JPH08271426A - Infrared gas analyzer - Google Patents

Abstract

PURPOSE: To provide a highly stable infrared gas analyzer unsusceptive to disturbance noise of electric and magnetic fields. CONSTITUTION: The infrared gas analyzer comprises a light sources 14A, 14B, a sample cell 1, and a detector 6. A diaphragm 19 displaceable according to the pressure difference between a measuring side detection chamber 3A and a comparing side detection chamber 3B in the detector 6 is disposed therebetween and irradiated with light. The detector 6 is mounted with an optical fiber 25 for detecting displacement of the diaphragm 19 by detecting the transmitted light or reflected light. The sample cell 1 and the detector 6 are constructed by bonding three single crystal silicon plate members. Measuring side gas channel 2A and detection chamber 3A and comparing side gas channel 2B and detection chamber 3B are formed, respectively, on two bonding face parts of the bonded body thus integrating the sample cell 1 and the detector 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared gas analyzer which is resistant to disturbance noise and has stable performance.

[0002]

2. Description of the Related Art Conventionally, an infrared gas analyzer is generally used for analysis of pollution gas and gas analysis of industrial furnaces.
Gas molecules composed of different atoms such as CO, CO ₂ , CH ₄ , SO _{4 and} NO _x have their own vibrations. When such a molecule is irradiated with infrared rays by continuously changing the wavelength, infrared rays having the same frequency as the natural vibration of the molecule are absorbed and a spectrum corresponding to the structure of the molecule is obtained. A method of analyzing the structure of a molecule from this spectrum is called an infrared absorption spectrum method, and the infrared gas analysis is based on this method, and quantitatively and qualitatively analyzes gas molecules composed of different atoms as described above.

As a conventional infrared gas analyzer, for example, one having a structure shown in a schematic vertical sectional view of FIG. 7 is widely known. This gas analyzer is basically
It comprises light sources 14A and 14B, a sample cell 11, and a detector 16. In the sample cell 11, two stainless steel pipes 11B are normally arranged in parallel in the main body 11A made of aluminum at predetermined intervals in the longitudinal direction, and one of the pipes is used as a measurement gas passage 12A and the other is provided. The reference gas passage 12B has a structure in which infrared transmitting windows 13 made of calcium fluoride or sapphire are attached to both end surfaces of the main body.

Further, the detector 16 has two detection chambers, a measurement side detection chamber 10A and a comparison side detection chamber 10B, which are formed of a metal such as aluminum or aluminum alloy or stainless steel, and a metal thin film is provided between them. Capacitor 19 is provided. In addition, both detection chambers 10A,
10B is filled with a measurement component or a gas having the same infrared absorption band as that component. In the figure, reference numeral 18
Is an infrared transmitting window, reference numeral 17 is an optical chopper, and reference numeral 15 is a light quantity balancer. The light quantity balancer 15 and the light chopper 17 may be arranged at opposite positions.

In the infrared gas analyzer having such a structure, the amount of infrared rays emitted from the two light sources 14A and 14B is adjusted by the light amount balancer 15, and the infrared transmitting window portion 13 of the sample cell 11 is adjusted. Then, the gas reaches the detector 16 through the gas passages 12A and 12B. The reference gas passage 12B contains an inert gas, and the reference gas passage 12B does not absorb irradiation infrared rays. on the other hand,
When the measurement gas flowing through the measurement gas passage 12A contains the component to be measured, infrared absorption is caused by this component. Therefore, as described above, the absorption of infrared rays in the measurement side detection chamber 10A and the comparison side detection chamber 10B in which the measurement component or the gas having the same infrared absorption band as that component is sealed becomes smaller on the measurement side than on the comparison side. At this time, the difference in thermal energy becomes the pressure difference between the two chambers, and the membrane capacitor 19 is displaced. This capacitance change is detected, and after signal processing, it is taken out as an output signal.

[0006]

However, when the sample cell and the detector are made of a metal such as aluminum or an aluminum alloy, stainless steel, etc. as described above, welding technology or the like is required, and downsizing is structurally required. It is difficult, and even if it can be downsized, there is a high possibility that the performance will be deteriorated.

Further, in the conventional infrared gas analyzer, the differential pressure between the two detection chambers 10A and 10B is electrically measured, and a signal is output due to a change in the measurement environment, for example, an influence of an electric field or a magnetic field. However, there was a problem that the analysis accuracy was reduced due to the inclusion of noise.

The present invention has been made in view of such circumstances, and a main object of the present invention is to provide an infrared gas analyzer which is highly resistant to disturbance noises such as electric fields and magnetic fields and has high stability.
Another object of the present invention is to provide an inexpensive infrared gas analyzer with high analysis accuracy and good analysis response even if it is downsized.

[0009]

In order to achieve the above object, an infrared gas analyzer according to the present invention is an infrared gas analyzer provided with a light source, a sample cell and a detector. By installing a diaphragm between the measurement side detection chamber and the comparison side detection chamber that is displaced by the pressure difference between the two chambers, irradiating the diaphragm with light, and detecting the reflected or transmitted light of the light An optical fiber for detecting the displacement of the diaphragm is attached to the detector.

It is preferable that the detector is composed of a bonded body of three silicon single crystal plate materials, and a measurement-side detection chamber and a comparison-side detection chamber are respectively formed on two bonded surface portions of the bonded body. In addition, the sample cell and the detector are configured by a bonded body of three silicon single crystal plate materials, and a measurement-side gas passage, a measurement-side detection chamber, and a comparison-side gas passage are provided at two joint surfaces of the jointed body, respectively. It is also preferable to form the detection chamber on the comparison side and integrate the sample cell and the detector.

[0011]

In the infrared gas analyzer according to the present invention, the diaphragm of the detector is irradiated with light through the optical fiber, and the reflected light or the transmitted light of the light is detected through the optical fiber to detect the displacement of the diaphragm. . Therefore, not only the sample cell but also the detector need not be equipped with electrical components. Therefore, it is possible to provide an infrared gas analyzer that is highly resistant to disturbance noise such as an electric field and a magnetic field and has high stability.

In particular, by lengthening the optical fiber, the infrared gas analyzer can be remotely controlled, and the analyzer can be used even in an atmosphere where explosion proof is required. In addition, the detector is composed of a bonded body of three silicon single crystal plate materials, and a measurement-side detection chamber and a comparison-side detection chamber are respectively formed on the two bonded surface portions of the bonded body, so that it is easy and inexpensive. In addition, a lightweight detector can be created.

Further, the sample cell and the detector are constituted by a bonded body of three silicon single crystal plate materials, and a measurement side gas passage, a measurement side detection chamber and a comparison side gas are respectively provided on two bonding surface portions of the bonded body. By forming the passage and the comparison-side detection chamber and integrating the sample cell and the detector, the size and weight of the device can be further reduced.

By using the laminated bonded body of the silicon plate materials processed in this way, the size can be reduced more accurately than the conventional detector, and the formation of the sample cell and the detection chamber and the formation of the diaphragm etc. can be performed by the semiconductor technology and Since it can be performed simultaneously by the micromachining technology centering on anisotropic etching, it is advantageous not only for downsizing but also for mass production.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 is a schematic perspective view of an infrared gas analyzer according to an embodiment of the present invention, and FIG. 2 is a line II-II of FIG.
1 is a sectional view taken along line III-III in FIG. 1, FIG. 4 is a sectional view taken along line VI-VI shown in FIG. 1, and FIGS. 5 and 6 are other embodiments of the present invention. FIG. 3 is a cross-sectional view of a main part of the infrared gas analyzer according to FIG.

As shown in FIGS. 1 and 3, this gas analyzer is a double beam type infrared gas analyzer, and basically comprises light sources 14A and 14B, a sample cell 1, and
And a detector 6. Light source 14A, 14B and sample cell 1
An optical chopper 9 is attached between and. The optical chopper 9 intermittently emits light from the light sources 14A and 14B,
Facilitates detection and comparison. The light sources 14A and 14B emit infrared rays having the same frequency as the natural vibration of the molecules of the measurement gas, and the measurement gases absorb the infrared rays.

The sample cell 1 and the detection chamber 6 in this apparatus are each processed into a predetermined shape, for example, a length 60.
Three single crystal silicon wafers 21, 22, 23 each having a size of mm × width 30 mm × thickness 1.0 mm are laminated and integrally formed. More specifically, among these three single-crystal silicon wafers, the first silicon wafer 21 and the third silicon wafer 23 located outside are the crystal planes of the surfaces thereof (100) plane, Two anisotropic concave grooves 4A and 4B to 5A and 5B extending along the length direction are formed on each of the mirror-finished bonding surfaces facing the second silicon wafer 2 located at the center, For example, they are integrally formed by a micromachining technique such as anisotropic etching. In addition,
Of the anisotropic concave groove, the gas passage portion 2A of the sample cell,
Through holes 7A, 7B and 8A, 8B penetrating in the thickness direction of the wafer are formed near both ends in the longitudinal direction of the grooves 4A and 4B that will form the 2B. These respectively constitute a gas inlet and a gas outlet for each gas passage of the sample cell 1. The through hole 7A is an inlet for measuring gas, the through hole 7B is an outlet for measuring gas, the through hole 8A is an inlet for comparative gas, and the through hole 8B is an outlet for comparative gas.

The second silicon wafer 22 located at the center is detected to be formed by the anisotropic concave grooves 5B and 5B in the first and third silicon wafers when laminated and bonded. Anisotropic holes (having a bottom) are similarly formed by anisotropic etching or the like in the portions located inside the chambers 3A and 3B, and the diaphragm 19 is formed in this portion using a general semiconductor process. There is.
This diaphragm 19 is formed by anisotropically etching the bottom diaphragm of the hole, preferably leaving 0.1-0.3 .mu.m. The diaphragm 19 can be formed of, for example, a silicon nitride film formed in advance on the surface of the second silicon wafer 22. The diaphragm 19 includes a measurement-side detection chamber 3A and a comparison-side detection chamber 3A.
It is displaced according to the differential pressure of B.

Further, as shown in FIGS. 3 and 4, an optical fiber mounting hole 24 is formed from the outside at a position corresponding to the diaphragm 19 in the first wafer 21 which becomes the detector 6. The mounting hole 24 can be formed by means such as dry etching (for example, RIE) used in semiconductor technology. The tip of the optical fiber 25 is inserted and fixed in the optical fiber mounting hole 24. The bottom diaphragm of the mounting hole 24 must have a thickness that allows infrared rays emitted from the optical fiber 25 to pass through.

Then, these silicon wafers 21,
22 and 23 are laminated and adhered so that their ends are aligned, and the two gas passage portions 2A as described above,
Sample cell 1 in which 2B is arranged in parallel in the thickness direction of the joined body
A laminated structure in which the two detection chambers 3A and 3B are arranged in parallel in the thickness direction of the bonded body and the detection chamber 6 is integrally formed is obtained. Bonding of silicon wafers
The SiO ₂ layers formed by thermal oxidation at their interfaces may be anodically bonded in a measurement target gas atmosphere. Alternatively, depositing an Au thin film on the bonding surface of the silicon substrate,
It is also possible to perform the diffusion bonding process in the measurement target gas atmosphere. At the time of joining, each detection chamber 3A of the detector 6,
The gas to be measured is enclosed in 3B.

These silicon wafers 21, 22, 23
Before the bonding of (1), a reflecting film is provided on the surface of the diaphragm 19 on the optical fiber side. As the reflective film, a metal or metal alloy having a high reflectance with respect to infrared rays, such as Au—Cr, Ag or Pt, is used. In addition, the optical fiber 25,
Although the wafers 21, 22 and 23 are mounted in the mounting holes 24 after they are bonded to each other, they may be mounted before the bonding. The optical fiber 25 is mounted and fixed in the mounting hole 24 with an adhesive or the like. In the present embodiment, the optical fiber 25 emits infrared rays, and in order to make the infrared rays reflected by the diaphragm 19 incident, a multi-core optical fiber in which the incident optical fiber and the outgoing optical fiber are concentrically arranged, or scattered points. A multicore optical fiber or the like arranged in a shape is used.

The infrared rays emitted from the optical fiber 24 toward the diaphragm 19 are the light sources 14A and 14B.
It has a wavelength different from that of the infrared rays emitted from, and is not absorbed by the gas to be measured enclosed in the measurement side detection chamber 3A. In the apparatus of this embodiment, the sample cell 1 is constituted by bonding three silicon wafers as described above, and has a measurement gas passage 2A and a comparison gas passage 2B. Since the silicon of the material of the sample cell 1 is substantially transparent to infrared rays, the light source 14A,
The infrared light emitted from 14B passes through the silicon wall and reaches the detector 6 through the gas channels 2A and 2B. Therefore, the infrared light transmitting window conventionally required for a sample cell made of stainless steel or the like can be omitted in this sample cell. In addition, the detector 6 formed integrally with this sample cell
The measurement side detection chamber 3A and the comparison side detection chamber 3B are filled with a measurement component or a gas having the same infrared absorption band as that component. For the same reason as described above, the detector 6 according to the present embodiment does not include the infrared light transmitting window conventionally required for the detector made of stainless steel or the like.

In the infrared gas analyzer having such a structure, the infrared rays radiated from the two light sources 14A and 14B become intermittent light by the chopper 9 and are detected through the gas passages 2A and 2B of the sample cell 1. Reach vessel 6.
The reference gas passage 2B contains an inert gas, and the reference gas passage 2B does not absorb irradiation infrared rays. On the other hand, when the measurement gas flowing through the measurement gas passage 2A contains the component to be measured, infrared absorption due to this component occurs. Therefore, as described above, the absorption of infrared rays in the measurement side detection chamber 3A and the comparison side detection chamber 3B in which the measurement component or the gas having the same infrared absorption band as that component is sealed is smaller on the measurement side than on the comparison side. The diaphragm 19 is distorted by the change in capacity (pressure) caused by the absorbed thermal energy.

On the other hand, the infrared light emitted from the emitting optical fiber of the optical fiber 25 is reflected by the reflecting surface of the diaphragm 19 and returns to the incident optical fiber of the optical fiber 25. Due to the distortion of the diaphragm 19, the amount of light returning to the incident optical fiber fluctuates. Therefore, by detecting the fluctuation of the amount of the reflected light by the photoelectric conversion device connected to the rear end of the optical fiber 25, the differential pressure between the measurement side detection chamber 3A and the comparison side detection chamber 3B can be detected. . By calculating the result, the measurement gas flowing through the measurement gas passage 2A of the sample cell 1 can be analyzed.

Next, another embodiment of the present invention will be described. In the embodiment shown in FIGS. 1 to 4, in particular, as shown in FIG. 4, the diaphragm 19 is provided in the central portion of the cross section of the detector 6, and the optical fiber 25 is correspondingly arranged in the central portion, but the present invention is not limited to this. Instead, it can be configured as shown in FIG.

In the embodiment shown in FIG. 5, members common to those in the above embodiment are designated by the same reference numerals, and the description thereof will be partially omitted. Same as the example. As shown in FIG. 5, this embodiment uses three silicon wafers 21, 22,
The detector 36 is formed by stacking and joining 23 in the thickness direction.
Is common to the above-described embodiment in that However, the second
Of the diaphragm 19 formed on the silicon wafer 22 of
The formation position of is closer to the left end or the right end than the center of the cross section. In accordance therewith, the optical fiber attachment hole 24 formed in the first silicon wafer is also formed close to the left end or the right end.

Moreover, in this embodiment, the mounting hole 24 is formed to form the thick portion 38 in the portion for fixing the optical fiber 25, and the end space 34 between the tip of the optical fiber 25 and the diaphragm 19 is narrowed. I am doing it. Light from the light sources 14A and 14B shown in FIG. 3 passes near the center of the cross section of FIG. 5, so there is no problem even if the end space 34 is narrowed.

In this embodiment, in addition to the operation of the above-mentioned embodiment, the thick portion 38 is formed so that the end portion of the optical fiber 25 is fixed more firmly. Further, by narrowing the end space 34, the optical fiber 25
The distance between the diaphragm 19 and the diaphragm 19 is shortened, the influence of the fluctuation of the reflected light amount due to the distortion or displacement of the diaphragm 19 due to the pressure difference becomes relatively large, and the sensitivity is improved.

Further, the optical path of the infrared ray from the optical fiber 25 and the optical path of the infrared rays from the light sources 14A and 14B shown in FIG. 3 are deviated, and it is not necessary to consider their mutual influence. In each of the above embodiments, the mounting hole 24 in which the optical fiber 25 is mounted is not on the first silicon wafer 21 side but on the third silicon wafer 2 side.
It can also be formed on the 3 side. In that case, the etching performed on the second wafer to form the diaphragm 19 may be performed from the opposite surface direction. Further, the direction does not necessarily have to be the opposite direction. Furthermore, the reflective film is
It is preferably formed on the surface of the diaphragm 19 on the side where the optical fiber 25 is mounted. However, this is not necessarily the case. Furthermore, when the diaphragm 19 itself has a reflecting action, it is not necessary to provide a reflecting film.

Next, another embodiment of the present invention will be described. In the embodiment shown in FIG. 6, members common to those in the above embodiment are designated by the same reference numerals, and the description thereof is partially omitted. Members not shown or not described are the same as those in the embodiment. The same shall apply.

As shown in FIG. 6, in this embodiment, the detector 36 is formed by forming three silicon wafers 21, 22 and 23 by stacking them in the thickness direction and bonding them, which is the same as the previous embodiment. To do. However, the second silicon wafer 22
The diaphragm 19 is formed at a position closer to the left end or the right end than the center of the cross section. Also,
In accordance therewith, the first silicon wafer 21 and the second silicon wafer 23 are provided with optical fiber mounting holes 24A and 24B from the outside. The tips of the outgoing optical fiber 25A and the incoming optical fiber 25B are attached and fixed to these, respectively. These optical fibers 25A and 25B can be composed of a single-core optical fiber, and emit infrared rays from one side, and the other side,
It receives infrared rays that have passed through the diaphragm 19.

In this embodiment, the diaphragm 19 does not have a reflective film formed thereon and allows infrared rays to pass therethrough. Each room 3A, 3B
The pressure difference is detected by utilizing the fact that the amount of infrared rays entering the incident optical fiber 25B changes due to the displacement of the diaphragm 19 based on the pressure difference between the two. From such a viewpoint, Fresnel lens-shaped or other minute protrusions may be provided on the front surface or the back surface of the diaphragm 19 to increase the variation of the incident amount on the optical fiber 25B due to the displacement of the diaphragm 19.

In this embodiment, except that the pressure difference is detected by the variation of the amount of transmitted light through the diaphragm 19, FIG.
It has an operation similar to that of the embodiment shown in FIG. Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments. For example, in the embodiment shown in FIG. 1, the sample cell and the detector are made of the same silicon. Although it is formed integrally with the wafer bonded body, the sample cell and the detector may be formed by separate silicon wafer bonded bodies, or only one of them may be formed by the silicon wafer bonded body. It is also possible to form the bonded body constituting such a sample cell or detector by four or more silicon plate materials. However, from the viewpoint of thinning and downsizing of the apparatus, a structure in which the sample cell and the detector are integrally formed by a bonded body of three silicon wafers as shown in FIG. 1 is most desirable.

Further, in the above-mentioned embodiment, since silicon has an infrared ray transmitting property, no infrared ray transmitting window portions are formed at both ends of each detecting chamber of the detector and each gas passage of the sample cell. It is also optional to form an infrared transmitting window portion made of calcium fluoride, sapphire, germanium, or the like. Further in the present invention,
In order to prevent a decrease in sensitivity due to miniaturization, an applied technique is applied such that the inner wall of each gas passage of the sample cell is coated with a highly reflective film made of Au, Ag, Pt, Al or an alloy of these metals. It is also possible.

The infrared gas analyzer of the present invention thus produced is used for monitoring the emission of soot and smoke from facilities such as large boilers, monitoring automobile exhaust gas, monitoring the working environment, monitoring and controlling the atmosphere of the firing furnace, and energy saving of the power generation boiler. It can be used for applications such as performance quality control of burning appliances, and monitoring of fruit and vegetable storage.

[0036]

The infrared gas analyzer according to the present invention provides an infrared gas analyzer which is more resistant to disturbance noise such as an electric field and a magnetic field and has higher stability than a conventional analyzer.
Further, since silicon can be used as a material, the size can be accurately reduced, and the sample cell and the detector can be integrally manufactured, so that an inexpensive analyzer can be provided without lowering the analysis accuracy.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an infrared gas analyzer according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG.

FIG. 4 is a sectional view taken along line VI-VI shown in FIG.

FIG. 5 is a cross-sectional view of an essential part of an infrared gas analyzer according to another embodiment of the present invention.

FIG. 6 is a sectional view of an essential part of an infrared gas analyzer according to another embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of an infrared gas analyzer according to a conventional example.

[Explanation of Codes] 1 ... Sample cell 2A ... Measurement gas passage 2B ... Comparison gas passage 3A ... Measurement side detection chamber 3B ... Comparison side detection chamber 4A, 4B, 5A, 5B ... Groove 6 ... Detector 14A, 14B ... Light source 19 ... Diaphragm 21 ... First silicon wafer 22 ... Second silicon wafer 23 ... Third silicon wafer 24, 24A, 24B ... Mounting holes 25, 25A, 25B ... Optical fiber

Claims (3)

[Claims] 1. An infrared gas analyzer including a light source, a sample cell, and a detector, wherein a pressure difference between the measurement-side detection chamber and the comparison-side detection chamber is provided in the detector. An infrared type that is equipped with an optical fiber for detecting the displacement of the diaphragm by providing a displacing diaphragm, irradiating the diaphragm with light, and detecting reflected light or transmitted light of the light. Gas analyzer. 2. The detector is composed of a bonded body of three silicon single crystal plate materials, and two bonded surface portions of the bonded body are
The infrared gas analyzer according to claim 1, wherein a measurement side detection chamber and a comparison side detection chamber are formed respectively. 3. The sample cell and the detector are composed of a bonded body of three silicon single crystal plate materials, and a measurement-side gas passage, a measurement-side detection chamber, and a comparison side are provided on two bonded surfaces of the bonded body, respectively. The infrared gas analyzer according to claim 1 or 2, wherein a gas passage and a comparison-side detection chamber are formed, and the sample cell and the detector are integrated.