KR20090012952A - Non-dispersive infra-red absorption (ndir) type gas sensor with collimated light source - Google Patents

Abstract

A non-dispersive infrared gas sensor having a parallel light source is provided to improve the sensitivity of the sensor and reduce an optical path required to achieve the same sensitivity. A non-dispersive infrared gas sensor includes an infrared light source(300), an optical cavity(100) having a geometrically arranged reflecting surface and forming an extended optical path according to multi-reflection, and an optical sensor unit(500) which is located at the termination of the optical path and measures the intensity of infrared rays of a specific wavelength, which are partially absorbed by specific gas on the optical path and then arrived at the optical sensor unit.

Description

Non-dispersive Infra-Red Absorption (NDIR) Type Gas Sensor with Collimated Light Source}

1A schematically illustrates a planar configuration of a non-dispersive infrared gas sensor in accordance with a preferred embodiment of the present invention.

FIG. 1B schematically illustrates the light path inside the light cavity in the gas sensor shown in FIG. 1A.

2 is a schematic diagram showing a more detailed configuration of a light source unit 300 according to an embodiment of the present invention.

Figure 3 shows the external and internal light path of another embodiment of the light cavity to which the light source unit according to the present invention can be applied.

4A and 4B schematically show the geometry of two conventional light sources.

FIG. 5A shows the dimension marker of the vertical cylindrical bulb surface, and FIG. 5B shows the dimension marker with its reflector.

FIG. 5C shows the dimension marker of the hemispherical bulb, and FIG. 5D shows the dimension marker with its reflector.

6A shows specific dimensions of a light source according to one embodiment of the invention.

6B shows specific dimensions of a reflector designed for the vertical cylindrical surface of the light source according to one embodiment of the present invention.

6C shows specific dimensions of a reflector designed for the hemispherical surface of the light source according to one embodiment of the invention.

6D illustrates specific dimensions of the concave reflector in accordance with one embodiment of the present invention.

7A and 7B are simulation results of light distribution curves and light amounts of a light source unit in which a vertical cylindrical surface and a hemisphere are not specifically designed with conventional reflectors.

7C and 7D are simulation results of light distribution curves and light amounts of the same light source unit including the reflector according to the present invention.

8A shows the appearance of one light cavity known in the art.

FIG. 8B shows the light path of the light cavity shown in FIG. 8A.

9A, 9B, and 9C show the results of simulating the intensity of light incident on each sensor unit in the sensors according to the prior art, the first embodiment, and the second embodiment using optical ray tracing software. do.

10A and 10B are actual photographs of actual gas sensors according to the first and second embodiments, respectively.

11A and 11B are plots of changes in detection voltage over time of the sensor according to the prior art and the sensor according to the first embodiment, respectively.

11C and 11D are plots of detection voltages according to carbon dioxide concentrations of the sensor according to the prior art and the sensor according to the first embodiment, respectively.

The present invention relates to a gas sensor, and more particularly to a non-dispersive infrared absorption type (NDIR) gas sensor.

NDIR gas sensor is a gas sensor that detects the concentration of a particular gas by using the nature of the absorption spectrum of the gas molecules in the infrared region. This type of gas sensor is more selective, more reliable, and more durable and stable than electrochemical or semiconductor. Because of these advantages, the NDIR method is widely used for the detection and precise measurement of harmful gases despite the high price. In Korea, in particular, the law stipulates the measurement method in the NDIR method in the process of mandatory fine dust concentration measurement in the classroom, mandatory vehicle refrigerant sensor, and mandatory installation of exhaust gas self-diagnosis device (OBD).

The NDIR method utilizes gases having specific absorption spectra for infrared light. The amount of infrared light transmitted after the infrared light incident on the light cavity is absorbed by the gaseous substance is governed by the Ber-Lambert law.

  I (L) = Io * exp (-ACL),

Where I is the amount of transmitted light, Io is the amount of incident light, A is the intrinsic constant (absorption rate of the measured gas), C is the concentration of the component, and L is the length of the light path (transmission length).

The gas sensor of NDIR type is composed of light source part and optical cavity through which light passes, and sensor part that senses it. Determined by the length of the furnace. The commercialized NDIR gas sensor increases the sensitivity by lengthening the optical path as much as possible in the optical cavity of the same size by geometrically arranging a plurality of reflectors inside the optical cavity. In general, an important issue for NDIR gas sensors is their sensitivity and sensor size. In order to improve the sensitivity of the sensor, the optical length must be increased, which means that the size of the sensor is increased. Therefore, in the existing NDIR gas sensor design, the approach is focused on ensuring the longest optical length within the same size by designing the reflector geometrically optimally. However, in order to satisfy the attempt to increase the sensitivity of the sensor and the miniaturization of the sensor at the same time, there is a limit in the light cavity design alone.

In the NDIR type gas sensor, the incident light is generally radiated forward from the light source. However, according to the Ber-Lambert law, the sensitivity of the sensor depends on the spectral components absorbed by the gas in the optical path, and for effective optical response, the light incident from the light source is preferably parallel light. Conventional NDIR sensors do not seem to pay much attention to this. In particular, in the NDIR-type gas sensor, the light source has a shape in which a plurality of basic solids are concatenated rather than having a single basic three-dimensional geometry. Nevertheless, no research or product focuses on keeping the light emitted from these light sources as parallel light inside the light cavity.

The present invention is to solve such a problem, it is an object of the present invention to provide a NDIR-type gas sensor with a small and improved sensitivity.

A non-dispersion infrared gas sensor according to an aspect of the present invention for achieving the above object is a light source formed by the combination of a plurality of geometric three-dimensional light source, and the light emitted from each surface of the plurality of geometric three-dimensional surface constituting the light source It characterized in that it comprises a concave reflector formed by the multi-stage junction of a plurality of concave reflector three-dimensional surface to form parallel light with respect to each other.

According to this aspect of the present invention, the non-dispersion infrared gas sensor according to the present invention improves the actual light intensity on the optical path while miniaturizing the sensor while simultaneously improving the sensitivity.

In the non-dispersion infrared gas sensor according to another aspect of the present invention, the light path of the light intensity detected by the light sensor unit is maintained in the range of 50% or more and less than 100% of the light intensity emitted from the infrared light source unit at least 5 times or more. Characterized in that it is formed to pass through the reflection.

According to this additional aspect, the non-dispersion infrared gas sensor according to the present invention may maintain the intensity of the light reaching the optical sensor part even by increasing the optical path due to the improved light intensity, thereby further improving the sensitivity.

The non-dispersion infrared gas sensor according to another aspect of the present invention is characterized in that the optical length is formed to undergo only three reflections or less while maintaining the sensitivity at the existing sensor sensitivity level.

According to this aspect, the non-dispersion infrared gas sensor according to the present invention can be further downsized while maintaining the sensitivity.

The foregoing and further aspects of the present invention will become apparent from the following examples. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily understand and reproduce.

1 schematically shows a planar configuration of a non-dispersive infrared gas sensor according to a preferred embodiment of the present invention. As shown, the non-dispersion infrared gas sensor according to an embodiment has an infrared light source unit 300 and a reflective surface that is geometrically arranged to continuously reflect the light incident from the infrared light source unit 300 to the multiple reflections The optical cavity 100 including an air hole through which an external gas enters and exits, and is positioned at an end of the optical path of the optical cavity 100 so as to extend a specific optical path on the optical path; It includes a light sensor unit 500 for measuring the amount of infrared light in a particular wavelength band reaches after being absorbed by a portion.

The optical sensor unit 500 is a conventional optical sensor used for the gas sensor of the NDIR type.

2 is a schematic diagram showing a more detailed configuration of a light source unit 300 according to an embodiment of the present invention. As shown, the light source unit 300 according to the embodiment is a light source 310 formed by the combination of a plurality of geometric three-dimensional surfaces (311,313), and the light emitted from the surface of the plurality of geometric three-dimensional surface constituting the light source It characterized in that it comprises a concave reflector portion 330 formed by the multi-stage bonding of a plurality of concave reflector three-dimensional surfaces (331,333) for forming parallel light with respect to.

More specifically, in the light source unit 300 according to an embodiment, the light source 310 is a joining shape of the vertical cylindrical surface 311 and the hemispherical surface 313, the concave reflector 330 is a vertical cylindrical surface of the light source portion A parabolic surface 331 intersecting at the end of 311 and a hemispherical surface 333 joined to the parabolic surface 331 while being opposite to the hemispherical surface 313 of the light source.

Hereinafter, the configuration of the light source unit 300 will be described in more detail. In general, simple concave reflectors are not possible to make light emitted from various light sources into parallel light. The present invention models a light source as a combination of a plurality of geometric solid surfaces, and proposes a multi-stage reflector design method for this.

Generally, the light source surface can be approximated by a combination of a cylindrical surface, a hemispherical surface, a spherical surface, and an elliptic sphere. For example, the light source of FIG. 4A may be viewed as a combination of a vertical cylindrical surface and a hemisphere, and the light source of FIG. 4B may be viewed as a combination of a vertical cylindrical surface and an ellipsoidal surface. The light source is divided into a plurality of geometric three-dimensional faces, and a corresponding concave reflector three-dimensional face is designed to form parallel light respectively for the light emitted from the surface of each geometric three-dimensional face. In this embodiment, the light source adopts the light source shown in Fig. 4A, which is a structure used in most NDIR gas sensors. A reflector is obtained for each geometric three-dimensional surface constituting the light source shown in FIG. 4A.

(1) vertical cylindrical bulb

Figure 5a shows a method for obtaining the reflector of the vertical cylindrical bulb. A reflector for making parallel rays of light emitted from a vertical cylindrical bulb surface having a radius r and a height H is designed as a parabolic surface intersecting at the end of the cylindrical surface as shown in FIG. 5B. If Q is the point where the extension line of the upper surface of the vertical cylinder meets the reflector (parabola), and Q 'is the point where the bottom side meets the reflector (parabola),

The equation for the reflector is from the parabolic general formula

Becomes

(2) hemispherical bulb

5C shows a hemispherical bulb surface with radius r. In order for the light beam emitted from this bulb surface to become parallel light, the reflector which has a hemispherical surface of radius P is designed like FIG. 5D. If the center of the hemispherical bulb is O ', the center of the reflector is O, and the point where the extension line of the bulb diameter meets the reflector is Q',

The equation for the reflector is

Becomes

Hereinafter, specific embodiments will be described by applying the multi-stage reflector design method described above. 6A shows specific dimensions of an infrared light source in accordance with one preferred embodiment of the present invention. The light source has a shape in which a hemispherical surface having a radius r = 1.5 mm and a height H = 6.3 mm and a vertical cylindrical surface whose inner diameter is equal to the diameter of the upper hemisphere surface are joined. First, we design the reflector structure by dividing the shape of the bulb into two parts, a vertical cylinder and a hemisphere, and then optimize the reflecting mirror to maximize the parallel light by combining the two reflecting surfaces.

<Reflector Design for Vertical Cylinder of Light Source>

From equation (1) R = 2.5 mm

Equation for reflector from equations (2) and (3):

(1.5 ≤|x|≤ 2.5) (9)

(1.5 ≤ | x | ≤ 2.5) (9)

<Reflector Design for Hemispherical Surface of Light Source>

From equation (4) P = 3.5 mm

From equation (5) R = 2.25 mm

B = 3 mm from equation (6)

Equation for reflector from equations (7) and (8):

(2.25 ≤|x|≤ 3.75) (10)

(2.25 ≤ | x | ≤ 3.75) (10)

FIG. 6D shows the complete concave reflector for the light source of FIG. 6A optimized to obtain a maximum parallel light by joining the reflector corresponding to the separately designed vertical cylindrical surface and the reflector corresponding to the hemisphere.

7A and 7B are simulation results of light distribution curves and light amounts of a light source unit in which a vertical cylindrical surface and a hemisphere are not specifically designed with conventional reflectors. The light irradiation range was limited to 30 ° controllable angle in the light cavity. 7C and 7D are simulation results of light distribution curves and light amounts of the same light source unit including the reflector according to the present invention. Here, the light distribution curve is a curve representing the distribution of light intensity emitted along the direction of the light source.

 While the light distribution curve of the existing light source part is biased in one direction, in the case of the embodiment of the present invention, it can be seen that it is uniformly irradiated to the center part. In addition, when the output light from the light source is 100, the amount of light emitted within the three-dimensional angle of 30 degrees is found to reach 49 in the exemplary embodiment of the present invention, whereas the conventional light source unit is only 23.

8A shows the appearance of one light cavity known in the art. 8B shows the light path of this light cavity. The illustrated light cavity has a structure in which four reflective surfaces are superposed in order to maximize the light path while miniaturizing the size. However, due to the limitation of the light intensity of the light source part, the light cavity no longer detects the light intensity incident on the sensor part when the light path is longer, and thus requires an infrared sensor with high sensitivity. In the illustrated embodiment, the length of the light cavity is about 20 cm.

Hereinafter, a first embodiment of an optical cavity for providing a practical non-dispersion infrared gas sensor employing the above-described light source unit will be described. In the light cavity according to the first embodiment shown in FIG. 1A, the length of the light cavity is about 20 cm, which is the same as the conventional embodiment, but the light intensity detected by the optical sensor unit is greater than or equal to 50% of the light intensity emitted from the infrared light source unit. The optical path is designed to reflect at least five times, while remaining in the range of less than%. That is, since the light output of the light source according to the present invention is much higher than the conventional light source, it is possible to secure a sufficient amount of light detected by the optical sensor even if the light path is longer than the conventional. Therefore, even if the light path is the same or longer as in the prior art, the sensitivity of the sensor can be greatly increased according to the above-described Berer-Lambert's law.

As shown, the light cavity 100 according to the embodiment is a light source fixing portion 120 is fixed to the light source unit 300,

Located on the left side of the light source fixing unit 120, the left rear reflector 130 for reflecting the light incident from the light source to the rear left and right of the light cavity, and the left rear reflector 130 is reflected to the front left A left reflecting surface structure composed of a left front reflector 170 reflecting the reflected light to the right and the rear of the light cavity, and a left reflector 150 reflecting the light incident to the center of the light cavity to the right center of the light cavity;

Located on the right side of the light source fixing part 120, the right rear reflector 110 for reflecting the light reflected from the left front reflector 170 to the right front of the light cavity, and the right rear reflector 110 A right reflecting surface structure including a right front reflector 190 for reflecting light toward the left reflector;

It is connected to the right side of the right reflective surface structure, and includes a sensor fixing part 140 to which the optical sensor unit 500 is fixed.

The light path of the illustrated embodiment is shown in FIG. 1B. Although the overall size of the sensor and the length of the optical path are similar to existing products, the optical path is designed to be incident perpendicularly to the light receiving surface of the sensor by adding a path through which light crosses in the long axis direction. This embodiment is an example for showing how the sensitivity is improved when the optical path is the same as the existing product.

Figure 3a shows the appearance of another embodiment of the light cavity to which the light source unit according to the present invention can be applied. In the illustrated embodiment, the light cavity has a light path of only 9 cm. FIG. 3B shows the light path of the light cavity shown in FIG. 3A. As shown, the light cavity according to the present embodiment is formed so that the light length passes only three reflections while maintaining the sensor sensitivity in the same range as the existing sensor. Accordingly, the light cavity can be further downsized while maintaining the sensor sensitivity.

In the illustrated embodiment, the light cavity is located on the light source fixing part 740 to which the light source part 300 is fixed, and on the opposite surface of the light source fixing part 740, and reflects the incident light to the side. A slope 710, a second reflection surface 730 positioned on an opposite surface of the first reflection surface 710, reflecting incident light to one side of the first reflection surface, and the second reflection surface 730. And a third reflection surface 750 positioned at the opposite surface of the second reflection surface and reflecting the incident light to one side of the second reflection surface 730, and the light reflected from the third reflection surface 750 is incident, and The optical sensor unit 500 is composed of a sensor fixing part 740 is fixed.

9A, 9B and 9C show the sensor according to the prior art (Figs. 8A and 8B) using optical ray tracing software, the sensor according to the first embodiment shown in Figs. 1A and 1B and Fig. 3, respectively. In the sensor according to the second embodiment, a result of simulating the intensity of light incident on each sensor unit is shown. In the sensor according to the prior art, the intensity of the light incident on the sensor unit is 29%, whereas it can be seen that the maximum 2 times increased to 39.4% in the first embodiment and 55% in the second embodiment.

FIG. 10A is a real photograph of a gas sensor according to the first embodiment shown in FIGS. 1A and 1B. FIG. 10B is a real photograph of a gas sensor actually manufactured according to the second embodiment of FIG. The actual gas sensor is designed to detect CO ² gas. 11A to 11D show that when the input light pulse is irradiated with a 20% duty at 450 mHz, the output change of the sensor according to the carbon dioxide concentration change of the sensor according to the first embodiment is compared with the gas sensor according to the prior art. It is. 11A and 11B are plots of changes in detection voltage over time of the sensor according to the prior art and the sensor according to the first embodiment, respectively. 11C and 11D are plots of detection voltages according to carbon dioxide concentrations of the sensor according to the prior art and the sensor according to the first embodiment, respectively.

From the measurement result, it can be seen that the sensor output change in the change of carbon dioxide concentration 500-2000ppm was improved by about 3.6 times to 130 mV for the sensor according to the prior art and 474 mV for the sensor according to the first embodiment. In other words, the sensor sensitivity can not be expressed as a single value because it shows a non-linear characteristic, but the average sensitivity of the sensor of the comparative example according to the prior art is about 0.1 mV / ppm, while 0.3 mV / ppm in the first embodiment Sensitivity is shown. In particular, it can be seen that the sensitivity of the sensor using the optical cavity of the present invention in the low concentration region is much better.

12 is a curve showing light absorption characteristics of sensors according to the prior art, the first embodiment, and the second embodiment in a range of 0-2000 ppm of carbon dioxide concentration using a Berer-Lambert's Law. From this curve we see the following:

(1) When the optical path lengths are the same, the sensor sensitivity of the present invention is much superior and resistant to noise (comparison of Example 1 and conventional products).

(2) When the sensitivity is the same, the larger the output of the light cavity, the shorter the optical path can be, and the sensor can be miniaturized, and the intensity of light incident on the sensor is increased, which is more resistant to noise. ). That is, in the case of the second embodiment and the product according to the prior art, the shape of the curve is similar, but in the case of the second embodiment, the light intensity incident on the sensor is much higher on average.

(3) When the light paths are the same, the stronger the output of the light cavity is, the more advantageous it is for detecting low concentrations of carbon dioxide.

(4) When the output of light cavity is weak, if the light path is short, it is impossible to detect low concentration of carbon dioxide.

As described in detail above, the gas sensor according to the present invention condenses the output of the light source by parallel light by a concave reflector designed and manufactured according to the newly proposed design method, and is about twice as large as that of the conventional light cavity. About twice the light output is possible in the negative.

Accordingly, the gas sensor according to the present invention can improve the sensor sensitivity when using the light cavity of the same size.

In addition, the gas sensor according to the present invention can reduce the optical path required to achieve the same degree of sensitivity, it is possible to manufacture a more compact high-sensitivity gas sensor is much advantageous in terms of performance or price.

The present invention has been described with reference to the accompanying examples, but is not limited thereto, and encompasses many modifications that will be apparent to those skilled in the art. The appended claims are intended to cover such obvious variations.

Claims (6)

An infrared light source unit; An optical cavity having a geometrically arranged reflective surface for continuously reflecting light incident from the infrared light source unit to form an extended optical path by multiple reflections, and including air holes through which external gas enters and exits; and; In the non-dispersion infrared gas sensor comprising a; optical sensor unit located at the end of the optical path of the optical cavity to measure the amount of infrared light in a specific wavelength band that is reached after being partially absorbed by a specific gas on the optical path, The light source unit: A light source formed by combining a plurality of geometric solid surfaces; A concave reflector formed by multi-stage bonding of a plurality of concave reflector solid surfaces each forming parallel light with respect to light emitted from surfaces of a plurality of geometrical solid surfaces constituting the light source; Non-dispersive infrared gas sensor comprising a. 2. The light source of claim 1, wherein the light source has a joining shape between a vertical cylindrical surface and a hemisphere, and the concave reflector is joined to the parabolic surface in a direction opposite to the hemispherical surface of the light source and the parabolic surface intersecting at an end of the vertical cylindrical surface. Non-dispersive infrared gas sensor, characterized in that consisting of the surface. The optical path of claim 1, wherein the optical path undergoes reflection at least six times while maintaining the light intensity detected by the optical sensor unit within a range of 50% or more and less than 100% of the light intensity emitted from the infrared light source unit. Non-dispersive infrared gas sensor, characterized in that it is formed to. 4. The light cavity of claim 3 wherein the light cavity of the non-dispersive infrared gas sensor is: A light source fixing part to which the light source part is fixed; Located at the left side of the light source fixing part, the left rear reflector reflects the light incident from the light source to the rear cavity of the light cavity to the front of the light cavity, and the light reflected from the left rear reflector to the front left to the rear of the light cavity A left reflecting surface structure comprising a left front reflecting mirror and a left reflecting mirror reflecting light incident to the center of the light cavity to the right center of the light cavity; A right rear reflector positioned on the right side of the light source fixing part and reflecting the light reflected from the left front reflector to the right front of the light cavity; and a right front reflector reflecting the light reflected from the right rear reflector to the left reflector side. A right reflecting surface structure comprising; A sensor fixing part connected to the right side of the right reflecting surface structure and having the optical sensor part fixed thereto; Non-dispersive infrared gas sensor, characterized in that consisting of. The non-dispersion infrared gas sensor according to claim 1, wherein the light cavity is formed so as to pass only a reflection having a light length of at least three times while maintaining a sensor sensitivity in a range of 0.05 to 0.15 mV / ppm. The optical cavity of claim 5, wherein the light cavity of the non-dispersive infrared gas sensor is: A light source fixing part to which the light source part is fixed; A first reflecting surface positioned on an opposite surface of the light source fixing part and reflecting incident light laterally; A second reflecting surface positioned on an opposite surface of the first reflecting surface and reflecting incident light to one side of the first reflecting surface; A third reflecting surface positioned on an opposite surface of the second reflecting surface and reflecting incident light to one side of the second reflecting surface; A sensor fixing part in which light reflected from the third reflecting surface is incident, and the optical sensor part is fixed; Non-dispersive infrared gas sensor, characterized in that consisting of.

Images