A Mud Level Measurement System Based on Frequency Recognition

Abstract

The present invention discloses a mud level measurement system based on frequency recognition, which relates to the field of mud-water interface measurement and includes 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 modulated light signals with different modulation frequencies. The receiving module is arranged in a vertical direction and is used to receive the residual part of the modulated light signal after it penetrates the water body and output an electrical signal. The signal processing module is used to extract frequency components from the electrical signal and identify whether the modulation frequency is included. The mud level calculation module is used to determine the location of the mud-water interface based on whether the modulation frequency is identified at different heights. The system of the present invention solves the problems of low recognition accuracy, low resolution, and poor adaptability of existing methods in complex water environments.

Description

Technical Field

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

[0002] In fields such as water conservancy, environmental protection, urban drainage, and sludge treatment, accurately determining the height of the mud-water interface within a water body is a critical step in ensuring process efficiency and engineering safety. Traditional mud level measurement techniques primarily include float, electrode, ultrasonic, and laser ranging methods. These methods have numerous limitations. For example, floats are significantly affected by water flow disturbances, electrode methods are susceptible to interference from electrolyte concentrations in water, ultrasonic methods suffer from unstable reflected waves at multiphase turbidity interfaces, and laser methods are limited by insufficient penetration.

[0003] Optical methods, a technology approach that has gained increasing attention in recent years, offer advantages such as non-contact, fast response, and strong anti-interference capabilities. However, conventional optical measurement systems currently rely on intensity detection, which determines the location of the mud-water interface by observing the attenuation of a certain wavelength of light in water. However, due to the influence of suspended particle concentration, light scattering characteristics, and ambient light interference in the water, this method often suffers from unstable measurement accuracy in practical applications. This is especially true when the interface is blurred, the distribution is gradually changing, or the background light is complex, making it difficult for traditional intensity-based optical measurement methods to achieve effective resolution and reliable positioning.

[0004] Furthermore, relying on a single measurement layer to obtain mud level information often limits its resolution due to the spacing between sensors, making it difficult to provide continuous depth values and unable to cope with signal distortion caused by changes in turbidity, illumination, and sediment composition. In practical applications, when the interface transition bandwidth is wide and there are no obvious faults, single-layer detection methods are more prone to misjudgment or positioning errors. Therefore, a mud level measurement technology that can overcome the limitations of interlayer spacing and possess good anti-interference capabilities is urgently needed. 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 recognition to solve the problems mentioned in the background technology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A mud level measurement system based on frequency recognition, comprising:

[0008] Light emitting module, receiving module, signal processing module and mud level calculation module;

[0009] The light emitting module is used to emit modulated light signals in a manner with different modulation frequencies;

[0010] The receiving module is arranged in a vertical direction and is used to receive the residual part of the modulated light signal after it penetrates the water body and output an electrical signal;

[0011] The signal processing module is used to extract frequency components from the electrical signal and identify whether the signal contains the modulation frequency;

[0012] The mud level calculation module is used to determine the position of the mud-water interface based on whether the modulation frequency is identified at different heights.

[0013] 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 at corresponding height positions.

[0014] In some embodiments, the light emitting module includes a PWM controller, which is used to generate a square wave signal of a preset frequency to drive the light source to emit pulsed light.

[0015] The receiving module includes a bandpass filter and a signal amplifier, and the center frequency of the bandpass filter is consistent with the modulation frequency.

[0016] In some embodiments, after the receiving module measures the discrete data corresponding to the relationship between light intensity and height, the mud level calculation module uses a spline interpolation method to fit the discrete data to generate a continuous function corresponding to the light intensity and height, and further calculates the first-order derivative of the continuous function. After obtaining the derivative function, the height corresponding to the maximum point of the absolute value of the derivative function is found through a numerical search algorithm as the mud level height.

[0017] In some embodiments, the light emitting module further comprises a modulated light source of multiple colors, and each color of the light source is modulated at a different frequency through an independent PWM channel;

[0018] 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 respectively identify the color optical signals corresponding to each modulation frequency.

[0019] In some embodiments, the mud level calculation module calculates the corresponding mud level heights for light of different frequencies, and determines the mud level heights by any one of the following methods:

[0020] 1) The intervals of mud level heights measured by multiple frequency lights are used as the height intervals of the mud level;

[0021] 2) Take the average value of the mud level heights measured by light of different frequencies as the optimal mud level measurement height;

[0022] 3) Compare the maximum points of the absolute value of the derivative function corresponding to each frequency of light, and select the height corresponding to the largest maximum point as the optimal measurement height of the mud level.

[0023] In some embodiments, the signal processing module uses a frequency domain analysis algorithm to separate the composite electrical signal and output a frequency intensity spectrum containing different frequency components;

[0024] Each frequency in the frequency intensity spectrum is matched one-to-one with the corresponding modulation frequency of the light emitting module, so as to reconstruct the response data of each color light at each height position.

[0025] In some embodiments, the light emitting module uses red, green and blue light sources.

[0026] In some embodiments, the receiving module includes a high-speed analog-to-digital converter, which synchronously samples the output signals of all receivers; the signal processing module includes a sliding window filter and a multi-frame averaging unit to improve the extraction stability of the frequency component.

[0027] The advantage of this invention over existing technologies lies in its use of frequency coding instead of simple light intensity measurement. The light-emitting module generates multiple optical signals with different modulation frequencies. After the receiving module collects the residual signals along the height layer, the signal processing module extracts the frequency components, and the calculation module determines whether transmitted light exists in the corresponding layer, thereby accurately locating the mud-water interface. This solution fundamentally enhances resistance to environmental interference, overcomes the limitations of interlayer spacing on accuracy, and enables sub-level mud level determination.

[0028] On this basis, the introduction of spline interpolation and derivative extreme value search can convert discrete interlayer data into continuous depth estimates, further improving resolution. The combination of multiple color light sources and their respective frequencies allows the system to output a complete height range or weighted average even in the presence of blurred interfaces or uneven particle distribution, balancing boundary width perception with measurement stability. High-speed synchronous sampling, bandpass filtering, and multi-frame averaging ensure the stability of frequency domain extraction, ensuring that the overall measurement maintains high accuracy and reliability even in complex and changing water quality environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic diagram of a monochromatic red light embodiment of the present invention;

[0030] Figure 2 This is a flow chart of the present invention for calculating mud level height using interpolation and derivative methods;

[0031] Figure 3 It is a flow chart of the present invention for calculating mud level height for multiple frequency channels. DETAILED DESCRIPTION

[0032] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0033] like Figures 1 to 3 As shown, the present invention proposes a mud level measurement system based on frequency recognition, which is mainly used for high-precision measurement of the mud-water interface position in a water environment.

[0034] Specifically, the system of the present invention includes a sturdy and durable probe rod, which is placed vertically in the water body to be measured. The structure is encapsulated with corrosion-resistant stainless steel or polymer materials to ensure long-term durability. Multiple electronic modules are installed in the probe rod, including a light-emitting module, a receiving module, a signal processing module, and a mud level calculation module. The modules are interconnected through internal integrated circuits and wires to achieve collaborative operation. To adapt to different measurement environments and detection requirements, the total length of the probe rod, the spacing between the modules, and the specific parameters of the settings can be customized according to actual conditions.

[0035] 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. The light source adopts a light-emitting diode (LED) device. Its current is precisely controlled by an internal constant current driver chip to ensure that the light intensity is stable and does not fluctuate with voltage changes.

[0036] The light-emitting module drives the LED through pulse-width modulation (PWM) control, generating a modulated light signal output at a specific frequency. To improve measurement accuracy and adapt to complex operating conditions, the light-emitting module can output a variety of different frequencies, each representing a specific modulated light signal. The distinct differences between the frequencies facilitate accurate identification at the receiving end.

[0037] In a monochrome embodiment, a red light source with a wavelength of about 630 nm is preferably used for PWM modulation at a fixed frequency (eg, 100 Hz) to ensure suitable penetration and easy identification characteristics under most water conditions.

[0038] The receiving modules are arranged at certain intervals along the vertical direction of the detection rod to form a row of multiple vertically arranged receiving units. Each receiving unit is provided with a photodiode for receiving the modulated light signal after penetrating the water body and converting the received light signal into an analog electrical signal for output.

[0039] To ensure high signal quality, each receiving unit is backed by a transimpedance amplifier and bandpass filter to effectively filter out noise signals outside the modulation frequency range and improve signal purity. The center frequency of the bandpass filter is precisely matched to the PWM frequency of the light-emitting module, providing significant gain for signals of the required frequency. The filter output signal is then further amplified by a subsequent signal amplifier to ensure accurate subsequent signal processing.

[0040] Taking a single red light source as an example, the basic principle of the present invention for measuring mud level is described in detail:

[0041] like Figure 1 As shown in the flowchart, the PWM module within the microcontroller generates a fixed-frequency square wave signal, for example, 100Hz. This square wave signal drives a red light-emitting diode (LED) to emit a modulated red light signal. The red light signal from the LED propagates downward through the water. Multiple red light receivers are positioned vertically along the water column to receive the remaining light signal after passing through the water and convert it into a weak electrical signal. These electrical signals are first filtered and amplified by a pre-stage transimpedance amplifier and a bandpass filter to ensure that only the 100Hz modulated signal is effectively amplified.

[0042] In the absence of silt, the water is highly transparent. At this point, a 100Hz modulated red light signal can effectively penetrate the water and reach the red light receiver at the corresponding height. Consequently, the receiver's output signal contains a significant 100Hz frequency component. The signal processing module then performs frequency domain analysis on the received signal. If a significant 100Hz signal component is detected, the location is not obscured by mud. Conversely, when mud appears and blocks the red light propagation path, the 100Hz red light signal intensity received by the receiver drops sharply until it becomes undetectable. At this point, the signal processing module determines that mud is obstructing the location.

[0043] The system sequentially polls the signal strength of all receivers and performs the aforementioned frequency identification, thereby identifying the distribution of mud layers at all height levels. Finally, the mud level calculation module determines the actual sediment depth based on the receiver's installation location, spacing, and signal processing results. For example, if a receiver at a certain height cannot detect a 100Hz red light signal, but a receiver above it can, it indicates that the mud-water interface is located near that location. This method enables the system to accurately and reliably measure mud level height.

[0044] In the aforementioned mud level measurement scheme, the receiver can only read the presence of light signals in each layer at a fixed interlayer spacing, and can therefore only conclude that the mud-water interface roughly falls between the Nth layer or the N+1th layer. The resolution is limited to an integer multiple of the receiver spacing.

[0045] like Figure 2 As shown, in order to overcome this limitation, the present invention obtains the light intensity-height discrete data corresponding to each modulation frequency, first uses a cubic spline function to perform smooth interpolation on the discrete points, regards the light intensity value as a function of height S(z), and constructs a cubic polynomial between each two adjacent measurement layers to ensure not only accurate fitting at the original node but also second-order continuous derivatives within the interval. The first-order derivative function is obtained by differentiating this smooth curve , which shows the steepest negative slope at the mud-water interface. Use the golden section or chord intercept method to find By using the maximum point of the image, a continuous height value that may be between different layers can be accurately located, and the resolution is far superior to the simple inter-layer method.

[0046] like Figure 3 As shown, in a further embodiment, the present invention also introduces multi-frequency light. At a single frequency, once the ambient spectrum or water turbidity changes, causing the frequency signal to decay too quickly, the entire mud level judgment 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, light of different frequencies exhibits different absorption and scattering characteristics under different wavelengths and water conditions, allowing us to observe changes in the mud-water interface from multiple dimensions at the same time. By comparing the response differences of different frequency channels, we can not only accurately determine the interface position, but also provide a credible interval or weighted average value in the interface gradient area.

[0047] Specifically, after introducing multiple color light sources and assigning them different modulation frequencies, each color of light will also have a gradient peak at the same interface depth. After the above fitting and derivative extreme value search, a set of different interface candidate heights can be obtained. There are different approaches to the final overall measured height:

[0048] One approach is to directly use the minimum and maximum values of all candidate heights as the interface range, that is, to consider the interval from the shallowest to the deepest estimate as the height band where the mud-water interface lies. This interval method fully preserves the multi-channel perception of the boundary fuzzy zone and is suitable for use in scenarios with wide mud-water transition zones or uneven particle concentration distribution.

[0049] Another approach is to take the arithmetic average of all height measurements at different frequencies to obtain a central tendency value. This averaging method can smooth out occasional measurement noise when small random drifts occur in the channel estimates, outputting a single, representative interface height. This approach is suitable for applications that require a single, stable value for the measurement result.

[0050] The third approach is to compare the peak values of each channel in the derivative absolute value curve and use the mud level corresponding to the channel with the largest peak as the final height. The peak method uses the fact that the signal with the largest slope typically corresponds to the frequency with moderate penetration and the highest signal-to-noise ratio. This method determines the interface location using the clearest attenuation inflection point, while also prioritizing the channel most sensitive to sudden changes.

[0051] Through the flexible switching or combination of these three strategies, the system can adapt to different working conditions with clear or fuzzy mud layer boundaries, and achieve the best balance between accuracy and robustness.

[0052] 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 light channel frequency is 100Hz, the green light channel uses 271Hz, and the blue light channel uses 433Hz. The non-integer multiple relationship can avoid signal aliasing problems.

[0053] More specifically, when using a multi-color light source solution, each color is modulated at a different frequency via an independent PWM channel. These frequencies are rationally distributed and non-overlapping, facilitating subsequent signal separation and identification. The corresponding receiving module incorporates a composite wide-spectrum photodetector capable of simultaneously receiving composite optical signals from multiple colors. After filtering and amplification, these signals are then sent to the signal processing module for further separation and identification.

[0054] The signal processing module is primarily responsible for frequency-domain signal demodulation and analysis. It utilizes a high-speed analog-to-digital conversion chip to synchronously sample the analog output signals of each receiving unit at a sampling rate no less than ten times the PWM modulation frequency of the light-emitting module. The sampled digital signal is fed into a field-programmable gate array (FPGA) or digital signal processor (DSP). The internal high-speed Fourier transform (FFT) algorithm performs frequency-domain analysis on the collected data, extracting the signal strength corresponding to each frequency component and obtaining a frequency intensity spectrum encompassing all modulated frequency components. To effectively reduce the impact of environmental noise and interference on spectral analysis, the signal processing module employs a sliding window filter to perform multi-frame averaging of the spectral data, making the extracted frequency signal more stable and reliable.

[0055] Due to the complexity of actual water conditions, the mud level meter measurement system has adaptive and dynamic adjustment functions. The PWM controller provides a wide adjustable output frequency range of 50Hz to 10kHz and supports real-time frequency and color combination switching for remote or local control commands.

[0056] The system also features an automatic calibration function. When initially installed, the system records baseline light intensity data in a clean water environment. During long-term operation, the signal from each receiving channel is regularly compared to the initial baseline data. If significant attenuation is detected, a cleaning or maintenance reminder is automatically triggered, ensuring the reliability of the system's long-term measurement data. To facilitate long-term data analysis and maintenance, the system can optionally be equipped with a storage unit to store real-time measured data in external memory. This data can also be uploaded to a host computer system or cloud server in real time via industrial communication interfaces such as Ethernet, RS-485, and CAN bus, forming a comprehensive data monitoring, management, and analysis platform.

[0057] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A mud level measurement system based on frequency recognition, characterized in that: include: Light emitting module, receiving module, signal processing module and mud level calculation module; The light emitting module is used to emit modulated light signals in a manner of different modulation frequencies; The receiving module is arranged in a vertical direction and is used to receive the residual part of the modulated light signal after it penetrates the water body and output an electrical signal; The signal processing module is used to extract frequency components from the electrical signal and identify whether the signal contains the modulation frequency; The mud level calculation module is used to determine the position of the mud-water interface based on whether the modulation frequency is recognized at different heights; After the receiving module measures the corresponding discrete data of the relationship between light intensity and height, the mud level calculation module uses a spline interpolation method to fit the discrete data to generate a continuous function corresponding to light intensity and height, and further calculates the first-order derivative of the continuous function. After obtaining the derivative function, the height corresponding to the maximum point of the absolute value of the derivative function is found through a numerical search algorithm as the mud level height; The light emitting module includes modulated light sources of multiple colors, and each color of the light source is modulated at a different frequency 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 respectively identify the color optical signals corresponding to each modulation frequency; The signal processing module uses a frequency domain analysis algorithm to separate the composite electrical signal and output a frequency intensity spectrum containing different frequency components; Each frequency in the frequency intensity spectrum is matched one-to-one with the corresponding modulation frequency of the light emitting module, so as to reconstruct the response data of each color light at each height position.

2. The mud level measurement system based on frequency recognition according to claim 1 is characterized in that: The light-emitting module includes a PWM controller, which is used to generate a square wave signal of a preset frequency to drive the light source to emit pulsed light. The receiving module includes a bandpass filter and a signal amplifier, and the center frequency of the bandpass filter is consistent with the modulation frequency.

3. The mud level measurement system based on frequency recognition according to claim 1 is characterized in that: The mud level calculation module calculates the corresponding mud level height for light of different frequencies, and determines the mud level height by any of the following methods: 1) The intervals of mud level heights measured by multiple frequency lights are used as the height intervals of the mud level; 2) Take the average value of the mud level heights measured by light of different frequencies as the optimal mud level measurement height; 3) Compare the maximum points of the absolute value of the derivative function corresponding to each frequency of light, and select the height corresponding to the largest maximum point as the optimal measurement height of the mud level.

4. The mud level measurement system based on frequency recognition according to claim 1, characterized in that: The modulated light sources of multiple colors include red light, green light and blue light sources.

5. The mud level measurement system based on frequency recognition according to claim 1, characterized in that: The receiving module includes a high-speed analog-to-digital converter, which 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.

Images