Fire smoke particle detection device and method based on scattering difference spectrum

Abstract

The present invention discloses a fire smoke particle detection device and method based on scattering differential spectrum. The combination of an aerosol generator and an air pump can simulate a smoke environment and adjust the concentration of smoke particles in the environment to maintain the stability of the smoke environment. A xenon lamp is used as a light source to provide a wide-band spectral output. A reflective spectrometer detects the spectral characteristics of light, and a polarizer and a photoelastic modulator are used to convert the light into linearly polarized light, which is then irradiated on smoke particles to generate scattered light in different directions. The polarizer can receive scattered light in different directions through a rotating base and only allows light with a specific polarization angle to be transmitted to the detector, thereby simulating different smoke particle emission conditions and obtaining corresponding scattered photoelectric signals. Finally, a Labview program is used to deduce the matrix elements of the fire smoke particles, and then the type and particle size of the smoke particles are calculated, so that the present invention has good real-time performance and accuracy.

Description

Technical Field

[0001] The present invention relates to a fire smoke particle detection device and method, in particular to a fire smoke particle detection device and method based on scattering difference spectrum, belonging to the technical field of fire smoke monitoring. Background Art

[0002] Optical sensors are a common technology used in fire detection and smoke monitoring. Optical sensors use optical principles to measure or detect certain physical quantities. In fire detection, optical sensors can be used to detect light signals in smoke and thereby determine whether a fire has occurred. Existing technologies have already begun to be applied, such as patent publication number CN105043944A, entitled "Device and Method for Detecting Haze Particles Based on Solar-Blind Ultraviolet Light." This method uses an LED to emit UV light, which passes through a series of optical components. A photodetector receives the scattered light. A stepper motor controller adjusts the position of the polarizer and λ / 4 wave plate to obtain light in different polarization states. Finally, the Stokes vector matrix and Mie scattering theory are used to calculate the particle size of haze particles. However, this method has the following drawbacks: 1. It is limited by the propagation characteristics of UV light and the sensitivity of the detector. 2. Mie scattering theory is not accurate enough for non-spherical or irregularly shaped particles.

[0003] Another example is patent publication number CN111947783A, titled "Polarization Transmission Characteristics Testing and Simulation Verification Method for Spherical Multiple Scattering Media." This invention simulates a non-spherical particle environment using a particle generator and a smoke chamber, measures particle morphology and size using an electron microscope, and measures medium concentration using an optical power meter. Finally, the T-matrix and Monte Carlo methods are used to simulate and verify the experimental data. While this approach has some effectiveness, the high computational complexity of the T-matrix and Monte Carlo methods results in low processing efficiency and an inability to output processed data in a timely manner. This results in poor real-time performance and accuracy, failing to meet requirements.

[0004] In summary, the technical problem to be solved by the present invention is how to provide a new device and method that can simulate different smoke particle emission conditions and, after denoising the corresponding optical scattering signal, ultimately output the type and particle size of fire smoke particles in real time and accurately. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention provides a fire smoke particle detection device and method based on scattering differential spectrum, which can simulate different smoke particle emission conditions and, after denoising the corresponding optical scattering signal, finally analyze the fire smoke particles through scattering differential spectrum, and can output the type and particle size of the fire smoke particles in real time and accurately.

[0006] To achieve the above-mentioned object, the technical solution adopted by the present invention is as follows: a fire smoke particle detection device based on scattering differential spectrum, comprising a light source, a reflective spectrometer, a lens, a chopper, a polarizer, a photoelastic modulator, a smoke particle generation system, an analyzer, a detector, a dual-channel lock-in amplifier and a computer;

[0007] The smoke particle generating system includes an aerosol generator, a nozzle, an air extraction nozzle, and an air extraction pump. The nozzle and the air extraction nozzle are arranged opposite to each other with a gap between them. The aerosol generator sprays the collected smoke particles into the gap through the nozzle; the air extraction pump is used to suck the smoke particles around the gap through the air extraction nozzle to adjust the concentration of the smoke particles in the gap.

[0008] The light source excites light toward the reflective spectrometer, which detects the spectral characteristics of the light. The detected light is transmitted to a lens for collimation, and then reaches a chopper. The chopper modulates the light, converts the light into linearly polarized light through a polarizer, and transmits the light to a photoelastic modulator. The photoelastic modulator polarizes the linearly polarized light, so that the modulated linearly polarized light illuminates the smoke particles in the gap, thereby generating scattered light in different directions.

[0009] The analyzer and detector are both mounted on a rotating base, with the analyzer located in the optical path of light received by the detector. The analyzer is used to filter the incoming light, transmitting the filtered scattered light to the detector, which converts the optical signal into an electrical signal and transmits it to a dual-channel lock-in amplifier. The rotating base can rotate about its central axis, driving the analyzer and detector to rotate, thereby enabling the detector to receive scattered light from different directions.

[0010] The dual-channel lock-in amplifier is connected to a chopper and a photoelastic modulator, which provide a reference frequency for denoising the electrical signal transmitted from the detector and transmit the processed signal to a computer; the computer processes the signal and ultimately determines the type and particle size of the fire smoke particles.

[0011] Furthermore, the light source is a xenon lamp. Using a xenon lamp as a light source can provide a wide-band spectral output, which enables detection to cover a wider wavelength range, and the wide-band measurement can better capture the scattering characteristics of aerosol particles at different wavelengths.

[0012] Furthermore, the polarizer and analyzer are both Glan Taylor prisms.

[0013] Furthermore, the polarizer forms an angle of 45° with the horizontal direction to facilitate subsequent calculations.

[0014] Furthermore, the angle between the photoelastic modulator and the analyzer and the horizontal direction is 0°, which facilitates the analyzer to filter the scattered light and filter the interference light from the surrounding environment.

[0015] Furthermore, the rotation of the rotating base can drive the detector to receive scattered light with a scattering angle ranging from 0° to 180°, so that scattered light with different scattering angles can be received to ensure the data required for subsequent calculations.

[0016] The detection method of the fire smoke particle detection device based on the scattering difference spectrum mentioned above has the following specific steps:

[0017] Step 1: Smoke particle generation: First, collect the smoke particles to be tested and put them into the aerosol generator, then start the aerosol generator to spray the collected smoke particles through the nozzle to the gap; at the same time, control the air pump to start, and the air pump sucks the smoke particles around the gap through the air nozzle to keep the smoke particle concentration in the gap stable;

[0018] Step 2, exciting light and receiving scattered light: start the light source, and the light source excites light toward the reflective spectrometer. The reflective spectrometer detects the spectral characteristics of the light. After detection, the light is transmitted to the lens for collimation, and then the light reaches the chopper; after the chopper chops and modulates the light, the light is converted into linearly polarized light through the polarizer and transmitted to the photoelastic modulator. The photoelastic modulator polarization modulates the linearly polarized light so that the modulated linearly polarized light illuminates the smoke particles in the gap, thereby generating scattered light in different directions; then one of the scattered light in different directions will be transmitted to the current position of the analyzer. At this time, the analyzer will filter the incoming light and only allow the linearly polarized light with the same direction to pass through, so that the filtered scattered light is transmitted to the detector. The detector converts the optical signal into an electrical signal and transmits it to the dual-channel phase-locked amplifier; then the rotating base is controlled to rotate, driving the analyzer and the detector to rotate, so that the detector can receive scattered light in different directions;

[0019] Step 3: Calculate the light intensity signal: The dual-channel lock-in amplifier denoises the electrical signal from the detector based on the reference frequency provided by the chopper and photoelastic modulator, and transmits the processed signal to the computer, which processes the signal to obtain the light intensity signal of the scattered light in different directions;

[0020] Step 4: Determine the type and size of the fire smoke particles: Use the light intensity signal obtained in step 3 to calculate the matrix elements of the fire smoke particles using the existing Labview program, and then calculate the type and size of the smoke particles.

[0021] Furthermore, the step 3 of calculating the light intensity signal is specifically as follows:

[0022] The light intensity signal received by the detector should satisfy the following formula:

[0023] I∝S0′+S1′cos2(AM)+(S2′cosδ-S3′sinδ)sin2(AM)

[0024] Wherein, δ(t)=φsinωt is the modulation function of the photoelastic modulator, φ represents the modulation amplitude of the photoelastic modulator, and ω represents the modulation frequency of the photoelastic modulator;

[0025] Performing Bessel expansion on this function yields:

[0026] cosδ=cos(φsin(ωt))=J0+2J2(φ)cos(2ωt)+2J4(φ)cos(4ωt)+…

[0027] sinδ=sin(φsin(ωt))=2J1(φ)cos(ωt)+2J3(φ)cos(3ωt)+…

[0028] Among them, J n is an n-order Bessel function; in the formula, only the first and second harmonic terms with the largest contribution need to be considered, and the contributions of other terms are negligible; the first and second harmonic terms of the photoelastic modulator are used as reference frequencies;

[0029] That is, the measured 1f harmonic signal and 2f harmonic signal are:

[0030] I 1f ∝-S3′sin 2(AM)sinδ

[0031] I 2f ∝S2′sin2(AM)cosδ

[0032] Thus, the light intensity signals of scattered light in different directions can be calculated.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The present invention adopts a specific detection device, in which the combination of an aerosol generator and an air pump can simulate a smoky environment, and can adjust the concentration of smoke particles in the environment to maintain the stability of the smoky environment; the light source adopts a xenon lamp to provide a wide-band spectral output, which enables the detection to cover a wider wavelength range, and the wide-band measurement can better capture the scattering characteristics of aerosol particles at different wavelengths; the reflective spectrometer detects the spectral characteristics of light, and adopts a combination of a polarizer and a photoelastic modulator to convert the light into linearly polarized light, irradiates the smoke particles, and thereby generates scattered light in different directions; the polarizer can receive scattered light in different directions through a rotating base, and only allows light with a specific polarization angle to transmit, thereby filtering out interfering light and transmitting it to the detector, thereby simulating different smoke particle emissions and obtaining corresponding scattered photoelectric signals after filtering.

[0035] 2. In the detection method of the present invention, after receiving the scattered photoelectric signal fed back by the detector, the dual-channel phase-locked amplifier denoises the electrical signal transmitted from the detector according to the reference frequency provided by the chopper and the photoelastic modulator, and transmits the processed signal to the computer. The computer uses a specific scattered differential spectrum processing method to obtain the light intensity signal of scattered light in different directions; finally, the Labview program is used to calculate the matrix elements of the fire smoke particles, and then the type and particle size of the smoke particles are calculated, so that the present invention has better real-time performance and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the overall structure of the detection device of the present invention;

[0037] Figure 2 It is a flow chart of the detection method of the present invention.

[0038] In the figure: 1. Light source, 2. Reflection spectrometer, 3. Lens, 4. Chopper, 5. Polarizer, 6. Photoelastic modulator, 7. Aerosol generator, 8. Analyzer, 9. Detector, 10. Rotating base, 11. Air pump, 12. Dual-channel lock-in amplifier, 13. Computer. DETAILED DESCRIPTION

[0039] The present invention will be further described below.

[0040] like Figure 1 As shown, a fire smoke particle detection device based on scattering differential spectrum includes a light source 1, a reflective spectrometer 2, a lens 3, a chopper 4, a polarizer 5, a photoelastic modulator 6, a smoke particle generation system, an analyzer 8, a detector 9, a dual-channel lock-in amplifier 12 and a computer 13;

[0041] The smoke particle generating system includes an aerosol generator 7, a nozzle, an air extraction nozzle, and an air extraction pump 11. The nozzle and the air extraction nozzle are arranged opposite to each other with a gap between them. The aerosol generator 7 sprays the collected smoke particles into the gap through the nozzle; the air extraction pump 11 is used to suck the smoke particles around the gap through the air extraction nozzle to adjust the concentration of the smoke particles in the gap.

[0042] The light source 1 excites light toward the reflective spectrometer 2, which detects the spectral characteristics of the light. The detected light is then passed to the lens 3 for collimation, and then reaches the chopper 4. After the chopper 4 modulates the light, the polarizer 5 converts the light into linearly polarized light and passes it to the photoelastic modulator 6. The photoelastic modulator 6 performs polarization modulation on the linearly polarized light, so that the modulated linearly polarized light illuminates the smoke particles in the gap, thereby generating scattered light in different directions. The light source 1 is a xenon lamp. Using a xenon lamp as a light source can provide a wide-band spectral output, which enables the detection to cover a wider wavelength range, and the wide-band measurement can better capture the scattering characteristics of aerosol particles at different wavelengths.

[0043] The analyzer 8 and detector 9 are both mounted on a rotating base 10, and the analyzer 8 is located in the optical path of the detector 9 for receiving light. The analyzer 8 is used to filter the incoming light so that the filtered scattered light is transmitted to the detector 9, and the detector 9 converts the optical signal into an electrical signal and transmits it to a dual-channel lock-in amplifier 12; the rotating base 10 can rotate around its central axis, driving the analyzer 8 and detector 9 to rotate, so that the detector 9 can receive scattered light in different directions; the polarizer 5 and analyzer 8 are both Glan Taylor prisms.

[0044] The dual-channel lock-in amplifier 12 is connected to the chopper 4 and the photoelastic modulator 6, which provide a reference frequency for denoising the electrical signal transmitted from the detector 9 and transmit the processed signal to the computer 13; the computer 13 processes the signal and ultimately determines the type and particle size of the fire smoke particles.

[0045] As an improvement to the present invention, the polarizer 5 forms a 45° angle with the horizontal direction to facilitate subsequent calculations. The photoelastic modulator 6 and analyzer 8 both form a 0° angle with the horizontal direction to facilitate the analyzer 8 to filter scattered light and eliminate interference from the surrounding environment.

[0046] As another improvement of the present invention, the rotation of the rotating base 10 can drive the detector 9 to receive scattered light with a scattering angle ranging from 0° to 180°. In this way, scattered light with different scattering angles can be received to ensure the data required for subsequent calculations.

[0047] like Figure 2As shown, the detection method of the fire smoke particle detection device based on the scattering difference spectrum has the following specific steps:

[0048] Step 1: Smoke particle generation: First, collect the smoke particles to be tested and put them into the aerosol generator 7, then start the aerosol generator 7 to spray the collected smoke particles through the nozzle to the gap; at the same time, control the air pump 11 to start, and the air pump 11 sucks the smoke particles around the gap through the air nozzle to keep the smoke particle concentration in the gap stable;

[0049] Step 2, exciting light and receiving scattered light: Start the light source 1, and the light source 1 excites light toward the reflective spectrometer 2. The reflective spectrometer 2 detects the spectral characteristics of the light. After detection, the light is transmitted to the lens 3 for collimation, and then the light reaches the chopper 4; after the chopper 4 chops and modulates the light, the light is converted into linearly polarized light through the polarizer 5 and transmitted to the photoelastic modulator 6. The photoelastic modulator 6 polarization-modulates the linearly polarized light so that the modulated linearly polarized light irradiates the smoke particles in the gap, thereby generating scattered light in different directions; then one of the scattered light in different directions will be transmitted to the current position of the polarizer 8. At this time, the polarizer 8 will filter the incoming light and only allow the linearly polarized light with the same direction to pass through, so that the filtered scattered light is transmitted to the detector 9. The detector 9 converts the optical signal into an electrical signal and transmits it to the dual-channel lock-in amplifier 12; then the rotating base 10 is controlled to rotate, driving the polarizer 8 and the detector 9 to rotate, so that the detector 9 can receive scattered light in different directions;

[0050] Step 3: Calculate the light intensity signal: The dual-channel lock-in amplifier 12 performs denoising on the electrical signal from the detector 9 based on the reference frequency provided by the chopper 4 and the photoelastic modulator 6, and transmits the processed signal to the computer 13. The computer 13 processes the signal to obtain the light intensity signal of the scattered light in different directions, which is specifically:

[0051] First, the plane optical anisotropy signal of fire smoke particle measurement is defined as:

[0052]

[0053] Among them, s x and s y represent the amplitude scattering coefficients of the sample in the x and y directions, respectively;

[0054] When the incident light passes through the polarizer, its electric vector is expressed as (E0,0); after being modulated by the photoelastic modulator (PEM), the electric vector of the incident light will be added with a phase δ(t) = φsinωt along the main axis of the PEM; φ represents the modulation amplitude of the PEM, and ω represents the modulation frequency of the PEM. Then the electric vector of the light passing through the PEM is expressed as After reflection from smoke particles, the electric vector of the reflected light is expressed as After passing through the analyzer with the polarization direction along the y direction, the electric vector and light intensity of the outgoing light are expressed as:

[0055]

[0056]

[0057] Where S=|s x +s y | 2 / 4 represents the scattering rate of the sample, Im and Re represent the imaginary part and real part of the complex number respectively. Usually around 10 -3 ~10 -5 Below the order of magnitude, so it can be ignored The square term of ; expanded using Bessel functions:

[0058] cosδ(t)=cos(φsinωt)=J0(φ)+2J2(φ)cos2ωt+2J4(φ)cos4ωt+…

[0059] sinδ(t)=sin(φsinωt)=2J1(φ)sinωt+2J3(φ)sin3ωt+…

[0060] And set φ = 0.383λ in the detection, then J0 = 0; then the detected light intensity can be expressed as:

[0061]

[0062] It can be seen that by using the dual-channel lock-in amplifier 12 to simultaneously collect the signals corresponding to the chopper, PEM single frequency and PEM double frequency, the values ​​of Im and Re can be obtained, and then the scattered light intensity signal can be obtained.

[0063] The degree of polarization of light is described by the Muller matrix, which can clearly and comprehensively reflect the polarization state of light. Therefore, the Stokes vector is used to describe the polarization state of polarized light.

[0064] S0=I x +I y ,

[0065] S1=I x -I y ,

[0066] S2=I 45° -I -45° ,

[0067] S3=I R -I L .

[0068] Among them, S0 is the sum of the light intensities in the x and y directions, that is, the total light intensity; S1 is the difference between the light intensities in the x and y directions, reflecting the linear polarization degrees in the horizontal and vertical directions; S2 is the difference between the light intensities in the +45° and -45° directions, reflecting the linear polarization degrees in the ±45° directions; the combination of S1 and S2 can represent linear polarization light of any polarization direction; S3 reflects the difference between the intensities of right-handed circularly polarized light and left-handed circularly polarized light, and can represent any elliptically polarized light. According to the fire smoke scattering differential spectrum system, the Stokes vector of the outgoing light entering the detector can be expressed as:

[0069] L out =AR(A)R(-M)MR(M)SR(-P)PL in

[0070] Among them, L out and L in are the Stokes parameters of the output and input light, A, M, S, and P are the Muller matrices of the analyzer, PEM, smoke particles, and polarizer, respectively, and R(±M) is the Muller matrix of the coordinate axis rotation. The expressions of the Muller matrices of the linearly polarized incident light and the optical elements involved in the scattering difference system are all known, so:

[0071]

[0072] Let S′=R(M)SR(-P)PL in ,but

[0073]

[0074]

[0075] Finally, the light intensity signal received by the detector 9 is calculated to satisfy the following formula:

[0076] I∝S0′+S1′cos2(AM)+(S2′cosδ-S3′sinδ)sin2(AM)

[0077] Wherein, δ(t)=φsinωt is the modulation function of the photoelastic modulator, φ represents the modulation amplitude of the photoelastic modulator, and ω represents the modulation frequency of the photoelastic modulator;

[0078] Performing Bessel expansion on this function yields:

[0079] cosδ=cos(φsin(ωt))=J0+2J2(φ)cos(2ωt)+2J4(φ)cos(4ωt)+…

[0080] sinδ=sin(φsin(ωt))=2J1(φ)cos(ωt)+2J3(φ)cos(3ωt)+…

[0081] Among them, J n is an n-order Bessel function; in the formula, only the first and second harmonic terms with the largest contribution need to be considered, and the contributions of other terms are negligible; the first and second harmonic terms of the photoelastic modulator are used as reference frequencies;

[0082] That is, the measured 1f harmonic signal and 2f harmonic signal are:

[0083] I 1f ∝-S3′sin2(AM)sinδ

[0084] I 2f ∝S2′sin2(AM)cosδ

[0085] Thus, the light intensity signals of scattered light in different directions can be calculated.

[0086] Step 4: Determine the type and size of the fire smoke particles: Use the light intensity signal obtained in step 3 to calculate the matrix elements of the fire smoke particles using the existing Labview program, and then calculate the type and size of the smoke particles.

[0087] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fire smoke particle detection device based on scattering difference spectrum, characterized in that: It includes a light source, a reflective spectrometer, a lens, a chopper, a polarizer, a photoelastic modulator, a smoke particle generation system, an analyzer, a detector, a dual-channel lock-in amplifier, and a computer; The smoke particle generating system includes an aerosol generator, a nozzle, an air extraction nozzle, and an air extraction pump. The nozzle and the air extraction nozzle are arranged opposite to each other with a gap between them. The aerosol generator sprays the collected smoke particles into the gap through the nozzle; the air extraction pump is used to suck the smoke particles around the gap through the air extraction nozzle to adjust the concentration of the smoke particles in the gap. The light source excites light toward the reflective spectrometer, which detects the spectral characteristics of the light. The detected light is transmitted to a lens for collimation, and then reaches a chopper. The chopper modulates the light, converts the light into linearly polarized light through a polarizer, and transmits the light to a photoelastic modulator. The photoelastic modulator polarizes the linearly polarized light, so that the modulated linearly polarized light illuminates the smoke particles in the gap, thereby generating scattered light in different directions. The analyzer and detector are both mounted on a rotating base, with the analyzer located in the optical path of light received by the detector. The analyzer is used to filter the incoming light, transmitting the filtered scattered light to the detector, which converts the optical signal into an electrical signal and transmits it to a dual-channel lock-in amplifier. The rotating base can rotate about its central axis, driving the analyzer and detector to rotate, thereby enabling the detector to receive scattered light from different directions. The dual-channel lock-in amplifier is connected to a chopper and a photoelastic modulator, which provide a reference frequency for denoising the electrical signal transmitted from the detector and transmit the processed signal to a computer; the computer processes the signal and ultimately determines the type and particle size of the fire smoke particles.

2. The fire smoke particle detection device based on scattering difference spectrum according to claim 1, characterized in that: The light source is a xenon lamp.

3. The fire smoke particle detection device based on scattering difference spectrum according to claim 1, characterized in that: The polarizer and analyzer are both Glan Taylor prisms.

4. The fire smoke particle detection device based on scattering difference spectrum according to claim 1, characterized in that: The polarizer forms an angle of 45° with the horizontal direction.

5. The fire smoke particle detection device based on scattering difference spectrum according to claim 1, characterized in that: The angle between the photoelastic modulator and the analyzer and the horizontal direction is 0°.

6. The fire smoke particle detection device based on scattering difference spectrum according to claim 1, characterized in that: The rotation of the rotating base can drive the detector to receive scattered light with a scattering angle of 0° to 180°.

7. A detection method for a fire smoke particle detection device based on scattering difference spectrum according to any one of claims 1 to 6, characterized in that: The specific steps are: Step 1: Smoke particle generation: First, collect the smoke particles to be tested and put them into the aerosol generator, then start the aerosol generator to spray the collected smoke particles through the nozzle to the gap; at the same time, control the air pump to start, and the air pump sucks the smoke particles around the gap through the air nozzle to keep the smoke particle concentration in the gap stable; Step 2, exciting light and receiving scattered light: start the light source, and the light source excites light toward the reflective spectrometer. The reflective spectrometer detects the spectral characteristics of the light. After detection, the light is transmitted to the lens for collimation, and then the light reaches the chopper; after the chopper chops and modulates the light, the light is converted into linearly polarized light through the polarizer and transmitted to the photoelastic modulator. The photoelastic modulator polarization modulates the linearly polarized light so that the modulated linearly polarized light illuminates the smoke particles in the gap, thereby generating scattered light in different directions; then one of the scattered light in different directions will be transmitted to the current position of the analyzer. At this time, the analyzer will filter the incoming light and only allow the linearly polarized light with the same direction to pass through, so that the filtered scattered light is transmitted to the detector. The detector converts the optical signal into an electrical signal and transmits it to the dual-channel phase-locked amplifier; then the rotating base is controlled to rotate, driving the analyzer and the detector to rotate, so that the detector can receive scattered light in different directions; Step 3: Calculate the light intensity signal: The dual-channel lock-in amplifier denoises the electrical signal from the detector based on the reference frequency provided by the chopper and photoelastic modulator, and transmits the processed signal to the computer, which processes the signal to obtain the light intensity signal of the scattered light in different directions; Step 4: Determine the type and size of the fire smoke particles: Use the light intensity signal obtained in step 3 to calculate the matrix elements of the fire smoke particles using the Labview program, and then calculate the type and size of the smoke particles.

8. The detection method according to claim 7, characterized in that The step 3 of calculating the light intensity signal is specifically as follows: The light intensity signal received by the detector should satisfy the following formula: I∝S0′+S1′cos2(AM)+(S2′cosδ-S3′sinδ)sin2(AM) Wherein, δ(t)=φsinωt is the modulation function of the photoelastic modulator, φ represents the modulation amplitude of the photoelastic modulator, and ω represents the modulation frequency of the photoelastic modulator; Performing Bessel expansion on this function yields: cosδ=cos(φsin(ωt))=J0+2J2(φ)cos(2ωt)+2J4(φ)cos(4ωt)+… sinδ=sin(φsin(ωt))=2J1(φ)cos(ωt)+2J3(φ)cos(3ωt)+… Among them, J n is an n-order Bessel function; in the formula, only the first and second harmonic terms with the largest contribution need to be considered, and the contributions of other terms are negligible; the first and second harmonic terms of the photoelastic modulator are used as reference frequencies; That is, the measured 1f harmonic signal and 2f harmonic signal are: I 1f ∝-S′3sin2(A-M)sinδ I 2f ∝S′2sin2(A-M)cosδ Thus, the light intensity signals of scattered light in different directions can be calculated.

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