CN101949838A - Dispersive infrared absorption gas detection device and method - Google Patents

Abstract

The invention discloses a spectroscopic infrared absorption type gas detection device and method. The device and method use the principle of absorption of methane and carbon monoxide at wavelengths of 3.433 μm and 4.65 μm infrared spectral lines, and adopt MEMS infrared light source to emit infrared light through quasi-parallel light components. , after being projected to the blazed grating, the infrared spectra with wavelengths of 3.433 μm and 4.65 μm are obtained. By opening the gas chamber, the concentration detection of methane and carbon monoxide in the sampled gas is realized. The device combined with the method can not only detect the gas with high selectivity, speed and stability, improve the corresponding accuracy, but also realize the simultaneous detection of methane and carbon monoxide, and reduce the cost.

Description

A spectroscopic infrared absorption gas detection device and method

technical field

The invention relates to the field of mine gas detection, in particular to a spectroscopic infrared absorption type gas detection device and method.

Background technique

Gas accidents are one of the main threats to coal mine safety production. They have always been a major problem in the mining industry and have brought great losses to the country and enterprises. The main components of coal mine gas are methane and carbon monoxide, both of which are flammable and explosive gases. For example, when the concentration of methane in the atmosphere reaches 5.3% to 15%, it is explosive. Therefore, it is necessary to carry out early detection of ambient gas in mines, and timely detection of gas concentration plays a very important role in mine safety production and personal safety.

At present, the detection methods of the two dangerous gases methane and carbon monoxide in coal mines include electrochemical methods, optical methods, semiconductor methods, gas chromatography and infrared absorption methods. The infrared absorption sensors for methane and carbon monoxide gases commonly used at home and abroad are all non-dispersive infrared absorption gas sensors. This sensor uses a light emitting diode or an incandescent lamp as a light source, and after the light emitted by it is absorbed by the sampling gas chamber, a filter is used to filter out the intrinsic absorption wavelength of methane or carbon monoxide, and then a photodetector is used for photoelectric conversion, and The gas concentration is detected through the signal processing circuit; or the semiconductor laser is used to directly emit the infrared light of the intrinsic absorption wavelength of methane or carbon monoxide, which is processed by the photodetector and the signal processing circuit after passing through the sampling gas chamber, and the gas concentration is detected.

However, the non-dispersive infrared absorption gas sensor mainly has the following problems: (1) light-emitting diodes or incandescent lamps are used as light sources. Although the price is low, the infrared rays filtered by the filters in the system have a wide band, which affects the detection accuracy. However, narrow bandwidth filters are difficult to manufacture and expensive. (2) Using semiconductor lasers, although the detection accuracy is high, the cost of lasers is high, and the detection cost is relatively high. Therefore, it has great social significance and economic prospect to develop a gas detection system with high sensitivity, low price, reliability and safety.

Contents of the invention

The object of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a spectroscopic infrared absorption type gas detection device and method. The device can not only detect the gas with high selectivity, speed and stability in combination with the method, but also improve the corresponding Accuracy, but also to achieve simultaneous detection of methane and carbon monoxide, and reduce costs.

The purpose of the present invention is solved by the following technical solutions:

This spectroscopic infrared absorption gas detection device includes a gas chamber and a quasi-parallel light assembly. The gas chamber is provided with two planar reflective blazed gratings, and the upper end of the gas chamber is provided with two pyroelectric detectors. The quasi-parallel light assembly The light exit end of the parallel light component extends into the gas chamber, the light incident end of the quasi-parallel light component is provided with a MEMS infrared light source, and the two pyroelectric detectors are respectively connected with a signal processing circuit; The gas to be detected is passed in, and the gas is discharged from the lower end; the emitted light of the MEMS infrared light source enters the gas chamber after being processed by the quasi-parallel light component, and is respectively reflected to the two pyrothermal release gratings by two planar reflective blazing gratings set at different angles. On the electrical detector, the two pyroelectric detectors photoelectrically convert the test signal, and finally transmit it to the signal processing circuit, which judges whether the concentration of methane and carbon monoxide exceeds the limit, and makes an alarm.

The interior of the above-mentioned quasi-parallel component is in the shape of a circular hole, and metal anodization has been carried out to prevent stray light from being reflected in the cavity. A small circular hole at the angle of the outgoing light.

The surfaces of the above two planar reflective blazed gratings are both sawtooth-shaped.

Based on the above device, the present invention also proposes a gas detection method, comprising the following steps:

1) First, the gas to be detected is continuously passed into the gas chamber from the upper end;

2) Make the infrared light emitted by the MEMS infrared light source pass through the quasi-parallel component, and the quasi-parallel light emitted by the quasi-parallel component is incident on two planar reflective blazed gratings, so that the two planar reflective blazed gratings are respectively separated into methane and carbon monoxide. Absorb narrow-bandwidth infrared light centered on the wavelength. After the infrared light passes through the gas chamber filled with the gas to be monitored, two pyroelectric detectors are used to detect two beams of narrow-bandwidth infrared light respectively.

3) The two pyroelectric detectors respectively perform photoelectric conversion on the test signals and transmit them to the signal processing circuit, and the signal processing circuit realizes the detection of the concentration of the gas to be monitored by using the principle of infrared absorption.

Further, the above-mentioned MEMS infrared light source adopts a center wavelength of 4 μm, and satisfies the higher radiation amount at 3.433 μm and 4.65 μm.

The present invention has the following beneficial effects:

(1) The basic principle of the detection method of the present invention uses blazed gratings to obtain methane and carbon monoxide intrinsic absorption wavelengths of 3.433 μm and 4.65 μm narrow-band infrared light for testing, thereby having higher sensitivity and reducing the interference of other gases on the measurement results ;

(2) For the blazed grating required by the device of the present invention, the cost of a single blazed grating can be very low under MEMS batch processing, thereby reducing the cost of detection and early warning systems;

(3) The present invention uses a quasi-parallel light component to emit quasi-parallel light and enter the grating, which reduces the difficulty of installing the optical components of the system while ensuring the light splitting effect.

(4) The device of the present invention uses the different blaze angles of the blazed grating to correspond to different central wavelengths, so it can be applied to the detection of other gases, not only gas, but more widely.

Description of drawings

Fig. 1 is a schematic diagram of the present invention;

Among them, 1 is a MEMS infrared light source, 2 is a quasi-parallel light component, 3 and 4 are planar reflective blazed gratings, 5 and 6 are pyroelectric detectors, 7 is a signal processing circuit, and 8 is a gas chamber;

Figure 2 is a schematic diagram of the plane reflective blazed grating for light splitting;

Fig. 3 is a schematic diagram of the intrinsic wavelength and the position of the pyroelectric detector obtained from the light splitting of the blazed grating.

Detailed ways

The innovative design idea of the spectroscopic infrared absorption gas detection device and method provided by the present invention is mainly embodied in the use of quasi-parallel light components and blazed gratings for light splitting, and the design principle is the principle of blazed grating splitting.

Referring to Fig. 1, the detection device structure of the present invention is: this device comprises gas chamber 8 and quasi-parallel light assembly 2, is provided with two plane reflective blazed gratings 3,4 in gas chamber 8, two plane reflective blazed gratings 3, The surface of 4 is sawtooth shape. The upper end of the gas chamber 8 is provided with two pyroelectric detectors 5,6. The inside of the quasi-parallel component 2 is circular hole-shaped, and metal anodization has been carried out to prevent stray light from being reflected in the cavity. The exit end of the parallel component 2 is a small circular hole that limits the angle of exit light. The light exit end of the quasi-parallel light component 2 extends into the air chamber 8, the light incident end of the quasi-parallel light component 2 is provided with a MEMS infrared light source 1, and the two pyroelectric detectors 5, 6 are respectively connected to a signal processing circuit 7; The upper end of the gas chamber 8 is provided with a gas inlet, and the lower end is provided with a gas outlet. Therefore, the gas chamber 8 is fed into the gas to be detected from the upper end and discharged from the lower end; The quasi-parallel light with a certain divergence angle enters the air chamber 8, and the exit of the quasi-parallel light component 2 has a certain range. Two planar reflective blazed gratings 3 and 4 are placed in the exit area of the quasi-parallel light component 2, and are calculated according to the blazed grating formula After the installation angle is fixed (detailed introduction in conjunction with Fig. 2 below), two planar reflective blazed gratings 3 and 4 are set at different angles, and the outgoing light of the quasi-parallel light component 2 is incident on the two planar reflective blazed gratings 3 and 4 respectively. On the top, the two planar reflective blazed gratings 3 and 4 respectively split out the narrow bandwidth infrared light centered on the intrinsic absorption wavelength of methane and carbon monoxide. Detectors 5 and 6 respectively detect two beams of narrow bandwidth infrared light. The two pyroelectric detectors 5 and 6 respectively detect the intrinsic absorption wavelength light of methane and carbon monoxide emitted by the two planar reflective blazed gratings 3 and 4, and convert the test signal into photoelectricity, and finally transmit it to the signal processing circuit 7 for signal processing. Circuit 7 judges whether the concentration of methane and carbon monoxide exceeds the limit, and makes an alarm. Among them, in order to detect methane and carbon monoxide, the MEMS infrared light source 1 is required to adopt a center wavelength of 4 μm, which satisfies the higher radiation amount at 3.433 μm and 4.65 μm.

The above quasi-parallel light component 2 adopts a round hole inner cavity and a small hole to emit, and is subjected to metal anodic oxidation; the blazed grating adopts a plane blazed grating, which shows a zigzag shape; the gas chamber adopts an open type to connect with the ambient gas.

为入射角，即入射方向与光栅法线的夹角；θ为衍射角，即衍射方向与光栅法线的夹角。闪耀光栅可以把大部分光强集中到某特定的波长光谱中，而不会像透射光栅那样，没有色散的零极主极大占取了大部分光强。Referring to Fig. 2, this figure is a schematic diagram of the grating light splitting principle. Among them, N is the normal direction of the bottom surface, that is, the grating normal; n is the normal direction of the sawtooth slope; d is the grating constant;

is the angle of incidence, that is, the angle between the incident direction and the grating normal; θ is the diffraction angle, that is, the angle between the diffraction direction and the grating normal. The blazed grating can concentrate most of the light intensity into a specific wavelength spectrum, unlike the transmission grating, where the zero-pole main pole without dispersion occupies most of the light intensity.

According to the principle of blazed grating light splitting:

(m=0, ±1, ±2, ...) (1)

In the formula:

——入射角(入射方向与光栅法线的夹角)/°；

——incident angle (the angle between the incident direction and the grating normal)/°;

θ——diffraction angle (the angle between the diffraction direction and the grating normal)/°;

d——blazed grating constant/μm;

m——diffraction order;

θ _kb ——blaze angle/°;

After the grating constant is determined, different incident angles will produce different blaze wavelengths, and the same incident angle will diffract different wavelengths of light at different diffraction angles, so the wavelength of narrow-band infrared light is designed according to the width of the intrinsic absorption peaks of methane and carbon monoxide range, the angle of the quasi-parallel light emitted by the quasi-parallel component 2 is designed through this wavelength range. The installation angle of the two pyroelectric detectors 5 , 6 is thus spatially determined.

Referring to FIG. 3 , the intrinsic wavelength of gas absorption is obtained by splitting light through the plane reflective blazed grating 3 ( 4 ), and then detected and photoelectrically converted by the pyroelectric detector 5 ( 6 ) at the intrinsic wavelength angle.

For example, in the present invention, if the length of the quasi-parallel light component is 6cm and the diameter of the exit aperture is 5mm, then the divergence angle is 4.7°, which is less than 5°, calculated by using trigonometric functions. Plane blazed gratings 3 and 4 with a blaze angle of 31.7° and a grating constant of 3.33 μm and a blaze angle of 30° and a grating constant of 5 μm were respectively selected as the light splitting components. Using formula (2), the two gratings at 3.433 μm, 4.65 The incident angle and outgoing angle at μm diffraction wavelength are respectively: grating 3 corresponds to φ=43.19°, θ=20.21°; grating 4 corresponds to φ=51.57°, θ=8.43°. And when the incident angle range is below 5°, that is, φ=43.19°±2.5° or φ=51.57°±2.5°, using the formula (2), the diffraction wavelength range is within 3.433m±50nm and 4.65μm±50nm, And this bandwidth range belongs to the infrared absorption spectrum of methane and carbon monoxide, suitable for measurement. At the same time, the angles of the pyroelectric detectors 5 and 6 are arranged to be 20.21° and 8.43° respectively to complete the detection. The above angles are based on the normal of the blazed grating.

According to the infrared absorption principle formula Lambert-beer law, which is the law of light absorption:

I=I ₀ exp(-αLc)(4)

c=In(I ₀ /I)/αL(5)

In the formula:

I——transmitted light intensity/cd after light is absorbed by the medium;

I ₀ ——light intensity of the incident medium/cd;

α——is the absorption coefficient of the medium;

c—medium concentration/%;

L - is the length/m of light passing through the medium.

It can be seen from the above formula that when the absorption coefficient α of the medium, the length L of light passing through the medium, the transmitted light intensity I, and the incident light intensity _I0 are constant, the concentration of the target gas can be obtained.

Based on the detection device described in the present invention above, the specific steps of the gas detection method of the present invention are as follows:

1) First, the gas to be detected is continuously passed into the gas chamber 8 from the upper end, the gas is passed in from the upper end, and the gas chamber 8 is filled and discharged from the lower end;

2) The MEMS infrared light source adopts a central wavelength of 4 μm, and satisfies that there is a relatively high radiation amount at 3.433 μm and 4.65 μm, and then the infrared light emitted by the MEMS infrared light source 1 passes through the quasi-parallel component 2, and the quasi-parallel component 2 emerges. Parallel light is incident on the two planar reflective blazed gratings 3 and 4, so that the two planar reflective blazed gratings 3 and 4 respectively emit narrow-band infrared light centered on the intrinsic absorption wavelengths of methane and carbon monoxide. After monitoring the gas chamber 8 of the gas, two pyroelectric detectors 5 and 6 are used to respectively detect two beams of narrow bandwidth infrared light,

3) The two pyroelectric detectors 5 and 6 respectively perform photoelectric conversion on the test signals and transmit them to the signal processing circuit 7, and the signal processing circuit 7 realizes the detection of the concentration of the gas to be monitored by using the above-mentioned infrared absorption principle.

In summary, the present invention uses quasi-parallel light and blazed gratings to obtain the intrinsic wavelengths of methane and carbon monoxide infrared absorption, and realizes simultaneous detection of methane and carbon monoxide concentrations, which not only improves the accuracy of gas detection in the system, but also simplifies assembly and processing, and The cost is reduced, and the problems of high price and difficulty in improving the precision of the traditional non-dispersive infrared absorption sensor are solved. In addition, the present invention can also realize the detection of other gases by replacing and adjusting the flat reflective blazed grating, and can also be used for automobile exhaust detection, etc., and can continuously detect conventional gases such as CO ₂ , CO, CH ₄ , NO, SO ₂ , etc. Gas measurement, which may gradually replace the previous gas detection device.

Claims (5)

1. beam split type infrared absorption type gas detecting device, it is characterized in that: comprise air chamber (8) and quasi-parallel optical assembly (2), be provided with two plane reflection blazed gratings (3,4) in the described air chamber (8), the upper end of air chamber (8) is provided with two pyroelectric detectors (5,6), the light exit side of described quasi-parallel optical assembly (2) stretches in the described air chamber (8), the light incident side of quasi-parallel optical assembly (2) is provided with MEMS infrared light supply (1), and described two pyroelectric detectors (5,6) are connected with signal processing circuit (7) respectively; Described air chamber (8) is fed gas to be detected, is given vent to anger by the lower end by the upper end; The emission light of described MEMS infrared light supply (1) is handled in the laggard air inlet chamber (8) through quasi-parallel optical assembly (2), reflex to respectively on described two pyroelectric detectors (5,6) by the two plane reflection blazed gratings (3,4) that are set to different angles, described two pyroelectric detectors (5,6) transform test signal photoelectricity, transfer to signal processing circuit (7) at last, judge whether overrun of methane, carbonomonoxide concentration by signal processing circuit (7), and make warning.

2. beam split type infrared absorption type gas detecting device according to claim 1, it is characterized in that: the inside of described quasi-parallel assembly (2) is circular hole, and carried out anodic metal oxide, prevent that parasitic light is at intracavity reflecting, the incident end of this quasi-parallel assembly (2) is connected with the exit end of MEMS infrared light supply (1), and the exit end of quasi-parallel assembly (2) exceeds and makes the tiny circular hole of shooting angle.

3. beam split type infrared absorption type gas detecting device according to claim 1 is characterized in that the surface of described two plane reflection blazed gratings (3,4) is zigzag fashion.

4. the gas measuring method based on the described device of claim 1 is characterized in that, may further comprise the steps:

1) at first, gas to be detected is constantly fed in the air chamber (8) by the upper end;

2) the infrared light process quasi-parallel assembly (2) that MEMS infrared light supply (1) is sent, the quasi-parallel light of described quasi-parallel assembly (2) outgoing is incident to two plane reflection blazed gratings (3,4), make two plane reflection blazed gratings (3,4) splitting with methane and carbon monoxide intrinsic absorbing wavelength respectively is the narrow bandwidth infrared light at center, this infrared light by with the air chamber that is full of gas to be monitored (8) after, utilize two pyroelectric detectors (5 again, 6) survey two bundle narrow bandwidth infrared lights respectively

3) make two pyroelectric detectors (5,6) that test signal is carried out respectively transferring to signal processing circuit (7) after photoelectricity transforms, utilize infrared absorption principle to realize the detection of gas concentration to be monitored by signal processing circuit (7).

5. gas measuring method according to claim 4 is characterized in that: described MEMS infrared light supply adopts centre wavelength at 4 μ m, and satisfy 3.433 μ m, there is higher radiant quantity at 4.65 μ m places.

Images