Liquid level detection method and system

Abstract

The invention relates to the technical field of liquid level detection, and provides a liquid level detection method and system. The liquid level detection method comprises the following steps: sending detection light into the resonant cavity; the detection light is absorbed by the gas, and a detection light signal is converted into a photoacoustic signal; the sound acquisition device converts the photoacoustic signal into a first electric signal; the pre-amplification circuit amplifies the first electric signal; converting the amplified first electric signal into a second electric signal; and the liquid level is inverted based on the second electric signal. According to the liquid level detection method, the resonant frequency of the resonant cavity is determined by detecting the amplitude of the second electric signal, the liquid level is measured through the resonant frequency of the resonant cavity, the response speed is high, the sensitivity is high, the fine change of the liquid level can be accurately captured, and the detection precision of the liquid level is effectively improved. Meanwhile, according to the liquid level detection method, interference of factors such as turbidity, color and refractive index of liquid in the traditional liquid level detection process can be avoided, and high measurement precision can be kept for various complex liquid environments.

Description

Technical Field

[0001] The present application relates to the technical field of liquid level detection, and in particular to a liquid level detection method and system. Background Art

[0002] In many fields such as chemical production, metallurgical industry, and petroleum industry, real-time and accurate online monitoring of liquid level and hydraulic pressure is the key to ensuring the safe and normal operation of storage devices and systems.

[0003] Traditional sensors for liquid level detection include capacitive, ultrasonic, and magnetostrictive. However, in the detection process, traditional liquid level detection sensors can no longer meet the application requirements of multiple fields and multiple environments. Therefore, fiber optic sensing technology has a greater competitive advantage in harsh environments such as flammable and explosive, highly corrosive, and strong electromagnetic interference due to its advantages such as explosion-proof, passive, anti-electromagnetic interference, fireproof, small size, light weight, good multiplexing, fast response speed, and easy to form a telemetry network with optical fiber transmission systems. However, when fiber optic sensing technology is used for liquid level detection, the structural design of traditional fiber optic sensor heads is relatively simple, and the response to small changes in liquid level is not sensitive enough, resulting in the detection accuracy of this type of sensor being unable to meet the detection requirements.

[0004] Therefore, there is an urgent need for a liquid level sensor with high detection accuracy. Summary of the invention

[0005] The present application provides a liquid level detection method and system to solve the technical problem of low detection accuracy of existing optical fiber sensing technology.

[0006] The present application provides a liquid level detection method provided in a first aspect, comprising: sending detection light into a resonant cavity; wherein gas is passed through the resonant cavity, and the detection light carries a detection light signal; the detection light is absorbed by the gas, and the detection light signal is converted into a photoacoustic signal; a sound collection device converts the photoacoustic signal into a first electrical signal; wherein the first electrical signal is a time domain signal; a preamplifier circuit amplifies the first electrical signal; a fast Fourier transform circuit converts the amplified first electrical signal into a second electrical signal; wherein the second electrical signal is a frequency domain signal; and inverting the liquid level based on the second electrical signal.

[0007] In some feasible implementations, the liquid level is inverted based on the second electrical signal, including: determining the resonant frequency of the resonant cavity; wherein the resonant frequency is the frequency corresponding to when the amplitude of the second electrical signal reaches a maximum value; inverting the liquid level according to the resonant frequency; wherein the change in the liquid level causes a change in the length of the resonant cavity, and the change in the length of the resonant cavity causes a change in the resonant frequency.

[0008] In some possible implementations, the length of the resonant cavity is inversely related to the resonant frequency; the resonant frequency =1, 2, 3…; where is the order of the longitudinal resonance mode, is the speed of sound of the gas, is the length of the resonant cavity, is the radius of the resonant cavity.

[0009] In some feasible implementations, sending the detection light into the resonant cavity includes: a function signal generator sending a driving signal to a laser; and the laser sending the detection light according to the driving signal.

[0010] In some feasible implementations, the fast Fourier transform circuit converts the amplified first electrical signal into the second electrical signal, including: ;in, is the time domain signal, is the discrete time point index, is the frequency domain signal, is the discrete frequency point index, is the length of the first electrical signal, Is an imaginary unit.

[0011] In some feasible implementations, sending the detection light into the resonant cavity further includes: collimating the detection light.

[0012] The liquid level detection method provided in the first aspect determines the resonant frequency of the resonant cavity by detecting the amplitude of the second electrical signal obtained by converting the photoacoustic signal in the resonant cavity, and measures the liquid level through the resonant frequency of the resonant cavity. It has a fast response speed and high sensitivity. Compared with the traditional detection method, the liquid level detection method can accurately capture the subtle changes in the liquid level and effectively improve the detection accuracy of the liquid level. At the same time, the liquid level detection method detects the photoacoustic signal generated by the gas after absorbing light energy, which has little to do with the optical properties of the liquid to be measured. It can avoid the interference of factors such as liquid turbidity, color, refractive index, etc. in the traditional liquid level detection process, and can maintain a high measurement accuracy for various complex liquid environments. Moreover, the liquid level detection method has unique advantages for some liquids with special properties, such as flammable and explosive, toxic and harmful liquids, and for some special detection environments, such as small spaces and containers that are difficult to directly contact. This makes the liquid level detection method have broad application prospects in many industries such as chemical, petroleum, pharmaceutical, and environmental protection, and can meet the needs of different industries for liquid detection.

[0013] The present application provides a second aspect of a liquid level detection system, comprising: a laser, configured to send detection light into a resonant cavity; wherein gas is passed through the resonant cavity, and a detection light signal is carried in the detection light; the resonant cavity is arranged in a liquid level device to be measured, and the liquid to be measured is present in the liquid level device to be measured; a sound collection device, connected to the resonant cavity; the sound collection device is configured to convert a photoacoustic signal into a first electrical signal, wherein the detection light is absorbed by the gas, the detection light signal is converted into a photoacoustic signal, and the first electrical signal is a time domain signal; a preamplifier, connected to the sound collection device, configured to amplify the first electrical signal; a fast Fourier transform circuit, connected to the preamplifier, configured to convert the amplified first electrical signal into a second electrical signal; wherein the second electrical signal is a frequency domain signal; a processor, connected to the fast Fourier transform circuit, configured to invert the liquid level based on the second electrical signal.

[0014] In some feasible implementations, the processor is further configured to determine the resonant frequency of the resonant cavity and invert the liquid level based on the resonant frequency, wherein the resonant frequency is the frequency corresponding to when the amplitude of the second electrical signal reaches a maximum value, and the change in the liquid level causes the change in the length of the resonant cavity, and the change in the length of the resonant cavity causes the change in the resonant frequency.

[0015] In some feasible implementations, the liquid level detection system also includes: a photoacoustic cell, which is arranged in the liquid level device to be measured, and the photoacoustic cell includes a resonant cavity; a pressure film, which is arranged in the shell of the photoacoustic cell, and the pressure film is in contact with the liquid to be measured; a diaphragm, which is arranged in the resonant cavity, and the pressure film and the diaphragm are arranged opposite to each other.

[0016] In some feasible implementations, the liquid level detection system further includes: a fiber optic collimator connected to the photoacoustic cell and configured to collimate the detection light.

[0017] The liquid level detection system provided in the second aspect adopts the liquid level detection method provided in the first aspect. The beneficial technical effects thereof can be found in the first aspect and will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 It is a flow chart of a liquid level detection method provided in an embodiment of the present application; Figure 2 is a structural schematic diagram of a liquid level detection system provided in an embodiment of the present application; Figure 3 is a schematic diagram of the structure of a photoacoustic cell provided in an embodiment of the present application; Figure 4 is a schematic diagram of the relationship between the amplitude of a collected second electrical signal and the resonance frequency provided in an embodiment of the present application; Figure 5 It is a schematic diagram of the relationship between the resonance frequency and the liquid level change provided in an embodiment of the present application.

[0020] Graphic marking: 100-Liquid level detection system; 10-function signal generator; 20-laser; 30-fiber collimator; 40-photoacoustic cell; 41-resonant cavity; 42-pressure film; 43-diaphragm; 44-buffer chamber; 50-sound collection device; 60-preamplifier; 70-fast Fourier transform circuit; 80-processor; 200-Liquid level device to be measured. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments of the present application, other embodiments obtained by ordinary technicians in this field without making creative work all belong to the protection scope of the present application.

[0022] In the following, the terms "first", "second", etc. are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0023] In addition, in the present application, directional terms such as "upper", "lower", "inner" and "outer" are defined relative to the orientation of the components schematically placed in the drawings. It should be understood that these directional terms are relative concepts. They are used for relative description and clarification, and they can change accordingly according to the changes in the orientation of the components placed in the drawings.

[0024] See also Figure 1 and Figure 2 The liquid level detection method provided in the embodiment of the present application can be implemented by the following steps S1 to S6.

[0025] Step S1: Send detection light into the resonant cavity.

[0026] There is gas in the resonant cavity, and the detection light carries a detection light signal.

[0027] Before sending the detection light, you can build a liquid level detection system.

[0028] Specifically, step S1 can be implemented by steps S11 to S13.

[0029] Step S11: the function signal generator sends a driving signal to the laser.

[0030] The function signal generator can be connected to the laser and the signal transmission path can be reasonably set to ensure the stability and transmission speed of the signal transmission process, thereby ensuring the stable modulation of the laser by the function signal generator. The driving signal carries the control parameters of the laser, such as the wavelength and mode of the detection light emitted by the laser.

[0031] Step S12: The laser sends detection light according to the driving signal.

[0032] Step S13: Collimate the detection light.

[0033] The detection light can be collimated by a collimator, and the collimated detection light is injected into the resonant cavity for detection. Collimating the detection light is beneficial to improving the efficiency of the liquid level detection system.

[0034] Specifically, the central wavelength of the detection light of the laser as a photoacoustic excitation source should correspond to the absorption line strength of the gas in the resonant cavity, and the function signal generator can be used to set the frequency sweep mode to cover a preset frequency range, wherein the frequency range can be determined according to the parameters of the resonant cavity.

[0035] Step S2: The detection light is absorbed by the gas, and the detection light signal is converted into a photoacoustic signal.

[0036] Specifically, the photoacoustic cell includes a resonant cavity, and the photoacoustic cell is located in the liquid level device to be measured. The detection light passes through the collimator and enters the photoacoustic cell. The gas in the photoacoustic cell absorbs light energy to generate heat energy, and the gas in the cell expands due to heat to generate pressure waves, namely photoacoustic signals.

[0037] The resonant cavity can be a place where the gas absorbs the detection light and generates light-heat-acoustic energy conversion. This light-heat-acoustic physical process can be described by the following mathematical equation (1).

[0038] ; (1) in, is the sound pressure, is the speed of sound, is the thermal power density source, is the specific heat ratio of the gas, For time.

[0039] Step S3: The sound collecting device converts the photoacoustic signal into a first electrical signal.

[0040] A shielded cable can be used to connect the output end of the sound collection device, which is helpful to reduce external electromagnetic interference signal transmission.

[0041] The sound collection device can collect photoacoustic signals and convert the photoacoustic signals into a first electrical signal. At this time, the first electrical signal is a time domain signal.

[0042] In a specific implementation, the sound collecting device may be a microphone.

[0043] The concentration of the gas in the photoacoustic cell is positively correlated with the amplitude of the photoacoustic signal. For example, the higher the gas concentration in the photoacoustic cell, the larger the amplitude of the photoacoustic signal, and the lower the gas concentration in the photoacoustic cell, the smaller the amplitude of the photoacoustic signal. The relationship between the gas in the photoacoustic cell and the amplitude of the photoacoustic signal satisfies the following formula (2).

[0044] ; (2) In the formula, is the amplitude of the photoacoustic signal, The sensitivity of the microphone. To detect the optical power, is the cell constant of the photoacoustic cell, is the gas absorption coefficient, is the gas volume concentration.

[0045] Step S4: the preamplifier circuit amplifies the first electrical signal.

[0046] Since the first electrical signal output by the sound collection device is relatively weak, amplifying the first electrical signal can increase the amplitude of the first electrical signal to within the range required for detection, which is beneficial to reducing signal reflection and loss. The output end of the sound collection device can be connected to the input end of the preamplifier.

[0047] In some feasible implementations, the liquid level detection method may further include step S41.

[0048] Step S41: filtering the amplified first electrical signal.

[0049] By filtering the amplified first electrical signal, ineffective bands in the first electrical signal can be effectively eliminated, signal interference can be effectively reduced, and detection accuracy can be improved.

[0050] Step S5: The fast Fourier transform circuit converts the amplified first electrical signal into a second electrical signal, wherein the second electrical signal is a frequency domain signal.

[0051] Fast Fourier Transform (FFT) is an algorithm used to convert the type of signal from the time domain to the frequency domain. It can effectively reduce the time required to calculate the Discrete Fourier Transform (DFT), and provide a prerequisite for subsequent extraction of signal features and analysis.

[0052] The process of converting the time domain signal into the frequency domain signal by the fast Fourier transform circuit can be represented by the following formula (3).

[0053] ; (3) is the first electrical signal (time domain signal), is the discrete time point index, is the second electrical signal (frequency domain signal), is the discrete frequency point index, is the length of the first electrical signal, Is an imaginary unit.

[0054] Specifically, since the waveform of the first electrical signal is irregular and messy, by converting the time domain signal into a frequency domain signal, the converted second electrical signal can clearly present the different frequency components contained in the signal and the relative strength of each frequency component, thereby facilitating the subsequent acquisition of the resonant frequency of the resonant cavity, effectively shortening the detection time and improving the detection efficiency.

[0055] The output end of the preamplifier can be connected to the input end of the fast Fourier transform circuit. The output end of the sound collection device, the preamplifier and the fast Fourier transform circuit can all be connected by a shielded cable, thereby reducing the transmission of external electromagnetic interference signals.

[0056] Step S6: Invert the liquid level based on the second electrical signal.

[0057] In some feasible implementations, step S6 may be implemented by the following steps S61 and S62.

[0058] Step S61: Determine the resonant frequency of the resonant cavity.

[0059] A frequency spectrum of the second electrical signal is obtained, and the resonant frequency of the resonant cavity is a frequency corresponding to when the amplitude of the second electrical signal reaches a maximum value.

[0060] Step S62: Invert the liquid level according to the resonance frequency.

[0061] The change in liquid level causes the change in the length of the resonant cavity, and the change in the length of the resonant cavity causes the change in the resonant frequency.

[0062] Specifically, when the liquid level of the liquid to be measured changes, the length of the resonant cavity also changes, and the resonant frequency of the resonant cavity also changes. In this way, the liquid level value can be determined by detecting the resonant frequency.

[0063] In the process of determining the liquid level value, the relationship between the liquid level value and the resonance frequency can be fitted first, thereby obtaining the linear relationship between the two. Specifically, the entire system can be placed in a device presenting a liquid level to be measured, and the relationship between the liquid level of the liquid to be measured and the change in the resonance frequency can be established. The linear relationship between the two can be obtained by storing the resonance frequency data corresponding to different liquid level values, and then in the process of detection, the real-time liquid level value can be obtained by inverting the real-time resonance frequency and the linear relationship. Among them, the liquid level detection system can also include a processor, and a data communication connection can be established between the processor and the fast Fourier transform circuit, and the processor can display the transmission data transmitted by the fast Fourier transform circuit in real time and accurately, so as to invert the resonance frequency. Among them, the processor can be a computer, or it can be other devices with processing and display functions.

[0064] The photoacoustic cell provided in the embodiment of the present application is a T-type photoacoustic cell, and the physical state corresponding to the resonant cavity is one end open and the other end closed. In the process of liquid level detection, the length of the resonant cavity is most sensitive to the resonant frequency of the resonant cavity.

[0065] The relationship between the length of the resonant cavity and the resonant frequency can be expressed as the following formula (4).

[0066] Resonance frequency , =1, 2, 3…, (4) Where: is the order of the longitudinal resonance mode; is the sound velocity of the gas in the photoacoustic cell; is the length of the resonant cavity, is the radius of the resonant cavity. When the photoacoustic cell is in the first-order longitudinal resonance mode, the resonant frequency can be expressed as follows (5): ; (5) The length of the resonant cavity is inversely correlated with the pressure of the liquid and the resonant frequency. For example, when the liquid level rises, the liquid level value increases, the liquid pressure increases, the length of the resonant cavity decreases, and the resonant frequency increases; when the liquid level drops, the liquid level value decreases, the length of the resonant cavity increases, and the resonant frequency decreases.

[0067] In a specific implementation, Figure 2 and Figure 3As shown in the figure, a pressure film may be provided at the end of the photoacoustic cell, the pressure film is in contact with the liquid to be measured, the interior of the photoacoustic cell is a closed space, and a partition may be provided at the position corresponding to the pressure film. When the pressure in the liquid to be measured changes, the liquid pressure pushes the pressure film, forcing the pressure film to produce elastic deformation, thereby driving the partition to move, and then changing the length of the resonant cavity.

[0068] For example, when the pressure increases, the pressure can push the pressure film such as Figure 3 In the direction indicated by the arrow, deformation occurs inside the photoacoustic cell. As the pressure film deforms, the partition can be pushed to move in the direction indicated by the arrow, thereby reducing the cavity length of the resonant cavity.

[0069] See also Figure 4 As shown in Figure 1, the relationship between the amplitude of the second electrical signal and the resonant frequency for different liquid level change values. It can be seen that when the liquid level change value is different, the corresponding amplitude of the second electrical signal is different, and the corresponding resonant frequency is also different. Figure 4 The leftmost curve is shown) and 100cm ( Figure 4 Taking the rightmost curve as an example, the amplitude of the second electrical signal when the liquid level increases by 15 cm is greater than the amplitude of the second electrical signal when the liquid level increases by 100 cm; the resonant frequency when the liquid level increases by 15 cm is less than the resonant frequency when the liquid level increases by 100 cm.

[0070] See also Figure 5 As shown in the figure, it is the relationship between the liquid level change value and the resonance frequency. It can be seen that the resonance frequency is linearly related to the liquid level change value. For example, as the liquid level value increases, the resonance frequency continues to increase.

[0071] The liquid level detection method provided in the embodiment of the present application determines the resonance frequency of the resonance cavity by detecting the amplitude of the second electrical signal obtained by converting the photoacoustic signal in the resonance cavity, and measures the liquid level through the resonance frequency of the resonance cavity. It has a fast response speed and high sensitivity. Compared with the traditional detection method, the liquid level detection method can accurately capture the subtle changes in the liquid level and effectively improve the detection accuracy of the liquid level. At the same time, the liquid level detection method detects the photoacoustic signal generated after the gas absorbs light energy, which has little to do with the optical properties of the liquid to be measured. It can avoid the interference of factors such as liquid turbidity, color, and refractive index in the traditional liquid level detection process, and can maintain a high measurement accuracy for various complex liquid environments.

[0072] Moreover, this liquid level detection method has unique advantages for some liquids with special properties, such as flammable and explosive, toxic and harmful liquids, and for some special detection environments, such as small spaces and containers that are difficult to directly contact. This makes this liquid level detection method have broad application prospects in many industries such as chemical, petroleum, pharmaceutical, and environmental protection, and can meet the needs of different industries for liquid detection.

[0073] Corresponding to the above-mentioned embodiments of the liquid level detection method, the present application also provides an embodiment of a liquid level detection system. The liquid level detection system detects the liquid level using the liquid level detection method provided in the above-mentioned embodiments.

[0074] Continue to see Figure 2 The liquid level detection system 100 includes a function signal generator 10, a laser 20, a fiber collimator 30, a photoacoustic cell 40, a sound collection device 50, a preamplifier 60, a fast Fourier transform circuit 70 and a processor 80.

[0075] The output end of the function signal generator 10 is connected to the input end of the laser 20 , and the function signal generator 10 is used to send a driving signal to the laser 20 .

[0076] That is to say, the function signal generator 10 can be used to execute step S11 in the above liquid level detection method embodiment.

[0077] The input end of the laser 20 is connected to the output end of the function signal generator 10, and the laser 20 is used to receive the driving signal and send the detection light to the resonant cavity 41 according to the driving signal. The photoacoustic cell 40 includes a resonant cavity 41, and a gas of a preset concentration is passed through the photoacoustic cell 40, and the detection light carries a detection light signal.

[0078] That is to say, the laser 20 can be used to perform step S12 in the implementation of the above-mentioned liquid level detection method.

[0079] Among them, the gas is sealed in the photoacoustic cell 40, and the properties of the gas are adapted to the wavelength of the detection light emitted by the laser 20. A buffer chamber 44 is also provided in the photoacoustic cell 40, and the buffer chamber 44 is arranged between the resonant cavity 41 and the optical fiber collimator 30, and is used to cache the detection light. The buffer chamber 44 and the resonant cavity 41 form a T-type photoacoustic cell. The T-type photoacoustic cell can achieve low-frequency resonance in a limited space and amplify the photoacoustic signal. Moreover, the T-type photoacoustic cell has a compact structure. Compared with other types of photoacoustic cells, it can effectively control its own volume, which is conducive to miniaturization design and can obtain better photoacoustic signals at a smaller size. Specifically, the photoacoustic signal is obtained by converting the detection light signal after the detection light is absorbed by the gas.

[0080] The input end of the fiber collimator 30 is connected to the output end of the laser 20, and the output end of the fiber collimator 30 is connected to the buffer chamber 44 of the photoacoustic cell 40. The fiber collimator 30 is used to collimate the detection light and input the collimated detection light into the photoacoustic cell 40.

[0081] That is to say, the optical fiber collimator 30 can be used to perform step S13 in the implementation of the above-mentioned liquid level detection method.

[0082] The photoacoustic cell 40 is located in the liquid level device 200 to be measured, and the liquid level device 200 to be measured can be a container of liquid with a liquid level to be detected. A pressure film 42 is provided at the bottom of the shell of the photoacoustic cell 40, and the pressure film 42 is in contact with the liquid to be measured. The pressure film 42 is elastic, and when the pressure of the liquid changes with the liquid level, the pressure film 42 will deform with the pressure change of the liquid.

[0083] The optical fiber collimator 30 is sealedly connected to the pressure film 42 and the photoacoustic cell 40 to ensure the sealing of the photoacoustic cell 40 so as to ensure that the pressure film 42 can effectively sense the change of hydraulic pressure.

[0084] The partition 43 is slidably disposed in the resonance cavity 41, and the partition 43 is disposed opposite to the pressure film 42. The partition 43 can move in position as the pressure film 42 is deformed. For example, if the internal pressure of the liquid increases, the pressure film 42 will push the partition 43, thereby reducing the cavity length of the resonance cavity 41. It can be understood that the shell of the photoacoustic pool 40 can be made of a material that is not easy to rust and does not react with the liquid to be measured, and a cylindrical stainless steel shell can be arranged inside it. The sound collection device 50 can be connected to the center of the stainless steel shell. The bottom of the stainless steel shell is connected to the pressure film 42, and a partition 43 is arranged inside. A resonance cavity 41 is formed between the top of the stainless steel shell and the partition 43, and the length of the resonance cavity 41 changes with the movement of the partition 43. Combined with Figure 3 As shown, the length of the resonant cavity 41 is L, and the value of L is changed by moving the partition 43.

[0085] That is, the gas in the photoacoustic cell 40 can execute step S2 in the above-mentioned liquid level detection method embodiment.

[0086] The input end of the sound collection device 50 is connected to the resonant cavity 41, and the output end is connected to the input end of the preamplifier 60. The sound collection device 50 is used to convert the photoacoustic signal in the resonant cavity 41 into a first electrical signal. The type of the first electrical signal is a time domain signal.

[0087] That is to say, the sound collecting device 50 can be used to execute step S3 in the above liquid level detection method embodiment.

[0088] In a specific implementation, the sound collecting device 50 may be a microphone.

[0089] The input end of the preamplifier 60 is connected to the output end of the sound collecting device 50 and is used to amplify the first electrical signal.

[0090] That is, the preamplifier 60 can be used to execute step S4 in the above liquid level detection method embodiment.

[0091] The input end of the fast Fourier transform circuit 70 is connected to the output end of the preamplifier 60. The fast Fourier transform circuit 70 is used to convert the type of the amplified first electrical signal to obtain a second electrical signal, and the type of the second electrical signal is a frequency domain signal.

[0092] That is to say, the fast Fourier transform circuit 70 can be used to execute step S5 in the above liquid level detection method embodiment.

[0093] The input end of the processor 80 is connected to the output end of the fast Fourier transform circuit 70 . The processor 80 is used to receive and store the second electrical signal, and to invert the liquid level based on the second electrical signal.

[0094] Specifically, the process of the processor 80 inverting the liquid level may be a process of determining the resonance frequency of the resonant cavity 41 and inverting the liquid level according to the resonance frequency.

[0095] The length of the resonant cavity 41 is very sensitive to the resonant frequency of the resonant cavity 41. Even a slight change in length will cause a significant change in the resonant frequency. The resonant frequency is the frequency corresponding to when the amplitude of the second electrical signal reaches the maximum value. The change in liquid level causes the length of the resonant cavity 41 to change, and the change in the length of the resonant cavity 41 causes the change in the resonant frequency.

[0096] Thus, in the liquid level detection system 100, the change in liquid level will cause the change in hydraulic pressure, and the change in hydraulic pressure will cause the pressure film 42 connected to the photoacoustic cell 40 to deform, thereby changing the length of the resonant cavity 41. Since the change in the length of the resonant cavity 41 will cause the change in the resonant frequency, the change in liquid level can be inferred by detecting the change in the resonant frequency. This detection method can achieve non-contact, high-precision liquid level measurement.

[0097] That is, the processor 80 can be used to execute step S6 in the above liquid level detection method.

[0098] In some specific implementations, the processor 80 may be a device with processing functions, such as a computer or a host computer.

[0099] Before starting the detection, the parameters of each device in the optical path and the signal processing circuit can be set, and then the entire liquid level detection system 100 is placed on the liquid level device 200 to be measured for calibration operation, so as to establish the relationship between the liquid level and the change in the resonance frequency. When the liquid hydraulic pressure changes, the pressure film 42 will deform accordingly, and this deformation will further cause the length of the resonant cavity 41 to change. Since the length of the resonant cavity 41 is closely related to the resonance frequency, the resonance frequency will also change accordingly. The liquid level detection system 100 can monitor the change of the resonance frequency in real time, analyze and process the corresponding electrical signals, thereby obtaining the liquid level change value, and collecting and storing the liquid level change value. By fitting the change value of the liquid level with the resonance frequency of the resonant cavity 41, a linear relationship between the two can be obtained.

[0100] The liquid level detection system 100 provided in the embodiment of the present application adopts photoacoustic spectroscopy sensing technology, and has the advantages of explosion-proof, passive, anti-electromagnetic interference, fireproof, small size, light weight, good reusability, fast response speed, etc. The liquid level is measured by detecting the change of the resonant frequency of the optical resonant cavity 41, and the response to the change of the liquid level is very sensitive. It can capture the subtle changes of the liquid level more accurately, with high precision and good stability.

[0101] It should be noted that those skilled in the art will easily think of other embodiments of the present application after considering the specification and practicing the application disclosed herein. The present application is intended to cover any variation, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary technical means in the art that are not disclosed in the present application.

[0102] It should be understood that the present application is not limited to the precise construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof, the true scope being indicated by the present application.

Claims

1. A liquid level detection method, characterized in that: Applied in a liquid level detection system, the liquid level detection method comprises: Sending detection light into a resonant cavity, wherein gas is passed through the resonant cavity, and the detection light carries a detection light signal; The detection light is absorbed by the gas, and the detection light signal is converted into a photoacoustic signal; The sound collection device converts the photoacoustic signal into a first electrical signal; wherein the first electrical signal is a time domain signal; The preamplifier circuit amplifies the first electrical signal; The fast Fourier transform circuit converts the amplified first electrical signal into a second electrical signal; wherein the second electrical signal is a frequency domain signal; The liquid level is inverted based on the second electrical signal.

2. The liquid level detection method according to claim 1, characterized in that: The inverting of the liquid level based on the second electrical signal comprises: Determining the resonant frequency of the resonant cavity; wherein the resonant frequency is the frequency corresponding to when the amplitude of the second electrical signal reaches a maximum value; The liquid level is inverted according to the resonant frequency; wherein the change in the liquid level causes a change in the length of the resonant cavity, and the change in the length of the resonant cavity causes a change in the resonant frequency.

3. The liquid level detection method according to claim 2, characterized in that: The length of the resonant cavity is inversely related to the resonant frequency; The resonant frequency =1, 2, 3…; in, is the order of the longitudinal resonance mode, is the speed of sound of the gas, is the length of the resonant cavity, is the radius of the resonant cavity.

4. The liquid level detection method according to claim 3, characterized in that: The sending of detection light into the resonant cavity comprises: The function signal generator sends a driving signal to the laser; The laser transmits the detection light according to the driving signal.

5. The liquid level detection method according to claim 4, characterized in that: The fast Fourier transform circuit converts the amplified first electrical signal into a second electrical signal, including: ； in, is the time domain signal, is the discrete time point index, is the frequency domain signal, is the discrete frequency point index, is the length of the first electrical signal, Is an imaginary unit.

6. The liquid level detection method according to claim 5, characterized in that: The sending of the detection light into the resonant cavity further comprises: The detection light is collimated.

7. A liquid level detection system, characterized in that: According to any one of claims 1 to 6, the liquid level detection system comprises: A laser is configured to send detection light into a resonant cavity; wherein a gas is passed through the resonant cavity, and the detection light carries a detection light signal; The resonant cavity is arranged in a liquid level device to be measured, and the liquid level device to be measured contains liquid to be measured; a sound collecting device connected to the resonant cavity; the sound collecting device is configured to convert the photoacoustic signal into a first electrical signal, wherein the detection light is absorbed by the gas, the detection light signal is converted into the photoacoustic signal, and the first electrical signal is a time domain signal; a preamplifier, connected to the sound collecting device and configured to amplify the first electrical signal; a fast Fourier transform circuit, connected to the preamplifier, and configured to convert the amplified first electrical signal into a second electrical signal; wherein the second electrical signal is a frequency domain signal; A processor is connected to the fast Fourier transform circuit and is configured to invert the liquid level based on the second electrical signal.

8. The liquid level detection system according to claim 7, characterized in that: The processor is also configured to determine the resonant frequency of the resonant cavity and invert the liquid level according to the resonant frequency; wherein the resonant frequency is the frequency corresponding to when the amplitude of the second electrical signal reaches a maximum value, the change in liquid level causes a change in the length of the resonant cavity, and the change in the length of the resonant cavity causes a change in the resonant frequency.

9. The liquid level detection system according to claim 8, characterized in that: The liquid level detection system also includes: A photoacoustic cell, arranged in the liquid level device to be measured, wherein the photoacoustic cell comprises the resonant cavity; A pressure film is arranged on the housing of the photoacoustic cell, and the pressure film is in contact with the liquid to be measured; A partition is arranged in the resonance cavity, and the pressure film is arranged opposite to the partition.

10. The liquid level detection system according to claim 9, characterized in that: The liquid level detection system also includes: The optical fiber collimator is connected to the photoacoustic cell and is configured to collimate the detection light.

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