Gas analyzers

Abstract

A gas analyzer capable of stably measuring a plurality of gas components contained in a sample gas is provided. [Solution] The gas analyzer according to the present disclosure comprises a first gas filter that transmits infrared light from a light source and contains a reference gas that does not absorb infrared light; a second gas filter that transmits the infrared light and contains a gas to be measured; a light-shielding mask having a plurality of openings in areas corresponding to the first gas filter and the second gas filter; a gas filter wheel that stores at least one of the first gas filter and a plurality of the second gas filters and is rotatably mounted; and a sample gas cell into which the infrared light that has transmitted through the first gas filter or the second gas filter is incident and through which sample gas containing the gas to be measured flows, and each of the second gas filters stored in the gas filter wheel contains a different gas to be measured.

Description

[Technical Field]

[0001] The present disclosure relates to gas analyzers. [Background technology]

[0002] Gas analyzers that irradiate a gas with broadband infrared light to analyze the gas components to be measured are known. Patent Document 1 discloses a technique in which a gas correlation cell and a chopper, each having multiple pairs of light-transmitting and light-blocking sections, are driven and rotated in synchronization with an input pulse, and the concentration of carbon monoxide or the like is measured based on the detected light intensity. Patent Document 2 also discloses a technique for analyzing a specific gas component by irradiating a measurement cell with infrared light through a correlation filter that uses a light-blocking plate or an optical filter for simple calibration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-184562 [Patent Document 2] Japanese Patent Application Publication No. 10-82740 Summary of the Invention [Problem to be solved by the invention]

[0004] The techniques disclosed in Patent Documents 1 and 2 each measure a single gas component. It is desirable to be able to stably measure multiple gas components using a gas analyzer.

[0005] The present disclosure provides a gas analyzer capable of stably measuring a plurality of gas components contained in a sample gas. [Means for solving the problem]

[0006] a light source that emits infrared light; a first gas filter that transmits the infrared light from the light source and that contains a comparison standard gas that does not absorb the infrared light; a second gas filter that transmits the infrared light and that contains the target gas; a light-shielding mask that is attached to the outside of the first gas filter and the second gas filter and has a plurality of openings that transmit the infrared light in areas corresponding to the first gas filter and the second gas filter, respectively; a gas filter wheel that stores at least one of the first gas filter and a plurality of the second gas filters and is rotatably attached; and a sample gas cell into which the infrared light that has transmitted through the first gas filter or the second gas filter is incident and through which the sample gas containing the target gas flows, wherein each of the second gas filters stored in the gas filter wheel contains a different target gas. [Effects of the Invention]

[0007] The gas analyzer according to the present disclosure can stably measure a plurality of gas components contained in a sample gas. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an overall configuration diagram of a gas analyzer according to an embodiment of the present disclosure. [Figure 2A] FIG. 2 is a configuration diagram of a gas filter wheel of a gas analyzer according to an embodiment of the present disclosure. [Figure 2B] FIG. 2B is a cross-sectional view of the gas filter wheel shown in FIG. 2A. [Figure 3] FIG. 10 is a plan view illustrating a modified example of a gas filter wheel of a gas analyzer according to an embodiment of the present disclosure. [Figure 4] FIG. 2 is a configuration diagram of a signal processing unit of a gas analyzer according to an embodiment of the present disclosure. [Figure 5] FIG. 2 is a diagram showing a schematic configuration of a detection and sample-and-hold circuit of a gas analyzer according to an embodiment of the present disclosure. [Figure 6] FIG. 10 is a diagram illustrating an example of a received light signal in a gas analyzer according to an embodiment of the present disclosure. [Figure 7] FIG. 2 is a diagram illustrating an example of a circuit configuration of a detection and sample-and-hold circuit of a gas analyzer according to an embodiment of the present disclosure. [Figure 8] FIG. 10 is a diagram showing an example of a result of processing a received light signal in a gas analyzer according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes the preferred embodiments of the present invention with reference to the accompanying drawings. In the drawings, the same components are designated by the same reference numerals, and redundant explanations may be omitted.

[0010] <Background of the study leading to the idea of ​​the gas analyzer according to the embodiment> The gas analyzer detects infrared light of a specific wavelength that is absorbed by the gas being measured, and measures the amplitude ratio of the detected infrared light waveform as the amount of infrared light attenuation to determine the concentration of the gas being measured.

[0011] Gas filter correlation (GFC) gas analyzers use a rotating gas filter wheel to alternately transmit infrared light through each gas filter, housing two gas filters: one filled with a high-purity target gas and the other filled with a reference gas that does not absorb infrared light. This makes the analyzer less susceptible to optical noise, such as fluctuations in the intensity of the transmitted infrared light and interference from moisture contained in the sample gas and gases not being measured.

[0012] The gas analyzer described above includes a pair of gas filters, one of which is filled with a high-purity target gas, and the other is filled with a reference gas that does not absorb infrared light. When measuring the concentration of a target gas by combining an infrared light source that emits light over a wide wavelength range and a light-receiving element that is sensitive to that wide wavelength range, the amount of change in the amount of light absorbed by the target gas is extremely small. Therefore, an optical filter that transmits only infrared light in the wavelength range required to measure the target gas concentration is used.

[0013] When measuring the concentration of one type of target gas, it is sufficient to allow only infrared light of the required wavelength band to pass through somewhere along the infrared light path. However, when measuring the concentrations of multiple target gases, it is desirable to attach an optical filter to the gas filter.

[0014] If an optical filter is simply attached to the gas filter, the amount of light can only be measured once per rotation of the gas filter wheel, resulting in less data for measuring the concentration of the target gas.

[0015] Furthermore, a low-noise, inexpensive AC motor is used as the driving means for rotating the gas filter wheel. When using a commercial power source, the gas filter wheel rotates at a speed of approximately 1500 rpm to 1800 rpm. In this case, light intensity is measured approximately 25 to 30 times per second. This leaves little data for measuring the concentration of the target gas, making it difficult to measure the concentration of the target gas stably.

[0016] Therefore, a gas analyzer 1 according to the following embodiment has been found that can solve such problems.

[0017] [Embodiment] <Overall configuration of gas analyzer 1> The configuration of a gas analyzer 1 according to this embodiment will be described with reference to Figures 1, 2A, and 2B. Figure 1 is an overall configuration diagram of the gas analyzer 1 according to an embodiment of the present disclosure. Figure 2A is a configuration diagram of a gas filter wheel 20 of the gas analyzer 1 according to an embodiment of the present disclosure. Figure 2B is a cross-sectional view of the gas filter wheel 20 shown in Figure 2A.

[0018] The gas analyzer 1 measures the concentration of a target gas contained in a sample gas and includes a light source 10, a gas filter wheel 20, a rotating means 30, a sample gas cell 40, a light receiving unit 50, and a signal processing unit 60.

[0019] The light source 10 is a light source that emits infrared light rays. For example, a heat source light source such as a silicon nitride heater with a blackbody temperature of approximately 1000°C may be used as the light source 10. In order to convert the emitted infrared light rays into nearly parallel infrared light rays, optical components such as a lens or a parabolic mirror (not shown) may be provided. Also, an aperture may be provided to limit the half-value angle of the light source 10. Note that c in FIGS. 1 and 2B indicates the optical path of the infrared light rays.

[0020] As shown in FIGS. 2A and 2B, gas filter wheel 20 stores six gas filters 21a-21f. Optical filters 22a-22f are attached to gas filters 21a-21f, respectively. Light-shielding masks 23 are attached to the outside of gas filters 21a-21f. Furthermore, as shown in the drawings, position detectors 24a-24f are provided at positions on the outer periphery of gas filter wheel 20 corresponding to gas filters 21a-21f. Optical sensors 25 may be provided to receive infrared light from position detectors 24a-24f. The number of gas filters 21a-21f is not limited to six, and any even number may be provided.

[0021] In the following description, when there is no need to distinguish between the gas filters 21a to 21f, they will be simply referred to as "gas filter 21." Furthermore, when there is no need to distinguish between the optical filters 22a to 22f, they will be simply referred to as "optical filter 22." Furthermore, when there is no need to distinguish between the position detection units 24a to 24f, they will be simply referred to as "position detection unit 24."

[0022] The gas filter wheel 20 stores gas filters 21. The stored gas filters 21 may include a plurality of first gas filters containing a comparison reference gas and at least one second gas filter containing a measurement target gas.

[0023] In the gas analyzer 1 according to this embodiment, a plurality of pairs of first and second gas filters are stored and rotatably attached to the gas filter wheel 20. In the following description, the first gas filters are referred to as gas filters 21a, 21c, and 21e in the drawings, and the second gas filters are referred to as gas filters 21b, 21d, and 21f in the drawings.

[0024] Gas filters 21a, 21c, and 21e, which are first gas filters, transmit infrared light from light source 10 but contain a reference gas that does not absorb infrared light. Gas filters 21b, 21d, and 21f, which are second gas filters, transmit infrared light from light source 10 and contain a gas to be measured. Gas filter 21 seals the gas with a glass material that allows infrared light to pass through. Calcium fluoride, for example, is used as the glass material.

[0025] The comparison standard gas sealed in gas filters 21a, 21c, and 21e is, for example, nitrogen (N2), but is not limited to this and may be any gas that does not absorb infrared light, such as argon (Ar). When infrared light emitted from light source 10 enters gas filter 21, a portion of the infrared light is absorbed by the gas components sealed in gas filter 21. In the following description, the comparison standard gas is assumed to be N2.

[0026] The gas filters 21b, 21d, and 21f are filled with different gases to be measured. Therefore, the gas analyzer 1 according to this embodiment can measure the concentrations of three different gas components. The gases to be measured filled in the gas filters 21b, 21d, and 21f are high-concentration gases. Examples of the gases to be measured include, but are not limited to, CO, CO2, and CH4. A high concentration is preferably a concentration at which most of the light of the wavelengths absorbed by the gas components filled in the gas filter 21 is absorbed. In the following description, the gases to be measured are CO, CO2, and CH4.

[0027] The optical filters 22 are attached to the respective gas filters 21 and transmit infrared light of wavelength components absorbed by the gas to be measured. The optical filters 22 are provided to narrow the wavelength of infrared light detected by the light receiving unit 50 in order to reduce the influence of interference from components other than the gas to be measured. The optical filters 22 may be provided on the light source 10 side of the gas filters 21 or on the opposite side from the light source 10.

[0028] An optical filter 22 is attached to each gas to be measured. More specifically, in the gas analyzer 1 according to this embodiment, optical filters 22 that transmit infrared light of a wavelength component absorbed by the gas to be measured sealed in gas filter 21b are attached to gas filters 21a and 21b. Optical filters 22 that transmit infrared light of a wavelength component absorbed by the gas to be measured sealed in gas filter 21d are attached to gas filters 21c and 21d. Furthermore, optical filters 22 that transmit infrared light of a wavelength component absorbed by the gas to be measured sealed in gas filter 21f are attached to gas filters 21e and 21f.

[0029] In the above example, gas filters 21a and 21b, gas filters 21c and 21d, and gas filters 21e and 21f are paired and arranged adjacent to each other. By alternately detecting the comparison reference gas and the measurement target gas and calculating the difference in this way, the system is less susceptible to optical noise. Note that the gas filters 21 may be arranged such that the first gas filter containing the comparison reference gas and the second gas filter containing the measurement target gas are not adjacent to each other.

[0030] Light-shielding mask 23 is attached to the outside of gas filter 21 so as to cover gas filter 21 and optical filter 22. The outside of gas filter 21 may be the side opposite light source 10 of gas filter 21 as shown in FIG. 2B , but is not limited thereto and may also be the side of light source 10 of gas filter 21.

[0031] The light-shielding mask 23 also has a plurality of openings 231 in each region corresponding to the gas filters 21. The openings 231 are provided at positions that allow the infrared light emitted from the light source 10 to pass through. The light-shielding mask 23 has the openings 231, so that the infrared light that has passed through each gas filter 21 appears as repeated bright and dark regions when viewed from the light-receiving unit 50. In this embodiment, six openings 231 are provided in the regions corresponding to the gas filters 21. Therefore, the light-receiving unit 50 receives the infrared light that has passed through each gas filter 21 six times per rotation of the gas filter wheel 20.

[0032] The number of openings 231 may be, but is not limited to, about six. The shape of openings 231 may be, but is not limited to, a circular shape, and various shapes can be adopted.

[0033] Position detectors 24a-24f detect the positions of gas filters 21a-21f, respectively, in synchronization with the rotation of gas filter wheel 20. Position detectors 24a-24f are provided at positions corresponding to gas filters 21a-21f, respectively. When gas filter wheel 20 is rotated by rotation means 30, position detectors 24a-24f are detected by optical sensor 25 and transmit signals to optical sensor 25 synchronized with the positions of gas filters 21a-21f.

[0034] The method for detecting the position of the gas filter 21 by the position detector 24 is not limited to this, and various methods for generating position information corresponding to the position of the gas filter 21 as an electrical signal can be used. For example, instead of the optical sensor 25, a magnetic detection element such as a Hall element may be used to transmit a signal based on the magnetism emitted by the position detectors 24a to 24f. In this case, the position detectors 24a to 24f are formed by magnets that emit different magnetism for each of the gas filters 21a to 21f. The signal obtained by the optical sensor 25 is input to the signal processor 60 as a synchronization signal.

[0035] 3 is a plan view showing a modified example of the gas filter wheel 20 of the gas analyzer 1 according to an embodiment of the present disclosure. Position detectors 24a to 24f detect the positions of the plurality of gas filters 21a to 21f in synchronization with the rotation of the gas filter wheel 20.

[0036] 2A and 2B, the modified gas filter wheel 20 shown in Fig. 3 differs from the case of Figs. 2A and 2B in that the position detection units 24a-24f are provided on the rotation axis side of each of the gas filters 21a-21f. In addition, the optical sensor 25 is provided on the inner circumferential side of the gas filter wheel 20. As in the case of Figs. 2A and 2B, when the gas filter wheel 20 is rotated by the rotation means 30, the position detection units 24a-24f are detected by the optical sensor 25 and transmit signals synchronized with the positions of the gas filters 21a-21f to the optical sensor 25.

[0037] The rotating means 30 rotates the gas filter wheel 20 at any rotation speed. The gas filter wheel 20 may be rotated clockwise or counterclockwise by the driving force of the rotating means 30. In this embodiment, the motor constituting the rotating means 30 can rotate the gas filter wheel 20 at, for example, 1500 rpm.

[0038] From the viewpoint of suppressing inverter noise, it is desirable to use, for example, an AC (Alternating Current) motor, and more desirably, an AC synchronous motor, for the rotation means 30. However, the rotation means 30 is not limited to these motors, and a general motor can be used.

[0039] Gas containing the gas to be measured flows through the sample gas cell 40. Infrared light that has passed through the gas filter 21 and the optical filter 22 enters the sample gas cell 40. The infrared light that has passed through the sample gas cell 40 enters the light receiving unit 50.

[0040] The sample gas cell 40 is provided with a central mirror 41 and multiple reflecting mirrors 42, 43, 44, and 45 to multiple-reflect the incident infrared light. The infrared light incident on the sample gas cell 40 is reflected by the reflecting mirror 42, the reflecting mirror 43, the central mirror 41, the reflecting mirror 44, and the reflecting mirror 45 in this order, and is received by the light-receiving unit 50.

[0041] Central mirror 41 is disposed opposite reflecting mirror 43 and reflecting mirror 44. "Disposed opposite" may mean that the mirror surface of central mirror 41 faces the mirror surfaces of reflecting mirror 43 and reflecting mirror 44. "Disposed opposite" may mean that at least a portion of the mirror surface of central mirror 41 faces at least a portion of the mirror surface of each of reflecting mirror 43 and reflecting mirror 44. Note that only a portion of the surface of central mirror 41 may be a mirror surface, or all of the surfaces may be mirror surfaces.

[0042] The reflecting mirror 43 is disposed opposite the central mirror 41. The mirror surface of the reflecting mirror 43 may be disposed opposite the mirror surface of the central mirror 41. Note that only a portion of the surface of the reflecting mirror 43 may be a mirror surface, or all of the surfaces may be mirror surfaces.

[0043] The reflecting mirror 44 is disposed opposite the central mirror 41. The mirror surface of the reflecting mirror 44 may be disposed opposite the mirror surface of the central mirror 41. Note that only a portion of the surface of the reflecting mirror 44 may be a mirror surface, or all of the surfaces may be mirror surfaces.

[0044] The central mirror 41, the reflecting mirror 43, and the reflecting mirror 44 may each be a concave mirror. That is, the central mirror 41, the reflecting mirror 43, and the reflecting mirror 44 each have a radius of curvature. The central mirror 41, the reflecting mirror 43, and the reflecting mirror 44 may have the same radius of curvature. The radius of curvature of the mirror may be the radius of curvature of the mirror surface.

[0045] Since the central mirror 41, the reflecting mirror 43, and the reflecting mirror 44 have the same radius of curvature, the incident infrared light can be reflected multiple times. In other words, the sample gas cell 40 may be a White cell. By using a White cell, the optical path length of the infrared light incident on the sample gas cell 40 can be increased, and the concentration of the target component contained in the sample gas can be measured accurately even if the amount is small.

[0046] The light receiving unit 50 receives the infrared light transmitted through the sample gas cell. The light receiving unit 50 includes a light receiving element. The light receiving element may be a PbSe element that has high sensitivity in the mid-infrared region, but is not limited to this, and various elements that are sensitive in the mid-infrared region may be used.

[0047] The infrared light transmitted through the gas filter 21, the optical filter 22, and the sample gas cell 40 and received by the light receiving element of the light receiving unit 50 is converted into an electrical signal and input to the signal processing unit 60. The light receiving unit 50 may also include a temperature detection element such as a thermistor, and a Peltier element as a cooling means.

[0048] The signal processing unit 60 calculates the concentration of the target gas based on the electrical signal input from the light receiving unit 50. The signal processing unit 60 can measure the concentration of the target gas by acquiring the change in intensity of the infrared light at the absorption wavelength of the target gas.

[0049] The configuration of the signal processing unit 60 will be described below with reference to Fig. 4. Fig. 4 is a configuration diagram of the signal processing unit 60 of the gas analyzer 1 according to an embodiment of the present disclosure. The signal processing unit 60 includes a bias generation circuit 61, a preamplifier circuit 62, a TEC (Thermoelectric Cooler) control circuit 63, a synchronization signal generation circuit 64, a detection / sample-and-hold circuit 65, a differential amplifier circuit 66, and a processing unit 67.

[0050] The bias generation circuit 61 applies a bias voltage to the light receiving element 51. When the light receiving element 51 receives infrared light that has passed through the sample gas cell 40, it generates a photocurrent generated by the applied bias voltage as a light receiving signal Sig. The preamplifier circuit 62 amplifies the light receiving signal Sig from the light receiving element 51 and inputs it to the detection / sample hold circuit 65.

[0051] The TEC control circuit 63 receives an element temperature signal from the temperature detection element 53, which varies depending on the temperature of the light receiving unit 50, and controls the drive current supplied to the cooling means 52. The TEC control circuit 63 uses a preset temperature as a reference and supplies a drive current to the cooling means 52 so that the cooling means 52 operates as a cooler when the temperature of the light receiving element 51 is higher than the reference temperature.

[0052] The object to be cooled by the cooling means 52 is the light receiving element 51 and the like included in the light receiving unit 50. Since the light receiving element 51 may suffer from problems such as a drop in output due to temperature changes, it is preferable that the temperature be appropriately controlled by the cooling means 52. The cooling means 52 may be, for example, a Peltier element.

[0053] The synchronization signal generation circuit 64 generates synchronization signals Clk1p / b to Clk6p / b indicating the positions of the gas filters 21a to 21f based on a signal received from the optical sensor 25 and synchronized with the rotation of the gas filter wheel 20. The synchronization signal generation circuit 64 may generate synchronization signals Clk1p / b to Clk6p / b (Clk1 to Clk6) based on a modulated signal having a frequency of, for example, 1 kHz. The synchronization signals Clk1p / b to Clk6p / b are used to synchronize the detected positions of the gas filters 21a to 21f with time information about the infrared light beams that have passed through the gas filters 21a to 21f.

[0054] The synchronization signals Clk1p / b to Clk6p / b generated by the synchronization signal generation circuit 64 are used to detect the peak value and bottom value of the light-receiving signal Sig for each gas filter 21. The peak value of the light-receiving signal Sig is the signal value when the light-receiving unit 50 receives infrared light that has passed through the opening 231 of the light-shielding mask 23 and the sample gas cell 40. The bottom value of the light-receiving signal Sig is the signal value when the infrared light has not passed through the opening 231 of the light-shielding mask 23.

[0055] The synchronization signal generation circuit 64 generates synchronization signals Clk1p-Clk6p that are synchronized with the peak value of the light reception signal Sig that has passed through the gas filter 21a and synchronization signals Clk1b-Clk6b that are synchronized with the bottom value of the light reception signal Sig. The generated synchronization signals Clk1p / b-Clk6p / b are input to the detection and sample-and-hold circuit 65 as detection control signals for each of the comparison reference gas and the measurement target gas.

[0056] 5 is a diagram illustrating a schematic configuration of the detection / sample-and-hold circuit 65 of the gas analyzer 1 according to an embodiment of the present disclosure. As illustrated, the detection / sample-and-hold circuit 65 includes a first difference acquisition unit 65a, a second difference acquisition unit 65b, a third difference acquisition unit 65c, a fourth difference acquisition unit 65d, a fifth difference acquisition unit 65e, and a sixth difference acquisition unit 65f.

[0057] The first difference acquisition unit 65a receives the light receiving signal Sig from the preamplifier circuit 62 and also receives the synchronization signals Clk1p and Clk1b from the synchronization signal generation circuit 64, and smoothes the peak value p1 and bottom value b1 of the light receiving signal Sig. The first difference acquisition unit 65a then acquires the difference between the peak value p1 and the bottom value b1 of the light receiving signal Sig and sends it to the differential amplifier circuit 66.

[0058] Similar to the first difference acquisition unit 65a, the second difference acquisition unit 65b receives the synchronization signals Clk2p and Clk2b, acquires the difference between the peak value p2 and the bottom value b2 of the light reception signal Sig, and transmits this difference to the differential amplifier circuit 66. The third difference acquisition unit 65c receives the synchronization signals Clk3p and Clk3b, acquires the difference between the peak value p3 and the bottom value b3 of the light reception signal Sig, and transmits this difference to the differential amplifier circuit 66.

[0059] The fourth difference acquisition unit 65d receives synchronization signals Clk4p and Clk4b, acquires the difference between the peak value p4 and the bottom value b4 of the light reception signal Sig, and transmits this difference to the differential amplifier circuit 66. The fifth difference acquisition unit 65e receives synchronization signals Clk5p and Clk5b, acquires the difference between the peak value p5 and the bottom value b5 of the light reception signal Sig, and transmits this difference to the differential amplifier circuit 66. The sixth difference acquisition unit 65f receives synchronization signals Clk6p and Clk6b, acquires the difference between the peak value p6 and the bottom value b6 of the light reception signal Sig, and transmits this difference to the differential amplifier circuit 66.

[0060] 6 is a diagram showing an example of the light receiving signal Sig in the gas analyzer 1 according to an embodiment of the present disclosure. In FIG. 6, (a) shows an example of the waveform of the light receiving signal Sig, and (b) shows an example of the waveforms of the synchronization signals Clk1p / b to Clk6p / b generated by the synchronization signal generation circuit 64. The light receiving signal Sig is processed so as to be synchronized with the synchronization signals Clk1p / b to Clk6p / b, respectively.

[0061] 6(a), p1 to p6 indicate peak values ​​of the light receiving signal Sig, and b1 to b6 indicate bottom values ​​of the light receiving signal Sig. The peak value p1 and bottom value b1 are the peak value p1 and bottom value b1 of the light receiving signal Sig to gas filter 21a. Similarly, the peak value p2 and bottom value b2 are the peak value p3 and bottom value b3 of the light receiving signal Sig to gas filter 21b, gas filter 21c, gas filter 21d, peak value p5 and bottom value b5 of the light receiving signal Sig to gas filter 21e, and peak value p6 and bottom value b6 of the light receiving signal Sig to gas filter 21f.

[0062] 6(a), the light receiving signal Sig has a rectangular waveform. The light receiving signal Sig has peak values ​​p1 to p6 when the light receiving unit 50 receives infrared light that has passed through the opening 231 of the light-shielding mask 23 and the sample gas cell 40. The light receiving signal Sig has bottom values ​​b1 to b6 when the infrared light has not passed through the opening 231 of the light-shielding mask 23.

[0063] If the light-shielding mask 23 including the opening 231 is not provided, the peak value p1 and bottom value b1 for each gas to be measured are obtained only once per rotation of the gas filter wheel 20, and it is difficult to obtain stable measurement results when the smoothing process is taken into account.

[0064] If the number of peak values ​​and bottom values ​​of the received light signal Sig is n, then the arithmetic average of the noise components is 1 / √n. Therefore, the more peak values ​​and bottom values ​​of the received light signal Sig, the more the noise components are reduced by the smoothing process. Therefore, the more apertures 231 there are, the more errors caused by fluctuations in the amount of transmitted infrared light and the influence of optical noise, such as interference from moisture contained in the sample gas and gases not being measured, are reduced, contributing to stabilization of gas concentration measurements. Therefore, a light-shielding mask 23 having multiple apertures 231 that transmit infrared light from the light source 10 is provided for each region corresponding to the gas filter 21.

[0065] From the viewpoint of acquiring more peak values ​​and bottom values ​​of the light receiving signal Sig, it is preferable to have a larger number of openings 231, but if the number of openings 231 becomes too large, the amount of light received by the light receiving unit 50 decreases, so it is desirable to determine the number of openings 231 taking these factors into consideration. For example, the number of openings 231 may be six as in the example of this embodiment, but is not limited to this.

[0066] The light receiving signal Sig is the infrared light received by the light receiving unit 50 alternately each time the gas filter wheel 20 rotates once, passing through the gas filters 21a, 21c, and 21e, which are first gas filters containing a comparison reference gas, or the gas filters 21b, 21d, and 21f, which are second gas filters containing the gas to be measured.

[0067] As described above, in the gas analyzer 1 according to this embodiment, there are three types of gases to be measured, and six gas filters 21 are stored in the gas filter wheel 20. The light receiving signal Sig has a rectangular waveform having peak values ​​p1 to p6 and bottom values ​​b1 to b6, the number of which corresponds to the number of openings 231 in the light-shielding mask 23.

[0068] When sample gas containing the gas to be measured is flowed into the sample gas cell 40, the infrared light reception signal Sig that has passed through the gas filter 21 in which the comparison standard gas is sealed is attenuated according to the amount of light absorption in the sample gas cell 40. Furthermore, the infrared light reception signal Sig that has passed through the gas filter 21 in which the gas to be measured is sealed has already attenuated the light components in the wavelength band absorbed by the gas to be measured in the gas filter 21, so the amount of light absorption in the sample gas cell 40 is small and the amount of attenuation is also small.

[0069] The received light signal Sig includes signal portions s1 to s6 for each infrared ray that has passed through gas filters 21a to 21f. Signal portions s1, s3, and s5 are the received light signal Sig for the infrared ray that has passed through gas filters 21a, 21c, and 21e containing a reference gas and then passed through sample gas cell 40. Signal portions s2, s4, and s6 are the received light signal Sig for the infrared ray that has passed through gas filters 21b, 21d, and 21f containing a gas to be measured and then passed through sample gas cell 40.

[0070] Synchronization signal Clk1p turns on when the infrared light passes through opening 231 of light-shielding mask 23 that covers gas filter 21a, and a peak value p1 of received light signal Sig can be obtained. Synchronization signal Clk1b turns on when the infrared light does not pass through opening 231 of light-shielding mask 23 that covers gas filter 21a, and a bottom value b1 of received light signal Sig can be obtained. The same applies to synchronization signals 2p / b to 6p / b.

[0071] 7 is a diagram illustrating an example of the circuit configuration of the detection and sample-and-hold circuit 65 of the gas analyzer 1 according to an embodiment of the present disclosure. The illustrated circuit shows a first difference acquisition unit 65a of the detection and sample-and-hold circuit 65. Note that the second difference acquisition unit 65b, the third difference acquisition unit 65c, the fourth difference acquisition unit 65d, the fifth difference acquisition unit 65e, and the sixth difference acquisition unit 65f each have the same configuration as the first difference acquisition unit 65a, and therefore their description will be omitted.

[0072] FIG. 7 shows a circuit for obtaining the difference between the peak value p1 and bottom value b1 of the received light signal Sig from the received light signal Sig of infrared light transmitted through the gas filter 21a in the detection and sample-hold circuit 65 and the synchronization signals Clk1p and Clk1b.

[0073] The switch S11 selects the peak signal of the light receiving signal Sig when it receives an ON signal of the synchronization signal Clk1p, and the switch S12 selects the bottom signal of the light receiving signal Sig when it receives an ON signal of the synchronization signal Clk1b.

[0074] A low-pass filter formed by resistor R101 and capacitor C11 removes high-frequency components from the light-receiving signal Sig and smoothes it. A buffer circuit formed by operational amplifier A11 corrects the signal strength on the peak value side of the light-receiving signal Sig, correcting any time lag in the light-receiving signal Sig. At this time, peak value p1 of the light-receiving signal Sig is acquired at a1 in the diagram.

[0075] The low-pass filter formed by resistor R102 and capacitor C12 removes high-frequency components from the received light signal Sig and smoothes it. The buffer circuit formed by operational amplifier A12 then corrects the signal strength of the bottom value side of the received light signal Sig, correcting any time lag in the received light signal Sig. At this time, the bottom value b1 of the received light signal is acquired at a2 in the diagram.

[0076] A differential amplifier consisting of resistors R103 to R106, capacitors C15 and C16, and operational amplifier A13 obtains and amplifies the difference between the peak value p1 of the light receiving signal Sig input from the switch S11 side and the bottom value b1 of the light receiving signal Sig input from the switch S12 side.

[0077] Furthermore, a current clamp circuit formed by resistors R107 and R108 and diodes D11 and D12 can prevent surge voltages, overcurrents, and the like from flowing into the detector / sample-hold circuit 65.

[0078] The level shift circuit, which is composed of resistors R109 to R112, capacitor C17, and operational amplifier A14, adjusts the signal value of the light receiving signal Sig so that it does not contain negative values. The level shift circuit also smoothes the difference between the peak value p1 and bottom value b1 of the light receiving signal Sig acquired by the differential amplifier. The difference between the peak value p1 and bottom value b1 of the light receiving signal Sig is output to differential amplifier circuit 66 and amplified.

[0079] FIG. 8 is a diagram showing an example of the results of processing the received light signal Sig in the gas analyzer 1 according to an embodiment of the present disclosure. In FIG. 8, (a) and (b) show the peak and bottom values ​​of each signal for the reference gas and the measurement target gas, respectively, and (c) shows the gas concentration indication values ​​for each measurement target gas. In the example shown, the reference gas is N2, and the measurement target gases are CO, CO2, and CH4. In FIG. 8(c), C1, C2, and C3 show the gas concentration indication values ​​for the measurement target gases CO, CO2, and CH4, respectively.

[0080] In Fig. 8(a), Spn indicates the peak value of the signal of the comparison reference gas, and is acquired at a1 in the circuit of the first difference acquisition unit 65a shown in Fig. 7, or at a point corresponding to a1 in Fig. 7 in the third difference acquisition unit 65c and the fifth difference acquisition unit 65e. Spt indicates the peak value of the signal of each measurement target gas, and is acquired at a point corresponding to a1 in Fig. 7 in the second difference acquisition unit 65b, the fourth difference acquisition unit 65d, and the sixth difference acquisition unit 65f.

[0081] 8(b), Sbn indicates the bottom value of the signal of the comparison reference gas, and is acquired at a2 in the circuit of the first difference acquisition unit 65a shown in Fig. 7, or at a point corresponding to a2 in Fig. 7 in the third difference acquisition unit 65c and the fifth difference acquisition unit 65e. Spt indicates the peak value of the signal of each measurement target gas, and is acquired at a point corresponding to a2 in Fig. 7 in the second difference acquisition unit 65b, the fourth difference acquisition unit 65d, and the sixth difference acquisition unit 65f.

[0082] The processing unit 67 calculates the gas concentration indication values ​​for each of the plurality of measurement target gases as shown in FIG. 6(c) based on the peak and bottom values ​​of the rectangular waveform signals for the comparison reference gas and the measurement target gas.

[0083] More specifically, the difference between the peak value and the bottom value of the signal of the reference gas is V N2 , the difference between the peak value and the bottom value of the signal of the gas to be measured is V Targetand Target Gas Concentration is the gas concentration indication value, the relationship of the following formula (1) is satisfied. The processing unit 67 calculates the gas concentration indication value using formula (1). The waveform shown in FIG. 8(c) is generated in the processing unit 67 based on formula (1).

[0084]

number

[0085] <Effects> In the gas analyzer 1 according to this embodiment, multiple pairs of first gas filters containing a reference gas for comparison and second gas filters containing a gas to be measured are stored in the gas filter wheel 20. This allows multiple gas components contained in the sample gas to be measured.

[0086] Furthermore, the light-shielding mask 23 attached to the gas filters 21 has a plurality of openings 231 in regions corresponding to the respective gas filters 21. This increases the peak value and bottom value of the acquired light-receiving signal Sig, thereby reducing errors caused by the influence of optical noise such as fluctuations in the amount of infrared light received by the light-receiving unit 50 and interference from moisture contained in the sample gas and gases not being measured.

[0087] Then, the detection / sample-and-hold circuit 65 smoothes the peak values ​​p1 to p6 and bottom values ​​b1 to b6 of the light receiving signal Sig, obtains the differences, and amplifies them in the differential amplifier circuit 66. Then, in the processing unit 67, the peak values ​​p1 to p6 and bottom values ​​b1 to b6 of the light receiving signal Sig are smoothed, and gas concentration indication values ​​for a plurality of measurement target gases are calculated based on the smoothed differences.

[0088] Therefore, the gas analyzer 1 according to this embodiment can stably perform gas analysis on a plurality of gases to be measured.

[0089] Although the embodiments have been described above, they are presented as examples and the present invention is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims. [Explanation of symbols]

[0090] 1 Gas analyzer 10 light source 20 Gas filter wheel 21 Gas filter 22 Optical Filters 23 Light-shielding mask 231 Opening part 24 Position detection unit 30 Rotation means 40 Sample gas cell 50 Light receiving part 60 Signal Processing Unit 65 Detector / Sample-hold circuit 67 Processing section C1, C2, C3 gas concentration readings

Claims

1. A gas analyzer for measuring the concentration of a measurement target gas contained in a sample gas, a light source that emits infrared light; a first gas filter in which a reference gas that transmits the infrared light emitted from the light source but does not absorb the infrared light is sealed; a second gas filter that transmits the infrared light and in which the measurement target gas is sealed; a light-shielding mask attached to the outside of the first gas filter and the second gas filter, the light-shielding mask having a plurality of openings that transmit the infrared light in areas corresponding to the first gas filter and the second gas filter, respectively; a rotatably mounted gas filter wheel housing at least one of the first gas filter and a plurality of the second gas filters; a sample gas cell into which the infrared light transmitted through the first gas filter or the second gas filter is incident and through which the sample gas containing the measurement target gas flows; Equipped with a plurality of second gas filters housed in the gas filter wheel each contain a different gas to be measured; Gas analyzer.

2. The gas filter wheel stores a plurality of pairs of the first gas filter and the second gas filter.

2. The gas analyzer of claim 1.

3. a light receiving unit that receives the infrared light transmitted through the sample gas cell and converts it into an electrical light receiving signal; and a signal processing unit that calculates the concentration of the measurement target gas contained in the sample gas based on the light receiving signal.

2. The gas analyzer of claim 1.

4. the signal processing unit includes a detection and sample-and-hold circuit for acquiring a difference between a peak value and a bottom value of the rectangular wave-shaped light receiving signal; 4. The gas analyzer of claim 3.

5. the signal processing unit calculates a gas concentration indication value for each of the plurality of measurement target gases contained in the sample gas based on a difference between a peak value and a bottom value of the light receiving signal.

4. The gas analyzer of claim 3.

6. an optical filter attached to the first gas filter and the second gas filter, which transmits infrared light of a wavelength component absorbed by the measurement target gas; 2. The gas analyzer of claim 1.

7. a position detection unit that detects the positions of the plurality of pairs of first gas filters and second gas filters in synchronization with the rotation of the gas filter wheel; 2. The gas analyzer of claim 1.

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