Multi-channel leaky coaxial cable fault positioning system and method

Abstract

The invention discloses a multi-channel leaky coaxial cable fault positioning system and method, and belongs to the technical field of rail transit leaky coaxial cable fault positioning and monitoring. The system comprises a modulation signal generator, a circulator, an SPTD module, an FPGA signal processor and an upper computer. The system only needs to install a monitoring device at one end of the leaky coaxial cable, and is convenient to implement. The ZYNQ control panel is used for controlling IO signals, so that the SPTD switch is controlled to realize switching of monitoring channels, and multi-channel fault detection and positioning are realized; the unattended operation is realized, the detection and positioning cost is effectively reduced, and the detection efficiency is improved. According to the method, by introducing the phase error compensation function of the transmitting signal and the phase error compensation function of the echo signal, the phase compensation of the frequency mixing signal is realized, so that the phase error of the fault detection signal is reduced, the detection precision is improved, and the accuracy of fault judgment, fault point positioning and fault type judgment is effectively improved.

Description

Technical Field

[0001] The invention relates to a multi-channel leaky coaxial cable fault locating system and method, belonging to the technical field of rail transit leaky coaxial cable fault locating and monitoring. Background Art

[0002] Railway and urban rail transit systems usually use leaky coaxial cables (hereinafter referred to as "leaky cables") to transmit signals such as control communications, fire protection, passenger broadcasts, and mobile communications in tunnels and track areas. Once a signal cable fails, communication will be interrupted, which will seriously affect the safe operation of rail transit. Therefore, how to quickly and accurately detect leaky cable faults and locate the specific fault point has become a technical problem that needs to be solved urgently.

[0003] At present, there are two main ways to detect and locate leaky cable faults:

[0004] 1. Manual detection method:

[0005] During the train's travel window, workers hold professional equipment and use field strength testing methods to check the wireless coverage of the leaky cable. If a problem is found, it is generally necessary to disconnect the link and then use an offline antenna and feeder analyzer to detect the location of the leaky cable fault point. This method has the following defects: the detection process requires disconnecting the link, which can easily cause damage to the connector. The detection method relies on manual operation, which is inefficient and cannot provide early warning of faults. Problems can only be discovered through routine inspections or post-event troubleshooting.

[0006] 2. Master-slave monitoring system

[0007] This method is to install a transmitter and a receiver at the near end and the far end of the leaky cable respectively to build a master-slave monitoring system. The system can monitor whether there is a fault in the leaky cable in real time and send out an alarm signal in time, but due to the limitations of its detection principle, it is impossible to accurately locate the specific fault point.

[0008] In recent years, a monitoring technology based on sweep frequency signals has appeared on the market. This method uses the sweep frequency signal as the excitation signal and determines the fault of the leaky cable by measuring the standing wave ratio of the leaky cable (that is, the ratio of the reflected wave to the transmitted wave in the leaky cable). When there is a fault point in the leaky cable, the reflected wave is enhanced, resulting in an increase in the standing wave ratio. The fault location can be inferred by analyzing the standing wave ratio. However, this method still has the following problems:

[0009] Small number of measurement channels: In existing technologies, monitoring systems can usually only support a limited number of channels, which makes it difficult to meet the needs of multi-channel monitoring in complex rail transit environments.

[0010] Low positioning accuracy: The positioning accuracy of the fault point by the standing wave ratio analysis method depends on the characteristics of signal reflection. However, in actual applications, due to the complex electromagnetic environment of the leaky cable and signal attenuation, echo noise, phase error and other reasons, the positioning results often have large errors.

[0011] In summary, the existing technology still has many deficiencies in leaky cable fault detection, especially in multi-channel monitoring and high-precision positioning, which need to be improved urgently. Therefore, developing a technical solution that can support multi-channel monitoring and has high-precision fault positioning capabilities is of great significance to the safe operation of rail transit. Summary of the invention

[0012] In order to solve the problem of a small number of leaky cable fault monitoring and positioning channels and low positioning accuracy, the present invention provides a multi-channel leaky coaxial cable fault positioning system and method, and the technical solution is as follows:

[0013] The leaky coaxial cable fault location method of the present invention comprises:

[0014] Step 1: Send the sawtooth wave linear frequency modulation signal as a transmission signal to the leaky coaxial cable through a circulator;

[0015] Step 2: Acquire an original echo signal, where the original echo signal is a reflection echo of the transmission signal from the leaky cable fault point;

[0016] Step 3: Mixing the transmission signal and the original echo signal to generate a difference frequency signal;

[0017] Step 4: performing denoising, de-skewing, phase error compensation, sidelobe suppression and FFT transformation on the difference frequency signal in sequence;

[0018] Step 5: Calculate the centroid of the signal after FFT transformation, and calculate the return loss of the fault point, the standing wave ratio value of the fault point, and the distance of the fault point. Determine the fault type based on the size of the standing wave ratio value.

[0019] Optionally, the phase error compensation process in step 4 includes:

[0020] Design the transmission signal phase error compensation function as follows:

[0021] s′ t (t) = exp(jφ e (t))]

[0022] Among them, φ e (t) represents a phase error model of the transmitted signal;

[0023] Multiplying the phase compensation function of the transmission signal by the de-skewing difference frequency signal to remove the phase error of the transmission signal;

[0024] Design the phase error compensation function of the echo signal:

[0025]

[0026] In the formula, s r(e) (t) is the time domain transform of the echo signal, f c is the center frequency of the transmitted signal, γ is the slope of the frequency modulated continuous wave;

[0027] The phase compensation function of the echo signal is multiplied by the difference frequency signal for removing the phase error of the transmission signal, so as to further remove the phase error of the echo signal.

[0028] Optionally, the return loss calculation formula of the fault point is:

[0029] R L (n) = P r (n)-P ref (n)

[0030] Where n is the distance gate, i.e. the fault point, R L is the return loss power, P r is the transmitted echo power, P ref It is the maximum reflected power reference value.

[0031] Optionally, the standing wave ratio value of the fault point is:

[0032]

[0033] Optionally, the fault point distance is:

[0034]

[0035] Where R is the distance to the fault point, T is the time to receive the signal, and K V is the transmission rate coefficient of the leaky coaxial cable.

[0036] The present invention provides a leaky coaxial cable fault location system, comprising: a modulation signal generator, a circulator, an SPTD module, an FPGA signal processor and a host computer;

[0037] The modulation signal generator is used to generate a sawtooth wave linear frequency modulation signal; the sawtooth wave linear frequency modulation signal is sent to the leaky coaxial cable through the circulator and the SPTD module;

[0038] The SPTD module includes a ZYNQ control board and an SPTD switch. The ZYNQ control board controls the GPIO to output high and low levels, thereby controlling the SPTD switch to switch the monitoring channels, so as to achieve simultaneous monitoring of multi-channel leaky coaxial cable faults.

[0039] The FPGA signal processor receives the original echo signal, mixes the original echo signal with the sawtooth wave linear frequency modulation signal to generate a difference frequency signal, and then sequentially performs denoising, DeChirp de-skewing, phase error compensation, sidelobe suppression, and FFT transformation on the difference frequency signal;

[0040] The host computer calculates the centroid of the signal after FFT transformation, calculates the return loss and standing wave ratio of the fault point, and determines the position of the fault point and the fault type according to a preset standing wave ratio threshold.

[0041] Optionally, the phase error compensation process includes:

[0042] Design the transmission signal phase error compensation function as follows:

[0043] s′ t (t) = exp(jφ e (t))]

[0044] Among them, φ e (t) represents a phase error model of the transmitted signal;

[0045] Multiplying the phase compensation function of the transmission signal by the de-skewing difference frequency signal to remove the phase error of the transmission signal;

[0046] Design the phase error compensation function of the echo signal:

[0047]

[0048] In the formula, s r(e) (t) is the time domain transform of the echo signal, f c is the center frequency of the transmitted signal, γ is the slope of the frequency modulated continuous wave;

[0049] The phase compensation function of the echo signal is multiplied by the difference frequency signal for removing the phase error of the transmission signal, so as to further remove the phase error of the echo signal.

[0050] Optionally, the return loss calculation formula of the fault point is:

[0051] R L (n) = P r (n)-P ref (n)

[0052] Where n is the distance gate, the nth point after the distance calibration point N0, i.e. the fault point, R L is the return loss power, P r is the transmitted echo power, P ref It is the maximum reflected power reference value.

[0053] Optionally, the standing wave ratio value of the fault point is:

[0054]

[0055] Optionally, the fault point distance is:

[0056]

[0057] Where R is the distance to the fault point, T is the time to receive the signal, and K V is the transmission rate coefficient of the leaky coaxial cable.

[0058] The beneficial effects of the present invention are:

[0059] The leaky coaxial cable fault location method of the present invention realizes phase compensation of the mixed signal by introducing the phase error compensation function of the transmitted signal and the phase error compensation function of the echo signal, thereby eliminating the phase error of the fault detection signal, and calculates the fault point position, the return loss of the fault point, and the standing wave ratio of the fault point based on the signal after eliminating the phase error, thereby effectively improving the accuracy of fault judgment, fault point location and fault type judgment.

[0060] The leaky coaxial cable fault locating system of the present invention only needs to install a monitoring device at one end of the leaky cable to realize self-transmission and self-reception of detection. Compared with the master-slave monitoring system, it has a simple structure and is easy to implement. The ZYNQ control board is used to control the GPIO output high and low levels, thereby controlling the SPTD switch to realize the switching of the monitoring channel, so as to realize the simultaneous detection and positioning of multi-channel leaky coaxial cable faults, and can be unmanned. The system polls and monitors the leaky cables of multiple channels according to the preset time. One device can monitor multiple leaky cables at the same time, so the number of detection devices can be reduced. Compared with the existing solution of one device measuring one cable, the present invention effectively reduces the detection and positioning cost, which not only improves the economic benefit, but also improves the detection efficiency.

[0061] Practice has proved that the system and method of the present invention can locate leaky cable faults with a distance error of ≤3 meters, which is in a leading position in the industry.

[0062] In addition, the central frequency point of the excitation signal of the present invention can be set according to user requirements, so as to avoid business signals, not introduce interference, and ensure that the access of the monitoring system has no impact on business signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0064] Figure 1 It is a structural diagram of a leaky coaxial cable fault location system in Embodiment 2 of the present invention.

[0065] Figure 2 It is a flow chart of a leaky coaxial cable fault locating method in Embodiment 1 of the present invention. DETAILED DESCRIPTION

[0066] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0067] Embodiment 1:

[0068] This embodiment provides a leaky coaxial cable fault location method, including:

[0069] Step 1: Use the sawtooth linear frequency modulation signal as the transmission signal and send it to the leaky coaxial cable through the circulator.

[0070] According to the requirements of distance positioning accuracy and the minimum threshold value of the standing wave ratio, the bandwidth, modulation period and slope of the sawtooth linear frequency modulation signal are designed. By configuring the center frequency, gain, number of transmission channels, etc. of the D / A conversion chip, the digital signal generated by the baseband processor is converted into a sawtooth linear frequency modulation signal, and the signal is sent to the port for transmission. The center frequency can be customized according to the actual usage scenario.

[0071] The distance positioning accuracy design method is as follows:

[0072]

[0073] In the formula, ΔR represents the distance positioning accuracy, C represents the speed of light, and B represents the signal bandwidth.

[0074] This embodiment uses a high-isolation, low-insertion-loss circulator to send a sawtooth linear frequency modulation signal to a leaky coaxial cable.

[0075] Step 2: Get the original echo signal. The leaky cable fault location system transmits a sawtooth linear frequency modulation signal to the leaky cable. When there is a fault point in the leaky cable, the reflected wave will be enhanced. This reflected echo is called the original echo signal. By configuring a high-speed A / D conversion chip, the original echo signal is de-noised through a low-noise amplifier and a third-order Butterworth low-pass filter, and then the analog signal is converted into a digital signal that can be used by the baseband processor through an analog-to-digital converter.

[0076] Step 3: Mix the transmission signal and the original echo signal to generate a difference frequency signal.

[0077] The mixed signal is processed by beat processing, that is, the phase difference of two related signals is calculated. The method is to mix the echo signal with the transmitted signal, and then process the difference frequency signal with a smaller bandwidth, and then use the obtained phase difference to represent the frequency difference. Since the chirp signal time and frequency are linear, the chirp signal whose frequency changes linearly with time can be converted into a fixed frequency signal whose frequency depends completely on the relative position of the two signals.

[0078] Step 4: The difference frequency signal is subjected to denoising, DeChirp de-skewing, phase error compensation, sidelobe suppression and FFT transformation in sequence;

[0079] Step 41: DeChirp de-skew processing;

[0080] Using Dechirp technology for pulse compression can reduce the bandwidth of the signal, thereby reducing the system A / D sampling frequency and the amount of data processing, making signal processing more convenient and streamlining system equipment to reduce costs.

[0081] Step 42: Phase error compensation;

[0082] Although the DeChirp de-skewing technology effectively reduces the sampling frequency of analog-to-digital conversion and the amount of data in the system, and improves the sampling efficiency, it introduces a space-varying phase error and reduces the signal quality. Therefore, this embodiment proposes a method for compensating the space-varying phase error based on a transmitted signal phase error model to improve the accuracy of ranging.

[0083] Design the transmission signal phase error compensation function as follows:

[0084] s′ t (t) = exp(jφ e (t))]

[0085] Among them, φ e (t) represents a phase error model of the transmitted signal;

[0086] The transmit signal phase compensation function is multiplied by the difference frequency signal to remove the transmit signal phase error.

[0087] Design the echo signal phase error compensation function:

[0088]

[0089] In the formula, s r(e) (t) is the time domain transform of the echo signal, f c is the center frequency of the transmitted signal, γ is the slope of the frequency modulated continuous wave;

[0090] The echo signal phase compensation function is multiplied by the difference frequency signal from which the phase error of the transmission signal is removed to further remove the phase error of the echo signal.

[0091] Step 43: sidelobe suppression processing;

[0092] The difference frequency signal after phase error compensation is subjected to Hamming weighted filtering and denoising. After the processing, the side lobes near the main lobe and the side lobes far away are effectively suppressed.

[0093] Step 44: FFT transformation;

[0094] The echo signal is converted into a spectrum through FFT processing.

[0095] Step 45: Calculate the centroid of the spectrum amplitude:

[0096] The centroid operation is performed on the spectrum amplitude after FFT processing to accurately locate the position of the main frequency.

[0097] Step 46: Calculate the characteristic information of the fault point

[0098] Calculate the return loss of the fault point, the standing wave ratio value of the fault point and the distance to the fault point, and determine the fault type based on the size of the standing wave ratio value.

[0099] Realize the extraction of characteristic information of fault points.

[0100] The return loss formula is: R L (n) = P r (n)-P ref (n)

[0101] Where n is the distance gate, i.e. the fault point. L is the return loss power, P r is the transmitted echo power, P ref It is the maximum reflected power reference value.

[0102] According to the above formula, the standing wave ratio value of the fault point is calculated:

[0103]

[0104] Finally, the distance to the fault point is calculated:

[0105]

[0106] In the formula, R is the distance to the fault point, T is the time to receive the signal, and K V is the transmission rate coefficient of the leaky cable.

[0107] Finally, the distance to the fault point is output, and the fault type is determined based on the size of the standing wave ratio value.

[0108] The leaky coaxial cable fault location method of this embodiment realizes phase compensation of the mixing signal by introducing the phase error compensation function of the transmission signal and the phase error compensation function of the echo signal, thereby reducing the phase error of the fault detection signal, and calculates the fault point position, the return loss of the fault point, and the standing wave ratio of the fault point based on the optimized mixing signal, thereby effectively improving the accuracy of fault judgment, fault point location and fault type judgment.

[0109] Embodiment 2

[0110] This embodiment provides a multi-channel leaky coaxial cable fault location system. Figure 1 and Figure 2 ,The system includes: modulation signal generator, circulator, SPTD module, FPGA signal processor and host computer.

[0111] The modulation signal generator is used to generate a sawtooth linear frequency modulation signal. The parameters of the frequency modulation signal, such as the center frequency, bandwidth, modulation period and slope, can be adjusted according to the usage scenario to ensure that in the usage scenarios of service signals in different frequency bands, the detection signal is separated from the service signal band and does not affect the normal service signal.

[0112] The sawtooth linear frequency modulation signal is sent to the leaky coaxial cable through the circulator and the SPTD module. The SPTD module includes a ZYNQ control board and an SPTD switch. The ZYNQ control board controls the high and low levels of the GPIO output to control the SPTD switch to switch the monitoring channel. Figure 1 As shown, this embodiment has four monitoring channels, which can respectively perform fault monitoring on four leaky coaxial cables.

[0113] After the sawtooth linear frequency modulation signal is reflected by the coaxial cable fault point, the original echo signal is formed and received by the FPGA signal processor. The FPGA signal processor mixes the sawtooth linear frequency modulation signal (i.e., the transmitting signal) and the original echo signal to generate a difference frequency signal, and then performs denoising, DeChirp de-skewing, phase error compensation, sidelobe suppression, and FFT transformation on the difference frequency signal in turn.

[0114] The host computer calculates the centroid of the data after FFT transformation, and calculates the return loss and standing wave ratio of the fault point, and determines the location of the fault point and the fault type according to the preset standing wave ratio threshold.

[0115] In addition, the host computer can realize unattended polling to detect the working status of the four leaky cables, and use the SPTD module on the hardware to switch channels and connect the four leaky cables at the same time.

[0116] The leaky coaxial cable fault locating system of the present embodiment only needs to install a monitoring device at one end of the leaky cable to realize self-transmission and self-reception of detection. Compared with the master-slave monitoring system, it has a simple structure and is easy to implement. The ZYNQ control board is used to control the high and low levels of the IO output, thereby controlling the SPTD switch to realize the switching of the monitoring channel, so as to realize the simultaneous detection and positioning of multi-channel leaky coaxial cable faults, and can be unmanned. The system polls and monitors the leaky cables of multiple channels according to the preset time. One device can monitor multiple leaky cables at the same time, effectively reducing the detection and positioning cost and improving the detection efficiency.

[0117] Some steps in the embodiments of the present invention may be implemented using software, and the corresponding software program may be stored in a readable storage medium, such as a CD or a hard disk.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for locating a leaky coaxial cable fault, characterized in that: The method comprises: Step 1: Send the sawtooth wave linear frequency modulation signal as the transmission signal to the leaky coaxial cable through a circulator; Step 2: Acquire an original echo signal, where the original echo signal is a reflection echo of the transmission signal from the leaky cable fault point; Step 3: Mixing the transmission signal and the original echo signal to generate a difference frequency signal; Step 4: performing denoising, de-skewing, phase error compensation, sidelobe suppression and FFT transformation on the difference frequency signal in sequence; Step 5: Calculate the centroid of the signal after FFT transformation, and calculate the return loss of the fault point, the standing wave ratio value of the fault point and the distance of the fault point. Determine the fault type according to the size of the standing wave ratio value.

2. The method for locating a leaky coaxial cable fault according to claim 1, characterized in that: The process of phase error compensation in step 4 includes: Design the transmission signal phase error compensation function as follows: s′ t (t)=exp(jφ e (t))] Among them, φ e (t) represents a phase error model of the transmitted signal; Multiplying the phase compensation function of the transmission signal by the de-skewing difference frequency signal to remove the phase error of the transmission signal; Design the phase error compensation function of the echo signal: In the formula, s r(e) (t) is the time domain transform of the echo signal, f c is the center frequency of the transmitted signal, γ is the slope of the frequency modulated continuous wave; The phase compensation function of the echo signal is multiplied by the difference frequency signal for removing the phase error of the transmission signal, so as to further remove the phase error of the echo signal.

3. The method for locating a leaky coaxial cable fault according to claim 1, characterized in that: The return loss calculation formula of the fault point is: R L (n)=P r (n)-P ref (n) Where n is the distance gate, i.e. the fault point; R L is the return loss power, P r is the transmitted echo power, P ref It is the maximum reflected power reference value.

4. The method for locating a leaky coaxial cable fault according to claim 3, characterized in that: The standing wave ratio value of the fault point is:

5. The method for locating a leaky coaxial cable fault according to claim 1, characterized in that: The fault point distance is: Where R is the distance to the fault point, T is the time to receive the signal, and K V is the transmission rate coefficient of the leaky coaxial cable.

6. A leaky coaxial cable fault location system, characterized in that: The system comprises: a modulation signal generator, a circulator, an SPTD module, an FPGA signal processor and a host computer; The modulation signal generator is used to generate a sawtooth wave linear frequency modulation signal; the sawtooth wave linear frequency modulation signal is sent to the leaky coaxial cable through the circulator and the SPTD module; The SPTD module includes a ZYNQ control board and an SPTD switch. The ZYNQ control board controls the GPIO to output high and low levels, thereby controlling the SPTD switch to switch the monitoring channels, so as to achieve simultaneous monitoring of multi-channel leaky coaxial cable faults. The FPGA signal processor receives the original echo signal, mixes the original echo signal with the sawtooth wave linear frequency modulation signal to generate a difference frequency signal, and then sequentially performs denoising, DeChirp de-skewing, phase error compensation, sidelobe suppression, and FFT transformation on the difference frequency signal; The host computer calculates the centroid of the signal after FFT transformation, calculates the return loss and standing wave ratio of the fault point, and determines the position of the fault point and the fault type according to a preset standing wave ratio threshold.

7. The leaky coaxial cable fault location system according to claim 6, characterized in that: The phase error compensation process includes: Design the transmission signal phase error compensation function as follows: s′ t (t)=exp(jφ e (t))] Among them, φ e (t) represents a phase error model of the transmitted signal; Multiplying the phase compensation function of the transmission signal by the de-skewing difference frequency signal to remove the phase error of the transmission signal; Design the phase error compensation function of the echo signal: In the formula, s r(e) (t) is the time domain transform of the echo signal, f c is the center frequency of the transmitted signal, γ is the slope of the frequency modulated continuous wave; The phase compensation function of the echo signal is multiplied by the difference frequency signal for removing the phase error of the transmission signal, so as to further remove the phase error of the echo signal.

8. The leaky coaxial cable fault location system according to claim 6, characterized in that: The return loss calculation formula of the fault point is: R L (n)=P r (n)-P ref (n) Where n is the distance gate, i.e. the fault point, R L is the return loss power, P r is the transmitted echo power, P ref It is the maximum reflected power reference value.

9. The leaky coaxial cable fault location system according to claim 8, characterized in that: The standing wave ratio value of the fault point is:

10. The leaky coaxial cable fault location system according to claim 6, characterized in that: The fault point distance is: Where R is the distance to the fault point, T is the time to receive the signal, and K V is the transmission rate coefficient of the leaky coaxial cable.

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