阅读说明：本技术 一种消除异路干涉噪声的气体传感方法及系统 (Gas sensing method and system for eliminating different-path interference noise ) 是由 洪广伟 于 2021-07-23 设计创作，主要内容包括：本发明属于气体检测技术领域,具体为一种消除异路干涉噪声的气体传感方法及系统。本发明使用一个可调谐激光器、两个光电探测器和一个2×2耦合器,将相位型噪声分别通过两个路径传递,在耦合器侧形成叠加干涉,得到两路输出,将两路信号叠加就可以消除干涉信号,从合成的新信号可以反演出气体浓度。基于TDLAS的气体传感系统,由于反射等引起的异路干涉型噪声往往是最难处理的瓶颈,严重影响系统稳定性和可靠性的最大障碍。本发明可有效消除干涉型噪声被当成虚假吸收峰的影响,实现对有毒、易燃易爆气体、痕量气体的高效、快速检测,可广泛应用于化工、环保等工厂监控及大气监测等领域。(The invention belongs to the technical field of gas detection, and particularly relates to a gas sensing method and a gas sensing system for eliminating different-path interference noise. The invention uses a tunable laser, two photodetectors and a 2 x 2 coupler to transmit phase type noise through two paths respectively, and forms superposition interference at the side of the coupler to obtain two paths of output, and the interference signal can be eliminated by superposing the two paths of signals, and the gas concentration can be inverted from the synthesized new signal. In a TDLAS-based gas sensing system, the noise caused by reflection and other interferences in different paths is often the most difficult bottleneck to deal with, and the biggest obstacle to the stability and reliability of the system is seriously affected. The invention can effectively eliminate the influence of interference type noise as false absorption peak, realize the high-efficiency and quick detection of toxic, inflammable and explosive gas and trace gas, and can be widely applied to the fields of factory monitoring, atmosphere monitoring and the like in chemical engineering, environmental protection and the like.)

1. A gas sensing method for eliminating different-path interference noise is characterized in that a laser, two detectors and a 2 x 2 coupler are used, so that one path of light and the other path of light absorbed by a gas chamber generate phase interference, phase type noise respectively passes through two ports of the 2 x 2 coupler to form superposition interference in the coupler, two paths of output are obtained, and alternating current components in interference signals are in opposite phases; the two paths of signals are linearly superposed, alternating current components in interference signals are mutually offset, the influence of interference noise on gas absorption signals can be eliminated, and the gas concentration can be inverted by the synthesized new signals.

2. A gas sensing system for eliminating different-path interference noise is characterized by being formed by connecting a laser, an optical fiber circulator, two detectors, a coupler, a gas chamber of gas to be detected and an acquisition processing system through a light path; the coupler is a 2 x 2 coupler; wherein:

the laser emits tuning pulse light, the tuning pulse light passes through the optical fiber circulator and reaches the coupler for light splitting: wherein, one path of light reaches a reflection point through C1, and returns to the coupler after being reflected; the other path of light reaches the air chamber through C1, and returns to the coupler after being reflected; after the two beams of light are superposed by interference, the two beams of light are split at a coupler: wherein, after one path reaches the circulator, the other path of light is received by the first detector, and the other path of light directly reaches the second detector; amplifying light of the first detector and the second detector, and then entering an acquisition processing system for acquisition, analysis and storage;

wherein C1 is the optical path between the coupler and the reflection point, C2 is the optical path between the coupler and the air chamber, and the reflection point is the connector end face or the bend loss point.

3. The system of claim 2, wherein the optical fiber or the fiber delay line used in the system is a single mode fiber or a multimode fiber.

4. The gas sensing system for eliminating multipath interference noise of claim 2, wherein:

suppose the laser emits light of intensity I₀After passing through the gas chamber containing the gas to be measured, the light intensity can be attenuated, and the relationship between the output light intensity I (v) and the input light intensity is described by using the beer-Lambert law, which specifically comprises the following steps:

I(ν)＝I₀(ν)exp[-α(ν)CL] (1)

wherein C is the volume concentration of the gas to be detected, L is the effective absorption length of the gas passing through the gas chamber, and alpha (v) is the gas absorption intensity of light with different wavelengths;

according to the formula (1), when the effective absorption length L and the absorption alpha (v) of the gas to be detected under the wavelength are known, the concentration information of the gas to be detected can be calculated by detecting the light intensity after passing through the gas chamber and being absorbed and the initial incident light intensity of the laser;

suppose the phase difference of two-way phase type noise isThe light intensity of the two paths of light output by the photoelectric detector is as follows:

wherein, I₁And I₂The light intensities contributed to the light paths C2 and C2, respectively;

the C2 light path passes through the gas cell 7, and the light intensity of this path is obtained according to the beer-lambert law, which is expressed as:

I₂＝I₀exp[-α(ν)CL] (4)

the light intensities of the two detectors are expressed as:

in any path, there is the influence of interference type noise, which will cover useful signal, according to the characteristic of the inversion of the interference part of the system, the outputs are added to cancel the influence of interference type noise, that is:

I_t＝I_o1+I_o2＝2I₁+2I₀exp[-α(ν)CL] (7)

accordingly, the influence of interference type noise can be eliminated.

Technical Field

The invention belongs to the technical field of gas detection, and particularly relates to a gas sensing method and a gas sensing system for eliminating different-path interference noise.

Background

TDLAS (tunable semiconductor laser absorption spectroscopy) attracts more and more researchers' attention by virtue of the characteristics of strong gas selectivity, high sensitivity, interference resistance and applicability to flammable and explosive special environments, and has wide application prospects in the aspects of industrial process monitoring control, combustion process diagnosis and analysis, explosion detection, trace pollution gas monitoring in the atmosphere and the like. Particularly, in the aspect of methane detection, relatively mature commercial products appear, and related products provide better detection instruments for occasions such as coal mine gas leakage, natural gas inspection and the like. However, after a gas detection system based on TDLAS is used for a long time, due to the influence of complex external environments such as dust, salt fog and the like, a sensing result is often interfered, and stability and reliability are greatly challenged. Through researches of pen workers, the DFB laser used is mostly narrow in line width, interference type noise caused by reflection and the like is the bottleneck which is difficult to process, the interference noise can be superposed with a series of interference fringes on absorption output light, and in severe cases, useful spectrum absorption signals can be completely submerged.

Disclosure of Invention

The invention aims to provide a gas sensing method and a gas sensing system capable of effectively eliminating different-path interference noise.

The invention provides a gas sensing method for eliminating different-path interference noise, which uses a laser, two detectors and a 2 x 2 coupler, wherein one path of light and the other path of light absorbed by a gas chamber can generate phase interference, and phase type noise respectively passes through two ports of the 2 x 2 coupler to form superposition interference in the coupler to obtain two paths of output, wherein alternating current components in interference signals are in opposite phases; the two paths of signals are linearly superposed, alternating current components in interference signals are mutually offset, the influence of interference noise on gas absorption signals can be eliminated, and the gas concentration can be inverted by the synthesized new signals.

The gas sensing system for eliminating the different-path interference noise, which is provided by the invention, has the structure shown in figure 1, and is formed by connecting a laser 1, an optical fiber circulator 2, two detectors 3 and 4, a coupler 5, an equivalent reflection point 6 gas chamber 7 of gas to be detected, an acquisition processing system 8 and the like through optical fibers; the coupler 5 is a 2 × 2 coupler; wherein:

the laser 1 emits tuning pulse light, which passes through the circulator 2 and reaches the coupler 5 to be split: wherein, one path of light reaches the reflection point 6 through C1, and returns to the coupler 5 after being reflected; the other path of light reaches the air chamber 7 through C1, and returns to the coupler 5 after being reflected; after the two beams of light are superposed by interference, the two beams of light are split at the coupler 5: wherein, after one path reaches the circulator 2, the other path of light is received by the first detector 3, and the other path of light directly reaches the second detector 4; the light of the first detector 3 and the second detector 4 enters the acquisition processing system 8 after being amplified for acquisition, analysis and storage.

Wherein, C1 is the optical path between coupler 5 and reflection point 6, and C2 is the optical path between coupler 5 and gas cell 7; the reflection point 6 may be a reflection formed at the end face of the connector or a reflection caused by a bending loss point, or the like.

The optical fiber or optical fiber delay line used by the system can be a single mode optical fiber or a multimode optical fiber.

In the invention, the theoretical basis of the spectral absorption type gas sensing is the gas molecule selective absorption principle. If the emergent light of the tunable laser passes through the gas in the gas chamber, the gas can selectively absorb the light with the corresponding wavelength according to the absorption spectrum, so that the energy of the emergent light with the corresponding wavelength is changed. Assuming that the light source emits light of intensity I₀After passing through the gas chamber containing the gas to be measured, the optical fiber can be attenuated, and the relationship between the output light intensity I (v) and the input light intensity is described by using the beer-Lambert law, which specifically comprises the following steps:

I(ν)＝I₀(ν)exp[-α(ν)CL] (1)

wherein C is the volume concentration of the gas to be measured, L is the effective absorption length of the gas passing through the gas chamber, and alpha (v) is the gas absorption intensity of light with different wavelengths.

The above formula shows that if the effective absorption length L and the absorption α (v) of the gas to be measured at this wavelength are known, the concentration information of the gas to be measured can be calculated by detecting the light intensity after passing through the gas chamber and absorption and the initial incident light intensity of the laser. In use, the gas absorption spectrum line is very narrow, generally dozens of picometers, and the laser wavelength is difficult to be set right on the absorption spectrum line due to the influence of temperature and the like. Generally, a wavelength tuning pulse method is adopted, so that a tuning range covers an absorption spectrum line, and a concentration value can be calculated by one pulse. Meanwhile, due to factors such as light intensity jitter and gas wavelength fluctuation of the laser, various methods are often adopted to improve the accuracy of concentration calculation, such as second harmonic detection, differential detection, reference interpolation detection and the like.

The invention uses a tunable laser, two photodetectors and a 2 x 2 coupler to transmit phase type noise through two paths respectively, and forms superposition interference in the coupler to obtain two paths of output, interference signals can be eliminated by superposing two paths of signals, and gas concentration can be inverted from synthesized new signals. One path of the light passes through the air chamber, and the other path of the light is reflected and finally enters the coupler.

Suppose the phase difference of two-way phase type noise isThe light intensity of the two paths of light output by the photoelectric detector is as follows:

wherein, I₁And I₂The light intensities contributed by the light paths C1 and C2, respectively.

The C2 light path passes through the gas cell 7, and the light intensity of this path is obtained according to the beer-lambert law, which can be expressed as:

I₂＝I₀exp[-α(ν)CL] (4)

the light intensity of the detector can be expressed as:

therefore, in any path, the influence of interference type noise exists, the useful signal can be covered, and the output is added according to the characteristic of the inversion of the interference part of the system, so that the influence of the interference type noise is counteracted. Namely:

I_t＝I_o1+I_o2＝2I₁+2I₀exp[-α(ν)CL] (7)

accordingly, the influence of interference type noise can be eliminated.

In a TDLAS-based gas sensing system, the noise caused by reflection and other interferences in different paths is often the most difficult bottleneck to deal with, and the biggest obstacle to the stability and reliability of the system is seriously affected. The invention can effectively eliminate the influence of interference type noise as false absorption peak, realize the high-efficiency and quick detection of toxic, inflammable and explosive gas and trace gas, and can be widely applied to the fields of factory monitoring, atmosphere monitoring and the like in chemical engineering, environmental protection and the like.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention.

FIG. 2 is an output signal when methane is not passed through the gas cell. Channel 1 is the light intensity signal of detector 3, channel 2 is the light intensity signal of detector 4, and channel M is the addition signal of channel 1 and channel 2.

FIG. 3 shows the output signal of methane with a standard concentration of 20% in the gas cell. Channel 1 is the light intensity signal of detector 3, channel 2 is the light intensity signal of detector 4, and channel M is the addition signal of channel 1 and channel 2.

Reference numbers in the figures: 1 is a light source, 2 is a circulator, 3, 4 are photodetectors, 5 is a 2 × 2 fiber coupler, 6 is a reflection point, 7 is a detection gas chamber, 4 is a photodetector, 8 is an acquisition processing system, C1 is an optical path between 5 and 6, and C2 is an optical path between 5 and 7.

Detailed Description

The present invention will be described in further detail below by taking the detection of methane concentration as an example.

Referring to fig. 1, the laser used was DFB-BF14-1654 model DFB laser manufactured by wuhan sixjiu sensing technology ltd, the fiber coupler and the circulator were single mode fiber couplers manufactured by wuhan postal and telecommunications research institute, and the photodetector was an InGaAs photodetector model GT322C500 manufactured by 44. The DFB laser is a tunable laser which can cover the absorption peak wavelength of 1653.7nm of methane, and the used optical fiber is a single-mode fiber of 'corning' G.652 model produced in the United states. The light source, the detector, the coupler, the circulator, the air chamber and the like are connected in an FC/APC jumper connection mode, the acquisition card is the porphyry PCI9816, the effective detection optical path of the reflection-type air chamber 7 is 10cm, and the middle optical fiber connection is formed by fusion welding.

Fig. 2 is a waveform collected by the collection system when no methane is introduced into the gas chamber, wherein the channel 1 is a light intensity signal of the detector 3, the channel 2 is a light intensity signal of the detector 4, and the channel M is an added signal of the channel 1 and the channel 2, so that the added signals are original TDLAS tuned pulse scanning signals, and the waveform is an approximate triangular wave straight line, which indicates that the different-path interference noise has been effectively suppressed.

FIG. 3 shows that methane with a standard concentration of 20% is introduced into the gas chamber, wherein the channel 1 is a light intensity signal of the detector 3, the channel 2 is a light intensity signal of the detector 4, and the channel M is an added signal of the channel 1 and the channel 2, so that after the addition, an absorption peak at a corresponding position appears in the M channel signal. After the processing, absorption spectrum signals after the interference type noise influence is removed are shown, the triangular wave straight line waveform is concave, the surface point just covers the absorption spectrum line of methane, according to the signals, concentration inversion can be carried out based on the Bell-Lambert law, the calculated absorption concentration is 19.8%, and the accuracy of the system is also verified.

As a preferred embodiment of the present invention, the circulator 2 may be replaced with a fiber coupler.

The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.