Mud level measuring system based on frequency identification

Abstract

The invention discloses a mud level measurement system based on frequency identification, which relates to the field of mud-water interface measurement and comprises a light emitting module, a receiving module, a signal processing module and a mud level calculation module. The light emitting module is used for emitting modulated light signals in a mode with different modulation frequencies, the receiving module is arranged along the vertical direction and is used for receiving residual parts of the modulated light signals after penetrating through a water body and outputting electric signals, and the signal processing module is used for extracting frequency components from the electric signals and identifying whether modulation frequencies are included or not; and the mud level calculation module is used for judging the position of the mud-water interface according to whether modulation frequencies are identified at different heights. The system provided by the invention solves the problems of low recognition precision, low resolution and poor adaptability of the existing method in a complex water body environment.

Description

Technical Field

[0001] The present invention relates to the field of mud-water interface measurement, and more specifically, to a mud level measurement system based on frequency identification. Background Art

[0002] In the fields of water conservancy, environmental protection, urban drainage, sludge treatment, etc., accurately grasping the height position of the mud-water interface in water bodies is a key step to ensure process efficiency and engineering safety. Traditional mud level measurement techniques mainly include the float method, the electrode method, the ultrasonic method, and the laser ranging method. These methods have many limitations. For example, the float is greatly affected by water flow disturbance, the electrode method is easily interfered by the electrolyte concentration in water, the ultrasonic method has unstable reflected waves in a multi-phase turbid interface, and the laser method is restricted by insufficient penetration ability.

[0003] As a technical route that has gradually received attention in recent years, the optical method has the advantages of non-contact, fast response, strong anti-interference ability, etc. However, currently, conventional optical measurement systems mostly adopt the intensity detection method, and judge the position of the mud-water interface by observing the attenuation degree of light of a certain wavelength in water. However, due to the influence of the suspended particle concentration, light scattering characteristics, and ambient light interference in water, this method often has problems of unstable measurement accuracy in practical applications. Especially in the case of a fuzzy interface, a gradually changing distribution, or a complex background light, it is difficult for the traditional intensity-based optical measurement method to achieve effective resolution and reliable positioning.

[0004] In addition, relying on a single measurement layer to obtain mud level information, the resolution is usually limited by the sensor spacing, and it is difficult to give continuous depth values, nor can it cope with signal distortion caused by changes in turbidity, light, and sediment composition. In practical applications, when the interface transition bandwidth is wide and there is no obvious fault, the single-layer detection method is more likely to have misjudgment or positioning deviation. There is an urgent need for a mud level measurement technology that can break through the layer spacing limit and has good anti-interference ability. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a mud level measurement system based on frequency identification to solve the problems mentioned in the background art.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A mud level measurement system based on frequency identification, comprising: A light emitting module, a receiving module, a signal processing module, and a mud level calculation module; The light emitting module is used to emit a modulated optical signal in a manner of having different modulation frequencies; The receiving module is arranged vertically, and is used to receive the remaining part of the modulated optical signal after penetrating the water body and output an electrical signal; The signal processing module is used to extract the frequency components from the electrical signal and identify whether the modulation frequency is included; The mud level calculation module is used to judge the position of the mud-water interface according to whether the modulation frequency is identified at different heights.

[0007] In some embodiments, the light emitting module includes a light source modulated with a single color, the color is red light, the modulation frequency is a fixed frequency, and the receiving module includes a plurality of red light receivers corresponding to height positions.

[0008] In some embodiments, the light emitting module includes a PWM controller, and the PWM controller is used to generate a square wave signal with a preset frequency to drive the light source to emit pulsed light. The receiving module includes a band-pass filter and a signal amplifier, and the center frequency of the band-pass filter is consistent with the modulation frequency.

[0009] In some embodiments, after the receiving module measures the discrete data of the corresponding relationship between the light intensity and the height, the mud level calculation module uses the spline interpolation method to fit the discrete data, generates a continuous function corresponding to the light intensity and the height, and further calculates the first derivative of the continuous function. After obtaining the derivative function, the height corresponding to the maximum value point of the absolute value of the derivative function is found through a numerical search algorithm and used as the mud level height.

[0010] In some embodiments, the light emitting module further includes modulation light sources of multiple colors, and each color light source is modulated at different frequencies through an independent PWM channel; The receiving module includes a composite light receiver, and the signal processing module is used to perform frequency demodulation on the composite optical signal to respectively identify the color optical signals corresponding to each modulation frequency.

[0011] In some embodiments, the mud level calculation module calculates the corresponding mud level height for lights of different frequencies, and determines the mud level height in any of the following ways: 1) Taking the interval where the mud level heights measured for lights of multiple frequencies are distributed as the height interval where the mud level is located; 2) Taking the average value of the mud level heights measured for lights of different frequencies as the best measured height of the mud level; 3) Comparing the maximum value points of the absolute values of the derivative functions corresponding to the lights of each frequency, and selecting the height corresponding to the largest maximum value point as the best measured height of the mud level.

[0012] In some embodiments, the signal processing module uses a frequency domain analysis algorithm to separate the composite electrical signal and outputs a frequency intensity spectrum containing different frequency components; Each frequency in the frequency intensity spectrum matches one-to-one with the corresponding modulation frequency of the light-emitting module, and is used to reconstruct the response data of each color light at each height position.

[0013] In some embodiments, the light-emitting module uses red, green, and blue light sources.

[0014] In some embodiments, the receiving module includes a high-speed analog-to-digital converter, and the analog-to-digital converter synchronously samples the output signals of all receivers; the signal processing module includes a sliding window filter and a multi-frame averaging unit, which are used to improve the extraction stability of the frequency components.

[0015] The advantages of the present invention over the prior art are that the present invention replaces simple light intensity measurement with frequency coding. By generating multiple optical signals with different modulation frequencies through the light-emitting module, after the receiving module collects the residual signals layer by layer along the height, the signal processing module extracts each frequency component and the calculation module determines whether there is transmitted light in the corresponding layer, so as to accurately locate the muddy water interface. This solution enhances the anti-environmental interference ability from the source, breaks the limitation of layer spacing on the accuracy, and realizes sub-level mud level judgment.

[0016] On this basis, introducing spline interpolation and derivative extreme value search can convert discrete inter-layer data into continuous depth estimation, further improving the resolution; the combination of multiple color light sources and their respective frequencies enables the system to output a complete height interval or weighted average value in the case of fuzzy interface or uneven particle distribution, taking into account the boundary width perception and measurement stability. Technologies such as high-speed synchronous sampling, band-pass filtering, and multi-frame averaging processing also ensure the stability of frequency domain extraction, making the overall measurement still maintain high precision and reliability in a complex and changeable water quality environment. Description of the Drawings

[0017] Figure 1 is a schematic diagram of a monochromatic red light embodiment of the present invention; Figure 2 is a flowchart of calculating the mud level height by using the interpolation and derivative methods of the present invention; Figure 3 is a flowchart of calculating the mud level height for multiple frequency channels of the present invention. Detailed Embodiments

[0018] The following describes the specific embodiments of the present invention in conjunction with the drawings.

[0019] As Figures 1 to 3 shown, the present invention proposes a mud level measurement system based on frequency recognition, which is mainly applied to the high-precision measurement of the position of the muddy water interface in the water environment.

[0020] Specifically, the system of the present invention includes a sturdy and durable detection rod, which is vertically placed in the water body to be measured as a whole. The structure is encapsulated with corrosion-resistant stainless steel or polymer materials to ensure long-term durability. Multiple electronic modules are arranged inside the detection rod, including a light-emitting module, a receiving module, a signal processing module, and a mud level calculation module. The modules work together through internal integrated circuits and wire interconnections. To adapt to different measurement environments and detection requirements, the total length of the detection rod, the spacing between modules, and the specific set parameters can all be customized according to the actual situation.

[0021] A light-emitting module is provided at the upper end of the detection rod. The light-emitting module includes at least one group of light sources, and the light sources adopt light-emitting diode (LED) devices. The current is precisely controlled by an internal constant-current driving chip to ensure that the light-emitting intensity is stable and does not fluctuate with the voltage change.

[0022] The light-emitting module drives the LED through pulse-width modulation (PWM) control mode to generate a modulated optical signal output with a specific frequency. To improve the measurement accuracy and adapt to complex working conditions, the light-emitting module can output multiple different frequencies. Each frequency represents a specific modulated optical signal, and there are obvious differences between the frequencies, which is convenient for accurate identification at the receiving end.

[0023] In the monochromatic implementation scheme, it is preferably to use a red light source with a wavelength of about 630nm for PWM modulation with a fixed frequency (such as 100Hz) to ensure appropriate penetrability and easily recognizable characteristics under most water quality conditions.

[0024] The receiving module is arranged at a certain interval along the vertical direction of the detection rod to form a column of multiple vertically arranged receiving units. Each receiving unit is provided with a photodiode for receiving the modulated optical signal after passing through the water body and converting the received optical signal into an analog electrical signal for output.

[0025] To ensure the high quality of the received signal, a transimpedance amplifier circuit and a band-pass filter are arranged behind each receiving unit to effectively filter out the noise signals not within the modulation frequency range and improve the signal purity. The center frequency of the band-pass filter is set to be precisely matched with the PWM frequency of the light-emitting module, so that it has an obvious gain effect on the signals of the required frequency. The output signal of the filter is further amplified in amplitude by a post-stage signal amplifier to ensure the subsequent signal processing accuracy.

[0026] Taking the case of a single red light source as an example, the basic principle of measuring the mud level of the present invention is described in detail: As Figure 1For the shown flowchart, the internal PWM module of a single-chip microcomputer can be used to generate a square wave signal with a fixed frequency. For example, 100 Hz is selected as the modulation frequency, and this square wave signal is used to drive a red light-emitting diode (LED) to emit a modulated red light signal. The red light signal emitted by the LED propagates downward through the water body. A plurality of red light receivers are arranged vertically to receive the remaining light signal after transmission through the water body and convert it into a weak electrical signal. These electrical signals are first effectively filtered and signal-enhanced through a pre-stage transimpedance amplifier circuit and a band-pass filter to ensure effective amplification only for the modulation signal with a frequency of 100 Hz.

[0027] In the absence of silt, the water body has high transparency. At this time, the red light signal modulated at 100 Hz can effectively penetrate the water body to reach the red light receivers at corresponding height positions. Therefore, the received signal output by the receivers contains an obvious 100 Hz frequency component. Subsequently, the signal processing module performs frequency-domain analysis on the received signal. If an obvious 100 Hz signal component is detected, it indicates that this position is not blocked by the mud layer; on the contrary, when the mud layer appears and blocks the red light propagation path, the intensity of the 100 Hz red light signal received by the receivers drops sharply until it cannot be detected. At this time, the signal processing module determines that there is silt occlusion at this position.

[0028] The system sequentially polls the signal intensities of all receivers and performs the above frequency identification, thereby identifying the mud layer distribution at all height levels. Finally, the mud level calculation module determines the actual siltation depth based on the installation positions of the receivers, the interval heights, and the signal processing results. For example, if the receivers at a certain height position cannot detect the 100 Hz red light signal while the receivers at the position above can detect it, it indicates that the mud-water interface is exactly near this position. Through this method, the system can accurately and reliably measure the mud level height.

[0029] In the above mud level measurement scheme, the receivers can only read whether there is a light signal at each layer at a fixed layer spacing, so it can only be concluded that the mud-water interface is roughly between the Nth layer and the (N + 1)th layer, and the resolution is limited to an integer multiple of the receiver spacing.

[0030] As Figure 2 shown, in order to break through this limitation, after obtaining the discrete data of light intensity - height corresponding to each modulation frequency, the present invention first uses a cubic spline function to perform smooth interpolation on the discrete points, regards the light intensity value as a function S(z) of height, constructs a cubic polynomial between every two adjacent measurement layers, ensuring not only accurate fitting at the original nodes but also having a second-order continuous derivative within the interval. Taking the derivative of this smooth curve gives the first derivative function , which shows the steepest negative slope at the mud-water interface. Using the golden section or secant method to find By finding the maximum point, a continuous height value that may exist between different layers can be accurately located, with a resolution far exceeding that of the simple interlayer method.

[0031] As Figure 3 shown, in a further embodiment, the present invention also introduces light of multiple frequencies. At a single frequency, once the environmental spectrum or water turbidity changes, resulting in too rapid attenuation of the frequency signal, the entire mud level determination will lose reliability. After introducing multiple frequencies, it is equivalent to attaching an independent "identification label" to each light source. Even if a certain frequency is weakened due to particle refraction or electromagnetic noise interference, other frequencies can often still remain clearly distinguishable. More importantly, lights of different frequencies exhibit different absorption and scattering characteristics under different wavelengths and water conditions, enabling us to simultaneously observe the changes at the mud-water interface from multiple dimensions. By comparing the response differences of different frequency channels, not only can the interface position be accurately determined, but also a credible interval or weighted average can be given in the interface gradient region.

[0032] Specifically, after introducing multiple color light sources and assigning them different modulation frequencies, each color of light will also exhibit a gradient peak at the same interface depth. After respectively performing the above-mentioned fitting and derivative extreme value search, a set of different candidate heights of the interface can be obtained. For the final overall measured height, there are different methods: One method is to directly use the minimum and maximum values of all candidate heights as the interface range, that is, the interval from the shallowest estimate to the deepest estimate is regarded as the height band where the mud-water interface is located. This interval method can completely retain the perception of the boundary fuzzy zone by multiple channels and is suitable for use in scenarios where the mud-water transition zone is relatively wide or the particle concentration distribution is uneven.

[0033] Another method is to take the arithmetic mean of the heights measured at different frequencies to obtain a central tendency value. The averaging method can smooth out occasional measurement noise when there are small random drifts in the estimates of each channel and output a most representative interface height, which is suitable for applications that require a single stable value for the measurement result.

[0034] The third method is to compare the peak sizes of each channel in the absolute value curve of the derivative and directly use the mud level height corresponding to the channel with the largest peak as the final height. The peak method utilizes the fact that the frequency corresponding to the largest signal slope usually has a moderate penetration ability and the highest signal-to-noise ratio, thereby determining the interface position with the clearest attenuation inflection point and giving priority to the selection of the channel that is most sensitive to mutations.

[0035] By flexibly switching or combining these three strategies, the system can not only adapt to different working conditions where the mud layer boundary is clear or fuzzy, but also achieve the best balance between accuracy and robustness.

[0036] In one embodiment, the light-emitting module includes red, green, and blue light sources, and the corresponding frequencies are set to a non-integer multiple relationship. For example, the red channel frequency is 100 Hz, the green channel uses 271 Hz, and the blue channel uses 433 Hz. The non-integer multiple relationship can avoid signal aliasing problems.

[0037] More specifically, when a multi-color light source scheme is adopted, each color light source is modulated at different frequencies through independent PWM channels. These frequencies are reasonably allocated and non-overlapping, facilitating subsequent signal differentiation and identification. Correspondingly, the receiving module is provided with a composite wide-spectrum photodetector, which can simultaneously receive the composite light signals of multiple colors of light. After the aforementioned filtering and amplification, the signals enter the signal processing module for further separation and identification.

[0038] The signal processing module is mainly used for signal demodulation and analysis in the frequency domain. The signal processing module uses a high-speed analog-to-digital conversion chip to synchronously and high-speed sample the analog output signals of each receiving unit at a sampling rate not less than ten times the PWM modulation frequency of the light-emitting module. The sampled digital signals are sent to a field-programmable gate array (FPGA) or a digital signal processor (DSP), and the internal high-speed Fourier transform (FFT) algorithm is used to perform frequency domain analysis on the collected data, extract the signal intensities corresponding to each frequency component, and obtain a frequency intensity spectrum containing all modulation frequency components. In order to effectively reduce the influence of environmental noise and interference factors on spectrum analysis, the signal processing module uses a sliding window filter to perform multi-frame averaging processing on the spectrum data, making the extracted frequency signals more stable and reliable.

[0039] Due to the complexity of the actual environmental water body conditions, the sludge level gauge measurement system has the functions of self-adaptation and dynamic adjustment. The PWM controller provides a wide adjustable output frequency range from 50 Hz to 10 kHz and supports real-time frequency and color combination switching of remote or local control commands.

[0040] In addition, the system of the present invention is also equipped with an automatic calibration function. When initially installed, the system records the reference light intensity data in a clean water body environment. During the long-term operation process, the signals of each receiving channel are regularly compared with the initial reference data. If a significant attenuation is found, a cleaning or maintenance reminder is automatically triggered to ensure the reliability of the long-term measurement data of the system. For the convenience of long-term data analysis and maintenance, this system can be optionally equipped with a storage unit to save the real-time measurement data to an external memory, or can be uploaded to the host computer system or cloud server in real time through industrial communication interfaces such as Ethernet, RS-485, and CAN bus, forming a complete data monitoring, management, and analysis platform.

[0041] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A mud level measurement system based on frequency recognition, characterized in that Comprising: A light-emitting module, a receiving module, a signal processing module, and a mud level calculation module; The light-emitting module is used to emit a modulated optical signal in a manner with different modulation frequencies; The receiving module is arranged vertically, and is used to receive the residual part after the modulated optical signal penetrates the water body and output an electrical signal; The signal processing module is used to extract the frequency components from the electrical signal and identify whether the modulation frequency is included; The mud level calculation module is used to judge the position of the mud-water interface according to whether the modulation frequency is identified at different heights.

2. The mud level measurement system based on frequency recognition according to claim 1, wherein The light-emitting module includes a light source modulated with a single color, the color is red light, the modulation frequency is a fixed frequency, and the receiving module includes a plurality of red light receivers at corresponding height positions.

3. The mud level measurement system based on frequency recognition according to claim 2, characterized in that, The light-emitting module includes a PWM controller, and the PWM controller is used to generate a square wave signal with a preset frequency to drive the light source to emit pulsed light. The receiving module includes a band-pass filter and a signal amplifier, and the center frequency of the band-pass filter is consistent with the modulation frequency.

4. The mud level measurement system based on frequency recognition according to claim 1, wherein After the mud level calculation module measures the discrete data of the corresponding light intensity and height relationship, the mud level calculation module uses the spline interpolation method to fit the discrete data, generates a continuous function corresponding to the light intensity and height, and further takes the first derivative of the continuous function. After obtaining the derivative function, the height corresponding to the maximum value point of the absolute value of the derivative function is found through a numerical search algorithm and used as the mud level height.

5. The mud level measurement system based on frequency recognition according to claim 4, wherein, The light-emitting module further includes modulated light sources of multiple colors, and each color of light source is modulated at different frequencies through an independent PWM channel; The receiving module includes a composite optical receiver, and the signal processing module is used to perform frequency demodulation on the composite optical signal to separately identify the color optical signals corresponding to each modulation frequency.

6. The mud level measurement system based on frequency recognition according to claim 5, wherein The mud level calculation module calculates the corresponding mud level heights for lights of different frequencies, and determines the mud level height in any of the following ways: 1) Using the interval in which the mud level heights measured for lights of multiple frequencies are distributed as the height interval where the mud level is located; 2) Taking the average value of the mud level heights measured for lights of different frequencies as the optimal measurement height of the mud level; 3) Comparing the maximum value points of the absolute values of the derivative functions corresponding to the lights of each frequency, and selecting the height corresponding to the largest maximum value point as the optimal measurement height of the mud level.

7. The mud level measurement system based on frequency recognition according to claim 5, wherein The signal processing module uses a frequency domain analysis algorithm to separate the composite electrical signal and outputs a frequency intensity spectrum containing different frequency components; Each frequency in the frequency intensity spectrum is in one-to-one correspondence with the corresponding modulation frequency of the light-emitting module, and is used to reconstruct the response data of each color of light at each height position.

8. The mud level measurement system based on frequency recognition according to claim 5, characterized in that, The light-emitting module uses red light, green light, and blue light sources.

9. The mud level measurement system based on frequency recognition according to claim 7, characterized in that The receiving module includes a high-speed analog-to-digital converter, and the analog-to-digital converter synchronously samples the output signals of all receivers; the signal processing module includes a sliding window filter and a multi-frame averaging unit, which are used to improve the extraction stability of the frequency components.

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