieve the IP rating required by the customer by changing the method of attachment to the substrate 6 (adhesive, crimping, sealing member, etc.) or by changing the type (characteristics) of the filters provided in the openings 21A and 21B. Furthermore, by changing the size, number, and position of the openings 22 in the protective cover, it is possible to quickly respond to customer requests, or by preparing multiple types of protective covers in advance, it is possible to easily and quickly achieve the IP rating requested by the customer. In addition, it is possible to easily change the characteristics of the sensor, such as detection time and sensitivity, by changing not only the dustproof and waterproof performance but also the permeability of the gas to be detected.
[0028] Although the present inventors have described the invention in detail based on embodiments above, the present invention is not limited to the above embodiments. For example, in the above embodiments, it was explained that the size of the protective cover 20 is set so that the gap between the gas sensor 10 and the protective cover 20 is 1 mm or less, but a protective cover with a gap of 1 mm or more may be used, for example, depending on the installation environment of the sensor.
[0029] Furthermore, in the above embodiment, an opening 21A is provided in the upper wall portion of the protective cover 20 that faces the gas inlet ports 111 and 112 on the upper surface of the gas sensor 10. However, it is also possible to provide the opening only on the side that does not face the gas inlet ports 111 and 112, thereby further improving dustproof and waterproof performance. Furthermore, although the above embodiment described an example of a protective cover configuration for a gas sensor whose housing body is rectangular in shape when viewed from above, the gas sensor to be protected is not limited to a rectangular shape, and the present invention can also be applied to a protective cover for a gas sensor that is circular in shape when viewed from above. [Explanation of symbols]
[0030] 2 light source 3 Optical filters 4 Light receiving section 6 circuit boards 6a Engagement hole (locking part) 10 Optical gas sensors 11. Main unit 110A Upper part of the cover 110B Lower part of the cover 111,112 Gas intake (ventilation opening) 131,132 Gas inlet (vent outlet) 13 Light guide section 118A, 118B Half-pipe section 121,122 recess 123,124 Fixing pins 20 protective covers 21 Box-shaped body 21A,21B opening 21a Bulge 21b Recess 22 Locking piece 23 filters
Claims
1. A protective cover having a box-shaped wall with one side open is provided to cover an optical gas sensor, which is mounted on a substrate and detects the gas concentration in the cavity based on the detection signal obtained by receiving light emitted from the light source with the light receiving unit, the sensor comprising a housing body having a cavity into which the gas to be detected is introduced and a gas intake port communicating with the cavity, and a light source and a light receiving unit arranged opposite each other on either side of the cavity, wherein the sensor is mounted on a substrate and the light receiving unit receives light emitted from the light source and the sensor detects the gas concentration in the cavity based on the detection signal, A protective cover for an optical gas sensor, characterized in that an opening is formed in at least a part of the wall, a filter is provided in the opening, and at least one pair of locking pieces that engage with a locking portion provided on the substrate are provided on the opening edge of one side.
2. The protective cover for an optical gas sensor according to claim 1, characterized in that the housing body is rectangular in shape and the gas intake port is provided on the side opposite to the substrate, corresponding to the shape of the optical gas sensor, the housing has walls on five of the six sides of the rectangular parallelepiped, so that the remaining side is open, and the opening is formed in the wall on the side facing the gas intake port.
3. The protective cover for an optical gas sensor according to claim 2, characterized in that one or more of the five walls, excluding the wall in which the opening is formed, also have an opening equipped with a filter.
4. The protective cover for an optical gas sensor according to any one of claims 1 to 3, characterized in that the opening edge is provided with a recess to avoid interference with electronic components mounted on the substrate.
5. An optical gas sensor comprising a housing body having a cavity into which the gas to be detected is introduced and a gas intake port communicating with the cavity, and a light source and a light receiving unit arranged opposite each other on either side of the cavity, mounted on a substrate, which detects the gas concentration in the cavity based on the detection signal received by the light receiving unit from the light source, An optical gas sensor device comprising a box-shaped wall with one side open, and a protective cover fitted to cover the optical gas sensor, The optical gas sensor device is characterized in that the protective cover has an opening formed in at least a part of the wall, a filter is provided in the opening, and at least a pair of locking pieces are provided on the opening edge of one side which are locked into locking parts provided on the substrate.