JPS625153A - Optical gas analyzer - Google Patents

Abstract

PURPOSE:To compensate for a zero-point drift generated with changes in the attitude, by arranging more than one measuring cells and reference cells on a circumference centered on one shaft alternately to make light incident upon a photo detector alternately as passing through the cells with the rotation of a light chopper. CONSTITUTION:Four measuring cells M and four reference cells S are arranged at an equal interval alternately to be point symmetrical on the center axis. Light from a light source 1 is made parallel to the center axis with a mirror 5 to enter the measuring cells M1 and M3 passing through a light-transmitting plate 7. A gas to be analyzed runs into the measuring cells M through a path P and a measuring light enters a photo detector 3 passing through a light- transmitting plate 8, light passing hole H of a light chopper 2 and then, a mirror 6 and a bandpass filter 4. Then, the light chopper 2 is turned with a motor 9 to intercept the measuring cells M so that light is allowed to pass through the reference cells S positionally to focus each light on the photo detector 3.

Description

[Detailed Description of the Invention] [Summary] N measurement cells and reference cells (where n≧2) are arranged alternately, and the light passing through these cells is alternately made incident on a photodetector. Compensating for zero point drift in optical gas analyzers.

[Industrial application field]

The present invention relates to optical gas analyzers, and more particularly to gas analyzers that compensate for zero point drift.

[Prior Art and Problems to be Solved by the Invention] A conventional optical gas analyzer is composed of one or more measurement cells, one reference cell, and a photodetector. A measurement cell and one reference cell are used as a pair, and the light that has alternately passed through both cells is incident on a photodetector to detect the difference or ratio in intensity between the measurement light and the reference light.

Gas analyzers with multiple measuring cells and one reference cell are disclosed, for example, in Japanese Utility Model Application No. 58-109054 and U.S. Pat. No. 3,743,426; The latter introduces one gas in series into each measuring cell. However, in such gas analyzers, the difference or ratio between the intensity of the measurement light and the reference light changes due to changes in the temperature distribution of the light source, changes in the sensitivity distribution of the photodetector, or changes in the reflectance distribution of the mirror. This sometimes causes the zero point drift of the analyzer.

As an example of such a zero point drift occurring in a conventional analyzer, a zero point drift due to a change in the attitude of the optical system will be explained. The temperature distribution of the light source is such that the upper part of the light source is higher in temperature than the lower part due to thermal convection of the surrounding gas. Therefore, the light emitted from the top of the light source is stronger than the light emitted from the bottom. In the example of FIG. 4, when the analyzers are stacked vertically (A), the light incident on the measurement cell M and the light incident on the reference cell S have the same intensity, but
When the analyzer is horizontal (B), the light incident on the reference cell S is stronger than the light incident on the measurement cell M.

[Means for solving problems]

The above problem is that the measurement cell, the reference cell, and the photodetector are of equal length, and the measurement light that is passed from the same light source through the measurement cell and the reference light that is passed through the reference cell are alternately illuminated. An optical gas analyzer arranged so as to be incident on a detector, in which n measurement cells M and reference cells S are arranged alternately on a circumference centered on one axis. a gas passage P for introducing the same sample gas into each measurement cell M at the same time, an optical filter 2 having a light passage hole H provided therein so as to be rotatable about the axis; This problem can be solved by an optical gas analyzer characterized in that mirrors 5 and 6 are arranged so that the light passed through M or the reference cell S is alternately incident on the photodetector 3.

Advantageously, the light chopper 2 has n light passage holes H (n≧2) at positions corresponding to the measurement cells M or the reference cells S. Further, the optical chopper 2 may have only one light passing hole H.

If there is a change in the temperature distribution of the light source 1, a change in the reflectance distribution due to dirt on the mirror 5.6, mechanical displacement of the optical system, etc., the measurement light passing through the adjacent measurement cell M and reference cell S will change. Since the electrical signals corresponding to the reference light and the reference light undergo changes with the same tendency, the mutual intensity ratio is kept almost constant, and the drift of the zero point is compensated for.

Furthermore, if the intensity of light passing through cells of the same type at positions symmetrical to the central axis of the analyzer tends to change in opposite directions, such as when changing the orientation of the analyzer, each cell of the same type Since the sum of the corresponding electric signals hardly changes, the drift of the zero point is compensated for in combination with the effect that the intensity ratio of the electric signals corresponding to adjacent different types of passing light is constant.

This effect becomes more effective as the number of cells increases and as the different types of cells approach each other. Note that the cross-sectional shapes of the measurement cell M, the reference cell S, and the light passage hole H of the optical chopper are circular in FIGS. 1 and 2 (A) and (B), but are not limited to this, and may be oval. , oval,
It may be rectangular or fan-shaped.

〔Example〕

Example 1 As an embodiment of the analyzer of the present invention, as shown in FIG. 1, four measurement cells M and four reference cells S are arranged alternately at equal intervals, and the four measurement cells M and reference cell S
Each pair is located symmetrically about the central axis.

As shown in FIG. 2A, the optical chopper 2 has four light passage holes H at positions corresponding to the measurement cell M or the reference cell S. FIG. 3A is a cross-sectional view of this analyzer, in which the light emitted from the light source 1 is made parallel to the central axis by the mirror 5, passes through the light transmitting plate 7, and enters the measurement cells J and M. The same applies to measurement cells M2 and M4 (not shown).

The gas to be analyzed flows into the measurement cell M through the gas passage P, and the measurement light that has passed through each measurement cell passes through the light transmission plate 8.
The light passes through the light passage hole H of the light chopper 2, is focused by the mirror 6, passes through the bandpass filter 4, and enters the photodetector 3.

During this time, the reference cell S is blocked by the optical chopper 2, so that the reference light does not enter the photodetector 3.

Next, the optical chopper 2 is rotated by the motor 9, and the measurement cell M is
It is set at a position where the light is blocked and passes through each reference cell S, and each reference light is focused on the photodetector 3.

The electric signal from the photodetector 3 is obtained as a time-series signal in which each measurement signal and each reference signal corresponding to each measurement cell and each reference cell are obtained alternately. Gas concentration analysis is performed by comparing the sum of the signals.

Example 2 Another embodiment of the analyzer of the present invention has a structure that differs from Example 1 only in that the number of light passage holes H in the optical chopper 2 is one. A cross-sectional view of the analyzer is shown in FIG. 3(B). Further, an optical chopper having one light passage hole H is shown in FIG. 2(B). An optical chopper 2 with one optical passage hole H is provided rotatably around an axis, and each measuring cell M and each reference cell S
The light that has passed is collected and made to alternately enter the photodetector 3. The operation of comparing electrical signals from the photodetector 3 and performing gas concentration analysis is the same as in the first embodiment.

〔Effect of the invention〕

The optical gas analyzer of the present invention has almost no zero point drift due to attitude changes, so it can be made portable, and zero point drift is reduced even when the temperature changes, so there is no need for a temperature control device such as a thermostat. Moreover, since the zero point drift over time due to dirt on mirrors etc. is almost compensated for, zero point adjustment work by manual or automatic equipment is not required even when used continuously for a long period of time, resulting in high performance and compact size. Moreover, the operation can be stabilized.

[Brief explanation of drawings]

FIG. 1 shows the arrangement of the measuring cell and reference cell of the analyzer of the present invention, and is a sectional view taken along the line I-I of FIGS. 3A and B. FIG. The arrangement of the light passage holes of the light chopper is shown, and each n of FIG. 3A and B is
-II 3a sectional view, FIG. 3 is a longitudinal sectional view of the analyzer of the present invention, and FIG. 4 is an explanatory diagram of displacement of the conventional analyzer. M・-Measurement cell, S-・Reference cell, P...Gas passage, H・-Light passing hole, 1-Light source, 2-Light chopper, 3-
- Light detection i, 4-band pass filter, 5.6 - mirror, 7, 8 - light transmission plate, 9 - motor. Fig. 1 Fig. 2 M-m- Measuring cell H- Cross-sectional view of the light passing hole analyzer ---Mirror 7.8--One light transmission plate 9--Cross-sectional view of motor analyzer $3 Figure 1--Light source 2--Light chopper 3--Photodetector- 4--Band pass filter 5.6・-Mirror 7.8--One light transmission plate 9--MotorExplanatory diagram of displacement of conventional analyzerFigure 43・-Photodetector) August 73, 1960 Director General of the Patent Office Michibe Uga1, Indication of the case Patent Application No. 142425 of 19852, Name of the invention Optical gas analyzer3, Person making the amendment Relationship to the case Patent applicant Name: Komei Rikagaku Kogyo Co., Ltd. 4, Agent address: Shizukou Toranomon Building, 8-10 Toranomon-chome, Minato-ku, Tokyo, 105 Tel: 504-07215, Column 6 of “Claims” of the specification to be amended, Amendment Amend the claims in the description of contents as shown in the attached sheet. 7. List of attached documents amended claims 1 copy 2. Claim 1: Measuring cell and reference cell of equal length and photodetector An optical gas analysis needle arranged so that measurement light from the same light source passed through a measurement cell and reference light passed through a reference cell are alternately incident on a photodetector, N measurement cells (M) and reference cells (S) are arranged alternately on a circumference centered on one axis, and each measurement cell (M) is filled with the same sample gas. A gas passage (P) for simultaneous introduction is provided, an optical chopper (2) with a light passage hole (H) is provided rotatably about the axis, and these measurement cells (M) or reference cells ( An optical gas analyzer characterized in that mirrors (5, 6) are arranged so that the light passed through S) is alternately incident on a photodetector (3). 2. Light from an optical chopper (2) The passage hole (H) is connected to the measurement cell (M
The optical gas analyzer according to claim 1, wherein n (n≧2) holes are formed at positions corresponding to the reference cell (S) or the reference cell (S). 3. The optical gas analyzer according to claim 1, wherein the light passage hole (H) of the light chopper (2) is opened on one side.

Claims (1)

[Claims] 1. A measuring cell, a reference cell, and a photodetector element of equal length, and measuring light from the same light source passing through the measuring cell and reference light passing through the reference cell. An optical gas analyzer arranged so that the light is incident on a photodetector alternately, with n measurement cells (M) and reference cells (S) each centered on one axis (where n≧2). The gas passages (P) are arranged alternately on the circumference to introduce the same sample gas into each measurement cell (M) at the same time, and the optical choppers (2) with optical passage holes (H) are connected to the The mirrors (5, 6) are arranged so as to be rotatable about an axis, and the mirrors (5, 6) are arranged so that the light passed through the measurement cell (M) or the reference cell (S) is alternately incident on the photodetector (3). An optical gas analyzer characterized by: 2. The light passage hole (H) of the light chopper (2) is connected to the measurement cell (M
The optical gas analyzer according to claim 1, wherein n (n≧2) holes are formed at positions corresponding to the reference cell (S) or the reference cell (S). 3. The optical gas analyzer according to claim 1, wherein the optical chopper (2) has one light passage hole (H).