Disclosure of Invention
Aiming at the problems in the prior art, the method for detecting the floating frequency of the pointer of the liquid level meter based on image processing and wavelet transformation is provided in the disclosure, and liquid level data collected in practical application comprises high-frequency mechanical vibration of the environment besides low-frequency liquid level floating change. The wavelet analysis filtering and floating frequency detection method can realize rapid and accurate prediction and early warning of abnormal data.
The purpose of the disclosure is realized by the following technical scheme:
the method for detecting the floating frequency of the liquid level indicator based on image processing and wavelet transformation comprises the following steps:
s100: shooting a pointer of the liquid level meter by using a camera in the image liquid level acquisition module to obtain a liquid level meter image containing the pointer, and identifying a reading in the liquid level meter image through a deep neural network;
s200: forming a first time domain graph of liquid level changing along with time according to liquid level meter images and readings obtained at different moments;
s300: performing discrete wavelet transform on the first time domain graph to obtain a first time frequency graph, and obtaining a first frequency signal containing amplitude of time and frequency based on the first time frequency graph;
s400: quantizing the amplitude of the first type frequency signal with the duration time lower than a first threshold value into zero, and quantizing the amplitude of the second type frequency signal with the amplitude higher than a second threshold value into zero, so as to realize the denoising of the first frequency signal, and taking the rest frequency signals as denoised second frequency signals;
s500: and updating the first time-frequency graph according to the second frequency signal to obtain a denoised second time-frequency graph, performing wavelet inverse transformation on the second time-frequency graph to obtain a second time-frequency graph so as to obtain denoised liquid level data, and further detecting the floating frequency of the pointer of the liquid level meter when corresponding liquid level data in a period of time is detected according to the denoised liquid level data and the denoised second frequency signal.
Preferably, the first and second liquid crystal materials are,
in step S100, the identifying the reading in the liquid level meter image through the deep neural network includes the following steps:
s101: manually marking the position of an interest point of each acquired original liquid level meter image for training to obtain each marked image;
s102: and taking each marked image as input to construct an auxiliary neural network to assist the deep neural network in learning and training the liquid level meter image.
Preferably, the first and second liquid crystal materials are,
step S102 is to construct an auxiliary neural network to assist the deep neural network in learning and training the liquid level gauge image, specifically by:
s1021: taking each marked image as input, selecting a proper middle layer from the deep neural network, and obtaining the output of the middle layer;
s1022: establishing an auxiliary neural network formed by convolution functions;
s1023: inputting the output of the middle layer and the corresponding attitude estimation matrix of each original liquid level meter image into an auxiliary neural network;
s1024: and combining the outputs of the auxiliary neural network and the deep neural network, and jointly inputting the outputs into a loss function of the deep neural network to assist the deep neural network in learning and training the liquid level meter image.
Preferably, the first and second liquid crystal materials are,
the attitude estimation matrix in step S1023 is obtained by:
s10231: calibrating the camera, and solving the intrinsic parameters of the camera, wherein the intrinsic parameters comprise: the image optical axis principal point, the focal lengths in the X direction and the Y direction, the tangential distortion coefficient and the radial distortion coefficient;
s10232: the attitude estimation matrix is further solved as follows:
solving an attitude estimation matrix [ R | t ] (X = M [ R | t ])/X),
wherein M is an internal parameter of the camera, X is a world coordinate system, and X is an image pixel coordinate of a known shot object; r, t are the rotation vector and the translation vector of the attitude estimation matrix, respectively.
Preferably, the first and second liquid crystal materials are,
the solving of the intrinsic parameters of the camera in step S10231 is to solve the intrinsic parameters of the camera according to the zhangzhengyou scaling method and the checkerboard.
Preferably, the first and second liquid crystal materials are,
the grid is 10cm by 10 cm.
Preferably, the first and second liquid crystal materials are,
the deep neural network selects ResNet 50.
Preferably, the first and second liquid crystal materials are,
the auxiliary neural network selects ResNet 18.
Preferably, the first and second liquid crystal materials are,
the convolution function is Conv (input, w), where input represents the input and w represents the weight.
Preferably, the first and second liquid crystal materials are,
after the step S100 is executed and before the step S200 is executed, the method further includes the following steps:
s1000: the method comprises the steps that a laser ranging sensor is used for obtaining the height of a current liquid level indicating rod of a liquid level meter; and taking the current liquid level indicator rod height as: the reference of the reading in the level gauge image is identified by the deep neural network in step S100.
In addition, the present disclosure also discloses a method for detecting floating frequency of a pointer of a liquid level meter, which comprises the following steps:
the method comprises the following steps of firstly, acquiring a time domain graph of liquid level changing along with time;
secondly, performing discrete wavelet transformation on the time domain graph to obtain a time frequency graph from the time domain graph;
thirdly, obtaining a frequency signal containing time and frequency amplitude values based on the time-frequency diagram, and denoising by adopting time filtering and frequency threshold filtering, wherein the rest frequency signal is used as a denoised frequency signal;
the fourth step, updating the time-frequency graph by using the denoised frequency signal, and performing wavelet inverse transformation on the updated time-frequency graph to obtain a denoised time-domain graph;
and fifthly, obtaining denoised liquid level data by using the denoised time domain diagram, and further detecting the floating frequency of a liquid level meter pointer in a period of time when corresponding liquid level data is detected according to the denoised liquid level data and the denoised frequency signal.
Preferably, in the first step, the image liquid level acquisition module shoots the liquid level meter, and the image recognition obtains a reading.
Preferably, in the first step, the laser ranging sensor obtains the current level indicating rod height of the liquid level meter to identify the reading.
Preferably, for a discrete wavelet transform:
the basis functions of the continuous wavelet are:
wherein, FbAs a bandwidth parameter, FcIs the center frequency, i is the imaginary unit, t is the time unit,
and performing extension and translation on the basis function to obtain a family function:
wherein a is a scale, namely a telescopic parameter, and b is a translation parameter;
the method comprises the following steps of discretizing a scale parameter a and a translation parameter b of a definition formula of continuous wavelet transformation, wherein a discretized wavelet sequence is as follows:
the discretization formula of the scale and translation parameters a and b in continuous wavelet change is as follows:
a0is the extension step size, where the power of j represents the scale reduction multiple to a; when j is not equal to 0, a is changed from a0 j-1Become a0 jWhen a is enlarged by a0Multiple, i.e. the centre frequency of the wavelet is reduced by a0Multiple, bandwidth is also reduced by a0Doubling; k represents the uniform sampling rate for b; z represents an integer set;
the wavelet coefficients of different positions and different scales are solved through discrete wavelet transform, and the formula is as follows:
wherein,
is composed of
A complex conjugate function of; dt is the data sampling time; c
j,kFor the calculation of the resulting wavelet coefficients for each frequency and scale, f (t) is a function of the original signal.
When in reconstruction, each wavelet function is directly multiplied and accumulated by the coefficient, and the formula is as follows:
it can be understood that when the time domain graph is subjected to discrete wavelet transform, f (t) is time domain data;
when the time-frequency diagram is subjected to wavelet inverse transformation to obtain the liquid level data after denoising, the liquid level data obtained through inverse transformation is: f (t) obtained by performing inverse transformation on the time-frequency diagram.
In the method, if the liquid level value of the time domain exceeds the threshold value, an alarm signal is sent out, and if the frequency of the effective frequency of the frequency domain is abnormally floated and exceeds the threshold value, a higher-level emergency signal is sent out.
Advantageous effects
According to the method, the time domain graph and the frequency domain graph are obtained through wavelet processing, after the frequency signals with continuous time lower than a preset time range are quantized to be zero, the amplitude of the main frequency signal higher than a high-frequency threshold value is quantized to be zero, the rest frequency signals are used as the liquid level signal frequency, interference caused by noise such as high-frequency vibration is avoided, and the abnormal data can be quickly and accurately predicted and early warned.
The foregoing description is only an overview of the technical solutions of the present disclosure, and in order to make the technical solutions of the present disclosure more clearly understood, the technical solutions of the present disclosure are implemented to the extent that those skilled in the art can implement the technical solutions according to the description, and the above and other objects, features, and advantages of the present disclosure can be more clearly understood, the following description is given by way of example of the specific embodiments of the present disclosure.
Detailed Description
Specific embodiments of the present disclosure will be described in more detail below with reference to fig. 1(a) to 3. While specific embodiments of the disclosure are shown in the drawings, it should be understood that the disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
It should be noted that certain terms are used throughout the description and claims to refer to particular components. As one skilled in the art will appreciate, various names may be used to refer to a component. This specification and claims do not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. The description which follows is a preferred embodiment of the disclosure, but is made for the purpose of illustrating the general principles of the disclosure and not for the purpose of limiting the scope of the disclosure. The scope of the present disclosure is to be determined by the terms of the appended claims.
To facilitate an understanding of the embodiments of the present disclosure, the following detailed description is to be considered in conjunction with the accompanying drawings, and the drawings are not to be construed as limiting the embodiments of the present disclosure.
In one embodiment, the present disclosure discloses a method for detecting a floating frequency of a liquid level indicator pointer based on image processing and wavelet transform, the method comprising the steps of:
s100: shooting a pointer of the liquid level meter by using a camera in the image liquid level acquisition module to obtain a liquid level meter image containing the pointer, and identifying a reading in the liquid level meter image through a deep neural network;
s200: forming a first time domain graph of liquid level changing along with time according to liquid level meter images and readings obtained at different moments;
s300: performing discrete wavelet transform on the first time domain graph to obtain a first time frequency graph, and obtaining a first frequency signal containing amplitude of time and frequency based on the first time frequency graph;
s400: quantizing the amplitude of the first type frequency signal with the duration time lower than a first threshold value into zero, and quantizing the amplitude of the second type frequency signal with the amplitude higher than a second threshold value into zero, so as to realize the denoising of the first frequency signal, and taking the rest frequency signals as denoised second frequency signals;
s500: and updating the first time-frequency graph according to the second frequency signal to obtain a denoised second time-frequency graph, performing wavelet inverse transformation on the second time-frequency graph to obtain a second time-frequency graph so as to obtain denoised liquid level data, and further detecting the floating frequency of the pointer of the liquid level meter when corresponding liquid level data in a period of time is detected according to the denoised liquid level data and the denoised second frequency signal.
In the embodiment, after the frequency signal with the continuous time lower than the preset time range is quantized to be zero, the amplitude of the main frequency signal higher than the high-frequency threshold value is quantized to be zero, the rest frequency signal is used as the denoised frequency signal, and meanwhile, the floating frequency of the liquid level meter pointer is detected by combining the denoised liquid level data. The method avoids the interference caused by noise such as obvious external disturbance, high-frequency vibration and the like, and realizes the rapid and accurate prediction and early warning of abnormal data. It can be understood that, according to the corresponding relationship between the time domain diagram and the liquid level data, the liquid level data after denoising is obtained exactly according to the second time domain diagram, i.e. according to the new time domain diagram after denoising.
In another embodiment of the present invention, the substrate is,
in step S100, the identifying the reading in the liquid level meter image through the deep neural network includes the following steps:
s101: manually marking the position of an interest point of each acquired original liquid level meter image for training to obtain each marked image;
s102: and taking each marked image as input to construct an auxiliary neural network to assist the deep neural network in learning and training the liquid level meter image.
With this embodiment, it is considered that the final result of the image recognition is to output the coordinates of the respective interest points on the image. However, if the floating frequency of the pointer can be detected as per the previous embodiment, the deep neural network learns the image and directly outputs two-dimensional coordinates for optimization learning without adopting the optimization manner of the present embodiment, which obviously means that the previous embodiment is a very non-linear process, and the loss function for optimization is less constrained to the weights in the neural network during optimization learning. In this regard, those skilled in the art will appreciate. In order to solve this problem, in this embodiment, an intermediate state is finally constructed by constructing an auxiliary neural network according to the collected images and the positions of the artificially labeled interest points, so as to assist the training and learning of the deep neural network. That is, the auxiliary neural network is used to assist the training and learning of the deep neural network, compared to the previous embodiment, which is another technical contribution of the present disclosure.
In another embodiment of the present invention, the substrate is,
step S102 is to construct an auxiliary neural network to assist the deep neural network in learning and training the liquid level gauge image, specifically by:
s1021: taking each marked image as input, selecting a proper middle layer from the deep neural network, and obtaining the output of the middle layer;
s1022: establishing an auxiliary neural network formed by convolution functions;
s1023: inputting the output of the middle layer and the corresponding attitude estimation matrix of each original liquid level meter image into an auxiliary neural network;
s1024: and combining the outputs of the auxiliary neural network and the deep neural network, and jointly inputting the outputs into a loss function of the deep neural network to assist the deep neural network in learning and training the liquid level meter image.
It is to be appreciated that the present embodiment, in connection with the previous embodiment, is a further exemplary illustration of the technical contributions related to the ancillary neural network aspects of the present disclosure.
In another embodiment of the present invention, the substrate is,
after the step S100 is executed and before the step S200 is executed, the method further includes the following steps:
s1000: the method comprises the steps that a laser ranging sensor is used for obtaining the height of a current liquid level indicating rod of a liquid level meter; and taking the current liquid level indicator rod height as: the reference of the reading in the level gauge image is identified by the deep neural network in step S100.
It can be understood that since S200: forming a time domain graph of the liquid level changing along with time according to the liquid level meter images and the readings obtained at different moments; this means, this embodiment will be with the current liquid level of the liquid level table that laser rangefinder sensor obtained and instruct the pole height, has equallyd to an extra basis of "reading", and this disclosure can make the neural network of depth have clear external reference more, and this reference is the value of the higher precision of laser rangefinder. This facilitates more accurate readings by the deep neural network of the present disclosure.
It should be noted that the laser ranging can measure more than 100 times per second, and one or more laser ranging sensors can be used to obtain one or more references as needed, or even an average value reference can be formed by averaging a plurality of reference values.
Furthermore, in another embodiment, the present disclosure discloses a method for detecting a level gauge pointer floating frequency based on image processing and wavelet transform, the method comprising the steps of:
the method comprises the following steps of firstly, acquiring a time domain graph of liquid level changing along with time;
secondly, performing discrete wavelet transformation on the time domain graph to obtain a time frequency graph from the time domain graph;
thirdly, obtaining a frequency signal containing time and frequency amplitude values based on the time-frequency diagram, and denoising by adopting time filtering and frequency threshold filtering, wherein the rest frequency signal is used as a denoised frequency signal;
the fourth step, updating the time-frequency graph by using the denoised frequency signal, and performing wavelet inverse transformation on the updated time-frequency graph to obtain a denoised time-domain graph;
and fifthly, obtaining denoised liquid level data by using the denoised time domain diagram, and further detecting the floating frequency of a liquid level meter pointer in a period of time when corresponding liquid level data is detected according to the denoised liquid level data and the denoised frequency signal.
With respect to the above embodiments, it reveals the key technical idea of the present disclosure, and widens the scope of the present disclosure compared with the first embodiment.
Among these, temporal filtering is due to: the inventor finds that when the drilling platform works continuously, the drilling platform generates a discontinuous certain frequency signal in a low-frequency range, and the discontinuous frequency signal is quantized to be zero;
the frequency filtering is due to: the inventor finds that the vibration of a power system is one of the long-term continuous noises of a hydraulic pressure meter and a liquid level meter when the drilling platform works. For example, the drill pipe rotates at a speed of tens of revolutions per minute, and the inventor finds that the frequency of the maximum amplitude of the power system during the drilling operation is 17.5Hz, so that 40% of offset range can be reserved during frequency filtering, the high-frequency threshold value is set to be 10.5Hz, the amplitude of the main frequency signal higher than the high-frequency threshold value is quantized to be zero, and the rest frequency signal is taken as the liquid level signal frequency.
Referring to fig. 3, in another embodiment, the intermediate layer output is the output of C5:7 × 2048.
For the related embodiments described above, the present disclosure effectively reduces the fitting difficulty during the training of the relevant model, and simultaneously improves the robustness of the model. In the same test set, after the images are used as a training set and the training and optimizing methods are adopted, the map @0.5 precision of the model is 2.76% higher than that of the model which is not adopted. It is further noted that, when the attitude estimation matrix is solved by the PNP based on the rannsac algorithm, even if the average error of the PNP solution is found to be about 5% in the actual scene verification, the difficulty of fitting during the training of the relevant model is effectively reduced and the robustness of the model is improved, so that the subsequent actual scene verification is not affected by the error of the attitude estimation matrix.
In the preferred embodiment of the method, if the liquid level value in the time domain exceeds the threshold value, an alarm signal is sent out, and if the frequency fluctuation abnormality of the effective frequency in the frequency domain exceeds the threshold value, an emergency signal is sent out.
It should be noted that the above embodiments are key to the core concept and technical contribution of the present disclosure.
The following examples are more specific alternatives, are conventional in the art and are not critical to the present disclosure, nor are they intended to represent novel technical contributions to the following examples.
In another embodiment of the present invention, the substrate is,
the attitude estimation matrix in step S1023 is obtained by:
s10231: calibrating the camera, and solving the intrinsic parameters of the camera, wherein the intrinsic parameters comprise: the image optical axis principal point, the focal lengths in the X direction and the Y direction, the tangential distortion coefficient and the radial distortion coefficient;
s10232: the attitude estimation matrix is further solved as follows:
solving an attitude estimation matrix [ R | t ] (X = M [ R | t ])/X),
wherein M is an internal parameter of the camera, X is a world coordinate system, and X is an image pixel coordinate of a known shot object; r, t are the rotation vector and the translation vector of the attitude estimation matrix, respectively.
In another embodiment, the solving of the intrinsic parameters of the camera in step S10231 is based on the Zhang friend calibration method and the checkerboard.
Further, in another embodiment, the attitude estimation matrix [ R | t ] is solved by PNP based on the Ranssac algorithm.
In another embodiment of the present invention, the substrate is,
step S1021 includes:
and solving the internal parameters of the camera according to the Zhangyingyou calibration method and the checkerboard.
In short, the Zhangyingyou scaling method is taken as a means in the prior art, namely: the internal parameters of the camera are solved by shooting the pixel coordinates of checkerboard with known sizes in different directions and different positions in an image coordinate system.
In another embodiment of the present invention, the substrate is,
the grid is 10cm by 10 cm.
In another embodiment of the present invention, the substrate is,
the deep neural network selects ResNet 50.
For this example, the process is typically carried out by Python. This is a routine choice in the art.
In another embodiment of the present invention, the substrate is,
the auxiliary neural network selects ResNet 18.
It will be appreciated that this is again a routine choice in the art.
In another embodiment of the present invention, the substrate is,
the convolution function is Conv (input, w), where input represents the input and w represents the weight.
It will be appreciated that this is again a routine choice in the art.
In another embodiment, the loss function is selected as a mean square error function.
In another embodiment of the present invention, the substrate is,
in the discrete wavelet transform,
the basis functions of the continuous wavelet are:
wherein, FbAs a bandwidth parameter, FcIs the center frequency, i is the imaginary unit, t is the time unit,
and performing extension and translation on the basis function to obtain a family function:
wherein a is a scale, namely a telescopic parameter, and b is a translation parameter;
the method comprises the following steps of discretizing a scale parameter a and a translation parameter b of a definition formula of continuous wavelet transformation, wherein a discretized wavelet sequence is as follows:
the discretization formula of the scale and translation parameters a and b in continuous wavelet change is as follows:
a0is the extension step size, where the power of j represents the scale reduction multiple to a; when j is not equal to 0, a is changed from a0 j-1Become a0 jWhen a is enlarged by a0Multiple, i.e. the centre frequency of the wavelet is reduced by a0Multiple, bandwidth is also reduced by a0Doubling; k represents the uniform sampling rate for b; z represents an integer set;
the wavelet coefficients of different positions and different scales are solved through discrete wavelet transform, and the formula is as follows:
wherein,
is composed of
A complex conjugate function of; dt is the data sampling time; c
j,kFor the calculation of the resulting wavelet coefficients for each frequency and scale, f (t) is a function of the original signal.
When in reconstruction, each wavelet function is directly multiplied and accumulated by the coefficient, and the formula is as follows:
it can be understood that when the time domain graph is subjected to discrete wavelet transform, f (t) is time domain data;
when the time-frequency diagram is subjected to wavelet inverse transformation, since the inverse transformation is reconstruction, the liquid level data obtained by the inverse transformation is: f (t) obtained by performing inverse transformation on the time-frequency diagram.
To further understand the present disclosure, in one embodiment, the image level acquisition module uses a camera as a sensor input to observe and identify the level sensor reading as raw data to be transmitted to the subsequent module, and the data processing is divided into several steps of data screening, effective frequency detection, temporal filtering prediction, anomaly determination, and the like. Details include the following processing stages:
1.1. data screening
The module can be divided into: wavelet forward transform (decomposition), automatic frequency screening and wavelet inverse transform (reconstruction) to regenerate the signal without noise.
(1) Wavelet forward transform
FIG. 1(a) and FIG. 1(b) are time-frequency diagrams obtained by performing discrete wavelet transform on liquid level data. Wavelet transform is a time-frequency analysis method that approximates signals with a set of basis functions that attenuate rapidly.
Commonly used basis functions include Morlet, Meyer, Daubechies, Haar and the like, and cmor wavelets are selected according to actual conditions, and the expression form of the basis functions is as follows:
the wavelet basis functions are:
wherein, FbAs a bandwidth parameter, FcIs the center frequency, i is the imaginary unit, t is the time unit,
performing extension and translation on the basis function to obtain a family function
Wherein a is scale, namely a telescopic parameter, b is a translation parameter, and tau is expressed by b;
the method comprises the following steps of discretizing a scale parameter a and a translation parameter b of a definition formula of continuous wavelet transformation, wherein a discretized wavelet sequence is as follows:
the discretization formula of the scale and translation parameters a and b in continuous wavelet change is as follows:
a0is the extension step size, where the power of j represents the scale reduction multiple to a; when j is not equal to 0, a is changed from a0 j-1Become a0 jWhen a is enlarged by a0Multiple, i.e. the centre frequency of the wavelet is reduced by a0Multiple, bandwidth is also reduced by a0Doubling; k represents the uniform sampling rate for b; z represents an integer set;
the wavelet coefficients of different positions and different scales are solved through discrete wavelet transform, and the formula is as follows:
wherein,
is composed of
A complex conjugate function of; dt is the data sampling time; c
j,kTo calculate the resulting wavelet coefficients for each frequency and scale,
when in reconstruction, each wavelet function is directly multiplied and accumulated by the coefficient, and the formula is as follows:
in the specific implementation process, the Mallat algorithm is used for realizing the rapid wavelet decomposition, as shown in FIG. 1(a), a group of hydraulic data simulation graphs are shown, and original data are formed by 1.0-20.0 s of 10Hz sine + 0.9Hz +17.5Hz positive chord +0.02 white noise. Fig. 1(b) is a time-frequency spectrogram obtained after wavelet transform is performed on original data, wherein the abscissa is time, the ordinate is frequency, the pixel value is a wavelet coefficient value of the frequency at a certain time point, the larger the coefficient is, the heavier the weight of the principal component of the frequency is, and it can be clearly seen that the principal components of the data frequency have 0.9Hz,10Hz,17.5Hz, and the starting point and the ending point of low-frequency data.
(2) Automatic frequency screening
According to the observation and practice of the inventor, if the peak point of a long period of time exists in the time-frequency diagram for a long period of time, the frequency components are considered to be noise caused by long-term environmental vibration such as mechanical vibration of a working platform, and the waveform of the frequency can be filtered out from frequency domain and time domain data, so that effective data screening is realized. After wavelet decomposition of previous signals, respectively calculating a high-frequency coefficient and a low-frequency coefficient, and carrying out threshold hard quantization on frequency signals with continuous time exceeding a threshold to be zero.
(3) Inverse wavelet transform
The high-frequency coefficient and the low-frequency coefficient which are subjected to threshold quantization are subjected to discrete wavelet reconstruction by using the formula, a synthesized de-noised signal is shown as the following figure 2(b), the high-frequency signal coefficient is set to be 0, and then original data are reconstructed, so that de-noised liquid level data can be obtained.
1.2 effective frequency detection
While the noise data is removed by the automatic frequency filtering, the effective data frequency and the start-stop time can be obtained from fig. 1 (b).
1.3 temporal Filtering prediction
Fig. 2(b) shows reconstructed time domain data after data screening, and it can be seen that the data are not completely superimposed sinusoidally.
Like random white noise put in simulation, actual data generally exist, so that the noise can be further filtered through a Kalman filtering algorithm to prevent error identification of abnormal data.
1.4 abnormality determination
And (3) combining the simultaneous analysis of the frequency domain and the time domain, sending an alarm signal when the liquid level value of the time domain exceeds a threshold value, and sending a further emergency signal if the frequency fluctuation abnormality of the effective frequency of the frequency domain exceeds the threshold value.
While the embodiments of the disclosure have been described above in connection with the drawings, the disclosure is not limited to the specific embodiments and applications described above, which are intended to be illustrative, instructive, and not restrictive. Those skilled in the art, having the benefit of this disclosure, may effect numerous modifications thereto and changes may be made without departing from the scope of the disclosure as set forth in the claims that follow.