KR100954092B1 - Optical gas sensor and method for measuring mixed gases - Google Patents

Abstract

An optical sensor for measuring mixed gas is provided. An optical sensor for measuring the concentration of each gas constituting a mixed gas, comprising: a light source for irradiating an optical signal with the mixed gas; And a light detector for measuring the concentration of each gas of the mixed gas through a modulated light signal in which the optical signal passes through the mixed gas and changes optical characteristics, wherein the wavelength of the optical signal is a wavelength of an absorption spectrum of a gas to be measured. The optical sensor for measuring the mixed gas, which varies in a range, can measure the concentration and type of each gas constituting the mixed gas through a simple configuration.

Gas Sensor, Frequency Modulation, Multi Sensor

Description

Optical sensor and method for measuring mixed gases

The present invention relates to an optical sensor and a gas sensing method for gas detection, and more particularly, an optical sensor and mixed gas measurement for measuring a mixed gas for measuring the concentration of the mixed gas through a gas-specific light absorption spectrum. It is about a method.

The conventional gas sensor for gas detection is largely divided into a semiconductor gas sensor and a contact combustion gas sensor. The semiconductor gas sensor uses the principle that the electrical conductivity of the semiconductor is changed when the gas contacts the surface of the specific semiconductor crystal element in which the defective region exists. That is, the concentration of the gas is measured by converting the change in the electrical conductivity of the semiconductor due to the contact of the gas into a voltage, current or resistance value.

Contact combustion gas sensors are mainly used to measure flammable gases. The combustible gas reacts with oxygen to generate heat of reaction, and the catalytic combustion gas sensor converts the heat of reaction into an electrical signal to measure the gas. At this time, since the combustible gas is hydrocarbon-based, the calorific value is greatest when completely oxidized to water (H ₂ O) and carbon dioxide (CO ₂ ). However, the complete oxidation of the gas is difficult to occur at low temperatures, and even if it occurs, the reaction rate is slow, making real-time measurement impossible. Therefore, a catalyst that promotes complete oxidation and sufficient oxygen are required for faster measurement, and the temperature of the sensor reaction section must be increased to increase the reaction rate.

In the case of a semiconductor gas sensor, since it is greatly influenced by environmental factors such as ambient temperature and humidity, there is a disadvantage in that an additional sensor that can compensate for this is installed. In addition, it is effective only when measuring a single gas because it is difficult to measure the concentration of each gas of the mixed gas.

In addition, the contact combustion gas sensor is not significantly affected by the surrounding environment, and even if the gas to be measured is mixed, it is possible to accurately measure the concentration of the desired gas. However, because the measurement must go through a chemical process called combustion, secondary by-products are produced, and the process has a disadvantage in that accurate measurement is difficult in an environment where oxygen is deficient.

Accordingly, it is an object of the present invention to propose an optical sensor and a mixed gas measuring method for measuring a mixed gas, which can measure the concentration of each gas constituting the mixed gas by using a unique absorption spectrum existing for each gas. .

Another object of the present invention is to propose an optical sensor and a mixed gas measuring method for measuring a mixed gas capable of measuring a gas concentration irrespective of changes in the surrounding environment such as temperature and humidity changes.

According to an aspect of the present invention, an optical sensor for measuring the concentration of each gas constituting the mixed gas, the light sensor for irradiating an optical signal with the mixed gas; And a light detector for measuring the concentration of each gas of the mixed gas through a modulated light signal in which the optical signal passes through the mixed gas and changes optical characteristics, wherein the wavelength of the optical signal is a wavelength of an absorption spectrum of a gas to be measured. There is provided an optical sensor for measuring a mixed gas characterized by varying in a range.

Here, the wavelength of the optical signal can be changed within the wavelength range at the rate of the modulation frequency (f), the wavelength range of the absorption spectrum has the same value to measure one gas constituting the mixed gas The light sources may include a plurality of light sources having different modulation frequencies.

The light detector includes a signal converter converting the modulated light signal into an electrical signal; And a band pass filter separating the frequency component of the modulated light signal from the electrical signal, and measuring the concentration of each gas by using a change in transmittance of the modulated light signal.

Here, the minimum number of the light sources may be the same as the number of kinds of the gas to be measured, and the frequency of the modulated light signal may have a value twice that of the modulation frequency f.

The modulated light signal may further include information on a wavelength change range of the optical signal, and the light detector may measure the type of the gas through the modulated light signal.

According to another aspect of the present invention, a method for measuring the concentration of each gas constituting a mixed gas, comprising: irradiating an optical signal with the mixed gas; And measuring the concentration of each gas of the mixed gas through a modulated optical signal in which the optical signal passes through the mixed gas and has an optical characteristic changed, wherein the wavelength of the optical signal is in a wavelength range of an absorption spectrum of a gas to be measured. Provided is a mixed gas measurement method characterized in that it changes in.

Here, the wavelength of the optical signal may be changed within the wavelength range at a speed of a modulation frequency (f), and the step of measuring the concentration of each gas through the modulated light signal converts the modulated light signal into an electrical signal. Making; And measuring the concentration of the gas by means of the electrical signal, and through the band pass filter extracting only the frequency component of the modulated light signal before including measuring the concentration of the gas by means of the electrical signal. The method may further include separating the electrical signal.

Measuring the concentration of each gas of the mixed gas through the modulated light signal may be measured by the concentration of the gas by using a change in transmittance of the modulated light signal, the modulated light signal is a wavelength change range of the optical signal The method may further include measuring information about the type of gas through the modulated light signal.

According to the optical sensor and the mixed gas measuring method for measuring the mixed gas according to the present invention, it is possible to measure the concentration of each gas constituting the mixed gas through a simple configuration.

In addition, according to the optical sensor and the mixed gas measuring method for measuring the mixed gas according to the present invention, it is possible to accurately measure the concentration of each gas in spite of changes in the surrounding environment such as temperature and humidity changes.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to specific embodiments, it should be understood to include all transformations, equivalents, and substitutes included in the spirit and scope of the present invention. In the following description of the present invention, if it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "have" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, with reference to Figures 1 to 2 to look at the principle of the optical sensor for measuring the mixed gas according to an embodiment of the present invention. 1 is a conceptual diagram of an optical sensor for measuring a mixed gas according to an embodiment of the present invention, Figure 2 is a table showing the optical absorption spectrum for each gas.

Referring to FIG. 1, an optical sensor for measuring a mixed gas may include a light source 110, an optical signal 120, a mixed gas 140, a modulated light signal 160, and a photo detector 180. Can be. Mixed gas 140 refers to a gas composed of several types of gas, it can be composed of a single type of gas is apparent to those skilled in the art in view of the technical spirit of the present invention. Hereinafter, in order to facilitate the understanding and explanation of the present invention, the mixed gas 140 is assumed to have the same meaning as described above.

Looking at the schematic operation principle of the optical sensor for measuring the mixed gas according to the embodiment as follows. The light signal 120 may be irradiated from the light source 110 to the mixed gas 140. In this case, the optical signal 120 emitted from the light source 110 may have a different absorption spectrum according to the type of gas constituting the mixed gas 140.

As such, the optical signal 120 emitted from the light source 110 is reflected or scattered and modulated while passing through the mixed gas 140. The modulated light signal 160 is thus input to the photodetector 180, and the photodetector 180 measures the concentration of each gas constituting the mixed gas 140 based on the modulated light signal 160. .

As such, the concentration of each gas constituting the mixed gas 140 through the modulated light signal 160 modulated while passing through the mixed gas 140 may be measured for each gas as shown in FIG. 2. This is because it has its own absorption spectrum. Referring to FIG. 2, it can be seen that each gas has its own absorption spectrum. For example, carbon dioxide (CO 2) is 1.43 to 1.45 μm, and carbon monoxide (CO) is 1.56 to 1.60 μm and the like, and the gas-specific absorption spectrum is also different depending on the type of gas. Each gas has a greater degree of absorption in the range of intrinsic absorption spectrum compared to the range of other wavelengths. Thus, since the range of the intrinsic absorption spectrum which they have differs for each kind of gas, the density | concentration of each gas which comprises a mixed gas can be measured using this. These principles will be described later in more detail with reference to FIG. 3.

Hereinafter, the principle of the optical sensor for measuring the mixed gas according to the embodiment of the present invention will be described in detail with reference to FIG. 3. Figure 3 is a graph showing the change in wavelength according to the absorption rate and time of the light source according to the wavelength of the gas to be measured by the optical sensor for measuring the mixed gas of the present invention.

Referring to FIG. 3, graphs 310 and 320 showing changes in transmittance according to the wavelength of gas are shown. As shown in the graphs 310 and 320, most of light in a specific wavelength band λ 1 to λ 2 is absorbed to lower the transmittance. At this time, the degree to which the transmittance is lowered depends on the concentration of the gas. That is, when the concentration of the gas contained in the mixed gas is high, the decrease in transmittance becomes large as shown in 310, and when the concentration of the gas is low, the decrease in transmittance decreases as shown in 320. As described above, since the width of the transmittance decreases according to the concentration of the gas, the concentration of the gas can be measured by analyzing the modulated light signal passing through the gas.

As described above, the operation of the optical sensor using the absorption spectrum of the optical signal of the gas to be measured may be performed through wavelength modulation of the light (ie, the optical signal) emitted from the light source. In order to measure the concentration of gas using the absorption spectrum, a light source operating at a wavelength having the largest absorption degree in the absorption spectrum band, that is, the center wavelength λ ₀ , is required. The center wavelength λ ₀ refers to a wavelength having the largest absorption degree in the absorption spectrum band of gas, that is, the lowest transmittance. Hereinafter, in the present specification, the center wavelength λ ₀ is used to have the same meaning as described above. Therefore, as shown in the table of FIG. 2, the center wavelength λ ₀ value may vary depending on the type of gas.

The wavelength of the optical signal emitted from the light source can be changed by changing the value of the voltage or current applied to the light source. Since the wavelength of the optical signal emitted from the light source varies according to the value of the voltage or current applied to the light source, changing the voltage or current applied to the light source at the speed of the modulation frequency f causes the wavelength of the optical signal emitted from the light source. It also changes at the rate of modulation frequency f. In more detail, when the voltage or current value applied to the light source is changed at the speed of the modulation frequency f, the wavelength of the optical signal emitted from the light source changes according to the change of the voltage or current value. It is changed at the same speed as the change, that is, the speed of the modulation frequency f.

At this time, the wavelength of the optical signal emitted from the light source ranges from the first wavelength λ ₁ including the center wavelength λ ₀ to the second wavelength λ ₂ , ie, as shown in the graph 330. In the range of the absorption spectrum, the wavelength of the optical signal is changed at a rate of the modulation frequency f. In this manner, the optical signal 120 whose wavelength is changed in the range of the predetermined wavelength (Δλ = λ ₂ −λ ₁ ) at the speed of the modulation frequency f is passed through the mixed gas 140 to be measured. As such, the optical signal 120 is reflected or scattered while passing through the mixed gas 140.

As the light signal 120 reflected or scattered is absorbed according to the concentration of the gas as described above, the optical characteristic according to the concentration is changed accordingly. Optical properties refer to properties such as transmittance, absorption or wavelength. The optical signal thus changed and output is referred to as a modulated optical signal. Hereinafter, the modulated optical signal is used as described above. The modulated light signal may be detected by the photo detector 180, and the concentration of a specific gas constituting the mixed gas may be measured through the sensed modulated light signal.

The optical signal 120 whose wavelength is changed within the range of the first wavelength λ ₁ to the second wavelength λ ₂ passes through the gas to be measured, and the degree of absorption is reduced differently according to the concentration of the gas. That is, while passing through the mixed gas 140 of the optical signal 120, the transmittance is different depending on the concentration of the gas. More specifically, when the concentration of the gas is high, since the absorption amount of the mixed gas 140 with respect to the optical signal becomes large (that is, the transmittance is lowered), the intensity of the modulated light signal output is smaller than that of the case where the concentration of the gas is low. You lose. This can also be seen by looking at graphs 310 and 320 which show a decrease in the transmittance which varies with concentration. By measuring the intensity of the modulated light signal output through this principle it is possible to calculate the concentration of the gas.

Also, as illustrated in the graph 340, according to the present embodiment, the optical signal whose wavelength is changed at the modulation frequency f is twice as large as the modulation frequency f when first emitted from the light source while passing through the mixed gas. It can be changed into a modulated light signal having a corresponding frequency 2f. This is because when the half period of the optical signal is irradiated and passes through the mixed gas, one period of the modulated light signal is output. However, when one period of the optical signal is irradiated and passes through the mixed gas, the frequency may be half of the original modulation frequency f when the half cycle of the modulated optical signal is output. That is, the relationship between the modulation frequency and the frequency of the modulated light signal as described above is only one embodiment. The frequency of the modulated light signal does not necessarily have to be twice the modulated frequency f.

Since the changed intensity of the modulated light signal includes information on the gas concentration as described above, the photodetector 18 performs signal processing on the intensity of the modulated light signal having a frequency 2f twice the modulation frequency. The concentration of gas can be measured. In addition, since the modulated optical signal includes information of the central wavelength λ ₀ having the highest absorption rate or information on the wavelength change range of the optical signal, that is, the absorption spectrum, the type of gas can be known. . As described above, the optical sensor according to the present invention uses the absorption spectrum of the gas to be measured as described above, and these optical characteristics are independent of changes in the surrounding environment. Therefore, the gas measurement using the optical sensor according to the present invention can accurately measure the concentration or type of each gas in spite of changes in the surrounding environment such as temperature and humidity changes.

Hereinafter, a configuration of an optical sensor for measuring a mixed gas according to an embodiment of the present invention will be described in detail with reference to FIG. 4. 4 is a block diagram of an optical sensor for measuring a mixed gas according to an embodiment of the present invention.

An optical sensor for measuring a mixed gas according to an exemplary embodiment of the present invention includes a light source 110 and a light detector 180. At this time, the light source unit 110 is composed of a plurality of light sources (110a, 110b, 110c, ...). At this time, the minimum number of light sources included in the light source unit 110 varies according to the type of gas to be measured. For example, when there are three types of gas to be measured, at least three light sources are required.

Each of the light sources 110a, 110b, 110c,..., Optical signals 120a, 120b, 120c, having a wavelength corresponding to the center wavelengths λ _a , λ _b , λ _c ,... Of the absorption spectrum of the gas to be measured. 120). That is, the light source unit 110 includes light sources 110a, 110b, 110c,... That emit wavelengths corresponding to the center wavelengths λ _a , λ _b , λ _c ,... Of the gas to be measured. As such, since a light source having a different central wavelength is required according to the type of gas to be measured, the minimum number of light sources is determined according to the type of gas to be measured.

In addition, when a plurality of light sources having the same center wavelength but different modulation frequencies are assigned to one type of gas, even if a specific light source fails, the entire system can be operated without stopping, thereby increasing stability and precision. Therefore, in this case, the number of light sources included in the light source unit 110 may be larger than the type of gas to be measured.

At this time, the voltage or current applied to each of the light sources 110a, 110b, 110c, ... is changed at a speed of different modulation frequencies f _a , f _b , f _c ,... The wavelength of the optical signal 120 emitted from 110b, 110c, ... is changed within a specific wavelength range including the center wavelength, that is, within the wavelength range of the absorption spectrum.

The wavelengths of the optical signal 120 and the modulated optical signal 160 irradiated from the light sources 110a, 110b, 110c, ..., respectively, which are changed at different modulation frequencies f _a , f _b , f _c ,... The variation range of (corresponding to Fig. 3, Δλ) is the same. At this time, the speed at which the wavelength of the optical signal 120 irradiated from the light source 110 changes depends on the respective modulation frequencies f _a , f _b , f _c ,... In this way, the optical signal 120 that is emitted by changing the wavelength at the modulation frequencies (f _a , f _b , f _c ,...) Passes through the mixed gas 140 to be measured.

As described above, the optical signal 120 passes through the mixed gas 140, and the frequencies 2f ₁ , 2f ₂ , 2f corresponding to twice the modulation frequencies f _a , f _b , f _c ,... _The modulated light signals 160a, 160b, 160c, hereinafter referred to as 160 have a component ₃ , ..., and so on.

In this case, the absorption rate of the optical signal 120 is changed according to the concentration of the gas constituting the mixed gas 140. That is, when the concentration of the gas is low, the optical signal 120 is absorbed less, so that the amplitude of the modulated optical signal 160 is smaller than that of the optical signal 120, and the decrease is small. The reduction width of the signal 160 is greater than when the concentration is low.

As such, the modulated light signal 160 includes information on the concentration of the gas, and has a frequency 2f component twice the initial modulation frequency f. The modulated light signal 160 is converted into an electrical signal 150 by the signal converter 170. As shown in the graph 190, only the components of the frequency 2f ₁ , 2f ₂ , 2f ₃ ,..., Twice are left in the converted electrical signal 150.

The electrical signal 150 converted from the modulated light signal 160 including information on the concentration of the gas is referred to as band pass filter 171a, 171b, 171c, ..., 171 hereinafter, which extracts only a specific frequency component. As it passes, it is separated into signals corresponding to each specific frequency component. At this time, the specific frequency extracted by the band pass filter 171 is a frequency 2f ₁ , 2f ₂ , 2f ₃ ,..., Which has twice the modulation frequency of each light source. Since the signals 152a, 152b, 152c, ... which are separated through the bandpass filter contain the respective gas concentration information to be measured, the respective signals constituting the mixed gas by measuring the magnitude of the separated signals are measured. The gas concentration can be measured accurately. In addition, since the modulated light signal 160 includes information on the center wavelength λ ₀ of the absorption spectrum or information on the wavelength variation range of the optical signal, that is, the absorption spectrum, the type of gas can be accurately known. have.

Hereinafter, an application example of an optical sensor for measuring a mixed gas according to an embodiment of the present invention will be described with reference to FIGS. 5A to 5C. 5a to 5c is an application example of the optical sensor for measuring the mixed gas according to an embodiment of the present invention.

As shown in FIG. 5A, an optical sensor for measuring a mixed gas may be installed at a portion of the vehicle exhaust gas to analyze the concentration and type of the vehicle exhaust gas in real time. The light source unit 110 and the photodetector 180 may be disposed in the vehicle exhaust pipe 580 to analyze the concentration and type of the exhaust gas 582 of the vehicle through the above-described process.

In addition, as shown in Figure 5b, according to another embodiment of the present invention, it is possible to determine whether the air pollution by analyzing the gas in the vehicle interior 584 through the optical sensor for measuring the mixed gas. Since this method can measure the air pollution of a specific space as well as the vehicle interior 584, the optical sensor according to the present embodiment can be used to measure the air pollution of a space such as a room or office of a normal home.

In addition, as shown in Figure 5c, according to the optical sensor for measuring the mixed gas of the present invention can be applied to the remote gas detector 590 that can be moved since the remote detection is possible. The mixed gas such as the automobile exhaust gas 594 may be remotely analyzed through the process of analyzing the modulated light signal by irradiating the optical signal to the exhaust gas 594 of the vehicle itself from the light source unit 110 located outside.

Hereinafter, a mixed gas measuring method according to another exemplary embodiment of the present invention will be described with reference to FIG. 6. 6 is a control flowchart of a mixed gas measuring method according to another embodiment of the present invention. In the case of the mixed gas measurement method, since the same principle and the same operation process as the optical sensor for measuring the mixed gas have been described above, redundant description will be omitted and briefly described.

First, the optical signal is irradiated with the mixed gas to be measured (S610). The optical signal irradiated with the mixed gas is changed while passing through the mixed gas and output as a modulated light signal, and the concentration of each gas constituting the mixed gas is measured (S620). At this time, the step (S620) of measuring the concentration of each gas constituting the mixed gas through the modulated light signal may include three steps.

First, the modulated light signal changed through the mixed gas is converted into an electrical signal by the signal conversion unit as described above (S621). In this case, the modulated light signal has already been twice as high as the modulation frequency of the optical signal emitted from the initial light source. The electrical signal converted by the signal conversion unit is separated into a frequency having a magnitude twice that of each modulated light signal, that is, a modulation frequency of each light source, through a band pass filter capable of extracting a specific frequency band ( S622). Since the separated electrical signal includes information on the concentration and type of gas, the concentration and type of each gas constituting the mixed gas are measured through this (S623). At this time, it will be apparent to those skilled in the art that any one of the concentration and type of gas can be measured.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the appended claims. It will be understood that the invention may be varied and varied without departing from the scope of the invention.

1 is a conceptual diagram of an optical sensor for measuring a mixed gas according to an embodiment of the present invention.

Figure 2 is a table showing the optical absorption spectrum for each gas.

Figure 3 is a graph showing the change in wavelength according to the absorption rate and time of the light source according to the wavelength of the gas to be measured by the optical sensor for measuring the mixed gas of the present invention.

4 is a block diagram of an optical sensor for measuring a mixed gas according to an embodiment of the present invention.

5a to 5c is an exemplary view of the application of the optical sensor for measuring the mixed gas according to an embodiment of the present invention.

6 is a control flow chart of a mixed gas measuring method according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

110: light source

120: optical signal

140: mixed gas

160: modulated light signal

180: photodetector

Claims (10)

In the optical sensor for measuring the concentration for each gas constituting the mixed gas, A light source for irradiating the mixed gas with an optical signal having a wavelength varying in a wavelength range of an absorption spectrum of a gas to be measured; And It includes a light detector for measuring the concentration of each gas of the mixed gas through the modulated light signal through which the optical signal has changed the optical characteristics by passing the optical signal, The modulated light signal further includes information on a wavelength change range of the optical signal, and the light detector measures the type of the gas through the modulated light signal. The method of claim 1, The wavelength of the optical signal is An optical sensor for measuring a mixed gas, characterized by varying within the wavelength range at a rate of modulation frequency (f). The method of claim 2, To measure one gas constituting the mixed gas And a wavelength range of the absorption spectrum includes the plurality of light sources having the same value and having different modulation frequencies from each other. The method of claim 1, The light detector is A signal converter converting the modulated light signal into an electrical signal; And And a band pass filter for separating frequency components of the modulated light signal from the electrical signal. The method of claim 1, The minimum number of light sources Optical sensor for measuring the mixed gas, characterized in that the same as the number of types of gas to be measured. delete In the method for measuring the concentration for each gas constituting the mixed gas, Irradiating an optical signal having a wavelength varying in a wavelength range of an absorption spectrum of a gas to be measured with the mixed gas; And And measuring the concentration of each gas of the mixed gas through the modulated light signal in which the optical signal is changed through the mixed gas and the optical characteristic thereof is changed. The modulated light signal further includes information on a wavelength variation range of the optical signal, and the light detector measures the type of the gas through the modulated light signal. The method of claim 7, wherein Measuring the concentration for each gas through the modulated light signal Converting the modulated light signal into an electrical signal; And Mixed gas measurement method comprising the step of measuring the concentration of each gas through the electrical signal. The method of claim 8, Before measuring the concentration of the gas by means of the electrical signal And separating the electrical signal through a band pass filter for extracting only frequency components of the modulated light signal. delete

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