CN114777986A - A method and system for detecting looseness of transmission tower bolts based on correlation coefficient - Google Patents

Abstract

The invention discloses a method and a system for detecting the looseness of bolts of a power transmission tower based on correlation coefficients, wherein two optional tower materials are selected from tower materials connected with the bolts of the power transmission tower as a tower material 1 and a tower material 2, and the method comprises the following steps: respectively selecting points to be measured on the tower material 1 and the tower material 2, and collecting vibration signals of the points to be measured, wherein the number of the points to be measured selected by each tower material is at least 1; acquiring a time domain image and a frequency domain image of a vibration signal of each point to be measured; solving the correlation coefficient of each point to be measured of the tower material 1 and each point to be measured of the tower material 2 in the time domain and the frequency domain; detecting the bolt loosening condition according to the change of the correlation coefficient, and judging that the bolt is loosened when the increase proportion of the correlation coefficient is greater than a set threshold value; the system comprises a signal acquisition module, an image acquisition module, a correlation coefficient solving module and a judgment module; the loosening condition of the bolts of the power transmission iron tower is detected by a correlation coefficient analysis method, so that the influence of noise is eliminated conveniently, the operation is simple, the method is quick and effective, and the judgment is more accurate.

Description

A method and system for detecting looseness of transmission tower bolts based on correlation coefficient

technical field

The invention relates to the technical field of bolt loosening detection, in particular to a method for detecting bolt loosening of a transmission tower based on a correlation coefficient.

Background technique

The working environment of the transmission tower is complex, and it is repeatedly acted by external loads all year round, which reduces the pre-tightening force of the bolted connection or even loosens, which leads to the decrease of the overall rigidity of the transmission tower. In severe cases, the transmission tower may collapse. Therefore, it is imperative to study a fast and effective method to detect the looseness of the bolted connection structure of the transmission tower.

Many scholars have done a lot of simulation and experimental research on the loosening of bolted structures. In the detection method, Zhou Jing et al. applied the principle of machine vision to the measurement of the bolt loosening rotation angle, and then judged the bolt state. This method has good accuracy, but the height of the transmission tower and the bolt distribution will affect the acquisition of its visual signal; Li Lubing; The ultrasonic non-destructive testing method is used for bolt flaw detection. This method has the characteristics of strong anti-interference ability and high resolution, but this method has strict requirements on experimental instruments; Jiang Wenqiang et al. This method can accurately measure the axial force of the bolt to judge the state of the bolt, but in engineering practice, the loosening of the bolt is a long-term process, and it is not realistic to use strain gauges to monitor it in real time.

At present, the most widely used method is the detection method based on vibration response. However, due to the influence of various noises in the field test, Zhou Wenqiang et al. applied empirical mode decomposition (EMD) to the vibration signal of bolted connection structures in signal processing. In terms of processing, the EMD algorithm has many problems, such as low efficiency, mode aliasing and end-point effects. Li Qiyue et al. applied the EEMD algorithm to the noise reduction of blasting vibration signals. state aliasing problem, but it will affect the noise reduction effect.

Therefore, how to provide a method and system based on the correlation coefficient that can effectively reduce the influence of noise and facilitate more accurate detection of the looseness of the transmission tower bolts is an urgent problem to be solved by those skilled in the art.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a method and system for detecting the looseness of a transmission tower bolt based on a correlation coefficient to solve the problems mentioned in the background art.

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

A method for detecting looseness of transmission tower bolts based on correlation coefficient, selecting two tower materials as tower material 1 and tower material 2 from tower materials connected with transmission tower bolts, comprising the following steps:

S1. Select points to be measured on tower material 1 and tower material 2 respectively, collect vibration signals of each point to be measured, and the number of points to be measured selected for each tower material is at least 1;

S2. obtain the time domain image and frequency domain image of the vibration signal of each described point to be measured;

S3. Solve the correlation coefficients between the points to be measured of the tower material 1 and the points to be measured of the tower material 2 in the time domain and the frequency domain respectively;

S4. Detect the looseness of the bolts of the transmission tower according to the change of the correlation coefficient. When the increase ratio of the correlation coefficient is greater than the set threshold, the bolts of the transmission tower are loose.

Preferably, the process of acquiring the time domain image and the frequency domain image of the vibration signal of each of the points to be measured in S2 also includes performing noise reduction processing on the vibration signal, and the specific content of the noise reduction processing includes:

S21. carry out CEEMDAN decomposition to each described vibration signal, obtain K modal components respectively;

S22. Calculate the variance contribution rate of each of the modal components, and screen each of the modal components according to the variance contribution rate to eliminate noise components;

S23. Recombining the remaining modal components, and further denoising by using an autocorrelation function to obtain the denoised signal.

Preferably, the specific content of S21 includes:

S211. Add positive and negative Gaussian white noise signals to the vibration signal to obtain a reconstructed signal, and then perform EMD decomposition on the reconstructed signal to obtain the first-order modal component C ₁ :

S212. Solve the first modal component of the CEEMDAN decomposition:

S213. Calculate the first residual:

S214. Let y(t)=r ₁ (t), repeat S211, S212 and S213 to obtain the second modal component and the second residual component:

S215. Repeat S211, S212, S213 and S214, when the obtained residual component is a monotonic function, the decomposition is stopped and the algorithm ends, and the number of modal components obtained at this time is set to K, then the vibration signal y(t) Decomposed into:

为CEEMDAN分解的第k模态分量，ν^j是符合正态分布的高斯白噪声，j＝1，2，...，N为添加白噪声的次数，ε为白噪声的标准表。Among them, y(t) is the vibration signal, y(t)+(-1) ^q ∈υ ^j (t) is the reconstructed signal, q=1, 2, E _i (·) is the EMD decomposed signal the i-th modal component,

is the kth modal component of CEEMDAN decomposition, ν ^j is Gaussian white noise conforming to the normal distribution, j=1, 2,..., N is the number of times of adding white noise, and ε is the standard table of white noise.

Preferably, the specific content of S22 includes:

Calculate the variance D(k) of each modal component to obtain the variance contribution rate e(k) of each modal component:

Preferably, in S3

Wherein, ρ _xy is the correlation coefficient between each point to be measured of the tower material 1 and each point to be measured of the tower material 2, and μ _x and μ _y are the tower material 1 and the tower material, respectively 2 Mathematical expectation of the vibration signal of the point to be measured, σ _x and σ _y are the standard deviation of the vibration signal of the point to be measured for the tower material 1 and the tower material 2, respectively.

A correlation coefficient-based bolt loosening detection system for a transmission tower includes a signal acquisition module, an image acquisition module, a correlation coefficient solution module and a determination module;

The signal acquisition module is used to collect the vibration signal of each point to be measured from the points to be measured selected from the tower material 1 and the tower material 2 that are bolted to the transmission tower, and the number of points to be measured selected for each tower material is at least 1. 1;

The image acquisition module is used to acquire the time domain image and the frequency domain image of the vibration signal of each of the to-be-measured points;

The correlation coefficient solving module is used to solve the correlation coefficients between the points to be measured of the tower material 1 and the points to be measured of the tower material 2 in the time domain and the frequency domain respectively;

The determining module is used for detecting the looseness of the bolts of the transmission tower according to the change of the correlation coefficient, and when the change ratio of the correlation coefficient is greater than the set threshold, the bolts of the transmission tower are loose.

Preferably, the image acquisition module includes a signal decomposition unit, a modal component screening unit and a recombination noise reduction unit;

The signal decomposition unit is used to perform CEEMDAN decomposition on each of the vibration signals to obtain K modal components respectively;

The modal component screening unit is configured to calculate the variance contribution rate of each of the modal components, and screen each of the modal components according to the variance contribution rate to eliminate noise components;

The recombination denoising unit is used for recombining the remaining modal components, and further denoising by using an autocorrelation function to obtain the denoising signal.

Preferably, the signal decomposition unit includes an EMD decomposition subunit, a CEEMDAN decomposition subunit and a residual calculation subunit;

The EMD decomposition subunit is used to add positive and negative Gaussian white noise signals to the vibration signal to obtain a reconstructed signal, and perform EMD decomposition on the reconstructed signal to obtain an EMD modal component;

The CEEMDAN decomposition subunit is used to solve the modal component of the CEEMDAN decomposition;

The residual calculation subunit is used to calculate the residual.

Preferably, the modal component screening unit includes a variance calculation subunit, a variance contribution rate calculation subunit, and a noise elimination subunit;

The variance calculation subunit is used to calculate the variance of each modal component;

The variance contribution rate calculation subunit is used to calculate the variance contribution rate of each modal component according to the variance;

The noise-removing subunit is configured to screen each of the modal components according to the variance contribution rate, and remove the noise component.

Preferably, the system for detecting the looseness of the bolts of the transmission tower based on the correlation coefficient further includes an early warning module, which will give an alarm when the determination module determines that the bolts of the transmission tower are loose.

It can be seen from the above technical solutions that, compared with the prior art, the present invention provides a method and system for detecting the looseness of a transmission tower bolt based on a correlation coefficient. , so that the peak value corresponding to the resonance frequency of the vibration signal is well preserved, the non-resonant information is suppressed, and it is convenient to eliminate the influence of noise; through the correlation coefficient analysis method to detect the looseness of the transmission tower bolts, the operation is simple, fast and effective, and the determination is more accurate.

Description of drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention. For those of ordinary skill in the art, other drawings can also be obtained according to the provided drawings without creative work.

Fig. 1 accompanying drawing is a schematic diagram of a method for detecting the looseness of a transmission tower bolt provided by the present invention;

The accompanying drawing of Fig. 2 is a schematic diagram of a bolt to be measured and a point to be measured of a transmission tower provided by the present invention;

Fig. 3 accompanying drawing is the flow chart of CEEMDAN-autocorrelation function noise reduction provided by the present invention;

4 is a schematic diagram of the original vibration signal of the measuring point 3 of the embodiment provided by the present invention;

The accompanying drawing of FIG. 5 is a comparison diagram of the original signal and the noise reduction signal of the embodiment measuring point 3 provided by the present invention;

Fig. 6 accompanying drawing is the CEEMDAN exploded view of embodiment measuring point 3 provided by the present invention;

Fig. 7 accompanying drawing is the vibration time domain diagram after noise reduction of measuring points 1-4 when bolts are tightened according to the embodiment of the present invention;

The accompanying drawing of FIG. 8 is a time domain diagram of vibration after noise reduction of measuring points 1-4 when the bolts are loosened according to the embodiment of the present invention;

Fig. 9 accompanying drawing is the vibration frequency domain diagram after noise reduction of measuring points 1-4 when bolts are tightened according to the embodiment of the present invention;

FIG. 10 is a diagram of the vibration frequency domain after noise reduction of measuring points 1-4 when the bolts are loosened according to the embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The embodiment of the present invention discloses a method for detecting looseness of transmission tower bolts based on correlation coefficient. Two tower materials are selected from the tower materials connected with the transmission tower bolts as tower material 1 and tower material 2, as shown in FIG. 1 , including the following step:

S1. Select points to be measured on tower material 1 and tower material 2 respectively, collect vibration signals of each point to be measured, and the number of points to be measured selected for each tower material is at least 1;

S2. Obtain the time domain image and frequency domain image of the vibration signal of each point to be measured;

S3. Solve the correlation coefficient between each point to be measured of tower material 1 and each point to be measured of tower material 2 in time domain and frequency domain;

S4. Detect the looseness of the bolts of the transmission tower according to the change of the correlation coefficient. When the increase ratio of the correlation coefficient is greater than the set threshold, the bolts of the transmission tower are loose.

In this embodiment, an excitation hammer with a sensitivity of 4.44pC/N and a gain of 0.500mV/Pv is selected as the excitation source to apply pulse excitation to the transmission tower. point, use a piezoelectric acceleration sensor with a sensitivity of 5.072mv/g, and set the sampling frequency of the signal acquisition instrument to 5kHz.

In this embodiment, the bolts to be measured of the iron tower are fastened, the steps S1-S4 are implemented, and the solved correlation coefficient is used as the initial correlation coefficient, and the correlation coefficient of the point to be measured measured by S1-S4 in the later stage is compared with the initial correlation coefficient, When the increased ratio is greater than the set threshold, the bolts of the transmission tower are loose.

In order to further implement the above technical solution, as shown in Figure 2, the process of acquiring the time domain image and frequency domain image of the vibration signal of each point to be measured in S2 also includes noise reduction processing on the vibration signal, and the specific content of the noise reduction processing includes:

S21. Perform CEEMDAN decomposition on each vibration signal to obtain K modal components respectively;

S22. Calculate the variance contribution rate of each modal component, and screen each modal component according to the variance contribution rate to eliminate noise components;

S23. Recombining the remaining modal components, and using the autocorrelation function for further noise reduction processing to obtain a denoised signal.

In practical applications, CEEMDAN decomposition is an improved algorithm of EMD decomposition algorithm, which effectively solves the problem of mode aliasing caused by EMD decomposition and the problem of residual white noise caused by EEMD and CEEMD decomposition.

In this embodiment, modal components whose variance contribution rate is less than 5% are eliminated.

In order to further implement the above technical solution, the specific content of S21 includes:

S211. Add positive and negative Gaussian white noise signals to the vibration signal to obtain a reconstructed signal, and then perform EMD decomposition on the reconstructed signal to obtain the first-order modal component C ₁ :

S212. Solve the first modal component of the CEEMDAN decomposition:

S213. Calculate the first residual:

In order to further implement the above technical solution, the specific content of S21 also includes:

S214. Let y(t)=r ₁ (t), repeat S211, S212 and S213 to obtain the second modal component and the second residual component:

S215. Repeat S211, S212, S213 and S214. When the obtained residual component is a monotonic function, the decomposition is stopped and the algorithm ends. Assuming that the number of modal components obtained at this time is K, the vibration signal y(t) is decomposed into :

为CEEMDAN分解的第k模态分量，ν^j是符合正态分布的高斯白噪声，j＝1，2，...，N为添加白噪声的次数，ε为白噪声的标准表。Among them, y(t) is the vibration signal, y(t)+(-1) ^q ∈υ ^j (t) is the reconstructed signal, q=1, 2, E _i ( ) is the ith mode of the EMD decomposition state component,

is the kth modal component of CEEMDAN decomposition, ν ^j is Gaussian white noise conforming to the normal distribution, j=1, 2,..., N is the number of times of adding white noise, and ε is the standard table of white noise.

In this embodiment, taking measurement point 3 as an example, first, using the value range of each parameter in the EEMD decomposition, the basic parameters required for the CEEMDAN decomposition are determined by the trial-and-error method: set the standard deviation of positive and negative Gaussian white noise to 0.2, the noise The number of additions is 500, and the maximum number of iterations allowed is 5000. Finally, the original vibration signal of the three measuring points is shown in Figure 3 and decomposed into 11 modal parameters (IMF1, ..., IMF11) as shown in Figure 5.

In order to further implement the above technical solution, the specific content of S22 includes:

Calculate the variance D(k) of each modal component to obtain the variance contribution rate e(k) of each modal component:

In this embodiment, the variance contribution rate of each modal component of the original vibration signal of measuring point 3 is calculated according to the above method, as shown in the following table:

It can be seen that the variance contribution rates of IMF3-IMF11 in the 11 components are all below 5%, indicating that these 9 components are the interference of noise signals to the original signal, so the 9 components can be directly eliminated, and then the remaining components The two components of IMF1 and IMF2 are recombined, and the autocorrelation function is used to perform corresponding noise reduction processing to obtain the final denoised signal.

Perform noise reduction processing on each measurement point in turn according to the noise reduction process of measurement point 3 above, and obtain the vibration time domain diagram and frequency spectrum of each measurement point before and after the bolt loosening after filtering and noise reduction processing, as shown in Figure 6-9.

In order to further implement the above technical solution, in S3

Wherein, ρ _xy is the correlation coefficient of each point to be measured of tower material 1 and each point to be measured of tower material 2, respectively, μ _x and μ _y are the mathematical expectation of the vibration signal of the point to be measured of tower material 1 and tower material 2, respectively , σ _x and σ _y are the standard deviations of the vibration signals of the points to be measured for tower material 1 and tower material 2, respectively.

In this embodiment, the vibration signals of the tower material 1 and the tower material 2 to be measured are the vibration signals after noise reduction processing.

In this embodiment, the calculation result of the absolute value of the correlation coefficient between each measuring point is shown in the following table:

In this embodiment, when the bolted connection structure is loosened, the correlation coefficient between the vibration signals of each measuring point increases, whether in the time domain or in the frequency domain, and the correlation is enhanced.

When the bolts are tightened, tower material 1 and tower material 2 are equivalent to a whole. Under the action of pulse excitation, self-excited vibration occurs at each measuring point, and the correlation between the vibration signals of the measuring points is not strong; After the loosening, the tower material 2 is no longer a whole with the tower material 1. When the impact signal is applied to the tower material 1 with the vibration hammer, the tower material 1 vibrates and collides with the tower material 2, so that the tower material 2 vibrates together, while the tower material 1 vibrates. The vibration generated by the tower material 2 is the forced vibration caused by the tower material 1, so the correlation between the vibration signals of the measuring points is enhanced.

A correlation coefficient-based bolt loosening detection system for a transmission tower includes a signal acquisition module, an image acquisition module, a correlation coefficient solution module and a determination module;

The signal acquisition module is used to collect the vibration signal of each to-be-measured point from the to-be-measured points selected from the tower material 1 and the tower material 2 connected with the transmission tower bolts, and the number of the to-be-measured points selected for each tower material is at least 1;

The image acquisition module is used to acquire the time domain image and frequency domain image of the vibration signal of each point to be measured;

The correlation coefficient solving module is used to solve the correlation coefficient of each point to be measured of tower material 1 and each point to be measured of tower material 2 in time domain and frequency domain respectively;

The determination module is used to detect the looseness of the bolts of the transmission tower according to the change of the correlation coefficient. When the change ratio of the correlation coefficient is greater than the set threshold, the bolts of the transmission tower are loose.

In order to further implement the above technical solution, the image acquisition module includes a signal decomposition unit, a modal component screening unit and a recombination noise reduction unit;

The signal decomposition unit is used to perform CEEMDAN decomposition on each vibration signal to obtain K modal components respectively;

The modal component screening unit is used to calculate the variance contribution rate of each modal component, and screen each modal component according to the variance contribution rate to eliminate noise components;

The recombination denoising unit is used for recombining the remaining modal components, and further denoising by using the autocorrelation function to obtain denoising signals.

In order to further implement the above technical solution, the signal decomposition unit includes an EMD decomposition subunit, a CEEMDAN decomposition subunit and a residual calculation subunit;

The EMD decomposition sub-unit is used to add positive and negative Gaussian white noise signals to the vibration signal to obtain a reconstructed signal, and perform EMD decomposition on the reconstructed signal to obtain EMD modal components;

The CEEMDAN decomposition subunit is used to solve the modal components of the CEEMDAN decomposition;

Residual calculation subunit for calculating residuals.

In order to further implement the above technical solution, the modal component screening unit includes a variance calculation subunit, a variance contribution rate calculation subunit and a noise elimination subunit;

The variance calculation subunit is used to calculate the variance of each modal component;

The variance contribution rate calculation subunit is used to calculate the variance contribution rate of each modal component according to the variance;

The noise elimination subunit is used to filter each modal component according to the variance contribution rate, and eliminate the noise component.

In order to further implement the above technical solution, a system for detecting looseness of transmission tower bolts based on a correlation coefficient further includes an early warning module, which gives an alarm when the determination module determines that the bolts of the transmission tower are loose.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant part can be referred to the description of the method.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. a transmission tower bolt loosening detection method based on correlation coefficient, from the tower material that is connected with transmission tower bolts, optionally two tower materials as tower material 1 and tower material 2, is characterized in that, may further comprise the steps: S1. Select points to be measured on tower material 1 and tower material 2 respectively, collect vibration signals of each point to be measured, and the number of points to be measured selected for each tower material is at least 1; S2. obtain the time domain image and frequency domain image of the vibration signal of each described point to be measured; S3. Solve the correlation coefficients between the points to be measured of the tower material 1 and the points to be measured of the tower material 2 in the time domain and the frequency domain respectively; S4. Detect the looseness of the bolts of the transmission tower according to the change of the correlation coefficient, and determine that the bolts of the transmission tower are loose when the increase ratio of the correlation coefficient is greater than the set threshold. 2. a kind of transmission tower bolt loosening detection method based on correlation coefficient according to claim 1, is characterized in that, in S2, in the process of acquiring the time domain image and frequency domain image of the described vibration signal of each described point to be measured It also includes performing noise reduction processing on the vibration signal, and the specific content of the noise reduction processing includes: S21. carry out CEEMDAN decomposition to each described vibration signal, obtain K modal components respectively; S22. Calculate the variance contribution rate of each of the modal components, and screen each of the modal components according to the variance contribution rate to eliminate noise components; S23. Recombining the remaining modal components after culling, and further denoising using an autocorrelation function to obtain the denoising signal. 3. a kind of transmission tower bolt loosening detection method based on correlation coefficient according to claim 2, is characterized in that, the specific content of S21 comprises: S211. Add positive and negative Gaussian white noise signals to the vibration signal to obtain a reconstructed signal, and then perform EMD decomposition on the reconstructed signal to obtain the first-order modal component C ₁ :

S212. Solve the first modal component of the CEEMDAN decomposition:

S213. Calculate the first residual:

S214. Let y(t)=r ₁ (t), repeat S211, S212 and S213 to obtain the second modal component and the second residual component:

S215. Repeat S211, S212, S213 and S214, when the obtained residual component is a monotonic function, the decomposition is stopped and the algorithm ends, and the number of modal components obtained at this time is set to K, then the vibration signal y(t) Decomposed into:

Among them, y(t) is the vibration signal, y(t)+(-1) ^q ∈υ ^j (t) is the reconstructed signal, q=1, 2, E _i (·) is the EMD decomposed signal the i-th modal component,

is the kth modal component of CEEMDAN decomposition, ν ^j is Gaussian white noise conforming to the normal distribution, j=1, 2,..., N is the number of times of adding white noise, and ε is the standard table of white noise. 4. a kind of transmission tower bolt loosening detection method based on correlation coefficient according to claim 3, is characterized in that, the specific content of S22 comprises: Calculate the variance D(k) of each modal component to obtain the variance contribution rate e(k) of each modal component:

5. a kind of transmission tower bolt loosening detection method based on correlation coefficient according to claim 1, is characterized in that, in S3

Wherein, ρ _xy is the correlation coefficient between each point to be measured of the tower material 1 and each point to be measured of the tower material 2, and μ _x and μ _y are the tower material 1 and the tower material, respectively 2 Mathematical expectation of the vibration signal of the point to be measured, σ _x and σ _y are the standard deviation of the vibration signal of the point to be measured for the tower material 1 and the tower material 2, respectively. 6. A system for detecting looseness of transmission tower bolts based on correlation coefficient, characterized in that it comprises a signal acquisition module, an image acquisition module, a correlation coefficient solving module and a determination module; The signal acquisition module is used to collect the vibration signal of each point to be measured from the points to be measured selected from the tower material 1 and the tower material 2 that are bolted to the transmission tower, and the number of points to be measured selected for each tower material is at least 1. 1; The image acquisition module is used to acquire the time domain image and the frequency domain image of the vibration signal of each of the to-be-measured points; The correlation coefficient solving module is used to solve the correlation coefficients between the points to be measured of the tower material 1 and the points to be measured of the tower material 2 in the time domain and the frequency domain respectively; The determination module is used for detecting the looseness of the bolts of the transmission tower according to the change of the correlation coefficient, and when the change ratio of the correlation coefficient is greater than the set threshold, the bolts of the transmission tower are loose. 7. The system for detecting looseness of transmission tower bolts based on correlation coefficient according to claim 6, wherein the image acquisition module comprises a signal decomposition unit, a modal component screening unit and a recombination noise reduction unit; The signal decomposition unit is used to perform CEEMDAN decomposition on each of the vibration signals to obtain K modal components respectively; The modal component screening unit is configured to calculate the variance contribution rate of each of the modal components, and screen each of the modal components according to the variance contribution rate to eliminate noise components; The recombination denoising unit is used for recombining the remaining modal components, and further denoising by using an autocorrelation function to obtain the denoising signal. 8. a kind of transmission tower bolt loosening detection system based on correlation coefficient according to claim 7, is characterized in that, described signal decomposition unit comprises EMD decomposition subunit, CEEMDAN decomposition subunit and residual calculation subunit; The EMD decomposition subunit is used to add positive and negative Gaussian white noise signals to the vibration signal to obtain a reconstructed signal, and perform EMD decomposition on the reconstructed signal to obtain an EMD modal component; The CEEMDAN decomposition subunit is used to solve the modal components of the CEEMDAN decomposition; The residual calculation subunit is used for calculating residual. 9. The system for detecting looseness of transmission tower bolts based on correlation coefficient according to claim 7, wherein the modal component screening unit comprises a variance calculation subunit, a variance contribution rate calculation subunit and a noise elimination subunit ; The variance calculation subunit is used to calculate the variance of each modal component; The variance contribution rate calculation subunit is configured to calculate the variance contribution rate of each modal component according to the variance; The noise-removing subunit is configured to screen each of the modal components according to the variance contribution rate, and remove the noise component. 10 . The system for detecting the looseness of transmission tower bolts based on the correlation coefficient according to claim 6 , further comprising an early warning module, which performs an alarm when the determination module determines that the bolts of the transmission tower are loose. 11 .

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