KR20090004271A - Optical gas sensors - Google Patents

Abstract

An optical gas sensors is provided to make manufacturing process easy and elongate path by constituting sides with a flat mirror and embodying an optical chamber in a polygonal structure. An optical gas sensor(300) comprises an optical chamber(310) consisting of a polygon constituted with a top, a bottom, and sides; a light source transmitting a light toward sample gas; a plurality of first mirrors(320) reflecting the light, attached onto the side of the optical chamber; a filter filtering light of wave band similar to the wavelength of gas to be detected; and a light receiving element measuring intensity of light transmitted through the filter.

Description

Optical gas sensors

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical gas sensor, and more particularly, to an optical gas sensor by a non-dispersive infrared method (NDIR), in which a side of an optical chamber made of a polygon is composed of a plurality of reflectors. It's about structure.

There are two ways to measure the gas concentration. One is NDIR, and the other is disclosed, for example, in "A carbon dioxide gas sensor based on solid electrolyte for air quality control", Sensors and Actuators B, vol. 66, pp. 56-58, 2000 by K. Kaneyasu et al. Solid electrolyte such as.

While solid electrolyte sensors are less expensive than NDIR sensors, NDIR sensors are more advantageous in terms of long term stability, high accuracy, low power consumption, and the like. NDIR sensors also have good selectivity and sensitivity because they use the physical sensing principle that the target gas absorbs infrared radiation at specific wavelengths.

The optical characteristics of the NDIR sensor are as follows.

In general, light is reduced or increased in light intensity by diffraction, reflection, refraction and absorption on the optical path. In the case of the NDIR sensor, as the incident light passes through the light path, the light intensity is absorbed by the gas on the light path and the initial light intensity is reduced.

At this time, when the gas concentration J on the optical path is uniformly distributed, isotropic, and infrared light passes through the optical path L, the final light intensity I is the gas absorption coefficient k, This is explained by Beer-Lambert's law, which is a function of the initial light intensity I _{0 that} is detected by the IR detector when there is no gas on the optical path L and the optical path.

Beer-Lambert's law is expressed by Equation 1, and when the initial light intensity (I _O ) and the absorption coefficient (k) of the gas to be measured are constant, the final light intensity (I) is the gas concentration (J) on the optical path. And a function of the optical path (L). When there is no gas to be measured in Equation 1, that is, when J = 0, the final light intensity is equal to the initial light intensity.

Therefore, in the case where there is no gas to be measured and the gas concentration is J, the light intensity difference is as shown in equation (2).

However, since a general infrared sensor shows a small voltage proportional to the light intensity as its output, the output of the sensor according to the presence or absence of gas is expressed by Equation 3 below.

(Where α is proportional constant)

In this case, in order to manufacture an optical gas sensor having a wide range of measurement at low concentration and high concentration, first, an optical chamber having a large optical path L is formed, or second, a lower limit light intensity capable of detecting infrared rays is small. An infrared sensor is used. Third, an infrared sensor having a large saturated light intensity but slightly smaller than the initial light intensity (I ₀ ) emitted from the infrared light source should be used.

However, in the case of various infrared detection sensors currently provided on the market (Thermopile IR sensor or Passive IR sensor), it is difficult to satisfy all of the above, and there is a need for a method of forming an optical chamber with a large optical path.

1 is a view showing the structure of a conventional gas sensor by the NDIR, Figure 2 is a view showing the absorption spectrum (absorption spectrum) of various gases in the infrared region.

Referring to FIG. 1, the optical gas sensor 100 by NDIR includes an optical chamber 110, an infrared light source (IR source) 120, an infrared filter (IR filter) 130, and an infrared light detector (IR detector) ( 140). In the gas concentration detection principle, infrared light is emitted by the infrared light source 120, and the infrared light receiving element 140 measures the intensity of the infrared light.

In this case, the gas introduced into the optical chamber 110 absorbs infrared rays at a specific wavelength for each gas, as shown in FIG. 2, thereby decreasing the intensity of the infrared rays. In front of the infrared light receiving element 140 is inserted an infrared filter 130 that can transmit only the wavelength of the absorption spectrum band of the gas to be detected. Since the decrease of the intensity of the infrared rays is proportional to the gas concentration, the gas concentration can be detected by comparing the intensity of the infrared rays in the absence of gas with the intensity of the infrared rays in the presence of gas.

The range of gas concentrations to be detected by the NDIR optical gas sensor ranges from parts per million to as low as parts per billion (ppb). Since the absorption of is insignificant, the reduction of infrared rays is insignificant. Therefore, the optical path must be lengthened to increase the sensitivity of the sensor. That is, to reduce the infrared intensity at a low gas concentration, it is necessary to lengthen the optical chamber length (light path). Most conventional gas sensors secure a long optical path by lengthening the optical chamber in a straight line.

In order to secure a long optical path in the conventional optical gas sensor, when the optical chamber 110 is configured to have a long shape as shown in FIG. 1, the size of the sensor element is extremely long, and thus it is difficult to miniaturize the element. In addition, since the infrared rays generated from the light source do not have an appropriate optical system, the infrared rays spread widely, so that the intensity of the infrared rays reaching the infrared light receiving element is lowered and the light efficiency is lowered.

Accordingly, an object of the present invention is to provide an optical gas sensor having a long optical path and a high light efficiency in a narrow area by manufacturing a polygonal structure in which the side of the optical chamber reflects infrared rays in order to solve the conventional problems. have.

The object of the present invention comprises an optical chamber made of a polygon consisting of an upper surface, a lower surface and a side and for receiving a gas; A light source for projecting light toward the sample gas; A plurality of first reflectors attached to a side of the optical chamber and for reflecting the light; A filter for filtering light in a wavelength band similar to the wavelength of the gas to be detected; And it is achieved by an optical gas sensor comprising a light receiving element for measuring the intensity of light transmitted through the filter.

Preferably, the first reflecting mirror is a planar reflecting mirror having the same incident angle and reflecting angle.

Preferably, the optical gas sensor further comprises a second reflector made of a concave reflector for converting light generated from the light source into parallel light.

Preferably, the first reflector is a concave reflector whose horizontal cut surface is curved and is composed of a third or fourth reflector having different curvatures.

Preferably, the top or bottom surface of the optical chamber is a planar reflector.

Preferably, the path length of the infrared light is an optical gas sensor that is proportional to the number of sides of the polygon.

Therefore, the optical gas sensor of the present invention has an advantage that the manufacturing process is easy and the path can be lengthened by implementing the optical chamber in a polygonal structure and constituting the side with a planar reflector.

In addition, the present invention has the effect of reducing the loss of light by condensing the light to one focus in the vertical and horizontal directions by configuring the side of the optical chamber with a concave reflector.

In addition, the present invention has the effect of efficiently reflecting light by implementing different curvature of the concave reflectors constituting the side of the optical chamber.

In addition, the present invention has an easy effect in manufacturing the optical chamber by making the vertical cross section of the concave reflector constituting the side of the optical chamber in the shape of a fan.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only one of the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

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

Figure 3a is a three-dimensional perspective view of the optical gas sensor 300 according to the first embodiment of the present invention, Figure 3b is a view showing the reflection path of the infrared rays according to the first embodiment of the present invention, Figure 3c A cross-sectional view of the optical gas sensor 300 according to the first embodiment.

3C is a cross-sectional view of the optical gas sensor 300 illustrated in FIG. 3B taken along a dotted line of A-A`.

3A to 3C, the optical gas sensor 300 includes an optical chamber 310, a first reflector 320, a second reflector 330, an infrared light source 340, an infrared filter 350, and an infrared light receiving unit. Element 360 or the like.

The optical chamber 310 is formed of a polygon containing a gas, the upper surface, the lower surface and a plurality of side surfaces, and a plurality of first reflecting mirrors 320 are installed on the side surfaces.

The optical chamber 310 according to the first embodiment of the present invention is composed of a polygon having twelve sides and a first reflector 320 is attached to ten of twelve sides, and an infrared light source 340 and an infrared light receiving unit. The two surfaces where the element 360 is shaped are open. The number of sides of the polygon is a factor that determines the length of the infrared path.

Therefore, the optical chamber 310 may be formed in any polygonal shape in which infrared reflection may occur several times, and the polygons having the twelve sides are just one embodiment.

The first reflector 320 is composed of a plane reflector and has the same angle of incidence and reflection. Therefore, the first reflector 320 reflects the infrared light generated by the infrared light source 340 and becomes parallel light through the second reflector 330.

The second reflector 330 is composed of a concave reflector and reflects the infrared light generated by the infrared light source 340 to be parallel light. In addition, the light is reflected by the first reflector 320 in the optical chamber 310 to condense infrared rays incident to the infrared light receiving element 360.

The infrared light source 340 is composed of an infrared light bulb which is installed on the upper or lower surface of the optical chamber 310 and generates an infrared ray having a wavelength longer than visible light. The infrared light is used to measure the concentration of gas in the optical chamber 310. Used.

The infrared filter 350 has a characteristic of transmitting only a wavelength of infrared rays similar to the wavelength of the absorption spectrum band of the gas.

The infrared light receiving device 360 measures the intensity of the infrared light transmitted through the infrared filter 350.

Looking at the operation of the optical gas sensor of the first embodiment of the present invention, first, infrared light is generated from the infrared light source 340. The infrared light is not parallel light but is reflected by the second reflector 330 which is a concave reflector to become parallel light.

The infrared light, which has become parallel light, is subjected to a plurality of reflection processes by a plurality of first reflectors 320 which are planar reflectors provided in the optical chamber 310 having a polygonal shape. In the process, a collision with a gas in the optical chamber 310 occurs, where some wavelength bands of infrared rays having the same wavelength as the absorption spectrum of the gas are absorbed by the gas, thereby decreasing its intensity.

The infrared rays reflected by the first reflector 320 are incident to the second reflector 330 on the infrared filter 350 and the infrared light receiving element 360. Since the second reflector 330 is configured as a concave reflector, the second reflector 330 focuses the incident infrared rays. The collected infrared light is filtered by the infrared filter 350 and then its intensity is measured by the infrared light receiving device 360.

The intensity of the infrared rays is compared with the intensity of the infrared rays measured by the infrared light receiving element 360 when there is no gas in the optical chamber 310 to determine the degree of attenuation. Since the attenuation degree of the infrared intensity is proportional to the gas concentration, the gas concentration can be detected by comparing the intensity of the infrared rays in the absence of the gas and the intensity of the infrared rays in the presence of the gas.

4 is a diagram showing an infrared ray propagation path of the optical gas sensor 400 according to the first embodiment of the present invention.

The propagation path of the infrared rays shown in FIG. 4 is implemented through simulation, and the infrared rays generated from the infrared light source (not shown) become parallel light through the second reflector 430 which is a concave reflector, It may be confirmed that the light is reflected by the first reflector 420, which is a planar reflector forming the side surface of the optical chamber 410, and finally reaches an infrared light receiving element (not shown).

5A is a diagram illustrating an infrared ray propagation path of the optical gas sensor 500 according to the second exemplary embodiment of the present invention.

The optical gas sensor 500 according to the second embodiment of the present invention shown in FIG. 5A is only the first reflecting mirror 320 of the optical gas sensor 300 according to the first embodiment of the present invention shown in FIGS. 3A to 3C. The other configuration is the same.

That is, the optical chamber 510, the second reflector 520, the infrared light source (not shown), the infrared filter (not shown), and the infrared light receiving element (not shown) of the optical gas sensor 500 of FIG. 5A are illustrated in FIGS. 3C is the same as the optical chamber 310, the second reflector 330, the infrared light source 340, the infrared filter 350, and the infrared light receiving element 360. However, the optical gas sensor 500 of FIG. 5A further includes concave reflectors having different curvatures.

Although the infrared light generated from the infrared light source 340 according to the first embodiment becomes parallel light by the second reflector 330 which is a concave reflector, the infrared light is reflected by the first reflector 320 because it is difficult to become perfectly parallel light. As it progresses, the infrared rays gradually spread. Thus, the infrared rays may be attenuated considerably until they reach the infrared light receiving element 360.

For this reason, the side of the optical chamber 510 of FIG. 5A is composed of third or fourth reflectors 530, 540 which are concave reflectors.

FIG. 5B is a view showing an infrared ray propagation path of an optical gas sensor composed of reflectors having the same curvature according to the second embodiment of the present invention.

FIG. 5B is a result of a simulation performed when the curvatures of the third and fourth reflectors 530 and 540 shown in FIG. 5A are the same. Referring to FIG. 5B, since the side reflector reflects the initial parallel light, the gathering and spreading of the light cannot maintain a constant pattern.

Accordingly, the third reflector 530 and the fourth reflector 540 are concave reflectors having horizontal curved surfaces and different curvatures. Since the curvature is inversely proportional to the radius, the curvature of the third reflector 530 is designed to be smaller than the curvature of the fourth reflector 540. In addition, when the radius of the third reflector 530 is R _2, and the radius of the fourth reflector 540 is R ₁ , the above formula of R ₂ > R ₁ is satisfied.

The third reflector 530 is installed at the side of the optical chamber 510 that first reflects the parallel light infrared rays generated by the infrared reflector 520 by the infrared light generated from the infrared light source (not shown), and the parallel light It reflects infrared light and converts it into infrared light that passes through horizontal focus.

In addition, the third reflector 530 is also provided on the side of the optical chamber 510 for the last reflection directed to the second reflector 520 installed in the infrared light receiving element (not shown). The third reflector 530 reflects the parallel light infrared rays and converts the infrared rays passing through one focal point in the horizontal direction, but also converts the infrared rays passing through the horizontal focus rays into the parallel light infrared rays.

The fourth reflector 540 reflects the infrared rays spread beyond the horizontal focus, and the reflected infrared rays pass through the horizontal focus again. Accordingly, the fourth reflector 540 performs a plurality of reflection processes by collecting and spreading the horizontal pattern in a constant pattern.

That is, referring to the propagation process of the infrared rays in the optical gas sensor according to the second embodiment of the present invention shown in FIG. 5A, first, when the infrared rays are generated from the infrared light source (not shown), the infrared rays are reflected by the second reflector 520. It becomes parallel light. The infrared rays which become parallel light are directed to the third reflector 530, and the parallel light infrared rays reflected by the third reflector 530 pass through one focal point in the horizontal direction by collecting and spreading.

In addition, the spread infrared light is directed to the fourth reflector 540, and the fourth reflector 540 corresponding to each other performs a reflection process in which a gathering and spreading are a constant pattern. In the above process, the infrared rays have a lot of opportunities to be absorbed by the gas because the movement path in the optical chamber 510 becomes longer and spreads.

The infrared rays that have undergone several reflection processes by the fourth reflector 540 are directed to the third reflector 530, and the infrared rays reflected by the third reflector 530 are converted into parallel light. The infrared light, which is parallel light, is directed to the second reflector 520 and enters an infrared light receiving element (not shown) through an infrared filter (not shown), and the intensity thereof is measured.

6A is a vertical cross-sectional view of a reflector in the optical gas sensor according to the third embodiment of the present invention, and FIG. 6B is a view showing a propagation path of infrared rays according to the third embodiment of the present invention.

The third and fourth reflectors 630 and 640 illustrated in FIG. 6A may include the third and fourth reflectors 530, which form side surfaces of the optical chamber 510 according to the second embodiment of the present invention illustrated in FIG. 5A. 540 is a modified form.

That is, the optical gas sensor according to the third embodiment is the same as the component shown in FIG. 5A except for the third and fourth reflectors 630 and 640.

Although the propagation of the infrared rays shown in FIG. 5A decreases in the left and right directions while reflecting repeatedly, the infrared rays spread in the vertical direction cannot be reduced.

Accordingly, the third and fourth reflectors 630 and 640 according to the third embodiment are concave reflectors having horizontal and vertical cross-sections both curved and different curvatures.

The third reflector 630 reflects parallel light infrared rays and converts them into infrared rays passing through one focal point in the vertical and horizontal directions.

In addition, the third reflector 630 reflects infrared rays passing through one focal point in the vertical and horizontal directions and converts the infrared rays into parallel light infrared rays.

The fourth reflector 640 reflects infrared rays passing through one focus in the vertical and horizontal directions to pass through the other focus.

The propagation path of the infrared rays shown in FIG. 6B is implemented through simulation, and since the infrared rays pass through one focal point in the vertical and horizontal directions, the spread of the infrared rays in the vertical, horizontal, and right directions can be reduced.

7A is a vertical cross-sectional view of a reflector in the optical gas sensor according to the fourth embodiment of the present invention, and FIG. 7B is a view showing a propagation path of infrared rays according to the fourth embodiment of the present invention.

The third and fourth reflectors 730 and 740 illustrated in FIG. 7A may include the third and fourth reflectors 530 forming side surfaces of the optical chamber 510 according to the second embodiment of the present invention illustrated in FIG. 5A. 540 is a modified form.

That is, the optical gas sensor according to the fourth embodiment is the same as the component shown in FIG. 5A except for the optical chamber 710 and the third and fourth reflectors 730 and 740.

As shown in FIG. 7A, the third and fourth reflectors 730 and 740 are concave reflectors having vertical curvatures and having different curvatures.

In the optical chamber 710 according to the fourth embodiment of the present invention, the lower surface 720 is a planar reflector.

The third reflector 730 reflects the parallel light infrared rays and converts them into infrared rays passing through one focal point. In this case, the focus is formed on the lower surface 720 of the optical chamber 710, and the infrared rays are reflected by the lower surface 720.

In addition, the third reflector 730 reflects infrared rays passing through one focal point in the vertical and horizontal directions formed on the lower surface 720 and converts the infrared rays into parallel light infrared rays.

The fourth reflector 740 reflects infrared rays passing through one focus in the vertical and horizontal directions formed on the lower surface 720 to pass through the other focus of the lower surface 720.

The propagation path of the infrared rays shown in FIG. 7B is implemented through simulation, and since the infrared rays pass through a single focal point formed on the lower surface 720 formed of a planar reflector, the spread of infrared rays may be reduced in the up, down, left, and right directions.

If the shapes of the third and fourth reflectors 730 and 740 shown in FIGS. 7A and 7B are inverted, the upper surface 750 may be configured as a planar reflector.

In addition, the optical chamber 710 illustrated in FIGS. 7A and 7B facilitates an injection process during manufacturing.

The side of the optical chamber shown in FIGS. 5A-7B is constituted by respective reflectors.

Although the present invention has been shown and described with reference to the preferred embodiments as described above, it is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Various modifications and variations are possible without departing from the spirit of the present invention and equivalents of the claims to be described below.

The present invention can be used for an apparatus having the purpose of detecting gaseous pollutants in the atmosphere and harmful gases in the room by using an optical gas sensor.

1 is a view showing the structure of a conventional gas sensor by the NDIR,

2 is a diagram illustrating absorption spectra of various gases in an infrared region;

3A is a three-dimensional perspective view of an optical gas sensor according to a first embodiment of the present invention;

3B is a view showing a reflection path of infrared rays according to the first embodiment of the present invention;

3C is a cross-sectional view of an optical gas sensor according to a first embodiment of the present invention;

4 is a view showing a propagation path of infrared rays according to the first embodiment of the present invention;

5A is a view showing an infrared ray propagation path of an optical gas sensor according to a second embodiment of the present invention;

5B is a view showing an infrared ray propagation path of an optical gas sensor composed of reflectors having the same curvature according to a second embodiment of the present invention;

6A is a vertical sectional view of a reflector in an optical gas sensor according to a third embodiment of the present invention;

6B is a view showing a propagation path of infrared rays according to a third embodiment of the present invention;

7A is a vertical sectional view of a reflector in an optical gas sensor according to a fourth embodiment of the present invention;

7B is a view showing a propagation path of infrared rays according to the fourth embodiment of the present invention.

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

300: optical gas sensor 310: optical chamber

320: first reflecting mirror 330: second reflecting mirror

340: infrared light source 350: infrared filter

360: infrared light receiving element

Claims (9)

An optical chamber consisting of a polygon consisting of an upper surface, a lower surface and a side surface, for receiving gas; A light source for projecting light toward the sample gas; A plurality of first reflectors attached to a side of the optical chamber and for reflecting the light; A filter for filtering light in a wavelength band similar to the wavelength of the gas to be detected; And Light receiving element for measuring the intensity of light passing through the filter Optical gas sensor comprising a. The method of claim 1, And the first reflecting mirror is a planar reflecting mirror having the same incident angle and reflecting angle. The method of claim 1, A second reflector made of a concave reflector for converting light generated from the light source into parallel light Optical gas sensor further comprising. The method of claim 3, wherein The light source is an optical gas sensor is installed on the upper or lower surface of the optical chamber. The method of claim 1, The first reflector is a concave reflector whose horizontal cutting plane is curved, and is composed of a third or fourth reflector having different curvatures. The method of claim 5, The third or fourth reflector is an optical gas sensor having a vertical cut surface curved surface. The method of claim 1, An optical gas sensor, wherein the upper or lower surface of the optical chamber is a planar reflector. The method of claim 7, wherein The first reflector is an optical gas sensor consisting of a third or fourth reflecting mirror having a vertical cut surface is a concave reflector having a fan shape and having different curvatures and focusing on the upper or lower surface. The method of claim 1, And the path length of the light is proportional to the number of sides of the polygon.

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