JPS60140141A - Optical gas sensor - Google Patents

Abstract

PURPOSE:To facilitate not only the change-over but also the correction of sensitivity by perforing spot measurement with high sensitivity, by a small gas sensor wherein a light path reaching a light detector from wavelength variable laser is constituted of a multiple reflective light path formed of a pair of mirrors. CONSTITUTION:A variable wavelength laser 1 and a light detector 3 are mounted to one mirror 4 of mirrors set against each other at an interval (d) in a relatively fixed state. The other mirror 5 has a fixed furclum at one part and an adjusting fulcrum at the other part and is constituted so as to be capable of adjusting an angle theta by a means such as a screw. The matching mirrors 4, 5 are provided so as to be spaced apart to each othr at an interval (l) and, by setting theta, the number of turn-back times at the mirrors set against each other.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical gas sensor, and more particularly to an improved optical gas sensor that is of the L type and is capable of detecting gas in a small range with high sensitivity.

<Prior art and background> The phenomenon in which a specific gas component selectively absorbs or scatters a specific wavelength component in an optical wavelength band is known as a physical phenomenon, and is used as a so-called optical gas sensor, for example, in the air! ! It is used to detect or analyze volume gas components and moisture. As mentioned earlier, each component gas has a unique absorption or scattering wavelength, but it is also known that the amount of absorption or scattering in that wavelength band is proportional to the amount of the component, at least as long as the amount of the component is not very large. This is because it is

What's more, this characteristic absorption or evening wavelength width is extremely narrow, and it is difficult for a photodetector to detect only light with this growth width. Figure 1 shows the conventional configuration of such an optical gas sensor, where 1 is a tunable wavelength laser as a light source; 2 is the optical path, 3 photodetectors and L is the optical path length.

Among the tunable wavelength lasers, semiconductor lasers whose wavelength range can be varied by excitation longitudinal waves or by temperature are known and are already in practical use.

With this configuration, while changing the optical wavelength of the tunable wavelength laser 1, the amount of light received relative to the amount of light emitted corresponding to a specific wavelength is measured for the gas present in the long optical path, and the amount of light received relative to the amount of light emitted when there is no specific gas is measured. , 'I' 5When a known amount of constant gas is included, the light reception h1, NI? The concentration of a specific gas can be determined by comparing it with a previously known received light value for calibration.

However, when trying to detect low-concentration gases using this method, it is necessary to increase the optical path length for both legs in order to increase sensitivity, but increasing this length not only makes it difficult to align the optical paths, but also makes calibration difficult. , and y111 constant [7
Even if there is a distribution of both wavelengths in the measurement area, there is a disadvantage that it will be difficult to detect an average of 1b, and especially if there are solid particles such as dust in addition to gas in the measurement area, it will not be possible to detect a specific wavelength band. Since it affects the overall amount of light received, it has a non-negligible effect on calibration and reduces analysis accuracy.

<Purpose and Features> In view of the above, the present invention enables spot measurement by narrowing the measurement area by adjusting the measurement optical path length and realizing multiple reflections of mirrors, and also facilitates calibration and optical path alignment. The purpose of the present invention is to provide an optical gas sensor capable of selectively switching the optical path length.The feature of the present invention is to provide a wavelength tunable laser, a photodetector, and a pair of mirrors in order to realize the above purpose. an optical path from the wavelength tunable laser to the photodetector is constituted by a multiple reflection optical path formed by the pair of mirrors, and one of the pair of mirrors is equipped with the wavelength tunable laser and the photodetector. At the same time, the relative facing angle of the other mirror can be adjusted, and the multiple reflection optical path length can be changed.

〈Example〉 Figures 2, 3, and 4 are diagrams of one embodiment of the present invention. 4 is one mirror, 5 is common to
is the other mating mirror, and 6 and 7 are the laser beam entrance and exit to the photodetector 3 provided on the mating mirror, and the space between the mating mirror 4 is tilted from parallel by lV7 minor angle θ. The length of the optical path for measurement is L if the number of turns n at the alignment mirror 5 is set by setting θ above.
The length is set to 2 In.

The tunable wavelength laser 1 and the photodetector 3 are mounted in a relatively fixed manner on one side 4 of the mirror 5 at a distance d, and the other side mirror 5 has a fixed fulcrum on one side and an adjustment fulcrum on the other side. It is configured such that θ can be adjusted (selected and set) using means such as screws.

In this configuration, considering the condition that θ is small and n is large, in this example, the measurement area is i
Since L=2nl can be achieved as the -d optical path length, the necessary measurement optical path length can be made sufficiently large! It is possible to set the value to 1'8φ5, and the sensitivity can be changed by changing the measurement optical path length.

The relationship between n as the number of reflections and the corresponding θn when l and d are set is tanO in the range where θ is small.
Since θ is in the middle, the relationship n2·21θn in d should hold, and it is easy in principle to set n from θQt/C.

In FIG. 3, 8 is a container and 9 is a content. In an optical gas sensor with such a configuration, a transparent container 8 made of glass or the like contains not only gas 7 but also the content 9 as a sample such as a liquid. It is also possible to perform calibration by filling the container 8 with the content 9 as a calibration method created by adjusting the caulking component and the component concentration. This can also be done easily.

Figure 4 shows another 411 configuration of the combined mirror, with the fixed side being 4'.
5' and 5'' are used on the adjustment side and e, so that a more compact optical path can be set.

If you tilt the angle of incidence of the 151 outside 17) 1 ``button σ) zu 1000 br I and the angle of incidence of the 1 nose at θ', 2nl θ' in d holds true. The outside is the same 43t as in Figure 2.
L=2n6 holds true.

<Effects> As explained above, according to the present invention, it is possible to provide an optical gas sensor that is compact and capable of spot measurement with high sensitivity, and whose sensitivity is easily switched and calibrated.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a conventional optical mass sensor, and FIG. FIG. 3, FIG. 4, and FIG. 5 show explanatory diagrams of one embodiment of the present invention. In the figure, 1 is a 16J variable wavelength laser, 2 is an optical path, 3 is a photodetector, 4 and 5 are a pair of combinations, 6 and 7 are an entrance port. indicates the contents. Na is L (optical path length, l is the total distance of f'Q, θ is the tilt angle, and indicates the space between d and Shi University entrance 6 extraction lower. Kaya 1 Figure? Kaya and figure 5 figure sheep 4 figure kaya, 5 figure

Claims (1)

[Scope of Claims] ■) A wavelength tunable laser, a photodetector, and a pair of mirrors, and the optical path from the wavelength tunable laser to the photodetector is configured by a multiple reflection optical path formed by the pair of mirrors. Optical gas sensor featuring: 2) A wavelength tunable laser and a photodetector are attached to one of the pair of sharp mirrors, and a 4'A mirror is formed so that the relative angle of the other mirror can be adjusted and the multiple reflection optical path length can be changed. An optical gas sensor according to item 1 of the patent statement, characterized in that: 3) The above-mentioned pair of eyes are installed facing each other in parallel, and the large pull angle of the wavelength tunable laser is tilted at a required angle with respect to the ant,
The multiple reflection optical path length is configured to be switchable.
``C gas sensor'' according to claim 1, which refers to mold.