JP4842852B2 - Optical interference gas concentration measuring device - Google Patents

Description

  The present invention relates to an optical interference type gas concentration measuring apparatus.

  As a kind of device for measuring the gas concentration, the difference in the refractive index of light between the measurement target gas (hereinafter also referred to as “measured gas”) and a standard gas such as air is detected as displacement of interference fringes. In addition, an optical interference type gas concentration measuring apparatus that measures the gas concentration based on the displacement amount of the interference fringes is used.

As a certain kind of optical interference type gas concentration measuring device, as shown in FIG. 4, a measurement target gas cell unit 12 for introducing a gas to be measured and a standard gas such as air are filled. The chamber 11 in which the standard gas cell portions 13 and 14 are partitioned, the parallel plane mirror 16 that divides the light from the light source 15, and the light that has been split by the parallel plane mirror 16 and passes through the chamber 11 is reflected. The traveling direction is changed, and after passing through the chamber 11 again, it is superposed on the parallel plane mirror 16 and superimposed on the prism 41 arranged in an adjusted manner so that interference fringes can be generated. In addition, there is a configuration including interference fringe detection means 17 that receives the combined light (interference light) (see, for example, Patent Document 1).
In FIG. 4, 19 is a plane mirror that reflects the combined light, and 42 is a condensing lens for condensing the combined light, and interference fringe detecting means is disposed at the focal position of the condensing lens 42. Also, the alternate long and short dash line indicates a path until the light from the light source 15 is received by the interference fringe detector 17.

  Conventionally, in the optical interference type gas concentration measuring apparatus having such a configuration, as a method of adjusting the spatial frequency (width of the fringe) of the interference fringes, the mounting angle of the parallel plane mirror 16 and the prism 41 is adjusted (see FIG. 4). The method is adopted.

  However, the amount of displacement of the interference fringes that accompanies fluctuations in the characteristics (gas concentration) of the gas to be measured is extremely small, and therefore there is little deviation in the arrangement position and arrangement state (attachment angle) of the constituent members. However, since it has a great influence on the measurement accuracy, the optical interference type gas concentration measurement apparatus that adjusts the spatial frequency of the interference fringes according to the mounting angle of the parallel plane mirror and the prism is a fine device that requires skill in the manufacturing process. Since adjustment of the angle is required, and the arrangement position and arrangement state of the component members whose attachment angle can be adjusted by receiving external force such as vibration and impact are likely to be shifted, adjustment can be performed each time. There is a problem that it is necessary.

JP 2002-310909 A

  The present invention has been made based on the circumstances as described above, and its purpose is to provide an optical interference gas concentration measurement that can be easily manufactured and that can easily adjust the spatial frequency of interference fringes. To provide an apparatus.

An optical interference type gas concentration measuring apparatus according to the present invention includes a measurement target gas cell, a standard gas cell arranged in parallel with the measurement target gas cell, a beam splitter that splits light from a light source, and a beam splitter. A triangle having an upper bottom surface and a lower bottom surface, which is divided and combines the light that has passed through the measurement-target gas cell and the light that has passed through the standard gas cell on the beam splitter, and reflects them to produce interference fringes. An optical interference type gas concentration measuring device comprising a columnar prism and interference fringe detection means for receiving the synthesized light,
The triangular prism having the upper bottom surface and the lower bottom surface has a form in which the lower bottom surface is inclined with respect to the upper bottom surface, and the lower bottom surface is directed to the prism from each of the measurement object gas cell and the standard gas cell. It is fixed in a state parallel to the light emitted in the direction,
An interference fringe spatial frequency adjusting lens is movably provided along the optical path on the optical path from the light combined on the beam splitter to the interference fringe detection means.

  In the optical interference gas concentration measuring apparatus of the present invention, it is preferable that the triangular prism is obtained by polishing the lower bottom surface of a prism forming member having a right isosceles triangular prism.

  In the optical interference type gas concentration measuring apparatus of the present invention, it is preferable that the inclination angle of the lower bottom surface with respect to the upper bottom surface in the triangular prism prism is 0.5 to 4.5 °.

  In the optical interference type gas concentration measuring apparatus of the present invention, the prism is a triangular prism shaped body whose lower bottom surface is inclined with respect to the upper bottom surface, and the combined light split by the beam splitter and synthesized on the beam splitter is Since the interference fringe spatial frequency adjusting lens is movably provided on the optical path leading to the interference fringe detection means, the prism can be mounted without adjusting the mounting angle of the prism and the beam splitter. By arranging the lower bottom surface to be parallel to the light emitted from each of the measurement object gas cell and the standard gas cell in the direction toward the prism, interference fringes may be generated by the inclination of the prism itself. The interference fringe spatial frequency can be adjusted by an easy method of moving the interference fringe spatial frequency adjustment lens. The interference fringe image forming magnification in the interference fringe detection means can be changed depending on the relative position between the lens and the interference fringe detection means, and the spatial frequency of the interference fringes can be finely adjusted. In addition, it is possible to easily adjust the spatial frequency of the interference fringes.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is an explanatory view showing an example of the configuration of the optical interference type gas concentration measuring apparatus of the present invention.
This optical interference type gas concentration measuring apparatus is a measurement target gas cell section (hereinafter referred to as “measurement gas cell section”) for introducing a measurement target gas (measurement target gas) in a base (not shown). 12) and standard gas cell portions 13 and 14 for filling a standard gas such as air are partitioned in parallel so that the measured gas cell portion 12 is located in the center. A chamber 11, a light source 15, and interference fringe detection means 17 that receives light from the light source 15 are provided. On the outside of one end side (left side in FIG. 1) of the chamber 11, the light from the light source 15 is provided. A beam splitter composed of a parallel plane mirror 16 is arranged. On the other hand, a triangular prism 21 is fixed outside the other end side (right side in FIG. 1) of the chamber 11.

  In this optical interference type gas concentration measuring device, the light from the light source 15 is divided into two by the parallel plane mirror 16, passes through the chamber 11 in that state, and then further faces one side of the primum 21 (hereinafter referred to as “light incident / exit”). Also referred to as a “surface”) 22, and each light is individually reflected by the prism 21 to be emitted from the light incident / exit surface 22, and the two emitted lights emitted from the prism 21 pass through the chamber 11 again. Thereafter, the combined light (interference light) superimposed at the point P on the parallel plane mirror 16 and synthesized on the parallel plane mirror 16 is received by the interference fringe detection means 17 via the plane mirror 19.

  In the prism 21 constituting the optical interference type gas concentration measuring device, the lower bottom surface (lower surface in FIG. 2) 24 is inclined with respect to the upper bottom surface (upper surface in FIG. 2) 23, as shown in FIGS. The shape, that is, the triangular prism shaped body in which the three side surfaces are perpendicular to the upper bottom surface 23 only.

Each of the light beams divided into two by the parallel plane mirror 16 is incident on the prism 21 from a light incident / exit surface 22 composed of side surfaces other than the two side surfaces perpendicular to each other among the three side surfaces of the triangular prism. The light incident / exit surface 22 faces the light passage opening 11 </ b> A on the other end side of the chamber 11 and the lower bottom surface 24 is a gas to be measured in the chamber 11 so that the light reflected from the light incident / exit surface 22 is emitted. It arrange | positions in the state parallel to the light radiate | emitted from each of the cell part 12 for gas and the cell part 14 for standard gas toward the said prism 21 (right direction in FIG. 1).
In this way, in the prism 21, the lower bottom surface 24 passes through the chamber 11 and exits from the other end side in a direction toward the prism 21 (hereinafter, these are also simply referred to as “prism side chamber exit light”). )), The two side surfaces other than the side surfaces constituting the light incident / exit surface 22 are parallel to the prism-side chamber exit light (hereinafter also referred to as “exit light parallel surface”). .), That is, the axis of the prism 21 extending perpendicularly to the upper bottom surface 23 is inclined with respect to the parallel plane of the emitted light. Therefore, the prism 21 itself is inclined with respect to a reference plane (hereinafter also referred to as “optical system reference plane”) defined by the positional relationship between the light source 15 and the parallel plane mirror 16 and the normal line of the parallel plane mirror 16. Therefore, it is possible to change the traveling direction by reflecting each of the light from the light source 15 divided into two by the parallel plane mirror 16 and to superimpose on the parallel plane mirror 16.

In the prism 21, the inclination angle θ of the lower bottom surface 24 with respect to the upper bottom surface 23 is set to an appropriate angle required, and is, for example, 0.5 ° to 4.5 °.
When the inclination angle θ is excessive, the spatial frequency of the interference fringes is large, that is, the width of the interference fringes is small. On the other hand, when the inclination angle θ is excessively small, the spatial frequency of the interference fringes is small, that is, The width of the interference fringe is increased.

  The prism 21 can be obtained, for example, by preparing a prism forming member having a right isosceles triangular prism shape and polishing the lower bottom surface of the prism forming member.

Further, in the optical interference type gas concentration measuring apparatus, the combined light superimposed on the parallel plane mirror 16 interferes on the optical path (hereinafter also referred to as “interference light optical path”) until reaching the interference fringe detection means 17. The fringe spatial frequency adjusting lenses (hereinafter also simply referred to as “interference fringe adjusting lenses”) 31 and 32 are provided movably along the optical path for interference light.
In the example of this figure, the interference fringe adjusting lenses 31 and 32 are provided so as to be movable on the optical path formed between the plane mirror 19 and the interference fringe detecting means 17, respectively. The focal points 31 and 32 are adjusted so as to be positioned on the interference fringe detector 17.

The interference fringe adjusting lenses 31 and 32 may be any lens that can change the focal position by moving on the optical path for interference light. For example, a concave lens or a convex lens can be used.
In the example of this figure, the interference fringe adjusting lens 31 is a convex lens, and the interference fringe adjusting lens 32 is a concave lens.

  Each of the interference fringe adjusting lenses 31 and 32 is fixed so that the position can be adjusted. For example, the interference fringe adjusting lenses 31 and 32 are parallel to the optical path formed between the plane mirror 19 and the interference fringe detecting means 17 formed on the base. The lens is fixed so as to be movable in the length direction of the slit by screwing at a lens fixing portion made of a slit.

As the light source 15, for example, an incandescent bulb, an LED (light emitting diode) or the like can be used, and as the interference fringe detecting means 17, for example, a graduated glass plate, a CCD camera, or the like can be used.
Here, when a white interference fringe is formed as an interference fringe by using an incandescent light bulb or the like as the light source 15, the displacement amount of the interference fringe is determined by using a graduated glass plate, a CCD camera or the like as the interference fringe detection means 17. It will be measured directly. When a single-color interference fringe is formed as an interference fringe by using an LED or the like as the light source 15, for example, a CCD camera using a one-dimensional image sensor (linear image sensor) as an image sensor as the interference fringe detection means 17 is used. Displacement of interference fringes by using a fringe number counter and phase analysis by Fourier analysis technology based on the interference fringes detected by this CCD camera, and further using synthetic wavelength interferometry (using two LEDs as the light source 15). The amount will be calculated.

  In the optical interference type gas concentration measuring apparatus having such a configuration, the measurement gas is introduced into the measurement gas cell unit 12 with respect to the chamber 11 during the measurement operation, and the standard gas cell unit 13, When light is emitted from the light source 15 in a state where each of 14 is filled with the standard gas, the light from the light source 15 enters the parallel plane mirror 16 through the optical path L1, is reflected, and is divided into two. One of the divided lights passes through the standard gas cell portion 14 of the chamber 11, enters the prism 21 from the light incident / exit surface 22, is reflected, and exits from the light incident / exit surface 22. Thereafter, the light passes through the standard gas cell section 13 of the chamber 11, that is, enters the parallel plane mirror 16 by passing through the optical path L2, the optical path L4, and the optical path L6 in this order. The other light divided by the parallel plane mirror 16 passes through the measurement gas cell portion 12 of the chamber 11, enters the prism 21 from the light incident / exit surface 22, is reflected, and exits from the light incident / exit surface 22. After that, the light passes through the measured gas cell portion 12 of the chamber 11 again, that is, enters the parallel plane mirror 16 by passing through the optical path L3, the optical path L5, and the optical path L7 in this order. The light that has passed through the standard gas cell unit 14 and the standard gas cell unit 13 in this order and the light that has passed through the measured gas cell unit 12 twice are superimposed at a point P on the parallel plane mirror 16. The combined light is emitted from the parallel plane mirror 16 and reflected by the plane mirror 19, and the interference fringe detection unit 17 on which the focal points of the interference fringe adjustment lenses 31 and 32 are located via the interference fringe adjustment lenses 31 and 32. In other words, the interference fringes are detected by the interference fringe detecting means 17 by passing through the optical paths L8 and L9 in this order. In this way, in the optical interference type gas concentration measuring apparatus, the interference fringes formed at the focal points of the interference fringe adjusting lenses 31 and 32 and detected by the interference fringe detecting means 17 where the focal points are located are measured gas. For example, when an incandescent bulb is used as the light source 15 and a graduated glass plate is used as the interference fringe detecting means 17, the graduated glass is used. The gas concentration is detected by visually measuring the amount of displacement of the interference fringes projected on the plate.

In the optical interference type gas concentration measuring apparatus as described above, the prism 21 is a triangular prism with the lower bottom surface 24 inclined with respect to the upper bottom surface 23. By arranging the bottom surface 24 to be parallel and the light incident / exit surface 22 to face the light passage opening 11A of the chamber 11, an optical system reference defined by the light source 15 and the parallel plane mirror 16 of the prism 21 itself. An arrangement state in which the traveling direction is changed by reflecting each of the light divided into two by the parallel plane mirror 16 according to the inclination with respect to the surface, and after passing through the chamber 11 again, it can be superimposed on the parallel plane mirror 16 Therefore, even if the prism 21 is fixed without adjusting the mounting angle, interference fringes are generated. Door can be.
Further, since the interference fringe adjustment lenses 31 and 32 whose positions can be adjusted are provided on the optical path for interference light, the interference fringe adjustment lenses 31 and 32 can be adjusted without adjusting the mounting angles of the prism 21 and the parallel plane mirror 16. The interference fringe imaging magnification of the interference fringe detecting means 17 is determined by the relative position of the interference fringe adjusting lenses 31 and 32 and the interference fringe detecting means 17 by an easy method of moving the 32 on the optical path for interference light. Thus, the spatial frequency of the interference fringes can be finely adjusted.

  Therefore, this optical interference type gas concentration measuring apparatus can arrange the prism 21 in an inclined state with respect to the optical system reference plane without adjusting the mounting angle in the manufacturing process. Even if the prism 21 is obtained by polishing, the variation in the interference fringes caused by the variation in the inclination angle θ of the lower bottom surface 24 with respect to the upper bottom surface 23 in the prism 21 Since adjustment can be performed only by moving the adjustment lenses 31 and 32 and the interference fringes detected by the interference fringe detection means 17 can be set to have a desired spatial frequency, the prism 21 and the parallel plane mirror 16 are attached. Easy because fine adjustment of angle and fine adjustment by advanced polishing technology are not required for prism polishing It can be produced.

  Further, in the optical interference type gas concentration measurement device, since the adjustment of the mounting angle is not necessary, the prism 21 and the parallel plane mirror 16 can be firmly fixed. The interference fringe adjusting lens can be prevented from being displaced by receiving the external force, and can be prevented from shifting in the arrangement position and arrangement state of the prism 21 and the parallel plane mirror 16. Even if there is a deviation in the arrangement position and arrangement state between 31 and 32, it can be readjusted easily.

The optical interference type gas concentration measuring apparatus of the present invention has been specifically described above, but the present invention is not limited to the above examples, and various modifications can be made.
For example, the interference fringe spatial frequency adjusting lens provided movably on the optical path for interference light only needs to be able to change the imaging magnification of the interference fringes received by the interference fringe detection means, and the number thereof is two. It is not limited and any number may be used.

It is explanatory drawing which shows an example of a structure of the optical interference type gas concentration measuring apparatus of this invention. FIG. 2 is an explanatory perspective view showing a prism used in the optical interference gas concentration measuring device of FIG. 1. It is explanatory drawing which shows the upper surface and one side surface of the prism of FIG. It is explanatory drawing which shows an example of a structure of the conventional optical interference type gas concentration measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Chamber 11A Light passage opening 12 Measurement object gas cell part (measurement gas cell part)
13, 14 Standard gas cell part (standard gas cell part)
DESCRIPTION OF SYMBOLS 15 Light source 16 Parallel plane mirror 17 Interference fringe detection means 19 Plane mirror 21 Prism 22 One surface (light incident / exit surface)
23 Upper bottom surface 24 Lower bottom surface 31, 32 Interference fringe spatial frequency adjusting lens 41 Prism 42 Condensing lens

Claims (3)

Measurement target gas cell, standard gas cell arranged in parallel with the measurement target gas cell, a beam splitter that divides the light from the light source, and the beam splitter, each passing through the measurement target gas cell The synthesized light and the light that has passed through the standard gas cell are combined on the beam splitter and reflected so as to generate interference fringes, and a triangular prism having an upper bottom surface and a lower bottom surface, and the combined light is received. An optical interference type gas concentration measurement device comprising interference fringe detection means,
The triangular prism having the upper bottom surface and the lower bottom surface has a form in which the lower bottom surface is inclined with respect to the upper bottom surface, and the lower bottom surface is directed to the prism from each of the measurement object gas cell and the standard gas cell. It is fixed in a state parallel to the light emitted in the direction,
An optical interference type characterized in that an interference fringe spatial frequency adjusting lens is movably provided along the optical path on the optical path from the light combined on the beam splitter to the interference fringe detection means. Gas concentration measuring device.   2. The optical interference gas concentration measuring apparatus according to claim 1, wherein the triangular prism is obtained by polishing a lower bottom surface of a prism forming member having a right isosceles triangular prism.   3. The optical interference gas concentration measuring apparatus according to claim 1, wherein an inclination angle of the lower bottom surface with respect to the upper bottom surface of the triangular prism is 0.5 to 4.5 [deg.].

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