KR101760031B1

KR101760031B1 - Optical gas sensor with the improvement of sensitivity and reliability

Info

Publication number: KR101760031B1
Application number: KR1020150076656A
Authority: KR
Inventors: 이근헌; 이승환; 이수민
Original assignee: (주) 휴마스; 한국교통대학교산학협력단
Priority date: 2015-05-29
Filing date: 2015-05-29
Publication date: 2017-07-21
Also published as: KR20160140255A

Abstract

An optical gas sensor for improving sensitivity and reliability is disclosed. A reflector disposed at an arbitrary angle and having the same size; A concave reflecting mirror disposed on a surface corresponding to the reflecting mirror; An infrared light source having a parabolic reflector below the concave reflector; An infrared ray detection sensor disposed on both sides of the concave reflector; And a fourth reflector for transmitting a part of the light emitted from the infrared light source to the infrared detection sensor. Therefore, by providing two infrared detection sensors (reference wavelength, measurement wavelength), it is possible to smoothly perform the function of correction for the intensity change due to the temporal change of the infrared light source, thereby securing long-term reliability.

Description

TECHNICAL FIELD [0001] The present invention relates to an optical gas sensor for improving sensitivity and reliability,

The present invention relates to an optical gas sensor, and more particularly, to an optical gas sensor for improving sensitivity and reliability.

FIG. 1 shows a representative embodiment disclosed in Korean Patent Registration No. 10-1088360. As shown in FIG. 1, light emitted from the common light source 120 has a structure that reaches the optical sensor unit 130 on the right side through the elliptic reflectors 111 and 112, which share a common focus but are different from each other. The structure that can be measured by the above-described optical sensor is taken. Such a structure has the advantage that it is easy to fabricate a small structure and can collect light without an additional lens. However, the amount of light reaching two sensors can focus only a maximum of a quarter of light on the structure, It has a disadvantage that it is difficult to fabricate a three-dimensional optical structure and to irradiate a field of view (FOV) of an existing optical sensor (infrared thermopile, bolometer or PIR sensor).

3, which is shown in Korean Patent Registration No. 10-1108544 and Korean Patent Registration No. 10-0944273, which are shown in FIG. 2, includes an optical sensor 210 including a reference sensor or a measurement light source (310) and a reference light source (320) for correcting the aging of the measurement light source. The advantage of the structure of the sensor shown in FIG. 2 is that the same light source is used but two infrared sensors are used. One is a reference sensor that compares and evaluates the output state of the reference sensor with the change of the light source with time, The optical path has a long characteristic to compensate the change of output according to the change. However, since there is no special structure for condensing the infrared ray incident on the first end of the infrared sensor, It has a structural disadvantage that it has a small characteristic.

3, the output of the infrared sensor 330 can be periodically corrected using the reference light source 320 and the main light source 310, that is, a plurality of light sources, The sensitivity of the infrared sensor 330 can be improved, and the structure has a structure that can help improve long-term reliability. However, since the pattern of the light reaching the infrared sensor 330 is incident in parallel, it is not easy to measure gas of a long wavelength band (> 6 [mu] m) by improving the light intensity over structures using a lens or an elliptic structure .

4 is a view showing the features of Korean Patent Registration No. 10-0694635. In this patent, infrared rays emitted from a light source 420 provided at a first focus of an elliptical dome-shaped reflector 410 are reflected by the elliptical dome-shaped reflector 410 and then installed at a second focus of the elliptical dome- The number of times of reflection by the reflector is minimized to prevent light loss and the light emitted from the light source 420 is incident on the optical sensor 430 without loss, , But it adopts a structure in which half of the elliptical dichroic mirror is utilized and the light reflected from the lower surface is directed to the sensor unit through the reflector shown in the lower plate of the sensor unit . Such a structure uses only a luminous flux of less than half of the irradiation light. In the case of light irradiated and reflected on the lower plane, it is preferable to irradiate the light to the sensor part effectively by the filter attached to the optical sensor part, It is difficult to be irradiated to the infrared detecting element located at the bottom of the filter.

5 is a view showing the structure of Korean Patent Laid-Open No. 10-2013-0082482. The structure shown in FIG. 5 shows optical structures by two collimated and opposed two photoreceptors 510 and 520. As shown in FIG. 5, the light emitted from the light source located at the first focal point F1 using only two photographic lenses is converged by the photodetector located at the second focal point F2 to be condensed, and the shape and arrangement method of the paraboloid Therefore, it is possible to measure with two or more optical sensors. However, the structure using only the polygon is described in J.S. Park and S.H. As Yi proposed in Sensors and Materials (2011 paper), it can be said that the condensing pattern has a disadvantage that it can not be said to be efficient light because it shows a shape that is not circular.

In addition, the Korean Patent Registration No. 10-0959611 as shown in FIG. 6 has an advantage of improving the sensitivity of the sensor by efficiently condensing the light to the infrared sensor 620 by including the lens 610 for condensing . However, the optical path is relatively short, and the manufacturing cost is increased due to the mounting of the additional lens.

On the other hand, the Korean Patent Registration No. 10-1108495 shown in FIG. 7 has an advantage that a light intensity can be improved by adopting a lens in front of the infrared sensor 730. However, The use of additional components not only has a factor of cost increase but also employs a reflector 720 structure to artificially form reflection on the upper, lower, right and left wall surfaces of the optical structure 710 for increasing the optical path, The amount of light emitted from the light source is relatively small.

When the internal reflector of the optical gas sensor using all of the optical structures described above is operated in a high humidity region, that is, the ambient temperature is constant at 25 degrees, the gas to be measured contains a large amount of water vapor and the temperature of the introduced gas is 35 degrees The water vapor contained in the gas is condensed in the inner reflector of the optical structure to cause irregular reflection of the infrared rays to be irradiated, thereby causing reduction of light energy reaching the infrared sensor. In addition, since the optical path of the optical gas sensor known to date is about several centimeters to several tens centimeters, there is a limit to improvement in the measurement accuracy in low-concentration measurement.

It is an object of the present invention to solve the above problems and to provide a method and apparatus for improving the sensitivity and reliability of accurately measuring the concentration of gas while preventing the condensation of water vapor to the utmost when the gas containing steam having a temperature significantly higher than the ambient temperature is introduced And to provide an optical gas sensor.

According to an aspect of the present invention, there is provided an optical system including two reflectors having the same size and arranged at an arbitrary angle on the same plane; A concave reflector disposed on the surface corresponding to the two reflectors so as to be spaced apart by a predetermined distance R; An infrared light source disposed under the one concave reflector and having a parabolic reflector;
A first infrared ray detection sensor disposed on the one concave reflector and having the light emitted from the infrared ray source reflected through the two reflectors and the concave reflector and arriving with a long optical path; A second infrared ray detection sensor disposed below the infrared ray source; And a fourth reflector disposed between the second infrared ray detection sensor and the two reflectors for transmitting a part of the light emitted from the infrared ray source to the infrared ray detection sensor,
The two reflectors, the one concave reflector, and the fourth reflector have a substrate formed to have a specific radius of curvature; A reflection film formed on one side of the substrate and reflecting the infrared rays; And a thick film including an insulating film formed on the other side of the substrate and a heating element formed on the insulating film.

Here, there are two reflectors and one concave reflector.

At this time, the light emitted from the infrared light source is transmitted to the infrared ray detection sensor through the fourth reflector, the reflector, and the concave reflector.

At this time, the infrared detection sensor has the absorption wavelength of the gas to be measured.

At this time, the infrared detection sensor includes an infrared thermopile having an amplifier, a filtering circuit, and a DC voltage output function.

At this time, at least one of the fourth reflector, the reflector, and the concave reflector includes a heating element that is heated to a temperature higher than the ambient temperature on the rear surface.

At this time, at least one of the fourth reflector, the reflector, and the concave reflector is a plated film for infrared reflection; An insulating film deposited on the rear surface; A heating element formed on the insulating film; And a temperature sensor for measuring the temperature of the heating element.

When the optical gas sensor for improving the sensitivity and reliability according to the present invention as described above is used, since there are two infrared detection sensors (reference wavelength, measurement wavelength), the function of correcting the intensity change with time of the infrared light source It is possible to secure a long-term reliability since the structure can be smoothly performed.

Further, there is an advantage in that the sensitivity can be improved by using the output of the infrared sensor part having a long optical path in the structure using the output voltage ratio of the two infrared sensor.

In addition, the inner reflector of the optical gas sensor is manufactured through compression molding or glass molding of metal, and when a metal is used as a reflector, heat is generated through an insulating film and a heating body metal, or when the glass is molded into a reflecting mirror, There is an advantage that deterioration in sensitivity due to condensation of water vapor can be prevented when the high humidity gas reaches the measurement chamber by forming the anti-use gold / nickel plating and the patterning of the heating element metal.

Further, since the reflector is spaced apart from the reflector and is not completely sealed as seen from the conventional optical structure, it is possible to ensure a state where gas diffusion is easy.

In addition, an optical gas sensor can be fabricated with a structure that can minimize the sensitivity change of the gas sensor due to the improvement of the sensitivity, the securing of the reliability, and the light scattering due to the high humidity.

1 to 7 are prior art drawings.
FIG. 8 shows a white-cell structure (1942, Journal of Optical Society of America) using three concave reflectors.
9 shows the path of light emitted from the center of the light source when the incident angle is 10 degrees, the angle between the two lenses is 4 degrees, the length of the right reflector is 4 cm, and the distance between the three concave reflectors is 8 cm.
Fig. 10 shows an optical structure using three concave reflectors based on Fig.
11 is a view showing a state in which the light emitted from the infrared light source is reflected by the fourth concave reflector d and the three concave reflectors a, b, c a predetermined number of times, This is the result of tracking.
12 is an exemplary view showing a configuration of a reflector.

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

The Beer-Lambert law, which is extensively applied to the fabrication and application of infrared gas sensors, can be expressed as Equation (1)

I0 is the initial light intensity, a is the light absorption coefficient of the specific gas, x is the gas concentration, and 1 is the light path.

In order to improve the output of the infrared gas sensor, Park and S.H. As shown in Equation (2) as presented in Yi's Sensors and Materials (2011 paper), incident light arriving at the infrared sensor is more effective to follow the condensed shape than the initial light pattern.

Where ξ is a proportional constant, ri is the radius of the initial light pattern, and rd is the radius of the light pattern at the sensor end.

As shown in the above-mentioned equations, there are some considerations to be considered in the fabrication of the optical gas sensor: 1) The light source capable of emitting infrared rays has a problem in that the light intensity is reduced due to aging of the self filament, 2) When measuring long gas wavelengths, the light emitted from the infrared light source is high-performance sensor that can sufficiently detect the light because of its low strength, or to improve the light intensity (3) and (3) the sensitivity of the infrared gas sensor must be long enough to generate a high output voltage difference at the same concentration, so that an optical structure should be manufactured with a long possible path, Minimizing the reflection in the structure minimizes the amount of absorption in the reflection at the structure You need to ensure that you can.

In order to fabricate an optical gas sensor, the structure should be equipped with 1) structure that can improve the measurement reliability by automatically correcting the output change of the gas sensor by observing the aging of the infrared light source, 2) 3) a structure in which the optical path is long, the reflection inside is to be minimized, a structure in which high-humidity gas is prevented from condensing in the optical reflector when the gas is introduced, 4) a structure in which infrared rays The incident light arriving at the sensor should have the feature of being collected at the center of the infrared sensor at the smallest possible radius.

Therefore, the present invention is characterized in the structure of an optical gas sensor and the arrangement of a light source and an optical sensor that can satisfy the above-described requirements.

The present invention is characterized by the structure of an optical gas sensor and the arrangement of a light source and an optical sensor which can satisfy most of the above-mentioned matters.

FIG. 8 shows a white-cell structure (1942, Journal of Optical Society of America) using three concave reflectors. By controlling the angle of incidence of the incident light to the reference line, the angle between the two reflectors on the same side of the left side (θ), the length of the right reflector (L), and the distance between the three reflectors (R) The optical path can be maximized through a plurality of light reflections.

9 shows the path of light emitted from the center of the light source when the incident angle is 10 degrees, the angle between the two lenses is 4 degrees, the length of the right reflector is 4 cm, and the distance between the three concave reflectors is 8 cm. As shown in FIG. 9, it can be seen that the light incident on the center axis shown in FIG. 8 and having an inclination of about 10 degrees is emitted to the lower right side through the reflection of 16 times in the three concave reflectors. At this time, the path of the light is approximately 1.2 m, and the incident light is radiated to the lower right after 15 reflections inside. At this time, it can be expected that about 60 of the incident light is emitted when the reflectance of the reflective surface is 0.97 (reflectance when gold is plated).

On the other hand, FIG. 10 shows an optical structure using three concave reflectors based on FIG. As shown, the two reflectors b and c having the same size are arranged at an arbitrary angle, one concave reflector a is placed on the corresponding surface, and a parabolic reflector (Electro Optical Technologies MIRL 17-900) having a first reflector and a fourth reflector so as to reach a position near a radiated position of the emitted light, The results of simulated analysis of the optical path reaching the sensor portion according to the incident light by disposing the detection sensor are shown in Fig.

11 is a view showing a state in which the light emitted from the infrared light source is reflected by the fourth concave reflector d and the three concave reflectors a, b, c a predetermined number of times, As a result of the tracking, it can be seen that the light reflected from the fourth concave reflector reaches directly to the detecting unit 2, and the infrared rays reflected through the three concave reflectors reach the detecting unit 1 with a long path. Therefore, an infrared detector (for example, an infrared thermopile detector with a center wavelength of 3.91 mu m) equipped with a filter that does not react with other gases at all is disposed in the detection unit 2, An infrared ray detector having an absorption wavelength (for example, a thermopile detector for carbon dioxide having a center wavelength of 4.26 mu m) can be disposed so that an output voltage difference due to infrared flickering can be obtained in each thermopile when the infrared ray source is blinking. An infrared thermopile (HIS A21 F3.91, HIS A21 F4.26) having an amplifier, a filtering circuit, and a DC voltage output function is disposed in each of the detectors (1 and 2) And the output voltage ratio in the presence of a specific concentration of gas is more accurate, and even if the infrared light quantity according to the temporal change of the infrared light source changes, it is possible to make a structure capable of accurately measuring the concentration of the target gas.

In addition, the infrared thermopile for the gas to be measured is placed in the infrared ray detection unit (1) after passing through a long optical path, thereby causing a large voltage change with respect to the same gas concentration change as the optical path length becomes longer The output voltage ratio of the detection unit 1 and the detection unit 2 can be increased to improve the sensitivity.

On the other hand, when three concave reflectors having a predetermined thickness and a heating element are mounted on the rear surface of the fourth reflector and heated to about 30 to 40 degrees higher than the ambient temperature, a structure capable of preventing condensation of water vapor due to high- can do.

12 is a view for explaining the three concave reflectors and the fourth reflector according to FIG.

12, the concave reflector and the fourth reflector include a substrate 810 formed to have a specific radius of curvature, a reflective film 820 formed on one side of the substrate for improving infrared reflectance, And a thick film 830 formed on a surface opposite to the substrate 830. [

The substrate 810 may be formed of metal or glass and the reflective film 820 may be formed of an Au / Ti or Au / Ni plated film for efficient reflection of infrared rays

Further, the thick film 830 may include an insulating film 831, a heating element 832, and a temperature sensor 833.

The insulating layer 831 is formed by depositing or screen-printing an oxide such as SiO2 and then forming a heating element 832 including a heating electrode having a predetermined pattern on the insulating layer 831 so that the insulating layer 831 generates heat . In addition, a surface temperature is measured by attaching a temperature sensor (833, RTD, thermistor or the like) to prevent a temperature rise due to excessive heat, and compared with the ambient temperature (measured by a temperature sensor in the infrared thermopile) (30 to 40 DEG C) or more can be always maintained.

In order to increase the optical efficiency, a structure capable of improving the sensitivity by increasing the output voltage by attaching a lens capable of transmitting and collecting the infrared light to the front of the detection unit 1 can be adopted. The reflector, the thermopile detector, and the circuit unit having the heat generating function are configured to insulate the air by the medium, and are arranged in the optical sensor module so as to exclude the influence of the temperature of the heating element.

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 present invention as defined by the following claims It can be understood that

111, 112: oval reflector 120: light source
130: optical sensor unit 210: optical sensor
310: primary light source 320: reference light source
330: infrared sensor 410: oval domed reflector
420: light source 430: light sensor
510, 520: Portion 610: Lens
620: Sensor 710: Structure
720: reflector 730: sensor
810: substrate 820: reflective film
830: thick film 831: insulating film
832: Heating element 833: Temperature sensor

Claims

Two reflectors having the same size and arranged at an arbitrary angle on the same plane;
A concave reflector disposed on the surface corresponding to the two reflectors so as to be spaced apart from each other by a predetermined distance R;
An infrared light source disposed below the one concave reflector and having a parabolic reflector;
A first infrared ray detecting sensor disposed on the one concave reflector, the first infrared ray detecting sensor having the light emitted from the infrared ray source reflected through the two reflectors and the concave reflector and arriving with a long optical path;
A second infrared ray detection sensor disposed below the infrared ray source; And
And a fourth reflector disposed between the second infrared detection sensor and the two reflectors for directly transmitting a part of the light emitted from the infrared light source to the infrared detection sensor,
The two reflectors, the one concave reflector, and the fourth reflector,
A substrate formed to have a specific radius of curvature;
A reflection film formed on one side of the substrate and reflecting the infrared rays;
And a thick film including an insulating film formed on the other side of the substrate and a heating element formed on the insulating film.
Optical gas sensor for improved sensitivity and reliability.

delete

The method according to claim 1,
The first and second infrared ray detection sensors may include:
An optical gas sensor for improved sensitivity and reliability, including an infrared thermopile with amplifier, filtering circuit and direct voltage output.

delete

The method according to claim 1,
Wherein,
Optical gas sensor for improved sensitivity and reliability formed by Au / Ti or Au / Ni plated film.