JP2001188037A - Gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas analyzer miniaturized for requiring a long optical path length and measuring light intensity by time series and having an optical system condensing a laser beam. SOLUTION: Light from a light source 1 transmits a gas correlative filter 9 and a chopper 3 to be condensed by a lens 11, and introduced in a closed track optical system window 2 provided in a sample gas cell 10. The introduced light repeats reflection in order of a reflection mirror 1R, a reflection mirror 2R, a reflection mirror 3R, a reflection mirror 4R and a reflection mirror 5R in the inside, partially transmits in the window 2 of the reflection mirror 6 to be detected with a sensor 8. The remaining light is reflected, the reflection is repeated in the order from the reflection mirror 1, the same action as the above-mentioned is performed, and the light is detected by the time series. Each reflection mirror 1R, 2R, 3R, 4R, 5R, 6R of the inside has condensing action, beam size does not change from the beginning, and quantitative measurement is possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas analyzer for performing analysis by measuring light intensity, and more particularly to an optical system which requires a long optical path length and measures light intensity in time series.

[0002]

2. Description of the Related Art Carbon monoxide and suspended particulate matter in the atmosphere, along with sulfur dioxide, nitrogen dioxide and photochemical oxidants, pollute the atmosphere. Since the sources are diverse and the behavior in the atmosphere is extremely complex, the elucidation of pollution mechanisms and the development of pollution prediction methods are being carried out. As a conventional measurement method, an infrared absorption method is used for carbon monoxide, and a light scattering, a piezoelectric balance, a beta ray absorption method, and the like are used for suspended particulate matter. Among the variations of the infrared absorption method used for carbon monoxide measurement, a non-dispersive infrared gas filter correlation method characterized by using a gas correlation filter is mainstream. FIG. 2 shows a basic configuration of a detection unit of a carbon monoxide meter employing a non-dispersive infrared gas filter correlation method. Light from the light source 1 passes through the gas correlation filter 9, passes through the chopper 3, and is converged by the lens 11,
The light enters the multiple reflection cell 4 (sample gas cell), is reflected by the internal mirror 12, reflected by the object mirror 5, reflected by the field mirror 7, reflected again by the object mirror 5, reflected by the output mirror 6, and multiplexed. The light reaches the sensor 8 provided outside the reflection cell 4 and is detected. The multiple-reflection cell 4 (sample gas cell) includes a multiple-reflection sample cell that reflects light a plurality of times in the multiple reflection cell 4 in order to secure an optical path length sufficient to detect carbon monoxide in the atmosphere. Has adopted. The interior of the gas correlation filter 9 is divided into two chambers, and a target component gas and a gas (inert gas) having no absorption overlap with the target component are sealed therein. In the case of this carbon monoxide meter, one room is filled with a sufficient concentration of carbon monoxide gas, and the other room is filled with a nitrogen gas. By rotating the correlation filter 9,
The light transmitted through the carbon monoxide gas chamber and the light transmitted through the nitrogen gas chamber enter the sensor 8 alternately. The incident light from the light source 1 is transmitted and reflected by each part based on Lambert-Beer's law and enters the sensor 8.
If the concentration of the target component in the gas correlation filter is sufficiently high and the thickness of the gas correlation filter 9 itself is sufficient, a sufficient sample gas concentration signal can be obtained.

[0003]

The optical system of a conventional gas analyzer for measuring light intensity in a time series requiring a long optical path length is constructed as described above, but reciprocates on a straight line. There is a problem that a long box sample chamber is required to increase the optical path length. In addition, many of the mirrors provided in the sample chamber box have a small or no convergence effect, so if the optical path length is long, the size of the light beam becomes large, and it may protrude from the detection area. There is a problem that quantitative measurement cannot be performed.

The present invention has been made in view of such circumstances, and requires a long box sample chamber as an optical system of a gas analyzer which requires a long optical path length and measures light intensity in time series. It is an object of the present invention to provide a small optical system in which the size of a light beam is converged.

[0005]

In order to achieve the above object, a gas analyzer according to the present invention requires a long optical path length, and is used in an optical system of an analyzer for measuring light intensity in time series.
A matrix M having a reflecting surface having a converging action arranged on the circumference and representing paraxial characteristics when reflected n times and reflected k times
Has a closed orbit optical system having an arrangement and shape of an optical system that is a unit matrix or a negative unit matrix.

The optical system of the gas analyzer according to the present invention is configured as described above. A plurality of reflecting surfaces having a converging function are arranged on the circumference, and light is introduced from the outside to the inside through the window. Since the matrix M representing the optical paraxial characteristic is configured to be a unit matrix or a negative unit matrix when the light is reflected k times and makes n turns, the light that has made n turns from the light introduction window converges. Inject in the state. Therefore, if a gas sample to be measured is interposed inside a closed orbit optical system formed by a plurality of reflecting surfaces, it is possible to measure the light intensity in a time series through a long optical path for n rounds. it can. That is, the optical path length can be lengthened by the reflecting mirrors arranged on the circumference, and the shape of the sample cell box can be made spherical or cylindrical, and a compact closed orbit optical system can be obtained. Then, by introducing a reflecting mirror with a converging function so that the paraxial characteristics are always the same at the time of detection, the measurement light is guided to the sensor while converging, and the quantitative measurement can be performed without changing the beam size from the beginning. It becomes possible.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the gas analyzer of the present invention will be described with reference to FIG. FIG. 1 shows an optical path of a cross section of a closed orbit optical system of a gas analyzer according to the present invention. The optical system includes an infrared light source 1, a translucent window 2 provided in a part of a reflecting mirror for introducing and emitting measurement light into a closed orbit optical system, and a sample for introducing a gas to be measured. A gas cell 10 and reflecting mirrors 1R, 2R, 3R, 4R, 5R, and 6R that are provided on the inner circumference of the cell and have a converging function and perform multiple reflections;
A sensor 8 detects a signal from which the measurement light is reflected multiple times in the sample gas cell 10 and exits from the window 2.

The light source 1 uses an infrared light source for measuring carbon monoxide. Light from the light source 1 passes through the gas correlation filter 9 and the chopper 3, is converged by the lens 11, and is introduced into the closed orbit optical system. The incident light from the light source 1 is transmitted and reflected by each part based on Lambert-Beer's law and enters the sensor 8. The interior of the correlation filter 9 is divided into two chambers, and a target component gas (carbon monoxide) and a gas (inert gas: nitrogen) that does not overlap the absorption of the target component are sealed therein. As the correlation filter 9 rotates, light transmitted through the carbon monoxide gas chamber and light transmitted through the nitrogen gas chamber alternately enter the sensor 8. The chopper 3 detects the detection light detected by the sensor 8 by converting the detection light into an alternating current instead of a direct current. The window 2 is a window through which measurement light is introduced and emitted. The window 2 is provided at the center of the reflecting mirror 6R, and is made of a material that is translucent to infrared light. The reflecting mirrors 1R to 6R form a closed orbit optical system with six reflecting mirrors, are arranged on a circumference in the sample gas cell 10 into which the sample gas is introduced, and have a reflecting surface having a converging action. Matrix M representing paraxial characteristics when reflected n times and reflected n times
Has an arrangement and a shape that become a unit matrix or a negative unit matrix. Assuming that the optical distance from the reflecting surface to the reflecting surface is L and the focal length in the reflection is f, a matrix M representing one optical distance and paraxial characteristics in one reflection.
The matrix M after s and k reflections is given by the following equations (a) and (b).

(Equation 1) The sensor 8 detects measurement light that is reflected multiple times in the sample gas emitted from the window 2.

Next, a matrix display of paraxial characteristics of the optical system will be described. The radius of curvature when the reflecting mirror is placed on the circumference is Rm, the radius of curvature of the reflecting mirror is R, the angle of incidence on the reflecting mirror is θ, the focal length f in reflection and the optical distance L from the reflecting surface to the reflecting surface. Are equal to P, the matrix Ms representing the paraxial characteristic in one optical distance and one reflection is represented as the product of the matrix of the reflecting surface by the focal length P and the matrix of the free space of the optical distance P. be able to. Therefore, the matrix Ms is represented by the following equation (c). Then, a matrix (Ms) ² representing paraxial characteristics in the two reflections is given by equation (d). Further, a matrix (Ms) ³ representing paraxial characteristics in the three reflections is given by equation (e).

(Equation 2) Since a unit matrix is formed every three reflections, k = 3m is set here.
The relational expression to be satisfied by n and θ is as follows. k
(Π-2θ) = 2nπ, 3m (π-2θ) = 2nπ, θ
= (3m-2n) π / 6m where m = 2, n = 1 (6
(One round after reflection), θ = 60 degrees.

Next, the meridional direction and the sagittal direction of the light beam will be described. In order to make the focal length fm in the meridional direction equal to the optical distance L, if Rm = 4R, the following equation is automatically established at any angle θ. fm = Rm · COS θ / 2 = 2RCOS θ = L = P The focal length fs in the sagittal direction is expressed by the following equation. fs = Rs / 2COSθ The radius of curvature Rs in the sagittal direction may be determined so that this fs becomes equal to P. When θ = 60 °, P = L = R
= 0.25Rm = fm = fs = Rs

Next, the optical path of the present optical system will be described.
The infrared light from the light source 1 passes through the gas correlation filter 9, passes through the chopper 3, is converged by the lens 11, passes through the window 2 of the closed orbit optical system, and is introduced into the sample gas cell 10.
Internal reflector 1R, reflector 2R, reflector 3R, reflector 4
R, the reflection is repeated in the order of the reflector 5R, and the window 2 of the reflector 6
Are partially transmitted and detected by the sensor 8. The remaining light is reflected, and the reflection is repeated in order from the reflecting mirror 1 to perform the same operation as described above, and the light is detected in time series. As described above, the optical system of the present gas analyzer includes the sample gas cell 1
Six reflecting mirrors 1R to 6R are provided in 0, carbon monoxide in the atmosphere is introduced, and an optical path length sufficient to detect the carbon monoxide is secured by this closed orbit optical system. The measurement principle is based on the conventional non-dispersive infrared gas filter correlation method.

In the above embodiment, the case where m = 2 and n = 1 has been described. However, m = 1 and n = 1
Θ) = 30 degrees.

When the size of the sensor 8 (detector) in the sagittal direction is much larger than the size of the beam, the radius of curvature Rs in the sagittal direction can be made infinite.

Further, in the shape of FIG. 1, if the incident beam is made to enter with a slight inclination with respect to the plane of the drawing, the beam travels spirally, and measurement is performed by disposing a plurality of sensors 8 (detectors). You can also.

In addition, the measurement can be performed not once in a time series but by one time only.

[0016]

The gas analyzer of the present invention is constructed as described above, and has a plurality of converging reflecting mirrors arranged on a circumference in a sample cell box in which a gas sample to be measured is interposed. Is provided, measurement light is introduced into the inside from the outside through a window, and the light is reflected a plurality of times, passes through a long optical path of an optical system that makes n rounds, and the light intensity can be measured in time series. Therefore, the external shape can be made compact and the size can be reduced. In addition, the higher the reflection efficiency of the reflector, the more the size can be reduced. Further, by introducing a reflecting mirror having a converging function so that paraxial characteristics are always the same at the time of detection, quantitative measurement can be performed without changing the beam size from the beginning.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a closed orbit optical system of a gas analyzer according to the present invention.

FIG. 2 is a diagram showing a conventional optical system. DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Window 3 ... Chopper 4 ... Multiple reflection cell 5 ... Object mirror 6 ... Output mirror 7 ... Field mirror 8 ... Sensor 9 ... Gas correlation filter 10 ... Sample gas cell 11 ... Lens 12 ... Mirror 1R ... Reflection mirror 2R ... Reflector 3R Reflector 4R Reflector 5R Reflector 6R Reflector R Inscribed radius of curvature Rm Reflective surface radius of curvature θ Reflection angle

Claims (1)

[Claims] 1. A gas analyzer which requires a long optical path length and measures light intensity in time series, has a reflecting surface having a convergence function disposed on a circumference, and performs n rounds after reflecting k times. A gas analyzer having a closed orbit optical system having an arrangement and a shape of an optical system in which a matrix M representing paraxial characteristics at the time becomes a unit matrix or a negative unit matrix.