A parameter calibration method for online cable fault detection

Abstract

This invention belongs to the field of online cable fault detection, specifically a parameter calibration method for online cable fault detection. It is implemented based on an online cable fault detection circuit, which includes an information processing unit, a DAC, an ADC, and a transceiver isolation circuit. The information processing unit is composed of an FPGA or an ARM+FPGA, and is divided into a transmitting module and a receiving module according to its function. The transmitting module generates an SSTDR fault detection signal, which is converted into an analog waveform by the DAC and injected into the cable under test through the transceiver isolation circuit. The detection signal propagates in the cable, and when it encounters a fault point, it is reflected. The reflected echo propagates in the reverse direction along the cable, enters the ADC circuit through the transceiver isolation circuit, and is converted into a digital signal for processing by the receiving module of the information processing unit. The calibrated cable impedance can improve the performance of the transceiver isolation circuit, reduce interference of the transmitted signal to the receiving circuit, and increase the fault detection distance; the calibrated electromagnetic wave propagation speed can improve the accuracy of fault location.

Description

Technical Field

[0001] This invention belongs to the field of online cable fault detection, specifically a parameter calibration method for online cable fault detection. Background Technology

[0002] With the development of information technology, electronic equipment in transportation vehicles such as aircraft, ships, and high-speed trains is increasing, and the wiring harness networks between highly integrated and interconnected systems are becoming increasingly complex. These harnesses provide power and transmit signals to the electrical and electronic equipment of the systems, and their performance determines the overall safety and reliability of the equipment. The wires in the wiring harnesses are subjected to vibration, friction, high and low temperatures, and high humidity, which can easily cause wire faults or loose connectors, leading to abnormal or unstable signals or power supply, and even seriously affecting the safe operation of the system. The continuity, impedance, and insulation performance testing of cables, as well as rapid fault location, are crucial for the safe and reliable operation of equipment such as aircraft, ships, and high-speed trains. Faults such as short circuits, open circuits, and arcing can be unified into impedance change problems. Spread Spectrum Time Domain Reflectometry (SSTDR) can achieve real-time online detection of cable impedance changes. SSTDR utilizes correlation detection, has high processing gain, and features low test signal levels and strong anti-interference capabilities. When using SSTDR technology to detect cable faults, it is necessary to isolate the transmitted and received signals and calibrate the cable impedance to minimize interference from the transmitted signal to the receiving circuit. During fault location, the fault distance is calculated by measuring the fault echo delay and utilizing the propagation speed of electromagnetic waves in the cable. At this time, it is necessary to calibrate the propagation speed of electromagnetic waves in the cable to improve the location accuracy.

[0003] CN110703127A, concerning an aircraft cable fault detection device and method, relates to the field of cable fault detection. Specifically, it describes an aircraft cable detection device and method, comprising an upper housing, a lower housing, and a signal processing module, a signal conditioning module, a multimeter module, a display screen, a display screen adapter board, a heat sink, a detection port, probe jacks, an external input area, a lithium battery, and a charging management module located between the upper and lower housings. The device can perform three types of detection, excelling in anti-interference and measurement accuracy. It can achieve offline fault detection of aircraft cables, measuring and accurately locating short-circuit and open-circuit faults. The device can disable corresponding functions according to different operating states to reduce power consumption, making it energy-saving and environmentally friendly, and offering good economic benefits.

[0004] CN113281617A A method for diagnosing weak faults in aircraft cables.

[0005] This invention discloses a method for diagnosing weak faults in aircraft cables, comprising: acquiring reflected signals from aircraft cables using a detection device built based on virtual instrument technology; processing the acquired reflected signals using an improved variational mode decomposition; performing a short-time Fourier transform on the decomposed intrinsic mode components containing fault information; redistributing the time-frequency energy of the eigenmode components after the short-time Fourier transform using a rearranged spectrum method, distributing them to the centroid position; and then extracting the time energy information to plot the fault information curve of the aircraft cable, diagnosing the presence of weak faults in the aircraft cable from an energy perspective. The advantages of this invention are: overcoming the problem that traditional spread spectrum time-domain reflectometry cannot effectively detect weak faults, realizing the diagnosis of weak faults in aircraft cables, improving the early warning capability and detection rate of weak faults in aircraft cables, and providing support for aircraft cable maintenance.

[0006] CN110658418A A cable fault detection method and apparatus

[0007] This application discloses a cable fault detection method and apparatus. The method includes: a fault detection device sending a pulse signal to a cable under test; the fault detection device acquiring waveform data of the reflected pulse signal; the fault detection device, according to a preset pulse amplitude threshold, extracting waveforms from the waveform data whose absolute amplitude value is greater than the threshold; the fault detection device determining a fault waveform corresponding to a fault point based on the extracted waveform; and the fault detection device determining the fault point and its distance based on the fault waveform and its waveform data, wherein the distance to the fault point is the cable length between the fault point and the fault detection device. The technical solution provided by this application can improve the accuracy of the detection results.

[0008] However, the detection principle of this patent is different from those of the other patents, the circuit principle is quite different, and the focus is different. The circuit and strategy discussed here are not included in the scope of the other patents. Summary of the Invention

[0009] In view of this, the present invention aims to propose a parameter calibration method for online cable fault detection, designing a cable characteristic impedance matching circuit and calibrating the cable characteristic impedance and the propagation speed of electromagnetic waves in the cable. The calibrated cable impedance can improve the performance of the transmit / receive isolation circuit, reduce interference of the transmitted signal to the receiving circuit, and increase the fault detection distance; the calibrated electromagnetic wave propagation speed can improve the accuracy of fault location.

[0010] The parameter calibration method proposed in this invention can calibrate the parameters of any type of cable, thereby improving the performance of cable fault detection equipment.

[0011] Technical solution

[0012] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0013] A parameter calibration method for online cable fault detection is provided, based on an online cable fault detection circuit. The online cable fault detection circuit includes an information processing unit, a DAC, an ADC, and a transceiver isolation circuit. The information processing unit is composed of an FPGA or an ARM+FPGA, and is divided into a transmitting module and a receiving module according to its function. The transmitting module generates an SSTDR fault detection signal, which is converted into an analog waveform by the DAC and injected into the cable under test through the transceiver isolation circuit. The detection signal propagates in the cable, is reflected when it encounters a fault point, and the reflected echo propagates in the reverse direction along the cable, enters the ADC circuit through the transceiver isolation circuit, is converted into a digital signal, and then enters the receiving module of the information processing unit for processing.

[0014] Includes the following steps:

[0015] Step (1) Transmit the detection waveform, collect the signal leaked from the transmitted waveform to the receiving circuit, and calculate the power of the leaked signal;

[0016] Step (2) Adjust the resistance value of the matching resistor through the relay, repeat step (1), and record all leakage signal power;

[0017] After step (3) iterates through all the resistance values ​​of the matching resistor, find the minimum value of the leakage signal power, and the corresponding resistance value of the matching resistor is the characteristic impedance of the cable.

[0018] Step (4) Connect a cable of known length and measure the location of the fault point using a detection device;

[0019] Step (5) Without connecting the cable, measure the location of the fault point using the testing equipment;

[0020] Step (6) Based on the two measurements and the known cable length, the propagation speed of electromagnetic waves in the cable can be calculated.

[0021] Furthermore, step (1) specifically includes:

[0022] (1) A section of cable to be tested needs to be prepared. The cable length is D. One end is connected to the cable fault detection device, and the other end is open.

[0023] (2) The transmitting module of the information processing unit generates a detection signal, which is then converted by the DAC and injected into the cable under test. At the same time as the transmitting module transmits the signal, the receiving module receives the data collected by the ADC and processes it.

[0024] (3) The data sampled by the ADC is x(n), n = 1, 2, ..., N, where N represents the length of the sampled data. The power of the leaked interference signal is expressed as...

[0025] Furthermore, in step (1), since it takes a certain amount of time for the transmitted detection signal to propagate through the cable to the fault point (the other end of the cable) and then reflect back, before this time, the data collected by the ADC only includes the interference signal that leaks from the transmitted signal to the receiving interface through the transformer, and does not include the fault echo.

[0026] Furthermore, step (2) specifically involves controlling the ctrl1 to ctrl6 pins of the resistor network to change the resistance value of the resistor network from small to large. Each time the resistance value is changed, a detection signal is emitted. The receiving module receives N data points, calculates the power of the current interference signal, and records it.

[0027] Furthermore, step (3) specifically involves finding the minimum value of the N recorded power values ​​to obtain the resistance value of the resistor network corresponding to the minimum value and the control signals ctrl1 to ctrl6. At this time, the resistance value of the resistor network can balance the characteristic impedance of the cable under test and reduce the interference signal of the transmission leakage to the minimum.

[0028] Furthermore, step (4) specifically involves:

[0029] The calibration process requires a precisely measured cable of length L meters. One end of the cable is open-circuited, and the other end is connected to a cable fault detection device. The cable fault detection device is pre-set to allow electromagnetic waves to propagate in the cable at a speed of v × 10⁻¹⁰. 8 m / s, the fault echo return time can be obtained by measurement as t1, in ns. Therefore, the fault distance calculated by the cable fault detection equipment, i.e., the cable length, is:

[0030] Furthermore, according to the previous paragraph, the value of the electromagnetic wave propagation speed v is not accurate. The true value can be corrected to a·v, where a is the correction coefficient for the electromagnetic wave propagation speed, which is dimensionless.

[0031] Additionally, the distance error caused by system errors in cable fault detection equipment can be expressed as b, in meters (m). The actual length of the cable is expressed as: Where a is the correction factor for the propagation speed of electromagnetic waves, and b is the correction for system errors.

[0032] Furthermore, step (5) specifically includes:

[0033] The actual location of an open-circuit fault, i.e., without the cable being connected, should be 0, represented as L0 = 0. The fault echo return time, measured by the cable fault detection equipment, is t2 (in nanoseconds). Therefore, the calculated fault distance, i.e., the cable length, is:

[0034]

[0035] After correction, the actual length of the cable is expressed as:

[0036]

[0037] Furthermore, step (6) specifically involves:

[0038] The formulas from steps (4) and (5) form a system of equations, from which we obtain: This yields the correction factor 'a' for the electromagnetic wave propagation speed and the correction factor 'b' for the system error. The true value of the electromagnetic wave propagation speed in the cable is a·v×10. 8 m / s.

[0039] After the parameters are calibrated, when the cable fault detection equipment is working, if the time for the fault echo to return is measured to be t (in ns), the actual fault location should be:

[0040]

[0041] Technical effect

[0042] The innovation of this invention lies in proposing a parameter calibration method for online cable fault detection. It involves designing a cable characteristic impedance matching circuit to calibrate the cable's characteristic impedance and the propagation speed of electromagnetic waves within the cable. The calibrated cable impedance improves the performance of the transmit / receive isolation circuit, reduces interference from the transmitted signal to the receiving circuit, and increases the fault detection distance. The calibrated electromagnetic wave propagation speed improves the accuracy of fault location. This parameter calibration method can calibrate parameters for any type of cable, is applicable to both online and offline cable fault detection equipment, and improves the location accuracy of cable fault detection equipment, expands the measurement range, and eliminates measurement blind spots. Attached Figure Description

[0043] Figure 1 This is a structural block diagram of a cable fault detection device based on SSTDR technology;

[0044] Figure 2 This is a block diagram of the transceiver circuit of the cable fault detection device proposed in this invention;

[0045] Figure 3 This is a resistor network used to balance the characteristic impedance of cables in the transmit / receive isolation circuit proposed in this invention. Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments. The following description represents only a portion of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0047] This invention proposes a parameter calibration method for online detection of cable faults. A cable characteristic impedance matching circuit is designed to calibrate the cable characteristic impedance and the propagation speed of electromagnetic waves in the cable. The specific implementation of this invention is described in detail below.

[0048] 1. Cable fault detection equipment based on SSTDR technology

[0049] The structure of the cable fault detection equipment based on SSTDR technology is shown in the attached figure. Figure 1 As shown, the core components include an information processing unit, DAC, ADC, and transceiver isolation circuit. The information processing unit is generally composed of an FPGA or ARM+FPGA, and is divided into a transmitting module and a receiving module according to its functions. The transmitting module generates an SSTDR fault detection signal, which is converted into an analog waveform by the DAC and injected into the cable under test through the transceiver isolation circuit. The detection signal propagates in the cable, and when it encounters a fault point (short circuit or open circuit), it is reflected. The reflected echo propagates in the reverse direction along the cable, enters the ADC circuit through the transceiver isolation circuit, is converted into a digital signal, and then enters the receiving module of the information processing unit for processing.

[0050] In cable fault detection equipment, the performance of the transmit / receive isolation circuit is crucial. It ensures that the transmit signal generated by the DAC only enters the cable under test and does not enter the ADC interference fault echo detection.

[0051] 2. Design of matching resistor circuit

[0052] Appendix Figure 2 This invention relates to a transceiver circuit for a cable fault detection device. The transceiver circuit has four interfaces: a transmit interface, receive interfaces recv+ and recv-, and a cable interface P1. Figure 1 The cable fault detection device shown includes a DAC, ADC, and the cable under test; matching resistor interfaces res1 and res2 are attached. Figure 3 The resistor network shown is used to balance the characteristic impedance of the cable. The resistor network connected to the matching resistor interface is used to balance the characteristic impedance of the cable.

[0053] Appendix Figure 3 As a resistor network used to balance the characteristic impedance of the cable in the transmit / receive isolation circuit, interfaces res1 and res2 are connected to the attached... Figure 2The matching resistor interface is connected. Six control ports (Ctrl_1 to Ctrl_6) control the on / off state of six relays, further controlling whether resistors R2 to R7 are connected to the resistor network, thus changing the overall resistance value of the network. The fixed resistor has a value of 33Ω, and the six selectable resistors have values ​​of 1Ω, 2Ω, 4.3Ω, 8.2Ω, 15.8Ω, and 32.4Ω, resulting in a resistance range of 33Ω to 96Ω with a minimum interval of 1Ω.

[0054] The working principle of the transceiver circuit is as follows: (1) The transmitted waveform generated by the DAC in the cable fault detection device enters the transceiver isolation circuit through the transmitting interface; (2) The transceiver isolation circuit cancels each other out at the receiving interface; (2) The signal entering the cable interface encounters a cable fault and generates an echo. The echo signal appears at the receiving interface; (2) After the transceiver isolation circuit cancels out the signal, it enters the ADC in the cable fault detection device for further fault detection.

[0055] To prevent the transmitted signal from entering the receiving interface and causing interference, the parameters of the cable interface and the matching impedance interface should be as consistent as possible. Therefore, the matching resistor network needs to be consistent with the characteristic impedance of the cable under test connected to the cable interface. Thus, the characteristic impedance of the cable needs to be calibrated to determine the resistance value of the resistor network.

[0056] 3. Calibration of the characteristic impedance of the cable under test

[0057] During the calibration of the characteristic impedance of the cable under test, a section of cable of length D needs to be prepared. One end is connected to the cable fault detection device, and the other end is open-circuited. The transmitting module of the information processing unit generates a detection signal, which is converted by a DAC and then injected into the cable under test. Simultaneously, the receiving module receives and processes the data collected by the ADC. Because it takes time for the transmitted detection signal to propagate through the cable to the fault point (the other end of the cable) and then reflect back, before this time, the data collected by the ADC only contains the interference signal leaked from the transmitted signal through the transformer to the receiving interface, and does not include the fault echo. The data sampled by the ADC is x(n), n = 1, 2, ..., N, where N represents the length of the collected data. The power of the leaked interference signal is expressed as...

[0058]

[0059] By controlling the ctrl1 to ctrl6 pins of the resistor network, the resistance value of the resistor network is changed sequentially from small to large. Each time the resistance value is changed, a detection signal is emitted. The receiving module receives N data points, calculates the power of the current interference signal according to formula (1), and records it. The minimum value of the 64 recorded power values ​​is obtained to get the resistance value of the resistor network corresponding to the minimum value and the control signals of ctrl1 to ctrl6. At this time, the resistance value of the resistor network can balance the characteristic impedance of the cable under test, and reduce the interference signal of the emitted leakage to a minimum.

[0060] In a preferred embodiment, the cable under test is selected to be 20 meters long, and the time required for the transmitted signal to reach the fault point and be reflected back is... v represents the speed of electromagnetic wave propagation in the cable, which is taken as two-thirds of the speed of light in a vacuum. The time t is approximately 200 ns. The ADC has a sampling rate of 200 MHz and a sampling interval of 5 ns, so the interference data length N = 40.

[0061] 4. Calibration of the speed of electromagnetic wave propagation in cables

[0062] The basic principle of cable fault location is Where t represents the time it takes for the transmitted signal to reach the fault point and be reflected back, which can be measured by the cable fault detection equipment. v represents the propagation speed of electromagnetic waves in the cable, approximately two-thirds the speed of light in a vacuum, and is related to the cable type. To obtain the accurate fault location R, the propagation speed of electromagnetic waves in the cable needs to be calibrated, i.e., a relatively accurate propagation speed needs to be obtained through measurement. In addition, cable fault detection equipment may have certain systematic errors, such as timing errors in transmission and reception, which also need to be calibrated.

[0063] The calibration process requires a precisely measured cable of length L meters. One end of the cable is open-circuited, and the other end is connected to a cable fault detection device. The cable fault detection device is pre-set to allow electromagnetic waves to propagate in the cable at a speed of v × 10⁻¹⁰. 8 The speed is m / s. The time for the fault echo to return is measured as t1 (unit: ns). Therefore, the fault distance (i.e., the cable length) calculated by the cable fault detection equipment is:

[0064]

[0065] In reality, the value of the electromagnetic wave propagation speed *v* is not accurate; the true value can be corrected to *a*·v, where *a* is a dimensionless correction factor for the electromagnetic wave propagation speed. Additionally, the distance error caused by system errors in cable fault detection equipment can be expressed as *b*, in meters (m). The actual length of the cable can be expressed as:

[0066]

[0067] Where a is the correction factor for the propagation speed of electromagnetic waves, and b is the correction for system errors.

[0068] The actual location of an open-circuit fault, i.e., without the cable being connected, should be 0, represented as L0 = 0. The fault echo return time (t2 in ns) can be measured using cable fault detection equipment. Therefore, the calculated fault distance (i.e., the cable length) is:

[0069]

[0070] After correction, the actual length of the cable can be expressed as:

[0071]

[0072] Formulas (3) and (5) form a system of equations, from which the solution can be obtained.

[0073]

[0074] This allows us to obtain the correction factor 'a' for the electromagnetic wave propagation speed and the correction factor 'b' for the system error. The true value of the electromagnetic wave propagation speed in the cable is a·v×10. 8 m / s.

[0075] After the parameters are calibrated, when the cable fault detection equipment is working, if the time for the fault echo to return is measured to be t (in ns), the actual fault location should be:

[0076]

[0077] In a preferred embodiment, the value of v is recommended to be 2.0, which is approximately two-thirds of the speed of light. During calibration, the length L of the cable under test should be as close as possible to the maximum detection distance of the cable fault detection equipment to reduce the calibration error of the electromagnetic wave propagation speed and improve the fault location accuracy.

[0078] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein. The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A parameter calibration method for online cable fault detection, characterized in that, This is based on an online cable fault detection circuit, which includes an information processing unit, a DAC, an ADC, and a transceiver isolation circuit. The information processing unit is composed of an FPGA or an ARM+FPGA and is divided into a transmitting module and a receiving module according to its functions. The transmitting module generates an SSTDR fault detection signal, which is converted into an analog waveform by a DAC and injected into the cable under test through a transmit / receive isolation circuit. The detection signal propagates in the cable, is reflected when it encounters a fault point, and the reflected echo propagates in the opposite direction along the cable. After passing through the transceiver isolation circuit, it enters the ADC circuit, is converted into a digital signal, and then enters the receiving module of the information processing unit for processing. When using it, the following steps are included: Step (1) Transmit the detection waveform, collect the signal leaked from the transmitted waveform to the receiving circuit, and calculate the power of the leaked signal; Step (2) Adjust the resistance value of the matching resistor through the relay, repeat step (1), and record all leakage signal power; After step (3) iterates through all the resistance values ​​of the matching resistor, find the minimum value of the leakage signal power, and the corresponding resistance value of the matching resistor is the characteristic impedance of the cable. Step (4) Connect a cable of known length and measure the location of the fault point using a detection device; Step (5) Without connecting the cable, measure the location of the fault point using the testing equipment; Step (6) Based on the two measurements and the known cable length, calculate the propagation speed of electromagnetic waves in the cable and calculate the actual fault location; Step (4) specifically involves: During the calibration process, a precisely measured cable of length L meters is required. One end of the cable is open-circuited, and the other end is connected to a cable fault detection device. The cable fault detection device is pre-set to allow electromagnetic waves to propagate in the cable at a speed of v × 10⁻¹⁰. 8 m / s, the fault echo return time is measured as t1 (ns), therefore the fault distance calculated by the cable fault detection equipment, i.e., the cable length, is: Unit: m; After correcting for the electromagnetic wave propagation speed *v* in the above formula, and considering the distance error caused by the system error of the cable fault detection equipment, the actual length of the cable is expressed as: The unit is m, where a is the correction factor for the propagation speed of electromagnetic waves, and b is the correction for system errors.

2. The method as described in claim 1, characterized in that, The specific steps (1) are as follows: (1) A section of cable to be tested needs to be prepared. The cable length is D. One end is connected to the cable fault detection device, and the other end is open. (2) The transmitting module of the information processing unit generates a detection signal, which is then converted by a DAC and injected into the cable under test. At the same time as the transmitting module transmits the signal, the receiving module receives the data collected by the ADC and processes it. (3) The data sampled by the ADC is x(n), n = 1, 2, ..., N, where N represents the length of the collected data; the power of the leaked interference signal is calculated based on the data sampled by the ADC.

3. The method as described in claim 2, characterized in that, Step (2) specifically involves controlling the ctrl1 to ctrl6 pins of the resistor network to change the resistance value of the resistor network from small to large. Each time the resistance value is changed, a detection signal is emitted. The receiving module receives N data points, calculates the power of the current interference signal, and records it.

4. The method as described in claim 3, characterized in that, The specific steps (3) are as follows: find the minimum value of the N recorded power values, obtain the resistance value of the resistor network corresponding to the minimum value and the control signals of ctrl1 to ctrl6. At this time, the resistance value of the resistor network can balance the characteristic impedance of the cable under test and reduce the interference signal of the transmission leakage to the minimum.

5. The method as described in claim 4, characterized in that, Step (5) specifically involves: The actual location of the open circuit fault, i.e., without the cable being connected, is 0, represented as L0 = 0; the fault echo return time measured by the cable fault detection equipment is t2 (in nanoseconds). Therefore, the calculated fault distance, i.e., the cable length, is: Unit: m; After correction, the actual length of the cable is expressed as:

6. The method as described in claim 5, characterized in that, Step (6) specifically involves: The formulas from steps (4) and (5) form a system of equations, from which we obtain: This yields the correction factor 'a' for the electromagnetic wave propagation speed and the correction factor 'b' for the system error. The true value of the electromagnetic wave propagation speed in the cable is a·v×10. 8 m / s; After parameter calibration, when the cable fault detection equipment is working, if the fault echo return time is measured to be t (in ns), the actual fault location is: Unit: m.

7. The method as described in claim 6, characterized in that, In step (1), because the transmitted detection signal takes a certain amount of time to propagate through the cable to the fault point and then reflect back, before this time, the data collected by the ADC only includes the interference signal that leaks from the transmitted signal to the receiving interface through the transformer, and does not include the fault echo.

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