CN102353645A - NDIR (Non-Dispersive Infra-Red)-based intelligent infrared gas sensor - Google Patents

Abstract

The invention discloses an NDIR (Non-Dispersive Infra-Red)-based intelligent infrared gas sensor, which comprises a gas absorbing cavity, pyroelectric probes and a mesh enclosure, wherein the gas absorbing cavity consists of a first semispherical gas absorbing chamber and a second hollow concave-spherical-surface gas absorbing chamber; the top surface and the side wall of the gas absorbing cavity are provided with ventilation holes which are orthogonal to the inner wall surface of the gas absorbing cavity; at least one infrared light source and two orthogonal or non-orthogonal pyroelectric probes are arranged in the gas absorbing cavity; and each pyroelectric probe is provided with two narrow band pass filter ports of which one serves as a reference end while the other serves as a detection end. In the invention, the gas absorbing cavity is an open butterfly-shaped gas chamber, so that the utilization ratio of light energy and the signal-to-noise ratio of a light signal in the cavity are increased, a measure drift phenomenon caused by factors such as environmental disturbance, non-uniform light intensity and the like is eliminated, and real concentration of gas to be measured can be predicted; and the measured gas concentration can be corrected effectively with a weighted accumulation algorithm, so that the sensitivity of gas detection is increased, quick detection response time is prolonged, and the detection accuracy and detection stability of the sensor are enhanced.

Description

An Intelligent Infrared Gas Sensor Based on NDIR

technical field

The present invention relates to a gas sensor, specifically, an intelligent infrared gas sensor including a gas absorption chamber to be measured, an infrared light source, a pyroelectric probe and a signal acquisition control board.

Background technique

In coal mine safety production, reliable, accurate and real-time monitoring of gas (CH ₄ ) concentration is an important means to prevent coal mine gas explosion accidents. The existing commonly used instruments for automatic detection of CH ₄ are classified according to their detection principles, and can be mainly divided into catalytic combustion type, infrared spectrum type, semiconductor gas-sensitive type, gas chromatography type and optical fiber measurement type, etc., among which the most commonly used is There are two kinds of catalytic combustion gas sensors, portable and fixed. However, this kind of sensor has various disadvantages such as being easily affected by the environment, poor reliability and accuracy, short service life, high maintenance cost, and prone to catalytic poisoning, and it is a backward product that will be eliminated soon. The infrared spectrum sensor based on NDIR technology is one of the current research hotspots. It avoids the disadvantages of the old catalytic combustion sensor in principle. Relying on oxygen, less affected by environmental interference factors, long service life and no need for frequent adjustments, etc., it can realize continuous analysis and intelligent real-time detection and other functions.

The infrared spectrum gas sensor is based on the principle of infrared spectrum absorption, and uses the absorption performance of methane gas on the infrared spectrum to detect the gas concentration, which is not easily affected by the site environment. A differential measurement method is used to suppress zero drift. Compared with the traditional catalytic combustion sensor, it has significantly high reliability and accuracy. At the same time, it also has the advantages of long calibration period, good selectivity, strong anti-interference ability and long service life. It is a new type of intelligent sensor. Gas detection device.

The principle of infrared spectrum absorption is based on the fact that different compounds exhibit different absorption peaks due to vibration and rotation changes under the action of the spectrum. Different gases have different absorption spectra for infrared radiation. The characteristic spectral absorption intensity of a certain gas is related to the concentration of the gas. This principle can be used to measure the concentration of a certain gas. The type of gas can be known by measuring the absorption spectrum; the concentration of the gas can be known by measuring the absorption intensity. Each substance has a specific absorption spectrum, and the methane CH ₄ molecule has four inherent vibration modes, correspondingly producing four fundamental frequencies, the wavelengths are 3.433, 6.522, 3.392 and 7.658 μm. Thus, the gas concentration can be determined according to the changes of absorption peaks at certain specific wavelengths on the spectral curves of various gases. It can be seen that the absorption intensity of methane in the mid-infrared region far exceeds the absorption line intensity in the near-infrared region. Therefore, the present invention uses the wavelength of methane gas at 3.39 μm to detect the gas concentration.

When infrared light passes through the gas to be measured, its outgoing light intensity obeys the Lambert-Beer absorption law. In order to eliminate light source fluctuations and interference in the optical path, a dual-wavelength differential measurement technique is adopted, that is, a dual-window probe is introduced, one is the active probe (absorbing the target gas), and the other is the reference probe (not absorbing the target gas). The absorption wavelength and reference wavelength of the measured gas can be realized by adding a narrow-band filter in front of the detection head window. For methane gas, a narrow-band filter with a center wavelength of 3.39 μm is selected for the active detector window, and a narrow-band filter with a center wavelength of 3.9 μm is selected for the reference detector. The ratio of the active probe signal to the reference probe signal can be used to determine the concentration of the gas, and can eliminate the influence of factors such as light source and environmental changes on the probe signal.

Therefore, the calculation of the absorbed energy of the infrared light passing through the gas to be measured satisfies the Lambert-Beer (Lambert-Beer) absorption law, and it can be known that the relationship between the output signals of the two detector heads and the concentration of the target gas is:

是与活跃探测器成比例的信号，是与参考探测器成比例的信号，

为目标气体的吸收系数，

为目标气体浓度，

为光源到探测器的光路长度,即吸收气室长度。 In the formula,

is the signal proportional to the active detector, is the signal proportional to the reference detector,

is the absorption coefficient of the target gas,

is the target gas concentration,

is the length of the optical path from the light source to the detector, that is, the length of the absorbing gas chamber.

It can be seen from the above formula that increasing the absorption length of the gas cell optical path can improve the sampling accuracy, thereby improving the detection accuracy and sensitivity. However, simply increasing the absorption length of the air chamber will lead to the disadvantages of increasing the physical volume of the optical chamber and the light energy. European patent EP0896216A3 adopts the principle of optical focusing system, increases the optical path through multiple reflections of light, and finally focuses the light spot on the photosensitive element of the detection head, which has the advantages of high light energy utilization rate and high optical signal to noise ratio, but Its disadvantages are complex optical path focus adjustment, weak stability, and high difficulty in engineering; US Patent US20090268204A1 uses the addition of multiple detection heads to accumulate signals to improve the rapid response and sensitivity of gas detection. Shifting has a great impact on signal acquisition, and the system stability is poor, which is not conducive to low-cost production; US patent US6469303B1 designed the absorption gas chamber as a non-focusing system, and designed a reflective ellipsoid cylinder to make the light intensity of the absorption chamber uniform, and the signal stability was improved. Improvement, but its non-open chamber sacrifices the response speed and sensitivity of gas detection, and cannot solve the contradiction between gas detection stability, sensitivity and detection accuracy.

In the existing infrared gas sensors, most of the absorption gas chambers adopt the upper one-way ventilation hole method and optical focusing system. When performing gas detection, the chamber is easily disturbed by the direction of the gas to be measured or caused by factors such as uneven light intensity. Measurement drift and other phenomena, that is, when the gas to be measured diffuses from different directions or due to inaccurate optical path adjustment, the response time, detection accuracy and stability of the probe are not ideal. For this reason, people have been seeking a more stable, more reasonable and applicable solution in the contradiction of gas detection stability, sensitivity and detection accuracy.

Contents of the invention

The technical problem to be solved by the present invention is to improve the utilization rate of light energy and the signal-to-noise ratio of the light signal through the design of the absorption cavity air chamber structure and the corresponding components without increasing the manufacturing cost, and eliminate the hidden danger of measurement drift, so as to achieve detection The invention has the beneficial effects of quick response, improved detection accuracy and stability, and then provides an NDIR-based intelligent infrared gas sensor.

Based on the above problems and objectives, the technical measure adopted by the present invention is an intelligent infrared gas sensor based on NDIR, which includes a gas absorption chamber, a pyroelectric probe and a mesh cover.

The gas absorption chamber includes a first gas absorption chamber and a second gas absorption chamber; the first gas absorption chamber is provided with at least two side wall ventilation holes on its peripheral side wall, and correspondingly, the The top surface is provided with at least two top surface ventilation holes, and the two are perpendicular to and coincident with the inner wall surface of the gas absorption chamber; the outer cylinder of the first gas absorption chamber has a stepped surface of the first outer cylinder and a second outer cylinder Stepped top.

The pyroelectric probe is set in the second gas absorption chamber. When two pyroelectric probes are set, the two pyroelectric probes are set in an orthogonal 90o or non-orthogonal 120o, and each A pyroelectric probe is provided with two narrow-band filter ports, one for the reference end and the other for the detection end.

The net cover includes a first net cover and a second net cover, the first net cover is arranged on the upper end surface of the first gas absorption chamber; the second net cover is arranged on the round surface of the first gas absorption chamber inside the ring groove.

In the above technical solution, the first gas absorption chamber is in a hemispherical structure; the second gas absorption chamber is in a shallow concave spherical structure; the two ends of the first gas absorption chamber and the second gas absorption chamber are circumferentially joined The location is a convex-concave centering positioning bridging structure; the infrared light source is arranged on the symmetrical axis of the pyroelectric probe, and is arranged symmetrically about the center point.

The present invention adopts the structure of the absorption cavity air chamber and the design of related components, that is, adopts the open butterfly-shaped absorption cavity air chamber structure composed of the upper hemispherical shape and the lower shallow concave spherical surface, so that the light intensity tends to be equal to Uniform, the photosensitive element on the detection head is not affected by the deviation of the optical path, and the sampled gas can be received without focusing. The unique design of the air hole of the relevant components effectively improves the utilization rate of light energy in the chamber, which improves the signal-to-noise ratio of the optical signal; at the same time, due to the open butterfly-shaped gas chamber structure, it can be used for the horizontal or vertical diffusion of the gas to be measured. Effective reception can eliminate the measurement drift phenomenon caused by factors such as incoming interference and uneven light intensity of the gas to be measured; while the orthogonal or non-orthogonal dual-detector head four-channel structure setting can predict the true concentration of the gas to be measured, through The weighted accumulation algorithm can effectively correct the measured gas concentration, which improves the sensitivity of gas detection and fast detection response time, thereby improving the detection accuracy and detection stability of the sensor.

Description of drawings

Fig. 1 is a schematic cross-sectional structure diagram of a sensor probe of the present invention.

Fig. 2 is a schematic diagram of the outline structure of the first gas absorption chamber of the gas absorption chamber of the present invention.

Fig. 3 is a top view structure diagram of the first gas absorption chamber of the gas absorption chamber of the present invention.

Fig. 4 is a front view structural diagram of the first gas absorption chamber of the gas absorption chamber of the present invention.

Fig. 5 is a schematic cross-sectional structure diagram of the first gas absorption chamber of the gas absorption chamber of the present invention.

Fig. 6 is a schematic diagram of the top view of the second gas absorption chamber of the gas absorption chamber of the present invention.

Fig. 7 is a left view structural diagram of the second gas absorption chamber of the gas absorption chamber of the present invention.

Fig. 8 is an explosion diagram of the intelligent infrared gas sensor probe of the present invention.

In the figure: 1: circular groove; 2: shell; 3: first mesh cover; 4: gas absorption chamber; 5: side wall vent hole; 6: first gas absorption chamber; 7: second mesh cover; 8: Signal acquisition control board; 9: infrared light source; 10: pin pin; 11: second gas absorption chamber; 12: bottom plate; 13: pyroelectric probe; 14: first outer cylindrical stepped table; 15: second outer Cylindrical stepped mesa; 16: Convex mesa of the first gas absorption chamber; 17: Concave mesa of the second gas absorption chamber; 18: Vent hole on the top surface; 19: Shallow concave spherical reflector.

Detailed ways

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the implementation of the present invention includes a first gas absorption chamber 6, a second gas absorption chamber 11, an infrared light source 9, a pyroelectric probe 13, a first net cover 3, a second net cover 7, a signal acquisition control Board 8 , bottom plate 12 , housing 2 and pins 10 ; wherein, gas absorption chamber 4 is composed of first gas absorption chamber 6 and second gas absorption chamber 11 . The first gas absorption chamber 6 has a hemispherical reflective surface corresponding to the shallow concave spherical reflector 19 of the second gas absorption chamber 11 .

As shown in Figure 8, it is an explosion diagram of an intelligent infrared gas sensor probe in an open butterfly chamber. The net cover 3 is placed on the top of the first absorption chamber 6 and placed on the upper end of the shell 2, and the second net cover 7 is installed on the first In the annular groove 1 of the gas absorption chamber 6; the convex mesa 16 of the first gas absorption chamber and the concave mesa 17 of the second gas absorption chamber are centered and positioned at the connecting end surface; so that the inner surface of the gas absorption chamber 4 is a complete bridge without seam chamber. Infrared light source 9 and pyroelectric probe head 13 are connected on the signal acquisition control board 8; The sensing port is present in the gas absorption cavity 4; at the same time, the pin pin 10 is connected to the lower part of the signal acquisition control board 8, and the bottom plate 12 seals the shell 2 as a whole.

As shown in Figure 2, it is an outline view of the first gas absorption chamber 6 of the open butterfly gas absorption chamber 4, and the first gas absorption chamber 6 is a hemispherical symmetrical structure, which can effectively improve light reflection and Convergence ability, the light intensity tends to be uniform after multiple reflections, eliminating the hidden danger of measurement drift; the inner wall of the chamber is gold-plated, which is not easy to corrode, does not change color and has high reflectivity, which can improve the gas absorption rate.

As shown in Figures 3 and 4, the outer peripheral side wall of the first gas absorption chamber 6 is provided with at least two or more side wall ventilation holes 5, and correspondingly, the top surface is provided with at least two or more The vent holes 18 on the top surface, and the vent holes on both sides are orthogonal and coincide with the inner wall surface of the gas absorption chamber 4; such a structure forms a 360 ^° all-round open butterfly chamber, which can be used for gas diffusion no matter in the horizontal or vertical direction. Effective reception can improve the rapid detection and response time of the probe; the orthogonally overlapping side wall ventilation holes 5 are arranged so that there is no light leakage inside the chamber, the utilization rate of light energy is effectively improved, and the signal-to-noise ratio of the optical signal is also improved.

As shown in Fig. 4, the outer peripheral side wall of the first gas absorption chamber 6 is a cylindrical stepped mesa, and the first outer cylindrical stepped mesa 14 is located on the upper part of the outer peripheral side wall of the first gas absorption chamber 6, and its function is Cooperate with the inner wall of the housing 2 to determine the concentric circumferential position of the first gas absorption chamber 6; the second outer cylindrical step surface 15 and the inner wall of the housing 2 form a ring-shaped gas exchange space, so that the gas to be measured can thereby into the gas absorption chamber 4.

Correspondingly, as shown in FIG. 5 , a first mesh cover 3 is provided on the top surface of the first gas absorption chamber 6 to prevent substances other than gas molecules from entering the chamber. Correspondingly, the convex mesa surface 16 of the first gas absorption chamber has the function of cooperating with the upper end surface of the concave mesa surface 17 of the second gas absorption chamber to form a centered positioning, so as to form a bridging seamless chamber, and the circumference of the set convex and concave mesa surface produces a Z Glyph bridge.

Correspondingly, the lower stepped platform of the first gas absorption chamber 6 is provided with an annular groove 1, whose function is to place a net cover 7 to prevent substances other than gas molecules from entering the chamber, so as to ensure the cleanliness of the gas absorption chamber.

As shown in Figures 6 and 7, the inner gas chamber of the second gas absorption chamber 11 of the gas absorption chamber 4 has a shallow concave spherical structure, and its function is to efficiently reflect the light emitted by the infrared light source 9 to the first gas absorption chamber 6. On the hemispherical reflector, the surface of the inner wall of the chamber is plated with gold, which has the characteristics of not being easy to corrode, not changing color and high reflectivity, and can improve the gas absorption rate.

The second gas absorption chamber 11 is provided with at least one pyroelectric probe 13 and at least one infrared light source 9 , and is fixedly connected to the signal acquisition control board 8 .

The second gas absorption chamber 11 is provided with a pyroelectric probe 13, and when two pyroelectric probes 13 are provided, the two pyroelectric probes 13 are arranged in an orthogonal 90°, or in a non-orthogonal 120° Setting; each of the pyroelectric probes 13 is provided with two narrow-band filter ports, one is a reference end, and the other is a detection end.

The two pyroelectric probes 13 in the second gas absorption chamber 11 are arranged in an orthogonal 90° or non-orthogonal 120° dual-probe four-channel structure. The measured gas concentration can be effectively corrected, which improves the sensitivity of gas detection and fast detection response time, thereby improving the detection accuracy and detection stability of the sensor.

The infrared light source 9 in the second gas absorption chamber 11 is located on the axis of symmetry of the pyroelectric probe 13 and arranged symmetrically with respect to the center point.

As shown in Figure 6, the second gas absorption chamber 11 is a shallow concave spherical segment, and the shallow concave spherical reflector 19 can efficiently reflect the light emitted by the light source to the hemispherical reflector of the first gas absorption chamber 6 , and then reflected by the hemispherical reflector to the shallow concave spherical reflector 19 of the second gas absorption chamber 11, the light with a small number of refractions will leak out of the gas chamber, so that after multiple reflections, the light intensity tends to be uniform, and finally Converge on the photoreceptor of the pyroelectric probe 13 and convert it into an electrical signal.

The infrared light source 9 and the pyroelectric probe 13 are located at the lower end of the open butterfly-shaped gas absorption chamber 4, which are fixedly connected to the upper end of the signal acquisition control board 8, and the pin pins 10 are connected to the signal acquisition control board 8. At the lower end, the pins 10 are connected to the main control circuit board. the

The present invention disclosed above can also have other various embodiments. Without departing from the spirit and essence of the present invention, for those skilled in the art, various corresponding changes and modifications can be easily made according to the embodiments of the present invention, but these corresponding changes and modifications None of them deviate from the spirit and scope of the present invention, and all should fall within the protection scope of the appended claims of the present invention.

Claims (4)

1. An NDIR-based intelligent infrared gas sensor, including a gas absorption cavity, a pyroelectric probe and a mesh cover; The gas absorption chamber (4) includes a first gas absorption chamber (6) and a second gas absorption chamber (11); the first gas absorption chamber (6) is provided with at least two or more The side wall ventilation holes (5), and correspondingly, the top surface is provided with at least two top surface ventilation holes (18), and the two are orthogonal to and coincident with the inner wall surface of the gas absorption chamber (4); The outer cylinder of the first gas absorption chamber (6) is a first outer cylindrical stepped surface (14) and a second outer cylindrical stepped surface (15); The pyroelectric probe (13) is arranged in the second gas absorption chamber (11), and when two pyroelectric probes (13) are provided, the two pyroelectric probes (13) are in an orthogonal 90o set, or a non-orthogonal 120o setting, and each pyroelectric probe (13) is set with two narrow-band filter ports, one is a reference end and the other is a detection end; The net cover includes a first net cover (3) and a second net cover (7), the first net cover (3) is arranged on the upper end surface of the first gas absorption chamber (6); The mesh cover (7) is set in the circular groove (1) of the first gas absorption chamber (6); An NDIR-based intelligent infrared gas sensor according to claim 1, wherein the first gas absorption chamber (6) is in a hemispherical structure. 2. An NDIR-based intelligent infrared gas sensor according to claim 1, wherein the second gas absorption chamber (11) is in a shallow concave spherical structure. 3. An NDIR-based intelligent infrared gas sensor according to claim 1, wherein the circumferential junction of the two ends of the first gas absorption chamber (6) and the second gas absorption chamber (11) is a convex-concave centering positioning bridging structure . 4. An NDIR-based intelligent infrared gas sensor according to claim 1, wherein an infrared light source (9) is arranged on the symmetry axis of the pyroelectric probe (13), and is arranged symmetrically about the center point.

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