CN107014774B - A kind of gas chamber trace gas analysis systems in parallel double and gas concentration calculate method - Google Patents
A kind of gas chamber trace gas analysis systems in parallel double and gas concentration calculate method Download PDFInfo
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- CN107014774B CN107014774B CN201710435871.XA CN201710435871A CN107014774B CN 107014774 B CN107014774 B CN 107014774B CN 201710435871 A CN201710435871 A CN 201710435871A CN 107014774 B CN107014774 B CN 107014774B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
Abstract
The invention proposes a kind of double gas chamber trace gas analysis systems in parallel, which is characterized in that includes circuit module, optical module and gas path module, laser drive circuit and digital temperature control module are connected to laser；Laser is divided into two beams and passes through the laser light incident interface that optical fiber is connected to standard gas chamber and sample gas gas chamber respectively by beam splitter；Optical fiber is connected to standard gas chamber and the laser emitting interface of sample gas gas chamber is respectively connected to the second collimation plus lens and third collimation plus lens by optical fiber；First photodiode detector is connected to the first pre-amplification circuit, and the second photodiode detector is connected to the second pre-amplification circuit.This invention removes the influence of the unstable factors to gas analysis result such as laser wavelength drift in TDLAS technology and temperature, pressure variation, improve serious forgiveness of the system to laser performance and the adaptive faculty to environment.
Description
Technical field
The present invention relates to a kind of double gas chamber trace gas analysis systems in parallel and gas concentration to calculate method.
Background technique
Tunable diode laser absorption spectroscopy method (TDLAS, Tunable Diode Laser Absorption
Spectroscopy it is) a kind of technology for being widely used in trace gas concentration detection, is widely used in petrochemical industry, environment
The fields such as detection, biological medicine, aerospace have many advantages, such as that selectivity is good, precision is high, non-contact in real time.TDLAS technology base
In molecular absorption spectrum principle, since the vibration mode of gas with various molecule causes molecule that can absorb the laser of specific wavelength, than
Erlang wins (Beer-Lambert) law, i.e., contains the absorption of object gas by certain length when the laser of a branch of specific wavelength
Chi Hou, the decay intensity of output intensity and the proportional relationship of the concentration of gas.In practical applications, the driving current of laser
Increase high frequency sinusoidal modulation electric current with reduce low-frequency noise interference, improve measurement accuracy, by mathematical computations it can be proved that
Under the conditions of certain environment, the signal height of the second harmonic signal of spectral signal and the concentration of under test gas and absorption cell light path at
Direct ratio.
Existing TDLAS system often only one analysis gas chamber, under test gas is in the gas chamber by laser irradiation shape
At corresponding spectral signal, but since the property of gas itself is influenced by temperature and pressure, the gas of same concentrations is not
Absorption spectrum broadening and height under synthermal is all different, therefore generally needs to carry out the processing of constant temperature heat tracing to gas chamber, in addition inhaling
It receives spectral line positioning and temperature adjustmemt scheduling algorithm reduces the influence of unstable factor, and the tunable semiconductor that system uses
(DFB) laser all has higher requirements to laser breadth of spectrum line, side mode suppression ratio and stability, this laser price compared with
For valuableness.To sum up, the application of constant temperature system, precision components and correction algorithm can greatly improve the cost of equipment, increase equipment
Volume, it is often more important that determining for various corrected parameters needs a large amount of nominal data accumulation, cannot be completely secured on long terms
Measure the accuracy of concentration.
Summary of the invention
The present invention proposes a kind of in parallel pair of gas chamber trace gas analysis system and calculation method method, eliminates TDLAS skill
The influence of the unstable factors to gas analysis result such as laser wavelength drift and temperature, pressure variation in art, improves system to sharp
The serious forgiveness of light device performance and adaptive faculty to environment.
What the present invention was realized particular by following technical scheme:
A kind of gas chamber trace gas analysis systems in parallel double, include circuit module, optical module and gas path module,
The circuit module is divided into control circuit, signal processing circuit and data processing unit, and the control circuit includes
Modulation waveform generator, laser drive circuit and digital temperature control module, the modulation waveform generator and laser drive circuit phase
Even；The signal processing circuit includes the first processing circuit and second processing circuit, and first processing circuit includes successively connecting
The first pre-amplification circuit, the first filter circuit, the first lock-in amplifier connect；The second processing circuit respectively includes successively
The second pre-amplification circuit, the second filter circuit, the second lock-in amplifier of connection；First filter circuit, the first locking phase
Amplifier, the second filter circuit, the second lock-in amplifier are connected to data processing unit；The modulation waveform generator difference
It is connected to the first lock-in amplifier, the second lock-in amplifier；
The optical module include laser, first collimation plus lens, beam splitter, the first photodiode detector,
Second photodiode detector, the second collimation plus lens and third collimate plus lens, and the laser, the first collimation converge
Poly- lens, beam splitter are successively coupled；First photodiode detector and the second collimation plus lens are coupled；
Second photodiode detector and third collimation plus lens are coupled；
The gas path module includes the standard gas chamber being set side by side and sample gas gas chamber, the standard gas chamber and sample gas gas chamber
One end is respectively equipped with laser light incident interface and laser emitting interface, and the other end is equipped with reflecting mirror, and the access of laser light incident interface swashs
Light projects after reflecting mirror from laser emitting interface；
The laser drive circuit and digital temperature control module are connected to laser；Laser is divided into two beams by the beam splitter
The laser light incident interface of standard gas chamber and sample gas gas chamber is connected to by optical fiber respectively；The optical fiber is connected to standard gas chamber and sample
The laser emitting interface of gas gas chamber is respectively connected to the second collimation plus lens by optical fiber and third collimates plus lens；It is described
First photodiode detector is connected to the first pre-amplification circuit, and second photodiode detector is connected to second
Pre-amplification circuit.
A kind of gas concentration calculating method of double gas chamber trace gas analysis systems in parallel, comprising the following steps:
S1: standard gas chamber encapsulates the calibrating gas of known concentration, and sample gas gas chamber is passed through under test gas；
S2: adjusting modulation waveform generator, and the laser intensity of the laser transmitting after being tuned is I0(v), by the first standard
Being divided into laser intensity by beam splitter after straight plus lens collimation convergence is I1(v) and I2(v) two-way, wherein laser intensity is I1
(v) it is L that laser, which enters light path by the laser light incident interface of standard gas chamber,1Standard gas chamber, with the concentration encapsulated in gas chamber
For C1Calibrating gas act on and be reflected by a reflector, from the laser emitting interface of standard gas chamber project, the spectral signal of formation
It is introduced the first photodiode detector by optical fiber and the second collimation plus lens and is received；Laser intensity is I2(v) laser is logical
It is L that the laser light incident interface for crossing sample gas gas chamber, which enters light path,2Sample gas gas chamber, with concentration in gas chamber be C2Under test gas effect
And be reflected by a reflector, it is projected from the laser emitting interface of sample gas gas chamber, the spectral signal of formation is converged by optical fiber and third collimation
Poly- lens introduce the second photodiode detector and receive；
S3: the optical signal of above-mentioned first photodiode detector passes through the first pre-amplification circuit, the first filtering respectively
Circuit, the first lock-in amplifier obtain second harmonic, as reference signal；The optical signal of above-mentioned second photodiode detector
Second harmonic is obtained by the second pre-amplification circuit, the second filter circuit, the second lock-in amplifier respectively, as letter to be measured
Number；
S4: by the reference signal and measured signal of the second harmonic that data processing unit relatively obtains, be calculated to
Survey the concentration of gas.
Calculation method in above-mentioned steps S4 are as follows:
S4.1: calculating laser drive circuit is the actual current i (t) that laser provides:
I (t)=ic+imcosωt (I)
In public formula (I), icIndicate the central current of laser drive circuit, imIndicate the current-modulation of modulation waveform generator
Amplitude, ω indicate modulating frequency, and t indicates the time；
Calculate the actual frequency v (t) that laser issues laser:
V (t)=vc+vmcosωt (II)
In public formula (II), vcIndicate laser emitting light center frequency, vmIndicate frequency modulation(PFM) amplitude；
S4.2: establishing the second harmonic waveform of nondimensionalization, and mathematical computations are available: the wave of the second harmonic extracted
Shape A0(v) it can be written as:
Wherein, I0(v) indicate that frequency is the incident intensity of v；C indicates the concentration of tested component, and L indicates light beam in gas
The light path passed by, α (v) indicates the absorption cross-section of gas at frequency v, related with temperature T and pressure P, secondary after nondimensionalization
Harmonic amplitude, i.e. peak height are directly proportional to concentration of component to be measured；
S4.3: the second harmonic waveform of reference signal can be obtained according to public formula (III) are as follows:
The second harmonic waveform of measured signal are as follows:
It is available in conjunction with public formula (IV) and (V):
S4.4: the central light strength I that the amplitude A and detector for only needing to extract second harmonic in practical application are detected, i.e.,
Are as follows:
Wherein I1For the laser intensity for entering standard gas chamber, I2For the laser intensity for entering sample gas gas chamber, A1To obtain
Second harmonic reference signal value, A2Measured signal value for obtained second harmonic,
Above-mentioned formula (VII) the i.e. concentration calculation formula of under test gas.
The present invention is the beneficial effects are as follows: since the beam splitting laser entered in two gas chambers comes from same light source, wavelength
Drift it is with uniformity, therefore be synchronous with the influence of measured signal to reference signal；In addition, at double air chamber structures in parallel
Under the same environment temperature, the curve of spectrum of standard gas and sample gas is consistent with respect to variation degree.To sum up, even if laser wave
Long drift or environment temperature change, and have reference signal always to assess the influence of these unstable factors in real time, to realize
To the exact inversion of gas concentration to be measured.
Detailed description of the invention
In order to more clearly explain the embodiment of the invention or the technical proposal in the existing technology, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is only this
Some embodiments of invention for those of ordinary skill in the art without creative efforts, can be with
It obtains other drawings based on these drawings.
Fig. 1 is the structure principle chart of analysis system of the invention.
Fig. 2 is the second harmonic waveform diagram of nondimensionalization.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, complete
Site preparation description, it is clear that described embodiments are only a part of the embodiments of the present invention, instead of all the embodiments.It is based on
Embodiment in the present invention, it is obtained by those of ordinary skill in the art without making creative efforts every other
Embodiment shall fall within the protection scope of the present invention.
A kind of double gas chamber trace gas analysis systems in parallel as shown in Figure 1, include circuit module 1, optical module 2 and gas circuit
Module 3,
The circuit module 1 divides for control circuit 1.1, signal processing circuit 1.2 and data processing unit 1.3, the control
Circuit 1.1 processed includes modulation waveform generator 1.1.1, laser drive circuit 1.1.2 and digital temperature control module 1.1.3, the tune
Waveform generator 1.1.1 processed is connected with laser drive circuit 1.1.2；The signal processing circuit 1.2 includes the first processing circuit
It 1.2.1 include sequentially connected first pre-amplification circuit with second processing circuit 1.2.2, the first processing circuit 1.2.1
1.2.1.1, the first filter circuit 1.2.1.2, the first lock-in amplifier 1.2.1.3；The second processing circuit 1.2.2 is wrapped respectively
Include sequentially connected second pre-amplification circuit 1.2.2.1, the second filter circuit 1.2.2.2, the second lock-in amplifier
1.2.2.3；The first filter circuit 1.2.1.2, the first lock-in amplifier 1.2.1.3, the second filter circuit 1.2.2.2,
Two lock-in amplifier 1.2.2.3 are connected to data processing unit 1.3；The modulation waveform generator 1.1.1 is respectively connected to
First lock-in amplifier 1.2.1.3, the second lock-in amplifier 1.2.2.3；
The optical module 2 includes that laser 2.1, first collimates plus lens 2.2, beam splitter 2.3, two pole of the first photoelectricity
Pipe detector 2.5, the second photodiode detector 2.6, second collimation plus lens 2.7 and third collimate plus lens 2.8,
The laser 2.1, first collimates plus lens 2.2, beam splitter 2.3 is successively coupled；First photodiode is visited
It surveys device 2.5 and the second collimation plus lens 2.7 is coupled；Second photodiode detector 2.6 and third collimation converge
Poly- lens 2.8 are coupled；
The gas path module 3 includes the standard gas chamber 3.1 and sample gas gas chamber 3.2 being set side by side, 3.1 He of standard gas chamber
One end of sample gas gas chamber 3.2 is respectively equipped with laser light incident interface and laser emitting interface, and the other end is equipped with reflecting mirror 3.3, laser
The laser of incident interface access projects after reflecting mirror 3.3 from laser emitting interface；
The laser drive circuit 1.1.2 and number temperature control module 1.1.3 are connected to laser 2.1；The beam splitter
Laser is divided into two beams by 2.3 passes through the laser light incident interface that optical fiber is connected to standard gas chamber 3.1 and sample gas gas chamber 3.2 respectively；Institute
State that optical fiber is connected to standard gas chamber 3.1 and the laser emitting interface of sample gas gas chamber 3.2 is respectively connected to the second collimation by optical fiber
Plus lens 2.7 and third collimate plus lens 2.8；First photodiode detector 2.5 is put before being connected to first
Big circuit 1.2.1.1, second photodiode detector 2.6 are connected to the second pre-amplification circuit 1.2.2.1.
A kind of gas concentration calculating method of double gas chamber trace gas analysis systems in parallel, comprising the following steps:
S1: standard gas chamber 3.1 encapsulates the calibrating gas of known concentration, and sample gas gas chamber 3.2 is passed through under test gas；
S2: adjusting modulation waveform generator 1.1.1, and the laser intensity that the laser 2.1 after being tuned emits is I0(v),
It is I by dividing after the first collimation collimation convergence of plus lens 2.2 by beam splitter 2.3 for laser intensity1(v) and I2(v) two-way,
Middle laser intensity is I1(v) it is L that laser, which enters light path by the laser light incident interface of standard gas chamber 3.1,1Standard gas chamber 3.1,
It is C with the concentration encapsulated in gas chamber1Calibrating gas act on and be reflected by a reflector, connect from the laser emitting of standard gas chamber 3.1
Mouth projects, and the spectral signal of formation is introduced the first photodiode detector 2.5 and connect by optical fiber and the second collimation plus lens 2.7
It receives；Laser intensity is I2(v) it is L that laser, which enters light path by the laser light incident interface of sample gas gas chamber 3.2,2Sample gas gas chamber
Concentration is C in 3.2, with gas chamber2Under test gas act on and be reflected by a reflector, from the laser emitting interface of sample gas gas chamber 3.2
It projects, the spectral signal of formation is introduced the second photodiode detector 2.6 and connect by optical fiber and third collimation plus lens 2.8
It receives；
S3: the optical signal of above-mentioned first photodiode detector 2.5 passes through the first pre-amplification circuit respectively
1.2.1.1, the first filter circuit 1.2.1.2, the first lock-in amplifier 1.2.1.3 obtain second harmonic, as reference signal；On
The optical signal for stating the second photodiode detector 2.6 passes through the second pre-amplification circuit 1.2.2.1, the second filter circuit respectively
1.2.2.2, the second lock-in amplifier 1.2.2.3 obtains second harmonic, as measured signal；
S4: it by the reference signal and measured signal of the second harmonic that data processing unit 1.3 compares, is calculated
The concentration of under test gas.
Calculation method in above-mentioned steps S4 are as follows:
S4.1: calculating laser drive circuit 1.1.2 is the actual current i (t) that laser 2.1 provides:
I (t)=ic+imcosωt (I)
In public formula (I), icIndicate the central current of laser drive circuit, imIndicate the current-modulation of modulation waveform generator
Amplitude, ω indicate modulating frequency, and t indicates the time；
Calculate the actual frequency v (t) that laser 2.1 issues laser:
V (t)=vc+vmcosωt (II)
In public formula (II), vcIndicate laser emitting light center frequency, vmIndicate frequency modulation(PFM) amplitude；
S4.2: the second harmonic waveform of nondimensionalization is as shown in Fig. 2, mathematical computations are available: that extracts is secondary humorous
The waveform A of wave0(v) it can be written as:
Wherein, I0(v) indicate that frequency is the incident intensity of v；C indicates the concentration of tested component, and L indicates light beam in gas
The light path passed by, α (v) indicates the absorption cross-section of gas at frequency v, related with temperature T and pressure P, secondary after nondimensionalization
Harmonic amplitude, i.e. peak height are directly proportional to concentration of component to be measured；
S4.3: the second harmonic waveform of reference signal can be obtained according to public formula (III) are as follows:
The second harmonic waveform of measured signal are as follows:
It is available in conjunction with public formula (IV) and (V):
S4.4: the central light strength I that the amplitude A and detector for only needing to extract second harmonic in practical application are detected, i.e.,
Are as follows:
Wherein I1For the laser intensity for entering standard gas chamber, I2For the laser intensity for entering sample gas gas chamber, A1To obtain
Second harmonic reference signal value, A2Measured signal value for obtained second harmonic,
Above-mentioned formula (VII) the i.e. concentration calculation formula of under test gas.
Factor alpha not relevant to environmental condition in public formula (VII), also eliminates ν relevant to laser performance, remaining
Item is known terms and can survey item.It therefore, can be straight in inverting under test gas concentration after using this double air chamber structures in parallel
It connects and carries out ratio calculating using reference signal, eliminate the shadow of the unstable factors such as laser wavelength drift and temperature, pressure variation
It rings, improves serious forgiveness of the system to laser performance and the adaptive faculty to environment.
Laser drive circuit provides tuning and high frequency modulated electric current for laser in the present invention, and the control of digital temperature control module swashs
The temperature of light device and detector.Laser drive circuit controls the laser that laser issues certain frequency, and laser is saturating by the first collimation
Enter beam splitter after mirror convergence, then is introduced between in double air chamber structures in parallel by optical fiber；One of gas chamber is as reference gas
Room, for encapsulating certain density calibrating gas, another gas chamber is passed through under test gas as sample gas gas chamber with certain flow；
The same laser of two bundle natures is reflected by a reflector light echo after calibrating gas and under test gas effect in different gas chambers
Fibre is received after converging by respective photodiode detector；The optical signal that two detectors receive passes through respective letter
After the amplification of number processing circuit, filtering and locking phase processing, reference signal and measured signal are respectively obtained；Finally system is transported by analysis
It calculates inverting and obtains the concentration information of under test gas.This system is not necessarily to temperature correction coefficient and peak value tracking function, simplifies system and calculates
Method and demarcation flow avoid interference of the correction factor inaccuracy to measurement result.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all in essence of the invention
Within mind and principle, any modification, equivalent replacement, improvement and so on be should all be included in the protection scope of the present invention.
Claims (1)
1. a kind of gas chamber trace gas analysis systems in parallel double, which is characterized in that comprising circuit module (1), optical module (2) and
Gas path module (3),
The circuit module (1) is divided into control circuit (1.1), signal processing circuit (1.2) and data processing unit (1.3), institute
Stating control circuit (1.1) includes modulation waveform generator (1.1.1), laser drive circuit (1.1.2) and digital temperature control module
(1.1.3), the modulation waveform generator (1.1.1) are connected with laser drive circuit (1.1.2)；The signal processing circuit
It (1.2) include the first processing circuit (1.2.1) and second processing circuit (1.2.2), first processing circuit (1.2.1) includes
Sequentially connected first pre-amplification circuit (1.2.1.1), the first filter circuit (1.2.1.2), the first lock-in amplifier
(1.2.1.3)；The second processing circuit (1.2.2) respectively include sequentially connected second pre-amplification circuit (1.2.2.1),
Second filter circuit (1.2.2.2), the second lock-in amplifier (1.2.2.3)；First filter circuit (1.2.1.2), first
Lock-in amplifier (1.2.1.3), the second filter circuit (1.2.2.2), the second lock-in amplifier (1.2.2.3) are connected to data
Processing unit (1.3)；The modulation waveform generator (1.1.1) is respectively connected to the first lock-in amplifier (1.2.1.3), second
Lock-in amplifier (1.2.2.3)；
The optical module (2) includes laser (2.1), the first collimation plus lens (2.2), beam splitter (2.3), the first photoelectricity
Diode detector (2.5), the second photodiode detector (2.6), the second collimation plus lens (2.7) and third collimation converge
Poly- lens (2.8), the laser (2.1), the first collimation plus lens (2.2), beam splitter (2.3) are successively coupled；Institute
It states the first photodiode detector (2.5) and the second collimation plus lens (2.7) is coupled；Second photodiode
Detector (2.6) and third collimation plus lens (2.8) are coupled；
The gas path module (3) includes the standard gas chamber (3.1) and sample gas gas chamber (3.2) being set side by side, the standard gas chamber
(3.1) and one end of sample gas gas chamber (3.2) is respectively equipped with laser light incident interface and laser emitting interface, and the other end is equipped with reflecting mirror
(3.3), the laser of laser light incident interface access projects after reflecting mirror (3.3) from laser emitting interface；
The laser drive circuit (1.1.2) and digital temperature control module (1.1.3) are connected to laser (2.1)；The beam splitting
Laser is divided into two beams and passes through the laser light incident that optical fiber is connected to standard gas chamber (3.1) and sample gas gas chamber (3.2) respectively by device (2.3)
Interface；The optical fiber is connected to standard gas chamber (3.1) and the laser emitting interface of sample gas gas chamber (3.2) is separately connected by optical fiber
To the second collimation plus lens (2.7) and third collimation plus lens (2.8)；First photodiode detector (2.5)
It is connected to the first pre-amplification circuit (1.2.1.1), second photodiode detector (2.6) is put before being connected to second
Big circuit (1.2.2.1).
Gas concentration calculates method, comprising the following steps:
S1: standard gas chamber (3.1) encapsulates the calibrating gas of known concentration, and sample gas gas chamber (3.2) is passed through under test gas；
S2: being adjusted modulation waveform generator (1.1.1), and the laser intensity of laser (2.1) transmitting after being tuned is I0(v), quilt
Being divided into laser intensity by beam splitter (2.3) after first collimation plus lens (2.2) collimation convergence is I1(v) and I2(v) two-way,
Wherein laser intensity is I1(v) it is L that laser, which enters light path by the laser light incident interface of standard gas chamber (3.1),1Standard gas chamber
It (3.1), is C with the concentration encapsulated in gas chamber1Calibrating gas act on and be reflected by a reflector, from standard gas chamber (3.1) swash
Light is emitted interface and projects, and the spectral signal of formation introduces the first photodiode by optical fiber and the second collimation plus lens (2.7)
Detector (2.5) receives；Laser intensity is I2(v) laser enters light path by the laser light incident interface of sample gas gas chamber (3.2)
For L2Sample gas gas chamber (3.2), with concentration in gas chamber be C2Under test gas act on and be reflected by a reflector, from sample gas gas chamber
(3.2) laser emitting interface projects, and the spectral signal of formation introduces the second light by optical fiber and third collimation plus lens (2.8)
Electric diode detector (2.6) receives；
S3: the optical signal of above-mentioned first photodiode detector (2.5) passes through the first pre-amplification circuit respectively
(1.2.1.1), the first filter circuit (1.2.1.2), the first lock-in amplifier (1.2.1.3) obtain second harmonic, as reference
Signal；The optical signal of above-mentioned second photodiode detector (2.6) pass through respectively the second pre-amplification circuit (1.2.2.1),
Second filter circuit (1.2.2.2), the second lock-in amplifier (1.2.2.3) obtain second harmonic, as measured signal；
S4: by the reference signal and measured signal of the second harmonic that data processing unit (1.3) compares, be calculated to
Survey the concentration of gas；
Calculation method in above-mentioned steps S4 are as follows:
S4.1: calculating laser drive circuit (1.1.2) is the actual current i (t) that laser (2.1) provide:
I (t)=ic+im cosωt (I)
In public formula (I), icIndicate the central current of laser drive circuit, imIndicate the current-modulation amplitude of modulation waveform generator,
ω indicates modulating frequency, and t indicates the time；
Calculate the actual frequency v (t) that laser (2.1) issue laser:
V (t)=vc+vm cosωt (m)
In public formula (II), vcIndicate laser emitting light center frequency, vmIndicate frequency modulation(PFM) amplitude；
S4.2: establishing the second harmonic waveform of nondimensionalization, and mathematical computations are available: the waveform A of the second harmonic extracted0
(v) it can be written as:
Wherein, I0(v) indicate that frequency is the incident intensity of v；C indicates the concentration of tested component, and L indicates that light beam is passed by gas
Light path, α (v) indicate frequency v at gas absorption cross-section, second harmonic nondimensionalization after related with temperature T and pressure P
Amplitude, i.e. peak height are directly proportional to concentration of component to be measured；
S4.3: the second harmonic waveform of reference signal can be obtained according to public formula (III) are as follows:
The second harmonic waveform of measured signal are as follows:
It is available in conjunction with public formula (IV) and (V):
S4.4: the central light strength I that the amplitude A and detector for only needing to extract second harmonic in practical application are detected, i.e., are as follows:
Wherein I1For the laser intensity for entering standard gas chamber, I2For the laser intensity for entering sample gas gas chamber, A1For obtain two
The reference signal value of subharmonic, A2Measured signal value for obtained second harmonic,
Above-mentioned formula (VII) the i.e. concentration calculation formula of under test gas.
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| CN108426813B (en) * | 2018-04-08 | 2021-03-26 | 山东省科学院激光研究所 | Mixed gas concentration detection system, method and device |
| CN108507976A (en) * | 2018-04-17 | 2018-09-07 | 广东电网有限责任公司 | A kind of CO analyzers based on TDLAS technologies |
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