Gas measuring device
The gas measuring device addresses measurement inaccuracies in changing gas environments by using controlled gas intake and outlet mechanisms, ensuring precise gas composition analysis with reduced noise interference.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- HITACHI GLOBAL LIFE SOLUTIONS INC
- Filing Date
- 2024-12-02
- Publication Date
- 2026-06-12
Smart Images
Figure 2026096046000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a gas measurement device for measuring components of a gas, and particularly to a gas measurement device using a sensor cell in which a gas to be measured is taken in and measured inside.
Background Art
[0002] In production sites of fermented products such as miso and soy sauce, and cosmetics, etc., odor (also referred to as fragrance) is included in the quality control items. Also, for example, in a plant or the like, 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 using 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 pressure fluctuations in the cell do not escape to the outside from the opening.
[0004] Also, in Patent Document 2, as connection holes connecting the inside and outside of the cell, two connection holes in which the relationship between the opening area inside the cell and the opening area outside the cell of the connection hole is opposite are provided, 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
Patent Document 2
[0006] Odor detection using photoacoustic sensors involves intermittently (pulsing) light of a specific wavelength into the sensor cell, and measuring the acoustic waves generated when specific gas molecules, corresponding to the wavelength of the irradiated light, absorb light energy, causing the gas within the cell to expand and contract due to thermal stress.
[0007] When measuring the gas composition at a specific time in an environment where the composition and concentration of the gas in the atmosphere change, it is desirable to be able to introduce the gas into the sensor cell in the shortest possible time. However, the photoacoustic sensor described in Patent Document 1 introduces the gas into the cell by diffusion through a single opening, which takes time. For this reason, it is not suitable for measuring the gas composition at a specific time in an environment where the composition and concentration of the gas in the atmosphere change.
[0008] On the other hand, the photoacoustic sensor described in Patent Document 2 can efficiently exchange the gas inside the cell by separating the gas inlet and outlet into the cell. However, the inlet and outlet of the cell are always open, and the gas inside the cell is constantly being replaced. Therefore, when attempting to perform a measurement that takes a certain amount of time, such as detecting the components of an unspecified gas contained in the atmosphere, the photoacoustic sensor described in Patent Document 2 may experience changes in the components and concentration of the gas taken into the sensor cell during measurement, potentially leading to errors in the measurement results and a decrease in measurement accuracy. The same applies to the photoacoustic sensor described in Patent Document 1.
[0009] In view of the above-mentioned problems, the object of the present invention is to enable highly accurate measurement of gaseous components even in environments where the components and concentrations of gases in the atmosphere being measured change. [Means for solving the problem]
[0010] In one preferred embodiment, the gas measuring device according to the present invention comprises a sensor cell having a measuring chamber into which a gas to be measured is taken in, a light source that irradiates the measuring chamber with light, first and second cell openings that connect the space inside the measuring chamber to the outside, and a microphone that receives acoustic waves generated in the measuring chamber and outputs a measurement signal corresponding to the magnitude of the acoustic waves, an opening and closing mechanism for opening and closing the first cell opening, and a sensor case housing the sensor cell and the opening and closing mechanism and having the first and second openings, a control unit that controls the light source and the opening and closing mechanism, acquires a measurement signal and measures the gas to be measured, and a case housing the gas sensor and the control unit and having a third opening formed at a position corresponding to the first opening and a fourth opening formed at a position corresponding to the second opening.
[0011] Furthermore, in another preferred embodiment, the gas measuring device according to the present invention includes a measuring chamber into which a gas to be measured is taken in and the gas to be measured is measured; a sensor cell having first and second cell openings that connect the space inside the measuring chamber to the outside and outputting a signal corresponding to the measurement result; an opening / closing mechanism having an electrically driven actuator configured to open the first cell opening when the actuator is energized and close the first cell opening when the power to the actuator is cut off; and a sensor case having a first opening and a second opening that houses the sensor cell and the opening / closing mechanism; a control unit that controls the opening / closing mechanism, acquires a measurement value in the sensor cell, performs the measurement, and outputs the measurement result, wherein the control unit is configured to control the opening / closing mechanism prior to performing the measurement, open the first cell opening to take in the gas to be measured into the sensor cell, control the opening / closing mechanism to close the first cell opening, and then perform the measurement by the sensor cell to acquire a measurement value by the sensor cell; and a case housing the gas sensor and the control unit, having a third opening formed at a position corresponding to the first opening and a fourth opening formed at a position corresponding to the second opening. [Effects of the Invention]
[0012] According to the present invention, highly accurate measurements can be performed even in environments where the composition and concentration of gases in the atmosphere being measured change. Other novel features of the present invention and the technical problems solved thereby will become clear from the description and drawings herein. [Brief explanation of the drawing]
[0013] [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. [Figure 7] This is a schematic perspective view showing the appearance of a gas measuring device. [Figure 8] This is a schematic partial perspective view showing the interior of a soundproof chamber for a gas measuring device. [Figure 9] This is a schematic cross-sectional view showing the inside of a gas measuring device. [Figure 10] This is a schematic block diagram showing the configuration of the control unit. [Figure 11] This is a flowchart showing the measurement process flow. [Modes for carrying out the invention]
[0014] Hereinafter, representative embodiments of the present invention will be described with reference to the drawings. Note that the embodiments and drawings described below are examples for explaining the present invention, and for the sake of clarity of explanation, appropriate omissions or simplifications are made. Also, note that in order to facilitate understanding of the invention, the positions, sizes, shapes, ranges, etc. of the respective components shown in the drawings may not necessarily represent them accurately.
[0015] FIG. 1 is a perspective view schematically showing the external appearance of a gas sensor to which the present invention is applied.
[0016] The gas sensor 1 is configured by housing a sensor cell, which will be described later, in a sensor case 2. The sensor case 2 is formed using, for example, metal, synthetic resin, or the like. The sensor case 2 is provided with an inlet 3 for taking in outside air into the sensor case 2 and an exhaust port 4 for discharging the gas inside the sensor case 2 to the outside.
[0017] The gas sensor of the present embodiment can be used in a detection device that is installed in an atmosphere and detects the components of the gas in the atmosphere, for example, a fragrance detection device that detects the components of the fragrance (scent) in the atmosphere.
[0018] Hereinafter, in this specification, for the sake of convenience of explanation, the side where the inlet 3 of the gas sensor 1 is provided is referred to as the upper side, the opposite side is referred to as the lower side, the side where the exhaust port 4 is provided is referred to as the front side, the opposite side is referred to as the rear side, and the directions perpendicular to the vertical direction and the front-rear direction are described as the lateral direction or the width direction.
[0019] FIG. 2 is a schematic diagram showing the internal configuration when the inside of the gas sensor 1 is viewed from above (the direction of arrow A in FIG. 1).
[0020] Inside the sensor case 2, multiple sensor cells 10 are mounted horizontally on the circuit board 11. Each sensor cell 10 is equipped with the function of measuring acoustic waves generated by the photoacoustic effect when gas is introduced into it. In this embodiment, the sensor cell 10 is equipped with two light sources that emit light of different wavelengths, as will be described later. Furthermore, each of the four sensor cells 10 can be equipped with a light source of a different wavelength.
[0021] The circuit board 11 has a circuit formed on it that provides drive signals to control the light emission period and light emission intensity of the light source provided by each sensor cell 10, and extracts the acoustic signals, which are the measured values of each sensor cell 10, to the outside of the gas sensor 1.
[0022] A lid 12 is provided for each of the multiple sensor cells 10 to open and close the opening formed at the cell inlet of each sensor cell 10. The lid 12 acts as an acoustic filter to prevent acoustic waves from leaking out of the opening formed at the cell inlet. The lid 12 may be made of a material that is impermeable to gas molecules, such as resin or rubber. By using an elastic material such as rubber for the lid 12, the airtightness between the lid 12 and the cell inlet 25 can be increased when the lid 12 is closed, making it possible to more reliably prevent acoustic wave leakage.
[0023] Furthermore, by making the shape of the lid 12, for example, a bottomed cup shape that covers the cell inlet 25, and configuring it so that its outer wall deforms due to the pressing force of the spring 17 when the lid 12 is closed, not only is the airtightness between the lid 12 and the cell inlet 25 increased, but it also becomes possible to efficiently supply gas into the sensor cell 10 when closing the lid 12.
[0024] These multiple covers 12 are fixed to a plate-shaped connecting plate 14 that extends in the width direction (up and down direction in the figure) and is located below the connecting shaft 13, as shown by a dashed line in the figure. The connecting shaft 13 is rotatably supported at both ends, and by rotating the connecting shaft 13, the cell inlets of each sensor cell 10 can be opened and closed simultaneously.
[0025] 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.
[0026] 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.
[0027] Figure 3 is a schematic diagram showing the internal structure of the sensor cell 10.
[0028] 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. The sensor cell 10 measures gas by utilizing the photoacoustic effect, which causes the gas to expand and contract due to thermal effects upon light irradiation. For this reason, it is desirable that the inner wall of the measurement chamber 20 be made of a material with a low thermal absorption rate to suppress heat absorption. Note that 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.
[0029] Within the sensor cell 10, an LED chamber 21 is formed, in which a light source for irradiating the measurement chamber 20 is placed. 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 irradiate 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 irradiated into the measurement chamber 20. In the figure, two LEDs 23 are placed in one LED chamber 21, but an LED chamber 21 may be provided for each LED 23, so that one LED 23 is placed in one 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.
[0030] 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.
[0031] The measurement chamber 20 and the LED chamber 21 may be physically continuous spaces. To prevent the gas in the LED chamber 21 from expanding and contracting 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. If the above-mentioned optical filter is used, the optical filter can also be used as the shielding plate.
[0032] 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.
[0033] 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.
[0034] 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 sensor case 2.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] In this embodiment, the opening and closing mechanism that opens and closes the cell inlet 25 with the lid 12 includes the lid 12, a connecting shaft 13, a connecting plate 14, an actuator 16, and a spring 17. For example, an electrically operated electromagnetic solenoid can be used as the actuator 16 that opens and closes 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 the connecting shaft 13.
[0039] 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.
[0040] 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.
[0041] In this embodiment, the lid 12 is opened and closed by rotating the connecting plate 14 around the connecting shaft 13. However, the lid 12 may also be opened and closed by sliding the connecting plate 14 in a direction perpendicular to the opening surface of the cell inlet 25. By adopting such a configuration, the relative positioning accuracy between the lid 12 and the cell inlet 25 can be improved compared to the case where the connecting plate is rotated, thereby improving the reliability of the airtight seal between the lid 12 and the cell inlet 25.
[0042] The space (sensor cell chamber) 41 inside the sensor case 2 where the sensor cell 10 is located is connected to a duct 42 that leads to an 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 sensor case 2 from the inlet 3, and the gas inside the sensor 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.
[0043] The actuator 16 and fan 43 are controlled to be turned ON / OFF by a control signal provided from outside the gas sensor 1. The fan 43 may also have its rotation speed controlled externally as needed. When measuring gas, the actuator 16 and fan 43 can be controlled to efficiently guide the gas into the sensor cell 10.
[0044] Figure 6 is a schematic diagram showing the gas flow path inside the sensor 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.
[0045] When the gas inside the sensor 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 the sensor case 2.
[0046] As shown in the figure, the gas taken in from the inlet 3 is guided to the sensor cell chamber 41. The sensor 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 design of the case shape, 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 such 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.
[0047] 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.
[0048] 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.
[0049] 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 sensor case 2 and the circuit board 11 located on the cell inlet 25 side of the sensor cell 10. In addition, 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 sensor 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 sensor 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 also be increased, making it possible to replace the gas filling the measurement chamber 20 more efficiently.
[0050] Figure 7 is a schematic perspective view showing the external appearance of the gas measuring device using gas sensor 1, and Figure 8 is a schematic partial perspective view showing the interior of the soundproof chamber of the gas measuring device.
[0051] The gas measuring device 100 is constructed by housing a gas sensor 1 and a control board (described later) inside a box-shaped case 110. The case 110 is made of metal, resin, or the like. The inside of the case 110 is divided into two spaces (hereinafter referred to as chambers) by a partition plate 140. The inner wall forming the first chamber 150, where the gas sensor 1 is located, is made of soundproof material attached to suppress external noise from affecting the gas measurement by the gas sensor 1, thus suppressing sound reflection within the first chamber 150. Note that Figure 8 shows the first chamber transparently, and the second chamber is not visible because it is located on the opposite side of the partition plate 140.
[0052] An opening (gas inlet) 120 is formed in the wall of the first chamber 150 located above the gas sensor 1, so that the inlet 3 of the gas sensor 1 can face outwards from the case 110. Furthermore, an opening (gas outlet) 130 is formed in the wall of the first chamber 150 located in front of the gas sensor 1, so that the exhaust port 4 can face outwards from the case 110. Thus, in this embodiment, the opening forming the gas inlet 120 and the gas outlet 130 are formed on mutually adjacent surfaces of the case 110, opening in directions 90 degrees apart. The openings forming the gas inlet 120 and the gas outlet 130 may be formed on opposite walls of the case 110 with the gas sensor 1 in between, so that they open in opposite directions. In this case, the gas sensor 1 should be configured so that its inlet 3 and exhaust port 4 face in opposite directions.
[0053] By forming the gas inlet 120 and gas outlet 130 to open in different directions, it is possible to make it difficult for the gas discharged from the gas outlet 130 to return to the inside of the gas sensor 1 through the gas inlet 120. In particular, by forming the gas inlet 120 and gas outlet 130 on opposite walls of the case 110, a distance can be secured between them, making it difficult for the gas discharged from the gas outlet 130 to return to the gas inlet 120, even when the gas measuring device is miniaturized.
[0054] Figure 9 is a schematic cross-sectional view showing the inside of the gas measuring device 100.
[0055] The gas measuring device 100 is divided by a partition plate 140 into a first chamber 150, which houses the gas sensor 1, and a second chamber 160, which houses the gas sensor 1, on the upper side. The control board 170 is housed in the second chamber 160. The control board 170 has an electronic circuit that serves as a control unit for measuring the gas using the gas sensor 1.
[0056] In this way, by housing the control board 170 in a space separated from the gas sensor 1, it is possible to prevent external noise from being reflected by the control board 170 and affecting the measurement, as well as to prevent vibration noise from the control board 170 itself from affecting the measurement. Note that the second chamber 160 does not have to be configured as a soundproof room with sound-absorbing material lining its inner walls, like the first chamber 150. Furthermore, by placing the control board 170 in a separate space in this way, the gas sensor 1 can be miniaturized, reducing the volume of the sensor case 2. This relatively reduces the amount of gas taken into the sensor case 2, shortening the gas exchange time inside the sensor case 2, and thus shortening the measurement time.
[0057] In photoacoustic sensors, since acoustic waves based on the frequency of intermittent (pulsed) operation of light are used for odor detection, ambient noise becomes a noise component, leading to errors in odor detection. To address this, a known method exists in which the photoacoustic sensor (gas sensor 1 in this embodiment) is enclosed in a soundproof box with soundproofing material attached, or a soundproof box made of soundproofing material. However, when ambient noise is loud and it is necessary to improve sound insulation performance, the sound insulation performance of soundproofing material generally improves with increased volume, requiring a larger soundproof box, which creates a problem of an inconvenient sensor with limitations on installation location. In such cases, a sound-absorbing material or sound-insulating material with excellent sound insulation characteristics at the intermittent operating frequency of light and in a 1 / n octave band (n is 3 to 12) centered on that frequency may be used in the soundproof box. It is desirable that the sound-absorbing material can prevent disturbances when the frequency to be detected by the microphone occurs as a disturbance. In other words, it is desirable to use a sound-absorbing material in which the sound absorption coefficient peaks at the frequency to be detected by the microphone. In addition, a differential circuit that detects the difference between ambient sound and the sound source may be used. These measures allow for a smaller soundproof box even in situations where ambient noise is loud. Furthermore, there is little need to actively block frequencies other than those to be detected by the microphone using sound-absorbing materials. The sound absorption coefficient differs depending on the frequency. When a graph is drawn with the vertical axis representing the normal incidence sound absorption coefficient and the horizontal axis representing 1 / n octave bands (n is 3 to 12), the peak value of the normal incidence sound absorption coefficient and the corresponding frequency will differ for each sound-absorbing material. In this case, there may be two or more peaks.
[0058] Figure 10 is a schematic block diagram showing the configuration of a control unit consisting of electronic circuits formed on a control board 170.
[0059] The control unit 200 is comprised of a microcontroller unit (MCU) 210, an LED drive circuit 220, an acoustic signal processing circuit 230, an actuator drive circuit 240, a fan drive circuit 250, and an interface 260.
[0060] The MCU210 has an arithmetic unit and memory (not shown), and can perform various processes by executing programs stored in memory. The MCU210 also has I / O ports, and the LED drive circuit 220, acoustic signal processing circuit 230, actuator drive circuit 240, fan drive circuit 250, and interface 260 are connected to the I / O ports of the MCU210. In the gas measuring device 100, the MCU210 functions as a control unit that controls these parts to perform measurements.
[0061] The LED driving circuit 220 is connected to the LED 23 of the sensor cell 10 via the circuit board 11 inside the gas sensor 1, and drives the LED 23 in accordance with the control commands output from the MCU 210, thereby controlling the illumination of the LED 23.
[0062] The acoustic signal processing circuit 230 is connected to the microphone 30 via the circuit board 11 in the gas sensor 1, and processes the acoustic signal output from the microphone 30 and provides it to the MCU 210.
[0063] The actuator drive circuit 240 is connected to the actuator 16 and drives the actuator 16 in response to control commands output from the MCU 210, operating the opening and closing mechanism to control the opening and closing of the cell inlet 25 of the sensor cell 10.
[0064] The fan drive circuit 250 is connected to the fan 43 and drives the fan 43 according to control commands output from the MCU 210, controlling its ON / OFF state.
[0065] Here, for example, the LED driving circuit 220 and the sound signal processing circuit 230 may be partially or entirely provided on the circuit board 11.
[0066] Interface 260 is connectable to an external device (not shown) located outside the gas measuring device 100, and the MCU 210 can exchange information with the external device via interface 260. Interface 260 can be, for example, a wired interface such as USB (Universal Serial Bus) or a wireless interface such as WiFi. Furthermore, if the external device can be directly connected to an interface built into the MCU 210, interface 260 may be omitted.
[0067] The external device may be, for example, a personal computer (PC) or a dedicated device that utilizes the gas measurement results. The MCU210 can receive information such as operation commands from the external device via the interface 260 and perform gas measurements accordingly, and can also send information about the status of the gas measuring device 100 and measurement result data from the gas sensor 1 to the external device via the interface 260.
[0068] Figure 11 is a flowchart showing the flow of the measurement process performed by the MCU210.
[0069] The MCU210 starts the gas measurement process in response to a measurement instruction from an external device. In the initial processing, the MCU210 first energizes the actuator 16 via the actuator drive circuit 240, operates the opening and closing mechanism to open the lid 12, and opens the cell inlet 25 (step S300).
[0070] Next, the MCU 210 supplies power to the fan 43 via the fan drive circuit 250 to operate the fan 43, causing gas to flow from the inlet 3 of the gas sensor 1 to the exhaust port 4 (step 310).
[0071] After operating the fan 43 for a predetermined time, the MCU 210 cuts off the power supply from the fan drive circuit 250 to the fan 43, thereby stopping the fan 43. The operating time of the fan 43 may be configured to be set by an external device prior to the start of measurement, or the operating time may be stored in the memory of the MCU 210 in advance (step 320).
[0072] After stopping the fan 43, the MCU 210 controls the actuator drive circuit 240 to turn the power to the actuator 16 ON / OFF, and repeats the opening and closing of the cell inlet 25 by the opening and closing mechanism for a predetermined time or a predetermined number of times. By repeating the opening and closing of the cell inlet 25 multiple times, the gas around the cell inlet 25 is stirred by the connecting plate 14, and the measurement chamber 20 of the sensor cell 10 can be filled more reliably with the gas taken into the gas sensor 1 (step 330).
[0073] After stopping the fan 434 and closing the cell inlet 25 with the opening / closing mechanism, the MCU 210 drives the LED 23 of the sensor cell 10 via the LED drive circuit 220 to make it blink, and starts measuring the gas stored in the measurement chamber 20. The MCU 210 then acquires acoustic data corresponding to the acoustic signal acquired by the microphone 30 via the acoustic signal processing circuit 230. A method for measuring gas using photoacoustic effects is known, for example, in Japanese Patent Application Publication No. 2022-26652, and a detailed explanation is omitted here (step S340).
[0074] Once the measurement is complete, the MCU210 transmits the measurement results to an external device via interface 260 (step S350).
[0075] According to this embodiment, when gas measurement is being performed, the actuator 16 and the fan 43 are both de-energized. Therefore, electromagnetic noise and operating noise generated from the actuator 16 and the fan 43 do not affect the gas measurement, making it possible to perform highly accurate measurements with reduced noise interference.
[0076] In this embodiment, the cell inlet 25 is opened and closed after the fan 43 stops, but the cell inlet 25 may be opened and closed repeatedly while the fan 43 is operating. In this case, the fan 43 may be stopped either before the cell inlet 25 is closed for the last time, or after the cell inlet 25 has been closed.
[0077] Furthermore, the measurement results obtained by the MCU210 do not necessarily have to be information such as the composition or concentration of the gas being measured. For example, the MCU210 can acquire information such as the intensity and peak frequency of acoustic waves obtained by the microphone 30 and send this information to an external device, which can then obtain information such as the composition and concentration of the gas based on this information.
[0078] The gas measuring device according to this embodiment can be used, for example, to detect the concentration of a specific gas in the air inside a building, or to detect odor (fragrance) components. It can also be used to measure gases with different components, such as numerous fragrance samples, to quantify the differences between them, or to measure changes in the gas components over time (changes in fragrance over time).
[0079] According to the above-described embodiment, not only can the gas to be measured be efficiently taken into the sensor cell, but the inflow of gas into the sensor cell during measurement can also be suppressed. Therefore, even in environments where the composition and concentration of the gas in the atmosphere being measured change, highly accurate measurement of gas components can be performed. Furthermore, since the measurement by the sensor cell is performed with the lid opening / closing mechanism and the fan powered off, it is possible to suppress the influence of electromagnetic noise, vibration noise, and electrical noise generated in these parts and perform accurate measurements.
[0080] In the above-described embodiment, a sensor cell utilizing the photoacoustic effect is used as the sensor cell. However, any sensor cell that stores gas in a closed space and performs measurements may be used instead of a sensor cell utilizing the photoacoustic effect.
[0081] 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.
[0082] 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 comprising all the configurations described. [Explanation of Symbols]
[0083] 1: Gas sensor, 2: Sensor 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, 100: Gas measuring device, 110: Case, 120: Gas inlet, 130: Gas outlet, 140: Partition plate, 150: First chamber, 160: Second chamber, 170: Control board, 200: Control unit, 210: MCU, 220: LED drive circuit, 230: Acoustic signal processing circuit, 240: Actuator drive circuit, 250: Fan drive circuit, 260: Interface
Claims
1. A gas sensor comprising a sensor cell having 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 cell opening and a second cell opening that connect the space inside the measurement chamber to the outside, a microphone that receives acoustic waves generated in the measurement chamber and outputs a measurement signal corresponding to the magnitude of the acoustic waves, an opening and closing mechanism for opening and closing the first cell opening, and a sensor case having the first opening and the second opening that houses the sensor cell and the opening and closing mechanism, A control unit that controls the light source and the opening / closing mechanism and acquires the measurement signal, A gas measuring device having the following features.
2. The gas measuring device according to claim 1, further comprising a case for housing the gas sensor and the control unit, the case having a third opening formed at a position corresponding to the first opening and a fourth opening formed at a position corresponding to the second opening.
3. The case has a first chamber in which the gas sensor is housed, and a second chamber in which the control unit is housed, which are separated from each other. The gas measuring device according to claim 2, wherein a sound-absorbing material is attached to the inner wall of the first chamber such that the sound absorption coefficient is peaked at the frequency to be detected by the microphone.
4. The opening and closing mechanism includes a plate-shaped member on which a lid for opening and closing the first cell opening is provided at a position corresponding to the first cell opening, an actuator that is electrically driven to move the plate-shaped member in the direction that opens the first cell opening when energized, and a biasing member that biases the plate-shaped member toward the sensor cell. The control unit controls the opening and closing of the first cell opening by the opening and closing mechanism by controlling the supply of power to the actuator. The gas measuring device according to claim 3.
5. The gas sensor further comprises a second sensor cell having a second measurement chamber into which the gas to be measured is taken in, a second light source that irradiates the second measurement chamber with light, a third cell opening and a fourth cell opening that connect the space inside the second measurement chamber to the outside, and a second microphone that receives acoustic waves generated in the second measurement chamber and outputs a measurement signal corresponding to the magnitude of the acoustic waves. The gas measuring device according to claim 4, wherein the plate-shaped member has a second lid at a position corresponding to the third cell opening, and is configured such that the opening and closing of the first cell opening and the third cell opening are performed together.
6. The gas measuring device according to claim 4, wherein the lid is formed of an elastic material.
7. The gas measuring device according to claim 6, wherein the lid has a bottomed cup shape that covers the first cell opening, and the outer peripheral wall is formed to be deformable.
8. The gas measuring device according to claim 4, further comprising a fan whose operation is controlled by the control unit to circulate gas from the first opening to the second opening, wherein the gas sensor is further equipped with a fan.
9. The control unit, The actuator is energized to open the first cell opening, and the fan is activated to allow gas to flow into the sensor cell. The fan is stopped, power to the actuator is cut off, and the first cell opening is closed. The light source is then driven to acquire the measurement signal, and the gas to be measured is performed. The gas measuring device according to claim 8, configured in such a manner.
10. The gas measuring device according to claim 9, wherein the control unit is configured to stop the fan, then repeatedly open and close the first cell opening using the opening and closing mechanism multiple times, and then close the first cell opening.
11. The gas measuring device according to claim 9, wherein the control unit is configured to open and close the first cell opening multiple times by the opening and closing mechanism while the fan is in operation.
12. The gas measuring device according to claim 2, wherein the first opening and the third opening are opened in a direction different from the direction in which the second opening and the fourth opening are opened.
13. The gas measuring device according to claim 1, wherein the second cell opening is provided with an acoustic filter that suppresses the transmission of the acoustic waves.
14. A gas sensor comprising: a measurement chamber into which a gas to be measured is taken in and the gas to be measured is measured; a sensor cell having a first cell opening and a second cell opening that connect the space inside the measurement chamber to the outside and outputting a signal corresponding to the gas components contained in the gas to be measured; an opening / closing mechanism having an electrically driven actuator configured to open the first cell opening when the actuator is energized and close the first cell opening when the power to the actuator is cut off; and a sensor case having a first opening and a second opening that houses the sensor cell and the opening / closing mechanism. A control unit that controls the opening / closing mechanism, acquires a measurement value in the sensor cell, performs the measurement, and outputs the result of the measurement, wherein the control unit is configured to control the opening / closing mechanism prior to performing the measurement, open a first cell opening to take in the gas to be measured into the sensor cell, and then control the opening / closing mechanism to close the first cell opening, and then perform the measurement by the sensor cell and acquire a measurement value by the sensor cell, A case comprising the gas sensor and the control unit, having a third opening formed at a position corresponding to the first opening and a fourth opening formed at a position corresponding to the second opening, A gas measuring device having the following features.
15. The gas sensor further comprises a fan for circulating gas from one of the first openings and the second openings towards the other within the sensor case. The control unit activates the fan when the gas to be measured is taken in, and stops the fan when the measurement is being performed. The gas measuring device according to claim 14.