gas sensor

Abstract

In a gas sensor utilizing photoacoustic effects, the aim is to efficiently replace the gas within the cell while suppressing the leakage of acoustic waves. [Solution] The gas sensor 1 has a gas sensor cell 10 housed in a case 2 equipped with an inlet 3 and an exhaust port 4. The gas sensor cell 10 includes a measurement chamber into which the gas to be measured is taken in, a light source that irradiates the measurement chamber with light, a first connection passage that guides the gas from the cell inlet to the measurement chamber, a second connection passage that discharges the gas in the measurement chamber from the cell outlet, and a microphone that converts acoustic waves generated in the measurement chamber into electrical signals and outputs them. The cell inlet and outlet are provided with a lid 12 that is opened and closed by an actuator 16 housed in the case 2, or an acoustic filter 28 having a porous membrane. In addition, a fan 43 is provided inside the case 2 to circulate gas between the inlet 3 and the exhaust port 4.

Description

【Technical Field】 【0001】 The present invention relates to a gas sensor for detecting components of a gas, and particularly to a gas sensor that detects components of a gas by utilizing the photoacoustic effect. 【Background Art】 【0002】 In production sites of fermented products such as miso and soy sauce, and cosmetics, etc., odor (also called fragrance) is included in the quality control items. Also, for example, in a plant, etc., in order to detect abnormalities and state changes, in addition to various detectors, changes such as abnormalities are detected by confirming the odor. Conventionally, these operations have been carried out relying on the experience and senses of on-site workers, and the mechanization of these operations has been desired from the viewpoints of reducing the burden on workers and reducing management costs. 【0003】 In recent years, attempts have been made to detect gas molecules that are odor components by sensors and to quantify the odor. As a sensor for detecting specific gas molecules (gas components) in the air, a sensor that utilizes the photoacoustic effect is known. For example, in Patent Document 1, by providing a porous gas permeable membrane at an opening formed in a cell, the surrounding gas is diffused into the cell through the opening, and a photoacoustic sensor is disclosed in which the pressure fluctuation in the cell does not escape to the outside through the opening. 【0004】 Also, in Patent Document 2, as a connection hole connecting the inside and the outside of the cell, two connection holes are provided in which the relationship between the opening area inside the cell and the opening area outside the cell of the connection hole is opposite, and outside air is allowed to flow in from one of them, and gas is allowed to flow out from the other, and a photoacoustic sensor is disclosed. 【Prior Art Documents】 【Patent Documents】 【0005】 【Patent Document 1】 Japanese Patent Publication No. 2022-543887 【Patent Document 2】 Japanese Unexamined Patent Application Publication No. 2022-23324 [Overview of the Initiative] [Problems that the invention aims to solve] 【0006】 Odor detection using photoacoustic sensors involves intermittently (pulsing) light of a specific wavelength into the sensor cell. The acoustic waves generated by the thermal expansion and contraction of the gas within the cell, caused by the absorption of light energy by specific gas molecules corresponding to the wavelength of the irradiated light, are then measured. Since the acoustic waves generated within the cell are weak, minimizing leakage of acoustic waves outside the cell is desirable to obtain accurate measurement of these waves. 【0007】 Patent Document 1 describes preventing acoustic wave leakage by sealing the openings leading to the outside with a porous membrane. However, the photoacoustic sensor in Patent Document 1 takes in gas into the cell by diffusion through a single opening, which takes time to take in gas into the cell. On the other hand, the photoacoustic sensor in Patent Document 2 has connection holes for outside air to flow in and connection holes for gas to flow out of the cell, so it can take in sufficient outside air in a shorter time compared to the photoacoustic sensor disclosed in Patent Document 1. However, although Patent Document 2 describes confining acoustic waves by adjusting the opening area on the smaller diameter side of the connection hole, a certain opening area is necessary to obtain sufficient gas flow, and in order to obtain measurement accuracy for weak acoustic waves, it is necessary to suppress acoustic wave leakage to the outside of the cell as much as possible. 【0008】 In view of the above-mentioned problems, the object of the present invention is to provide a gas sensor that can efficiently replace the gas inside the cell and perform highly accurate measurements while suppressing acoustic wave leakage. [Means for solving the problem] 【0009】 In one preferred embodiment, the gas sensor according to the present invention comprises a case having first and second openings, a measurement chamber into which a gas to be measured is taken in, a light source for irradiating the measurement chamber with light, a first connection passage forming a first cell opening with one end opening into the measurement chamber and the other end opening into a space inside the case, a second connection passage forming a second cell opening with one end opening into the measurement chamber and the other end opening into a space inside the case, and a microphone that receives acoustic waves generated in the measurement chamber, converts the acoustic waves into electrical signals corresponding to the acoustic waves, and outputs them, and a sensor cell housed in the case, a first acoustic filter provided in the first cell opening for suppressing the transmission of acoustic waves, a second acoustic filter provided in the second cell opening for suppressing the transmission of the acoustic waves, and a circuit board on which the sensor cell is mounted and which has an electrical circuit formed thereon for transmitting control signals given from the outside to control the light source to the sensor cell and for transmitting the electrical signals output from the microphone to the outside. 【0010】 Furthermore, according to another preferred embodiment of the present invention, a measurement chamber into which the gas to be measured is taken in, A gas sensor cell is disclosed, comprising: a light source for irradiating a measurement chamber with light; a first connecting passage having a first cell opening at one end that opens into the measurement chamber and the other end that opens to the outside; a second connecting passage having a second cell opening at one end that opens into the measurement chamber and the other end that opens to the outside; a microphone that receives acoustic waves generated in the measurement chamber, converts the acoustic waves into electrical signals corresponding to the acoustic waves, and outputs them; a first acoustic filter provided at the first cell opening to suppress the transmission of acoustic waves; and a second acoustic filter provided at the second cell opening to suppress the transmission of acoustic waves. [Effects of the Invention] 【0011】 According to the present invention, the gas inside the cell can be efficiently replaced, and measurements can be performed with higher accuracy during measurement. Other novel features of the present invention and the technical problems solved thereby will become apparent from the description and drawings herein. [Brief explanation of the drawing] 【0012】 [Figure 1] This is a schematic perspective view showing the appearance of a gas sensor in one embodiment. [Figure 2] This is a schematic diagram showing the internal structure of a gas sensor as viewed from above. [Figure 3] This is a schematic diagram showing the internal structure of a sensor cell. [Figure 4] This is a schematic diagram showing the inside of a gas sensor viewed from the side. [Figure 5] This is a schematic diagram showing the inside of a gas sensor viewed from the side. [Figure 6] This is a schematic diagram showing the gas flow inside a gas sensor. [Modes for carrying out the invention] 【0013】 Hereinafter, representative embodiments of the present invention will be described with reference to the drawings. Note that the embodiments and drawings described below are illustrative examples for explaining the present invention, and have been omitted or simplified as appropriate for clarity of explanation. Furthermore, please note that the position, size, shape, and extent of each component shown in the drawings may not necessarily accurately represent them, in order to facilitate understanding of the invention. 【0014】 Figure 1 is a schematic perspective view showing the appearance of a gas sensor to which the present invention is applied. 【0015】 The gas sensor 1 is constructed by housing a sensor cell, described later, inside a case 2. The case 2 is molded using, for example, metal or synthetic resin. The case 2 is provided with an inlet 3 for taking in outside air and an exhaust port 4 for discharging the gas inside the case 2 to the outside. 【0016】 The gas sensor of this embodiment can be used in a detection device that is installed in an atmosphere to detect the components of gases in that atmosphere, such as an odor detection device that detects the components of odors (fragrances) in an atmosphere. 【0017】 Hereinafter, for the convenience of explanation in this specification, the side where the inlet 3 of the gas sensor 1 is provided is defined as the upper side, the opposite side as the lower side, the side where the exhaust port 4 is provided as the front side, the opposite side as the rear side, and the directions perpendicular to the up-down direction and the front-rear direction respectively are defined as the lateral direction or the width direction for the description. 【0018】 FIG. 2 is a schematic diagram showing the internal configuration when looking at the inside of the gas sensor 1 from above (the direction of arrow A in FIG. 1). 【0019】 Inside the case 2, a plurality of sensor cells 10 are mounted side by side in the lateral direction on the circuit board 11. Each sensor cell 10 has a function of measuring an acoustic wave generated by the photoacoustic effect when gas is introduced therein. In the present embodiment, as will be described later, the sensor cell 10 includes two light sources that irradiate light of different wavelengths. Also, the four sensor cells 10 can each have a light source of a different wavelength. 【0020】 On the circuit board 11, a circuit for controlling the emission period, emission intensity, etc. of the light sources included in each sensor cell 10 based on signals given from the outside of the gas sensor 1 via a connector (not shown) or the like is formed. 【0021】 In order to open and close the openings formed at the cell inlets of each sensor cell 10, a lid 12 is provided corresponding to each of the plurality of sensor cells 10. The lid 12 serves as an acoustic filter to prevent acoustic waves from leaking through the openings formed at the cell inlets. The lid 12 may be formed of a member such as resin or rubber that is impermeable to gas molecules. These plurality of lids 12 are fixed to a plate-like connecting plate 14 extending in the width direction (the vertical direction in the figure) provided on the lower side of the connecting shaft 13 shown by a broken line in the figure. The connecting shaft 13 is supported rotatably at both ends, and by rotating the connecting shaft 13, the cell inlets of each sensor cell 10 can be opened and closed simultaneously. 【0022】 A lever 15 is provided near the center of the connecting shaft 13, extending from the connecting shaft 13 to the rear of the gas sensor 1. When the lever 15 is lifted by the actuator 16, the connecting shaft 13 rotates, causing the lid 12 to separate from the sensor cell 10, opening the cell inlet. A spring 17, which is a biasing member, is provided on the side of the connecting plate 14 opposite to the side where the sensor cell is positioned. The spring 17 applies a force to the connecting plate 14 that rotates the connecting shaft 13 in the direction that closes the cell inlet with the lid 12. 【0023】 In this embodiment, a single connecting plate 14 extending from the connecting shaft 13 is provided with pressing portions for the lid 12 and the spring 17. However, the connecting plate 14 may be realized, for example, as a lever-shaped member extending from the connecting shaft 13, corresponding to the pressing portions for the lid 12 and the spring 17, respectively. 【0024】 Figure 3 is a schematic diagram showing the internal structure of the sensor cell 10. 【0025】 The sensor cell 10 is molded from metal or synthetic resin. Inside the sensor cell 10, a measurement chamber 20 is formed where the gas to be measured is stored. The measurement chamber 20 is formed as a cylindrical space within the sensor cell 10. However, the shape of the space that becomes the measurement chamber 20 is not limited to a cylindrical shape; it can also be other shapes, such as a rectangular parallelepiped. 【0026】 Within the sensor cell 10, an LED chamber 21 is formed in which a light source is placed to illuminate the measurement chamber 20. In this embodiment, an LED (light-emitting diode) is used as the light source, and two LEDs 23 mounted on a substrate 22 are placed in the LED chamber 21. The two LEDs 23 are used to illuminate the measurement chamber 20 with light of different wavelengths. For this purpose, the two LEDs 23 can be LEDs that emit light of different wavelengths. Alternatively, light filters that transmit light of different wavelengths can be placed on the light-emitting surfaces of the LEDs 23, so that the light that passes through the light filters is illuminated into the measurement chamber 20. Note that in the figure, two LEDs 23 are placed in one LED chamber 21, An LED chamber 21 may be provided for each LED 23, with one LED 23 placed in each LED chamber 21. The number of LEDs 23 may be one or any number of two or more. In addition to LEDs, other light-emitting means, such as semiconductor lasers, can also be used as the light source. 【0027】 LED23 can control its light emission in response to an external control signal provided via the circuit board 11. Gas measurement is performed by intermittently illuminating the measurement chamber 20 with pulsed light of a predetermined period by turning LED23 ON / OFF at a predetermined interval. When light is shone into the measurement chamber 20, specific gas molecules in the gas filling the chamber that correspond to the wavelength of the light absorb the light energy, generate heat, and undergo thermal expansion. As the light is shone in pulses at a predetermined interval, expansion and contraction are repeated, generating acoustic waves within the measurement chamber 20. Gas measurement can be performed by detecting these acoustic waves. 【0028】 The measurement chamber 20 and the LED chamber 21 may be physically continuous spaces. In order to prevent the gas in the LED chamber 21 from expanding due to the heat generated by the LED 23 and affecting the photoacoustic effect in the measurement chamber 20, a shielding plate that is light-transmitting and suppresses pressure propagation between the two chambers may be placed between the measurement chamber 20 and the LED chamber 21. 【0029】 The inner wall forming the measurement chamber 20 has an opening for a first connection passage 24 that leads to the outside in order to take in external gas into the measurement chamber 20. The opening of the first connection passage 24 on the outside of the sensor cell 10 becomes the cell inlet 25 for introducing outside air. If the inner diameter of the first connection passage 24 is large, light irradiated into the measurement chamber 20 will enter more easily. If light enters the first connection passage 24 more easily, the reflection of light within the measurement chamber 20 will decrease, the optical path length of the light incident on the measurement chamber 20 will shorten, and the intensity of the generated acoustic waves will weaken. In this embodiment, by dividing the first connection passage 24 into two, the inner diameter (cross-sectional area) of the entire first connection passage is secured to allow smooth introduction of external gas, while the inner diameter of each of the first connection passages 24 is reduced to suppress the incidence of light into the first connection passage 24. The number of first connection passages 24 does not necessarily have to be two; it can be one or three or more as long as the effect on acoustic waves is minimized and external gas can be introduced smoothly. 【0030】 A second connection passage 27 is formed in the inner wall of the measurement chamber 20, opposite to the opening of the first connection passage 24. This second connection passage 27 leads to the cell outlet 26 of the sensor cell 10, which opens on the opposite side of the cell inlet 25. Similar to the first connection passage 24, the inner diameter of the second connection passage 27 should be small, as too large a diameter would allow light from inside the measurement chamber 20 to easily enter. On the other hand, in this embodiment, acoustic waves are measured via the second connection passage 27, as will be described later. If the inner diameter of the second connection passage 27 is too small, the acoustic waves entering the second connection passage 27 will be attenuated, reducing the sensitivity of the measurement. Therefore, it is desirable to set the inner diameter of the second connection passage 27 taking both of these factors into consideration. 【0031】 The openings of the first connection passage 24 and the second connection passage 27 do not necessarily have to be located opposite each other, and may be formed at any position on the inner wall forming the measurement chamber 20. However, in order to efficiently exchange the gas in the measurement chamber 20, it is preferable that there is a distance between the openings of the first connection passage 24 and the second connection passage 27 rather than being located close to each other. Similarly, the cell inlet 25 and the cell outlet 26 do not necessarily have to be formed on opposite sides of the sensor cell 10, but it is preferable that they open in different directions to allow for smooth inflow and outflow of gas to the sensor cell 10, in accordance with the gas flow path inside the case 2. 【0032】 The cell outlet 26 is sealed with an acoustic filter 28 to prevent acoustic waves from leaking outside the sensor cell 10. The acoustic filter 28 is formed of a porous membrane with numerous fine permeable holes that allow gas molecules in the gaseous atmosphere to be measured to pass through while suppressing the transmission of acoustic waves. The acoustic filter 28 is attached to the outer surface of the sensor cell around the cell outlet 26, for example, with an adhesive or glue. As described above, the inner diameter of the second connection passage 27 is kept small, so the diameter of the cell outlet 26 is also small. Therefore, the area of ​​the part where the acoustic filter 28 is attached can be made relatively large compared to the size of the part of the acoustic filter 28 through which gas molecules pass, thereby improving the mounting accuracy of the acoustic filter 28 and reducing the possibility of acoustic wave leakage due to improper mounting, etc. 【0033】 Furthermore, the second connection passage 27 branches off into a third connection passage 29, which is formed perpendicular to the second connection passage 27, on its way to the cell outlet 26. One end of the third connection passage 29 opens into the inner circumferential wall of the second connection passage 27, and a microphone 30 for detecting acoustic waves is positioned at the other end. The acoustic waves detected by the microphone 30 are output as an electrical signal corresponding to their strength. In this embodiment, acoustic waves are guided to the microphone 30 via the second connection passage 27 and the third connection passage 29, making it possible to position the microphone 30 outside the measurement chamber 20. By positioning the microphone 30 outside the measurement chamber 20, the spatial volume of the measurement chamber 20 can be reduced, and the detection response characteristics of the acoustic waves can be improved. In addition, the distance between the LED 23 and the microphone 30 can be increased, preventing the effects of vibrations caused by the LED itself heating up and expanding and contracting. 【0034】 Figures 4 and 5 are schematic diagrams of the inside of the gas sensor 1 viewed from the side (indicated by arrow B in Figure 1). Figure 4 shows the cell inlet 25 closed with the lid 12, while Figure 5 shows the cell inlet 25 open, allowing outside air to be introduced into the cell. 【0035】 In this embodiment, an electrically operated electromagnetic solenoid can be used as the actuator 16 for opening and closing the lid 12. The actuator 16 has a plunger 40 that moves up and down when energized. One end of the plunger 40 is in contact with the other end of a lever 15, one end of which is fixed to a connecting shaft 13. 【0036】 When the actuator 16 is not energized (power OFF), the plunger 40 is in the lowered position, as shown in Figure 4. The connecting plate 14 is pressed to the right in the figure by the biasing force of the spring 17, so when the plunger 40 is in the lowered position, the biasing force of the spring 17 acts to rotate the connecting shaft 13 counterclockwise in the figure, causing the cell inlet 25 of the sensor cell 10 to be blocked by the cover 12. In other words, in this embodiment, when the actuator 16 is energized, the cell inlet 25 is open, allowing for the exchange of gas in the measurement chamber 20. 【0037】 On the other hand, when the actuator 16 is energized (power ON), the plunger 40 protrudes upward, as shown in Figure 5, pushing up the lever 15. When the lever 15 is pushed up, a force is applied to the connecting shaft 13, causing it to rotate clockwise. When the connecting shaft 13 rotates clockwise, the spring 17 is compressed by the connecting plate 14, the cover 12 separates from the sensor cell 10, and the cell inlet 25 is opened. In other words, in this embodiment, when the actuator 16 is not energized, the cell inlet 25 is closed, gas is stored in the measurement chamber 20, and the leakage of acoustic waves generated in the measurement chamber 20 from the cell inlet 25 is suppressed. 【0038】 In this embodiment, the opening and closing mechanism that opens and closes the cell inlet 25 with the lid 12 is configured to include a connecting shaft 13, a connecting plate 14, an actuator 16, and a spring 17. 【0039】 As shown in the figure, the space (sensor cell chamber) 41 where the sensor cell 10 is located inside the case 2 is connected to a duct 42 that leads to the exhaust port 4 below the circuit board 11. A fan 43 is positioned between the space where the sensor cell 10 is located and the duct 42. By operating the fan 43, outside air can be drawn into the case 2 from the inlet 3, and the gas inside the case 2 can be discharged through the duct 42 to the exhaust port 4. In this embodiment, the fan 43 is provided between the sensor cell 10 and the exhaust port 4, but the fan 43 may also be provided between the inlet 3 and the sensor cell 10. 【0040】 The actuator 16 and fan 43 are controlled to be turned ON / OFF by an externally provided control signal. The fan 43 may also have its rotation speed externally controllable as needed. When measuring gas, the actuator 16 and fan 43 can be controlled externally to introduce gas into the sensor cell 10. Specifically, the actuator 16 is powered ON to open the cover 12 covering the cell inlet 25, allowing gas to be introduced into the sensor cell 10. The fan 43 is then operated to draw in outside air through the inlet 3 and expel the gas inside the case 2 through the exhaust port 4, thereby replacing the gas inside the case 2. 【0041】 When measuring the gas taken into the gas sensor 1, the power to the actuator 16 is turned OFF to block the cell inlet 25 of the sensor cell 10, and the fan 43 is stopped. After this, the blinking of the LED 23 on the sensor cell 10 is controlled, and measurement is performed using the acoustic signal acquired by the microphone 30. In this way, by turning off the power to the actuator 16 and stopping the fan 43 during measurement, electromagnetic and acoustic noise generated from the actuator 16 and fan 43 is suppressed, making it possible to perform highly accurate measurements with reduced noise influence. 【0042】 Figure 6 is a schematic diagram showing the gas flow path inside the case 2 of the gas sensor 1 during gas exchange. Note that, for ease of understanding, the lid 12, connecting shaft 13, connecting plate 14, lever 15, and spring 17 are omitted from Figure 6. Furthermore, the following explanation assumes that the lid 12 is in the open position. 【0043】 When the gas inside case 2 is replaced, the fan 43 is activated, creating a gas flow from the inlet 3 through the sensor cell chamber 41, the fan 43, and the duct 42 to the exhaust port 4. The solid line in Figure 6 schematically shows the gas flow inside case 2. 【0044】 As shown in the figure, the gas taken in from the inlet 3 is guided to the sensor cell chamber 41. Case 2 is shaped to suppress the flow rate of gas that flows from the inlet 3 to the space on the cell outlet 26 side without passing through the space on the cell inlet 25 side within the sensor cell chamber 41 (the part enclosed by the dashed line C in the figure), thereby creating a gas flow (flow path) from the space on the cell inlet side to the space on the cell outlet side. In addition to the shaping of the case, to create such a gas flow path, for example, a fin-shaped flow straightening plate may be provided in the sensor cell chamber 41 to create a gas flow from the space on the cell inlet 25 side to the space on the cell outlet 26 side. Alternatively, the sensor cell 10 may be arranged along a gas flow path determined by the shape of the sensor cell chamber 41 and the positional relationship of the fan 43, inlet 3, and exhaust port 4 (or duct 42). Specifically, the sensor cell 10 is preferably arranged so that the opening surface of the cell inlet 25 opens toward the upstream direction of the gas flow path, and the opening surface of the cell outlet 26 opens toward the downstream direction of the gas flow path. 【0045】 A portion of the gas introduced into the sensor cell chamber 41 flows into the measurement chamber 20 through the cell inlet 25 of the sensor cell 10, filling the measurement chamber 20. The gas that was in the measurement chamber 20 is then discharged from the cell outlet 26 via the second connection passage 27 and returned to the sensor cell chamber 41. The gas inside the sensor cell chamber 41 is drawn in by the fan 43, sent to the duct 42, and discharged to the outside through the exhaust port 4. 【0046】 In this way, by creating a gas flow from the inlet 3 to the exhaust port 4 inside the case using the fan 43, the gas filling the measurement chamber 20 can be efficiently replaced without increasing the inner diameter of the first connection passage 24 and the second connection passage 27 inside the sensor cell 10. 【0047】 In this embodiment, gas can flow from the sensor cell chamber 41 on the cell inlet 25 side to the duct 42 through the gap (area enclosed by dashed line D) between the case 2 located on the cell inlet 25 side of the sensor cell 10 and the circuit board 11. Also, gas taken in from the inlet 3 can flow directly to the space on the cell outlet 26 side without going around to the side with the cell inlet 25 through the gap (area enclosed by dashed line E) between the case 2 and the sensor cell. By placing, for example, a shielding plate that blocks the flow of gas in one or both of these areas, the flow of gas in these areas can be blocked, so that most of the gas taken into the case 2 flows from the space on the cell inlet 25 side of the sensor cell chamber 41 to the space on the cell outlet 26 side. In this way, by allowing more gas to flow from the cell inlet 25 side to the cell outlet 26 side, the proportion of gas flowing into the sensor cell 10 can be increased, making it possible to replace the gas filling the measurement chamber 20 more efficiently. 【0048】 According to the embodiments described above, it is possible to prevent the leakage of acoustic waves from the measurement chamber of the sensor cell while more efficiently replacing the gas inside the measurement chamber, thereby enabling efficient measurements with high measurement accuracy. 【0049】 In the embodiment described above, the cell inlet is sealed with a lid to prevent acoustic wave leakage. However, similar to the cell outlet, a porous membrane acoustic filter may be attached to the cell inlet to seal the cell inlet and suppress acoustic wave leakage. By sealing the cell inlet with a porous membrane acoustic filter, the mechanism for opening and closing the lid can be omitted, allowing for miniaturization of the gas sensor. Furthermore, in the embodiment described above, the cell outlet is sealed with a porous membrane acoustic filter. However, similar to the cell inlet, an acoustic filter can also be formed using an openable and closable lid. In this way, it becomes possible to design a gas sensor without considering the size of gas molecules passing through the porous membrane. In other words, it is possible to provide a gas sensor that can measure multiple types of unspecified gas molecules, which is a characteristic of gas sensors using an acoustic method. 【0050】 Furthermore, in the above-described embodiment, the connection passage to which the microphone for measuring acoustic waves is provided is formed to branch off from the connection passage leading to the cell outlet. However, the relationship between the cell inlet and the cell outlet may be reversed, so that the connection passage to which the microphone is provided branches off from the connection passage leading from the cell inlet to the measurement chamber. In other words, gas can be introduced into the measurement chamber from the cell outlet in the above-described embodiment, and the gas inside the measurement chamber can be discharged from the cell inlet. 【0051】 Although the present invention has been described above using representative embodiments as examples, the present invention is not limited thereto and can be implemented in various ways without departing from the spirit of the invention as described in the claims. Furthermore, the embodiments described above are explained in detail for the purpose of clearly illustrating the present invention and are not necessarily limited to those having all the configurations described. [Explanation of Symbols] 【0052】 1: Gas sensor, 2: Case, 3: Inlet, 4: Exhaust port, 10: Sensor cell, 11: Circuit board, 12: Cover, 13: Connecting shaft, 14: Connecting plate, 15: Lever, 16: Actuator, 20: Measurement chamber, 21: LED chamber, 22: Circuit board, 23: LED, 24: First connection passage, 25: Cell inlet, 26: Cell outlet, 27: Second connection passage, 28: Acoustic filter, 29: Third connection passage, 30: Microphone, 40: Plunger, 41: Sensor cell chamber, 42: Duct, 43: Fan

Claims

[Claim 1] A case having first and second openings, A sensor cell comprising: a measuring chamber housed in the case into which the gas to be measured is taken in; a light source that irradiates the measuring chamber with light; a first connecting passage that forms a first cell opening with one end opening into the measuring chamber and the other end opening into the space inside the case; a second connecting passage that forms a second cell opening with one end opening into the measuring chamber and the other end opening into the space inside the case; and a microphone that receives acoustic waves generated in the measuring chamber, converts the acoustic waves into electrical signals corresponding to the acoustic waves, and outputs them. A first acoustic filter is provided in the first cell opening to suppress the transmission of the acoustic waves, A second acoustic filter is provided in the second cell opening to suppress the transmission of the acoustic waves, A circuit board is formed on which the aforementioned sensor cell is mounted, which transmits an externally supplied control signal to the sensor cell for controlling the light source, and which transmits the electrical signal output from the microphone to the outside. A gas sensor having the following features. [Claim 2] The gas sensor according to claim 1, further comprising a fan housed in the case for circulating gas within the case from one of the first and second openings toward the other. [Claim 3] The first acoustic filter is a lid-shaped member that covers the first cell opening and opens and closes the first cell opening. The gas sensor according to claim 2, further comprising an opening / closing mechanism housed in the case for opening and closing the first cell opening with the first acoustic filter. [Claim 4] The gas sensor according to claim 3, wherein the opening and closing mechanism includes an actuator that operates the first acoustic filter by an electrical signal supplied from an external source. [Claim 5] The gas sensor according to claim 3, wherein the second acoustic filter is a porous membrane having pores through which gas molecules in the atmosphere to be measured can pass. [Claim 6] The gas sensor according to claim 5, wherein the first cell opening is open toward the upstream direction of the gas flow path, and the second cell opening is open toward the downstream direction of the gas flow path. [Claim 7] The gas sensor according to claim 1, wherein the sensor cell further has a third connection passage that has one end opening to the inner wall of the second connection passage and branches off from the second connection passage, and the microphone is located at the other end of the third connection passage. [Claim 8] At least one of the first acoustic filter and the second acoustic filter is a lid-shaped member that covers a corresponding opening among the first cell opening and the second cell opening, and opens and closes the corresponding opening. The gas sensor according to claim 1, further comprising an opening / closing mechanism housed in the case for opening and closing the corresponding opening by at least one of the acoustic filters. [Claim 9] The gas sensor according to claim 1, wherein at least one of the first and second acoustic filters is a porous membrane having pores through which gas molecules in the atmosphere to be measured can pass. [Claim 10] The measurement chamber into which the gas to be measured is taken, A light source that irradiates the aforementioned measurement chamber with light, A first connecting passage having a first cell opening at one end that opens into the measurement chamber and at the other end that opens to the outside, A second connecting passage having a second cell opening at one end that opens into the measurement chamber and at the other end that opens to the outside, A microphone that receives acoustic waves generated in the measurement room, converts the acoustic waves into electrical signals corresponding to the acoustic waves, and outputs them; A first acoustic filter is provided in the first cell opening to suppress the transmission of the acoustic waves, A second acoustic filter is provided in the second cell opening to suppress the transmission of the acoustic waves, A gas sensor cell having [Claim 11] The gas sensor cell according to claim 10, further having a third connection passage that has one end opening into the inner wall of the second connection passage and branches off from the second connection passage, wherein the microphone is located at the other end of the third connection passage. [Claim 12] The gas sensor cell according to claim 10, wherein at least one of the first acoustic filter and the second acoustic filter is a porous membrane having pores through which gas molecules in the atmosphere to be measured can pass.

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