Gas concentration measurement device

A gas concentration measurement device includes a light source that emits infrared light, a detector that detects the infrared light through a band pass filter, and a waveguide including a wave-guiding portion that includes a tubular inner peripheral surface, an entrance that introduces the infrared light from the light source to the wave-guiding portion, and an exit that guides the infrared light that passes through the wave-guiding portion toward the detector. A portion or the entirety of the inner peripheral surface of the wave-guiding portion includes a tapered region that includes a cross section that decreases along a direction extending from the entrance to the exit. The waveguide reflects the infrared light that enters the wave-guiding portion to reduce energy of the infrared light that is obliquely incident on the band pass filter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an infrared-light-absorption gas concentration measurement device.

2. Description of the Related Art

Various types of gas concentration measurement devices for analyzing various types of exhaust, gas contained in the atmosphere, or gas contained in the air in a building have been developed. In particular, infrared-light-absorption gas concentration measurement devices are used to analyze sample gas because the sample gas absorbs infrared light in a specific wavelength range.

International Publication No. 01/27596, for example, discloses an infrared-light-absorption gas concentration measurement device. In the gas concentration measurement device disclosed in International Publication No. 01/27596, an anti-reflection film is applied to inner walls of an analysis chamber (sample cell) that defines a flow channel for the sample gas. Accordingly, the risk of the infrared light being incident on a band pass filter, which is provided on a surface of a detector, at an angle greater than a predetermined angle is somewhat reduced.

The anti-reflection film disclosed in International Publication No. 01/27596 must be made of a material including a reflectance close to zero. Thus, the material of the anti-reflection film is limited. If an inexpensive material including a reflectance that is not close to zero is used, the infrared light is reflected by the anti-reflection film such that the reflected infrared light is incident on the band pass filter at an angle greater than the predetermined angle. Thus, the transmission band of the band pass filter is shifted and the measurement accuracy of the gas concentration measurement device decreases.

Therefore, a gas concentration measurement device including a new structure that is able to be substituted for the anti-reflection film made of a specified material and that can reduce the risk of the reflected infrared light being incident on the band pass filter at an angle greater than the predetermined angle is needed.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a gas concentration measurement device with significantly increased measurement accuracy.

A gas concentration measurement device according to a preferred embodiment of the present invention includes a light source that emits infrared light; a detector that detects the infrared light from the light source through a band pass filter; and a waveguide that includes a wave-guiding portion with a tubular inner peripheral surface, an entrance that is provided at one side of the wave-guiding portion and through which the infrared light from the light source is introduced, and an exit that is provided at the other side of the wave-guiding portion and guides the infrared light that passes through the wave-guiding portion toward the detector. A portion or an entirety of the inner peripheral surface of the wave-guiding portion includes a tapered region that includes a cross section that decreases along a direction extending from the entrance to the exit. The waveguide reflects the infrared light that enters the wave-guiding portion through the entrance in the tapered region, so that energy of the infrared light that is obliquely incident on the band pass filter is significantly reduced.

In a gas concentration measurement device according to a preferred embodiment of the present invention, preferably, the tapered region of the inner peripheral surface of the wave-guiding portion includes a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal portion including a perimeter that decreases along a direction extending from the entrance to the exit.

In a gas concentration measurement device according to a preferred embodiment of the present invention, preferably, an opening area of the entrance is greater than an opening area of the exit.

In a gas concentration measurement device according to a preferred embodiment of the present invention, preferably, the tapered region of the inner peripheral surface of the wave-guiding portion includes a first curved portion with a perimeter that decreases along a direction from the entrance to the exit.

In a gas concentration measurement device according to a preferred embodiment of the present invention, preferably, a length of the first curved portion in an axial direction of the wave-guiding portion is greater than, equal to, or substantially equal to about half a length of the wave-guiding portion in the axial direction of the wave-guiding portion.

In a gas concentration measurement device according to a preferred embodiment of the present invention, preferably, the inner peripheral surface of the wave-guiding portion includes a second curved portion with a perimeter that decreases along a direction from the exit to the entrance.

In a gas concentration measurement device according to a preferred embodiment of the present invention, preferably, the waveguide is made of a resin material.

According to preferred embodiments of the present invention, gas concentration measurement devices with significantly increased measurement accuracy are provided.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described in detail with reference to the drawings. In the preferred embodiments described below, components that are the same or similar are denoted by the same reference numerals in the drawings, and descriptions thereof will not be repeated.

First Preferred Embodiment

FIG. 1is a schematic sectional view of a gas concentration measurement device according to the present preferred embodiment. The gas concentration measurement device according to the present preferred embodiment will be described with reference toFIG. 1.

As illustrated inFIG. 1, a gas concentration measurement device100according to the present preferred embodiment includes a sample cell10, a light source20, a band pass filter41, a detector60, and a waveguide90. The gas concentration measurement device100measures a gas concentration in accordance with the absorbance of sample gas that flows through a space between the light source20, which emits infrared light, and the detector60, which includes a light-receiving portion62that receives the infrared light.

The sample cell10includes a sample-gas flow space and allows the sample gas to flow therethrough. For example, a sample-gas introduction hole (not shown) is connected to one end of the sample cell10(an end close to the light source20), and a sample-gas discharge hole (not shown) is connected to the other end of the sample cell10(an end close to the detector60). The sample gas introduced into the sample cell10through the sample-gas introduction hole is discharged through the sample-gas discharge hole.

The sample cell10contains the light source20, the waveguide90, the band pass filter41, and the detector60. The light source20, the waveguide90, the band pass filter41, and the detector60are arranged, for example, in that order from one end of the sample cell10(from the left side in the figure).

The light source20emits infrared light. The light source20may be, for example, a filament lamp or an LED lamp that emits wide-band infrared light including the desired infrared light. A portion of the infrared light emitted from the light source20is absorbed depending on infrared light absorption wavelength characteristics of the sample gas. The sample gas is, for example, carbon dioxide, and the absorption band thereof is about 4.3 μm.

The waveguide90includes a wave-guiding portion93that includes a tubular inner peripheral surface; an entrance91that is provided at one end of the wave-guiding portion93and introduces the infrared light from the light source20; and an exit92that is provided at the other end of the wave-guiding portion93and guides the infrared light that passes through the wave-guiding portion93toward the detector60. The waveguide90guides the infrared light toward the detector60after a portion of the infrared light is absorbed by the sample gas.

The inner peripheral surface of the wave-guiding portion93includes a tapered region that includes a cross-sectional area that decreases from the entrance91toward the exit92. The tapered region includes a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape with a circumference that decreases from the entrance91toward the exit92. The truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape includes a truncated conical or substantially truncated conical shape and a truncated polygonal pyramidal or substantially truncated polygonal pyramidal shape.

The waveguide90may be made of a resin material, such as acrylonitrile butadiene styrene copolymer synthetic resin (ABS resin) or polycarbonate resin (PC resin). In particular, the waveguide90is preferably made of a resin material including a reflectance of about 20% or less in the infrared wavelength range, for example.

The band pass filter41is provided at an end of the detector60that is adjacent to the waveguide90. The band pass filter41is securely fitted in a recess64provided in a surface of the detector60that faces the waveguide90.

The band pass filter41transmits the infrared light in an absorption band of the sample gas to be detected. Thus, only the infrared light including a desired wavelength band reaches the detector60.

The detector60may be an infrared light detector, such as a thermopile or a bolometer. The detector60includes a main portion61, a light-receiving portion62, and the recess64. The light-receiving portion62is embedded in the main portion61. The light-receiving portion62receives the infrared light guided out of the exit92of the waveguide90through the band pass filter41.

The detector60is electrically connected to a signal processing circuit board (not shown). The detector60outputs an output signal to the signal processing circuit board based on the infrared light received by the light-receiving portion62. The signal processing circuit board calculates the concentration of the sample gas based on the output signal.

The infrared light incident on the band pass filter41will now be described. In general, the transmission band of the band pass filter41shifts toward the short-wavelength side of the infrared light as the incident angle of the infrared light increases. The measurement accuracy of the gas concentration measurement device decreases when the transmission band varies. Therefore, when gas concentration is measured, the incident angle of the infrared light incident on the band pass filter41is preferably small.

In the present preferred embodiment, the waveguide90is provided to significantly reduce or prevent the influence on the measurement accuracy of the infrared light with a large incident angle on the band pass filter41located in the transmitting position.

The infrared light that linearly travels through the region that is equal or substantially equal to the logical sum of the region surrounded by the outermost rays of infrared light L1and the region surrounded by the outermost rays of infrared light L2(for example, arrow L inFIG. 1) mainly reaches the light-receiving portion62through the band pass filter41. The infrared light L1is light including a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape that linearly travels along the peripheral surface of the wave-guiding portion93toward the detector60. The infrared light L2is light including two truncated cone or substantially truncated cone shapes obtained by rotating, for example, a ray of light that linearly travels from the bottom end of the entrance91of the waveguide90inFIG. 1to the top end of the light-receiving portion62inFIG. 1, approximately one turn along the opening shape of the entrance91.

The infrared light that linearly travels through the region that is or is substantially the logical sum of the region surrounded by the outermost rays of the infrared light L1and the region surrounded by the outermost rays of the infrared light L2passes through the band pass filter41at a small angle.

Infrared light L4and infrared light L5enter the wave-guiding portion93through the entrance91at a large angle with respect to the axial direction of the wave-guiding portion93. The infrared light L4and the infrared light L5travel toward the detector60while being reflected by the inner peripheral surface of the wave-guiding portion93a plurality of times.

If the reflectance of the wave-guiding portion93is about 100%, the infrared light L4and the infrared light L5may be incident on the band pass filter41at a large incident angle.

In the present preferred embodiment, the waveguide90is preferably made of a resin material including a reflectance of about 20% or less. Therefore, the infrared light L4and the infrared light L5are absorbed and attenuated by being repeatedly reflected in the wave-guiding portion93. For example, when the reflectance of the material is about 10%, the attenuation effect obtained when the infrared light is reflected five times is similar to that obtained when the infrared light is reflected once by a component including a reflectance of about 0.001%. The number of times the infrared light L4and the infrared light L5are reflected is able to be significantly increased by setting an opening area S1of the entrance91of the waveguide90to be greater than an opening area S2of the exit92and defining the wave-guiding portion93to include a tapered region.

Thus, the waveguide90repeatedly reflects the infrared light that has entered the wave-guiding portion93through the entrance91in the tapered region, thus significantly reducing the energy of the infrared light that is obliquely incident on the band pass filter41. Accordingly, the measurement accuracy of the gas concentration measurement device is significantly increased.

As described above, in the gas concentration measurement device100according to the present preferred embodiment, since the waveguide90is provided, the energy of the obliquely incident infrared light is significantly reduced. Therefore, the measurement accuracy of the gas concentration measurement device100is significantly increased.

Although the sample gas is carbon dioxide in the present preferred embodiment, the sample gas is not so limited, and alternatively may be, for example, carbon monoxide, CH4, or NOx.

Second Preferred Embodiment

FIG. 2is a schematic sectional view of a gas concentration measurement device according to the present preferred embodiment. A gas concentration measurement device100A according to the present preferred embodiment will be described with reference toFIG. 2.

As illustrated inFIG. 2, the gas concentration measurement device100A according to the present preferred embodiment includes a waveguide90A including a wave-guiding portion93A that includes a shape that differs from that in the gas concentration measurement device100according to the first preferred embodiment. Other structures are substantially the same as those in the first preferred embodiment.

An opening area S1of an entrance91A of the waveguide90A, is greater than an opening area S2of an exit92A of the waveguide90A. The internal shape of the wave-guiding portion93A preferably is partially spherical or substantially partially spherical. A portion of the inner peripheral surface of the wave-guiding portion93A that defines a portion of a spherical or substantially spherical surface is located between the entrance91A and the exit92A.

The portion that defines a portion of the spherical or substantially spherical surface includes a first spherical surface portion95, which extends toward the exit92A from a boundary at or substantially at the center M of the sphere, and a second spherical surface portion96, which extends toward the entrance91A from the boundary at or substantially at the center M. The region from the first spherical surface portion95to the exit92A corresponds to a tapered region including a cross-sectional area that decreases along the direction extending from the entrance91A to the exit92A, and also corresponds to a first curved or substantially curved portion including a circumference that decreases along the direction extending from the entrance91A to the exit92A. The second spherical surface portion96corresponds to a second curved or substantially curved portion including a circumference that decreases along the direction extending from the exit92A to the entrance91A.

When the wave-guiding portion93A includes the above-described shape, the infrared light that linearly travels through the region that is or is substantially the logical sum of the region surrounded by the outermost rays of infrared light L1and the region surrounded by the outermost rays of infrared light L2(for example, arrow L inFIG. 2) mainly reaches the light-receiving portion62. The infrared light L1is light including a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape that linearly travels along the peripheral surfaces of the entrance91A and the exit92A toward the detector60. The infrared light L2is similar to that in the first preferred embodiment.

Infrared light L4and infrared light L5that enter the wave-guiding portion93A through the entrance91A at a large angle with respect to the axial direction of the wave-guiding portion93A is reflected by the first spherical surface portion95and the second spherical surface portion96a plurality of times and emitted from the entrance91A.

The infrared light L4and the infrared light L5emitted from the entrance91A is not incident on the band pass filter41. To increase the number of times the light is reflected by the wave-guiding portion93A, the distance Lb from the first spherical surface portion95to the exit92A in the axial direction of the wave-guiding portion93A is preferably greater than, equal to, or substantially equal to about half the length La of the waveguide90.

Thus, in the present preferred embodiment, the energy of the infrared light that is obliquely incident on the band pass filter41is significantly reduced, and a portion of the obliquely incident infrared light is emitted from the entrance91A. Accordingly, the measurement accuracy of the gas concentration measurement device100A is significantly increased.

Third Preferred Embodiment

FIG. 3is a schematic sectional view of a gas concentration measurement device according to the present preferred embodiment. A gas concentration measurement device100B according to the present preferred embodiment will be described with reference toFIG. 3.

As illustrated inFIG. 3, the gas concentration measurement device100B according to the present preferred embodiment includes a waveguide90B including a wave-guiding portion93B with a shape that differs from that in the gas concentration measurement device100according to the first preferred embodiment. Other structures are substantially the same as those in the first preferred embodiment.

An opening area S1of an entrance91B of the waveguide90B is greater than an opening area S2of an exit92B of the waveguide90B. The internal shape of the wave-guiding portion93B includes a first curved portion93B1and a second curved portion93B2. The wave-guiding portion93B includes a maximum circumference portion94B. The maximum circumference portion94B is located between the entrance91B and the exit92B.

The first curved portion93B1defines the internal shape of the wave-guiding portion93B in a region that extends from the maximum circumference portion94B to the exit92B. The first curved portion93B1includes a circumference that decreases along the direction extending from the entrance91B to the exit92B.

The second curved portion93B2defines the internal shape of the wave-guiding portion93B in a region that extends from the maximum circumference portion94B to the entrance91B. The second curved portion93B2includes a circumference that decreases along the direction extending from the exit92B to the entrance91B.

The infrared light that linearly travels through the region that is equal to or substantially equal to the logical sum of the region surrounded by the outermost rays of infrared light L1and the region surrounded by the outermost rays of infrared light L2mainly reaches the light-receiving portion62. The infrared light L1is light including a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape that linearly travels along the peripheral edges of the entrance91B and the exit92B toward the detector60. The infrared light L2is similar to that in the first preferred embodiment.

The length Lb of the first curved portion93B1in the axial direction of the waveguide90B is preferably greater than, equal to, or substantially equal to about half the length La of the waveguide90B in the axial direction. When this length relationship is satisfied, infrared light L4and infrared light L5, which enter through the entrance91B at a large angle with respect to the axial direction of the wave-guiding portion93B, are reflected a plurality of times in the first curved portion93B1and the second curved portion93B2and emitted from the entrance91B.

Accordingly, in the present preferred embodiment, the energy of the infrared light that is obliquely incident on the band pass filter41is reliably reduced by a significant amount. As a result, the measurement accuracy of the gas concentration measurement device100B is significantly increased.

Fourth Preferred Embodiment

FIG. 4is a schematic sectional view of a gas concentration measurement device according to the present preferred embodiment. A gas concentration measurement device100C according to the present preferred embodiment will be described with reference toFIG. 4.

As illustrated inFIG. 4, the gas concentration measurement device100C according to the present preferred embodiment includes a waveguide90C including a wave-guiding portion93C with a shape that differs from that in the gas concentration measurement device100according to the first preferred embodiment. Other structures are substantially the same as those in the first preferred embodiment.

In the waveguide90C, an opening area S1of an entrance91C is greater than an opening area S2of an exit92C. The internal shape of the wave-guiding portion93C includes a first truncated conical or pyramidal portion93C1and a second truncated conical or pyramidal portion93C2. The first and second truncated conical or pyramidal portions93C1and93C2each include a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape. The wave-guiding portion93C includes a maximum circumference portion94C. The maximum circumference portion94C is located between the entrance91C and the exit92C.

The first truncated conical or pyramidal portion93C1defines the internal shape of the wave-guiding portion93C in a region that extends from the maximum circumference portion94C to the exit92C. The first truncated conical or pyramidal portion93C1includes a circumference that decreases along the direction extending from the entrance91C to the exit92C.

The second truncated conical or pyramidal portion93C2defines the internal shape of the wave-guiding portion93C in a region that extends from the maximum circumference portion94C to the entrance91C. The second truncated conical or pyramidal portion93C2includes a circumference that decreases along the direction extending from the exit92C to the entrance91C.

The infrared light that linearly travels through the region that is equal to or substantially equal to the logical sum of the region surrounded by the outermost rays of infrared light L1and the region surrounded by the outermost rays of infrared light L2mainly reaches the light-receiving portion62. The infrared light L1is light including a truncated conical, substantially truncated conical, pyramidal, or substantially pyramidal shape that linearly travels along the peripheral edges of the entrance91C and the exit92C toward the detector60. The infrared light L2is similar to that in the first preferred embodiment.

The length Lb of the first truncated conical or pyramidal portion93C1in the axial direction of the waveguide90C is preferably greater than, equal to, or substantially equal to about half the length La of the waveguide90C in the axial direction. When this length relationship is satisfied, infrared light L4, for example, which enters through the entrance91C at a large angle with respect to the axial direction of the wave-guiding portion93C, is reflected a plurality of times in the first truncated conical or pyramidal portion93C1and the second truncated conical or pyramidal portion93C2.

Accordingly, in the gas concentration measurement device100C according to the present preferred embodiment, the energy of the infrared light that is obliquely incident on the band pass filter41is reliably reduced by a significant amount. As a result, the measurement accuracy of the gas concentration measurement device is significant increased.

Fifth Preferred Embodiment

FIG. 5is a schematic sectional view of a gas concentration measurement device according to the present preferred embodiment. A gas concentration measurement device100D according to the present preferred embodiment will be described with reference toFIG. 5.

As illustrated inFIG. 5, the gas concentration measurement device100D according to the present preferred embodiment includes a waveguide90D including a wave-guiding portion93D with a shape that differs from that in the gas concentration measurement device100C according to the fourth preferred embodiment.

An opening area S1of an entrance91D of the waveguide90D is greater than an opening area S2of an exit92D of the waveguide90D. The internal shape of the wave-guiding portion93D includes a truncated conical or pyramidal portion93D1and a columnar portion93D2. The shape of the truncated conical or pyramidal portion93D1is substantially the same as that of the first truncated conical or pyramidal portion93C1according to the fourth preferred embodiment. The truncated columnar portion93D2includes a columnar or substantially columnar shape. The relationship between the length of the truncated conical or pyramidal portion93D1and the length of the waveguide90D is also similar to the relationship between the length of the first truncated conical or pyramidal portion93C1and the length of the waveguide90C according to the fourth preferred embodiment.

The circumference of the columnar portion93D2is constant or substantially constant over a region that extends from the entrance91D to the upstream end of the truncated conical or pyramidal portion93D1. The circumference of the columnar portion93D2is equal or substantially equal to the maximum circumference of the truncated conical or pyramidal portion93D1.

Infrared light L4and infrared light L5, which enter through the entrance91D at a large angle with respect to the axial direction of the wave-guiding portion93D, is reflected a plurality of times in the truncated conical or pyramidal portion93D1and the columnar portion93D2.

Accordingly, in the gas concentration measurement device100D according to the present preferred embodiment, the energy of the infrared light that is obliquely incident on the band pass filter41is reliably reduced by a substantial amount. As a result, the measurement accuracy of the gas concentration measurement device is significantly increased.

In the present preferred embodiment, the columnar portion93D2is adjacent to the entrance91D, and the truncated conical or pyramidal portion93D1is adjacent to the exit92D. However, the arrangement of the truncated conical or pyramidal portion93D1and the columnar portion93D2is not so limited, and the columnar portion93D2may alternatively be adjacent to the exit92D while the truncated conical or pyramidal portion93D1is alternatively adjacent to the entrance91D. In this alternative arrangement, the circumference of the columnar portion93D2is preferably set to the minimum circumference of the truncated conical or pyramidal portion93D1.

In the above-described second preferred embodiment, a portion that connects the entrance91A to the upstream end of the second spherical surface portion96(first connecting portion) and a portion that connects the downstream end of the first spherical surface portion95to the exit92A (second connecting portion) include circumferences that decrease along the direction extending from the entrance91A to the exit92A. However, the first and second connecting portions are not so limited, and at least one of the first and second connecting portions may include a columnar or substantially columnar shape with a constant or substantially constant circumference.

In the above-described third preferred embodiment, the second curved portion93B2extends from the entrance91B to the maximum circumference portion94B. However, the second curved portion93B2may be replaced by a columnar or substantially columnar portion including a circumference that is constant or substantially constant over a region that extends from the entrance91B to the maximum circumference portion94B.