A method for measuring the overflow water level in manholes based on electronic smart manhole covers
By installing displacement sensors in electronic smart manhole covers and analyzing ultrasonic echo signals, the measurement error caused by manhole cover vibration or displacement is solved, improving the accuracy and reliability of measuring the overflow water level in manholes.
Patent Information
- Application Number
- CN202611372986.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-04
- Publication Date
- 2026-11-06
AI Technical Summary
The ultrasonic water level sensor in traditional electronic smart manhole covers can cause the ultrasonic pulse emission direction to deviate due to vibration or displacement of the manhole cover, affecting the accuracy and reliability of the measurement.
By installing displacement sensors in electronic smart manhole covers, vertical displacement signals at the edges of the manhole covers are collected. Combined with the peak points and time interval difference coefficients of the ultrasonic echo signals, the confidence level of the measured water level in the manhole is calculated, reducing measurement errors caused by manhole cover vibration or displacement.
It improves the accuracy and reliability of measuring the overflow water level in the well and reduces the impact of measurement errors caused by vibration or displacement of the well cover.
Smart Images
Figure CN123045485A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of ultrasonic water level sensor measurement technology, specifically to a method for measuring the height of overflow water level in a well based on an electronic smart manhole cover. Background Technology
[0002] Electronic smart manhole covers are integrated devices that combine manhole covers and monitoring terminals based on Internet of Things (IoT) technology. They use built-in water level sensors to monitor the overflow of water levels in manholes in real time, providing accurate data support for urban flooding early warning, urban drainage system operation status assessment, and underground pipe network maintenance.
[0003] Most existing electronic smart manhole covers use ultrasonic water level sensors. These sensors are installed beneath the cover and emit ultrasonic pulses, receiving the echoes reflected from the water surface. The water level is calculated based on the pulse propagation time and the speed of sound in air. However, traditional electronic smart manhole covers do not consider vibrations or displacements caused by vehicle traffic, loose installation, or aging during operation. These factors can cause the ultrasonic pulse emission direction to deviate from the ideal vertical path. When the ultrasonic pulse is incident on the manhole wall due to this directional deviation, multiple reflections occur between the wall and the water surface, creating multiple interfering echoes. This affects the accuracy and reliability of the ultrasonic water level sensor in measuring the overflow water level. Summary of the Invention
[0004] To address the aforementioned technical problems, this application provides a method for measuring the overflow water level in manholes based on electronic smart manhole covers, thereby resolving the existing issues.
[0005] The present application discloses a method for measuring the overflow water level in manholes based on electronic smart manhole covers, which employs the following technical solution: One embodiment of this application provides a method for measuring the overflow water level in a manhole based on an electronic smart manhole cover. The method includes the following steps: During each well water level measurement, an ultrasonic water level sensor transmits ultrasonic pulses from the center of the smart manhole cover into the well, and obtains the received ultrasonic echo signal and the corresponding well water level measurement value; a displacement sensor collects the vertical displacement signal of the edge of the smart manhole cover. Suspected water surface echo peak points are determined based on the number of ultrasonic pulses emitted during each measurement and the peak amplitude of the received ultrasonic echo signals; a time interval difference coefficient is constructed based on the degree of disorder in the distribution of time intervals between all adjacent suspected water surface echo peak points. Based on the number and amplitude of peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window, and the number and amplitude of peaks in the ultrasonic echo signal, combined with the time interval difference coefficient, the confidence level of the downhole water level measurement value for each measurement is calculated. The results of the well overflow water level measurement are determined based on the corresponding well water level height measurements and the confidence level for each measurement within the collection period.
[0006] In a preferred embodiment, the method for determining the suspected water surface echo peak point is as follows: The number of ultrasonic pulses emitted during each measurement is denoted as M. The envelope of the ultrasonic echo signal received in each measurement is extracted using Hilbert transform. The top M peaks in the envelope, from largest to smallest amplitude, are taken as the suspected water surface echo peaks.
[0007] In a preferred embodiment, the time interval difference coefficient is specifically: Calculate the ratio of the time interval between adjacent suspected water surface echo peak points in each group to the maximum ultrasonic propagation time downhole, and use the ratio of the variance of all such ratios of the ultrasonic echo signal to the corresponding upper bound of the variance as the time interval difference coefficient.
[0008] In a preferred embodiment, the maximum downhole ultrasonic propagation time is the time obtained by dividing twice the well depth by the speed of sound.
[0009] In a preferred embodiment, the start time of the ultrasonic transmission and reception time window is the moment when the ultrasonic water level sensor begins to emit ultrasonic pulses, and the end time is the moment when the ultrasonic water level sensor just receives the ultrasonic echo signal.
[0010] In a preferred embodiment, the confidence level is calculated as follows: The number of all peaks and valleys in the vertical displacement signal within the ultrasonic transmission and reception time window corresponding to each measurement, as well as the mean absolute value of the amplitude of all peaks and valleys, are obtained to determine the characteristic value of the manhole cover change. The average of the time interval difference coefficient of each measurement and the characteristic value of the change of the manhole cover is recorded as the first influence coefficient; A second influence coefficient is constructed based on the number and amplitude of peak points in the ultrasonic echo signals corresponding to each measurement. The confidence level of the downhole water level measurement value for each measurement is determined based on the first influence coefficient and the second influence coefficient, wherein the confidence level is negatively correlated with the first influence coefficient and the second influence coefficient, respectively.
[0011] In a preferred embodiment, the characteristic value of the manhole cover variation is specifically: Calculate the ratio of the number of all peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window to the total number of data points in the vertical displacement signal, and the ratio of the mean of the absolute value of the amplitude to the radius of the electronic smart manhole cover; take the mean of the two ratios as the characteristic value of the manhole cover change.
[0012] In a preferred embodiment, the second influence coefficient is the average of the normalized values of the number of all peak points in the ultrasonic echo signal corresponding to each measurement and the normalized values of the mean amplitude of all peak points.
[0013] In a preferred embodiment, the confidence level is the negative of the mean of the first influence coefficient and the second influence coefficient.
[0014] In a preferred embodiment, the measurement result of the downhole overflow water level is specifically as follows: The top N well water level measurements with the highest confidence level from the lowest among all well water level measurements within the collection period are obtained. The water level interval formed by the minimum and maximum values among the obtained N well water level measurements is taken as the well overflow water level measurement result of the electronic smart manhole cover.
[0015] Compared with the prior art, this application has at least the following beneficial effects: This application utilizes an ultrasonic water level sensor within an electronic smart manhole cover to emit ultrasonic pulses and receive ultrasonic echo signals. A displacement sensor collects vertical displacement signals from the edge of the electronic smart manhole cover. Based on the amplitude of peak points in the ultrasonic echo signals, suspected water surface echo peak points are identified. A time interval difference coefficient is constructed based on the temporal regularity of the suspected water surface echo peak points, and the probability of the ultrasonic pulse emission direction deviating from the ideal vertical path is analyzed. Based on the number and amplitude of wave peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window, as well as the number and amplitude of peak points in the ultrasonic echo signals, the vibration frequency and displacement of the manhole cover are evaluated. The invention also considers the impact of ultrasonic pulse emission direction deviation caused by vibration or displacement of the manhole cover edge on the accuracy of water level measurement. Combined with the time interval difference coefficient, the confidence level of each measurement of the underground water level is calculated. The measurement result of the underground overflow water level of the electronic smart manhole cover is determined by the measurement value with high confidence. Compared to the traditional measurement method using a built-in ultrasonic water level sensor in an electronic smart manhole cover, this application can effectively reduce the impact of emission direction deviation and interference reflected echoes caused by manhole cover vibration or displacement on the final measurement result, thereby improving the accuracy and reliability of the underground overflow water level measurement. Attached Figure Description
[0016] Figure 1 A flowchart of a method for measuring the overflow water level in a manhole based on an electronic smart manhole cover, provided for this application; Figure 2 A schematic diagram illustrating the calculation process of the confidence level of the measured water level in the well. Detailed Implementation
[0017] The following description, in conjunction with the accompanying drawings, details a specific scheme for measuring the overflow water level in a manhole based on an electronic smart manhole cover, as provided in this application.
[0018] One embodiment of this application provides a method for measuring the overflow water level in a manhole based on an electronic smart manhole cover.
[0019] Specifically, the following method for measuring the overflow water level in manholes based on electronic smart manhole covers is provided. Please refer to [link / reference]. Figure 1 The method includes the following steps: Step 1: During each well water level measurement, an ultrasonic water level sensor transmits ultrasonic pulses from the center of the smart manhole cover into the well, and obtains the received ultrasonic echo signal and the corresponding well water level measurement value; a displacement sensor collects the vertical displacement signal of the edge of the smart manhole cover.
[0020] This application incorporates an ultrasonic water level sensor within an electronic smart manhole cover. The sensor emits ultrasonic pulses into the manhole and receives the echo signals to measure the water level height. In this embodiment, the water level signal is acquired at a frequency of 1Hz, meaning the water level is measured every 1 second. The ultrasonic water level sensor is installed at the center of the electronic smart manhole cover to minimize the impact of vibrations or vertical displacement of the cover on the emission direction of the ultrasonic pulses.
[0021] Ultrasonic water level sensors typically emit ultrasonic pulses continuously or at equal intervals. In this application, M ultrasonic pulses are emitted at equal intervals each time the water level is measured. The time interval between adjacent ultrasonic pulses must be greater than the maximum ultrasonic propagation time in the well where the electronic smart manhole cover is located (i.e., twice the well depth divided by the speed of sound). This is to suppress pulse echo overlap in the ultrasonic echo signal received by the ultrasonic water level sensor and to avoid the inability to extract the signal peak value corresponding to the water surface reflection echo formed during the propagation of each emitted ultrasonic pulse using Hilbert transform. The carrier frequency of the ultrasonic transducer used is 40kHz (corresponding to a carrier period of 25 microseconds). In this embodiment, the number of ultrasonic pulses emitted in a single measurement is set to M=8. Considering that the time interval between adjacent ultrasonic pulses must be greater than the maximum ultrasonic propagation time in the well, the time interval between adjacent ultrasonic pulses is set to a preset reference duration of 50 milliseconds to ensure that each emitted pulse is completely independent in time.
[0022] Furthermore, during each measurement, based on the propagation time of the water surface reflected echoes generated by the M ultrasonic pulses, M reference water level heights are calculated, and the arithmetic mean of the M reference water level heights is used as the measured value of the well water level height corresponding to that measurement.
[0023] A displacement sensor is built into the electronic smart manhole cover to collect its vertical displacement signal. Furthermore, for each water level measurement, a time window for ultrasonic wave transmission and reception is determined: the start time is when the ultrasonic water level sensor begins to emit ultrasonic pulses, and the end time is when the ultrasonic water level sensor just receives the ultrasonic echo signal. Subsequently, the signal segment corresponding to this time window is extracted from the vertical displacement signal collected by the displacement sensor for subsequent processing. It should be noted that the data acquisition frequency of the vertical displacement signal needs to be much higher than the sampling frequency of the water level height signal to facilitate subsequent analysis of the edge vibration and vertical displacement of the electronic smart manhole cover during each water level measurement. In this embodiment, the data acquisition frequency of the vertical displacement signal is 100Hz. Since the displacement sensor is installed at the edge of the electronic smart manhole cover, edge vibration and vertical displacement of the cover more easily cause a shift in the emission direction of the ultrasonic pulses in the ultrasonic water level sensor.
[0024] Each water level measurement time is used as a sampling point. This allows us to obtain the ultrasonic echo signal, downhole water level measurement value, and vertical displacement signal corresponding to each sampling point.
[0025] Furthermore, the acquisition period was set to 20 seconds to obtain the water level height signal within a single acquisition period. The ultrasonic echo signals from each sampling point were then denoised using a moving average filtering algorithm to reduce the impact of random noise in the acquired ultrasonic echo signals on subsequent data processing.
[0026] Step 2: Determine the suspected water surface echo peak points based on the number of ultrasonic pulses emitted during each measurement and the peak amplitude of the received ultrasonic echo signals; construct the time interval difference coefficient based on the degree of disorder in the distribution of time intervals between all adjacent suspected water surface echo peak points.
[0027] Because this application uses equally spaced ultrasonic pulses, under the premise that the vibration of the electronic smart manhole cover does not cause the ultrasonic emission direction to deviate from the ideal vertical direction, the position and direction of each emitted pulse of the ultrasonic water level sensor remain consistent, causing the propagation and reflection paths to tend to overlap; thus, the arrival time interval of the reflected echo from the water surface in the well exhibits a consistent characteristic.
[0028] Ultrasonic energy attenuates with increasing propagation distance. Compared to ultrasonic echoes reflected via the well wall-water surface path, ultrasonic echoes reflected directly from the water surface have a shorter propagation distance and therefore exhibit higher amplitude.
[0029] S2.1 Therefore, taking the ultrasonic echo signal A at any sampling point as an example, firstly, the envelope of the ultrasonic echo signal A at that sampling point is extracted using the Hilbert transform, which is used to characterize the contour curves of all echoes in the ultrasonic echo signal A; then, all peak points in the envelope are extracted using the second-order difference peak-valley identification algorithm, which is recorded as the reflected echo peak points to identify the peak positions of each reflected echo, including water surface reflected echoes, in the ultrasonic echo signal A; finally, the M peak points with the largest amplitude among all reflected echo peak points are recorded as suspected water surface echo peak points, where M is the number of ultrasonic pulses emitted each time the water level is measured. The Hilbert transform and the second-order difference peak-valley identification algorithm are both well-known techniques, and their specific processes will not be elaborated further.
[0030] S2.2 Then, the sampling times of all suspected water surface echo peaks in the ultrasonic echo signal A of the sampling point are arranged in temporal order, and the first-order difference sequence of the resulting time sequence is obtained, denoted as the echo reception time interval sequence. This sequence quantitatively describes the numerical distribution of the reception time intervals of reflected echoes from adjacent water surfaces. The calculation of the first-order difference sequence is a well-known technique, and the specific process will not be elaborated here.
[0031] Following S2.3, each data point in the echo reception time interval sequence of the sampling point is divided by the maximum downhole ultrasonic propagation time to eliminate the influence of dimensions. The variance of all data points in the dimensionless echo reception time interval sequence is calculated, and this variance is divided by the upper bound of the data point variance of the sequence. The result is recorded as the time interval difference coefficient. As a special case, when the entire echo reception time interval remains stable, causing the maximum value of the data points in the sequence to equal the minimum value, resulting in the upper bound of the data point variance of the sequence being 0, the aforementioned division operation is skipped, and the obtained time interval difference coefficient is directly set to 0. The upper bound of the data point variance in the sequence is a well-known concept, specifically the square of the difference between the maximum and minimum values of the data points in the sequence. The time interval difference coefficient assesses the inconsistency of the water surface reflected echo reception time interval. The larger the coefficient, the stronger the inconsistency, and the higher the probability that the corresponding transmission direction deviates from the ideal vertical path. The purpose of introducing the upper bound of the variance here is to map the value range of this coefficient to the [0,1] interval.
[0032] Step 3: Based on the number and amplitude of peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window, and the number and amplitude of peaks in the ultrasonic echo signal, combined with the time interval difference coefficient, calculate the confidence level of the downhole water level measurement values for each measurement.
[0033] Furthermore, random noise can also cause inconsistencies in the arrival time interval of water surface reflected echoes. Although the ultrasonic echo signal has been denoised, it is impossible to completely filter out all noise. When the edge of the electronic smart manhole cover experiences large vibration frequencies or vertical displacement during the ultrasonic pulse transmission and reception phases, the arrival time interval of the water surface reflected echoes will become significantly discrete; at this time, the ultrasonic pulse transmission direction has shifted significantly, thereby reducing the accuracy of the retrieved water level height.
[0034] Therefore, as Figure 2 As shown, in order to evaluate the accuracy of the well water level measurement values at each sampling point, the following processing is performed to obtain the confidence level of the well water level measurement values.
[0035] S3.1.1 First, obtain the vertical displacement signal corresponding to each sampling point, that is, the vertical displacement signal within the ultrasonic transmission and reception time window during each water level measurement, which is used to characterize the displacement state of the electronic smart manhole cover during the ultrasonic transmission and reception period.
[0036] S3.1.2 Then, taking the vertical displacement signal W of any sampling point as an example, the peak and trough points in the vertical displacement signal W of the sampling point are extracted using the second-order difference identification algorithm of peaks and troughs. The sum of the number of all peak and trough points obtained is recorded as the number of extreme points. If the vertical displacement signal W contains enough calculation points, the ratio of the number of extreme points to the total number of data points in the vertical displacement signal W is recorded as the relative vibration frequency of the manhole cover. If there are not enough points in the vertical displacement signal W for peak and trough point extraction, or the total number of peak and trough points obtained is 0, the relative vibration frequency of the manhole cover is directly set to 0. The relative vibration frequency of the manhole cover is used to evaluate the relative magnitude of the vibration frequency of the edge of the electronic smart manhole cover during ultrasonic pulse transmission and reception. The larger the relative vibration frequency of the manhole cover, the larger the relative magnitude of the vibration frequency of the edge of the electronic smart manhole cover.
[0037] S3.1.3 Subsequently, the mean of the absolute values of the amplitudes of all peaks and troughs in the vertical displacement signal W at the sampling point is calculated. The ratio of this mean to the radius of the electronic smart manhole cover is recorded as the relative displacement value of the manhole cover. In particular, when the total number of peaks and troughs acquired is 0, in addition to setting the relative vibration frequency of the manhole cover to 0 according to the aforementioned rules, the relative displacement value of the manhole cover corresponding to the sampling point is directly set to 0. This parameter is used to evaluate the relative magnitude of the overall vertical displacement of the edge of the electronic smart manhole cover during the ultrasonic pulse transmission and reception period. The larger the relative displacement value of the manhole cover, the larger the relative magnitude of the overall vertical displacement offset distance of the edge of the electronic smart manhole cover.
[0038] Following S3.1.4, the mean value of the relative vibration frequency and relative displacement of the manhole cover at the sampling point is calculated and recorded as the characteristic value of the manhole cover change at that sampling point. This characteristic value comprehensively reflects the degree of vibration and vertical displacement change of the edge of the electronic smart manhole cover during the ultrasonic pulse transmission and reception period; the larger the value, the more significant the disturbance.
[0039] S3.1.5 Finally, calculate the average of the time interval difference coefficient and the characteristic value of the manhole cover change at this sampling point, denoted as the first influence coefficient. This coefficient is used to evaluate the impact of propagation time error on the calculated water level when the ultrasonic pulse emission direction deviates from the ideal vertical direction due to vibration or vertical displacement of the manhole cover edge. The larger this first influence coefficient is, the more likely the difference in the time interval between the water surface reflected echo reception is caused by the deviation of the emission direction, the greater the degree to which the measured water level at this sampling point deviates from the actual water level, and the less it reflects the true water level.
[0040] S3.2 Furthermore, the ultrasonic pulses emitted by the built-in ultrasonic water level sensor in the electronic smart manhole cover are deflected due to a deviation in the emission direction, causing the ultrasonic pulses to be incident on the manhole wall and forming multiple reflections between the manhole wall and the water surface, generating multiple interference echoes. After these interference echoes are received by the sensor, they will affect the accuracy of the water level calculation; the greater the number and amplitude of the interference echoes, the greater the deviation between the obtained water level and the actual water level.
[0041] Therefore, the number of all reflected echo peaks and the average amplitude of all reflected echo peaks in the ultrasonic echo signal at each sampling point are calculated and denoted as the number of peaks and the average peak amplitude, respectively. The Min-Max normalization method is used to normalize the number of peaks and the average peak amplitude of all sampling points in a single acquisition cycle to remove the influence of data dimensions. For the static data environment of the entire monitoring cycle, the following setting is added: if all sampling parameters in a certain acquisition cycle remain completely equal, resulting in the same maximum and minimum values in the sequence, the above normalization calculation will no longer be used, and the relevant normalization coefficient under this index will be directly assigned to a constant of 0. The average of the normalized results of the number of peak values and the normalized results of the average peak amplitude at each sampling point is calculated and denoted as the second influence coefficient for each sampling point. This coefficient is used to evaluate the impact of interference echoes generated when ultrasonic pulses are incident on the well wall due to the deviation of the ultrasonic pulse emission direction caused by the vibration or vertical displacement of the edge of the electronic smart manhole cover. The larger the second influence coefficient, the more prominent the number and amplitude of interference echoes at that sampling point are compared with other sampling points in the same acquisition period, and the greater the deviation between its measured water level and the actual water level. The Min-Max normalization method is a well-known technique, and its specific process will not be described in detail.
[0042] S3.3 Calculate the mean of the first influence coefficient and the second influence coefficient for each sampling point, and use the negative of this mean as the confidence level of the well water level measurement value corresponding to each sampling point. The confidence level is used to assess the accuracy of the well water level measurement value reflected by the well water level measurement value corresponding to each sampling point. The higher the confidence level, the more accurately the well water level measurement value corresponding to each sampling point reflects the true well water level.
[0043] Step 4: Determine the measurement results of the well overflow water level based on the corresponding downhole water level height measurements and the confidence level for each measurement within the acquisition period.
[0044] In a single acquisition cycle, the N sampling points with the highest confidence are selected as all valid sampling points at time t when the water level is measured. In this embodiment, the number of valid sampling points is set to 5.
[0045] The system acquires all valid sampling points from the entire sampling period up to the current moment. The water level range formed by the minimum and maximum values of the downhole water level measurements of all valid sampling points is taken as the current downhole overflow water level measurement result of the electronic smart manhole cover and transmitted to the remote monitoring center for real-time assessment and early warning of the downhole overflow status.
[0046] In summary, this application embodiment uses an ultrasonic water level sensor in an electronic smart manhole cover to emit ultrasonic pulses and receive ultrasonic echo signals; a displacement sensor collects vertical displacement signals from the edge of the electronic smart manhole cover; based on the amplitude of peak points in the ultrasonic echo signals, suspected water surface echo peak points are determined; based on the temporal regularity of the occurrence of suspected water surface echo peak points, a time interval difference coefficient is constructed to analyze the probability that the ultrasonic pulse emission direction deviates from the ideal vertical path; based on the number and amplitude of peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window, and the number and amplitude of peak points in the ultrasonic echo signals, the vibration frequency of the manhole cover is evaluated. The displacement and the impact of ultrasonic pulse emission direction deviation caused by vibration or displacement of the manhole cover edge on the accuracy of water level measurement are considered. Combined with the time interval difference coefficient, the confidence level of each measurement of the underground water level is calculated. The measurement result of the underground overflow water level of the electronic smart manhole cover is determined by the measurement value with high confidence. Compared to the traditional measurement method using an ultrasonic water level sensor built into an electronic smart manhole cover, this application can effectively reduce the impact of emission direction deviation and interference reflected echoes caused by manhole cover vibration or displacement on the final measurement result, thereby improving the accuracy and reliability of the underground overflow water level measurement.
Claims
1. A method for measuring the overflow water level in a manhole based on an electronic smart manhole cover, characterized in that, The method includes the following steps: During each well water level measurement, an ultrasonic water level sensor transmits ultrasonic pulses from the center of the smart manhole cover into the well, and obtains the received ultrasonic echo signal and the corresponding well water level measurement value; a displacement sensor collects the vertical displacement signal of the edge of the smart manhole cover. Suspected water surface echo peak points are determined based on the number of ultrasonic pulses emitted during each measurement and the peak amplitude of the received ultrasonic echo signals; a time interval difference coefficient is constructed based on the degree of disorder in the distribution of time intervals between all adjacent suspected water surface echo peak points. Based on the number and amplitude of peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window, and the number and amplitude of peaks in the ultrasonic echo signal, combined with the time interval difference coefficient, the confidence level of the downhole water level measurement value for each measurement is calculated. The results of the well overflow water level measurement are determined based on the corresponding well water level height measurements and the confidence level for each measurement within the collection period.
2. The method for measuring the overflow water level in a well based on an electronic smart manhole cover as described in claim 1, characterized in that, The specific method for determining the suspected peak point of the water surface echo is as follows: The number of ultrasonic pulses emitted during each measurement is denoted as M. The envelope of the ultrasonic echo signal received in each measurement is extracted using Hilbert transform. The top M peaks in the envelope, from largest to smallest amplitude, are taken as the suspected water surface echo peaks.
3. The method for measuring the overflow water level in a well based on an electronic smart manhole cover as described in claim 1, characterized in that, The time interval difference coefficient is specifically: Calculate the ratio of the time interval between adjacent suspected water surface echo peak points in each group to the maximum ultrasonic propagation time downhole, and use the ratio of the variance of all such ratios of the ultrasonic echo signal to the corresponding upper bound of the variance as the time interval difference coefficient.
4. The method for measuring the overflow water level in a well based on an electronic smart manhole cover as described in claim 3, characterized in that, The maximum ultrasonic propagation time in the well is the time obtained by dividing twice the well depth by the speed of sound.
5. The method for measuring the overflow water level in a well based on an electronic smart manhole cover as described in claim 1, characterized in that, The start time of the ultrasonic transmission and reception time window is the moment when the ultrasonic water level sensor starts to emit ultrasonic pulses, and the end time is the moment when the ultrasonic water level sensor just receives the ultrasonic echo signal.
6. The method for measuring the overflow water level in a well based on an electronic smart manhole cover as described in claim 1, characterized in that, The confidence level is calculated as follows: The number of all peaks and valleys in the vertical displacement signal within the ultrasonic transmission and reception time window corresponding to each measurement, as well as the mean absolute value of the amplitude of all peaks and valleys, are obtained to determine the characteristic value of the manhole cover change. The average of the time interval difference coefficient of each measurement and the characteristic value of the change of the manhole cover is recorded as the first influence coefficient; A second influence coefficient is constructed based on the number and amplitude of peak points in the ultrasonic echo signals corresponding to each measurement. The confidence level of the downhole water level measurement value for each measurement is determined based on the first influence coefficient and the second influence coefficient, wherein the confidence level is negatively correlated with the first influence coefficient and the second influence coefficient, respectively.
7. The method for measuring the overflow water level in a well based on an electronic smart manhole cover as described in claim 6, characterized in that, The specific characteristic values of the manhole cover variation are: Calculate the ratio of the number of all peaks and troughs in the vertical displacement signal within the ultrasonic transmission and reception time window to the total number of data points in the vertical displacement signal, and the ratio of the mean of the absolute value of the amplitude to the radius of the electronic smart manhole cover; take the mean of the two ratios as the characteristic value of the manhole cover change.
8. A method for measuring the overflow water level in a manhole based on an electronic smart manhole cover as described in claim 6, characterized in that, The second influence coefficient is the average of the normalized value of the number of all peak points in the ultrasonic echo signal corresponding to each measurement and the normalized value of the mean amplitude of all peak points.
9. A method for measuring the overflow water level in a manhole based on an electronic smart manhole cover as described in claim 6, characterized in that, The confidence level is the negative of the mean of the first influence coefficient and the second influence coefficient.
10. A method for measuring the overflow water level in a manhole based on an electronic smart manhole cover as described in claim 1, characterized in that, The specific results of the downhole overflow water level measurement are as follows: The top N well water level measurements with the highest confidence level from the lowest among all well water level measurements within the collection period are obtained. The water level interval formed by the minimum and maximum values among the obtained N well water level measurements is taken as the well overflow water level measurement result of the electronic smart manhole cover.