JP2000019108A - Infrared gas analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared gas analyzer capable of ensuring miniaturization and structural simplification. SOLUTION: This analyzer comprises a concave reflector 11 and a flat reflector 15 arranged mutually on opposite sides, an infrared light source 13 provided on the flat-reflector 15 side in such a way as to radiate infrared lights S1, S2 in the direction of the concave reflector 11, and an infrared radiation detector 14 provided in or near a position where the reflected rays A3, B3 are focused after the multiple reflection of the infrared lights S1, S2 radiated from the infrared light source 13 off the concave reflector 11 and the flat reflector 15. Also, the infrared light source 13 is arranged on the flat-reflector 15 side in such a way that the reflected light flux A1, B1 by the first reflection of the infrared lights S1, S2 radiated from the infrared light source 13 off the concave reflector 11 form the parallel rays A1//B1 at a predetermined angle α to a principal axis X of the concave reflector 11, reaching the flat reflector 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a gas sensor for air conditioning control, a gas alarm or a gas concentration measuring instrument installed in a work site where gas safety management is required, such as in a gas management area such as a factory. Infrared gas analyzer.

[0002]

2. Description of the Related Art In many cases, an absorption cell used in an infrared gas analyzer utilizing infrared absorption has a cylindrical shape, and an infrared light source and an infrared detector are generally located at both ends of the absorption cell. It is.

For example, a double beam type infrared absorbing system employing two light sources [NDIR (Non Dispersive Inf
rared analyzer) type CO ₂ gas concentration meter (hereinafter, C
In the case of O ₂ meter), as shown in FIG. 9, a comparison cell 91 through which a reference gas flows and a measurement cell 9 through which a gas to be measured flows
2 and an infrared detector 93 corresponding to the measurement cell 92 and an infrared detector 94 corresponding to the comparison cell 91, a total of two detectors constitute an optical system bench. And
The infrared detector 93 corresponding to the measurement cell 92 is provided with an optical filter (for example, a band-pass filter having a central transmission wavelength of 4.3 μm) 95 on the front surface thereof, which transmits infrared light in a characteristic absorption band of only CO ₂ . The infrared detector 94 corresponding to the comparison cell 91 is an optical filter (for example, a band-pass filter having a central transmission wavelength of 3.7 μm) that allows infrared light having a wavelength not having an absorption band for CO ₂ to pass in front of the infrared detector 94. Infrared light equally emitted from the infrared light sources 97 and 98 is absorbed by CO ₂ in the measurement cell 72, and the detection signal output from each of the detectors 93 and 94 is processed to calculate the CO ₂ gas. The density value of is output.

[0004]

The object of the invention is to be Solved by the way, as the increased interest in the safety of the work environment, small in size and have come to maintenance of the excellent CO ₂ meter is obtained at a low cost, air-conditioning control the CO ₂ meter In order to use the optical system bench as a gas sensor or a gas alarm device or a gas concentration measuring device installed in a gas management area, it is desired that the structure of the optical bench be reduced in size and simplified. On the other hand, in principle, the NDIR method is required to secure an appropriate optical path length (absorption length) for obtaining sufficient absorption according to the concentration of the gas to be measured. However, the CO ₂ meter having the above configuration requires a cell tube having a length (cell length) substantially equal to the optical path length for absorption. In particular, in order to detect a low-concentration gas, the optical path length must be as long as possible, an absorption cell having a long cell length is required, and the overall configuration of the CO ₂ meter becomes large. In addition, since the light source and the detector have to be installed at both ends of the absorption cell, wiring to the infrared light source and the infrared detector is required, and the configuration of the electric circuit therefor is complicated.

The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide an infrared gas analyzer which can be reduced in size and simplified in structure.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a concave reflector and a plane reflector which are arranged opposite to each other, and an infrared ray is provided on the side of the plane reflector toward the concave reflector. An infrared light source provided so that light is emitted radially, and after the infrared light emitted from the infrared light source is multiple-reflected between the concave reflecting mirror and the plane reflecting mirror, the reflected light flux is converged. An infrared detector provided at the position or in the vicinity thereof, and further, the reflected light flux of the infrared light emitted radially from the infrared light source by the first reflection at the concave reflecting mirror is the main axis of the concave reflecting mirror. An infrared light source is arranged on the side of the plane reflecting mirror so as to reach the plane reflecting mirror as a parallel light beam having a predetermined angle, and the concave reflecting mirror is also provided after the parallel light beam is reflected by the plane reflecting mirror. The reflected light traveling toward is a parallel light Remains at, and is characterized in that set up at an angle to the plane reflecting mirror so that the principal axis of the concave reflector and the optical axis of the reflected light beam coincides.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show an infrared gas analyzer according to a first embodiment of the present invention, and FIG. 3 is a diagram showing an operation. As the infrared gas analyzer in this embodiment, for example, a CO ₂ gas concentration meter (hereinafter, referred to as a CO ₂ meter) that detects the CO ₂ concentration in the atmosphere is employed.

First, in FIGS. 1 and 2, reference numeral 1 denotes, for example, a rectangular parallelepiped case, and a lower case 2 and an upper case 3 are provided.
Consists of Both of these 2 and 3 are made of, for example, a metal plate. That is, the lower case 2 is formed by bending two opposing sides of a rectangular metal plate upward at right angles. Upper case 3
Is bent in a rectangular parallelepiped shape so that the lower side is opened, and a plurality of strip-shaped holes (long in the vertical direction) 4 for allowing gas such as air to pass therethrough are formed on two opposing side walls. And, the upper case 3 with respect to the lower case 2
Are fixed to each other by the screw member 5 to form the case 1. Reference numeral 6 denotes a filter provided so as to correspond to the hole 4 for preventing foreign matter such as dust contained in the gas from entering the case 1.

The following components are accommodated in the case 1. That is, reference numeral 7 denotes a circuit board also having a function as a base board which is horizontally held above the lower case 2 via a spacer member 8 of an appropriate length, for example, a printed board. Although not shown in detail, the circuit board 7 amplifies and calculates two outputs of a constant current drive circuit for supplying a current to an infrared light source (described later) and an infrared detector (described later). Amplification / arithmetic circuit for received light output
An instruction calibration circuit, a voltage stabilizing circuit, and the like (both not shown) are formed. Reference numeral 9 denotes a fixing screw member which is screwed with a female screw portion formed on the inner periphery of the spacer member 8.

Reference numeral 10 denotes a gate-shaped holding member which stands upright on the circuit board 7, and comprises two leg portions 10A having appropriate heights and a horizontal top plate portion 10B connecting these leg portions 10A. The circuit board 7 is erected by fixing a bent portion 10a formed by bending the lower ends of both leg portions 10A in the horizontal direction so as to face each other to the circuit board 7 with a screw member (not shown). A concave reflecting mirror 11 is held on the lower surface side of the top plate portion 10B of the holding member 9 using an adhesive member 12 such as a double-sided tape.

That is, the concave reflecting mirror 11 is made of a casting metal or a synthetic resin for injection molding such as ABS.
One surface (lower surface in FIGS. 1 and 2) 1
It is formed by depositing or coating a metal such as aluminum or chromium, which has a high reflectance in the infrared region, so that 1a becomes, for example, a concave reflecting surface. Symbol X is the main axis of the concave reflecting mirror 11.

Reference numerals 13 and 14 denote infrared light sources and infrared detectors provided on the circuit board 7, respectively. These 13 and 14 are respectively disposed at two focal positions of the concave reflecting mirror 11.

Reference numeral 15 denotes a flat reflecting mirror provided on the side of the infrared light source 13 and the infrared detector 14 so as to face the concave reflecting mirror 11. The flat reflecting mirror 15 is box-shaped and is made of a casting metal or a synthetic resin for injection molding such as ABS. Reference numeral 15a denotes a lower horizontal plane (a lower surface in FIGS. 1 and 2) constituting the bottom surface of the plane reflecting mirror 15, and
Reference numeral 15b denotes an upper inclined surface (upper surface in FIGS. 1 and 2) which forms the upper surface of the flat reflecting mirror 15. That is, the upper inclined surface (the upper surface of the plane reflecting mirror 15) 15b is inclined upward from the infrared light source 13 side to the infrared detector 14 side with a slight angle θ with respect to the lower horizontal surface 15a. That is, the upper surface 15b of the plane reflecting mirror 15
The flat reflecting mirror 15 is arranged to face the concave reflecting mirror 11 in a state where the normal line n (see FIG. 3) is inclined at a fixed angle θ with respect to the main axis (X). The upper inclined surface (upper surface) 15b is formed by vapor deposition or coating of a metal such as aluminum or chromium having a high reflectance in the infrared region so as to be a plane reflecting surface.

Further, the flat reflecting mirror 15 is mounted on the circuit board 7.
And a housing 16 for the infrared light source 13 and a housing 17 for the infrared detector 14 which house the infrared light source 13 and the infrared detector 14 provided in a state of being covered from above.

The housing portion 16 of the infrared light source 13 has a tapered hole 18 on the light exit side, which tapers from the upper inclined surface 15b to the lower horizontal surface 15a. In this embodiment, the infrared light source 13 is made of a tungsten lamp, is controlled by a control circuit (not shown) so as to be turned on or off at a constant cycle, and is configured as a direct modulation method.

The receiving portion 17 of the infrared detector 14 has a circular opening 85 substantially at the center of the upper inclined surface 15b.
Are formed, and two types of narrow-band transmission type optical filters 86 (center wavelength: 3.7 μm and 4.3 μm) are held so as to close the opening 85. An accommodation space S is formed so as to communicate with the opening 85, and the accommodation space S is provided with the infrared detector 14 and a cover 41 made of a material that blocks infrared light. This coating 4
Reference numeral 1 denotes an opening 43 for detachably provided so as to cover the infrared detector 14 from above.
Having. In addition, the communication portion P between the opening portion 85 and the accommodation space S has a tapered portion extending downward.

Further, the circuit board 7 has a notch 7b formed so as to partition the infrared light source 13 and the infrared detector 14. The notch 7b is formed so as to be located immediately below the vertical plane portion 41a of the cover 41 when the infrared detector 14 is installed on the circuit board 7 in a state covered by the cover 41.

The structure of the infrared detector 14 will now be described with reference to FIGS. 4 and 5. The infrared detector 14 is, for example, a pyroelectric infrared detector. Are configured as a composite detector in which independent light receiving sections are accommodated in one package, that is, a so-called dual twin type.

More specifically, in FIG. 4, reference numeral 19 denotes a cylindrical container main body 20 having an open bottom,
And a stem 21 for closing a lower opening of the container. A rectangular opening 22 is formed substantially at the center of the upper surface of the container body 20, and a window material 23 made of a material having an excellent infrared transmittance such as BaF ₂ or Al ₂ O ₃ so as to close the opening 22. Is attached.

In the container body 20, for example, PZT
An infrared detecting element 24 made of (lead zirconate titanate-based ceramics) is accommodated, and four light receiving elements 25, 26, 27, and 28 are formed in the infrared detecting element 24. The light receiving elements 25 and 26 and the light receiving elements 27 and 28 have the same shape and the same light receiving area, and are symmetrical (the light receiving elements 25 and 26 and the light receiving elements 27 and 28 are line-symmetrical, respectively).
And in close proximity to each other. The light receiving elements 25 and 26 constitute a pair of dual elements 29, and the light receiving elements 27 and 28 constitute another pair of dual elements 30.

As shown in FIG. 5, the light receiving elements 25 and 26 and 27 and 28 have their electrodes (+ and-).
) Are connected in series in reverse. In FIG.
31 and 32 are FETs for impedance conversion;
4 is a high resistance for adjusting the time constant, 35 is a dual element 29,
A power supply terminal for supplying a voltage to the power supply 30. These circuit members 31 to 35 are provided on the lower surface of the circuit board 7, though not shown in FIGS. 2 and 5. Also, 3
Reference numerals 6 and 37 denote output terminals of the dual elements 29 and 30, and reference numeral 38 denotes a ground terminal common to the dual elements 29 and 30.

In the dual elements 29 and 30 electrically connected as described above, the light receiving elements 25 to 28 do not all receive infrared light, but as shown in FIG. Light-shielding portions 39 (hatched portions indicated by phantom lines in the figure) are provided on both front and back (upper and lower) sides of the window material 23 so that external infrared light is incident on the elements 25 and 27. Only the light transmitting portion 40
(Opened portions in the figure), and the other light receiving elements 26 and 28
To prevent external infrared light from entering the
6, 28 are used for temperature compensation.

Further, the optical filter 86 has the structure described above.
As described above, provided on the front surface of one of the light receiving elements 25 and 26.
CO_TwoInfrared light with a wavelength where there is no absorption band
An optical filter portion to be passed, and the other light receiving element 27,
28 provided on the front of _TwoOnly characteristic absorption band of red
It consists of an optical filter that allows outside light to pass through,
Therefore, one of the light receiving elements 25 and 26 is CO_TwoAnd other moths
3.7μm ± 0.1μ which is a wavelength band without absorption
m and the other light receiving elements 27 and 28
Is CO_Two4.3 μm ± 0.01 μ which is the characteristic absorption band of
It is configured to have sensitivity only to m. This place
In this case, each of the filters comprises the light receiving elements 25 and 26 and the light receiving element 2
7 and 28, respectively.
And the infrared detector 14 are positioned.

The operation of the infrared gas analyzer having the above configuration will be described. The case 1 is provided in a state where the lower case 2 is attached to the wall between the ceiling and the floor, with the strip-shaped holes 4 of the upper case 3 facing the ceiling and the floor of a work site such as a factory (see FIG. 3). Since the hole 4 is formed in the case 1, the air flowing into the case 1 flows through the space between the concave reflecting mirror 11, the infrared light source 13, and the flat reflecting mirror 15 on the infrared detector 14 side. I do. In this state, when the infrared light source 13 is turned on and off in a predetermined state, the infrared lights S ₁ and S ₂ radially emitted from the infrared light source 13 toward the concave reflecting mirror 11 are concave as shown in FIG. Reflector 11
, And become parallel lights A ₁ and B ₁ .

In this case, the infrared light source 13 is
Is located at the focal position of
The reflected lights A ₁ and B ₁ by the second reflection are parallel light fluxes (A ₁ ‖
B ₁ ). That is, the reflected light beams (A ₁ , B ₁ ) become parallel light beams having a predetermined angle α with the main axis X of the concave reflecting mirror 11 and reach the plane reflecting mirror 15.

Subsequently, the parallel lights A ₁ and B ₁ are reflected by the plane reflecting mirror 15. Then, the reflected lights A ₂ and B ₂ return to the concave reflecting mirror 11 again.

In this case, the reflected light beam (A ₂ , B ₂ ) traveling from the plane reflecting mirror 15 toward the concave reflecting mirror 11 remains a parallel light beam (A ₂ ‖B ₂ ) and the reflected light beam (A ₂ ,
Since the plane reflecting mirror 15 is inclined so that the optical axis of B ₂ ) and the main axis X of the concave reflecting mirror 11 coincide, the parallel light A ₁ ,
Even after B ₁ is reflected, it can travel toward the concave reflecting mirror 11 while maintaining the parallel light flux.

The reflected lights A ₃ and B ₃ reflected once again by the concave reflecting mirror 11 are condensed on an infrared detector 14 arranged at another focal position of the concave reflecting mirror 11.

That is, the light beam emitted from the infrared light source 13 is reflected twice by the concave reflecting mirror 11 and once by the plane reflecting mirror 15, that is, three times in total, and the optical path length (absorption length) is four times as large as the conventional one. ) Can be obtained. In addition, since the opening angle of the optical path related to infrared absorption (the opening angle of the infrared light source 13 and the receiving angle of the infrared detector 14) can be increased, the transmission efficiency of light emission can be higher than that of the conventional structure. For example, in this embodiment, the emission power from the infrared light source 13 can be effectively used by providing the tapered hole 18 on the exit side of the housing 16 of the infrared light source 13. Further, by providing a downwardly expanding tapered portion in the communication portion P on the light entrance side of the housing portion 17 of the infrared detector 14, reflected light (stray light) reflected toward the infrared detector 14 side on the light entrance side. Can be prevented from occurring.

As described above, the infrared light source 13 and the infrared detector 14 are arranged on the same circuit board 7 on the side of the plane reflecting mirror 15 so as to face the concave reflecting mirror 11 so that the infrared detection in the infrared detector 14 can be performed. Since the reflected lights A ₃ and B ₃ are focused on the element 24, multiple reflections are possible. Therefore, the optical path relating to the infrared absorption is folded, and an optical path length four times that of the conventional one (two reciprocations in the cell) can be obtained. Also, for example, a low-concentration CO ₂ measuring range of 500 ppm
In the case of the total, the length W of the cells 92 and 91 of the conventional structure is 240
In this embodiment, the distance M between the infrared light source 13 and the concave reflecting mirror 11 is equal to the length W of the cells 92 and 91.
60 mm, which is 1/4 of the above, and the attenuation of light in the optical path is small. Therefore, sufficient infrared absorption and absorbance can be obtained even with a small size while having a sufficient absorption length as compared with the conventional structure. In FIG. 2, the lateral length N of the upper case 3 is 72 mm.

Since the infrared light source 13 and the infrared detector 14 can be installed on one circuit board 7, the structure of the circuit board 7 can be simplified. Furthermore, the number of components can be reduced as compared with the conventional configuration, and the configuration inside the case can be simplified.

Further, the present invention has the following specific advantages. That is, the concave reflecting mirror 11 and the flat reflecting mirror 1
5 since the opposed to the installation distance L ₁ between the infrared light source 13 and infrared detector 14, the concave reflector is placed opposite, when installing the infrared light source and an infrared detector on one side It can be much larger. Moreover, since the notch 7b is provided between the infrared light source 13 and the infrared detector 14 on the circuit board 7, there is an advantage that heat conduction and electric noise from the infrared light source 13 can be suppressed. Thereby, the infrared detector 1
(4) Heat insulation design of the surroundings and reduction of electrical noise can be easily performed. In the case of a low concentration CO ₂ meter with a measurement range of 500 ppm,
The inclination angle θ of the plane reflecting mirror 15 is about 3.5 °, and the installation distance L ₁ is 17 mm.

Therefore, the infrared light source 13 and the infrared detector 1
4 can be thermally stabilized, and the change in the indicated value is small with respect to the change in the ambient temperature.
Further, a CO ₂ meter that is strong against external noise can be easily obtained.

FIG. 6 shows that the measuring range using the concave reflecting mirror 11 'whose curvature is set to be larger than that of the concave reflecting mirror 11 used for a low concentration of 500 ppm is 2,000.
1 shows an infrared gas analyzer for high concentrations of ppm. In FIG. 5, the same reference numerals as those shown in FIGS. In this case, the length of the cell having the conventional structure is 80 mm, but in this embodiment, it is only 1/4 of 20 mm. The horizontal length N of the upper case 3 is about 30 mm, the inclination angle θ of the plane reflecting mirror 15 is about 4.5 °, and the installation distance L ₂ between the infrared light source 13 and the infrared detector 14 is 12 mm. It is.

FIG. 7 shows two inclined surfaces 15b 'and 15b on a plane reflecting mirror provided on the side of the infrared light source and the infrared detector.
FIG. 7 shows a second embodiment of the present invention in which b ″ is formed and two optical paths are formed so that two components of CO ₂ and CO can be detected at the same time. Those with the same reference numerals are the same or equivalent.

In FIG. 7, reference numerals 70 and 71 denote inclined surfaces 15.
b ′, 15b ″. An infrared light source (not shown) is housed in the tapered hole 18.

This embodiment is different from the first embodiment in that two inclined surfaces 15b 'and 15b are used instead of the plane reflecting mirror 15 composed of a single inclined surface 15.
b ″ and the concave reflecting surface 11 a of the concave reflecting mirror 11.
The light reflected multiple times between the inclined surfaces 15 b ′ of the plane reflecting mirror 70 is condensed on a CO ₂ measuring infrared detector (not shown) housed in one housing part 72, and the concave reflecting mirror 11 is Concave reflecting surface 11a and flat reflecting mirror 71
The light reflected multiplely between the inclined surfaces 15b ″ is focused on a CO measurement infrared detector (not shown) housed in the other housing 73.

Each infrared detector has the same configuration as the infrared detector 14 used in the first embodiment, and is configured as a dual twin type as shown in FIG. And the infrared detector for CO measurement has 2
It has a kind of narrow band transmission type optical filter f. That is, two types (center wavelengths of 3.7 μm and 4.7 μm) are provided in the optical filter f installation holes 77 formed in the plane reflecting mirror 71.
m) a narrow band transmission type filter is installed. One filter passes infrared light at a wavelength where there is no absorption band for CO, and the other filter
It has sensitivity only at a wavelength of 3.7 μm without absorption.

In this case as well, the light beam emitted from the infrared light source is reflected twice by the concave reflecting mirror 11 and once by the inclined surface 15b ', that is, three times in total, and is reflected by the concave reflecting mirror 11 twice and the inclined surface 15b'.
b "is repeated three times once, so that an optical path length (absorption length) four times as large as that of the related art can be obtained.
Since the opening angle of the optical path related to infrared absorption (the opening angle of the infrared light source, the receiving angle of each infrared detector) can be made large, the transmission efficiency of light emission can be higher than in the conventional structure.

Since CO ₂ and CO have different sensitivity ratios, it is preferable that the shape of each of the inclined surfaces 15 b ′ and 15 b ″ is set in advance to an appropriate one according to the sensitivity ratio. surface 15b ', 15b performs a sensitivity up by changing dividing ratio (area ratio) of ", it is possible to change the optical gain (optical gain) for each CO _2, CO. For example, since CO is more sensitive than CO ₂ ,
If the measured density range is the same, the area of the inclined surface 15b 'may be set to be larger than that of the inclined surface 15b ".

As described above, two optical paths can be formed for gas species having different sensitivity ratios such as CO ₂ and CO to be measured, and by changing the division ratio of the inclined surfaces 15 b ′ and 15 b ″, CO ₂ and CO can be changed. Since the optical gain can be changed for each CO, the burden on circuit design can be reduced.

FIG. 8 shows a third embodiment of the present invention in which three components of CO ₂ , CO and HC can be detected simultaneously. In FIG. 8, those having the same reference numerals as those in FIGS. 1 to 7 are the same or equivalent.

In this case, instead of the concave reflecting mirror 11 composed of a single mirror as used in the first and second embodiments, a concave reflecting mirror 80 composed of two concave reflecting surfaces 78 and 79 is used. , 81 and two inclined surfaces 15
b ', 15b "
1a is provided. In addition, the concave reflecting surfaces 78 and 79 and the plane reflecting mirrors 70a and 71a are both arranged opposite to each other with the split axes X and Y orthogonal to each other, thereby efficiently detecting the reflected light beam for each measurement infrared ray. Can be focused on a vessel. Each of the housing sections 72, 73, 74, 75 has a C
The infrared detector for O ₂ measurement (not shown), the infrared detector for CO measurement (not shown), the infrared detector for HC measurement (not shown), and the infrared detector for comparison (not shown) are accommodated. ing.

Instead of turning on and off the infrared light source 13 to perform direct modulation, a mechanical chopper may be provided on the infrared light source 13 side or the infrared detector 14 side.

Also, the infrared detector 14 may be configured using a thermopile.

[0046]

As described above, according to the present invention, the concave reflecting mirror and the plane reflecting mirror which are arranged to face each other, and the infrared light is radiated on the side of the plane reflecting mirror toward the concave reflecting mirror. An infrared light source provided so as to emit light, and after the infrared light emitted from the infrared light source is multiple-reflected between the concave reflecting mirror and the plane reflecting mirror, a position where the reflected light flux converges or in the vicinity thereof And an infrared detector provided in the
Further, a reflected light beam of the infrared light emitted radially from the infrared light source due to the first reflection by the concave reflecting mirror becomes a parallel light beam having a predetermined angle with respect to the main axis of the concave reflecting mirror. While the infrared light source is arranged on the side of the plane reflecting mirror to reach, the reflected light traveling toward the concave reflecting mirror even after the parallel light is reflected by the plane reflecting mirror, the parallel light remains as it is, In addition, since the plane reflecting mirror is installed so as to be inclined so that the optical axis of the reflected light beam and the main axis of the concave reflecting mirror coincide, the following effects are obtained.

Since the opening angle of the optical path relating to infrared absorption can be increased and a folded optical path can be formed, sufficient infrared absorption and absorbance can be obtained while having a sufficient absorption length and a small size as compared with the conventional structure. By performing arithmetic processing on the output of the infrared detector, the concentration value of the gas species or an alarm is output, and the air conditioning control can be reliably performed.

Further, since the infrared detector and the infrared light source can be installed on one circuit board, the configuration of the circuit board can be simplified. Furthermore, the number of components can be reduced as compared with the conventional configuration, and the configuration inside the case can be simplified.

Further, since the concave reflecting mirror and the flat reflecting mirror are arranged to face each other, the installation distance between the infrared light source and the infrared detector can be reduced by disposing the concave reflecting mirror to face each other, and the infrared light source and the infrared light As compared with the case where a detector is provided, the size can be made larger, so that heat conduction and electric noise from the infrared light source can be suppressed, and thereby, insulation design around the infrared detector and reduction of electric noise can be easily performed. As a result, the entire circuit board including the infrared detector and the infrared light source can be thermally stabilized, and the change in the indicated value is small with respect to the change in the ambient temperature.
Further, an infrared gas analyzer that is strong against external noise can be easily obtained.

Further, by combining a plurality of inclined surfaces and concave reflecting surfaces, a multi-optical path can be easily realized.
Therefore, it is easy to increase the number of components, and the optical gain can be changed for each gas type by changing the division ratio of each inclined surface even for gas types having different sensitivity ratios. Can also be reduced.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a first embodiment of the present invention.

FIG. 2 is a configuration explanatory view showing the first embodiment.

FIG. 3 is a diagram showing an operation in the first embodiment.

FIG. 4 is a structural explanatory view showing an infrared detector used in the present invention.

FIG. 5 is an equivalent circuit diagram in the first embodiment.

FIG. 6 is a diagram showing an operation in a modified example of the first embodiment.

FIG. 7 is a configuration explanatory view showing a second embodiment of the present invention.

FIG. 8 is a configuration explanatory view showing a third embodiment of the present invention.

FIG. 9 is a configuration explanatory view showing a conventional example.

[Explanation of symbols]

 7 circuit board, 11 concave mirror, 13 infrared light source, 1
4: infrared detector, 15: flat mirror, S₁, S_Two…Red
Infrared light emitted from an external light source, A₁, B₁, A _Two, B_Two
... Multiple reflected light, A_Three, B_Three… Reflection convergent light, θ… Plane reflection
Mirror tilt angle.

Claims (2)

[Claims] 1. A concave reflecting mirror and a plane reflecting mirror arranged to face each other, and an infrared light source provided on the side of the plane reflecting mirror so that infrared light is emitted radially toward the concave reflecting mirror. An infrared detector provided at or near a position where the reflected light flux converges after the infrared light emitted from the infrared light source is multiply reflected between the concave reflecting mirror and the plane reflecting mirror, and The reflected light beam of the infrared light emitted radially from the infrared light source due to the first reflection by the concave reflecting mirror becomes a parallel light beam having a predetermined angle with the main axis of the concave reflecting mirror, and is reflected by the flat reflecting mirror. While the infrared light source is arranged on the side of the plane reflecting mirror so as to reach, the reflected light traveling toward the concave reflecting mirror even after the parallel light is reflected by the plane reflecting mirror, remains a parallel light, and The optical axis of this reflected light beam and the main axis of the concave reflecting mirror An infrared gas analyzer, wherein the flat reflecting mirror is installed at an angle so that the axis coincides with the axis. 2. The infrared light source and the infrared detector are arranged on the same circuit board provided on the plane reflecting mirror side, and the infrared detector is mounted on a main axis of the opposing concave reflecting mirror. On the other hand, the infrared light source is installed outside the main axis of the concave reflecting mirror with a predetermined distance from the infrared detector, and the flat reflecting mirror is reflected by the flat reflecting mirror. The infrared ray according to claim 1, wherein the infrared ray is installed in a state where the normal line on the upper surface of the plane reflecting mirror is inclined at a fixed angle with respect to the main axis so that the optical axis of the reflected light beam coincides with the main axis of the concave reflecting mirror. Gas analyzer.