JP5695301B2 - Multipass cell and gas meter - Google Patents

Description

  The present invention relates to, for example, a multipass cell using laser light and a gas measuring device including the multipass cell.

Currently, for example, a gas using infrared absorption spectroscopy that detects the concentration of the detection target gas in accordance with the degree of attenuation of the amount of infrared radiation caused by absorption of infrared light from a laser light source by the detection target gas (specific gas component) Many measuring instruments have been proposed.
In such a gas measuring instrument, for example, as the optical path length of infrared light in a measurement cell into which a gas to be inspected such as air in an ambient atmosphere is introduced, the sensitivity to a specific gas component in a low concentration range increases. Is known, and a configuration using a multiple reflection type measurement cell has been proposed (see, for example, Patent Document 1).

FIG. 8 is an explanatory perspective view schematically showing the main configuration of an example of a conventional multiple reflection type measurement cell.
This measurement cell uses the principle of operation of a so-called “Heliot cell” (hereinafter referred to as “Heliot type measurement cell”), and is a spherical surface that is arranged to face each other with the optical axes L coincident with each other. Cell body is provided with two reflecting mirrors 61, 65 having a reflecting surface 61A, 65A, and a laser beam emitted from a light source through an opening (not shown) formed in one reflecting mirror 61. The light is incident on the inside of the two reflecting mirrors 61 and 65, and after being reflected multiple times between the two reflecting mirrors 61 and 65, is again emitted to the outside of the cell body through the opening in one of the reflecting mirrors 61 and is detected by the light receiving sensor (incident) (A configuration in which the position and the emission position coincide with each other) (see Non-Patent Document 1).
The multiple reflection optical path MP0 formed in this heliot type measurement cell is formed in an annular space region A0 extending along the optical axis L of the reflection mirror 61 (65), and is reflected by the reflection mirrors 61 and 65. The reflection points on the surfaces 61A and 65A are positioned so as to be aligned on, for example, a circular orbit C0 centered on the optical axis L of the reflecting mirrors 61 and 65. In this example, one reflecting mirror is configured such that the position of the reflection point is moved in a constant direction with respect to the circumferential direction at predetermined intervals along with multiple reflections and circulates on a circular orbit C0.
The optical path length in the multiple reflection optical path MP0 is set according to the purpose by appropriately setting, for example, the focal length of the reflecting mirrors 61 and 65, the separation distance between the reflecting mirrors 61 and 65, the number of reflections, and other optical conditions. Can be set.

Off-Axis Paths in Spiral Mirror Interferometers Herriot, H.C. Kogelnik, and R.K. Kompner (April 1964 / Vol. 3, No. 4 / APPLIED OPTICS)

JP 2006-58009 A

  Thus, in the Heliot type measurement cell, the multiple reflection optical path (optical measurement system) formed between the reflecting mirrors is one system, and the fact is that one gas component is the measurement target, For example, it is desired that a plurality of types of gas components can be detected simultaneously without increasing the size of the apparatus itself.

The present invention has been made based on the above situation, and an object of the present invention is to provide a multipass cell having a novel structure capable of simultaneously detecting a plurality of types of gas components.
Another object of the present invention is to provide a gas measuring instrument that can detect a plurality of types of gas components simultaneously and with high accuracy and can be configured as a miniaturized one.

Multipath cell of the present invention comprises a cell body, within the cell body, which is opposed in a state where the optical axes coincide with each other, and two reflectors having a spherical or parabolic reflecting surface, respectively A reference optical measurement system and another optical measurement system configured to form independent multiple reflection optical paths in the same annular space region extending along the optical axis of the reflector,
The multiple reflection optical path of the reference optical measurement system is a reference in which the position of the reflection point on the reflection surface of each reflection mirror circulates on a circular or elliptical orbit around the optical axis of the reflection mirror due to multiple reflection. It is constituted by a part of the multiple reflection optical path, and the incident position of the laser beam on the cell body and the emission position of the laser beam to the outside of the cell body are formed at different reflection points in the reference multiple reflection optical path,
The multiple reflection optical path of the other optical measurement system is constituted by another part of the reference multiple reflection optical path different from the multiple reflection optical path in the reference optical measurement system, and the incident position of the laser beam on the cell body and the outside of the cell body The laser light emission position is formed at a position of a different reflection point other than the reflection point related to the multiple reflection optical path in the reference optical measurement system in the reference multiple reflection optical path .

  In the multipass cell of the present invention, each of the reference optical measurement system and the other optical measurement system may include a light source that emits light of different wavelengths, or a multiple reflection optical path that is formed. If the optical path lengths are different from each other, they may be configured to include light sources that emit light having the same wavelength.

  The gas measuring instrument of the present invention comprises the multipass cell.

  According to the multi-pass cell of the present invention, the light source and the light receiving sensor constituting the optical measurement system are physically arranged because the incident position of the laser beam with respect to the cell body and the exit position to the outside of the cell body are different. In addition, the light source and the light receiving sensor can be arranged close to the cell body, and the size can be reduced.

  In addition, when a plurality of independent optical measurement systems are formed in one cell body, basically, different wavelengths are used as light sources in each of the multiple optical measurement systems. It is possible to obtain a high gas selectivity and to detect a plurality of types of gas components at the same time, and the incident position of the laser beam with respect to the cell body and the cell body. Since the emission positions to the outside are different positions, the optical path lengths of the multiple reflection optical paths in each optical measurement system can be set to different sizes, so that the light sources in each of the plurality of optical measurement systems By using one that emits laser light having the same wavelength, a wide measurement range can be obtained for one gas component.

  According to the gas measuring instrument of the present invention, the multi-pass cell is provided so that a plurality of types of gas components can be detected simultaneously, while the gas measuring instrument itself is small. In addition, the desired gas detection can be performed with high accuracy.

It is explanatory drawing which shows the outline of a structure in an example of the multipass cell of this invention, Comprising: (a) Sectional drawing which shows the cross section along the optical axis of a reflecting mirror, (b) Left side view, (c) Right side view It is. In the multipass cell shown in FIG. 1, the multiple reflection optical path formed in each of the two optical measurement systems of the reference optical measurement system and the other optical measurement system is arranged on the reflection surface of one reflection mirror and the other reflection mirror. It is explanatory drawing shown in the state which projected the reflective point on the reflective surface. It is a perspective view for demonstrating the multiple reflection optical path formed in the multipass cell shown in FIG. It is explanatory drawing which shows the outline of the structure in the other example of the multipass cell of this invention, Comprising: (a) Sectional drawing which shows the cross section along the optical axis of a reflective mirror, (b) Left side view, (c) Right side FIG. In the multi-pass cell shown in FIG. 4, the multiple reflection optical path formed in each of the two optical measurement systems of the reference optical measurement system and the other optical measurement system is arranged on the reflection surface of one reflection mirror and the other reflection mirror. It is explanatory drawing shown in the state which projected the reflective point on the reflective surface. It is a perspective view for demonstrating the multiple reflection optical path formed in the multipass cell shown in FIG. It is a block diagram which shows the outline of a structure in an example of the gas measuring device of this invention. It is a perspective view for explanation which shows roughly the principal part composition in an example of a Heriot cell type measurement cell.

Hereinafter, embodiments of the present invention will be described in detail.
<First Embodiment>
FIG. 1 is an explanatory diagram showing an outline of a configuration in an example of a multipath cell of the present invention, where (a) a cross-sectional view showing a cross section along an optical axis of a reflecting mirror, (b) a left side view, (c) FIG. 2 is a right side view, and FIG. 2 is a diagram illustrating a multi-reflection optical path formed in each of the two optical measurement systems of the reference optical measurement system and the other optical measurement system in the multipass cell shown in FIG. FIG. 3 is an explanatory view showing a state in which a reflection point on the reflection surface of the other reflection mirror is projected on the reflection surface of the other mirror, and FIG. 3 is for explaining the multiple reflection optical path formed in the multipath cell shown in FIG. FIG.
This multi-pass cell has a cylindrical cell body 11 into which a gas to be inspected (sample gas) is introduced and a spherical shape having the same focal length (curvature radius) at each of both end positions in the axial direction. The first reflecting mirror 21 and the second reflecting mirror 31 having the reflecting surfaces 21A and 31A are held and fixed by the reflecting mirror holding member 40, and the first reflecting mirror 21 and the second reflecting mirror 31 are provided. Both mirrors 31 are arranged to face each other with the optical axes L1 and L2 being coincident with each other. Reference numerals 41 </ b> A and 41 </ b> B in FIG. 1 are openings communicating with the internal space of the cell body 11, one being a test gas introduction opening and the other being a test gas discharge opening.

A light receiving sensor 28 that detects light emitted from the cell body 11 via the first light source 26 and an appropriate reflection mirror 27 is disposed outside the cell body 11 on the first reflecting mirror 21 side. The laser light emitted from the first light source 26 enters the cell body 11 through one opening 22A formed in the first reflecting mirror 21 and is multiplexed by the two reflecting mirrors 21 and 31. After being reflected, the reference optical measurement system is emitted to the outside of the cell body 11 through the other opening 22B formed in the first reflecting mirror 21 and received by the light receiving sensor 28 through the reflecting mirror 27. The first optical measurement system 25 is configured.
Each of the openings 22A and 22B in the first reflecting mirror 21 is airtightly closed by a window plate member 45 having translucency from the back side of the reflecting mirror 21.

The multiple reflection optical path MP1 of the first optical measurement system 25 in the multipass cell is configured such that the incident position of the laser light into the cell body 11 and the emission position of the laser light to the outside of the cell body 11 coincide. In addition, it constitutes a part of a so-called “Heliot-type” multiple reflection optical path (hereinafter referred to as “reference Heliot-type optical path”), and is repeatedly reflected by the two reflecting mirrors 21 and 31 for laser. The position before the light reaches the incident position on the first reflecting mirror 21, in this embodiment, for example, the reflecting surface 21A of the first reflecting mirror 21 after being reflected three times by the two reflecting mirrors 21 and 31. The light is emitted from the upper position 4 (A) to the outside of the cell body 11.
Therefore, in the multiple reflection optical path MP1 of the first optical measurement system 25, the reflection point on the reflecting surface 21A of the first reflecting mirror 21 (indicated by the reference numerals with (A) in FIGS. 2 and 3). The number indicates the reflection order.) Is a radius centered on the optical axis L1 of the reflecting mirror 21 including the incident position of light (formation position of the opening 22A) 0 (A) into the cell body 11. It is positioned so as to line up on the circular orbit of the circle C1 of R1, and is also indicated by a reflection point on the reflecting surface 31A of the second reflecting mirror 31 (indicated by reference numeral with (B) in FIGS. 2 and 3). The numbers indicate the order of reflection.) Are positioned on a circular orbit C1 having a radius R1 centered on the optical axis L2 of the second reflecting mirror 31.
The reference heliot type optical path is provided with the positions of reflection points on the reflection surfaces 21A and 31A of the respective reflecting mirrors 21 and 31 (including those indicated by [] in FIG. 2 (A) and (B)). ) Is moved in a certain circumferential direction (counterclockwise in FIG. 2) at predetermined intervals with multiple reflections, and is configured to circulate on the circular orbit C1, for example, 5 laps. When the reflection point of the second reflection mirror 31 is projected on the reflection surface 21A of the reflection mirror 21 in the axial direction, two reflection points adjacent to each other in the first reflection mirror 21, for example, 2 (A) and [ 28 (A)], one reflection point in the second reflecting mirror 31, for example, [15 (B)] is arranged.

  The optical path length (number of reflections) of the multiple reflection optical path MP1 in the first optical measurement system 25 is not particularly limited and can be appropriately set according to the purpose. Also, for the reference heliot type optical path, For example, the focal length (curvature radius) of the reflecting mirrors 21 and 31, the separation distance between the reflecting mirrors 21 and 31 (distance between the center positions), the number of reflections, and other optical conditions are appropriately selected according to the purpose. Each of the opening 22A for laser beam incidence and the opening 22B for emission in the first reflecting mirror 21 can be set as appropriate on the circular orbit C1 set according to the purpose. What is necessary is just to form.

Thus, in this multipath cell, a plurality of multiple reflection optical paths using the operation principle of so-called “Heliot cells” independent from each other are formed in one cell body 11.
That is, the multiple reflection optical path MP1 in the first optical measurement system 25 constituting a part of the reference heliot type optical path is in the annular space region A1 extending along the optical axis L1 (L2) of the reflecting mirror 21 (31). One other optical measurement system (hereinafter referred to as “multiple reflection optical path”) that is independent of the multiple reflection optical path MP1 in the first optical measurement system 25 and is formed in the annular space region A1. , "Second optical measurement system").

The second optical measurement system 35 forms a multiple reflection optical path MP2 constituting a part other than the multiple reflection optical path MP1 in the first optical measurement system 25 of the reference Heliot type optical path. The light receiving sensor 38 that detects the light emitted from the cell body 11 via the second light source 36 and the appropriate reflecting mirror 37 disposed at the outer position of the cell body 11 on the second reflecting mirror 31 side. The laser light emitted from the second light source 36 passes through one opening 32A formed in the second reflecting mirror 31 (for example, the position of the reflection point 5 (B) in the reference heliot type optical path). Then, the light is incident on the cell body 11 and subjected to multiple reflection by the two reflecting mirrors 21 and 31, and then the other opening 32B formed in the second reflecting mirror 31 (for example, the reflecting point 31 (B in the reference heliot type optical path) ) Position) via, is emitted to the outside of the cell body 11, and is configured to be received by the light receiving sensor 38 via the reflecting mirror 37.
The openings 32A and 32B in the second reflecting mirror 31 are airtightly closed by a window plate member 45 having translucency from the back side of the reflecting mirror 31.

  Therefore, in the multiple reflection optical path MP2 of the second optical measurement system 35, the reflection point on the reflection surface 31A of the second reflecting mirror 31 (indicated by reference numeral with (C) in FIGS. 2 and 3). The numbers indicate the reflection order.) Includes the incident position of light with respect to the inside of the cell body 11 (formation position of the opening 32A) 0 (C) ([5 (B)] in the reference heliot type optical path). The second reflecting mirror 31 is positioned so as to line up on a circular orbit C1 having a radius R1 centered on the optical axis L2 of the second reflecting mirror 31, that is, on a circular orbit where the reflection point in the first optical measurement system 25 is located. Further, the reflection point on the reflecting surface 21A of the first reflecting mirror 21 (in FIG. 2 and FIG. 3, it is indicated by a reference numeral (D) and the number indicates the reflection order). Radius R1 about the optical axis L1 of the first reflecting mirror 21 Circular path C1 is positioned so as to align on (reflecting point of the first optical measuring system 25 is the circular path is located).

  The optical path length of the multiple reflection optical path MP2 in the second optical measurement system 35 can be appropriately set in relation to the optical path length of the multiple reflection optical path MP1 in the first optical measurement system 25.

The first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 can be constituted by, for example, a near infrared semiconductor laser.
An example of the wavelength of laser light from the light sources 26 and 36 constituting the first optical measurement system 25 and the second optical measurement system 35 in relation to the detection target gas is ¹² CO ₂ (mass number is 12). The wavelength of the laser beam used for detection of carbon is 2.014 or 2.004 [μm], and the wavelength of the laser beam used for detection of ¹³ CO ₂ (carbon having a mass number of 13) is 2.040 [μm]. In the detection of CH ₄ , 1.651 or 1.654 [μm], in the detection of CO 1.568 [μm], in the detection of C ₂ H ₂ , 1.520 or 1.530 [μm] ] 1.517 [μm] for detection of NH ₃ , 1.516 [μm] for detection of N ₂ O, 1.364 or 1.847 [μm] for H ₂ O, In detection, 1.747 or 1. Is 43 [μm].

Even if the first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 emit light having the same wavelength, they emit light having different wavelengths. Irradiation or any one may be used.
When the first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 irradiate laser beams having different wavelengths, a high gas selection Thus, a plurality of types of gas components can be detected simultaneously. For example, a specific gas component and its interference gas component can be detected, or an isotope measurement can be performed.
Further, when the first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 irradiate laser beams having the same wavelength, By obtaining different optical path lengths for the multiple reflection optical path MP1 in the first optical measurement system 25 and the multiple reflection optical path MP2 in the second optical measurement system 35, a wide measurement range can be obtained for one gas component. Can do.

  A configuration example of the multi-pass cell having the above configuration will be described. The first reflecting mirror 21 and the second reflecting mirror 31 have a focal length of 360 mm, a radius of curvature of 720 mm, and a diameter of the outer peripheral edge of the reflecting surface 21A (31A). The diameter of the effective reflecting surface is 45 mm, the separation distance between the reflecting mirrors 21 and 31 (the distance between the center positions) is 320 mm, and the multiple reflection optical path MP1 related to the first optical measurement system 25 has three reflections. (Two reciprocations), the radius R1 of the circular orbit C1 where the reflection point is located on the reflecting surfaces 21A and 31A of the reflecting mirrors 21 and 31 is 30 mm, the optical path length is about 1.28 m, and the second optical measurement The multiple reflection optical path MP2 related to the system 35 has 25 reflections (13 reciprocations) and an optical path length of about 8.3 m.

Thus, according to the multipass cell having the above-described configuration, the two optical measurement systems 25 and 35 that are independent from each other are formed in one cell body 11, for example, in the first optical measurement system 25. As the second light source 36 in the first light source 26 and the second optical measurement system 35, those that irradiate laser beams having different wavelengths can be used, so that high gas selectivity can be obtained and the gas to be inspected can be obtained. Two types of gas components contained in can be detected simultaneously.
For example, as the first light source 26 in the first optical measurement system 25, for example, an infrared light source having a center wavelength of about 1.651 μm is used, and as the second light source 36 in the second optical measurement system 35, for example, the center wavelength. In the case where an infrared light source having a wavelength of about 1.364 μm is used, CH ₄ can be detected by the first optical measurement system 25 and H ₂ O can be detected by the second optical measurement system 35. Can do. As a combination of the detection target gas related to the first optical measurement system 25 and the detection target gas related to the second optical measurement system 35, for example, detection of CH ₄ (center wavelength near 1.651 μm) and detection of NH ₃ ( Examples include detection of CH ₄ (around a central wavelength of 1.651 μm) and detection of CO (around a central wavelength of 1.568 μm), but are not particularly limited. For example, in detecting CO, a mid-infrared laser beam having a center wavelength of about 4.7 μm can be used. Furthermore, for example, a specific gas component and its interference gas component can be detected, or isotopes such as ¹² CO ₂ and ¹³ CO ₂ can be measured.
Moreover, the multiple reflection optical path MP1 of the first optical measurement system 25 and the multiple reflection optical path MP2 of the second optical measurement system 35 both constitute different parts of the common reference Heliot type optical path. The optical path length of a necessary size can be ensured without interfering with each other.
Furthermore, the first optical measurement system 25 and the second optical measurement system 35 form multiple reflection optical paths MP1 and MP2 having different optical path lengths, and the first light source 26 in the first optical measurement system 25 is used. As the second light source 36 in the second optical measurement system 35, one that emits laser beams having the same wavelength is used, so that a wide measurement range can be obtained for one gas component.

Second Embodiment
FIG. 4 is an explanatory diagram showing an outline of the configuration of another example of the multipath cell of the present invention, in which (a) a sectional view showing a section along the optical axis of the reflecting mirror, (b) a left side view, FIG. 5C is a right side view, and FIG. 5 shows multiple reflected light paths formed in each of the two optical measurement systems of the reference optical measurement system and the other optical measurement system in the multipass cell shown in FIG. FIG. 6 is an explanatory view showing a state in which a reflection point on the reflection surface of the other reflection mirror is projected on the reflection surface of the other reflection mirror, and FIG. 6 illustrates a multiple reflection optical path formed in the multipass cell shown in FIG. It is a perspective view for doing. This multi-pass cell has a cylindrical cell body 11 into which a gas to be inspected (sample gas) is introduced and a spherical shape having the same focal length (curvature radius) at each of both end positions in the axial direction. The first reflecting mirror 21 and the second reflecting mirror 31 having the reflecting surfaces 21A and 31A are held and fixed by the reflecting mirror holding member 40, and the first reflecting mirror 21 and the second reflecting mirror 31 are provided. Both mirrors 31 are arranged to face each other with the optical axes L1 and L2 being coincident with each other. Reference numerals 41 </ b> A and 41 </ b> B in FIG. 1 are openings communicating with the internal space of the cell body 11, one being a test gas introduction opening and the other being a test gas discharge opening.

A light receiving sensor 28 that detects light emitted from the cell body 11 via the first light source 26 and an appropriate reflection mirror 27 is disposed outside the cell body 11 on the first reflecting mirror 21 side. The laser light emitted from the first light source 26 enters the cell body 11 through the opening 22 formed in the first reflecting mirror 21 and is multiple-reflected by the two reflecting mirrors 21 and 31. After that, the first optical measurement system 25 is configured as a reference optical measurement system that is emitted to the outside of the cell body 11 through the opening 22 and received by the light receiving sensor 28 through the reflection mirror 27. ing.
The opening 22 in the first reflecting mirror 21 is airtightly closed by a window plate member 45 having translucency from the back side of the reflecting mirror 21.

In the multiple reflection optical path MP1 in the first optical measurement system 25, the reflection point on the reflection surface 21A of the first reflecting mirror 21 (in FIG. 5, a reference numeral (A) is given, and in FIG. Is indicated by a circle number for convenience, and the number indicates the reflection order.) Is a reflecting mirror including a light incident position (a position where the opening 22 is formed) 0 (A) into the cell body 11. For example, the emission position 32 (A) is positioned so as to coincide with the incident position 0 (A).
Further, the reflection point on the reflecting surface 31A of the second reflecting mirror 31 (indicated by reference numeral with (B) in FIG. 5, and in FIG. 6 is indicated by a round numeral for convenience, The numbers indicate the order of reflection.) Are positioned so as to be arranged on a circular orbit C1 having a radius R1 centered on the optical axis L2 of the second reflecting mirror 31.
The multiple reflection optical path MP1 in this embodiment is such that, for example, in one reflecting mirror 21 (31), the position of the reflection point is a constant direction in the circumferential direction (counterclockwise in FIG. ), Orbits, for example, 5 times on the circular orbit C1, and when the reflection point of the second reflecting mirror 31 is projected on the reflecting surface 21A of the first reflecting mirror 21 in the axial direction, One reflection point, for example, 15 (B) in the second reflection mirror 31 is positioned at a position between two reflection points, for example, 2 (A) and 28 (A), adjacent to each other in one reflection mirror 21. It is comprised so that.

  The optical path length of the multiple reflection optical path MP1 is not particularly limited. For example, the focal length (curvature radius) of the reflection mirrors 21 and 31, the separation distance between the reflection mirrors 21 and 31 (distance between center positions), and the number of reflections. And other optical conditions can be appropriately set according to the purpose, and the opening 22 for entering and exiting the laser beam in the first reflecting mirror 21 can be set according to the purpose. What is necessary is just to form in the position on the circular track | orbit C1 to be set.

Thus, in this multipath cell, a plurality of multiple reflection optical paths using the operation principle of so-called “Heliot cells” independent from each other are formed in one cell body 11.
That is, the multiple reflection optical path MP1 in the first optical measurement system 25 is formed in an annular space region (cylindrical space region) A1 extending along the optical axis L1 (L2) of the reflecting mirror 21 (31). In the cylindrical space region inside the annular space region A1, that is, the space region not used in the multiple reflection optical path MP1 of the first optical measurement system 25, at least one other optical measurement system, in this embodiment, Two other optical measurement systems (hereinafter referred to as “second optical measurement system”) are located.

The second optical measurement system 35 is, for example, from the cell main body 11 via the second light source 36 and an appropriate reflection mirror 37 disposed at the outer position of the cell main body 11 on the second reflecting mirror 31 side. A light receiving sensor 38 for detecting the emitted light is provided, and the laser light emitted from the second light source 36 enters the cell body 11 through one opening 32A formed in the second reflecting mirror 31. After being incident and multiple-reflected by the two reflecting mirrors 21 and 31, it is emitted to the outside of the cell body 11 through the other opening 32 </ b> B formed in the second reflecting mirror 31, and passes through the reflecting mirror 37. The light receiving sensor 38 receives light.
The openings 32A and 32B in the second reflecting mirror 31 are airtightly closed by a window plate member 45 having translucency from the back side of the reflecting mirror 31.

  The multiple reflection optical path MP2 of the second optical measurement system 35 constitutes a part of a so-called “Heliot type” multiple reflection optical path (reference heliot type optical path), and is reflected by the two reflecting mirrors 21 and 31. The position before the laser beam reaches the incident position 0 (C) on the reflecting surface 31A of the second reflecting mirror 31 repeatedly, for example, 15 times by the two reflecting mirrors 21 and 31 in this embodiment. The reflected light is emitted from the position 16 (C) on the reflecting surface 31 A of the second reflecting mirror 31 after being reflected to the outside of the cell body 11.

  Accordingly, the multiple reflection optical path MP2 of the second optical measurement system 35 is formed in an annular space region (cylindrical space region) A2 extending along the optical axis L1 (L2) of the reflecting mirror 21 (31). The reflection points on the reflection surface 31A of the second reflecting mirror 31 (indicated by reference numerals with (C) in FIG. 5 and in FIG. 6 for the sake of convenience, are indicated by numbers surrounded by squares. The number indicates the reflection order.) Is the optical axis of the second reflecting mirror 31 including the light incident position (the position where the one opening 32A is formed) 0 (C) into the cell body 11. It is positioned so as to be aligned on a circular orbit C2 having a radius R2 centered on L2, and is also a reflecting point on the reflecting surface 21A of the first reflecting mirror 21 (denoted by a symbol (D) in FIG. 5). In FIG. 6, for the sake of convenience, a number enclosed in a square is shown. In is shown, numerals indicate the reflection order.) Is positioned so as to align on circular path C2 of radius R2 centered on the optical axis L1 of the first reflecting mirror 21. The reference Heliot type optical path for the multiple reflection optical path MP2 in the second optical measurement system 35 is the position of the reflection point on the reflection surfaces 21A and 31A of the respective reflection mirrors 21 and 31 (indicated by [] in FIG. 5). (Symbols including (C) and (D)) are moved in a constant circumferential direction (counterclockwise in FIG. 5) at predetermined intervals with multiple reflections, and are moved on the circular orbit C2. For example, when the reflection point in the second reflecting mirror 31 is projected in the axial direction on the reflecting surface 21A of the first reflecting mirror 21, the first reflecting mirror 21 in the first reflecting mirror 21 is mutually connected. One reflection point, for example, 2 (C) in the second reflecting mirror 31 is positioned at a position between two adjacent reflection points, for example, 15 (D) and [21 (D)]. And multiplexing in the first optical measurement system 25 Shako path MP1 substantially mutually have the same optical path length.

  The optical path length (number of reflections) of the multiple reflection optical path MP2 in the second optical measurement system 35 is not particularly limited, and can be appropriately set according to the purpose.

  The first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 can be constituted by, for example, a near-infrared semiconductor laser, and have the wavelength exemplified in the first embodiment. Things can be used.

The light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 irradiate light having different wavelengths even if they irradiate light having the same wavelength. Or any of them.
When the first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 irradiate laser beams having different wavelengths, a high gas selection Thus, a plurality of types of gas components can be detected simultaneously. For example, a specific gas component and its interference gas component can be detected, or an isotope measurement can be performed.
Further, when the first light source 26 in the first optical measurement system 25 and the second light source 36 in the second optical measurement system 35 irradiate laser beams having the same wavelength, By obtaining different optical path lengths for the multiple reflection optical path MP1 in the first optical measurement system 25 and the multiple reflection optical path MP2 in the second optical measurement system 35, a wide measurement range can be obtained for one gas component. Can do.

A configuration example of the multi-pass cell having the above configuration will be described. The first reflecting mirror 21 and the second reflecting mirror 31 have a focal length of 360 mm, a radius of curvature of 720 mm, and a diameter of the outer peripheral edge of the reflecting surface 21A (31A). The diameter of the effective reflection surface is 45 mm, the separation distance between the reflecting mirrors 21 and 31 (the distance between the center positions) is 320 mm, and the multiple reflection optical path MP1 in the first optical measurement system 25 has 31 reflections ( 16 reciprocations), the radius R1 of the circular orbit C1 where the reflection point is located on the reflecting surfaces 21A and 31A of the reflecting mirrors 21 and 31 is 30 mm, the optical path length is about 10.24 m, and the second optical measurement system In the multiple reflection optical path MP2 at 35, the number of reflections is 15 (8 reciprocations), the radius R2 of the circular orbit C2 where the reflection point is located on the reflection surfaces 21A and 31A of the respective reflection mirrors 21 and 31 is 15 mm, light The length is about 5.12m.
The innermost position of the annular space region A1 where the multiple reflection optical path MP1 is formed in the first optical measurement system 25 is a position about 26.4 mm from the optical axis L1 (L2) of the reflecting mirror 21 (31). The laser beam has a beam diameter of about φ3 mm. Therefore, the first optical measurement system 25 and the second measurement optical system 35 are configured as independent from each other without causing optical interference. .

Thus, even in the multipath cell having the above configuration, the same effects as those according to the first embodiment can be obtained. That is, two independent optical measurement systems 25, 35 are formed in one cell body 11. For example, the first light source 26 and the second optical measurement system in the first optical measurement system 25 are formed. As the second light source 36 in FIG. 35, one that emits laser beams having different wavelengths can be used, so that high gas selectivity can be obtained and two types of gas components contained in the gas to be inspected can be detected simultaneously. Furthermore, it is assumed that the required optical path length is ensured without interfering with the multiple reflection optical path MP1 of the first optical measurement system 25 and the multiple reflection optical path MP2 of the second optical measurement system 35. Can be configured.
For example, as the first light source 26 in the first optical measurement system 25, for example, an infrared light source having a center wavelength of about 1.651 μm is used, and as the second light source 36 in the second optical measurement system 35, for example, the center wavelength. In the case where an infrared light source having a wavelength of about 1.364 μm is used, CH ₄ can be detected by the first optical measurement system 25 and H ₂ O can be detected by the second optical measurement system 35. Can do. As a combination of the detection target gas related to the first optical measurement system 25 and the detection target gas related to the second optical measurement system 35, for example, detection of CH ₄ (center wavelength near 1.651 μm) and detection of NH ₃ ( Examples include detection of CH ₄ (around a central wavelength of 1.651 μm) and detection of CO (around a central wavelength of 1.568 μm), but are not particularly limited. For example, in detecting CO, a mid-infrared laser beam having a center wavelength of about 4.7 μm can be used. Furthermore, for example, a specific gas component and its interference gas component can be detected, or isotopes such as ¹² CO ₂ and ¹³ CO ₂ can be measured.
Furthermore, the first optical measurement system 25 and the second optical measurement system 35 form multiple reflection optical paths MP1 and MP2 having different optical path lengths. The light source 26 and the second optical measurement system 25 in the first optical measurement system 25 are the same. As the light source 36 in the optical measurement system 35, a light source that emits laser beams having the same wavelength is used, so that a wide measurement range can be obtained for one gas component.

As described above, the multipass cell as described above is suitably used for, for example, a gas measuring device by infrared absorption spectroscopy.
As shown in FIG. 7, the gas measuring instrument of the present invention includes a gas detector 50 constituted by the multipass cell, a first light source 26 constituting a first optical measurement system 25 in the multipass cell, and a first light source 26. A function of controlling the operation of each of the second light sources 36 constituting the second optical measurement system 35 and a function of calculating the concentrations of the two types of gas components based on detection signals from the light receiving sensors 28 and 38. And a control means 55 having
In the gas detection, the light source control unit 56 in the control means 55 controls the magnitude of the current supplied to each of the first light source 26 and the second light source 36, for example, so that the first optical measurement system. For example, frequency-modulated laser light is incident into the cell body 11 from each of the first light source 26 in 25 and the second light source 36 in the second measurement optical system 35, whereby the multiple reflection optical paths MP 1 and MP 2 are formed. In the formed state, the gas to be inspected is supplied into the cell body 11, whereby the laser light related to the first optical measurement system 25 is absorbed by the first detection target gas having absorption characteristics near the wavelength. As a result, the amount of infrared light detected by the light receiving sensor 28 is reduced, and the gas concentration corresponding to the degree of attenuation of the amount of infrared light is controlled by the signal processing unit 55. While being detected by the unit 57, the laser light related to the second optical measurement system 35 has absorption characteristics near its wavelength and is absorbed by the second detection target gas different from the first detection target gas. As a result, the amount of infrared light detected by the light receiving sensor 38 decreases, and the gas concentration corresponding to the degree of attenuation of the amount of infrared light is detected by the signal processing unit 57 in the control means 55.

  Thus, according to the gas measuring instrument including the multipath cell, the multipath cell is formed of two types of optical measurement systems 25 and 35 (multiple reflection optical paths MP1 and MP2) independent of each other. The gas measuring device itself can be configured as a small one while being configured to be able to detect a plurality of types of gas components at the same time. In addition, in each of the multiple reflection optical paths MP1 and MP2, a required optical path length can be secured without interfering with each other, so that two types of gas components can be detected simultaneously and with high accuracy. it can.

As mentioned above, although embodiment of this invention was described, this invention is not limited to said embodiment, A various change can be added.
For example, the number of multiple reflection optical paths formed in the cell main body is not limited to two systems, and may be, for example, three systems or more, or only one system.
In each of the multipass cells according to the first embodiment and the second embodiment, the light source and the light receiving sensor in the first optical measurement system and the light source and the light receiving sensor in the second optical measurement system are In the multi-pass cell according to the second embodiment, the multiple reflection optical path in the reference optical measurement system has an incident position and an output position that are mutually different. It may be configured to be a different position (that constitutes a part of the reference heliot type optical path).
Furthermore, the multiple reflection optical path (reference heliot type optical path) in each optical measurement system does not need to be configured such that the position of the reflection point on the reflection surface of the reflecting mirror circulates along with the multiple reflection. The reflection points may be configured to be sequentially arranged in a predetermined direction with respect to the circumferential direction.
Furthermore, the configuration of the reflecting mirror, the size of the separation distance between the two reflecting mirrors, the number of reflections, the size of the optical path length in the multiple reflection optical path, and other specific configurations are not limited to the above embodiments. It can be set appropriately according to the purpose.

DESCRIPTION OF SYMBOLS 11 Cell main body 21 1st reflective mirror 21A Reflective surface 22 Opening part 22A One opening part 22B The other opening part 25 1st optical measurement system 26 1st light source 27 Reflecting mirror 28 Light receiving sensor 31 2nd reflecting mirror 31A Reflecting surface 32A One opening 32B The other opening 35 Second optical measurement system 36 Second light source 37 Reflecting mirror 38 Light receiving sensor 40 Reflecting mirror holding member 41A, 41B Opening 45 Window plate member 50 Detector 55 Control means 56 Light source control unit 57 Signal processing unit 61, 65 Reflective mirror 61A, 65A Reflective surface L1 Optical axis of the first reflective mirror L2 Optical axis of the second reflective mirror MP1 Multiple reflection optical path in the first optical measurement system MP2 Second Multiple reflection optical path in the optical measurement system of A1
A2 annular space area (cylindrical space area)

Claims (4)

A cell body, two reflecting mirrors having a spherical or parabolic reflecting surface arranged in a state where the optical axes coincide with each other in the cell body, and each along the optical axis of the reflecting mirror A reference optical measurement system and other optical measurement systems configured to form multiple reflection optical paths independent from each other in the same annular space region extending in
The multiple reflection optical path of the reference optical measurement system is a reference in which the position of the reflection point on the reflection surface of each reflection mirror circulates on a circular or elliptical orbit around the optical axis of the reflection mirror due to multiple reflection. It is constituted by a part of the multiple reflection optical path, and the incident position of the laser beam on the cell body and the emission position of the laser beam to the outside of the cell body are formed at different reflection points in the reference multiple reflection optical path,
The multiple reflection optical path of the other optical measurement system is constituted by another part of the reference multiple reflection optical path different from the multiple reflection optical path in the reference optical measurement system, and the incident position of the laser beam on the cell body and the outside of the cell body The laser light emission position is formed at a position of a reflection point different from the reflection point of the multiple reflection optical path in the reference optical measurement system other than the reflection point in the reference multiple reflection optical path. . 2. The multipass cell according to claim 1 , wherein each of the reference optical measurement system and the other optical measurement system includes a light source that emits light having different wavelengths . Each of the reference optical measurement system and the other optical measurement system has a light source that irradiates light having the same wavelength, and the optical path lengths of the formed multiple reflection optical paths are different from each other. The multipath cell according to claim 1 . A gas measuring instrument comprising the multipass cell according to any one of claims 1 to 3 .

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