Optical concentration measuring device, module for optical concentration measuring device, and optical concentration measuring method

Abstract

To provide an optical concentration measurement device that can highly accurately measure the concentration of measurement object gas, while removing an impact on absorption of light by interference gas.SOLUTION: An optical concentration measurement device 1 comprises: a first optical filter 41 that uses a wavelength band region including a wavelength in which measurement object gas and interference gas absorb an infrared ray, as a first transmission band region; a second optical filter 42 that uses the wavelength band region including the wavelength in which the measurement object gas and interference gas absorb the infrared ray, as a second transmission band region; and a computation unit 60. A difference between a peak wavelength of a first effective sensitivity spectrum and a peak wavelength of a second effective sensitivity spectrum is equal to or more than ±0.2 times and equal to or less than ±0.8 times a full width at half maximum of the first effective sensitivity spectrum. The computation unit 60 is configured to subtract a second amount of attenuation from an amount obtained by multiplying a first amount of attenuation with a proportionality constant, or subtract the first amount of attenuation from an amount obtained by multiplying the second amount of attenuation with a different proportionality constant, and remove an amount of attenuation of first intensity by the interference gas and an amount of attenuation of second intensity by the interference gas.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical density measuring device, a module for an optical density measuring device, and an optical density measuring method.

Background Art

[0002] Conventionally, an optical density measuring device has been known which uses a light source with a wide spectral width such as a tungsten lamp instead of a laser light source to measure the density of a measurement target gas contained in a gas in which the measurement target gas and an interference gas are mixed, thereby achieving low power consumption.

[0003] For example, Patent Document 1 discloses a sensor that includes a light source that emits infrared rays, a first light receiving unit that has a filter with a transmission band that allows only the measurement target gas to absorb infrared rays, and a second light receiving unit that has a filter with a transmission band different from the wavelength band, and measures the density of the measurement target gas while removing the influence of infrared absorption by the interference gas.

[0004] For example, Patent Document 2 discloses a gas density measuring device that includes a light source that emits infrared rays, a first filter that transmits infrared rays in the absorption band of the measurement target gas and a second filter that transmits infrared rays in the non-absorption band of the measurement target gas, a rotating member that selectively rotates each filter, and a light receiving unit that receives infrared rays transmitted through each filter, thereby achieving miniaturization.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, conventional optical concentration measuring devices used optical filters with a transmission band that specified a wavelength range in which only the target gas absorbs infrared radiation, in order to avoid the influence of infrared absorption by interfering gases. As a result, if the wavelength range in which only the target gas absorbs infrared radiation is narrow, the amount of light received by the light-receiving unit is drastically reduced, leading to a problem where the measurement accuracy of the optical concentration measuring device deteriorates.

[0007] In view of these circumstances, the object of the present invention is to provide an optical concentration measuring device, a module for an optical concentration measuring device, and an optical concentration measuring method that can measure the concentration of a target gas with high accuracy while eliminating the effect of light absorption by interfering gases. [Means for solving the problem]

[0008] An optical concentration measuring device according to one embodiment is an optical concentration measuring device for measuring the concentration of a target gas contained in a gas in which the target gas and an interfering gas are mixed, comprising: a first light source that emits infrared rays; a first optical filter whose first transmission band is a wavelength band including wavelengths in which the target gas and the interfering gas absorb the infrared rays; a first light receiving unit that is sensitive to the first transmission band and outputs a first detection signal corresponding to a first intensity of received light; a first light guiding unit that guides the infrared rays to the first light receiving unit; a second light source that emits infrared rays; a second optical filter whose second transmission band is a wavelength band including wavelengths in which the target gas and the interfering gas absorb the infrared rays; a second light receiving unit that is sensitive to the second transmission band and outputs a second detection signal corresponding to a second intensity of received light; a second light guiding unit that guides the infrared rays to the second light receiving unit; and based on the first detection signal, the device measures the concentration of the target gas The device includes a calculation unit which calculates a first attenuation of the first intensity due to the interfering gas, calculates a second attenuation of the second intensity due to the target gas and the interfering gas based on the second detection signal, and calculates the concentration of the target gas based on the first attenuation and the second attenuation, wherein the difference between the peak wavelength of the first effective sensitivity spectrum based on the first transmission band in the first light receiving unit and the peak wavelength of the second effective sensitivity spectrum based on the second transmission band in the second light receiving unit is ±0.2 times or more and ±0.8 times the full width at half maximum of the first effective sensitivity spectrum, and the calculation unit subtracts the second attenuation from an amount obtained by multiplying the first attenuation by a proportionality constant, or subtracts the first attenuation from an amount obtained by multiplying the second attenuation by a proportionality constant different from the proportionality constant, thereby removing the attenuation of the first intensity due to the interfering gas and the attenuation of the second intensity due to the interfering gas.

[0009] A module for an optical concentration measuring device according to one embodiment is a module for an optical concentration measuring device that measures the concentration of a target gas contained in a gas in which the target gas and an interfering gas are mixed, comprising: a first light source that emits infrared rays; a first optical filter whose first transmission band is a wavelength band that includes wavelengths in which the target gas and the interfering gas absorb the infrared rays; a first light receiving unit that is sensitive to the first transmission band and receives light transmitted through the first optical filter; a first light guiding unit that guides the infrared rays to the first light receiving unit; a second light source that emits infrared rays; and the measurement target The device comprises a second optical filter having a second transmission band that includes wavelengths in which the elephant gas and the interfering gas absorb the infrared light; a second light receiving unit that is sensitive to the second transmission band and receives light transmitted through the second optical filter; and a second light guiding unit that guides the infrared light to the second light receiving unit, wherein the difference between the peak wavelength of the first effective sensitivity spectrum based on the first transmission band in the first light receiving unit and the peak wavelength of the second effective sensitivity spectrum based on the second transmission band in the second light receiving unit is ±0.2 times or more and ±0.8 times or less the full width at half maximum of the first effective sensitivity spectrum.

[0010] An optical concentration measurement method according to one embodiment is an optical concentration measurement method for an optical concentration measuring device that measures the concentration of a target gas contained in a gas in which the target gas and an interfering gas are mixed, wherein the optical concentration measuring device comprises: a first light source that emits infrared rays; a first optical filter whose first transmission band is a wavelength band including wavelengths in which the target gas and the interfering gas absorb the infrared rays; a first light receiving unit that is sensitive to the first transmission band and outputs a first detection signal corresponding to a first intensity of received light; a first light guiding unit that guides the infrared rays to the first light receiving unit; a second light source that emits infrared rays; a second optical filter whose second transmission band is a wavelength band including wavelengths in which the target gas and the interfering gas absorb the infrared rays; a second light receiving unit that is sensitive to the second transmission band and outputs a second detection signal corresponding to a second intensity of received light; a second light guiding unit that guides the infrared rays to the second light receiving unit; and a calculation unit, wherein the first effective sensitivity spectrum based on the first transmission band in the first light receiving unit is calculated The difference between the wavelength and the peak wavelength of the second effective sensitivity spectrum based on the second transmission band in the second light receiving unit is ±0.2 times or more and ±0.8 times or less of the full width at half maximum of the first effective sensitivity spectrum, and the calculation unit includes the steps of: calculating a first attenuation amount of the first intensity due to the target gas and the interfering gas based on the first detection signal; calculating a second attenuation amount of the second intensity due to the target gas and the interfering gas based on the second detection signal; and calculating the concentration of the target gas based on the first attenuation amount and the second attenuation amount, wherein the calculation unit includes the steps of: subtracting the second attenuation amount from an amount obtained by multiplying the first attenuation amount by a proportionality constant, or subtracting the first attenuation amount from an amount obtained by multiplying the second attenuation amount by a proportionality constant different from the proportionality constant, and removing the attenuation amount of the first intensity due to the interfering gas and the attenuation amount of the second intensity due to the interfering gas. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an optical concentration measuring device, a module for an optical concentration measuring device, and an optical concentration measuring method that can measure the concentration of a target gas with high accuracy while eliminating the effect of light absorption by interfering gases. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing an example of the configuration of an optical concentration measuring device according to one embodiment of the present invention. [Figure 2] This is a partially transparent perspective view showing an example of the configuration of an optical density measuring device according to one embodiment of the present invention. [Figure 3A] This figure shows an example of the relationship between wavelength and absorption coefficient when carbon dioxide absorbs infrared radiation. [Figure 3B] This figure shows an example of the relationship between wavelength and absorption coefficient when methane gas absorbs infrared radiation. [Figure 3C] This figure shows an example of the relationship between wavelength and absorption coefficient when water vapor absorbs infrared radiation. [Figure 4] This figure shows an example of the relationship between wavelength and the intensity ratio of the effective sensitivity spectrum in the first effective sensitivity spectrum and the second effective sensitivity spectrum according to one embodiment of the present invention. [Figure 5] This figure shows an example of the relationship between water vapor concentration and infrared attenuation in the first effective sensitivity spectrum and the second effective sensitivity spectrum according to one embodiment of the present invention. [Figure 6] This figure shows an example of the relationship between water vapor concentration and infrared attenuation ratio in the first effective sensitivity spectrum and the second effective sensitivity spectrum according to one embodiment of the present invention. [Modes for carrying out the invention]

[0013] Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. In principle, identical components will be given the same reference numeral, and redundant explanations will be omitted. For the sake of clarity, the aspect ratios of each component in each drawing are exaggerated from their actual proportions.

[0014] In addition, hereinafter, "infrared rays" means electromagnetic waves with wavelengths ranging from 2.0 μm to 10.0 μm. Also, "transmission" means that the amount of light transmitted through the optical filter is 3% or more of the amount of light incident on the optical filter. Also, "sensitivity" means that the light-receiving part absorbs light in a predetermined wavelength band and outputs a current signal or a voltage signal. Also, "light-receiving sensitivity band" means a wavelength band including wavelengths from the center wavelength ±50 nm or more to ±500 nm or less when the wavelength with the highest sensitivity among the wavelength bands in which the light-receiving part has sensitivity is taken as the center wavelength. However, these terms are only defined for convenience and should not be interpreted restrictively.

[0015] <Optical density measuring device> Referring to FIGS. 1 to 6, an example of the configuration of the optical density measuring device 1 according to the present embodiment will be described.

[0016] The optical density measuring device 1 is an NDIR (Non Dispersive InfraRed) type device that measures the concentration of a measurement target gas contained in a gas in which the measurement target gas and an interference gas are mixed, utilizing the fact that the wavelengths of infrared rays absorbed by different types of gases are different.

[0017] The measurement target gas is, for example, carbon dioxide, methane, water vapor, propane, formaldehyde, carbon monoxide, nitric oxide, ammonia, sulfur dioxide, alcohol, alternative Freon, etc.

[0018] The interference gas is a gas other than the measurement target gas, and is, for example, carbon dioxide, methane, water vapor, propane, formaldehyde, carbon monoxide, nitric oxide, ammonia, sulfur dioxide, alcohol, alternative Freon, etc. The interference gas may be singular or plural.

[0019] For example, optical concentration measuring device 1 measures the concentration of carbon dioxide indoors or outdoors. For example, optical concentration measuring device 1 measures the concentration of methane in order to detect natural gas leaks in a pipeline transporting natural gas whose main component is methane, which exists in nature at a concentration of only about 2.0 ppm.

[0020] The optical density measuring device 1 comprises a first light guide unit 21, a second light guide unit 22, a first light source 31, a second light source 32, a first optical filter 41, a second optical filter 42, a first light receiving unit 51, a second light receiving unit 52, a calculation unit 60, a drive unit 70, and a substrate 80.

[0021] [1st light source] The first light source 31 is preferably an incoherent light source, such as an LED (Light Emitting Diode), an organic light-emitting element, or a MEMS (Micro Electro Mechanical Systems) heater. The first light source 31 emits infrared radiation based on a drive current or drive voltage supplied from the drive unit 70. The first optical path L1 is the path of infrared radiation emitted by the first light source 31 through the first light guide unit 21 to the first light receiving unit 51 in the space where the gas to be measured and the interfering gas are present. The first optical path length l1 is the average optical distance of the path.

[0022] The first light source 31 may be integrated into the second light source 32. When the first light source 31 is integrated into the second light source 32, the first light guide unit 21 and the second light guide unit 22 should be configured so that the infrared radiation emitted by the light source is extracted to their respective light guide units. In this case, it is necessary that the light intensity of either the first light source 31 or the second light source 32 is sufficiently large.

[0023] [Second light source] The second light source 32 is preferably an incoherent light source, such as an LED (Light Emitting Diode), an organic light-emitting element, or a MEMS (Micro Electro Mechanical Systems) heater. The second light source 32 emits infrared radiation based on a drive current or drive voltage supplied from the drive unit 70. The second optical path L2 is the path of infrared radiation emitted by the second light source 32 through the second light guide unit 22 to the second light receiving unit 52 in the space where the gas to be measured and the interfering gas are present. The second optical path length l2 is the average optical distance of the path.

[0024] The second light source 32 may be integrated with the first light source 31. When the second light source 32 is integrated with the first light source 31, the first light guide unit 21 and the second light guide unit 22 should be configured so that the infrared radiation emitted by the light source is extracted to their respective light guide units. In this case, it is necessary that the light intensity of either the first light source 31 or the second light source 32 is sufficiently large.

[0025] It is preferable that the second light source 32 has the same manufacturing materials, manufacturing process, etc., as the first light source 31. In particular, if the first light source 31 is an LED made of a semiconductor or compound semiconductor, the wavelength of infrared radiation emitted from the first light source 31 is easily affected by the temperature characteristics due to the band gap. For this reason, from the viewpoint of matching the temperature characteristics, it is preferable that the second light source 32 is also an LED and is identical to the first light source 31.

[0026] [First optical filter] The first optical filter 41 transmits light in the first transmission band. The first transmission band is a wavelength band that includes wavelengths at which the gas being measured and the interfering gas absorb infrared light.

[0027] As shown in Figure 3A, for example, carbon dioxide mainly absorbs infrared radiation in the wavelength band from 4.0 μm to 4.5 μm. As shown in Figure 3B, for example, methane mainly absorbs infrared radiation in the wavelength band from 3.1 μm to 3.7 μm and in the wavelength band from 7.1 μm to 8.5 μm. This wavelength band is determined based on the molecular vibrational modes of methane. As shown in Figure 3C, for example, water vapor mainly absorbs infrared radiation in the wavelength band from 2.5 μm to 3.0 μm and in the wavelength band from 5.0 μm to 8.0 μm.

[0028] For example, when the gas to be measured is carbon dioxide and the interfering gas is water vapor, the center wavelength of the first transmission band in the first optical filter 41 is preferably 4.0 μm or more and 4.5 μm or less (see Figures 3A and 3C).

[0029] For example, when the gas to be measured is methane and the interfering gas is water vapor, the center wavelength of the first transmission band in the first optical filter 41 is preferably between 3.2 μm and 3.4 μm (see Figures 3B and 3C). In the wavelength band between 7.1 μm and 8.5 μm, there is a large overlap between the wavelength band in which methane absorbs infrared radiation and the wavelength band in which water vapor absorbs infrared radiation, so the first transmission band is preferably within the range described above.

[0030] Furthermore, the full width at half maximum (FMAX) of the transmission spectrum of the light transmitted through the first optical filter 41 is preferably between 80 nm and 300 nm. A wider FMAX allows for the capture of more wavelengths in which the target gas absorbs infrared light, thus increasing infrared attenuation. However, capturing an unnecessarily wide wavelength range increases the amount of light unrelated to infrared absorption, resulting in a relatively smaller infrared attenuation rate. For this reason, the FMAX is preferably within the range described above.

[0031] [Second optical filter] The second optical filter 42 transmits light in the second transmission band. The second transmission band is a wavelength band that includes wavelengths at which the gas being measured and the interfering gas absorb infrared light.

[0032] The full width at half maximum (FMAX) of the transmission spectrum of the light transmitted through the second optical filter 42 is preferably between 80 nm and 300 nm. A wider FMAX allows for the capture of more wavelengths in which the target gas absorbs infrared light, thus increasing infrared attenuation. However, capturing an unnecessarily wide range of wavelengths increases the amount of light unrelated to infrared absorption, resulting in a relatively smaller infrared attenuation rate. Therefore, the FMAX is preferably within the range described above.

[0033] When the first light-receiving unit 51 and the second light-receiving unit 52 have the same configuration, it is preferable that the second optical filter 42 has a different configuration from the first optical filter 41.

[0034] [1st light receiving section] The first light-receiving unit 51 is, for example, a photodiode or a phototransistor. The first light-receiving unit 51 is sensitive to a first transmission band and receives light that has passed through the first optical filter 41. Preferably, the first light-receiving sensitivity band in the first light-receiving unit 51 is optimized with respect to the first transmission band. Furthermore, it is preferable that the first light-receiving sensitivity band encompasses the first transmission band. By the first light-receiving sensitivity band encompassing the first transmission band, the first light-receiving unit 51 can receive light that has passed through the first optical filter 41 with high efficiency.

[0035] The first light receiving unit 51 generates a first detection signal corresponding to the first intensity of the received light and outputs it to the calculation unit 60. The first detection signal is either a current signal or a voltage signal. Based on this first detection signal, the calculation unit 60 calculates the first attenuation amount, which will be described later.

[0036] For example, the first light receiving unit 51 outputs a first detection signal corresponding to the first intensity of the received light to the calculation unit 60 when the target gas and interference gas are present in the first optical path L1. Also, for example, the first light receiving unit 51 outputs a first detection signal corresponding to the first intensity of the received light to the calculation unit 60 when the target gas and interference gas are not present in the first optical path L1. The first attenuation is a quantity calculated by the calculation unit 60 based on the difference between the first detection signal output from the first light receiving unit 51 when the target gas and interference gas are not present in the first optical path L1 and the first detection signal output from the first light receiving unit 51 when the target gas and interference gas are present in the first optical path L1. Note that in actual use environments, it is difficult for the first light receiving unit 51 to detect the first detection signal when the target gas and interference gas are not present in the first optical path L1. Therefore, the first detection signal when there is no gas to be measured and no interfering gas in the first optical path L1 may be pre-set and stored in the calculation unit 60, or it may be calculated by the calculation unit 60 based on environmental information such as ambient temperature.

[0037] [Second light receiving section] The second light-receiving unit 52 is, for example, a photodiode or a phototransistor. The second light-receiving unit 52 is sensitive to the second transmission band and receives light that has passed through the second optical filter 42. Preferably, the second light-receiving sensitivity band in the second light-receiving unit 52 is optimized with respect to the second transmission band. Furthermore, it is preferable that the second light-receiving sensitivity band encompasses the second transmission band. By the second light-receiving sensitivity band encompassing the second transmission band, the second light-receiving unit 52 can receive light that has passed through the second optical filter 42 with high efficiency.

[0038] The second light-receiving sensitivity band may be optimized for the second transmission band, unlike the first light-receiving sensitivity band, but if the first and second transmission bands are different, it may be equal to the first light-receiving sensitivity band.

[0039] The second light receiving unit 52 generates a second detection signal corresponding to the second intensity of the received light and outputs it to the calculation unit 60. The second detection signal is either a current signal or a voltage signal. Based on this second detection signal, the calculation unit 60 calculates the second attenuation amount, which will be described later.

[0040] For example, the second light receiving unit 52 outputs a second detection signal corresponding to the second intensity of the received light to the calculation unit 60 when the target gas and interference gas are present in the second optical path L2. Also, for example, the second light receiving unit 52 outputs a second detection signal corresponding to the second intensity of the received light to the calculation unit 60 when the target gas and interference gas are not present in the second optical path L2. The second attenuation is a quantity calculated by the calculation unit 60 based on the difference between the second detection signal output from the second light receiving unit 52 when the target gas and interference gas are not present in the second optical path L2 and the second detection signal output from the second light receiving unit 52 when the target gas and interference gas are present in the second optical path L2. Note that in actual use environments, it is difficult for the second light receiving unit 52 to detect the second detection signal when the target gas and interference gas are not present in the second optical path L2. Therefore, the second detection signal when the target gas and interference gas are not present in the second optical path L2 may be pre-set and stored in the calculation unit 60, or it may be calculated by the calculation unit 60 based on environmental information such as ambient temperature.

[0041] It is preferable that the second light-receiving unit 52 uses the same manufacturing materials and manufacturing process as the first light-receiving unit 51. In particular, if the first light-receiving unit 51 is a photodiode or phototransistor made of a semiconductor or compound semiconductor, the first light-receiving sensitivity band of the first light-receiving unit 51 becomes susceptible to the influence of temperature characteristics. For this reason, from the viewpoint of matching temperature characteristics, it is preferable that the second light-receiving unit 52 is also a photodiode or phototransistor, the same as the first light-receiving unit 51.

[0042] Furthermore, the first light-receiving unit 51 does not detect infrared radiation emitted from heat-containing devices such as processors in wavelength bands other than the first transmission band. Similarly, the second light-receiving unit 52 also does not detect infrared radiation emitted from heat-containing devices such as processors in wavelength bands other than the second transmission band. Therefore, it is preferable that the first light-receiving unit 51 and the second light-receiving unit 52 each have different optical filters directly above them.

[0043] [Effective Sensitivity Spectrum] Here, with reference to Figure 4, the first and second effective sensitivity spectra are described. The horizontal axis represents wavelength [μm], and the vertical axis represents the intensity ratio of the effective sensitivity spectrum [au]. The solid line represents the first effective sensitivity spectrum, and the dashed and dotted lines represent the second effective sensitivity spectrum.

[0044] The first effective sensitivity spectrum of the first light-receiving unit 51 is the spectrum of light in the wavelength band for which the first light-receiving unit 51 has effective sensitivity, and is defined as the spectrum obtained by multiplying the spectrum of light in the first transmission band of the first optical filter 41 and the spectrum of light in the first light-receiving sensitivity band of the first light-receiving unit 51. In other words, it can be said that the general characteristics of the first effective sensitivity spectrum of the first light-receiving unit 51 are determined based on the first transmission band.

[0045] The second effective sensitivity spectrum of the second light-receiving unit 52 is the spectrum of light in the wavelength band in which the second light-receiving unit 52 has effective sensitivity, and is defined as the spectrum obtained by multiplying the spectrum of light in the second transmission band of the second optical filter 42 and the spectrum of light in the second light-receiving sensitivity band of the second light-receiving unit 52. In other words, it can be said that the general characteristics of the second effective sensitivity spectrum of the second light-receiving unit 52 are determined based on the second transmission band.

[0046] The full width at half maximum (FMAX) of the first effective sensitivity spectrum is preferably between 80 nm and 300 nm. Similarly, the full width at half maximum (FMAX) of the second effective sensitivity spectrum is preferably between 80 nm and 300 nm. A wider FMAX of each effective sensitivity spectrum allows for the capture of more wavelengths in which the target gas absorbs infrared light, thereby increasing infrared attenuation. However, capturing an unnecessarily wide wavelength range increases the amount of light unrelated to infrared absorption, resulting in a relatively smaller infrared attenuation rate. For this reason, the FMAX of the first and second effective sensitivity spectra are preferably within the ranges described above.

[0047] As shown in Figure 4, the difference ΔP between the peak wavelength P1 of the first effective sensitivity spectrum and the peak wavelength P2 of the second effective sensitivity spectrum is preferably 0.2 to 0.8 times the full width at half maximum W1 of the first effective sensitivity spectrum. In other words, the peak wavelength P2 of the second effective sensitivity spectrum is preferably a wavelength that is shifted to a lower energy side from the peak wavelength P1 of the first effective sensitivity spectrum by 0.2 to 0.8 times the full width at half maximum W1 of the first effective sensitivity spectrum. Alternatively, the peak wavelength P2 of the second effective sensitivity spectrum is preferably a wavelength that is shifted to a higher energy side from the peak wavelength P1 of the first effective sensitivity spectrum by 0.2 to 0.8 times the full width at half maximum W1 of the first effective sensitivity spectrum.

[0048] For example, if the peak wavelength P1 of the first effective sensitivity spectrum is 3.3 μm and the full width at half maximum W1 of the first effective sensitivity spectrum is 140 nm, then the peak wavelength P2 of the second effective sensitivity spectrum is preferably 3.23 μm (= 3.3 μm - 0.07 μm), which is a wavelength shifted to a higher energy side by 0.5 times (= 70 nm) of the full width at half maximum W1 of the first effective sensitivity spectrum, or 3.37 μm (= 3.3 μm + 0.07 μm), which is a wavelength shifted to a lower energy side by 0.5 times (= 70 nm) of the full width at half maximum W1 of the first effective sensitivity spectrum.

[0049] The difference ΔP between the peak wavelength P1 of the first effective sensitivity spectrum and the peak wavelength P2 of the second effective sensitivity spectrum is between 0.2 and 0.8 times the full width at half maximum W1 of the first effective sensitivity spectrum. This means that the optical concentration measuring device 1 does not need to use an optical filter whose transmission band is the wavelength band in which only the target gas absorbs infrared light, as is the case with conventional optical concentration measuring devices, in order to avoid the influence of infrared absorption by interfering gases. Therefore, even if the wavelength band in which the target gas absorbs infrared light is narrow, the light receiving unit can receive a sufficient amount of light, thus enabling the realization of an optical concentration measuring device 1 that can perform highly reliable measurements.

[0050] Furthermore, by ensuring that the difference ΔP between the peak wavelength P1 of the first effective sensitivity spectrum and the peak wavelength P2 of the second effective sensitivity spectrum is between 0.2 and 0.8 times the full width at half maximum W1 of the first effective sensitivity spectrum, the structure or composition of the first optical filter 41 and the second optical filter 42 can be made closer. This is expected to improve the temperature characteristics.

[0051] Here, we will explain why an improvement in temperature characteristics can be expected.

[0052] Conventional optical concentration measuring devices, for example, include a light-receiving unit having a first optical filter whose transmission band is the wavelength band in which the target gas and the interfering gas absorb infrared radiation, and a light-receiving unit having a second optical filter whose transmission band is the wavelength band in which only the interfering gas absorbs infrared radiation. This completely separates the transmission bands of the two optical filters and eliminates the influence of infrared absorption by the interfering gas. As a result, it is difficult to make the structure or composition of the first and second optical filters similar, leading to differences in the temperature characteristics of the two optical filters, and this difference also deteriorates the measurement accuracy of the optical concentration measuring device.

[0053] However, the optical concentration measuring device 1 according to this embodiment does not require the transmission bands of the two optical filters to be completely separated, as in conventional optical concentration measuring devices. Instead, it uses two optical filters with similar transmission bands and applies interference removal calculations by the calculation unit 60, which will be described in detail later, to eliminate the effect of infrared absorption by interfering gases. In other words, it is not necessary to completely separate the transmission bands of the two optical filters, and the structure or composition of the first optical filter 41 and the second optical filter 42 can be made similar. This makes it possible to reduce differences in the temperature characteristics of the first optical filter 41 and the second optical filter 42. Therefore, an optical concentration measuring device 1 can be realized that avoids the deterioration of measurement accuracy caused by differences in temperature characteristics.

[0054] Furthermore, the wider the overlap region between the first effective sensitivity spectrum and the second effective sensitivity spectrum, the closer the first transmission band and first light-receiving sensitivity band become to the second transmission band and second light-receiving sensitivity band. Therefore, in the optical density measuring device 1, further improvements in temperature characteristics can be expected by making the structure or composition of the first optical filter 41 and the second optical filter 42 closer, as well as the structure or composition of the first light source 31 and the second light source 32, and the structure or composition of the first light-receiving unit 51 and the second light-receiving unit 52 closer.

[0055] As described above, by appropriately adjusting the peak shift at the peak wavelength of the second effective sensitivity spectrum relative to the peak wavelength of the first effective sensitivity spectrum, an optical concentration measuring device 1 can be realized that can measure the concentration of the target gas with high accuracy, even when the wavelength band in which the target gas absorbs infrared rays is narrow, without drastically reducing the amount of light received by the first light receiving unit 51 and the second light receiving unit 52, while also improving the temperature characteristics.

[0056] [First light guide section] The first light guide unit 21 guides the infrared radiation emitted from the first light source 31 to the first light receiving unit 51. For example, the first light guide unit 21 reflects the infrared radiation multiple times or rotates the radiation angle when the infrared radiation is emitted, thereby ultimately bringing the infrared radiation emitted from the first light source 31 to the first light receiving unit 51.

[0057] The first light guide section 21 includes mirrors 211 and 212. Mirrors 211 and 212 are preferably made of the same material, such as metal, glass, ceramics, or stainless steel.

[0058] From the viewpoint of improving sensitivity, mirrors 211 and 212 are preferably formed from a material with a low light absorption coefficient and high reflectivity. Examples of such materials include alloys containing aluminum, gold, and silver, dielectrics, or resin housings coated with laminates thereof. Examples of resin housing materials include LCP (liquid crystal polymer), PP (polypropylene), PEEK (polyether ether ketone), PA (polyamide), PPE (polyphenylene ether), PC (polycarbonate), PPS (polyphenylene sulfide), PMMA (polymethyl methacrylate resin), or rigid resins that are mixtures of two or more of these.

[0059] Furthermore, from the viewpoint of improving reliability and suppressing deterioration over time, it is preferable that the mirrors 211 and 212 be formed from a resin housing coated with a gold or gold-containing alloy layer. In addition, it is preferable that a dielectric laminate film be formed on the surface of the metal layer to increase reflectivity. When the inner surface of the first light guide section 21 is formed by vapor deposition or plating on the resin housing, productivity can be improved and weight can be reduced.

[0060] Furthermore, the first light guide unit 21 is not limited to mirrors 211 and 212, but may be any optical element. For example, the first light guide unit 21 may be a plurality of lenses. For example, the first light guide unit 21 may be a combination of a plurality of mirrors and a plurality of lenses.

[0061] [Second light guide section] The second light guide unit 22 guides the infrared radiation emitted from the second light source 32 to the second light receiving unit 52. For example, the second light guide unit 22 causes the infrared radiation emitted from the second light source 32 to reach the second light receiving unit 52 by reflecting the infrared radiation multiple times or by rotating and changing the radiation angle during infrared radiation.

[0062] The second light guide section 22 includes mirrors 221 and 222. Mirrors 221 and 222 are preferably made of the same material, such as metal, glass, ceramics, or stainless steel.

[0063] From the viewpoint of improving sensitivity, mirrors 221 and 222 are preferably formed from materials with a low light absorption coefficient and high reflectivity. Examples of such materials include alloys containing aluminum, gold, and silver, dielectrics, or resin housings coated with laminates thereof. Examples of resin housing materials include LCP (liquid crystal polymer), PP (polypropylene), PEEK (polyether ether ketone), PA (polyamide), PPE (polyphenylene ether), PC (polycarbonate), PPS (polyphenylene sulfide), PMMA (polymethyl methacrylate resin), or rigid resins that are mixtures of two or more of these.

[0064] Furthermore, from the viewpoint of improving reliability and suppressing deterioration over time, it is preferable that the mirrors 221 and 222 be formed from a resin housing coated with a gold or gold-containing alloy layer. In addition, it is preferable that a dielectric laminate film be formed on the surface of the metal layer to increase reflectivity. When the inner surface of the second light guide section 22 is formed by vapor deposition or plating on the resin housing, productivity can be improved and weight can be reduced.

[0065] Furthermore, the second light guide unit 22 is not limited to mirrors 221 and 222, but may be any optical element. For example, the second light guide unit 22 may be a plurality of lenses. For example, the second light guide unit 22 may be a combination of a plurality of mirrors and a plurality of lenses.

[0066] [Arithmetic unit] The arithmetic unit 60 may include a drive unit 70, a general-purpose processor that performs functions according to the program to be read, and at least one dedicated processor specialized for a particular process. The dedicated processor may include an application-specific integrated circuit (ASIC) or non-volatile / volatile memory.

[0067] The calculation unit 60 calculates a first attenuation amount of the first infrared intensity due to the gas to be measured and the interfering gas present in the first optical path L1, based on the first detection signal output from the first light receiving unit 51. The first attenuation amount is a quantity calculated based on the difference between the first detection signal output from the first light receiving unit 51 when the gas to be measured and the interfering gas are not present in the first optical path L1, and the first detection signal output from the first light receiving unit 51 when the gas to be measured and the interfering gas are present in the first optical path L1.

[0068] Next, the calculation unit 60 calculates the second attenuation amount of the second infrared intensity due to the gas to be measured and the interfering gas present in the second optical path L2, based on the second detection signal output from the second light receiving unit 52. The second attenuation amount is calculated based on the difference between the second detection signal output from the second light receiving unit 52 when the gas to be measured and the interfering gas are not present in the second optical path L2, and the second detection signal output from the second light receiving unit 52 when the gas to be measured and the interfering gas are present in the second optical path L2.

[0069] Next, the calculation unit 60 calculates the concentration of the target gas based on the first and second attenuations. For example, the calculation unit 60 subtracts the second attenuation from the amount obtained by multiplying the first attenuation by a proportionality constant, performs interference removal calculations to remove the attenuation of the first intensity of infrared radiation due to the interfering gas present in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas present in the second optical path L2, and calculates the concentration of the target gas. For example, the calculation unit 60 subtracts the first attenuation from the amount obtained by multiplying the second attenuation by a proportionality constant, performs interference removal calculations to remove the attenuation of the first intensity of infrared radiation due to the interfering gas present in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas present in the second optical path L2, and calculates the concentration of the target gas.

[0070] Here, we will explain that the attenuation of the first intensity of infrared radiation due to the interfering gas in the first optical path L1 is proportional to the attenuation of the second intensity of infrared radiation due to the interfering gas in the second optical path L2. For example, we will explain the case where the gas being measured is methane and the interfering gas is water vapor.

[0071] The attenuation of infrared radiation intensity ΔI due to gas is expressed by the Lambert-Beer law as follows (1):

[0072]

number

[0073] From equation (1), we can see that the attenuation of infrared intensity ΔI due to the gas behaves exponentially. However, when ecl is close to 0, the attenuation of infrared intensity ΔI due to the gas can be expressed using a polynomial, which is the Maclaurin expansion of an exponential function, as shown in equation (2).

[0074]

number

[0075] In particular, when ecl is near zero, the attenuation of infrared radiation intensity ΔI due to the gas behaves like a linear function. For example, when measuring a methane concentration of 100 ppm, the water vapor concentration is approximately 15,000 ppm in an environment with a temperature of 25°C and a relative humidity of 50% RH, so the water vapor concentration is about 150 times that of methane. However, as shown in Figures 3B and 3C, the absorption coefficient of infrared radiation due to methane is extremely large around a wavelength of 3.3 μm, while the absorption coefficient of infrared radiation due to water vapor is extremely small. In other words, the attenuation of infrared radiation intensity due to water vapor is a linear function with respect to the water vapor concentration.

[0076] Figure 5 shows the relationship between water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the first and second effective sensitivity spectra. The horizontal axis represents water vapor concentration [ppm], and the vertical axis represents the attenuation of infrared radiation intensity [%]. The graphs shown in Figure 5 were calculated using a spectrum with a peak wavelength P1 of 3.3 μm and a full width at half maximum W1 of 140 nm as the first effective sensitivity spectrum, and a spectrum with a peak shift of ±70 nm between the peak wavelength P1 and the peak wavelength P2 as the second effective sensitivity spectrum (see Figure 4).

[0077] Graph 201 (solid line) shows the relationship between water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the first effective sensitivity spectrum. Graph 202 (dashed line) shows the relationship between water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the second effective sensitivity spectrum. Graph 203 (dotted line) shows the relationship between water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the second effective sensitivity spectrum.

[0078] From Figure 5, Graph 201 shows a linear function, indicating that the attenuation of infrared radiation intensity due to water vapor in the first effective sensitivity spectrum is proportional to the water vapor concentration. Similarly, Graph 202 shows a linear function, indicating that the attenuation of infrared radiation intensity due to water vapor in the second effective sensitivity spectrum is proportional to the water vapor concentration. Furthermore, Graph 203 shows a linear function, indicating that the attenuation of infrared radiation intensity due to water vapor in the second effective sensitivity spectrum is proportional to the water vapor concentration.

[0079] Furthermore, Figure 5 shows that graphs 201, 202, and 203 have different slopes for their respective linear functions. In other words, the slope of each linear function changes as the effective sensitivity spectrum changes. This is because the value of e in equation (2) changes as the effective sensitivity spectrum changes.

[0080] Figure 6 shows the relationship between water vapor concentration and the ratio of infrared intensity attenuation due to water vapor in the first and second effective sensitivity spectra. The horizontal axis represents water vapor concentration [ppm], and the vertical axis represents the ratio of infrared intensity attenuation [au]. The ratio is based on the attenuation of infrared intensity due to water vapor concentration in the first effective sensitivity spectrum. The graph shown in Figure 6 was calculated using a spectrum with a peak wavelength P1 of 3.3 μm and a full width at half maximum W1 of 140 nm as the first effective sensitivity spectrum, and a spectrum with a peak shift of ±70 nm between the peak wavelength P1 and the peak wavelength P2 as the second effective sensitivity spectrum (see Figure 4).

[0081] Graph 301 (solid line) shows the relationship between the water vapor concentration and the ratio of the attenuation of infrared radiation intensity due to water vapor in the first effective sensitivity spectrum, which is used as a reference. Graph 302 (dashed line) shows the relationship between the ratio of the water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the second effective sensitivity spectrum, relative to the water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the first effective sensitivity spectrum. Graph 303 (dotted line) shows the relationship between the ratio of the water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the second effective sensitivity spectrum, relative to the water vapor concentration and the attenuation of infrared radiation intensity due to water vapor in the first effective sensitivity spectrum.

[0082] Figure 6 shows that graph 302 is nearly horizontal, and the attenuation ratio remains approximately 1.3. Graph 303 is also nearly horizontal, and the attenuation ratio remains approximately 0.6. In other words, even if the effective sensitivity spectrum changes, the attenuation ratio remains approximately constant, independent of the water vapor concentration.

[0083] Therefore, from Figures 5 and 6, it can be seen that the attenuation of the first intensity of infrared radiation due to water vapor in the first optical path L1 is proportional to the attenuation of the second intensity of infrared radiation due to water vapor in the second optical path L2.

[0084] As described above, since the attenuation of the first intensity of infrared radiation due to the interfering gas in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas in the second optical path L2 are proportional, the calculation unit 60 can remove the attenuation of the first intensity of infrared radiation due to the interfering gas in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas in the second optical path L2 by subtracting the second attenuation from the amount obtained by multiplying the first attenuation by a proportionality constant. Alternatively, since the attenuation of the first intensity of infrared radiation due to the interfering gas in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas in the second optical path L2 are proportional, the calculation unit 60 can remove the attenuation of the first intensity of infrared radiation due to the interfering gas in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas in the second optical path L2 by subtracting the first attenuation from the amount obtained by multiplying the second attenuation by a proportionality constant.

[0085] Generally, when an optical concentration measuring device measures the concentration of a target gas in a gas containing both the target gas and an interfering gas, it is extremely difficult to determine the extent of the attenuation of infrared radiation intensity due to the target gas and the extent of the attenuation due to the interfering gas. However, as is clear from Figures 5 and 6, the attenuation of the first infrared intensity due to water vapor in the first optical path L1 and the attenuation of the second infrared intensity due to water vapor in the second optical path L2 are proportional. Therefore, the calculation unit 60 can easily eliminate the effect of infrared absorption by water vapor by using the ratio of the slopes of the linear functions shown in Figures 5 and 6 as a proportionality constant in its calculations.

[0086] Therefore, unlike conventional optical concentration measuring devices, the optical concentration measuring device 1 does not require the transmission bands of the two optical filters to be completely separated. Instead, it uses two optical filters with similar transmission bands and performs interference removal calculations using the calculation unit 60 described above, thereby eliminating the effect of infrared absorption by interfering gases. As a result, even when the wavelength band in which the target gas absorbs infrared rays is narrow, the amount of light received by the first light receiving unit 51 and the second light receiving unit 52 is not drastically reduced, making it possible to measure the concentration of the target gas with high accuracy.

[0087] Furthermore, it is preferable that the SNR (Signal to Noise Ratio) for the first attenuation and the second attenuation are approximately equal. This is because when the calculation unit 60 calculates the concentration of the target gas based on the first attenuation and the second attenuation, it is always affected by the worse of the SNRs. Therefore, it is preferable that the difference between the first optical path length l1 of the infrared radiation guided by the first light guide unit 21 and the second optical path length l2 of the infrared radiation guided by the second light guide unit 22 is 0% to 5% of the first optical path length l1, if the relationship that the first optical path length l1 is longer than the second optical path length l2 (l1≧l2) is satisfied. Alternatively, it is preferable that the difference between the first optical path length l1 of the infrared radiation guided by the first light guide unit 21 and the second optical path length l2 of the infrared radiation guided by the second light guide unit 22 is 0% to 5% of the second optical path length l2, if the relationship that the second optical path length l2 is longer than the first optical path length l1 (l2≧l1) is satisfied. Furthermore, if there is no difference between the first optical path length l1 of the infrared rays guided by the first light guide 21 and the second optical path length l2 of the infrared rays guided by the second light guide 22, it is more preferable because no difference in the SNR of the first attenuation and the second attenuation occurs due to the difference in optical path length.

[0088] [Drive unit] The drive unit 70 supplies a drive current or drive voltage to the first light source 31 to drive or stop it. For example, when the drive unit 70 stops the first light source 31, it supplies the same voltage to the anode electrode and the cathode electrode of the first light source 31. For example, when the drive unit 70 drives the first light source 31, it supplies different voltages to the anode electrode and the cathode electrode of the first light source 31. The drive current signal or drive voltage signal output from the drive unit 70 to drive or stop the first light source 31 may be used by the calculation unit 60 when performing calculations.

[0089] Furthermore, the drive unit 70 supplies a drive current or drive voltage to the second light source 32 for driving or stopping the second light source 32. For example, when the drive unit 70 stops the second light source 32, it supplies the same voltage to the anode electrode and the cathode electrode of the second light source 32. For example, when the drive unit 70 drives the second light source 32, it supplies different voltages to the anode electrode and the cathode electrode of the second light source 32. The drive current signal or drive voltage signal output from the drive unit 70 for driving or stopping the second light source 32 may be used by the calculation unit 60 when performing calculations.

[0090] The drive unit 70 is composed of, for example, a power supply, an amplifier, etc. The drive unit 70 may be integrated with the calculation unit 60, or it may be provided separately from the calculation unit 60. Furthermore, the drive unit 70 may be mounted on the circuit board 80, or it may be provided outside the circuit board 80.

[0091] 〔substrate〕 The substrate 80 is equipped with a first light guide unit 21, a second light guide unit 22, a first light source 31, a second light source 32, a first optical filter 41, a second optical filter 42, a first light receiving unit 51, a second light receiving unit 52, a calculation unit 60, a drive unit 70, and the like. The substrate 80 electrically connects the various electronic components mounted on it. Note that the calculation unit 60 and the drive unit 70 may be provided outside the substrate 80.

[0092] The substrate 80 is preferably formed from a material such as phenolic resin, epoxy resin, polyimide resin, or alumina resin, which are referred to as FR-1, FR-2, FR-3, FR-4, FR-5, GPY, CEM-1, or CEM-3.

[0093] Furthermore, it is preferable that the first light source 31, the second light source 32 and the first light receiving unit 51, the second light receiving unit 52 are mounted on the same substrate. By mounting these components on the same substrate, it is unnecessary to prepare separate substrates, which reduces manufacturing costs and improves measurement accuracy.

[0094] In this embodiment, the optical concentration measuring device 1 has a difference between the peak wavelength of the first effective sensitivity spectrum and the peak wavelength of the second effective sensitivity spectrum that is between 0.2 and 0.8 times the full width at half maximum of the first effective sensitivity spectrum, and the calculation unit 60 performs the interference removal calculation described above. As a result, the effect of infrared absorption by interfering gases can be removed without completely separating the transmission bands of the two optical filters, as in conventional optical concentration measuring devices. Furthermore, even when the wavelength band in which the target gas absorbs infrared rays is narrow, the amount of light received by the light receiving unit can be significantly increased compared to conventional optical concentration measuring devices. Therefore, an optical concentration measuring device 1 can be realized that can measure the concentration of the target gas with high accuracy while removing the effect of light absorption by interfering gases.

[0095] <Optical density calculation method> Next, the optical concentration measurement method according to this embodiment will be explained with specific examples. For example, the case where the target gas is methane and the interfering gas is water vapor will be explained.

[0096] First, the calculation unit 60 calculates the first attenuation amount of the first infrared intensity due to the gas to be measured and the interfering gas present in the first optical path L1, based on the first detection signal output from the first light receiving unit 51.

[0097] TIFF0007850575000003.tif35170

[0098]

number

[0099] Next, the calculation unit 60 calculates the second attenuation of the second infrared intensity due to the gas to be measured and the interfering gas present in the second optical path L2, based on the second detection signal output from the second light receiving unit 52.

[0100] TIFF0007850575000005.tif35170

[0101]

number

[0102] Originally, there are higher-order absorption terms that show the effects of both methane and water vapor, but the amount of water vapor absorption is small enough to be expressed by the Maclaurin series. Therefore, the higher-order absorption terms can be ignored.

[0103] Next, the calculation unit 60 calculates the concentration of the gas to be measured based on the first and second attenuations. As described above, the attenuation of the first intensity of infrared radiation due to the interfering gas in the first optical path L1 and the attenuation of the second intensity of infrared radiation due to the interfering gas in the second optical path L2 are proportional.

[0104] Therefore, first, the calculation unit 60 subtracts the second attenuation amount from the amount obtained by multiplying the first attenuation amount by a proportionality constant, and removes the attenuation amount of the first intensity of infrared radiation due to the interfering gas present in the first optical path L1 and the attenuation amount of the second intensity of infrared radiation due to the interfering gas present in the second optical path L2, thereby performing an interference removal calculation that removes the influence of infrared radiation due to the interfering gas. Alternatively, the calculation unit 60 subtracts the first attenuation amount from the amount obtained by multiplying the second attenuation amount by a proportionality constant, and removes the attenuation amount of the first intensity of infrared radiation due to the interfering gas present in the first optical path L1 and the attenuation amount of the second intensity of infrared radiation due to the interfering gas present in the second optical path L2, thereby performing an interference removal calculation that removes the influence of infrared radiation due to the interfering gas. As a result, the calculation unit 60 can calculate the concentration of the target gas even if the concentration of the interfering gas is unknown.

[0105] TIFF0007850575000007.tif25170

[0106]

number

[0107] TIFF0007850575000009.tif36170

[0108] TIFF0007850575000010.tif26170

[0109]

number

[0110] TIFF0007850575000012.tif37170

[0111] Finally, the calculation unit 60 calculates the concentration of the target gas by applying a concentration calculation table or exponential function fitting to the output after interference removal calculation, which removes the effect of infrared absorption by the interfering gas. Preferably, the calculation unit 60 calculates the concentration of the target gas using a polynomial of order 3 or higher in equation (2). This allows the calculation unit 60 to calculate the concentration of the target gas with high accuracy and ease.

[0112] The optical density measurement method according to this embodiment utilizes the fact that, when the difference between the peak wavelength of the first effective sensitivity spectrum and the peak wavelength of the second effective sensitivity spectrum is defined as 0.2 to 0.8 times the full width at half maximum of the first effective sensitivity spectrum, the attenuation of the first infrared intensity due to the interfering gas present in the first optical path and the attenuation of the second infrared intensity due to the interfering gas present in the second optical path are proportional, and performs interference removal calculation to eliminate the effect of infrared absorption by the interfering gas. The optical density measurement device 1 to which this optical density measurement method is applied can measure the concentration of the target gas with high accuracy while eliminating the effect of light absorption by the interfering gas.

[0113] <Variation> In this specification, the Gaussian function was chosen as the function representing the intensity distribution of the effective sensitivity spectrum shown in Figure 4 for explanation purposes, but the function representing the intensity distribution of the effective sensitivity spectrum is not limited to this. For example, the Lorentz function may be chosen. Also, although the wavelength characteristics of the light source or optical path were not mentioned in the explanation of the principle of interference rejection calculation, the same results can be obtained even if these wavelength characteristics are included. For example, the wavelength characteristics of the light source may be included by multiplying it by Planck's law, which represents the wavelength distribution of infrared radiation emitted from the light source. Alternatively, the wavelength characteristics of the light source and optical path may be included by multiplying the density of states distribution function by the reflectivity characteristics of the optical element.

[0114] Furthermore, although this specification has described the case where there is one interfering gas as an example, the number of interfering gases is not limited to one, but may be multiple. Even if there are multiple interfering gases, the attenuation of the first intensity of infrared radiation due to each interfering gas and the attenuation of the second intensity of infrared radiation due to each interfering gas are proportional. Therefore, by applying the calculation method described above, it is possible to perform an interference removal calculation that removes the attenuation of the first intensity of infrared radiation and the attenuation of the second intensity of infrared radiation due to each interfering gas. In other words, whether there is one interfering gas or multiple interfering gases, the optical concentration measuring device 1 can measure the concentration of the target gas with high accuracy while removing the effect of light absorption by the interfering gases.

[0115] <Other variations> Furthermore, optical density measuring devices that do not require a calculation unit as an essential component are understood as modules for optical density measuring devices, and thus as independent embodiments.

[0116] <Application of Embodiments> The optical concentration measuring device 1 according to this embodiment can be applied to various devices. For example, it can be applied to devices for detecting natural gas leaks in pipelines transporting natural gas, devices for detecting gas concentrations contained in means of transportation such as automobiles, trains, and aircraft, and devices for detecting specific gas concentrations.

[0117] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments described above, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple component blocks shown in the configuration diagram of the embodiments into one, or to divide one component block. For example, the order of each operation described in the embodiments is not limited to the above and can be changed as appropriate. [Explanation of Symbols]

[0118] 1 Optical concentration measuring device 21 1st light guide section 22 Second light guiding section 31 1st light source 32 Second light source 41. First Optical Filter 42. Second optical filter 51 1st light receiving section 52 2nd light receiving section 60 Arithmetic section 70 Drive unit 80 circuit boards 211 Mirror 212 Mirror 221 Miller 222 Miller

Claims

1. An optical concentration measuring device for measuring the concentration of the target gas contained in a gas in which the target gas and interfering gases are mixed, A first light source that emits infrared rays, A first optical filter having a first transmission band that includes a wavelength band in which the gas to be measured and the interfering gas absorb the infrared light, A first light receiving unit that has sensitivity to the first transmission band and outputs a first detection signal corresponding to the first intensity of the received light, A first light guide unit that guides the infrared light to the first light receiving unit, The second light source that emits infrared radiation, A second optical filter having a second transmission band that includes a wavelength band in which the gas to be measured and the interfering gas absorb the infrared light, A second light receiving unit that has sensitivity to the second transmission band and outputs a second detection signal corresponding to the second intensity of the received light, A second light guide unit that guides the infrared light to the second light receiving unit, A calculation unit that calculates a first attenuation of the first intensity due to the target gas and the interfering gas based on the first detection signal, calculates a second attenuation of the second intensity due to the target gas and the interfering gas based on the second detection signal, and calculates the concentration of the target gas based on the first and second attenuations, Equipped with, The difference between the peak wavelength of the first effective sensitivity spectrum based on the first transmission band in the first light-receiving unit and the peak wavelength of the second effective sensitivity spectrum based on the second transmission band in the second light-receiving unit is ±0.2 times or more and ±0.8 times or less the full width at half maximum of the first effective sensitivity spectrum. The calculation unit subtracts the second attenuation amount from the amount obtained by multiplying the first attenuation amount by a proportionality constant, or subtracts the first attenuation amount from the amount obtained by multiplying the second attenuation amount by a proportionality constant different from the proportionality constant, and removes the attenuation amount of the first intensity due to the interfering gas and the attenuation amount of the second intensity due to the interfering gas. Optical concentration measuring device.

2. The full width at half maximum of the first effective sensitivity spectrum or the second effective sensitivity spectrum is 80 nm or more and 300 nm or less. Optical density measuring device according to claim 1

3. The center wavelength of the first transmission band is 3.2 μm or more and 3.4 μm or less. The optical concentration measuring device according to claim 1 or 2.

4. If the first optical path length of the infrared light guided by the first light guide is greater than or equal to the second optical path length of the infrared light guided by the second light guide, the difference between the first optical path length and the second optical path length is 0% or more and 5% or less of the first optical path length. An optical density measuring device according to any one of claims 1 to 3.

5. If the second optical path length of the infrared light guided by the second light guide is greater than or equal to the first optical path length of the infrared light guided by the first light guide, the difference between the first optical path length and the second optical path length is 0% or more and 5% or less of the second optical path length. An optical density measuring device according to any one of claims 1 to 3.

6. The first light source and the second light source are the same. An optical density measuring device according to any one of claims 1 to 5.

7. The first light source and the second light source, or the first light receiving unit and the second light receiving unit, are composed of a semiconductor or a compound semiconductor. An optical density measuring device according to any one of claims 1 to 6.

8. A module for an optical concentration measuring device that measures the concentration of the target gas in a gas containing a mixture of the target gas and an interfering gas, A first light source that emits infrared rays, A first optical filter having a first transmission band that includes a wavelength band in which the gas to be measured and the interfering gas absorb the infrared light, A first light-receiving unit that is sensitive to the first transmission band and receives light that has passed through the first optical filter, A first light guide unit that guides the infrared light to the first light receiving unit, The second light source that emits infrared radiation, A second optical filter having a second transmission band that includes a wavelength band in which the gas to be measured and the interfering gas absorb the infrared light, A second light-receiving unit that is sensitive to the second transmission band and receives light that has passed through the second optical filter, A second light guide unit that guides the infrared light to the second light receiving unit, Equipped with, The difference between the peak wavelength of the first effective sensitivity spectrum based on the first transmission band in the first light-receiving unit and the peak wavelength of the second effective sensitivity spectrum based on the second transmission band in the second light-receiving unit is ±0.2 times or more and ±0.8 times or less the full width at half maximum of the first effective sensitivity spectrum. Module for optical concentration measuring devices.

9. An optical concentration measuring device for measuring the concentration of a target gas contained in a gas in which the target gas and interfering gases are mixed, The aforementioned optical concentration measuring device, A first light source that emits infrared rays, A first optical filter having a first transmission band that includes a wavelength band in which the gas to be measured and the interfering gas absorb the infrared light, A first light receiving unit that has sensitivity to the first transmission band and outputs a first detection signal corresponding to the first intensity of the received light, A first light guide unit that guides the infrared light to the first light receiving unit, The second light source that emits infrared radiation, A second optical filter having a second transmission band that includes a wavelength band in which the gas to be measured and the interfering gas absorb the infrared light, A second light receiving unit that has sensitivity to the second transmission band and outputs a second detection signal corresponding to the second intensity of the received light, A second light guide unit that guides the infrared light to the second light receiving unit, The calculation unit and Equipped with, The difference between the peak wavelength of the first effective sensitivity spectrum based on the first transmission band in the first light-receiving unit and the peak wavelength of the second effective sensitivity spectrum based on the second transmission band in the second light-receiving unit is ±0.2 times or more and ±0.8 times or less the full width at half maximum of the first effective sensitivity spectrum. The calculation unit performs the steps of calculating a first attenuation amount of the first intensity due to the gas to be measured and the interfering gas based on the first detection signal, The calculation unit performs the following steps: calculates the second attenuation amount of the second intensity due to the gas to be measured and the interfering gas based on the second detection signal; The calculation unit performs the steps of calculating the concentration of the gas to be measured based on the first decay amount and the second decay amount, Includes, The step of calculating the concentration of the gas to be measured includes the calculation unit subtracting the second attenuation amount from the amount obtained by multiplying the first attenuation amount by a proportionality constant, or subtracting the first attenuation amount from the amount obtained by multiplying the second attenuation amount by a proportionality constant different from the proportionality constant, thereby removing the attenuation amount of the first intensity and the attenuation amount of the second intensity due to the interfering gas. Optical concentration measurement method.

Images