JP5104809B2 - Gas cell - Google Patents

Description

  The present invention relates to a gas cell used in measurement of various gas components in a spectrophotometer and an environment measurement device.

The exhaust gas that causes environmental pollution and air pollution contains sulfur compounds such as H ₂ S and SO _x , nitrogen compounds such as NO _x and NH ₃ , various hydrocarbons, etc. The influence of these substances on the health status of residents has been pointed out, and the measurement of their concentration in the air is regarded as important. On the other hand, the measurement of the concentration of carbon dioxide, methane, and the like as greenhouse gases in the air is becoming more and more widely performed.

  In these gas analyses, in general, a gas cell is filled with a sample, light is transmitted through the gas cell, light absorption by the target component is measured, and the concentration of the target component is obtained therefrom. In this case, in order to perform measurement with as high sensitivity as possible using a relatively small volume of sample gas, a multi-reflection gas cell that expands the optical path length in the gas cell is generally used to improve the measurement accuracy. Various ideas have been proposed (see, for example, Patent Document 1).

  Further, depending on the measurement object, the sample gas may contain a component that contaminates the optical element. A device for improving the durability of the apparatus in such measurement has also been proposed (see, for example, Patent Document 2).

  An example of a commonly used multiple reflection gas cell is shown in FIG. The gas cell in FIG. 5 is held by a method such as adhesion to the cylinder 1 that contains the sample gas, the two concave mirror holders 3 and 4 attached to both ends thereof with bolts 9, and the inner surfaces of the concave mirror holders 3 and 4. The two concave mirrors 2 whose reflecting surfaces are opposed to each other are the main components. The cylinder 1 is provided with a gas introduction hole 5 for introducing a sample gas to the side surface and a gas discharge hole 6 for discharging the sample gas after measurement. The concave mirror holder 4 is provided with an entrance window 11 for entering measurement light and an exit window 12 through which light is emitted from the gas cell. The entrance window 11 and the exit window 12 are respectively light-transmissive. Window plate 7 is held by window plate presser 8. In order to ensure airtightness inside the gas cell, a gasket 10 is sandwiched between the contact portions of the concave mirror holders 3, 4 and the cylinder 1, and the contact portions of the window plate 7 and the concave mirror holder 4.

  In actual measurement, sample gas is introduced through the gas introduction hole 5 by means such as a pump or a valve (not shown) to fill the inside of the gas cell. Next, light from a light source not shown in FIG. 5 enters the gas cell from the incident window 11 through the window plate 7. The light is repeatedly reflected a certain number of times between the reflecting surfaces of the two concave mirrors 2 and then exits from the exit window 12 through the window plate 7 to the outside. The emitted light is measured by a detector not shown in FIG.

  The light source used is a case where a white light source such as a halogen lamp or a deuterium lamp is used together with wavelength selection means such as a spectrometer, or a case where a sample gas is directly irradiated with light of a monochromatic laser or a wavelength tunable laser. It is used properly according to the.

JP 2006-58009 A Japanese Utility Model Publication No. 3-122351

  The sample gas introduced into the gas cell may contain components that contaminate and corrode the surface of the concave mirror. For example, a large amount of moisture condenses on the surface of the concave mirror and causes fogging. In addition, acidic gases such as SOx and NOx, hydrogen sulfide, and the like gradually corrode the metal deposition film on the surface of the concave mirror during long-term use, causing a decrease in reflectivity and surface accuracy. To prevent these, the surface of the concave mirror must be cleaned, but this operation requires great care and skill and is difficult to fully repair. Finally, the concave mirror must be replaced.

  In order to solve the above-described problems of the conventional method, the present invention is introduced into a space sandwiched between two mirrors facing each other, and from the intensity of a light beam that is multiple-reflected between the two mirrors any number of times. In the gas cell for performing qualitative and quantitative analysis of the gas to be measured filled in the space, a removable protective coating is attached to a part of the reflecting surface of the mirror.

  On the concave mirror involved in the multiple reflection, the region irradiated with the light beam is limited to a part. If a protective coating is provided in an area where the light beam is not irradiated, the mirror surface under the coating is protected from the sample gas and maintained as a high-quality mirror surface without deterioration. When the mirror surface of the irradiated area deteriorates due to long-term use, the life of the concave mirror can be doubled by removing the coating of the non-irradiated area and using this area as a new irradiated area.

  Even when the sample gas contains a contaminating / corrosive component, a gas cell having a concave mirror having twice the durability of the conventional method can be realized.

It is a figure which shows one Example of this invention. It is a figure which shows the attachment method of the concave mirror and protective cover concerning this invention. It is a figure which shows the firmer attachment method of the protective cover of this invention. It is a figure which shows the relationship between the degradation site | part after a protective cover removal, and a light beam spot. It is a figure which shows the structure of the gas cell of a conventional method. It is a figure which shows the example of the light beam spot on the concave mirror by a laser light source.

In general gas cells, the part irradiated by the light beam on the mirror surface involved in multiple reflection does not cover the entire area on the mirror surface, but is limited to a part of the area, and other areas are used as mirrors. It has not been. For example, when a laser is used as the light source in the gas cell of the example of FIG. 5, the region on the concave mirror irradiated with the laser beam in the process of multiple reflection is shown in FIG. As seen in this figure, on the reflecting surface of the concave mirror 2, the laser beam irradiates only nine light beam spots 13 arranged at equal intervals at an angle of 40 degrees. The shape of each beam spot 13 is a circle having a diameter of about 3 mm.
The gas cell according to the present invention coats the unused area on such a mirror surface to protect it from contamination / corrosion, and when the used area becomes unusable due to contamination / corrosion, the above unused area is used. Remove the area covering and use this area as a new reflective surface.

  One embodiment of the gas cell according to the present invention has basically the same structure as the conventional gas cell shown in FIG. 5, and uses a laser as a light source. The novelty of the present invention lies in the concave mirror used in the gas cell, which is shown in FIG.

  As shown in FIG. 1, a protective cover 14 is detachably attached to the surface of the concave mirror 2. The protective cover 14 is formed in a size that fits the outer shape of the concave mirror 2, and nine cuts 15 are formed at equiangular intervals on the peripheral edge. Each notch 15 is shaped into a truncated sector with a central angle of 20 degrees, and the portion left between two adjacent notches 15 is also formed into a truncated sector with a central angle of 20 degrees. .

The protective cover 14 is manufactured using a metal thin plate or a plastic thin plate having excellent chemical resistance such as PTFE. The protective cover 14 needs to be easily detachable from the surface of the concave mirror 2. For this reason, as shown in FIG. 2, the tips of the nine protrusions around the protective cover 14 are bent at the back, and the side of the concave mirror 2 is fitted into this portion.
Thereby, the protective cover 14 can be easily attached and detached.

  Further, in order to fix the protective cover 14 to the concave mirror 2 more stably, as shown in FIG. 3, a thin band 16 made of plastic or metal is wound around the outside of the folded portion of the protective cover 14, and FIG. As shown, a method of fastening the band 16 with a screw 17 and a nut 18 can also be employed.

  When the protective cover 14 is attached to the concave mirror 2 for the first time, the attachment angle of the protective cover 14 is adjusted so that the light beam spot 13 coincides with the center of the notch 15. In this state, the concave mirror 2 is attached to the concave mirror holder 3 shown in FIG. The description of the structure of each part of the gas cell assembled as described above and the operation in actual measurement is the same as the conventional gas cell detailed in the background art section, and the description thereof is omitted.

  When the measurement of a large number of sample gases leads to deterioration of the unprotected portion of the concave mirror 2 and the measurement is disturbed, the protective cover 14 shown in FIG. To expose. Then, the concave mirror 2 is attached to the concave mirror holder 3 (FIG. 5) while being rotated about the central axis by 20 degrees, or the concave mirror holder 3 to which the concave mirror 2 is attached is similarly rotated by 20 degrees to obtain the cell cylindrical portion. Attach to. The state is shown in FIG. In FIG. 4, the portion that was in contact with the sample gas when the protective cover 14 was attached is shown as a degraded portion 19. By rotating the concave mirror 2 by 20 degrees, the deteriorated portion 19 moves from the position of the light beam spot 13 to a position where there is no light beam spot 13, and the light beam spot 13 is positioned at a portion where there is no deterioration. This immediately returns the cell performance to its initial best state.

  In order to further enhance the effect of the present invention, it is necessary that the optical axis of the concave mirror 2 is not distorted when the concave mirror 2 is removed and reattached. In this embodiment, the concave mirror 2 in FIG. The concave mirror holder 3 or the concave mirror holder 3 and the cylinder 1 are precisely fitted to each other, so that the optical axis can be set with high accuracy.

  As described above, according to the present invention, it is possible to easily restore the deterioration of the concave mirror to the initial performance, and it is possible to double the life of the gas cell without performing a highly difficult cleaning operation.

  The features of the present invention are as described above. However, the present invention is not limited to the above and illustrated examples, and includes various modifications. For example, in the embodiment, there are nine light beam spots, but the number of optical spots can be increased or decreased by changing the specifications of the optical system of the gas cell, and the present invention includes these. In addition to the laser, the present invention can also be applied to a gas cell that uses white light or monochromatic light separated by a spectroscope.

  The present invention relates to a gas cell used in measurement of various gas components in a spectrophotometer and an environment measurement device.

DESCRIPTION OF SYMBOLS 1 Cylinder 2 Concave mirror 3, 4 Concave mirror holder 5 Gas introduction hole 6 Gas discharge hole 7 Window plate 8 Window plate holder 9 Bolt 10 Gasket 11 Incident window 12 Outgoing window 13 Light beam spot 14 Protective cover 15 Cut 16 Band 17 Screw 18 Nut 19 Deterioration Part

Claims (1)

  Qualitative and quantitative analysis of the gas to be measured filled in the space from the intensity of the light beam introduced into the space between two mirrors facing each other and reflected multiple times between the two mirrors any number of times A gas cell comprising: a protective coating that can be attached to and detached from a part of the reflecting surface of the mirror.

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