CN113295081B - Time-frequency domain-based coiled cable length measurement system and method - Google Patents
Time-frequency domain-based coiled cable length measurement system and method Download PDFInfo
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- CN113295081B CN113295081B CN202110404336.4A CN202110404336A CN113295081B CN 113295081 B CN113295081 B CN 113295081B CN 202110404336 A CN202110404336 A CN 202110404336A CN 113295081 B CN113295081 B CN 113295081B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
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Abstract
The invention discloses a time-frequency domain-based length measurement system and a time-frequency domain-based length measurement method for a coiled cable, wherein the system comprises the following steps: a cable to be tested; the signal injection module is used for inputting voltage signals to the cable to be tested; the signal detection module is used for acquiring a voltage signal in the cable to be detected; the data processing module is used for calculating the length of the cable on the disc according to the measurement result of the signal detection module; the signal injection module comprises a pair of output terminals, a signal detection module, a cable core and a metal sheath, wherein the pair of output terminals of the signal injection module are respectively connected to the cable core and the metal sheath at one end of a cable to be detected, one channel of the signal detection module is connected to the cable core and the metal sheath at the head end of the cable to be detected, and the other channel of the signal detection module is connected to the cable core and the metal sheath at the tail end of the cable to be detected. The method is based on the measurement of the propagation time and propagation speed of the high-frequency sinusoidal voltage signal in the coiled cable, calculates the length of the cable, ensures the precision of the detection of the coiled cable length from the aspects of wave speed and traveling wave time, is simple and practical, and has wide practical value.
Description
Technical Field
The invention belongs to the field of power cable detection, and particularly relates to a time-frequency domain-based coiled cable length measuring system and method.
Background
The power cable is one of core equipment for bearing power transmission in a power system, has a series of advantages of small space occupation, small environmental impact, high reliability and the like, and is a main power transmission way for urban power supply at present. At present, in the construction process of the power cable, the problems of increased cost, delayed construction period and the like caused by the fact that the actual length of the cable is smaller than the nominal length occur. Therefore, it is necessary to perform length detection before cabling.
The length measurement of the traditional coiled cable needs rewinding, is time-consuming and labor-consuming, and can damage the insulation appearance of the cable in the operation process. The direct current resistance measurement is greatly influenced by temperature, and in addition, the quality problems of inferior filling, insufficient section and the like of cable materials can also directly influence the measurement result.
Disclosure of Invention
The invention aims to: the invention aims to provide a time-frequency domain-based length measuring system for a coiled cable, which can be used for rapidly and effectively measuring the length of the coiled cable; the invention also aims to provide a measuring method suitable for the system, which solves the problem of large error caused by judging the time difference by a threshold value only by adopting a time-frequency domain combination mode and realizes the accurate verification of the length of the coiled cable.
The technical scheme is as follows: a coil cable length measuring system based on a time-frequency domain comprises a cable to be measured; the signal injection module is used for inputting voltage signals to the cable to be tested; the signal detection module is used for acquiring a voltage signal in the cable to be detected; the data processing module is used for calculating the length of the cable on the disc according to the measurement result of the signal detection module; the signal injection module comprises a pair of output terminals, a signal detection module, a cable core and a metal sheath, wherein the pair of output terminals of the signal injection module are respectively connected to the cable core and the metal sheath at one end of a cable to be detected, one channel of the signal detection module is connected to the cable core and the metal sheath at the head end of the cable to be detected, and the other channel of the signal detection module is connected to the cable core and the metal sheath at the tail end of the cable to be detected.
Further, the signal injection module is a high-frequency alternating current signal source.
Further, the signal detection module is a multichannel high-speed oscilloscope.
Further, the impedance of the signal cable of the multichannel high-speed oscilloscope is matched or approximate to that of the cable to be tested, so that the reflection of the travelling wave signal is reduced.
Further, the parameters of the cable to be tested are the same as those of the coiled cable, and the cable to be tested is clung to other turns of the cable along the winding direction of the coiled cable.
The length measuring method of the coiled cable based on the time-frequency domain comprises the following steps of:
step 1, selecting a set length L 0 Is input with a set frequency f to the head end of the cable to be tested 0 Is measured at the head end 01 End measuring first end voltage signal u 02 ；
Step 2, using the first head-end voltage signal u 01 And a first terminal voltage signal u 02 The time difference of the wave crest or the wave trough of the corresponding sequence is combined with the first head-end voltage signal u 01 And a first terminal voltage signal u 02 Calculating the propagation time t of the first voltage signal in the cable under test 0 Thereby obtaining the wave velocity v of the coiled cable;
step 3, inputting the set frequency f to the head end of the coiled cable 0 A second head-end voltage signal u is measured at the head-end 1 End measuring second end voltage signal u 2 ，
Step 4, using the second head-end voltage signal u 1 And a second terminal voltage signal u 2 The time difference of the wave crest or the wave trough of the corresponding sequence is combined with the second head end voltage signal u 1 And a second terminal voltage signal u 2 Calculates a second voltageThe propagation time t of the signal in the cable in a reel;
and 5, obtaining the length of the coiled cable according to the wave speed v in the step 2 and the propagation time t in the step 4.
Further, in step 1, the parameters of the cable to be tested and the parameters of the coiled cable are the same, and the length of the cable to be tested is greater than 1 meter.
Further, in step 1, the frequency f of the first voltage signal 0 The value range of (2) is f 0 ≥20MHz。
Further, in step 2, the propagation time t of the signal in the cable under test is calculated 0 The expression of (2) is:
wherein:
Δt 0 representing a first head-end voltage signal u 01 And a first terminal voltage signal u 02 The time differences of the peaks or troughs of the corresponding sequence,
f 0 representing the frequency of the first voltage signal,
representing the rounding-down symbol,
representing the first terminal voltage signal u 02 Leading the first head-end voltage signal u 01 Is a function of the angle of (2);
the wave speed of the coiled cable is the same as the wave speed of the cable to be tested, and the wave speed v expression of the cable to be tested is as follows:
wherein:
L 0 indicating the length of the cable to be tested,
t 0 representing the propagation time of the signal in the cable under test.
Further, in step 4, the expression for calculating the propagation time t of the signal in the cable is:
wherein:
Δt represents the head-end voltage signal u obtained from the measurement result of the high-speed oscilloscope 1 And a terminal voltage signal u 2 The time difference between the first peak values,
f 0 representing the frequency of the second voltage signal,
representing the rounding-down symbol,
representing a second terminal voltage signal u 2 Leading the second head-end voltage signal u 1 Is a function of the angle of (2);
in step 5, the expression for calculating the length L of the cable is:
L＝vt
wherein:
v represents the cable wave velocity of the cable under test,
t represents the propagation time of the second voltage signal in the cable of the reel.
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages: calculating the length of the cable based on the measurement of the propagation time and propagation speed of the high frequency sinusoidal voltage signal in the coiled cable; adopting a cable to be tested with the same parameters as the coiled cable, and carrying out on-site calibration of the wave speed by considering the turn-to-turn mutual inductance of the cable under the same environment; the method has the advantages that the mode of detecting the two ends of the head and the tail ends of the cable is adopted, the traveling wave signals injected into the cable and reaching the tail ends of the cable are accurately detected, the traveling time and the traveling speed of the traveling wave in the cable are accurately obtained, the precision of the length detection of the coiled cable is ensured from the two aspects of the traveling wave speed and the traveling wave time, and the method is simple and practical.
Drawings
Fig. 1 is a flowchart of a time-frequency domain-based length measurement method for a coiled cable provided by the invention;
fig. 2 is a schematic diagram of a time-frequency domain combined cable length measurement system.
Detailed Description
As shown in fig. 1, the invention provides a time-frequency domain-based length measurement method for a coiled cable, which comprises the following steps:
step 1, selecting a set length L 0 A pair of output terminals of the high-frequency alternating current signal source 4 are respectively connected to the cable core 2 and the metal sheath 3 of the calibration cable 1, and a set frequency f is input to the head end of the calibration cable 0 Is provided for the first voltage signal of (a). One channel of the multichannel high-speed oscilloscope 5 is connected to the cable core and the metal sheath at the head end of the calibration cable 1, the other channel is connected to the cable core and the metal sheath at the tail end of the calibration cable 1, and the first head-end voltage signal u is synchronously measured at the head end 01 End measuring first end voltage signal u 02 。
When the wave speed is marked, the double-end signal measurement is adopted, so that the signal recognition rate can be effectively improved.
Wherein the parameters of the calibration cable and the coiled cable are the same, the short cable with the same model and the same batch is selected, or a section of the short cable is directly cut at the head end of the coiled cable to be used as the calibration cable, the length can be between 1 and 2 meters, and the actual length L is obtained by measuring by using a length measuring tool, such as a meter or a tape measure 0 。
Under the same environment, the calibrating cable is tightly attached to other turns of cables along the cable winding direction in the wire loading disc, and is used for wave speed calibration under the condition of considering mutual inductance.
Frequency f of the first voltage signal 0 The value range of (2) is f 0 ≥20MHz。
Step 2, using the first head-end voltage signal u 01 And a first terminal voltage signal u 02 Peaks or waves of corresponding orderThe time difference of the valley is combined with the first head-end voltage signal u 01 And a first terminal voltage signal u 02 Calculating the propagation time t of the first voltage signal in the calibration cable 0 And further obtaining the wave velocity v of the coiled cable.
Calculating the propagation time t of the signal in the calibration cable 1 0 ：
Wherein:
Δt 0 representing a first head-end voltage signal u 01 And a first terminal voltage signal u 02 The time difference of the peaks or troughs of the corresponding sequence.
f 0 The frequency at which the high-frequency ac signal source 4 outputs a sinusoidal ac voltage is shown.
Representing a rounding-down symbol, e.g.>Representing the number of cycles that a signal has undergone from the time it is injected into the head end of the calibration cable to the time it reaches the end of the coiled cable.
Representing the first terminal voltage signal u 02 Leading the first head-end voltage signal u 01 In angular units, is obtained from measurement signals over a plurality of periods, such as, but not limited to, calibrating the average phase difference over a plurality of periods of the cable head and end signals.
The cable wave velocity v of the calibration cable is calculated by the following formula:
wherein:
L 0 indicating the length of the calibration cable.
t 0 Representing the propagation time of the signal in the calibration cable 1.
Step 3, the same high-frequency signal source 4 as the calibration of the cable is adopted to replace the calibration cable 1 shown in fig. 2 with a coiled cable by a multichannel high-speed oscilloscope 5, a pair of output terminals of the high-frequency alternating-current signal source 4 are respectively connected to a cable core and a metal sheath at the head end of the coiled cable, the high-frequency alternating-current signal source 4 outputs a high-frequency sinusoidal alternating-current voltage with the same frequency as the wave speed calibration, namely, the set frequency f is input to the head end of the coiled cable 0 One channel of the multichannel high-speed oscilloscope 5 is connected to the cable core and the metal sheath at the head end of the coiled cable, the other channel is connected to the cable core and the metal sheath at the tail end of the coiled cable, and the multichannel high-speed oscilloscope 5 synchronously measures a second head-end voltage signal u at the head end 1 End measuring second end voltage signal u 2 。
Step 4, using the second head-end voltage signal u 1 And a second terminal voltage signal u 2 The time difference of the wave crest or the wave trough of the corresponding sequence is combined with the second head end voltage signal u 1 And a second terminal voltage signal u 2 Calculates the propagation time t of the second voltage signal in the cable.
The propagation time of the signal in the cable is calculated with the following formula:
wherein:
Δt represents the head-end voltage signal u obtained from the measurement result of the high-speed oscilloscope 5 1 And a terminal voltage signal u 2 The time difference between the first peaks.
f 0 The frequency at which the high-frequency ac signal source 4 outputs a sinusoidal ac voltage is shown.
Representing a rounding-down symbol, e.g.>Representing the number of cycles that a signal has undergone from the start of the signal injection into the cable to the end of the cable.
Representing the terminal voltage signal u 2 Leading head end voltage signal u 1 The angular unit may be obtained from measurement signals over a plurality of periods, such as, but not limited to, the average phase difference over a plurality of periods of the head and tail signals of the cable.
And 5, multiplying the wave velocity v of the coiled cable obtained in the step 2 by the propagation time t of the second voltage signal in the coiled cable obtained in the step 4 to obtain the length of the coiled cable.
The length of the cable L is calculated as follows:
L＝vt
wherein:
v represents the cable wave speed of the calibration cable.
t represents the propagation time of the signal in the cable.
As shown in fig. 2, the present invention further provides a time-frequency domain combined length measurement system for a coiled cable, which includes: the device comprises a wave speed calibration module, a signal injection module, a signal detection module and a data processing module.
The wave speed calibration module comprises a calibration cable and is used for acquiring the signal propagation speed in the coiled cable. The wave speed calibration module further comprises: a length measuring tool for measuring and obtaining the actual length L of the calibration cable 0 The parameter of the marked cable is the same as that of the coiled cable, and the marked cable is clung to other turns of cable along the cable winding direction in the wire-loading disc.
The signal injection module is connected with the head end of the calibration cable or the coiled cable and is used for inputting the set frequency f to the head end of the calibration cable 0 Or input a set frequency f to the head end of the coiled cable 0 Is a second electricity of (2)A pressure signal; the signal injection module includes: the high-frequency alternating current signal source 4, and a pair of output terminals of the high-frequency alternating current signal source 4 are respectively connected to a cable core and a metal sheath at the head end of the calibration cable or the coiled cable. Frequency f of the first and second voltage signals 0 The value range of (2) is f 0 ≥20MHz。
The signal detection module is respectively connected with the head end and the tail end of the calibration cable or the head end and the tail end of the coiled cable to obtain the time difference and the phase difference of the signals at the head end and the tail end; the signal detection module includes: a multichannel high-speed oscilloscope 5, wherein one channel of the multichannel high-speed oscilloscope 5 is connected to a cable core and a metal sheath at the head end of a calibration cable or a coiled cable, and the other channel of the multichannel high-speed oscilloscope 5 is connected to a cable core and a metal sheath at the tail end of the calibration cable or the coiled cable; measuring a first head-end voltage signal u at the head end of the calibration cable 01 End measuring first end voltage signal u 02 Measuring a second head-end voltage signal u at the head end of the coiled cable 1 End measuring second end voltage signal u 2 Obtaining a first head-end voltage signal u 01 And a first terminal voltage signal u 02 Time differences of peaks or troughs of corresponding order, and first head-end voltage signal u 01 And a first terminal voltage signal u 02 Obtain the second head-end voltage signal u 1 And a second terminal voltage signal u 2 Time differences of peaks or troughs of corresponding order, and a second head-end voltage signal u 1 And a second terminal voltage signal u 2 Is a phase difference of (a) and (b).
The signal cable of the multichannel high-speed oscilloscope 5 is matched or approximate to the impedance of the calibration cable or the coiled cable, and is used for reducing the reflection of traveling wave signals. A preferred but non-limiting embodiment is one where a standing wave ratio of less than 3 is considered to be close to the impedance of the nominal or coiled cable.
And the data processing module is used for calculating the wave speed v of the cable and the length of the cable by using the measurement result of the signal detection module. The data processing module is combined with the first head-end voltage signal u 01 And a first terminal voltage signal u 02 Calculates the phase difference of the first voltage signal in the calibration cablePropagation time t of (2) 0 Further obtaining the wave velocity v of the coiled cable, using the second head-end voltage signal u 1 And a second terminal voltage signal u 2 The time difference of the wave crest or the wave trough of the corresponding sequence is combined with the second head end voltage signal u 1 And a second terminal voltage signal u 2 Calculates the propagation time t of the second voltage signal in the cable.
The implementation of the invention is beneficial to accurately acquiring the actual length of the cable during the test of the coiled cable, on one hand, whether the supplier has the work-stealing and material-reducing effects or not can be timely found, and unnecessary economic loss is avoided; on the other hand, the construction inconvenience caused by the inconsistency of the nominal length and the actual length can be avoided.
Claims (3)
1. A length measuring method of a coiled cable length measuring system based on a time-frequency domain is characterized in that the coiled cable length measuring system based on the time-frequency domain comprises a cable to be measured; the signal injection module is used for inputting voltage signals to the cable to be tested; the signal detection module is used for acquiring a voltage signal in the cable to be detected; the data processing module is used for calculating the length of the cable on the disc according to the measurement result of the signal detection module; the signal injection module comprises a signal injection module, a signal detection module and a signal detection module, wherein the signal injection module is connected with a cable core and a metal sheath at one end of a cable to be detected respectively; the signal injection module is a high-frequency alternating current signal source; the signal detection module is a multichannel high-speed oscilloscope; the signal cable of the multichannel high-speed oscilloscope is matched with or close to the impedance of the cable to be tested; the parameters of the cable to be tested are the same as those of the coiled cable, and the cable to be tested is clung to other turns of cables along the winding direction of the coiled cable;
the length measuring method comprises the following steps:
step 1, selecting a set length L 0 Is input with a set frequency f to the head end of the cable to be tested 0 Is measured at the head end 01 End measurement of first endVoltage signal u 02 ；
Step 2, using the first head-end voltage signal u 01 And a first terminal voltage signal u 02 The time difference of the wave crest or the wave trough of the corresponding sequence is combined with the first head-end voltage signal u 01 And a first terminal voltage signal u 02 Calculating the propagation time t of the first voltage signal in the cable under test 0 Thereby obtaining the wave velocity v of the coiled cable;
calculating the propagation time t of a signal in a cable under test 0 The expression of (2) is:
wherein:
Δt 0 representing a first head-end voltage signal u 01 And a first terminal voltage signal u 02 The time differences of the peaks or troughs of the corresponding sequence,
f 0 representing the frequency of the first voltage signal,
representing the rounding-down symbol,
representing the first terminal voltage signal u 02 Leading the first head-end voltage signal u 01 Is a function of the angle of (2);
the wave speed of the coiled cable is the same as the wave speed of the cable to be tested, and the wave speed v expression of the cable to be tested is as follows:
wherein:
L 0 indicating the length of the cable to be tested,
t 0 representation ofPropagation time of the signal in the cable under test;
step 3, inputting the set frequency f to the head end of the coiled cable 0 A second head-end voltage signal u is measured at the head-end 1 End measuring second end voltage signal u 2 ；
Step 4, using the second head-end voltage signal u 1 And a second terminal voltage signal u 2 The time difference of the wave crest or the wave trough of the corresponding sequence is combined with the second head end voltage signal u 1 And a second terminal voltage signal u 2 Calculating the propagation time t of the second voltage signal in the cable; the expression for calculating the propagation time t of the signal in the cable is:
wherein:
Δt represents the head-end voltage signal u obtained from the measurement result of the high-speed oscilloscope 1 And a terminal voltage signal u 2 The time difference between the first peak values,
f 0 representing the frequency of the second voltage signal,
representing the rounding-down symbol,
representing a second terminal voltage signal u 2 Leading the second head-end voltage signal u 1 Is a function of the angle of (2);
step 5, obtaining the length of the coiled cable according to the wave velocity v in the step 2 and the propagation time t in the step 4; the expression of the length L of the coiled cable is:
L＝vt
wherein:
v represents the cable wave velocity of the cable under test,
t represents the propagation time of the second voltage signal in the cable of the reel.
2. The length measuring method of the time-frequency domain-based reeled cable length measuring system according to claim 1, wherein in the step 1, the cable to be measured has the same parameters as the reeled cable, and the length of the cable to be measured is greater than 1 meter.
3. The length measuring method using a time-frequency domain based cable-on-board system according to claim 1, wherein in step 1, the frequency f of the first voltage signal 0 The value range of (2) is f 0 ≥20MHz。
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