Waste cable identification method based on low-frequency signals

Abstract

The invention belongs to the technical field of cable identification, and discloses a waste cable identification method based on a low-frequency signal, and the method comprises the following steps: S1, signal injection; s2, signal detection; s3, signal anti-interference processing; s4, identifying the waste cable; the method has the advantages that the waste cable and the ground form a loop, low-frequency characteristic signals are input and injected into the loop, original current signals are detected through the handheld device and the split core type current transformer, anti-interference processing is carried out on the signals, the recognition accuracy is improved, detection characteristic information is obtained through FFT calculation, the detection characteristic information is compared with reference characteristic information, and the recognition accuracy is improved. Based on error judgment, whether a dog is a waste target cable is judged, operation is convenient and can be operated by a single person, efficiency is greatly improved, and major potential safety hazards such as direct-current locking caused by mistakenly cutting the running cable are prevented.

Description

Technical Field

[0001] This invention relates to the field of cable identification technology, and specifically to a method for identifying waste cables based on low-frequency signals. Background Technology

[0002] As converter stations operate for longer periods and more upgrade projects are undertaken, abandoned cables accumulate in cable trenches, occupying significant space and hindering the laying of new cables. Currently, when handling abandoned cables, both ends have labels, making it easy to identify the same cable. However, due to the complex environment within the cable trench, the large number of cables, and their similar appearances, it is difficult to accurately identify abandoned cables in the middle section. The only solution is to cut and extract them in sections, which poses a significant safety hazard, such as accidentally cutting an operational cable and causing DC power outage. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for identifying waste cables based on low-frequency signals. This invention is achieved through the following technical solutions.

[0004] A method for identifying waste cables based on low-frequency signals includes the following steps:

[0005] S1, signal injection;

[0006] One end of the waste cable is grounded, and the other end is connected to the signal output terminal of the portable signal source. The power terminal of the portable signal source is connected to the ground. The waste cable and the ground form a detection circuit. The portable signal source injects a low-frequency characteristic signal into the circuit.

[0007] S2, signal detection;

[0008] Connect the handheld device to the clamp-on current transformer, use the clamp-on current transformer to clamp the scrap cable, the clamp-on current transformer detects the original current signal of the scrap cable through its built-in sampling circuit, and converts the original current signal into an original voltage analog signal.

[0009] S3, signal anti-interference processing;

[0010] The original analog voltage signal is amplified by a two-stage amplifier circuit to obtain an amplified analog voltage signal. The handheld device has a built-in microcontroller. The amplified analog voltage signal is input into the microcontroller through the analog-to-digital sampling interface and stored. The microcontroller processes the stored amplified analog voltage signal using a low-pass filtering algorithm to obtain a filtered digital voltage signal.

[0011] S4, identification of waste cables;

[0012] The handheld device's built-in microcontroller is wirelessly connected to a portable signal source. The portable signal source transmits reference feature information of the low-frequency characteristic signal to the microcontroller via wireless communication. The microcontroller performs FFT calculation on the filtered voltage digital signal to obtain detection feature information. It then calculates the error between the reference feature information and the detection feature information to determine whether the target cable is a waste cable.

[0013] As a further aspect of the present invention, in step S1, the low-frequency characteristic signal is a voltage sine wave signal with a voltage of 5V, a frequency of 0.5Hz, and a power of 0.03W.

[0014] As a further embodiment of the present invention, in step S1, the power interface of the portable signal source is connected to the output end of the power adapter, and the input end of the power adapter is connected to a 220V AC power supply.

[0015] As a further aspect of the present invention, in step S2, the sampling time of the clamp-on current transformer is 5 seconds, and the sampling frequency is 2 times / second.

[0016] As a further embodiment of the present invention, in step S3, the secondary amplifier circuit includes operational amplifier U1 and operational amplifier U2;

[0017] The operational amplifier U1's interface 2 is electrically connected to the output of the sampling circuit; the operational amplifier U1's interface 3 is connected to a 2.2V DC power supply through resistor R2 and grounded through resistor R3; the operational amplifier U1's interface 5 is connected to a 3.3V DC power supply and grounded through capacitor C2; the operational amplifier U1's interface 4 is grounded; a resistor R4 and a capacitor C1 are connected in parallel between the operational amplifier U1's interfaces 1 and 2.

[0018] The 7th port of the operational amplifier U2 is connected to the 1st port of the operational amplifier U1 via resistor R7; the 6th port of the operational amplifier U2 is connected in parallel with one end of capacitor C3, resistor R6, and resistor R5, the other end of resistor R5 is connected to the digital analog reference voltage DAC_VOL, and the other end of capacitor C3 is connected to the other end of resistor R6 on one side and grounded on the other side; the 7th and 8th ports of the operational amplifier U2 are directly connected in parallel with resistor R8 and capacitor C4.

[0019] The 8th pin of the operational amplifier U2 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the analog-to-digital sampling interface of the microcontroller.

[0020] As a further embodiment of the present invention, the end of the resistor R9 away from the No. 8 interface of the operational amplifier U2 is grounded through the capacitor C5.

[0021] As a further embodiment of the present invention, the resistance values ​​of resistors R2, R3, R4, R5, R6, R7, R8 and R9 are 100KΩ, 10Ω, 50Ω, 10Ω, 20KΩ, 2KΩ, 40KΩ and 1KΩ, respectively.

[0022] As a further embodiment of the present invention, the capacitance values ​​of capacitors C1, C2, C3, C4 and C5 are 1μF, 0.1μF, 0.01μF, 1μF and 0.1μF, respectively.

[0023] As a further aspect of the present invention, the FFT calculation method in step S4 is as follows:

[0024] The detection circuit of the waste cable is simplified into an equivalent circuit. In the equivalent circuit, the resistance of the equivalent resistor is R and the capacitance of the equivalent capacitor is C.

[0025] An impedance-capacitive reactance circuit model is established based on the equivalent circuit, where the impedance Z R The expression is:

[0026] Z R =R (1)

[0027] Capacitive Z C The expression is:

[0028]

[0029] Where ω is the angular frequency;

[0030] The total impedance Z is Z0 R With Z C If the cables are connected in parallel, then the expression for the current I in the waste cable is:

[0031]

[0032] From equation (3), the expressions for the amplitude and phase of the current can be derived as follows:

[0033] Amplitude:

[0034] Phase:

[0035] Among them, V S This refers to the voltage in the discarded cable.

[0036] As a further aspect of the present invention, the amplitude and phase of the current can be calculated according to equations (4) and (5), and compared with the reference feature information transmitted by the portable signal source. If the amplitude error is within 10% and the phase error is within 5%, the cable is determined to be a scrap target cable.

[0037] The beneficial effects of this invention are that it forms a loop between the waste cable and the ground, injects a low-frequency characteristic signal into the loop, detects the original current signal through a handheld device and a clamp-on current transformer, performs anti-interference processing on the signal to improve the identification accuracy, obtains the detection feature information through FFT calculation, compares it with the reference feature information, and judges the cable as a waste cable based on the error. The operation is convenient and can be operated by a single person, which greatly improves efficiency and prevents major safety hazards such as DC blockage caused by accidental cutting of operating cables. Attached Figure Description

[0038] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart illustrating the method for identifying waste cables;

[0040] Figure 2 Wiring diagram for identifying scrap cables;

[0041] Figure 3 Wiring diagram for the sampling circuit and the second-stage amplifier circuit;

[0042] Figure 4 A schematic diagram of the equivalent circuit for identifying waste cables. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] A method for identifying waste cables based on low-frequency signals includes the following steps:

[0045] S1, signal injection.

[0046] like Figure 1 As shown, one end of the waste cable is grounded, and the other end is connected to the signal output terminal of the portable signal source. The power terminal of the portable signal source is connected to the ground. The waste cable and the ground form a detection loop, and the portable signal source injects a low-frequency characteristic signal into the loop.

[0047] The low-frequency characteristic signal is a voltage sine wave signal with a voltage of 5V, a frequency of 0.5Hz, and a power of 0.03W. The power interface of the portable signal source is connected to the output terminal of the power adapter, and the input terminal of the power adapter is connected to a 220V AC power supply.

[0048] The specific steps are as follows:

[0049] S1.1, ground one end of the waste cable;

[0050] S1.2, the other end of the waste cable is connected to the signal output terminal of the portable signal source;

[0051] S1.3, simultaneously connect the grounding terminal of the portable signal source to the earth;

[0052] S1.4, after confirming that the portable signal source is switched to "off", connect the dedicated connector of the power adapter to the "power" interface of the portable signal source and connect the adapter to a 220V AC power supply.

[0053] S1.5, switch the portable signal source from "off" to "on" and wait for the portable signal source test circuit status to ensure that the low-frequency characteristic signal is accurately injected into the located waste cable.

[0054] S1.6 When the portable signal source displays "Circuit normal, please find the cable", it means that the signal circuit of the scrap cable has been established;

[0055] S1.7 When the portable signal source displays "Circuit abnormal, please confirm that the other end of the cable is reliably grounded", it means that the other end of the waste cable is not grounded or the grounding is unreliable. The portable signal source has no reliable circuit to inject signals. Then, repeat the troubleshooting steps in S1.1-S1.6.

[0056] S2, signal detection.

[0057] like Figure 2 As shown, the handheld device is connected to the clamp-on current transformer. The clamp-on current transformer is used to clamp the waste cable. The clamp-on current transformer detects the original current signal of the waste cable through its built-in sampling circuit and converts the original current signal into an original voltage analog signal. The sampling time of the clamp-on current transformer is 5 seconds and the sampling frequency is 2 times / second.

[0058] like Figure 3 As shown, in the sampling circuit, JACK1 and JACK2 are the CT parts of the clamp-on current transformer, which are responsible for acquiring low-frequency signals from the waste cable.

[0059] The specific steps are as follows:

[0060] S2.1 Connect the clamp-on current transformer and the handheld device.

[0061] S2.2, turn on the handheld device and ensure it has sufficient power. If the handheld device displays "Low battery power", please replace the handheld device battery before continuing to use it.

[0062] S2.3 When the handheld device displays "Please follow the prompts, please press the test button to continue operation", press the "test" button to enable communication between the portable signal source and the handheld device;

[0063] S2.4 When the handheld device displays "Please press the zero adjustment key, please keep the clamp suspended and still", keep the clamp current transformer in a suspended horizontal state and press the "zero adjustment" key to zero it;

[0064] S2.5 When the handheld device displays "Please press the self-calibration button, please clamp the clamp onto the yellow ground wire and keep it still", clamp the clamp-on current transformer onto the ground wire, keep the clamp still, and press the "self-calibration" button to perform self-calibration.

[0065] S2.6 When the handheld device displays "Equipment normal, please press the test button to find grounding", it means that the handheld device has passed self-calibration. When locating and finding the cable, clamp the clamp current transformer onto the corresponding cable and press the "test button" to perform the test.

[0066] S3, signal anti-interference processing;

[0067] like Figure 3 As shown, the original analog voltage signal is amplified by a two-stage amplifier circuit to obtain an amplified analog voltage signal. The handheld device has a built-in microcontroller. The amplified analog voltage signal is input into the microcontroller through the analog-to-digital sampling interface and stored. The microcontroller processes the stored amplified analog voltage signal using a low-pass filtering algorithm to obtain a filtered digital voltage signal.

[0068] The two-stage amplifier circuit includes operational amplifier U1 and operational amplifier U2;

[0069] The second port of operational amplifier U1 is electrically connected to the output of the sampling circuit; the third port of operational amplifier U1 is connected to a 2.2V DC power supply through resistor R2 and grounded through resistor R3; the fifth port of operational amplifier U1 is connected to a 3.3V DC power supply and grounded through capacitor C2; the fourth port of operational amplifier U1 is grounded; a resistor R4 and a capacitor C1 are connected in parallel between the first and second ports of operational amplifier U1.

[0070] Pin 7 of operational amplifier U2 is connected to pin 1 of operational amplifier U1 via resistor R7; pin 6 of operational amplifier U2 is connected in parallel with one end of capacitor C3, resistor R6, and resistor R5, with the other end of resistor R5 connected to the digital analog reference voltage DAC_VOL; the other end of capacitor C3 is connected to the other end of resistor R6 on one side and grounded on the other; pins 7 and 8 of operational amplifier U2 are directly connected in parallel with resistor R8 and capacitor C4.

[0071] The 8th pin of the operational amplifier U2 is connected to one end of the resistor R9. The other end of the resistor R9 is connected to the analog-digital sampling interface of the microcontroller on one hand, and grounded through the capacitor C5 on the other.

[0072] The resistance values ​​of resistors R2, R3, R4, R5, R6, R7, R8, and R9 are 100KΩ, 10Ω, 50Ω, 10Ω, 20KΩ, 2KΩ, 40KΩ, and 1KΩ, respectively; the capacitance values ​​of capacitors C1, C2, C3, C4, and C5 are 1μF, 0.1μF, 0.01μF, 1μF, and 0.1μF, respectively.

[0073] Figure 3 In the circuit, operational amplifiers U1 and U2 are model AD8552. Feedback capacitors C1 and C4 are low-pass amplifiers, C5 is used to filter high-frequency interference signals, DAC_VOL is the digital analog reference voltage, and AD_MAX is the input voltage signal to the microcontroller.

[0074] S4, identification of scrap cables;

[0075] The handheld device's built-in microcontroller is wirelessly connected to a portable signal source. The portable signal source transmits reference feature information of the low-frequency characteristic signal to the microcontroller via wireless communication. The microcontroller performs FFT calculation on the filtered voltage digital signal to obtain detection feature information. It then calculates the error between the reference feature information and the detection feature information to determine whether the target cable is a waste cable.

[0076] Figure 4 This is a schematic diagram of the equivalent circuit.

[0077] The method for calculating FFT is as follows:

[0078] The detection circuit of the waste cable is simplified into an equivalent circuit. In the equivalent circuit, the resistance of the equivalent resistor is R and the capacitance of the equivalent capacitor is C.

[0079] An impedance-capacitive reactance circuit model is established based on the equivalent circuit, where the impedance Z R The expression is:

[0080] Z R =R (1)

[0081] Capacitive Z C The expression is:

[0082]

[0083] Where ω is the angular frequency;

[0084] The total impedance Z is Z0 R With Z C If the cables are connected in parallel, then the expression for the current I in the waste cable is:

[0085]

[0086] From equation (3), the expressions for the amplitude and phase of the current can be derived as follows:

[0087] Amplitude:

[0088] Phase:

[0089] Among them, V S This refers to the voltage in the discarded cable.

[0090] As can be seen from the above formula, considering the distributed parameters of the waste cable, at a low frequency of 0.5Hz, if the waste cable is short, ωRC is much less than 1, so the distributed capacitive reactance has little impact on the low frequency current signal; if the cable is long, capacitive phase shift needs to be considered.

[0091] According to equations (4) and (5), the amplitude and phase of the current can be calculated respectively. They are compared with the reference characteristic information sent by the portable signal source. If the amplitude error is within 10% and the phase error is within 5%, the cable is judged to be a scrap target cable.

[0092] The handheld device's built-in microcontroller wirelessly connects to a portable signal generator. The portable signal generator transmits reference characteristic information of the low-frequency characteristic signal to the microcontroller via wireless communication. The microcontroller performs FFT calculations on the filtered voltage digital signal to obtain detection characteristic information. It then calculates the error between the reference characteristic information and the detection characteristic information to determine whether the cable is a waste cable.

[0093] The specific steps are as follows:

[0094] S4.1 Perform FFT calculation on the digital signal of the filtered voltage to obtain detection feature information such as current amplitude and phase, and obtain detection feature information of circuit frequency;

[0095] S4.2, compare the reference feature information received from the portable signal source with the detection feature information and calculate the error;

[0096] S4.3 If the frequency error is within ±0.05Hz, the amplitude error is within 10%, and the phase error is within 5%, the cable is determined to be the scrap target cable. When the handheld device displays "Correct cable, grounding end is in the positive direction", the clamped cable is the scrap target cable to be located, and the direction pointed to by the arrow of the clamp-on current transformer is the grounding end of the scrap cable.

[0097] S4.4 If the error requirement is not met, the handheld device will display "Incorrect cable, please continue searching". Clamp the clamp current transformer to the other cable for testing.

[0098] The flowchart of the waste cable identification method is as follows: Figure 1 As shown.

[0099] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to any specific implementation. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A method for identifying waste cables based on low-frequency signals, characterized in that, Includes the following steps: S1, signal injection; One end of the waste cable is grounded, and the other end is connected to the signal output terminal of the portable signal source. The power terminal of the portable signal source is connected to the ground. The waste cable and the ground form a detection circuit. The portable signal source injects a low-frequency characteristic signal into the circuit. S2, signal detection; Connect the handheld device to the clamp-on current transformer, use the clamp-on current transformer to clamp the scrap cable, the clamp-on current transformer detects the original current signal of the scrap cable through its built-in sampling circuit, and converts the original current signal into an original voltage analog signal. S3, signal anti-interference processing; The original analog voltage signal is amplified by a two-stage amplifier circuit to obtain an amplified analog voltage signal. The handheld device has a built-in microcontroller. The amplified analog voltage signal is input into the microcontroller through the analog-to-digital sampling interface and stored. The microcontroller processes the stored amplified analog voltage signal using a low-pass filtering algorithm to obtain a filtered digital voltage signal. S4, identification of waste cables; The handheld device's built-in microcontroller is wirelessly connected to a portable signal source. The portable signal source transmits reference feature information of the low-frequency characteristic signal to the microcontroller via wireless communication. The microcontroller performs FFT calculation on the filtered voltage digital signal to obtain detection feature information. It then calculates the error between the reference feature information and the detection feature information to determine whether the target cable is a waste cable.

2. The method for identifying waste cables based on low-frequency signals according to claim 1, characterized in that, In step S1, the low-frequency characteristic signal is a voltage sine wave signal with a voltage of 5V, a frequency of 0.5Hz, and a power of 0.03W.

3. The method for identifying waste cables based on low-frequency signals according to claim 1, characterized in that, In step S1, the power interface of the portable signal source is connected to the output end of the power adapter, and the input end of the power adapter is connected to a 220V AC power supply.

4. The method for identifying waste cables based on low-frequency signals according to claim 1, characterized in that, In step S2, the sampling time of the clamp-on current transformer is 5 seconds, and the sampling frequency is 2 times / second.

5. The method for identifying waste cables based on low-frequency signals according to claim 1, characterized in that, In step S3, the secondary amplifier circuit includes operational amplifier U1 and operational amplifier U2; The operational amplifier U1's interface 2 is electrically connected to the output of the sampling circuit; the operational amplifier U1's interface 3 is connected to a 2.2V DC power supply through resistor R2 and grounded through resistor R3; the operational amplifier U1's interface 5 is connected to a 3.3V DC power supply and grounded through capacitor C2; the operational amplifier U1's interface 4 is grounded; a resistor R4 and a capacitor C1 are connected in parallel between the operational amplifier U1's interfaces 1 and 2. The 7th port of the operational amplifier U2 is connected to the 1st port of the operational amplifier U1 via resistor R7; the 6th port of the operational amplifier U2 is connected in parallel with one end of capacitor C3, resistor R6, and resistor R5, the other end of resistor R5 is connected to the digital analog reference voltage DAC_VOL, and the other end of capacitor C3 is connected to the other end of resistor R6 on one side and grounded on the other side; the 7th and 8th ports of the operational amplifier U2 are directly connected in parallel with resistor R8 and capacitor C4. The 8th pin of the operational amplifier U2 is connected to one end of the resistor R9, and the other end of the resistor R9 is connected to the analog-to-digital sampling interface of the microcontroller.

6. The method for identifying waste cables based on low-frequency signals according to claim 5, characterized in that, The end of resistor R9 that is furthest from pin 8 of operational amplifier U2 is grounded via capacitor C5.

7. The method for identifying waste cables based on low-frequency signals according to claim 5, characterized in that, The resistance values ​​of resistors R2, R3, R4, R5, R6, R7, R8 and R9 are 100KΩ, 10Ω, 50Ω, 10Ω, 20KΩ, 2KΩ, 40KΩ and 1KΩ, respectively.

8. The method for identifying waste cables based on low-frequency signals according to claim 5, characterized in that, The capacitance values ​​of capacitors C1, C2, C3, C4 and C5 are 1μF, 0.1μF, 0.01μF, 1μF and 0.1μF, respectively.

9. The method for identifying waste cables based on low-frequency signals according to claim 1, characterized in that, In step S4, the FFT calculation method is as follows: The detection circuit of the waste cable is simplified into an equivalent circuit. In the equivalent circuit, the resistance of the equivalent resistor is R and the capacitance of the equivalent capacitor is C. An impedance-capacitive reactance circuit model is established based on the equivalent circuit, where the impedance Z R The expression is: Z R =R (1) Capacitive Z C The expression is: Where ω is the angular frequency; The total impedance Z is Z0 R With Z C If the cables are connected in parallel, then the expression for the current I in the waste cable is: From equation (3), the expressions for the amplitude and phase of the current can be derived as follows: Amplitude: Phase: Among them, V S This refers to the voltage in the discarded cable.

10. The method for identifying waste cables based on low-frequency signals according to claim 9, characterized in that, The amplitude and phase of the current are calculated according to equations (4) and (5) respectively. They are compared with the reference characteristic information sent by the portable signal source. If the amplitude error is within 10% and the phase error is within 5%, the cable is judged to be a scrap target cable.

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