KR20210055933A - Acoustic Sensor for gas measurement - Google Patents

Abstract

The present invention relates to an acoustic sensor for gas measurement using a non-dispersive optical system, and more particularly to an acoustic sensor for gas treatment comprising a gas chamber. By applying two microphones with a symmetrical structure to a gas chamber, noise (background signal) caused by vibrations caused by light reflection and disturbance inside the gas chamber is removed, and a high signal-to-noise ratio and dynamic range are realized by correcting the disturbance signal.

Description

Acoustic Sensor for gas measurement

The present invention relates to an acoustic sensor for gas measurement using a non-dispersive optical system, and more specifically, a gas measurement for measuring the composition and concentration of a gas by measuring a change in pressure caused by absorption of light inside a gas cell. It relates to an acoustic sensor.

As a method of measuring the components and concentration of gas, methods such as infrared absorption method, gas chromatography separation analysis method, electrochemical sensor measurement method, and mass spectrometry method are used, and the measurement method depends on the composition of the gas to be measured and the purpose of the analysis. Is determined, and in general, an infrared absorption method, which is easy to measure due to a simple structure of a measuring device, is widely used for gas component measurement.

In the infrared absorption method, the gas concentration is measured by measuring the amount of light transmitted through the gas after irradiating infrared light to a cell filled with a measurement sample. It is a gas measurement method. Although there is no absorption, many other gases have characteristic infrared absorption spectra. That is, the location of the absorption band of the infrared absorption method varies depending on the material, and the absorbed amount depends on the concentration of the gas and the extinction coefficient.In the case of measuring a gas having an absorption coefficient and a low concentration, the absorption of light is small, making the measurement less reliable. Accordingly, there is a limitation that a gas cell having a long path is required to increase sensitivity.

Thus, conventionally, as disclosed in Korean Patent Application Publication No. 10-2019-0048836 (TDLAS alignment system for simultaneous measurement of multiple gases using microscopic optical paths, published on May 9, 2019), a laser is used as a light source to dramatically increase the amount of light. do. However, as it is clear that the laser light source is not suitable for practical use due to limitations in the selection and change of wavelength, cost and product size, Korean Patent Publication No. 10-0788795 (CO2 concentration measuring apparatus using a photoacoustic detector, As in 2007.12.27.Announcement), when a light source including an infrared absorption band is modulated, a sound pressure with an amplitude proportional to the gas concentration and the same modulation frequency as the light source is generated in the measurement cell by the absorbed light energy. The acoustic sensor provided at the rear of the cell calculates the concentration according to the gas component by comparing the magnitude of the sound pressure signal with the absorption band and the same amount of light and when a standard gas is used. Here, the intensity of the detection signal provided by this method is directly proportional to the gas concentration, and if the light intensity in the gas cell is sufficiently high, it is useful for measuring low gas concentrations, thus solving the difficulty of measuring low concentrations in the absorbance measurement method. I can.

However, as in the prior art, the method of measuring the intensity of light incident by the acoustic sensor provided at the rear of the gas cell is to detect the change in the amount of light absorbed by the gas cell, and the light passing through the cell hits the wall of the cell. Some of the light is reflected and the remaining light is absorbed by the cell body, causing a background signal (noise) according to the vibration of the light absorbed by the cell body.

In other words, environmental influences such as the background signal and the vibration of the acoustic sensor affect the detection limit and the reliability of the measurement. The use of a high-performance condenser microphone for measurement with a very high and wide dynamic range and high sensitivity has led to the technical challenge of avoiding possible effects of external vibrations and noise sources.

Korean Patent Laid-Open Publication No. 10-2019-0048836 (TDLAS alignment system for simultaneous measurement of multiple gases using a fine optical path, published on May 9, 2019) Korean Registered Patent Publication No. 10-0788795 (Measurement device for carbon dioxide concentration using photoacoustic detector, 2007.12.27 announcement)

The present invention was conceived to solve the above problems, and implements a high signal-to-noise ratio and dynamic range by removing noise (background signal) caused by vibration due to light reflection and disturbance inside a gas chamber and correcting disturbance signals. Provides an acoustic sensor for gas measurement.

In addition, the present invention provides an acoustic sensor for gas measurement, which increases the measurement limit by increasing the amount of light of an infrared light source to improve detection performance.

In order to solve the above problems, the present invention is a light source, a sample gas for measurement is filled therein, an optical window is formed on one side of the light source to enter the light irradiated from the light source, and the light incident therein A gas chamber including an inner reflective surface for reflecting the light and each side of the gas chamber in a direction perpendicular to the optical window are provided so as to face each other, and receive a sound pressure signal according to the expansion of the sample gas filled in the gas chamber. It characterized in that it comprises a pair of microphones to measure.

In addition, each of the pair of microphones outputs an input signal including the sound pressure signal and a disturbance signal caused by vibration of light reflected from an inner reflective surface formed inside the gas chamber, from the pair of microphones. Including an adder for synthesizing a pair of input signals respectively applied, the sound pressure signal having the same phase is amplified and the disturbance signal having different phases is attenuated. It is characterized by that.

In addition, the addition circuit unit includes a preamplifier for amplifying the input signal output from the pair of microphones, and a high-pass filter provided between the preamplifier and an adder to remove disturbance caused by the amplified input signal from the preamplifier. It characterized in that it further includes.

In addition, an optical chopper that is provided between the light source and the optical window of the gas chamber and modulates the light irradiated from the light source to have a pulse phase, a photo interrupter outputting a reference signal according to the pulse phase of the optical chopper, and the photo interrupter And a disturbance correction circuit unit for receiving the reference signal output from and outputting an output signal having the same frequency component as the reference signal from the target signal applied from the addition circuit unit.

In addition, the disturbance correction circuit unit includes a multiplier for synthesizing a target signal input from the addition circuit unit and a reference signal applied from the photointerrupter, and a positive phase output having the same frequency component as the reference signal among the output signals synthesized from the multiplier. It is characterized in that it comprises a low-pass filter for outputting the signal (I), and a positive phase output line including a.

In addition, the disturbance correction circuit unit includes a phase shift circuit for varying the phase of the reference signal applied from the photointerrupter, a multiplier for synthesizing a target signal received from the addition circuit and a shifted reference signal output from the phase shift circuit, and And a quadrature phase output line including a low-pass filter for outputting a quadrature phase output signal Q having the same frequency component as the shifted reference signal among the output signals synthesized by the multiplier.

Further, it characterized in that it further comprises a detector configured to receive the positive phase output signal (I) and the quadrature phase output signal (Q) output from the disturbance correction circuit unit and analyze the gas sample filled in the gas chamber.

In addition, the light source in a direction opposite to the gas chamber further includes an elliptical reflector having an elliptical surface to focus light emitted from the light source and irradiate it to the optical window of the gas chamber, wherein the light source is It is characterized by emitting infrared light.

In addition, it characterized in that it further comprises a band filter provided between the light source and the optical window, passing light having a predetermined wavelength to be measured, and entering the optical window.

In addition, an optical chopper that is provided between the light source and the optical window of the gas chamber and modulates the light irradiated from the light source to have a pulse phase, a photo interrupter outputting a reference signal according to the pulse phase of the optical chopper, and the photo interrupter Further comprising a disturbance correction circuit unit for receiving the reference signal output from and outputting an output signal having the same frequency component as the reference signal from the target signal applied from the addition circuit unit, It is characterized in that to remove.

In addition, the present invention is provided in the rear of the light source emitting infrared light, the light source in a direction opposite to the gas chamber, one side is oval to focus the light emitted from the light source to irradiate the optical window of the gas chamber. An elliptical reflector consisting of, the sample gas for measurement is filled inside, an optical window is formed on one side of the light source to inject the light irradiated from the light source into the inside, and an inner reflective surface for reflecting the light incident therein is formed. It characterized in that it comprises a gas chamber and a microphone installed in the gas chamber to measure a sound pressure signal according to the expansion of the sample gas filled in the gas chamber.

In the present invention according to the above configuration, disturbance can be eliminated by applying two microphones having a symmetrical structure to an acoustic sensor. In more detail, there is an advantage that gas detection sensitivity and measurement reliability are improved by separating disturbance signals having different phases caused by sound pressure signals having the same phase, respectively measured by a pair of microphones arranged to be opposed to each other.

In addition, in general, only one gas component can be measured when a specific infrared wavelength range is used, but when multiple infrared filters are applied, several types of gas components can be measured at the same time and the interference between the selected wavelengths according to the complex gas can be corrected. I can. In other words, in this case, only the signal component can be detected using a phase detection circuit that is synchronized with the on-off switching phase of the chopper after effectively removing the effect of vibration caused by alternately applying multiple filters to one cell. Efficiency can be guaranteed.

1 is a block diagram showing a conventional gas measurement acoustic sensor.
2 is a block diagram showing an acoustic sensor according to an embodiment of the present invention.
3 to 5 are enlarged main parts for explaining the light source and the gas chamber according to FIG. 1.
6 is a block diagram showing a phase sensitive circuit unit according to an embodiment of the present invention.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments are illustrated in the drawings and will be described in detail. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. It should be.

Unless otherwise defined, all terms used herein including technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

Terms such as those defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in the present application. Does not.

Hereinafter, the technical idea of the present invention will be described in more detail using the accompanying drawings.

The accompanying drawings are only an example illustrated to describe the technical idea of the present invention in more detail, so the technical idea of the present invention is not limited to the form of the accompanying drawings.

2 is a configuration diagram showing an acoustic sensor according to an embodiment of the present invention. Referring to FIG. 2, the acoustic sensor 1000 for gas detection according to an embodiment of the present invention includes a light source 100 and a gas chamber. It may be configured to include 200, a microphone 300, a phase-sensitive circuit unit 400, and a detection unit 500.

The light source 100 is a configuration for projecting light to the optical window 210 formed on one surface of the gas chamber 200, and in one aspect for improving the detection sensitivity of the acoustic sensor 1000, the gas chamber There is a method of increasing the magnitude of the signal level by increasing the intensity of light incident on 200.

)을 이루며, 이때 셀 윈도우(4a)의 직경이 클수록 많은 광량을 전달하는 데에 용이하지만 구성품의 제작의 어려움에 의해 설계가 제한된다. 즉, 셀에 측정가스를 채운 후 솔레노이드 밸브가 닫히고 초퍼(2)로 입사광을 변조한 상태에서 가스가 광 에너지를 흡수하여 생성한 음압 신호를 하나의 음향센서(5)를 이용해 측정하게 된다.As shown in FIG. 1, in the general gas measurement acoustic sensor 10, the divergence angle incident from the light source 1 to the cell 4 is the sum of the angle toward the parabolic reflector 2 and the angle toward the cell (

), and the larger the diameter of the cell window 4a, the easier it is to transmit a larger amount of light, but the design is limited due to the difficulty of manufacturing components. That is, after filling the cell with the measurement gas, the solenoid valve is closed and the incident light is modulated by the chopper 2, and the sound pressure signal generated by the gas absorbing light energy is measured using one acoustic sensor 5.

)은 상기 광원(100)으로부터 타원면반사경(110)으로 향하는 빛의 각도(

)와 가스챔버(200)로 향하는 빛의 각도(

)의 합을 이루며, 상기 광원(100)으로부터 방출된 빛이 상기 가스챔버(200)내부로 입사되는 광량에 비례한다.On the contrary, as shown in FIG. 3, the acoustic sensor 1000 of the present invention is provided at the rear of the light source 100 in a direction opposite to the gas chamber 200, and is emitted from the light source 100. To increase the amount of light incident into the gas chamber 200 by further including an elliptical reflector 110 having an elliptical shape so as to focus the light to be irradiated to the optical window 210 of the gas chamber 200. It is composed. At this time, preferably, since high-rate multiple reflections on the inner surface of the gas chamber 200 are used to improve detection sensitivity, the light incident to the gas chamber 200 may be condensed. Here, the divergence angle incident from the light source 100 to the gas chamber 200 (

) Is the angle of light directed from the light source 100 to the elliptical reflector 110 (

) And the angle of light directed to the gas chamber 200 (

), and the light emitted from the light source 100 is proportional to the amount of light incident into the gas chamber 200.

)은 상기 가스챔버(200) 내부에 반사효과가 가장 높게(즉, 반사된 빛의 경로가 가장 길도록) 설정하는 것이 바람직하다. 즉, 상기 타원면반사경(120)의 외측단부는 상기 광원(100)으로부터 같거나 더 길도록 상기 가스챔버(200)를 향하는 방향으로의 전방으로 연장 형성되어, 상기 광원(100)으로부터 방출된 빛을 전방으로 집광시킬 수 있도록 구성되는 것이 바람직하다.At this time, the focus of the incident light reflected from the inside of the elliptical reflector 110 is configured to be focused on the optical mounting 210, so that a larger amount of light can be transmitted even when the optical window 210 having a small diameter is used. There is an advantage. At this time, the divergence angle (

) Is preferably set so that the reflection effect is the highest (that is, the path of the reflected light is the longest) inside the gas chamber 200. That is, the outer end of the elliptical reflector 120 is formed to extend forward in the direction toward the gas chamber 200 so as to be equal to or longer than the light source 100, so that the light emitted from the light source 100 is It is preferable that it is configured to be able to condense light forward.

The gas chamber 200 is filled with a gas sample for measurement, and an optical window 210 for transmitting light incident on one surface facing the light source 100 is formed therein, and the gas chamber ( 200) A configuration for measuring a pressure change of a gas sample that is expanded by light incident therein, and the gas chamber 200 of the present invention includes an inner reflective surface 220 for reflecting light incident therein. . At this time, the wall surface of the gas chamber 200 is made of a highly thermally conductive material such as copper, and an inner reflective surface 220 formed by thinly coating a metal having a high reflectivity such as gold on the inner surface of the gas chamber 200 is formed. It is formed, by reducing absorption of light incident on the inner reflective surface 220, it is possible to reduce the background signal due to the reflection of light.

At this time, the sound pressure P of the optical sound signal due to the expansion of the gas sample generated inside the gas chamber 200 may be expressed by Equation 1 below.

Equation 1:

{Where, C: concentration of gas, K: absorbance coefficient of gas, I: intensity of light in the gas chamber, w: modulation frequency, Cp: amount of heat required to heat 1 mol at constant pressure, Cv: constant volume It is the amount of heat required to heat 1 mole of 1 degree.}

According to Equation 1, the light sensitivity is proportional to the light intensity (I) and inversely proportional to the modulation frequency (w). That is, since the lower limit of the modulation frequency is determined in advance according to the size of the gas chamber, in order to improve the sensitivity, the intensity of light such as increasing the amount of incident light incident into the gas chamber and increasing the path of light using the internal reflection of the gas chamber (I) It is important to increase.

Accordingly, in order to maximize the amount of light directed to the gas chamber 200, the present invention uses an elliptical reflector instead of a conventional parabolic reflector to condense so that the focus is positioned on the optical window 210 of the gas chamber 200, and the gas chamber (200) Light incident into the interior is radiated to generate multiple reflections from the inner wall of the gas chamber 200. Accordingly, the amount of incident light inside the gas chamber 200 is increased and the path of light is formed to be long, so that the detection signal strength of the acoustic sensor 1000 is increased, and the detection limit of the gas sample can be improved.

The microphone 300 is installed in the gas chamber 200 and is configured to detect a change in sound pressure generated inside the gas chamber 200. A high-sensitivity microphone having a high signal-to-noise ratio in order to improve the detection limit. It is preferable to use a high-sensitivity microphone, which has a disadvantage in that it is greatly affected by disturbances even with very small external vibrations near the detection limit. Accordingly, the acoustic sensor 1000 of the present invention is provided so as to face each other on both sides of the gas chamber in a direction perpendicular to the optical window 210, It is characterized by using a pair of microphones (310, 320) for measuring the sound pressure signal according to the expansion. In other words, the sound pressure signal S11 measured from the pair of microphones 310 and 320, respectively, is caused by vibration of light reflected from the inner reflective surface 220 formed inside the gas chamber 200 and external disturbance. The resulting background signal S12 is mixed.

Accordingly, the acoustic sensor 1000 of the present invention receives the input signal S1 including the acoustic signal S11 and the background signal S12 measured from the pair of microphones 300, and the pair of The amplitude and phase of the output signal from which the background signal (S12) is removed from the phase sensitive circuit unit 400 and the phase sensitive circuit unit 400 formed to satisfy the correction speed of the disturbance with respect to the output from the microphone 300 of It may be configured to include a detection unit 500 that analyzes and calculates the component and concentration of the gas sample filled in the gas chamber 200.

4 is an exemplary view showing a light path formed by reflecting light incident into the gas chamber 200 of the present invention by the inner reflective surface 220, and FIG. 5 is a view showing the inside of the gas chamber 200 of the present invention. As an exemplary diagram showing an example in which a negative pressure is generated due to the expansion of the gas sample charged therein by the incident light, with reference to FIGS. 4 and 5, the input detected from the pair of microphones 310 and 320 When the signal S1 is described in detail, the light emitted from the light source 100 and incident into the gas chamber 200 forms a long reflection path by the inner reflective surface 220 forming the inner surface of the gas chamber 200. Reflection is made to achieve. At this time, the light emitted at 180 degrees from the light source 100 and condensed by the optical window 210 passes through the optical window 210 and forms a side surface inside the gas chamber 200. Light incident on the reflective surface 221 and reflected, and then reflected from the first reflective surface 221 is incident on the rear surface 222 inside the gas chamber 200, and the other first reflective surface ( After incident on the gas chamber 200, the incident on the third reflective surface 223 constituting the front surface of the gas chamber 200 is repeatedly incident to form a long reflection path. That is, it is preferable that the gas chamber 200 is configured such that all inner surfaces form a reflective surface to increase a reflection path of light incident therein, and at this time, the pair of microphones 300 are the gas chambers ( It is preferable to be provided so as to face each other on the side of the gas chamber 200, each sample gas inlet 230 and the gaseous gas outlet 240 for introducing and discharging a gas sample for measurement into the gas chamber 200 The sample gas inlet 230 and the sample gas outlet 240 are disposed at the rear of the chamber 200, that is, in a direction facing the optical window 210, and the sample gas inlet 230 and the sample gas outlet 240 It is preferable that it is formed in the sample gas communication ports 311 and 321 formed in the. That is, the pair of microphones 300 may sense a change in pressure of the expanded gas through the sample gas communication ports 311 and 321 formed at the edges of the inner surface of the gas chamber 200.

This??, the sound pressure signal (S11) of the gas sample expanded by the light incident inside the gas chamber 200 is measured as a signal of the same phase to the pair of microphones (300). However, the background signals S12, which are affected by vibration, impact, noise, etc., caused by light reflected through the inner reflective surface 220 have opposite phases or have different phase differences, so that the pair of The background signal S12 measured by any one of the microphones 300 first microphone 310 is measured to have a different phase difference from the background signal S12′ measured by the other second microphone 320, By adding the measured pair of input signals S1 without the need for separate phase modulation, the background signals S12 having different phases may be canceled or the intensity of the background signals S12 may be reduced.

6 is a configuration diagram of an acoustic sensor 1000 showing in detail the phase sensing circuit unit 400 according to an embodiment of the present invention, and referring to FIG. 6, the phase sensing circuit unit 400 of the present invention includes the light source. An optical chopper 120 provided between the optical window 210 of the gas chamber 200 and the 100 and modulating the light irradiated from the light source 100 to have a pulse phase, the light source 100 and the optical window A band filter 130 provided between 210 and passing light having a constant wavelength to be measured and incident on the optical window, and reference signals R, R according to the pulse phase of the optical chopper 120 A photointerrupter 140 for outputting') is further included, and the phase sensitive circuit unit 400 is an adder 413 for synthesizing a pair of input signals S1 respectively applied from the pair of microphones 300 Including, the sound pressure signal (S11) having the same phase is amplified and the disturbance signals (S12) having different phases are attenuated so that an addition circuit unit (410) for outputting a synthesized target signal (S2) and the photo interrupter An output signal (I) having the same frequency component as the reference signals (R, R') from the target signal (S2) received from the reference signal (R) output from 140 and applied from the addition circuit unit 410 It may be configured to include a disturbance correction circuit unit 420 for outputting, G).

At this time, the addition circuit unit 410 is provided between the preamplifier 411 for amplifying the input signal S1 output from the pair of microphones 300 and the preamplifier 411 and the adder 413, It is configured to further include a high pass filter 412 for removing disturbances caused by the input signal S1 amplified from the preamplifier 411, and the input signal S1 output from the pair of microphones 300 Background signals S12 having different phases are synthesized and attenuated by the adder 413.

In addition, the optical chopper 120 modulates light to have a pulse phase, and the pair of microphones 300 energizes a signal corresponding to the modulation frequency of the light source 100, and operates in synchronization with phase detection. By using it as an input to the disturbance correction circuit unit 420, a signal having a size proportional to the concentration may be obtained.

At this time, the disturbance correction circuit unit 420 includes a multiplier 421a for synthesizing the target signal S2 received from the addition circuit unit 410 and the reference signal R applied from the photointerrupter 140, and the multiplier. Among the output signals synthesized from 421, a low-pass filter (422a) for outputting a positive-phase output signal (I) having the same frequency component as the reference signal (R) and a signal output through the low-pass filter (422a) A positive phase output line L1 including a power amplifier 424a to amplify, a phase shift circuit 423 for varying the phase of the reference signal R applied from the photointerrupter 140, and the addition circuit unit ( The shift among the multiplier 422b which combines the target signal S2 received from 410 and the shifted reference signal R'output from the phase shift circuit 423 and the output signal synthesized from the multiplier 422b A low-pass filter (422b) for outputting a quadrature phase output signal (Q) having the same frequency component as the reference signal (R') and a power amplifier (424b) for amplifying the output signal through the low-pass filter (422b). It may be formed by including the included orthogonal phase output line (L2). Here, the phase shift circuit 423 is a configuration for obtaining the highest output signal by adjusting the phase difference between the target signal S2 and the reference signal R. As an example, the square of each output signal by adding a 90 degree phase difference output By calculating the flat half of the sum as a value proportional to the concentration of the sample, only the sound pressure signal to be detected can be amplified.

More preferably, the positive phase output signal (I) and the quadrature phase output signal (Q) output from the disturbance correction circuit unit 420 are applied to the detector 500, and the amplitude (X) and The phase (Y) can be calculated according to Equation 2 below.

Equation 2:

{Here, in order to have the output range for the phase angle covering all quadrants, that is, (-∏, ∏), the function atan2 should be used instead of atan.}

The present invention is not limited to the above-described embodiments, and of course, various modifications can be made without departing from the gist of the present invention as claimed in the claims.

1000: Acoustic sensor for gas detection
100: light source 110: elliptical reflector
120: optical chopper 130: band filter
140: photo interrupter
200: gas chamber 210: optical window
220: inner reflective surface 221: first reflective surface
222: second reflective surface 223: third reflective surface
230: sample gas inlet 240: sample gas outlet
300: microphone 310: first microphone
320: second microphone 311, 321: sample gas communication port
400: phase sensitive circuit part
410: addition circuit part 411: preamplifier
412: high pass filter 413: adder
420: disturbance correction circuit unit 421: multiplier
422: low pass filter 423: phase shift circuit
424: power amplifier
500: detection unit
L1: Positive phase output line L2: Quadrature phase output line
S1: input signal S2: destination signal
S11, S21: sound pressure signal S12, S22: disturbance signal
I: Positive phase output signal Q: Quadrature phase output signal
R: reference signal R': phase modulated reference signal

Claims (11)

Light source;
A gas chamber is filled with a sample gas for measurement, an optical window is formed on one side of the light source for incidence of light irradiated from the light source, and includes an inner reflective surface for reflecting the light incident therein; And
A pair of microphones provided to face each other on both sides of the gas chamber in a direction perpendicular to the optical window, and measuring a sound pressure signal according to the expansion of the sample gas filled in the gas chamber;
Acoustic sensor for gas detection comprising a.
The method of claim 1,
Each of the pair of microphones outputs an input signal including the sound pressure signal and a disturbance signal caused by vibration of light reflected from an inner reflective surface formed inside the gas chamber,
Including an adder for synthesizing a pair of input signals respectively applied from the pair of microphones, the sound pressure signal having the same phase is amplified and the disturbing signals having different phases are attenuated. An addition circuit unit;
Acoustic sensor for gas detection, characterized in that it further comprises.
The method of claim 2,
The addition circuit unit,
A preamplifier for amplifying the input signal output from the pair of microphones, and
A high-pass filter provided between the preamplifier and an adder to remove disturbance caused by the amplified input signal from the preamplifier,
Acoustic sensor for gas detection, characterized in that it further comprises.
The method of claim 2,
An optical chopper provided between the light source and the optical window of the gas chamber to modulate the light irradiated from the light source to have a pulse phase;
A photo interrupter for outputting a reference signal according to the pulse phase of the optical chopper; And
A disturbance correction circuit unit receiving the reference signal output from the photointerrupter and outputting an output signal having the same frequency component as the reference signal from a target signal applied from the addition circuit unit;
Acoustic sensor for gas detection, characterized in that it further comprises.
The method of claim 4,
The disturbance correction circuit unit,
A multiplier that combines a target signal input from the addition circuit unit and a reference signal applied from the photointerrupter, and outputs a positive phase output signal (I) having the same frequency component as the reference signal among the output signals synthesized from the multiplier. A positive phase output line including a low-pass filter,
Acoustic sensor for gas detection, characterized in that configured to include.
The method of claim 5,
The disturbance correction circuit unit,
A phase shift circuit for varying the phase of the reference signal applied from the photointerrupter, a multiplier for synthesizing a target signal received from the addition circuit and a shifted reference signal output from the phase shift circuit, and an output signal synthesized from the multiplier A quadrature phase output line including a low-pass filter for outputting a quadrature phase output signal (Q) having the same frequency component as the shifted reference signal,
Acoustic sensor for gas detection, characterized in that it further comprises.
The method of claim 6,
A detector configured to receive the positive phase output signal (I) and the quadrature phase output signal (Q) output from the disturbance correction circuit unit and analyze a gas sample filled in the gas chamber;
Acoustic sensor for gas detection, characterized in that it further comprises.
The method of claim 1,
An elliptical reflector provided at the rear of the light source in a direction opposite to the gas chamber and having an elliptical surface to focus light emitted from the light source and irradiate it to the optical window of the gas chamber;
Including more,
The light source is an acoustic sensor for gas detection, characterized in that to emit infrared light.
The method of claim 8,
A band filter provided between the light source and the optical window, passing light having a predetermined wavelength to be measured, and entering the optical window;
Acoustic sensor for gas detection, characterized in that it further comprises.
The method of claim 9,
An optical chopper provided between the light source and the optical window of the gas chamber to modulate the light irradiated from the light source to have a pulse phase;
A photo interrupter for outputting a reference signal according to the pulse phase of the optical chopper; And
A disturbance correction circuit unit receiving the reference signal output from the photointerrupter and outputting an output signal having the same frequency component as the reference signal from a target signal applied from the addition circuit unit;
Including more,
Acoustic sensor for gas detection, characterized in that to remove the disturbance caused by the replacement of the band filter.
A light source that emits infrared light;
An elliptical reflector provided at the rear of the light source in a direction opposite to the gas chamber and having an elliptical surface to focus light emitted from the light source and irradiate it to the optical window of the gas chamber;
A gas chamber is filled with a sample gas for measurement, an optical window is formed on one side of the light source for incidence of light irradiated from the light source, and includes an inner reflective surface for reflecting the light incident therein; And
A microphone installed in the gas chamber to measure a sound pressure signal according to the expansion of the sample gas filled in the gas chamber;
Acoustic sensor for gas detection comprising a.

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