JPS61254835A - Measuring cell - Google Patents

Abstract

PURPOSE:To prolong the effective section of a measuring cell so as to make a gas analyzing instrument high in sensitivity and compact in constitution, by forming the cross-sectional shape of the measuring cell parallel with the optical path to have an angular shape of odd vertices having an inner surface whose width is almost the same as the width of the optical path when viewed from the incident direction. CONSTITUTION:A measuring cell 1 is constituted in such a way that its cross-sectional shape parallel with the optical path (a) is formed to have an angular shape with odd vertices having an inner surface, whose width is almost the same as the width (l) of the optical path (a) when viewed from the incident direction and its entire inner surface except cell windows 5 and 6 is constituted to mirror surfaces M1 and M2 so as to reflect the optical path (a) with the mirror surfaces M1 and M2. Lights radiated from a light source 2 are intermittently discontinued by a chopper 3 and vertically made incident to the cell window 5. The lights entering into the measuring cell 1 are reflected by the mirror surfaces M1 and M2 and made incident to a detector 4 after passing through the cell window 6. The light made incident to the mirror surface M1 from the cell window 5 and the light reflected by the mirror surface M1 are almost superposed upon each other and the light made incident to the mirror surface M2 and the light reflected by the mirror surface M2 are almost superposed upon each other, and thus, doubled sensitivity is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a measurement cell for a gas analyzer using a light absorption method, and in particular, by forming the inner surface of the cell into a mirror surface to reflect the optical path, This invention relates to an improvement in a measurement cell that increases the effective cell length.

[Conventional technology]

As shown in FIG. 7, a measurement cell in which the inner surface of the cell is formed into a mirror surface to reflect the optical path to increase the effective cell length has a cross-sectional shape parallel to the optical path a of the measurement cell. Formed in a rectangular shape like a general straight cell,
A mirror d... is provided on the inner surface perpendicular to the cell window c, and the cell window is also provided.

At positions facing the inner surface of C, there are (
The width when viewed from the incident direction is approximately equal to the width l of optical path a)
There is a known structure in which a mirror e is provided, and light incident through the cell window is reflected in a zigzag pattern between the mirrors d and enters the detector f from the cell window C. In the figure, g is a light source and h is a chopper.

[Problem that the invention seeks to solve]

A measurement cell in which the inner surface of the cell is mirror-finished to reflect the optical path to increase the effective cell length is very effective in increasing the sensitivity of a gas analyzer.

However, in the conventional measurement cell, the structure is as shown in Fig. 7, and the optical path a having a width is reflected in a zigzag pattern between the mirrors d..., so there is little overlap between the optical paths a. The ratio of the effective cell volume (volume of the part through which light passes) to the measurement cell volume is low, and when the width of the optical path a is constant and the effective cell length is lengthened, it is necessary to increase the measurement cell volume.

Therefore, it has been difficult to simultaneously achieve high sensitivity and compactness in a gas analyzer. In a so-called double cell type fluid modulation type gas analyzer, in which the gases flow through the cells alternately at a constant period and a constant amount, when the cell volume is constant, the higher the gas flow rate, the higher the gas flow rate. , the gas in the cell can be switched quickly, but there is a limit to the amount of gas that can flow into the cell, and this gas amount limits the cell volume, resulting in a small cell volume. ,
With the conventional structure described above, it was not possible to increase the effective cell length, and it was difficult to achieve high sensitivity.

The present invention provides a measurement cell that allows the effective cell length to be long relative to the cell volume when the width of the optical path is constant, thereby making it possible to simultaneously achieve high sensitivity and compactness of the gas analyzer. It is something to do.

[Means for solving problems]

In order to achieve the above object, the present invention makes the cross-sectional shape of the measurement cell parallel to the optical path into an odd-numbered angular shape or a combination of the odd-numbered angular shapes having an inner surface that is approximately the same width as the optical path width when viewed from the incident direction. The interior surface except for the cell window is formed into a mirror surface over almost the entire area, and the optical path is reflected by the mirror surface.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an outline of a gas analyzer using a light absorption method using a measuring cell 1 according to the present invention, where 2 is a light source, 3 is a chopper, 4 is a detector, and 5 and 6 are cells made of infrared transmitting materials, etc. It's a window.

The cross-sectional shape of the measuring cell 1 parallel to the optical path a is an odd square having an inner surface approximately the same width as the width l of the optical path a when viewed from the incident direction, and the inner surface except for the cell window 5.6 is mirror-finished over almost the entire area. , , M, and the optical path a is formed on the mirror surface M1.
It is configured to reflect at Mt.

More specifically, the measurement cell 1 has a cross-sectional shape of a right-angled isosceles triangle as shown in FIG. 1σ, cell windows 5.6 with a width l are arranged linearly in the portion corresponding to the base, and the entire inner surface of the portion corresponding to the oblique side is formed into a mirror surface M, . . . Ml. When forming the entire inner surface into a mirror surface M, , M, for example, gold plating,
Any method such as attaching a mirror can be used. 7 is a gas inlet, and 8 is a gas outlet.

According to the above configuration, the light emitted from the light source 2 is interrupted by the chopper 3 and enters the cell window 5 perpendicularly. The light entering the measurement cell 1 is reflected by the mirror surface Ml, and further reflected by the mirror surface M
2 and then enters the detector 4 through the cell window 6.

The width of the inner surface when viewed from the direction of incidence on the inner surface (the width when viewed from the direction of incidence of mirror surface M+, Mt) is approximately equal to the width l of optical path a, so optical path a overlaps twice within measurement cell 1. It turns out. In other words, the light incident on the mirror surface M1 from the cell window 5 and the light reflected on the mirror surface M+ almost overlap,
The light incident on the mirror surface M2 and the light reflected on the mirror surface M2 almost overlap.

Therefore, the optical path a passes through an effective volume twice the actual volume of the measurement cell 1. This means that, in principle, twice the sensitivity can be obtained compared to the case where a straight cell with the same actual volume is used. Further, although the effective cell length is increased by the reflection of the optical path a, almost no dead space (a space through which light does not pass) is generated within the measurement cell 1.

FIG. 2 shows another embodiment of the present invention. In this embodiment, the cross-sectional shape of the measurement cell 1 is a right-angled isosceles triangle, and a cell window 5.6 is formed in a portion corresponding to the hypotenuse, and a cell window 5.6 is formed in a portion corresponding to the base. The feature is that the inner surface of the portion is formed into a mirror surface M over almost the entire area. The length of the oblique side is set to be approximately equal to the width l of the optical path a.

According to this configuration, in addition to the effect that the optical path a passes through an effective volume twice the volume of the measurement cell 1 and the sensitivity increases by that magnification, as in the previous embodiment, the light source 2 and the chopper 3 and the detector 4 are placed at appropriate distances from each other, and the detector 4 is caused by the vibration of the chopper 3 and its driving part.
It has the advantage of being able to easily eliminate any negative effects on it.

FIGS. 3 and 4 each illustrate another embodiment of the present invention.
In the embodiment shown in the figure, the cross-sectional shape of the measurement cell 1 is basically a regular pentagon, and only the cell window 5.6, which serves as the incident surface and the light exit surface, is used to prevent reflections at the cell windows 5 and 6. The three inner surfaces other than the cell windows 5 and 6 are mirrored over almost the entire area M + , M t , M
It is distinctive in that it is formed in the shape of s. The width of the inner surface as viewed from the direction of incidence is set equal to the width l of the optical path a, which is the same as in the previous embodiment.

In the embodiment shown in FIG. 4, the cross-sectional shape of the measurement cell 1 is basically a regular heptagon, and only the cell windows 5 and 6, which are the incident surface and the light exit surface, are perpendicular to the optical path a. 5 inner surfaces other than 6 are mirrored over almost the entire area M,,M,
M! , M a , M s . The rest of the structure is the same as the embodiment shown in FIG.

According to the embodiment shown in FIG. 3, due to the overlap of the optical paths a,
The effective volume of measurement cell 1 is approximately 2.6 of the actual volume of measurement cell 1.
The sensitivity of the gas analyzer is about 3.2 times greater in the embodiment shown in Figure 4, compared to when a straight cell with the same actual volume is used. In principle, it will increase by 3.2 times.

FIGS. 5 and 6 each illustrate another embodiment of the present invention.
In the embodiment shown in the figure, the cross-sectional shape of the measurement cell 1 is a combination of two right-angled isosceles triangles shown in FIG. , is characterized by doubling the cell length. In the embodiment shown in FIG. 6, the cross-sectional shape of the measurement cell 1 is a combination of two shapes shown in FIG. The cell length is doubled by reflecting light in the order of mirror surfaces M1→M, →M, →M, .-M, .→M, .

〔Effect of the invention〕

The present invention has the above-mentioned configuration, and since the cell volume is effectively utilized by overlapping optical paths, the effective cell length can be made long in proportion to the cell volume, and thus the gas analysis needle can be made highly sensitive and compact at the same time. It is possible to achieve this.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a gas analyzer showing an embodiment of the present invention, and FIGS. 2 to 6 are cross-sectional views of measurement cells showing other embodiments of the present invention. FIG. 7 is a sectional view showing a conventional example. 1...Measurement cell, 5.6...Cell window, M, M
+, Mz. Ms, Ma, Ms, M+・, Mt・, Ms・− mirror surface, a
”'Optical path!...Optical path width. Figure 1 1-Optical path width 2° diagram

Claims (1)

[Claims] The cross-sectional shape of the measurement cell parallel to the optical path is an odd-numbered square having an inner surface approximately the same width as the width of the optical path when viewed in the direction of incidence, or a combination of the odd-numbered squares, and the inner surface other than the cell window is spread over approximately the entire area. 1. A measurement cell characterized in that the measurement cell is formed with a mirror surface, and is configured such that an optical path is reflected by the mirror surface.