JPS62266440A - Gas detector - Google Patents

Abstract

PURPOSE:To enable the measurement of the concentration of a gas to be measured in the atmospheric air, by employing an absorption spectrum of a reference gas cell with the wavelength of the absorption spectrum approximate to that of the gas being measured and sealed with a chemically stable gas. CONSTITUTION:A semiconductor laser 1 is cooled 14 and a light emitted from a laser is divided in two directions with a half mirror 3 through a lens 2. One part of the light is received with an infrared sensor 11 through a lens 10 passing through a reference cell 13 by way of through mirrors 8a and 8b and inputted into a signal processing circuit 7 after subjected to a photoelectric conversion processing. The cell 13 has an absorption spectrum with the wavelength thereof approximate to that of a gas to be measured and is sealed with NH3 of the chemically stable known concentration. Then, an optical system on the other measuring side divided by the mirror 3 composes a long optical path comprising mirrors 15a-15e, spherical mirrors 16a-16c and lenses 5a and 5b. Light absorbed by the gas being measured is received with an infrared sensor 6 to be inputted into the circuit 7, with which 7 the concentration of NO2 of the gas being measured is determined and displayed 12.

Description

[Detailed Description of the Invention] [4 Already Required] The present invention relates to the production of nitrogen dioxide gas (N2) using an infrared semiconductor laser.
In the O□) sensor, nitrogen dioxide gas (No□
) In order to solve the problem of adsorption of nitrogen dioxide gas (No. be.

[Industrial application field]

The present invention relates to a gas detection device, and particularly to an infrared laser type gas sensor.

Pollution gas sensors are required to be small, fast, and highly accurate. Although infrared laser gas sensors are portable and have desirable features, they are also required to have high environmental performance.

[Conventional technology]

FIG. 4 shows a principle diagram of a conventional infrared laser type gas detection device. In the figure, the emitted light from a semiconductor laser 1 is made into parallel light by a lens 2, passes through a half mirror 3, and is transmitted to a gas to be measured 4 in the atmosphere [for example, nitrogen dioxide gas (NO2)].
) ] is transmitted to an infrared sensor 6 by a lens 5.
The light is focused and photoelectrically converted here. This converted signal is input to the signal processing circuit 7.

On the other hand, the laser beam reflected by the half mirror 3 passes through the fE quasi gas cell (preliminarily filled with a gas to be measured at a known concentration) 9 via the mirror 8, and passes through the infrared sensor 1) via the lens 10. The light is focused, and after photoelectric conversion, it is manually input to the signal processing circuit 7.

Since the wavelength of the light incident on the infrared sensor 6.1) from the semiconductor laser 1 can be continuously swept by changing the current, the absorption spectrum of the measurement gas as shown in FIG. 5 can be measured. Note that the signal processing circuit 7 also controls the temperature of the semiconductor laser 1 based on the signal transmitted through the reference gas cell 9.

FIG. 5 shows the absorption spectrum of the measurement gas. Hereinafter, FIG. 4 will be explained with reference to FIG. FIG. 5 is a characteristic curve when nitrogen dioxide gas (NO2) is selected as the gas to be measured, and the vertical axis represents the transmittance and the horizontal axis represents the wavelength.

In the figure, the characteristics shown by the solid line represent the absorption spectrum of the base <1 (gas cell 9), and the characteristics shown by the broken line represent the absorption spectrum due to nitrogen dioxide gas (No. □), which is the gas to be measured 4 in the atmosphere.

Since nitrogen dioxide gas (NO2) in the atmosphere is normally as small as 301 ρb, a reference gas cell 9 (filled with the same gas as the gas to be measured) with a known high concentration is used to tune the laser oscillation wavelength. The absorption spectrum characteristics of this reference gas cell have peaks at wavelengths λl and λ, and a minimum point at wavelength k.

The signal processing circuit 7 calculates the transmittance between the intersection point P of the line connecting the two peak points and the vertical line drawn from the minimum point of the wavelength to the minimum point, corresponding to the characteristics of the solid line and the broken line. Find the difference. This difference in transmittance is a value proportional to the concentration, and since the concentration of the reference gas cell 9 is known, the ratio of the image density is calculated by 21, and the measured gas 4 in the atmosphere, nitrogen dioxide gas (N (h ) can be calculated.This calculated concentration is displayed on the display 12.

[Problem that the invention seeks to solve]

In a conventional reference gas cell filled with nitrogen dioxide gas (No□), nitrogen dioxide gas (No□) is chemically unstable and therefore adsorbs against the inner surface of the gas cell. As a result, the concentration of nitrogen dioxide gas (NO,) within the cell gradually decreases. Therefore, in order to maintain the reference concentration, it is necessary to frequently refill the gas, resulting in troublesome maintenance.

The present invention was created in view of the above-mentioned conventional drawbacks, and aims to provide a determination means that uses an easy-to-maintain reference gas cell to measure the concentration of nitrogen dioxide gas (No□) in the atmosphere. .

[Means for solving problems]

As shown in FIG. 1, the gas detection device of the present invention is an infrared laser type gas detection device that measures the absorption spectrum in the atmosphere to detect the concentration of a gas to be measured 4 contained in the atmosphere. This is characterized in that a chemically stable gas having an absorption spectrum at a wavelength similar to that of the gas to be measured 4 is sealed in the reference gas cell 13.

A specific example is nitrogen dioxide gas (Not
) When detecting the concentration of nitrogen dioxide gas (NOZ
), ammonia gas (Nl+1) which is chemically stable and does not easily cause an adsorption phenomenon on the inner wall of the container of the reference gas cell 13 is added to the reference gas cell 1.
It is characterized by being enclosed in 3.

[Effect]

As shown in FIG. 2, in the present invention, λ+, h.

Each wavelength of the stone is not determined from the absorption spectrum due to nitrogen dioxide gas (NO2) in the atmosphere, but is determined from the absorption spectrum due to ammonia gas (Ni1.).

λ1 of the absorption spectrum of ammonia gas (Nlh), and λ1 of the absorption spectrum of nitrogen dioxide gas (NO2). 712. Since the difference from As is known,
Reference gas cell 13 filled with ammonia gas (Nlh)
It becomes possible to tune the laser oscillation wavelength using , and thereby the concentration of nitrogen dioxide gas (No□) in the atmosphere can be calculated.

〔Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

In order to make it easier to understand the explanation of the operation of the F1) 4 structure, the same parts are given the same reference numerals throughout the drawings, and their repeated explanation will be omitted.

FIG. 2 shows the absorption spectrum of the measurement gas of the present invention. In the figure, the absorption spectrum of ammonia gas (Ni13) sealed in the reference gas cell 13 shown by the solid line has the characteristic that the transmittance is minimum at wavelength 4, and the absorption spectrum of nitrogen dioxide gas (NO The two transmittance peak points A3 and one minimum point that appear in the spectrum have a known relationship that is close to the wavelength.

Therefore, the presence or absence of the gas to be measured can be determined by tuning based on wavelength 4 and r1.

When its presence can be determined, the concentration of the gas to be measured in the atmosphere can be determined from the difference in transmittance at each wavelength, as explained with reference to FIG.

FIG. 3 shows a block diagram of an embodiment of the invention. In the figure, a semiconductor laser 1 is cooled by a 14-circuit refrigeration system. The light emitted from the semiconductor laser 1 is made into parallel light through a lens 2, and is split into two directions by a half mirror 3. One direction is the mirror 8a.

The light passes through the reference gas cell 13 via the light source 8b, and is received by the infrared sensor 1) via the lens 10. Reference gas cell 13
is ammonia gas (N
I+3) is enclosed.

Since ammonia gas (N1) 3) is a chemically stable gas, even if it is sealed in the reference gas cell 13, it does not react with the inner wall of the reference gas cell 13, and the gas concentration can be maintained stably.

The optical system on the measurement side in the other direction separated by the half mirror 3 includes mirrors 152 to 15e and mirrors 16a to 16c.
A long optical path cell is composed of a spherical mirror 5a and a lens 5b, and is incident on an infrared sensor 6. The infrared sensor 6 receives the light that is absorbed by the gas to be measured 4 in the atmosphere while passing through this long optical path.

By applying the measuring means according to the present invention to the reference gas cell 13, ammonia gas (N
Since i13') is used for laser oscillation wavelength tuning, a nitrogen dioxide gas detection device that does not require the trouble of refilling the cell can be realized.

〔Effect of the invention〕

As described in detail above, according to the gas detection device of the present invention, the life of the reference gas cell 13 is extended, and the concentration of the gas to be measured in the atmosphere can be measured.

[Brief explanation of the drawing]

Fig. 1 is a diagram of the principle of the present invention, and Fig. 2 is an absorption spectrum of a measurement gas of the present invention. FIG. 3 is a block diagram of an embodiment of the present invention, FIG. 4 is a principle diagram of a conventional gas detection device, and FIG. 5 is a diagram showing the absorption spectrum of a measurement gas. In the figure, 4 indicates a gas to be measured, and 13 indicates a reference gas cell. 4 Winter U yodo γzu (No'z) Unexploded gi (~1Y2 Fig. 1 Hitsuji ≦ 4. + Blade U bundle L Keiψ Ki”/Z: zr; B-ru 1
) View 2b Calyx T

Claims (2)

[Claims] (1) In an infrared laser gas detection device that measures the concentration of a gas to be measured (4) contained in the atmosphere by measuring the absorption spectrum in the atmosphere, the absorption of the gas to be measured (4) A gas detection device characterized in that the laser oscillation wavelength is tuned using the absorption spectrum of a reference gas cell (13) which has a wavelength spectrum similar to the spectrum and which is filled with a chemically stable gas. (2) When detecting the concentration of nitrogen dioxide gas (NO_2) in the atmosphere, ammonia gas (NH_3), which has an absorption spectrum at a wavelength similar to that of the nitrogen dioxide gas (NO_2) and is chemically stable, is used as described above. The gas detection device according to claim 1, characterized in that the gas detection device is sealed in a reference gas cell (13).