Variable width pulse train TDR cable fault identification device and method

Abstract

The invention relates to a variable width pulse train TDR cable fault identification device and method, and belongs to the technical field of cable detection, and the device comprises a test signal generator, a loop isolator, a received signal processing circuit, and a digital cross-correlation operation module. The test signal generation module is used for generating two paths of waveforms, one path of variable width pulse train is used as an excitation signal and is injected into a tested cable as an incident signal through a loop isolator, and a reflection signal is formed at a fault position of the tested cable and is used as a receiving signal through the loop isolator to enter the digital cross-correlation operation module; the other path of signal of the test signal generation module is subjected to different time shifts to form a plurality of groups of time shift reference signals to enter the digital cross-correlation operation module; and the digital cross-correlation operation module carries out sliding cross-correlation operation on the two paths of incoming signals and identifies a fault type and a fault distance.

Description

Technical Field

[0001] The invention belongs to the technical field of cable detection, and relates to a variable width pulse group TDR cable fault identification device and method. Background Art

[0002] Cables are the main carrier of signal transmission, assisting various facilities to achieve the transmission of power and information. They are widely used, including but not limited to energy extraction, aerospace, construction engineering, agricultural production equipment, marine exploration, and transportation. Most cables are laid directly buried, and natural aging and human damage can lead to cable failures, which have a great impact on the economy and society. Rapid and accurate detection of cable fault points is conducive to repair and restoration as soon as possible, reducing direct economic losses.

[0003] As a classic traveling wave fault detection method, Time Domain Reflectometry (TDR) mainly processes and calculates the reflected echo of the test traveling wave at the fault location. It has a simple principle and is easy to operate. It is currently the main method used at home and abroad. In view of the fact that the TDR measurement distance is affected by the attenuation of the test pulse and the sampling accuracy, and the problem that the wavefront time of the reflected wave is difficult to identify, improvements have been made on the basis of TDR to produce two measurement methods: Sequence Time Domain Reflectometry (STDR) and Spread Spectrum Time Domain Reflectometry (SSTDR). Both STDR and SSTDR upgrade a single pulse excitation signal to a sequence code continuous signal, and use the cross-correlation detection method to improve the accuracy of weak signal recognition. However, the sequence code pulse width is directly related to the measurement accuracy. High accuracy determines the narrow code element. The weak reflected signal after long-distance attenuation affects the judgment result and measurement accuracy. At the same time, the excitation signal that has been continuously present at the receiving end and the superposition of the reflected signal affects the result recognition to a certain extent.

[0004] In summary, the prior art has the following technical problems:

[0005] (1) When measuring long distances, the excitation signals of TDR, STDR, and SSTDR are all attenuated, and the reflected signals are weak, which affects the judgment results and measurement accuracy.

[0006] (2) The fault location accuracy of TDR relies on high-speed digital sampling, while the fault location accuracy of STDR and SSTDR relies on reducing the sequence code pulse width. It is difficult to achieve a high cost-effectiveness between measurement performance and hardware cost.

[0007] (3) The wavefront of the TDR reflected wave is difficult to identify, and the superposition of the reflected signal at the STDR and SSTDR receiving end and the continuously existing excitation signal affects the cross-correlation judgment. Summary of the invention

[0008] In view of this, an object of the present invention is to provide a variable width pulse group TDR cable fault identification device and method.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] On the one hand, the present invention provides a variable width pulse group TDR cable fault identification device, including a test signal generator, a loop isolator, a receiving signal processing circuit, and a digital cross-correlation operation module;

[0011] The test signal generating module is used to generate two waveforms, one of which is a widened pulse group as an excitation signal, which is injected into the cable under test as an incident signal through a loop isolator, and a reflected signal is formed at the fault location of the cable under test, which enters the digital cross-correlation operation module through the loop isolator as a receiving signal; the other signal of the test signal generating module is subjected to different time shifts to form multiple groups of time-shifted reference signals and enter the digital cross-correlation operation module; the digital cross-correlation operation module performs sliding cross-correlation operation on the two incoming signals to identify the fault type and fault distance.

[0012] Furthermore, the variable width pulse group generated by the test signal generating module adopts a positive and negative bipolar N-level m-sequence code, the variable pulse width automatically changes between [T1, T2] according to the measurement distance [0, L], and the positive and negative bipolar code element amplitude is +E / -E.

[0013] Furthermore, the test signal generating module generates another signal by passing the N-level m-sequence code of the excitation signal through different time shift circuits to generate multiple groups of time shift reference signals, with a unit time shift of ΔT. A time shift of 1 ΔT is recorded as a reference m-sequence time shift 1. After 2 n -1 ΔT is recorded as the time shift of the reference m sequence 2 n -1, all time-shifted sequences are synthesized together into multiple groups of time-shifted reference signals.

[0014] Furthermore, the digital cross-correlation operation module directly digitizes the received signal and multiple groups of time-shifted reference signals according to the logic level, performs digital cross-correlation operation, and accumulates and sums the operation results to obtain the pulse group multi-time-shift cross-correlation value; the pulse group multi-time-shift cross-correlation value is compared with a preset identification threshold, and the timing is stopped when the identification threshold is exceeded. The sign of the pulse group multi-time-shift cross-correlation value at this time is used to identify the fault type, and the counted time is used to calculate the fault distance.

[0015] Furthermore, the sign of the pulse group multi-time shift mutual correlation value is used to identify the fault type, specifically: when the pulse group multi-time shift mutual correlation value is positive, the fault type is determined to be an open circuit; when it is negative, the fault type is determined to be a short circuit.

[0016] On the other hand, the present invention provides a variable width pulse group TDR cable fault identification method, comprising the following steps:

[0017] S1: Use the test signal generation module to generate two waveforms, one of which is a pulse group with variable width as the excitation signal, which is injected into the cable under test as the incident signal through the loop isolator; the other signal is formed into multiple groups of time-shifted reference signals after different time shifts and enters the digital cross-correlation operation module;

[0018] S2: The incident signal forms a reflected signal at the fault location of the cable under test and enters the digital cross-correlation operation module as a receiving signal through the loop isolator;

[0019] S3: Perform sliding cross-correlation operation on the two signals entering the digital cross-correlation operation module to identify the fault type and fault distance.

[0020] Furthermore, the variable width pulse group adopts a positive and negative bipolar N-level m-sequence code, the variable pulse width automatically changes between [T1, T2] according to the measurement distance [0, L], and the positive and negative bipolar code element amplitude is +E / -E.

[0021] Furthermore, the test signal generating module generates another signal by passing the N-level m-sequence code of the excitation signal through different time shift circuits to generate multiple groups of time shift reference signals, with a unit time shift of ΔT. A time shift of 1 ΔT is recorded as a reference m-sequence time shift 1. After 2 n -1 ΔT is recorded as the time shift of the reference m sequence 2 n -1, all time-shifted sequences are synthesized together into multiple groups of time-shifted reference signals.

[0022] Furthermore, the received signal and multiple groups of time-shifted reference signals entering the digital cross-correlation operation module are directly digitized according to the logic level, and digital cross-correlation operation is performed. The operation results are accumulated and summed to obtain the pulse group multi-time-shift cross-correlation value; the pulse group multi-time-shift cross-correlation value is compared with a preset identification threshold, and the timing is stopped when the identification threshold is exceeded. The sign of the pulse group multi-time-shift cross-correlation value at this time is used to identify the fault type, and the counted time is used to calculate the fault distance.

[0023] Furthermore, the sign of the pulse group multi-time shift mutual correlation value is used to identify the fault type, specifically: when the pulse group multi-time shift mutual correlation value is positive, the fault type is determined to be an open circuit; when it is negative, the fault type is determined to be a short circuit.

[0024] The beneficial effects of the present invention are as follows: 1. The present invention uses a variable width pulse group as an excitation signal, adopts positive and negative bipolar encoding, has a small DC component and small attenuation, and a variable pulse width, thereby improving the energy of the excitation signal, reducing attenuation, improving the energy, and enhancing the amplitude of the reflected signal, which is beneficial to fault type identification and distance calculation; 2. The present invention uses multiple groups of reference sequences with different time shifts to perform cross-correlation operations to control timing. The fault location accuracy only depends on the unit time shift of the reference signal, and has nothing to do with the sequence code pulse width and the digital signal sampling rate. Only by improving the time shift accuracy can high performance be obtained at low cost; 3. The present invention uses an m-sequence code with good correlation characteristics as an excitation signal pulse group, and the received signal slides over time and directly performs digital cross-correlation operations with multiple groups of reference sequences with different time shifts, thereby avoiding the problem of identifying the wavefront moment by the amplitude of the reflected signal.

[0025] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 This is the structure diagram of the variable width pulse group TDR cable fault identification device;

[0028] Figure 2 A schematic diagram of a set of variable width pulse group TDR excitation signals;

[0029] Figure 3 is a timing diagram of multiple groups of time-shifted reference signals;

[0030] Figure 4 This is the principle diagram of TDR cross-correlation detection of variable width pulse group;

[0031] Figure 5 It is a 4-level m-sequence widened pulse group TDR excitation signal. DETAILED DESCRIPTION

[0032] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0033] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0034] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] The invention provides a variable width pulse group TDR cable fault identification device and method. A group of variable width pulse groups is incident on a cable to be tested as a measurement excitation signal and timing is started. The pulse group adopts an N-level m-sequence code (generally 3 levels and 7 bits or 4 levels and 15 bits) with good equalization characteristics and autocorrelation characteristics. The variable pulse width automatically changes between [T1, T2] according to the measurement distance [0, L]. The positive and negative bipolar code element amplitude is +E / -E. The receiving end uses multiple groups of m-sequence codes with time shift characteristics as reference sequences. A correlation peak appears when and only when the received and reference sequences are exactly the same, and the other arbitrary time shift correlation values ​​are -1. Multiple groups of reference sequences with different time shifts are directly digitally correlated with the received signal, and the results are accumulated and summed. When the sum value exceeds the identification threshold, the timing is stopped. The fault type is determined to be open circuit / short circuit according to the positive / negative sign of the sum value, and the fault distance is calculated by timing and the electromagnetic wave propagation speed in the cable.

[0036] like Figure 1As shown, the test signal generation module generates two waveforms, one of which is a widened pulse group (excitation signal) injected into the tested cable as an incident signal through a loop isolator, and the tested cable forms a reflected signal from the fault location and enters the digital cross-correlation operation module as a receiving signal through the loop isolator; the other signal of the test signal generation module forms multiple groups of time-shifted reference signals after different time shifts and also enters the digital cross-correlation operation module, and the sliding cross-correlation operation with the receiving signal is performed to identify the fault type and fault distance.

[0037] Optionally, the test signal generation module generates a variable width pulse group such as Figure 2 As shown, a positive and negative bipolar N-level m-sequence code is used to automatically change the pulse width in [T1, T2] according to the measurement range [0, L].

[0038] Optionally, the test signal generation module generates multiple groups of time-shifted reference signals such as Figure 3 As shown, the unit time shift is ΔT, and the time shift of 1 ΔT is recorded as the reference m sequence time shift 1, after 2 n -1 ΔT is recorded as the time shift of the reference m sequence 2 n -1, all time-shifted sequences are synthesized together into multiple groups of time-shifted reference signals.

[0039] Optionally, the received signal and multiple sets of time-shifted reference signals are directly digitized according to the logic level and digital cross-correlation operations are performed such as Figure 4 As shown, the operation results are accumulated and summed to obtain the multi-time shift cross-correlation value of the pulse group. When the value exceeds the identification threshold, the timing is stopped. The sign of the value identifies the fault type, and the corresponding timing is used to calculate the fault distance.

[0040] Take 4-level 15-bit m-sequence pulse group as the excitation signal. Figure 5 As shown, the open circuit and short circuit faults of 0-10km cable are measured, the pulse width of the excitation signal varies between [0.1us, 2us], the unit time shift of the reference signal ΔT=0.5ns, and the received signal and multiple groups of time-shifted reference signals are digitally cross-correlated. The fault is judged based on the accumulation and the open circuit / short circuit fault can be accurately identified, and the fault distance resolution is 0.1m.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A variable width pulse group TDR cable fault identification device, characterized in that: It includes a test signal generator, a loop isolator, a receiving signal processing circuit, and a digital cross-correlation operation module; The test signal generation module is used to generate two waveforms, one of which is a widened pulse group as an excitation signal, which is injected into the tested cable as an incident signal through a loop isolator, and a reflected signal is formed at the fault location of the tested cable and enters the digital cross-correlation operation module through the loop isolator as a receiving signal; the other signal of the test signal generation module is subjected to different time shifts to form multiple groups of time-shifted reference signals and enter the digital cross-correlation operation module; The digital cross-correlation operation module performs sliding cross-correlation operation on the two incoming signals to identify the fault type and fault distance.

2. The variable width pulse group TDR cable fault identification device according to claim 1 is characterized in that: The variable width pulse group generated by the test signal generation module adopts a positive and negative bipolar N-level m-sequence code, and the variable pulse width automatically changes between [T1, T2] according to the measurement distance [0, L], and the positive and negative bipolar code element amplitude is +E / -E.

3. The variable width pulse group TDR cable fault identification device according to claim 1 is characterized in that: Another signal generated by the test signal generation module is to generate multiple groups of time-shifted reference signals by passing the N-level m-sequence code of the excitation signal through different time-shift circuits, with a unit time shift of ΔT. A time shift of 1 ΔT is recorded as a reference m-sequence time shift 1. After 2 n -1 ΔT is recorded as the time shift of the reference m sequence 2 n -1, all time-shifted sequences are synthesized together into multiple groups of time-shifted reference signals.

4. The variable width pulse group TDR cable fault identification device according to claim 1 is characterized in that: The digital cross-correlation operation module directly digitizes the received signal and multiple groups of time-shifted reference signals according to the logic level, performs digital cross-correlation operation, and accumulates and sums the operation results to obtain the multi-time-shift cross-correlation value of the pulse group; The pulse group multi-time shift mutual correlation value is compared with a preset identification threshold. When the identification threshold is exceeded, the timing is stopped. The sign of the pulse group multi-time shift mutual correlation value at this time is used to identify the fault type, and the counted time is used to calculate the fault distance.

5. The variable width pulse group TDR cable fault identification device according to claim 4 is characterized in that: The sign of the pulse group multi-time shift mutual correlation value is used to identify the fault type, specifically: when the pulse group multi-time shift mutual correlation value is positive, the fault type is determined to be an open circuit; when it is negative, the fault type is determined to be a short circuit.

6. A variable width pulse group TDR cable fault identification method, characterized in that: The following steps are involved: S1: Use the test signal generation module to generate two waveforms, one of which is a pulse group with variable width as the excitation signal, which is injected into the cable under test as the incident signal through the loop isolator; the other signal is formed into multiple groups of time-shifted reference signals after different time shifts and enters the digital cross-correlation operation module; S2: The incident signal forms a reflected signal at the fault location of the cable under test and enters the digital cross-correlation operation module as a receiving signal through the loop isolator; S3: Perform sliding cross-correlation operation on the two signals entering the digital cross-correlation operation module to identify the fault type and fault distance.

7. The variable width pulse group TDR cable fault identification method according to claim 6 is characterized in that: The variable width pulse group adopts a positive and negative bipolar N-level m-sequence code, and the variable pulse width automatically changes between [T1, T2] according to the measurement distance [0, L], and the positive and negative bipolar code element amplitude is +E / -E.

8. The variable width pulse group TDR cable fault identification method according to claim 6 is characterized in that: Another signal generated by the test signal generation module is to generate multiple groups of time-shifted reference signals by passing the N-level m-sequence code of the excitation signal through different time-shift circuits, with a unit time shift of ΔT. A time shift of 1 ΔT is recorded as a reference m-sequence time shift 1. After 2 n -1 ΔT is recorded as the time shift of the reference m sequence 2 n -1, all time-shifted sequences are synthesized together into multiple groups of time-shifted reference signals.

9. The variable width pulse group TDR cable fault identification method according to claim 6, characterized in that: The received signal and multiple groups of time-shifted reference signals entering the digital cross-correlation operation module are directly digitized according to the logic level, and digital cross-correlation operation is performed. The operation results are accumulated and summed to obtain the pulse group multi-time shift cross-correlation value; The pulse group multi-time shift mutual correlation value is compared with a preset identification threshold. When the identification threshold is exceeded, the timing is stopped. The sign of the pulse group multi-time shift mutual correlation value at this time is used to identify the fault type, and the counted time is used to calculate the fault distance.

10. The variable width pulse group TDR cable fault identification method according to claim 9, characterized in that: The sign of the pulse group multi-time shift mutual correlation value is used to identify the fault type, specifically: when the pulse group multi-time shift mutual correlation value is positive, the fault type is determined to be an open circuit; when it is negative, the fault type is determined to be a short circuit.

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