Linear frequency modulation variable wavelength infrared light NDIR multi-element gas concentration sensing system and method

Abstract

The invention provides a linear frequency modulation variable wavelength infrared light NDIR multi-element gas concentration sensing system and method, and belongs to the field of gas concentration detection. The problem that an existing gas chamber structure cannot detect the concentration of various harmful gases at the same time is solved. Comprising an upper computer system and a four-ellipsoid optical gas chamber, four ellipsoid gas chambers are arranged in the four-ellipsoid optical gas chamber, and at least one hole is formed in the bottom of each ellipsoid gas chamber; an infrared light source module, a multi-channel infrared detector driving module, a multi-channel infrared detector module, a signal amplifying and filtering module, a main controller, a signal generating module, an infrared light source driving module and a communication module are arranged in the four-ellipsoid optical gas chamber; the upper computer system sends a first signal to the signal generation module, the signal generation module sends an instruction sent by the upper computer system to the main controller, the main controller sends a second signal to the infrared light source driving module, and linear frequency modulation is carried out on infrared light; the device and the method are applied to concentration detection of various underground hazardous gases.

Description

Technical Field

[0001] This application relates to the technical field of gas concentration sensing, and particularly to a linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system and method. Background Art

[0002] As an important energy resource, the safe production of coal is directly related to the lives of miners and the economic benefits of enterprises. The working environment in coal mines is complex, and there are various harmful gases, such as methane, hydrogen sulfide, carbon monoxide, ammonia, etc. When the concentration of these gases reaches a certain value, serious accidents such as explosions and suffocation may occur. Therefore, timely and accurate detection and monitoring of the concentration of these harmful gases are crucial for miner safety and production. At present, for the detection of harmful gases in coal mines, structures such as direct light chambers and reflective light chambers are mostly used, which cannot meet the accurate detection of gas concentration, have large errors, and the detection accuracy is insufficient. Summary of the Invention

[0003] In order to solve the problems that the existing chamber structure cannot detect the concentrations of multiple harmful gases in coal mines at the same time, has low detection accuracy, and the detection method is difficult, etc., this application proposes a linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system and method, which uses a linearly frequency-modulated infrared light source, a four-ellipsoid optical chamber, and a multi-channel infrared detector to detect the absorption degree of infrared light by the gas to simultaneously detect the concentrations of multiple gases, so as to greatly increase the detection speed, detection accuracy, and improve the detection efficiency.

[0004] The technical solution adopted in this application is: a linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system, including a host computer system and a four-ellipsoid optical chamber. The four-ellipsoid optical chamber internally includes four ellipsoid chambers, and at least one hole for the gas to be measured to enter is provided at the bottom of each ellipsoid chamber. An infrared light source module, a multi-channel infrared detector driving module, a multi-channel infrared detector module, a signal amplification and filtering module, a main controller, a signal generation module, an infrared light source driving module, and a communication module are arranged inside the four-ellipsoid optical chamber, wherein the infrared light source module is placed at the center of the four-ellipsoid optical chamber;

[0005] The host computer system sends a first signal to the signal generation module, the signal generation module sends the instruction sent by the host computer system to the main controller, and the main controller sends a second signal to the infrared light source driving module. The main controller is used to linearly frequency-modulate the infrared light emitted by the infrared light source module so that the emitted infrared light can meet the wavelength of the infrared spectrum absorption corresponding to the gas to be measured;

[0006] The multi-channel infrared detector driving module drives the multi-channel infrared detector module to detect the remaining infrared light intensity and send it to the signal amplification and filtering module. The main controller obtains the corresponding gas concentration data value according to the intensity of the remaining infrared light.

[0007] The frequency of the first signal is in the Hz order of magnitude, and the frequency of the second signal is in the KHz order of magnitude.

[0008] The four-ellipsoid gas chamber is formed by superimposing the centers of two identical hollow ellipsoids.

[0009] The multi-channel infrared detector module includes eight channels, namely four measurement channels and four corresponding reference channels. The measurement channels are used to measure the infrared light intensity after passing through the gas to be measured, and the reference channels are used to provide reference signals.

[0010] One measurement channel and one reference channel are arranged in each ellipsoid gas chamber.

[0011] The infrared light source module uses a light source with an output infrared light wavelength range of 2 - 14 μm.

[0012] The four ellipsoid gas chambers respectively correspond to detecting the concentrations of methane, carbon monoxide, ammonia, and hydrogen sulfide gases.

[0013] Filter films with different infrared wavelengths are arranged in the multi-channel infrared detector module.

[0014] A method for sensing multi-component gas concentration with linearly frequency-modulated variable-wavelength infrared light NDIR includes the following steps:

[0015] S1. The main controller linearly frequency-modulates to control the infrared light source module to emit infrared lights with different wavelengths and inject them into the four-ellipsoid optical gas chamber;

[0016] S2. Collect the optical signals passing through the multi-channel infrared detector module;

[0017] S3. Preprocess the collected optical signals;

[0018] S4. Convert the processed optical signals into electrical signals, and through analog-to-digital conversion and by Lambert-Beer's law, determine the concentration value of the gas to be measured.

[0019] The specific steps of linearly frequency-modulating by the main controller to control the infrared light source module to emit infrared lights with different wavelengths in step S1 are as follows:

[0020] The relationship between the wavelength of the infrared light source and the frequency it emits is:

[0021]

[0022] Where λ represents the wavelength of infrared light, c represents the speed of light, and f is the frequency corresponding to the infrared light source;

[0023] By adjusting f, the control of the wavelength of the infrared light source is achieved. When performing linear frequency modulation, the frequency f is usually a function that changes with time. Assuming that the frequency changes with time, f is expressed as:

[0024] f(t) = f0 + kt;

[0025] Where f0 is the initial frequency, k is the rate of frequency change, and t represents time;

[0026] Substituting the expression of the frequency into the wavelength formula, we get:

[0027]

[0028] Input the modulation signal into the infrared light source driving module to adjust the corresponding infrared light wavelength absorbed by the gas to be measured. Then use an optical measurement device to monitor the output wavelength of the infrared light source module to ensure that it changes with the modulation signal.

[0029] The skeleton calculation of the four-ellipsoid optical gas chamber in step S1 is as follows:

[0030] First, according to Lambert-Beer's law, the transmitted light intensity is obtained:

[0031] I(λ) = I C (λ)exp{-K(λ)CL};

[0032] Where C is the concentration of the gas to be measured, I(λ) is the transmitted light intensity, I c (λ) is the incident light intensity, L is the total optical path length when light propagates in the gas, that is, the optical path length, and K(λ) is the absorption coefficient of the gas for infrared radiation light;

[0033] From Lambert-Beer's law, we have:

[0034]

[0035] According to the minimum resolution of the infrared light source module, the optical path length is obtained, and then the major axis length A of the ellipse in the cross-section of the X-axis of one of the ellipsoids in the ellipsoidal gas chamber is determined; set the placement point of the infrared light source module as O, and calculate the minor axis length B of the above ellipse according to the following formula:

[0036]

[0037] Where point O is the center point of the four-ellipsoid, and F1O is the distance between the infrared light source module and one of the foci F1 of the ellipsoid, where F1 is the focus located on the X-axis of the ellipsoid;

[0038] Assume that the rotation angle of the ellipsoid is θ, where θ is the angle between the plane of F1O and OF3. F1O lies in the plane of OXZ, and OF3 lies in the plane of OYZ. F3 is the focus on the X-axis of another ellipsoid. It can be obtained that:

[0039]

[0040] Finally, the rotation angle of a certain ellipsoid is:

[0041]

[0042] The beneficial effects of this application compared with the prior art are as follows:

[0043] 1. This application utilizes the linear frequency modulation technology, enabling the infrared light source to emit infrared light of different wavelengths for detecting the concentrations of different gases.

[0044] 2. This application adopts a four-ellipsoid optical gas chamber, greatly improving the detection speed and accuracy of multi-gas concentrations and solving the problem of complex multi-gas concentration detection.

[0045] 3. This application uses an infrared detector with multiple filter plates to form an eight-channel infrared detector, enhancing the accuracy of gas concentration detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The following further describes this application with reference to the drawings:

[0047] Figure 1 It is a schematic diagram of the system structure provided by the embodiment of this application;

[0048] Figure 2 It is a schematic diagram of the structure of the four-ellipsoid gas chamber provided by the embodiment of this application Figure 1 ;

[0049] Figure 3 It is a schematic diagram of the structure of the four-ellipsoid gas chamber provided by the embodiment of this application Figure 2 ;

[0050] Figure 4 It is a schematic diagram of the structure of the four-ellipsoid gas chamber provided by the embodiment of this application Figure 3 ;

[0051] Figure 5 It is a schematic diagram of the structure of the four-ellipsoid gas chamber provided by the embodiment of this application Figure 4 . DETAILED DESCRIPTION OF THE EMBODIMENTS

[0052] As Figures 1-5As shown in the figure, the present application provides a linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system, including a four-ellipsoid optical gas chamber and a host computer system. The four-ellipsoid optical gas chamber is formed by superposing the centers of two identical ellipsoids to form four ellipsoid gas chambers, and the inside of the ellipsoid is hollow. Two holes are drilled at the bottom of each ellipsoid gas chamber so that the gas to be measured can enter. Inside the four-ellipsoid optical gas chamber, there are an infrared light source module, a multi-channel infrared detector driving module, a multi-channel infrared detector module, a signal amplification and filtering module, a main controller, a signal generation module, an infrared light source driving module, and a communication module. Among them, the infrared light source module is placed at the position where the centers of the two ellipsoids are superposed. The communication module is connected to the main controller, and is used to transmit the instructions sent by the host computer system to the main controller and upload the result of the gas concentration calculated by the main controller to the host computer system. In this embodiment, the communication module can be a USB communication module.

[0053] The host computer system sends a first signal to the signal generation module, and the signal generation module sends the instructions sent by the host computer system to the main controller to ensure that the main controller can work normally. The main controller sends a second signal to the infrared light source driving module. The main controller is used to perform linear frequency modulation on the infrared light emitted by the infrared light source module so that the emitted infrared light can meet the wavelength corresponding to the infrared spectrum absorption of the gas to be measured; the frequency of the first signal emitted is in the order of Hz, and the frequency of the second signal is in the order of KHz; in this embodiment, the frequency range of the first signal is between 100 - 1000 Hz, and the frequency range of the second signal is between 30 - 60 KHz.

[0054] When multiple gases enter the four-ellipsoid optical gas chamber, the main controller generates a linearly frequency-modulated analog signal. The infrared light source driving module drives the infrared light source module to emit infrared light of different wavelengths according to the above analog signal. After the gas to be measured absorbs the corresponding infrared light, the multi-channel infrared detector driving module drives the multi-channel infrared detector module to detect it; the multi-channel infrared detector module is used to convert the optical signal absorbed by the gas to be measured into an electrical signal and send it to the signal amplification and filtering module, and the signal amplification and filtering module is used to perform differential amplification processing on the electrical signal. The main controller performs analog-to-digital conversion on the electrical conversion signal to obtain the corresponding data value of the gas concentration.

[0055] Specifically, in this embodiment, the multi-channel infrared detector module includes eight channels, namely four measurement channels and four corresponding reference channels. Each gas has two channels, one measurement channel and one reference channel, and a filter is added in front of them to filter out the infrared light of other gases and only receive the infrared light absorbed by the gas to be measured. The measurement channel is used to measure the intensity of the infrared light after passing through the gas to be measured. When the infrared light passes through the gas to be measured, the gas to be measured will absorb the emitted infrared light according to its concentration. The measurement channel will measure the intensity of the remaining light, and the reduction of this intensity directly reflects the amount of light absorbed by the gas to be measured. The reference channel only provides a reference signal to compensate for the influence of environmental changes such as temperature and humidity on the light intensity. By comparing the signals of the measurement channel and the reference channel, the actual concentration of the gas can be accurately calculated. These eight channels are respectively located at the bottom of each ellipsoidal gas chamber, that is, a measurement channel and a reference channel are respectively arranged at the bottom of each ellipsoidal gas chamber, and the detection of the concentrations of harmful gases such as methane, carbon monoxide, ammonia, and hydrogen sulfide in the coal mine shaft can be realized.

[0056] Specifically, in this embodiment, the infrared light source module is a MIR715 high-precision infrared light source with an operating temperature of 25°C to 35°C. The output infrared light wavelength range is 2 - 14 μm, which can cover the infrared absorption wavelengths of harmful gases in the coal mine shaft. For example, the infrared absorption wavelength of methane is 3.31 μm, the infrared absorption wavelength of sulfur dioxide is 7.3 μm, the infrared absorption wavelength of ammonia is 9.5 μm, and the infrared absorption wavelength of carbon monoxide is 4.67 μm. By linear frequency modulation, the infrared light source can emit the infrared absorption wavelengths of each gas.

[0057] In this embodiment, an NDIR multi-gas concentration sensing method is also proposed. Using the above system, it includes the following steps:

[0058] S1. Control the infrared light source module to emit infrared light with different wavelengths into the four-ellipsoid optical gas chamber through linear frequency modulation by the main controller;

[0059] S2. Collect the optical signals passing through the multi-channel infrared detector module;

[0060] S3. Preprocess the collected optical signals;

[0061] S4. Convert the processed optical signals into electrical signals, and through analog-to-digital conversion and by the Lambert-Beer law, determine the concentration value of the gas to be measured.

[0062] The specific steps of adjusting the wavelength of the infrared light source by the method of linear frequency modulation in step S1 are as follows:

[0063] The relationship between the wavelength of the infrared light source and the frequency it emits is:

[0064]

[0065] Where λ represents the wavelength of infrared light, c represents the speed of light (about 3×10 8 m / s), f is the frequency corresponding to the infrared light source. By adjusting f, the control of the wavelength of the infrared light source can be achieved. When performing linear frequency modulation, the frequency f is usually a function that changes with time. Assuming that the frequency changes with time, it can be expressed as:

[0066] f(t) = f0 + kt;

[0067] Where f0 is the initial frequency, k is the rate of frequency change (unit: hz / s), and t represents time (unit: s). Substituting the expression of frequency into the wavelength formula, we get:

[0068]

[0069] Input the modulation signal into the infrared light source driving module, and the corresponding infrared light wavelength absorbed by the gas to be measured can be adjusted. Then, use a spectrometer or other optical measurement equipment to monitor the output wavelength of the infrared light source to ensure that it changes with the modulation signal.

[0070] The framework calculation of the four-ellipsoid optical gas cell in step S1 is as follows:

[0071] First, according to Lambert-Beer's law, the transmitted light intensity is obtained:

[0072] I(λ) = I C (λ)exp{-K(λ)CL};

[0073] Where C is the concentration of the gas to be measured, I(λ) is the transmitted light intensity, I c (λ) is the incident light intensity, L is the total optical path when the light propagates in the gas, that is, the optical path length, and K(λ) is the absorption coefficient of the gas for infrared radiation light.

[0074] From Lambert-Beer's law, we have:

[0075]

[0076] When the minimum resolution of the sensor for detecting the gas concentration is set to 1000 ppm, we can get K(λ)CL ≈ 0.001.

[0077] K(λ) is the absorption coefficient of the gas for infrared radiation light. By referring to relevant materials, K(λ) is selected as 0.0000125, and the product of the optical path and the concentration is obtained as 80 mm. Therefore, the optical path is initially selected as 80 mm, and the light is reflected four times in the gas cell, so the length of the gas cell can be basically determined.

[0078] Since the optical path length is set to 80 mm, it can be known that the major axis of the ellipse (where the major axis is the section where the X-axis is located) is 80 mm. If the length of the major axis of the ellipse is A and the length of the minor axis is B, according to the characteristics of the ellipse, we can get:

[0079]

[0080] where F1 and F2 are respectively the two foci on the X-axis where Y = 0 and Z = 0 in one of the ellipsoids;

[0081] Set the placement point of the infrared light source module as O. Assuming the light rotation angle is θ, we can get:

[0082]

[0083] The final rotation angle of the ellipsoid is:

[0084]

[0085] where point O is the center point of the four-ellipsoid gas chamber, F1 is the point on the line where Y = 0 and Z = 0 in one of the ellipsoids (i.e., the focus on the X-axis of this ellipsoid), F3 is the point on the line where X = 0 and Y = 0 in another ellipsoid (i.e., the focus on the Z-axis of this ellipsoid), the rotation angle θ is the rotation angle of the plane where OF1 and OF3 are located. Among them, F1O is in the plane of OXZ, and OF3 is in the plane of OYZ. To sum up, the best rotation angle of one of the ellipsoids can be obtained to enhance the light concentration of the gas chamber. As Figures 2-5 shown, keep one of the ellipsoids stationary. According to the calculated rotation angle, keep the other ellipsoid stationary on the X-axis (or Y-axis or Z-axis), and rotate the other ellipsoid in the YZ plane (or XZ plane or XY plane).

[0086] The principle of converting the optical signal into an electrical signal and calculating the concentration of the gas to be measured in step S4 is as follows:

[0087] Gases have specific absorption characteristics for infrared light. These absorption characteristics cause the intensity of the infrared light signal to change differently due to different gas concentrations. When infrared light passes through the gas, part of the optical signal will be absorbed by the gas. The optical signal I(t) recorded by the detector is an analog signal that changes with different gas concentrations. The optical signal I(t) is converted into a frequency-domain signal F(v) by using the fast Fourier transform (FFT). The relationship is:

[0088]

[0089] where F(v) is the v-th frequency component of the frequency-domain signal, I(n) is the n-th sampling point of the time-domain signal, N is the total number of signal samplings, and k is the index of the frequency domain. The signal is decomposed into N discrete frequency components.

[0090] Through FFT processing, the time-domain signal I(t) is converted into a frequency-domain signal F(v), and the amplitude spectrum |F(v)| of the signal is analyzed to identify the frequency components related to the gas absorption characteristics. By analyzing the amplitude spectrum of the frequency-domain signal, the frequency v0 of the gas absorption characteristics can be identified. The output of an infrared detector is usually an electrical signal proportional to the light intensity. Assuming the responsivity of the detector is R (in units of A / W), the output of the infrared detector can be expressed as: I out = R·A(v0), where A(v0) is the amplitude value at a specific frequency v0.

[0091] According to Lambert-Beer's law, the relationship between the gas concentration C of the gas to be measured and the amplitude A(v0) of the absorption characteristics is:

[0092] A(v0) = A0e -αCL ;

[0093] where A0 is the amplitude value of the reference channel, α is the absorption coefficient of the gas, and L is the total optical path when light propagates in the gas, that is, the optical path length. Taking the logarithm gives the concentration C of the gas to be measured can be obtained. Then, through analog-to-digital conversion, the analog signal I out is converted into a digital signal D [N] , and it is uploaded to the host computer system for display.

[0094] This application uses broadband infrared light as the detection light source, realizes the detection of the concentration of harmful gases in the pipeline, and can detect the concentration of multiple harmful gases, improving the detection efficiency.

[0095] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of this application, rather than to limit it; although this application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system, characterized in that: It includes a host computer system and a four-ellipsoid optical gas chamber. Inside the four-ellipsoid optical gas chamber, there are four ellipsoid gas chambers. At least one hole for the gas to be measured to enter is provided at the bottom of each ellipsoid gas chamber. Inside the four-ellipsoid optical gas chamber, there are an infrared light source module, a multi-channel infrared detector driving module, a multi-channel infrared detector module, a signal amplification and filtering module, a main controller, a signal generation module, an infrared light source driving module, and a communication module. Among them, the infrared light source module is placed at the center of the four-ellipsoid optical gas chamber; The host computer system sends a first signal to the signal generation module. The signal generation module sends the instruction sent by the host computer system to the main controller. The main controller sends a second signal to the infrared light source driving module. The main controller is used to perform linear frequency modulation on the infrared light emitted by the infrared light source module so that the emitted infrared light can meet the wavelength of the infrared spectral absorption corresponding to the gas to be measured; The multi-channel infrared detector driving module drives the multi-channel infrared detector module to detect the intensity of the remaining infrared light and sends it to the signal amplification and filtering module. The main controller obtains the data value of the corresponding gas concentration according to the intensity of the remaining infrared light.

2. The linear frequency modulated variable wavelength infrared light NDIR multi-gas concentration sensing system according to claim 1, characterized in that: The frequency of the first signal is in the order of Hz, and the frequency of the second signal is in the order of KHz.

3. A linear frequency modulated variable wavelength infrared light NDIR multi-gas concentration sensing system according to claim 1, characterized in that: The four-ellipsoid gas chamber is formed by superimposing the centers of two identical hollow ellipsoids.

4. A linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system according to claim 1, characterized in that: The multi-channel infrared detector module includes eight channels, namely four measurement channels and four corresponding reference channels. The measurement channels are used to measure the intensity of the infrared light after passing through the gas to be measured, and the reference channels are used to provide a reference signal; One measurement channel and one reference channel are arranged in each ellipsoid gas chamber.

5. A linear frequency modulated variable wavelength infrared light NDIR multi-gas concentration sensing system according to claim 1, characterized in that: The infrared light source module uses a light source with an infrared light output wavelength range of 2 - 14 μm.

6. A linear frequency modulated variable wavelength infrared light NDIR multi-gas concentration sensing system according to claim 5, characterized in that: The four ellipsoid gas chambers respectively correspond to detecting the concentrations of methane, carbon monoxide, ammonia, and hydrogen sulfide gases.

7. A linear frequency modulated variable wavelength infrared light NDIR multi-gas concentration sensing system according to claim 1, characterized in that: Filtering films with different infrared wavelengths are provided in the multi-channel infrared detector module.

8. A gas concentration sensing method based on a linear frequency modulation variable wavelength infrared light NDIR multi-gas concentration sensing system according to any one of claims 1-7, characterized in that: It includes the following steps: S1. The main controller linearly frequency-modulates to control the infrared light source module to emit infrared light with different wavelengths into the four-ellipsoid optical gas chamber; S2. Collect the optical signals passing through the multi-channel infrared detector module; S3. Preprocess the collected optical signals; S4. Convert the processed optical signals into electrical signals, perform digital-to-analog conversion, and determine the concentration value of the gas to be measured through the Lambert-Beer law.

9. A method for sensing the concentration of multiple gases using linearly frequency modulated variable wavelength infrared light NDIR according to claim 8, characterized in that: The specific steps of the main controller linearly frequency-modulating to control the infrared light source module to emit infrared light with different wavelengths in step S1 are as follows: The relationship between the wavelength of the infrared light source and its emitted frequency is: Where λ represents the wavelength of the infrared light, c represents the speed of light, and f is the frequency corresponding to the infrared light source; By adjusting f, the control of the wavelength of the infrared light source is realized. When performing linear frequency modulation, the frequency f is usually a function that changes with time. Assuming that the frequency changes with time, then f is expressed as: f(t) = f0 + kt; Where f0 is the initial frequency, k is the rate of frequency change, and t represents time; Substitute the expression of the frequency into the wavelength formula to get: Input the modulation signal into the infrared light source driving module to adjust the corresponding infrared light wavelength absorbed by the gas to be measured, and then use an optical measurement device to monitor the output wavelength of the infrared light source module to ensure that it changes with the modulation signal.

10. A method for sensing the concentration of multiple gases with linearly frequency-modulated variable-wavelength infrared light NDIR according to claim 8, characterized in that: The framework calculation of the four-ellipsoid optical gas chamber in step S1 is as follows: First, obtain the outgoing light intensity according to Lambert-Beer's law: I(λ) = I C (λ) exp{-K(λ)CL}; Where C is the concentration of the gas to be measured, I(λ) is the intensity of the outgoing light, I c (λ) is the intensity of the incident light, L is the total optical path when the light propagates in the gas, that is, the optical path length, and K(λ) is the absorption coefficient of the gas for infrared radiation light; According to Lambert-Beer's law: Obtain the optical path length based on the minimum resolution of the infrared light source module, and then determine the major axis length A of the ellipse on the X-axis section of one of the ellipsoids in the ellipsoidal gas chamber; set the placement point of the infrared light source module as O, and calculate the minor axis length B of the above ellipse according to the following formula: Where point O is the center point of the four-ellipsoid, F1O is the distance between the infrared light source module and one of the ellipsoid foci F1, and F1 is the focus located on the X-axis of the ellipsoid; Assume that the rotation angle of the ellipsoid is θ, θ is the angle between the plane of F1O and the plane of OF3, where F1O is in the plane of OXZ, OF3 is in the plane of OYZ, and F3 is the focus located on the Z-axis of another ellipsoid, and we can get: Finally, the rotation angle of a certain ellipsoid is obtained as:

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