Concentration measurement device

Abstract

A concentration measurement device 100 comprises: a measurement cell 10 that has a flow path for a measurement fluid; a light source 2 that emits measurement light L1 that enters the measurement cell through a window 4A; a reference light detector 8 that is disposed laterally of the light source 2 and that part of light from the light source directly enters; a measurement light detector 6 that detects light transmitted through the measurement cell; and a light limiting member 20 that is disposed between the light source 2 and reference light detector 8 and the window 4A, the light limiting member 20 having a light transmitting portion 20b that transmits the measurement light, and a light blocking portion 20a that is disposed around the light transmitting portion.

Description

concentration measuring device

[0001] The present invention relates to a concentration measuring device, and more particularly to a concentration measuring device that measures the concentration of a fluid based on the intensity of light that has passed through the fluid in a measurement cell.

[0002] Conventionally, concentration measuring devices configured to optically measure the concentration of a source gas formed from a liquid material such as an organic metal or a solid material have been known. In this type of concentration measuring device, light of a predetermined wavelength is incident from a light source through an entrance window into a measurement cell into which the source gas is introduced, and the transmitted light that passes through the measurement cell is received by a light-receiving element to measure the absorbance. From the measured absorbance, the concentration of the fluid in the measurement cell can be determined according to the Beer-Lambert law.

[0003] Patent Documents 1 and 2 describe an in-line concentration measurement device that is installed in a gas supply line that supplies gas to a semiconductor manufacturing device. The in-line concentration measurement device can determine the concentration of the gas flowing through the line by measuring the absorbance of the gas in a measurement cell installed in the gas supply line.

[0004] In the concentration measuring devices described in Patent Documents 1 and 2, a portion of the light from the light source is incident on a reference light detector in addition to the measurement cell. The reference light detector receives direct light from the light source that has not passed through the measurement cell and has not been absorbed by gas. The output of the reference light detector can be used to monitor the state of the light source and to correct the measurement light.

[0005] Similarly, as a device for optically measuring fluid concentration, Patent Document 3 describes an ozone concentration meter that can measure concentration by utilizing ultraviolet absorption by ozone gas. The ozone concentration meter described in Patent Document 3 discloses that the ozone concentration in the atmosphere is measured by a differential absorption method using two LEDs that emit ultraviolet light of different wavelengths.

[0006] The ozone concentration meter described in Patent Document 3 also includes a reference light detector that receives part of the light from the light source. The output of the reference light detector is used to correct for the influence of the LED light intensity that varies depending on the external environment, thereby improving measurement accuracy.

[0007] International Publication No. WO 2017 / 029791 International Publication No. WO 2018 / 021311 JP 2012-13573 A International Publication No. WO 2020 / 213385

[0008] The present applicant is currently developing an apparatus for optically measuring the concentration of ozone gas. However, when a portion of the light source light is received by a reference light detector located near the light source as described above, not only the light source light but also light from unintended paths, such as reflected light from optical elements such as windows, so-called stray light, may be incident on the reference light detector from various directions.

[0009] It was found that the influence of such stray light can cause noise in the output of the reference light detector, which can lead to unstable measurements. If the output of the reference light detector is unstable, it becomes difficult to accurately grasp the light source state, which can lead to a problem of reduced accuracy in concentration measurements.

[0010] The present invention has been made to solve the above-mentioned problems, and its main object is to provide a concentration measuring device that can stably measure the concentration of a fluid (e.g., ozone gas) in a compact manner.

[0011] A concentration measuring device according to an embodiment of the present invention comprises a measurement cell having a flow path for a measurement fluid, a light source that emits measurement light that enters the measurement cell through a window, a reference light detector that is arranged to the side of the light source and into which a portion of the light from the light source is directly incident, a measurement light detector that detects light that has passed through the measurement cell, and a light-limiting member that is arranged between the light source, the reference light detector, and the window, the light-limiting member having a light-transmitting portion that transmits the measurement light and a light-blocking portion that is arranged around the light-transmitting portion.

[0012] In one embodiment, the light restricting member is formed by a light-blocking orifice plate having a hole provided in the center.

[0013] In one embodiment, the light-limiting member is disposed forward from the tip of the light source along the optical axis direction of the light source by a distance that is 10 to 50% of the distance from the tip of the light source to the window.

[0014] In one embodiment, the light source and the measurement light detector are arranged opposite each other across the measurement cell, and in the optical axis direction of the light source, the reference light detector is arranged to the side of the light source, further back than the tip of the light source, and a lens for focusing light from the light source is provided in front of the reference light detector.

[0015] In one embodiment, the concentration measuring device further includes a bandpass filter provided between the light restricting member and the window.

[0016] In one embodiment, the window has a protrusion that protrudes in the direction of the measurement cell.

[0017] In one embodiment, the light source includes two light-emitting elements that emit light of different wavelengths.

[0018] In one embodiment, the measurement fluid is ozone gas, and the light source is configured to emit near-ultraviolet light having a wavelength of at least 200 nm to 320 nm as the measurement light.

[0019] The concentration measuring device according to the embodiment of the present invention is provided in a relatively compact form, yet is capable of stably and accurately measuring the concentration of a fluid such as ozone gas.

[0020] 6 is a schematic cross-sectional view showing the configuration of a concentration measurement device of a comparative example. FIG. 7 is a diagram for explaining the path of light from a light source in the concentration measurement device of the comparative example. FIG. 7 is a schematic cross-sectional view showing the configuration of a concentration measurement device according to an embodiment of the present invention. (a) is a schematic cross-sectional view showing a fluid unit of the concentration measurement device according to an embodiment of the present invention, and (b) is a plan view showing a light limiting member. FIG. 8 is a diagram for explaining the path of light from a light source in the concentration measurement device of the embodiment shown in FIG. 3. FIG. 8 is a schematic cross-sectional view showing the configuration of a concentration measurement device according to another embodiment of the present invention. FIG. 9 is a graph showing the transmission characteristics of a bandpass filter provided in the concentration measurement device shown in FIG. 6. FIG. 9 is a schematic cross-sectional view showing the configuration of a concentration measurement device according to yet another embodiment of the present invention. FIG. 10 is a schematic cross-sectional view (cross-sectional view along a plane perpendicular to the flow path) showing the configuration of a concentration measurement device according to yet another embodiment of the present invention.

[0021] First, before describing a concentration measuring device according to an embodiment of the present invention, a concentration measuring device as a comparative example disclosed in International Publication No. 2023 / 013314 by the present applicant will be described.

[0022] 1 shows a concentration measuring device 900 of a comparative example. The concentration measuring device 900 is configured to measure the concentration of ozone gas G passing through an internal flow path of a measuring cell 10, and includes a light source 2 that emits measuring light L1 that enters the measuring cell 10 through a window 4A, and a measuring light detector 6 that receives the measuring light L1 that has passed through the measuring cell 10 through a window 4B and a lens 5.

[0023] The light source 2 and the measurement light detector 6 are arranged to face each other across a measurement cell 10 through which ozone gas G as a measurement fluid passes. The windows 4A and 4B have sufficiently high translucency to the measurement light L1, and allow the measurement light L1 to pass through while sealing the flow path of the measurement cell 10.

[0024] It is known that ozone in a gaseous state has a maximum absorption at approximately 254 nm. For this reason, near-ultraviolet light with a wavelength of 200 nm to 320 nm, for example, is used as the measurement light L1, and the windows 4A and 4B are formed from a material with high transmittance for near-ultraviolet light, such as sapphire glass, quartz, calcium fluoride, or magnesium fluoride. However, in addition to the ultraviolet absorption band, ozone also has an absorption band in the visible light region of 450 to 850 nm, although the degree of absorption is small. Therefore, visible light can also be used as the light source light when measuring the concentration of high-concentration ozone gas.

[0025] In the concentration measuring device 900, the concentration C of the ozone gas G in the measuring cell 10 is calculated by the Lambert-Beer law: Aλ=−log １０ (I / I ０ ) = α C L based on the output of the measurement light detector 6. Here, Aλ is the absorbance for light of wavelength λ, and the transmittance I / I of the measurement light L1 that has passed through the measurement cell 10 is ０ (i.e., incident light intensity I ０ It is defined as the inverse of the common logarithm of the ratio of transmitted light intensity I to transmitted light intensity I.

[0026] In the above formula, α is the absorption coefficient determined by the gas type and the wavelength λ of the transmitted light, and L is the optical path length (the distance between the windows 4A and 4B), which are known in advance. Therefore, it is possible to determine the concentration C of the gas G based on the transmitted light intensity I measured by the measurement light detector 6. Note that the incident light intensity I ０ may be substituted with the transmitted light intensity I detected by the measurement light detector 6 in a state where it is confirmed that no light absorption occurs, such as when the measurement cell 10 is filled with a gas that does not absorb the measurement light L1 or when it is maintained in a vacuum state.

[0027] Furthermore, in the concentration measuring device 900, a reference light detector 8 is provided near the light source 2. The reference light detector 8 is disposed to the side of the light source 2 and behind the tip of the light source 2 in the optical axis direction of the light source 2.

[0028] 2, the reference light detector 8 can detect a portion of the radially emitted light, including the measurement light L1, directed from the light source 2 (here, a bullet-shaped light-emitting diode) toward the measurement light detector 6, as reference light L2 via the lens 7. The light source 2 has directionality, and the element is designed so that most of the emitted light is directed toward the measurement light detector 6, but a certain amount of light, although a relatively small proportion, also reaches the reference light detector 8 located in front of it.

[0029] The use of the reference light detector 8 makes it possible to monitor fluctuations in the output of the light source 2 over time. In addition, the output of the reference light detector 8 can be used to correct the transmitted light intensity I detected by the measurement light detector 6, thereby making it possible to determine the concentration with greater accuracy.

[0030] For example, in Patent Document 1, instead of the detected transmitted light intensity I, ｃ = I × (I ｒ０ / I ｒ ) the corrected transmitted light intensity I ｃ In the above formula, I ｒ０ is the initial reference light intensity detected by the reference light detector 8 at the time of shipment, etc., and I ｒis the current reference light intensity measured by the reference light detector 8 at the same time that the transmitted light intensity I is measured by the measurement light detector 6 for concentration measurement. Also, the initially set incident light intensity I ０ To (I ｒ / I ｒ０ ) to perform correction, the density measurement may be performed taking into account the current light source condition. ０ However, when the output of the light source 2 fluctuates over time, the incident light intensity I ０ The incident light intensity I ０ The re-measurement may be performed when the output fluctuation of the reference light detector 8 over time exceeds a predetermined range.

[0031] Concentration calculations based on the outputs of the measurement light detector 6 and reference light detector 8 and drive control of the light source 2 can be performed by the connected external electric unit 12. In the concentration measuring device 900, the light source 2, measurement light detector 6, and reference light detector 8 are arranged near the measurement cell 10, so it can be manufactured in a compact form. Note that, because ozone gas is a gas at room temperature and normal pressure, there is no need to heat the measurement cell 10 to a high temperature, and there is no problem in arranging the light source 2 and light detectors 6 and 8 near the measurement cell 10.

[0032] Furthermore, in the concentration measuring device 900, the light source 2 and photodetectors 6 and 8 are integrally provided near the measurement cell 10, so there is no need to optically connect the light source and photodetectors provided in external devices to the measurement cell via optical transmission members such as optical fibers. Therefore, there is no influence of attenuation in the optical transmission path, and more accurate concentration measurement can be performed using direct detection light.

[0033] 2, in addition to the reference light L2 directly incident from the light source 2, reflected light from the surfaces of the windows 4A, 4B or the lens 5, or the surface of the measurement light detector 6 (more specifically, the surface of the light-receiving window) may also be incident as stray light L3 indicated by the dashed line on the reference light detector 8 disposed near the measurement cell 10. The stray light L3 also includes light reflected from, for example, a stainless steel housing.

[0034] In particular, the light reflected from the exit window 4B, lens 5, and measurement light detector 6 passes through the measurement cell 10 and may be absorbed by the gas present therein. This causes the intensity of stray light L3 to fluctuate depending on the gas concentration, impairing the stability of the light detected by the reference light detector 8. In fact, experiments by the inventors have confirmed that the output of the reference light detector 8 fluctuates somewhat in the same manner as the output of the measurement light detector 6, depending on the fluctuations in the gas pressure in the cell.

[0035] Furthermore, in order to efficiently measure the reference light L2, a lens 7 for focusing is provided in front of the reference light detector 8, but this lens 7 also allows stray light L3 over a wide angle range to be incident on the reference light detector 8. Therefore, particularly when the lens 7 is provided, while the reference light intensity can be increased, noise is more likely to occur in the output of the reference light detector 8 due to the influence of the stray light L3.

[0036] Thus, in the concentration measuring device 900 of the comparative example, even though it is intended to measure the intensity of the reference light L2 directly from the light source 2, it sometimes also detects the stray light L3, which includes light that has passed through the gas. This causes a problem in that the output of the reference light detector 8 becomes unstable due to the stray light L3.

[0037] To address this issue, the concentration measuring device 100 according to the embodiment of the present invention described below uses a light limiting member 20 to cut stray light L3, which is mainly reflected light from optical components such as windows and lenses, so that it does not enter the reference light detector 8. This stabilizes the output of the reference light detector, makes it possible to grasp the light source state more accurately, and perform appropriate concentration measurements over a long period of time.

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to the following embodiments. Furthermore, the following describes a concentration measurement device in which the measurement target is a gas (particularly ozone gas), but in other embodiments, the measurement target may be a fluid other than a gas, such as a liquid. In the following description, components similar to those in the concentration measurement device 900 of the comparative example described above will be given the same reference numerals, and detailed description may be omitted.

[0039] 3 shows a concentration measuring device 100 according to an embodiment of the present invention. The concentration measuring device 100 includes a light source 2 that emits measurement light L1 that enters a measurement cell 10 through a window 4A, and a measurement light detector 6 that receives the measurement light L1 that has passed through the measurement cell 10 through a window 4B and a lens 5. A reference light detector 8 is also provided near the light source 2, and receives light directly from the light source 2 through a lens 7.

[0040] The light source 2 and the measurement light detector 6 are arranged to face each other across a measurement cell 10 through which ozone gas G passes. The windows 4A and 4B have sufficiently high translucency to the measurement light L1, and allow the measurement light L1 to pass through while sealing the flow path of the measurement cell 10. The reference light detector 8 is arranged to the side of the light source 2, behind the tip of the light source 2 in the optical axis direction of the light source 2.

[0041] The light source 2 is configured using, for example, an LED as a light-emitting element, but an LD (laser diode) can also be used instead of an LED. Furthermore, the light-receiving elements that make up the measurement light detector 6 and the reference light detector 8 are, for example, photodiodes or phototransistors.

[0042] Concentration calculations based on the outputs of the measurement light detector 6 and the reference light detector 8, and drive control of the light source 2 can be performed in the connected external electric unit 12. The electric unit 12 is configured using circuit elements such as a processor and memory mounted on a circuit board, includes a computer program that executes predetermined calculations based on input signals, and is realized by a combination of hardware and software. Some or all of the components of the electric unit 12 (such as the CPU) may be provided in a device external to the electric unit 12.

[0043] The calculation of the concentration in the electric unit 12 is performed based on the Lambert-Beer law, Aλ=−log １０ (I / I ０ ) = α C L. When measuring the concentration of ozone gas G, the emission wavelength of the light source 2 is set to, for example, the near ultraviolet region of 200 to 320 nm. However, visible light can be used when measuring the concentration of high-concentration ozone gas.

[0044] The concentration measuring device 100 may also include a pressure sensor and a temperature sensor (both not shown) for measuring the pressure and temperature of the ozone gas in the measurement cell 10. In this case, the concentration measuring device 100 can also refer to the outputs of the pressure sensor and the temperature sensor to determine the concentration of the ozone gas flowing through the measurement cell 10, for example, from the following relational expression, as described in Patent Document 4 (WO 2020 / 213385): Cv=(RT / αLPt)·ln(I ０ / I)

[0045] In the above formula, Cv is the concentration (vol %) of the measurement gas in the total gas, α is the absorption coefficient of the measurement gas, Pt is the total pressure of the gas that can be measured by the pressure sensor, T is the gas temperature that can be measured by the temperature sensor, and R is the gas constant. Also, similar to the Beer-Lambert law, L is the optical path length of the measurement cell, I ０ is the incident light intensity, and I is the transmitted light intensity.

[0046] In the concentration measuring device 100 of this embodiment, a light limiting member 20 having an opening is provided between the light source 2 and the reference light detector 8 and the incident-side window 4A. The light limiting member 20 is provided to pass light traveling from the light source 2 toward the measurement light detector 6 and to prevent reflected light from optical elements such as the windows 4A and 4B, the lens 5, and the measurement light detector 6 from entering the reference light detector 8.

[0047] 4(a) shows the fluid unit 50 near the measurement cell 10 in the concentration measurement device 100, and FIG. 4(b) shows the light-limiting member 20 provided in the fluid unit 50. As can be seen from FIGS. 4(a) and 4(b), in this embodiment, the light-limiting member 20 is formed by a disk-shaped light-shielding plate having a light-transmitting portion 20b in the center and a light-shielding portion 20a surrounding the light-transmitting portion 20b.

[0048] In this embodiment, the light-limiting member 20 is formed by a light-shielding orifice plate, more specifically, an orifice plate (e.g., 0.1 mm to 3 mm thick) made of a metal such as stainless steel, aluminum, or steel. The orifice forming the light-transmitting portion 20b can be formed by mechanically processing or chemically etching the plate, and the orifice diameter is set to, for example, about 1 mm to 3 mm. Furthermore, in the light-limiting member 20, the area ratio of the light-transmitting portion 20b to the light irradiation surface (the sum of the light-shielding portion 20a and the light-transmitting portion 20b) is set to, for example, 0.005% to 10%.

[0049] However, it is sufficient that the light-shielding portion 20a and the light-transmitting portion 20b of the light-limiting member 20 are light-transmitting and light-blocking, respectively, with respect to the light emitted from the light source 2. Therefore, as described above, when ultraviolet light is emitted from the light source 2 to measure the ozone gas concentration, it is sufficient that the light-transmitting portion 20b is light-transmitting to the ultraviolet light, and the light-blocking portion 20a is light-blocking to the ultraviolet light. Note that, here, "light-transmitting" refers to a transmittance of 80% or more, and "light-blocking" refers to a transmittance of 20% or less and a reflectance of 50% or less.

[0050] The light-transmitting portion 20b may be formed from a material that transmits the measurement light, other than pores physically formed in the plate. For example, when ultraviolet light is used, the light-limiting member 20 may be formed by covering the entire portion of a plate made of sapphire, calcium fluoride, or magnesium fluoride except for the central portion with a material that blocks ultraviolet light (e.g., chromium).

[0051] Furthermore, the light-limiting member 20 may be disposed anywhere as long as it is located between the light source 2 and the reference light detector 8 and the entrance-side window 4A, and may be, for example, integrally attached to the light-source-side surface of the window 4A. In this case, the light-limiting member 20 may be formed of a light-shielding coating (e.g., a chrome film) disposed on the surface of the window 4A so as to surround the periphery except for the central portion.

[0052] However, in order not to reduce the intensity of the detected measurement light L1, it is preferable that the light limiting member 20 be disposed near the light source 2. For this reason, the light limiting member 20 is disposed, for example, between the tip of the light source 2 and the window 4A, at a position close to the light source 2, that is, at a distance of 10% to 50% of the distance from the tip of the light source 2 to the window 4A, and forward from the tip of the light source 2. The light limiting member 20 may also be disposed immediately in front of the reference light detector 8 as, for example, a pinpole member.

[0053] Furthermore, since a higher transmittance of the light-transmitting portion 20b improves the light utilization efficiency, the transmittance of the light-transmitting portion 20b is designed to be, for example, 90% or more, and by providing holes, reflection and absorption at the light-transmitting portion 20b can be eliminated, allowing approximately 100% of light to pass through. The planar shape of the light-transmitting portion 20b may be any shape other than a circle, such as a polygon.

[0054] 5 is a diagram showing the optical path of the light source light in the fluid unit 50 of the concentration measuring device 100 of this embodiment. As shown in Fig. 5, the measurement light L1, which is the main light emitted from the light source 2 having directivity in the optical axis direction, passes through the light-transmitting portion (here, the orifice) of the light-restricting member 20, and enters the measurement light detector 6 via the window 4A, the measurement cell 10, the window 4B, and the lens 5. Therefore, the concentration of the gas can be measured by measuring the light absorption of the gas in the measurement cell.

[0055] Furthermore, reference light L2 from the light source 2, which is focused by the lens 7, is incident on the reference light detector 8. As a result, similar to the concentration measuring device 900 of the comparative example, the state of the light source 2 can be detected and used to correct the concentration measurement.

[0056] On the other hand, the light limiting member 20 is provided in front of the light source 2 and the reference light detector 8 up to the window 4A on the entrance side, so that stray light L3 including reflected light from the windows 4A and 4B, the lens 5, and the measurement light detector 6 is effectively blocked by the light limiting member 20. Therefore, the stray light L3, whose intensity changes due to the influence of light absorption by these gases, is prevented from entering the reference light detector 8.

[0057] In this way, the light limiting member 20 can stabilize the output of the reference light detector 8 by limiting the incidence of light that has passed through the measurement cell 10 in particular. Experiments conducted by the inventors have confirmed that when the light limiting member 20 is provided, the output value of the reference light detector 8 is maintained approximately constant, regardless of fluctuations in the pressure (or concentration) of the gas in the measurement cell and the resulting fluctuations in the output of the measurement light detector 6.

[0058] 6 shows the configuration of a concentration measuring device 101 according to another embodiment. Hereinafter, the same components as those in the concentration measuring device 100 described above will be given the same reference numerals, and detailed description thereof may be omitted.

[0059] In the concentration measuring device 101, a bandpass filter 22 is provided between the light limiting member 20 and the incident-side window 4A to limit the wavelength band of light from the light source 2. As shown in Fig. 7, the bandpass filter 22 used in this embodiment has a peak wavelength at 300 nm and is configured to transmit only light having a wavelength of approximately 290 nm to approximately 310 nm.

[0060] In this way, while the output of the reference light detector 8 is stabilized by the light limiting member 20, the wavelength range of the measurement light L1 can be limited by providing a bandpass filter 22, thereby improving the accuracy of concentration measurement based on the output of the measurement light detector 6.

[0061] 8 shows the configuration of a concentration measuring device 102 according to yet another embodiment. Hereinafter, the same components as those in the concentration measuring device 100 described above will be given the same reference numerals, and detailed description thereof may be omitted.

[0062] In the concentration measuring device 102, the entrance and exit windows 24A, 24B that seal the measurement cell 10 are provided with portions that protrude toward the flow path. This shortens the optical path length through which the measurement light is absorbed inside the measurement cell 10. A concentration measuring device having such a configuration is disclosed in Japanese Patent Application Laid-Open No. 2023-105732 by the present applicant.

[0063] By using the protruding windows 24A and 24B as described above, it is possible to appropriately measure the concentration without saturating the output, even in a concentration range or light source wavelength where the gas has a high absorbance. For example, when the optical path length is about 10 mm, the transmittance of ozone gas for light with a wavelength of 260 nm drops to approximately zero at a concentration of several mass percent, making it difficult to measure the concentration of gases with higher concentrations. In contrast, by intentionally shortening the optical path length using the windows 24A and 24B, it is possible to appropriately measure ozone gas at higher concentrations using a 260 nm light source without changing the other components.

[0064] 9 is a cross-sectional view of a fluid unit provided in a concentration measuring device 103 of yet another embodiment, taken along a plane perpendicular to the flow path F through which gas flows. Hereinafter, components similar to those in the concentration measuring device 100 described above will be given the same reference numerals, and detailed description thereof may be omitted.

[0065] In the concentration measuring device 103, the light source 2 includes two light-emitting elements 2a and 2b that emit light of different wavelengths. In this embodiment, the emission wavelength of one light-emitting element 2a is, for example, 230 nm to 320 nm, and the emission wavelength of the other light-emitting element 2b is, for example, 520 nm to 680 nm. As described above, ozone gas has two absorption peak wavelengths, and near-ultraviolet light is preferably used when measuring low ozone gas concentrations, while visible light is preferably used when measuring high ozone gas concentrations. Therefore, by using the two light-emitting elements 2a and 2b with different emission wavelengths, it becomes possible to measure ozone gas concentrations over a wider concentration range.

[0066] Furthermore, the two light-emitting elements 2 a and 2 b may be LEDs, one of which has a peak wavelength near 250 nm and the other of which has a peak wavelength near 280 nm, similar to the light source described in Patent Document 3. By alternately lighting these elements and measuring the transmitted light intensity for light of each wavelength, the ozone concentration can be measured more accurately by applying the differential absorption method.

[0067] When two light-emitting elements 2a and 2b are used in this manner, the elements are typically arranged so that the optical axis of each light-emitting element is directed toward the measurement light detector 6. In this case, it is preferable that the measurement light of each light-emitting element 2a and 2b is appropriately incident on the measurement light detector 6, and that reflected light (stray light) from optical elements such as windows 4A and 4B is not incident on the reference light detector. Although the reference light detector is not shown in Figure 9, it is arranged so as to overlap with the light-emitting elements 2a and 2b on the front or back side of the paper.

[0068] For this reason, the light-limiting member 26 of this embodiment is provided with two light-transmitting portions 26b. The two light-transmitting portions 26b are typically arranged on the optical axes of the light-emitting elements 2a and 2b. However, the two light-transmitting portions 26b do not necessarily have to be provided independently, and may be connected to form a single light-transmitting portion (for example, a single elliptical hole that overlaps with both optical axes).

[0069] Although the above describes an embodiment of the present invention, various modifications are possible. For example, while the above describes an embodiment in which light from the light source 2 is directly incident on the reference light detector 8, a configuration in which only a portion of the light source light separated by a beam splitter is incident on the lateral reference light detector 8 may also be adopted. In this case, too, by providing a light-limiting member 20 between the light source 2 and the reference light detector 8 and the window 4A, stray light L3 affected by light absorption by gas can be prevented from entering the reference light detector 8, and the output of the reference light detector 8 can be stabilized.

[0070] Furthermore, when a beam splitter is used, the two light-emitting elements 2a and 2b of the concentration measuring device 103 may be arranged on different surfaces of the beam splitter to generate measurement light as combined light. In this case, the driving frequencies of the light-emitting elements are made different, and the transmitted light intensity for each wavelength component can be measured by frequency analyzing the output of the measurement light detector 6. In this case, the light-limiting member may be provided so that the transparent portion is positioned on the optical path of the combined light.

[0071] Furthermore, since there is a possibility that light reflected from the surface of the light-limiting member 20 may be detected by the reference light detector 8, a coating or processing that prevents light reflection may be applied to the surface of the light-shielding portion 20a of the light-limiting member 20. Furthermore, not only the surface of the light-limiting member 20, but also all parts that reflect light from the light source 2 toward the reference light detector 8 (for example, the inner surface of the fluid unit) may be similarly coated or processed to prevent light reflection. The object to be measured is not limited to ozone gas, and may be any fluid whose concentration can be measured using absorbance.

[0072] The concentration measuring device according to the embodiment of the present invention is suitably used to measure the concentration of ozone gas, for example.

[0073] 2 Light source 4A, 4B Window 5 Lens 6 Measurement light detector 7 Lens 8 Reference light detector 10 Measurement cell 12 Electric unit 20 Light limiting member 20a Light blocking portion 20b Light transmitting portion 22 Bandpass filter 50 Fluid unit 100 Concentration measuring device

Claims

1. A concentration measuring device comprising: a measurement cell having a flow path for a measurement fluid; a light source that emits measurement light that enters the measurement cell through a window; a reference light detector that is arranged to the side of the light source and into which a portion of the light from the light source is directly incident; a measurement light detector that detects light that has passed through the measurement cell; and a light limiting member that is arranged between the light source, the reference light detector, and the window, and that has a light-transmitting portion that transmits the measurement light and a light-blocking portion that is arranged around the light-transmitting portion.

2. The concentration measuring device according to claim 1, wherein said light restricting member is formed by a light-blocking orifice plate having a hole provided in the center thereof.

3. A concentration measuring device as described in claim 1 or 2, wherein the light limiting member is positioned forward from the tip of the light source along the optical axis direction of the light source by a distance of 10 to 50% of the distance from the tip of the light source to the window.

4. A concentration measuring device as described in claim 1 or 2, wherein the light source and the measurement light detector are arranged facing each other with the measurement cell in between, the reference light detector is arranged to the side of the light source and further back than the tip of the light source in the optical axis direction of the light source, and a lens for focusing light from the light source is provided in front of the reference light detector.

5. The concentration measuring device according to claim 1 or 2, further comprising a bandpass filter provided between said light restricting member and said window.

6. A concentration measuring device according to claim 1 or 2, wherein the window has a protrusion that protrudes toward the measuring cell.

7. The concentration measuring device according to claim 1 or 2, wherein the light source includes two light-emitting elements that emit light of different wavelengths.

8. A concentration measuring device according to claim 1 or 2, wherein the measurement fluid is ozone gas, and the light source is configured to emit near-ultraviolet light having a wavelength of at least 200 nm to 320 nm as the measurement light.