CN116381292B - Single-core cable characteristic impedance measuring clamp, measuring system and measuring method - Google Patents
Single-core cable characteristic impedance measuring clamp, measuring system and measuring method Download PDFInfo
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- 238000002847 impedance measurement Methods 0.000 claims description 33
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- 238000005259 measurement Methods 0.000 claims description 13
- 238000004364 calculation method Methods 0.000 claims description 7
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- 229910052802 copper Inorganic materials 0.000 claims description 3
- 239000010949 copper Substances 0.000 claims description 3
- 229920000915 polyvinyl chloride Polymers 0.000 claims description 3
- 239000004800 polyvinyl chloride Substances 0.000 claims description 3
- 238000012544 monitoring process Methods 0.000 abstract description 10
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- 230000036541 health Effects 0.000 description 8
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
- G01R1/02—General constructional details
- G01R1/04—Housings; Supporting members; Arrangements of terminals
- G01R1/0408—Test fixtures or contact fields; Connectors or connecting adaptors; Test clips; Test sockets
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
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Abstract
The invention discloses a single-core cable characteristic impedance measuring clamp, a measuring system and a measuring method, wherein an inner conductor and an outer conductor form a horn-shaped coaxial structure, a preset gap is reserved between the inner conductor and the outer conductor, insulating media are filled in the preset gap, the inner conductor comprises a connecting column, a horn-shaped inner core and an inner bayonet used for clamping a cable core in a clearance fit mode, the connecting column and the horn-shaped inner core are sequentially connected in an integrated mode, the outer conductor comprises a shell connected in an integrated mode and an outer bayonet used for clamping a cable shielding layer in a clearance fit mode, the tail end of one end, far away from the horn opening, of the horn-shaped coaxial structure is connected with an SMA joint, a needle core of the SMA joint and the connecting column are on the same horizontal line, and the connecting position of the connecting column of the inner conductor and the horn-shaped inner core forms a 135-degree transition angle. The technical effect of accurately measuring the characteristic impedance of the single-core cable and assisting the monitoring of the degradation state of the single-core cable is achieved.
Description
Technical Field
The invention relates to the technical field of cable state detection, in particular to a single-core cable characteristic impedance measuring clamp, a measuring system and a measuring method.
Background
In the transmission and distribution network, direct-buried power cables represented by crosslinked polyethylene cables are widely used because of their excellent characteristics, and annual usage amounts and total holding amounts tend to rise year by year. Researches show that the cable starts to have local cracks, water trees, electric trees and other degradation phenomena after being in service for 5-7 years due to the continuous action of electromagnetic, heat, temperature, mechanical vibration and other environmental factors, and is aggravated along with the time, and finally cable faults are caused, so that the safe operation of the power network is affected. Therefore, in order to reduce inconvenience and loss caused by cable faults to society, new requirements are also put forward on the technical requirements of monitoring the health state and detecting faults of the cable.
The current cable health state monitoring and fault detection technologies are developed according to transmission line theory, basically, the technologies can only judge whether the cable has faults and performance degradation, the degradation degree evaluation of the cable can be realized only by disassembling and analyzing the cable, the process involves various parameter measurement and analysis, and the implementation difficulty is high, so that the optimization method for the degradation degree evaluation of the cable needs to be researched. According to the theory of the transmission line, the characteristic impedance of the cable is determined by the structure and material parameters of the cable, is not influenced by frequency, can keep good consistency in a wide frequency band, and is more convenient and faster to analyze compared with parameters influenced by frequency such as a capacitor. Thus, the change in structure and material can be inversely deduced from the change in characteristic impedance for evaluating the degree of degradation of the cable. Compared with the traditional cable degradation degree evaluation method, the characteristic impedance measurement method has the advantages of simpler and quicker measurement steps, lower hardware requirements, no influence of frequency and higher efficiency. However, the existing device for measuring the characteristic impedance of the single-core cable is lacking, so that the characteristic impedance of the single-core cable is difficult to accurately measure, and the development of the degradation degree evaluation of the single-core cable is hindered.
Disclosure of Invention
The invention provides a single-core cable characteristic impedance measuring clamp, a measuring system and a measuring method, which are used for accurately measuring the characteristic impedance of a single-core cable and assisting in monitoring the degradation state of the single-core cable.
In view of this, a first aspect of the present invention provides a single-core cable characteristic impedance measurement jig comprising an inner conductor, an outer conductor, and an SMA joint;
the inner conductor and the outer conductor form a horn-shaped coaxial structure, a preset gap is reserved between the inner conductor and the outer conductor, and an insulating medium is filled in the preset gap;
the inner conductor comprises a connecting column, a horn-shaped inner core and an inner bayonet used for clamping the cable core in a clearance fit mode, which are integrally and sequentially connected;
the outer conductor comprises an integrally connected shell and an outer clamping opening for clamping the cable shielding layer in a clearance fit manner;
the tail end of one end of the horn-shaped coaxial structure, which is far away from the opening of the horn, is connected with an SMA connector, and the needle core of the SMA connector and the connecting column are on the same horizontal line;
the connecting column of the inner conductor and the connecting position of the horn-shaped inner core form a 135-degree transition angle.
Optionally, the inner bayonet is in clearance fit with the cable core with a thickness of 1mm tolerance, and the outer bayonet is in clearance fit with the cable shield with a thickness of 2mm tolerance.
Optionally, the inner conductor and the outer conductor are copper materials.
Alternatively, the SMA linker is a 50Ω SMA linker.
Optionally, the insulating medium is polyvinyl chloride.
The second aspect of the invention provides a single-core cable characteristic impedance measurement system, which comprises any one of the single-core cable characteristic impedance measurement clamps according to the first aspect, and further comprises a signal generating device, a signal measuring device, an upper computer and a single-core cable to be measured;
the upper computer is connected with the signal generating device and the signal measuring device;
the output end of the signal generating device is connected with the first port of the T-shaped connector through a first signal cable, the input end of the signal measuring device is connected with the second port of the T-shaped connector through a second signal cable, the third port of the T-shaped connector is connected with the SMA connector of the single-core cable characteristic impedance measuring clamp through a third signal cable, and the single-core cable characteristic impedance measuring clamp is connected with the single-core cable to be measured.
Optionally, the first signal cable and the second signal cable are 50Ω signal cables 1m long, and the third signal cable is 50Ω signal cable 5m long.
Optionally, the signal generator is configured to generate the excitation signal having an amplitude of 1V.
Optionally, the signal measurement device is used for measuring the reflection coefficient of the single-core cable to be measured;
the upper computer is used for calculating the characteristic impedance of the single-core cable to be measured according to the reflection coefficient measured by the signal measuring device, and the characteristic impedance calculation formula is as follows:
；
wherein,,is characteristic impedance->Is the reflection coefficient.
A third aspect of the present invention provides a measurement method applied to the single-core cable characteristic impedance measurement system described in any one of the second aspects, including:
connecting an upper computer with a signal generating device and a signal measuring device, connecting the signal generating device and the signal measuring device with a single-core cable characteristic impedance measuring clamp through a T-shaped connector, and connecting the single-core cable characteristic impedance measuring clamp with a single-core cable to be measured;
generating an excitation signal by an upper computer control signal generating device, and acquiring the reflection coefficient measured by a signal measuring device;
and the upper computer calculates the characteristic impedance of the single-core cable to be tested according to the reflection coefficient, and evaluates the degradation degree of the single-core cable to be tested according to the characteristic impedance calculation result of the single-core cable to be tested.
From the above technical scheme, the single-core cable characteristic impedance measuring clamp, the measuring system and the measuring method provided by the invention have the following advantages:
according to the single-core cable characteristic impedance measuring clamp provided by the invention, the inner conductor and the outer conductor form a horn-shaped coaxial structure, a preset gap is reserved between the inner conductor and the outer conductor, an insulating medium is filled in the preset gap, the inner conductor comprises a connecting column, a horn-shaped inner core and an inner bayonet used for clamping a cable core in a clearance fit mode, which are integrally and sequentially connected, and the outer conductor comprises an integrally connected shell and an outer bayonet used for clamping a cable shielding layer in a clearance fit mode. The single-core cable characteristic impedance measuring clamp is connected with the single-core cable in a clearance fit mode, so that the single-core cable characteristic impedance measuring clamp can be clamped on a tested cable, and good electrical contact between the single-core cable characteristic impedance measuring clamp and a cable core and a shielding layer can be maintained. The end of the horn-shaped coaxial structure, which is far away from the opening of the horn, is connected with the SMA connector, the needle core of the SMA connector and the connecting column are on the same horizontal line, and the connecting position of the connecting column of the inner conductor and the horn-shaped inner core is at a 135-degree transition angle, so that the loss and resonance of signals can be reduced. When the characteristic impedance of the cable is measured, the signal is reflected at the single-core cable characteristic impedance measuring clamp, and the characteristic impedance measurement of the single-core high-voltage power cable can be realized by estimating the intensity of the reflected signal. The technical effect of accurately measuring the characteristic impedance of the single-core cable and assisting the monitoring of the degradation state of the single-core cable is achieved.
Meanwhile, the single-core cable characteristic impedance measuring clamp provided by the invention not only can measure the reflection coefficient, but also can measure the reflection coefficient spectrum, and can realize the measurement of the characteristic impedance spectrum of the measured cable.
The invention provides a single-core cable characteristic impedance measurement system, which comprises the single-core cable characteristic impedance measurement clamp provided by the invention, and further comprises a signal generation device, a signal measurement device, an upper computer and a single-core cable to be measured, wherein the upper computer controls the signal generation device to generate an excitation signal, the signal measurement device measures the reflection coefficient of the single-core cable to be measured, and the upper computer calculates the characteristic impedance of the cable according to the reflection coefficient, so that the degradation degree evaluation result of the single-core cable is obtained, the degradation monitoring of the whole health state of the single-core cable is realized, and the single-core cable characteristic impedance measurement system has wide application prospect.
The measuring method applied to the single-core cable characteristic impedance measuring system provided by the invention realizes the overall health state degradation monitoring of the single-core cable.
Drawings
For a clearer description of embodiments of the invention or of solutions according to the prior art, the figures which are used in the description of the embodiments or of the prior art will be briefly described, it being obvious that the figures in the description below are only some embodiments of the invention, from which, without the aid of inventive efforts, other relevant figures can be obtained for a person skilled in the art.
FIG. 1 is a schematic cross-sectional view of a single-core cable characteristic impedance measuring clamp according to the present invention;
FIG. 2 is a schematic structural diagram of a single-core cable characteristic impedance measurement system according to the present invention;
FIG. 3 is a schematic flow chart of a measurement method applied to a single-core cable characteristic impedance measurement system according to the present invention;
wherein, the reference numerals are as follows:
101. the single-core cable characteristic impedance measuring clamp; 102. an upper computer; 103. signal generating devices, 104 and signal measuring devices; 105. a single-core cable to be tested; 106. a T-shaped connector; 107. a first signal cable; 108. a second signal cable; 109. a third signal cable; 1. an outer conductor; 2. an inner conductor; 3. an SMA joint; 4. an insulating medium; 1-1, a shell; 1-2, an outer clamping opening; 2-1, connecting columns; 2-2, a horn-shaped inner core; 2-3, inner bayonet; 2-4 and 135 degrees.
Detailed Description
In order to make the present invention better understood by those skilled in the art, the following description will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
For ease of understanding, referring to fig. 1, an embodiment of a single-core cable characteristic impedance measurement fixture is provided in the present invention, including an inner conductor 2, an outer conductor 1, and an SMA joint 3;
the inner conductor 2 and the outer conductor 1 form a horn-shaped coaxial structure, a preset gap is reserved between the inner conductor 2 and the outer conductor 1, and an insulating medium 4 is filled in the preset gap;
the inner conductor 2 comprises a connecting column 2-1, a horn-shaped inner core 2-2 and an inner bayonet 2-3 which are connected in sequence in an integrated manner and are used for clamping a cable core in a clearance fit manner;
the outer conductor 1 comprises an integrally connected shell 1-1 and an outer bayonet 1-2 for clamping a cable shielding layer in a clearance fit manner;
the tail end of one end of the horn-shaped coaxial structure, which is far away from the opening of the horn, is connected with an SMA connector 3, and the needle core of the SMA connector 3 and the connecting column 2-1 are on the same horizontal line;
the joint of the connecting post 2-1 of the inner conductor 2 and the horn-shaped inner core 2-2 forms a transition angle 2-4 of 135 degrees.
In the embodiment of the present invention, as shown in fig. 1, the inner conductor 2 and the outer conductor 1 form a horn-shaped coaxial structure, a preset gap is left between the inner conductor 2 and the outer conductor 1, and an insulating medium 4 is filled in the preset gap. In order to ensure good electrical contact, both the inner conductor 2 and the outer conductor 1 are made of copper material, and the insulating medium 4 is polyvinyl chloride. The left end of the horn-shaped coaxial structure is connected with the SMA connector 3 with the omega, the right end is matched with the inner bayonet 2-3 and the outer bayonet 1-2 which are designed according to the structure of the single-core cable core and the shielding layer, the inner bayonet 2-3 and the outer bayonet 1-2 are respectively connected with the single-core cable core and the shielding layer in a clearance fit mode, the clamp can be clamped on the tested single-core cable 105, and good electric contact between the clamp and the cable core and the shielding layer can be kept. Considering the skin effect of the high-frequency signal, the inner bayonet 2-3 is in clearance fit with the cable core with a thickness of 1mm with a fit tolerance, and the outer bayonet 1-2 is in clearance fit with the cable shielding layer with a thickness of 2mm with a fit tolerance. In order to reduce the loss and resonance of the signal, in the embodiment of the invention, the joint of the connecting post 2-1 of the inner conductor 2 and the horn-shaped inner core 2-2 is designed to form a 135-degree transition angle 2-4.
For the single-core cable 105 under test, it is known from the transmission line theory that the characteristic impedance is:
，
wherein,,for the characteristic impedance of the single-core cable 105 to be tested, +.>Equivalent resistance per unit length, omega/m,equivalent inductance in unit length, H/m,/L>Equivalent capacitance per unit length, F/m, < >>Equivalent conductance in unit length, in units of S/m, -/-, and>is the angular frequency. Primary parameterR、L、C、GIs determined by the geometry and material parameters of the single-core cable 105 to be tested and influences the secondary parameter +.>. From this, the characteristic impedance +.>Is determined by the geometric parameters and material parameters of the cable, and by drawing the frequency chart, the value of the cable is basically unchanged with the frequency, the linearity is good, and the characteristic impedance can be changedFor assessing the health, i.e. the degree of degradation, of the cable.
The single-core cable characteristic impedance measuring clamp 101 provided by the invention is used for measuring the reflection coefficient of the single-core cable 105 to be measured, and the calculation formula of the reflection coefficient is as follows:
；
wherein,,for the reflection coefficient +.>For the characteristic impedance of the signal cable itself, +.>For the amplitude of the reflected signal +.>Is the amplitude of the excitation signal. According to the above formula, the inverse of the characteristic impedance of the single-core cable 105 to be measured can be realized.
When the single-core cable characteristic impedance measuring clamp provided by the embodiment of the invention is used for measuring the characteristic impedance of the single-core cable, the upper computer 102 controls the signal generating device 103 to generate an excitation signal, the excitation signal is reflected at the single-core cable characteristic impedance measuring clamp 101, the reflection coefficient is measured by the signal measuring device 104, and the upper computer 102 calculates the characteristic impedance according to the reflection coefficient, so that the degradation degree of the single-core cable 105 to be measured can be estimated.
The invention provides a single-core cable characteristic impedance measuring clamp 101, wherein an inner conductor 2 and an outer conductor 1 form a horn-shaped coaxial structure, a preset gap is reserved between the inner conductor 2 and the outer conductor 1, an insulating medium 4 is filled in the preset gap, the inner conductor 2 comprises a connecting column 2-1, a horn-shaped inner core 2-2 and an inner bayonet 2-3 which are used for clamping a cable core in a clearance fit mode, the connecting column is connected with the inner conductor 2 in sequence, and the outer conductor 1 comprises a shell 1-1 which is connected with the outer bayonet 1-2 which is used for clamping a cable shielding layer in a clearance fit mode. The single-core cable is connected with the single-core cable in a clearance fit mode, so that the single-core cable characteristic impedance measuring clamp 101 can be clamped on the tested cable, and good electrical contact between the single-core cable characteristic impedance measuring clamp 101 and the cable core and the shielding layer can be kept. The end of the horn-shaped coaxial structure far away from the horn opening is connected with the SMA joint 3, the needle core of the SMA joint 3 and the connecting column 2-1 are on the same horizontal line, and the connecting position of the connecting column 2-1 of the inner conductor 2 and the horn-shaped inner core 2-2 is in a 135-degree transition angle 2-4, so that the loss and resonance of signals can be reduced. When the characteristic impedance of the cable is measured, the signal is reflected at the single-core cable characteristic impedance measuring clamp 101, and the characteristic impedance measurement of the single-core high-voltage power cable can be realized by estimating the intensity of the reflected signal. The technical effect of accurately measuring the characteristic impedance of the single-core cable and assisting the monitoring of the degradation state of the single-core cable is achieved.
Meanwhile, the single-core cable characteristic impedance measuring clamp 101 provided by the invention not only can measure the reflection coefficient, but also can measure the reflection coefficient spectrum, and can realize the measurement of the characteristic impedance spectrum of the measured cable.
For ease of understanding, referring to fig. 2, an embodiment of a single-core cable characteristic impedance measurement system is provided in the present invention, where the measurement system includes any of the single-core cable characteristic impedance measurement fixtures 101 provided in the present invention, and further includes a signal generating device 103, a signal measuring device 104, an upper computer 102, and a single-core cable 105 to be measured;
the upper computer 102 is connected with the signal generating device 103 and the signal measuring device 104;
the output end of the signal generating device 103 is connected with a first port of the T-shaped connector 106 through a first signal cable 107, the input end of the signal measuring device 104 is connected with a second port of the T-shaped connector 106 through a second signal cable 108, a third port of the T-shaped connector 106 is connected with the SMA connector 3 of the single-core cable characteristic impedance measuring clamp 101 through a third signal cable 109, and the single-core cable characteristic impedance measuring clamp 101 is connected with the single-core cable 105 to be measured.
It should be noted that, the upper computer 102 is configured to control the signal generator to generate a target excitation signal, obtain a reflection coefficient measurement result of the signal measurement device 104, calculate a characteristic impedance of the single-core cable 105 to be measured according to the reflection coefficient result, and determine a degradation degree of the single-core cable 105 to be measured according to a corresponding relationship between the characteristic impedance and the degradation degree of the single-core cable, so as to monitor a health state of the single-core cable 105 to be measured.
The output of the signal generating device 103 is connected to a first port of the T-connector 106 via a first signal cable 107, the first signal cable 107 being a 1m long 50Ω signal cable. The input end of the signal measuring device 104 is connected to the second port of the T-connector 106 via a second signal cable 108, the second signal cable 108 being a 1m long 50Ω signal cable. The third port of the T-connector 106 is connected to the SMA joint 3 of the single-core cable characteristic impedance measurement jig 101 via a third signal cable 109, the third signal cable 109 being a 50Ω signal cable 5m long. The inner bayonet 2-3 and the outer bayonet 1-2 of the single-core cable characteristic impedance measuring clamp 101 are respectively connected with the cable core and the shielding layer of the single-core cable in a clearance fit mode. The excitation signal generated by the signal generating device 103 is inputted to the single-core cable characteristic impedance measuring jig 101 and the signal measuring device 104 in the form of equal amplitude by the T-connector 106, and the reflected signal generated at the single-core cable characteristic impedance measuring jig 101 is inputted to the signal measuring device 104 by the T-connector 106.
For the excitation signal design of the signal generator, the invention takes the modulation step frequency signal as the excitation signal, and inputs the following modulation step frequency signal into the signal generator to generate a corresponding excitation signal waveform with the amplitude of 1V.
The modulated step frequency signal is:
；
wherein,,for modulating the step frequency signal +.>Is the firstiFrequency of the sinusoidal signal +.>Is the firstiThe duration of the waveform of the individual sinusoidal signals,Dis the firstiStart time difference of +1 sine wave.
To ensure the firstiThe reflected signal of the sine wave will not sum with the firsti+1 sine waveforms overlap at the input end, requiring pairs ofDAndthe following limitations were made:
；
；
in the method, in the process of the invention,Lfor a length of 50 omega signal cable, in the inventionLThe value of the water-based paint is 5m,is the signal transmission speed.
After the signal generator is controlled by the upper computer 102 to generate an excitation signal, the amplitude of the high-frequency signal input into the single-core cable is recorded by the signal measuring device 104U in And transmits it to the upper computer 102 for storage. Then when the high-frequency signal reaches the single-core cable characteristic impedance measuring clamp 101, the high-frequency signal is partially reflected back to the input end and captured by the signal measuring device 104 due to the inconsistent characteristic impedance at the two ends of the single-core cable characteristic impedance measuring clamp 101, and the amplitude of the captured reflected signal isU rf Which is also transmitted to the host computer 102. For the single pulse signal, the injection signal and the reflection signal are both single pulse signals. For a step frequency signal, the injection signal and the reflection signal are a series of step frequency sinusoidal signals, and the frequency components between the injection signal and the reflection signal are the same, and the difference is mainly in amplitude.
Due to the connection between the signal generating device 103, the signal measuring device 104 and the signal cableThe T-connector 106 is present, and the amplitude of the signal is attenuated by 1/3 of the amplitude of the signal when passing through the T-connector 106, so the actual reflected signal amplitude should be. The reflection coefficient measured by the signal measuring device 104 is therefore:
；
for the case where the injection signal is a single pulse signal, the reflection coefficient is a single value. For the case where the injection signal is a stepped frequency signal, a reflection coefficient can be calculated at each frequency point, so that a complete reflection coefficient spectrum is obtained.
For estimation of the characteristic impedance of the single-core cable, after obtaining the reflection coefficient, the characteristic impedance value may be obtained by the following formula:
；
an expression of the characteristic impedance of the single-core cable 105 to be measured can thus be obtained:
；
the characteristic impedance measurement result can be obtained quickly, and the degree of degradation of the single-core cable 105 to be measured can be estimated.
The single-core cable characteristic impedance measuring system provided by the invention comprises the single-core cable characteristic impedance measuring clamp 101 provided by the invention, and further comprises a signal generating device 103, a signal measuring device 104, an upper computer 102 and a single-core cable 105 to be measured, wherein the upper computer 102 controls the signal generating device 103 to generate an excitation signal, the signal measuring device 104 measures the reflection coefficient of the single-core cable, and the upper computer 102 calculates the characteristic impedance of the cable according to the reflection coefficient, so that the degradation degree evaluation result of the single-core cable is obtained, the degradation monitoring of the whole health state of the single-core cable is realized, and the single-core cable characteristic impedance measuring system has wide application prospect.
Meanwhile, the single-core cable characteristic impedance measurement system provided by the invention not only can measure the reflection coefficient, but also can measure the reflection coefficient spectrum, and can realize the measurement of the characteristic impedance spectrum of the measured cable.
For ease of understanding, referring to fig. 1 to 3, an embodiment of a measurement method applied to a single-core cable characteristic impedance measurement system provided in the present invention is provided in the present invention, including:
step 101, the host computer 102 is connected to the signal generating device 103 and the signal measuring device 104, the signal generating device 103 and the signal measuring device 104 are connected to the single-core cable characteristic impedance measuring jig 101 through the T-connector 106, and the single-core cable characteristic impedance measuring jig 101 is connected to the single-core cable 105 to be measured.
It should be noted that, the single-core cable characteristic impedance measurement system shown in fig. 2 is first constructed, the upper computer 102 is connected with the signal generating device 103 and the signal measuring device 104, the output end of the signal generating device 103 is connected with the first port of the T-type connector 106 through the first signal cable 107, the input end of the signal measuring device 104 is connected with the second port of the T-type connector 106 through the second signal cable 108, the third port of the T-type connector 106 is connected with the SMA joint 3 of the single-core cable characteristic impedance measurement fixture 101 through the third signal cable 109, and the single-core cable characteristic impedance measurement fixture 101 is connected with the single-core cable 105 to be measured.
Step 102, the upper computer 102 controls the signal generating device 103 to generate an excitation signal, and the reflection coefficient measured by the signal measuring device 104 is obtained.
After the single-core cable characteristic impedance measurement system is built, the signal generator 103 is controlled by the upper computer 102 to generate an excitation signal, the signal generator is controlled by the upper computer 102 to generate an excitation signal, and the signal measuring device 104 records the amplitude of the high-frequency signal input into the single-core cable and transmits the amplitude to the upper computer 102 for storage. Then, when the high-frequency signal reaches the single-core cable characteristic impedance measuring clamp 101, the high-frequency signal is partially reflected back to the input end and captured by the signal measuring device 104 due to the inconsistent characteristic impedance at the two ends of the single-core cable characteristic impedance measuring clamp 101, and is also transmitted to the upper computer 102. For the case where the injection signal is a single pulse signal, the reflection coefficient is a single value. For the case where the injection signal is a stepped frequency signal, a reflection coefficient can be calculated at each frequency point, so that a complete reflection coefficient spectrum is obtained.
Step 103, the upper computer 102 calculates the characteristic impedance of the single-core cable 105 to be measured according to the reflection coefficient, and evaluates the degradation degree of the single-core cable 105 to be measured according to the characteristic impedance calculation result of the single-core cable 105 to be measured.
It should be noted that, for estimation of the characteristic impedance of the single-core cable, after obtaining the reflection coefficient, the characteristic impedance value may be obtained by the following formula:
；
after the characteristic impedance calculation result of the single-core cable 105 to be measured is obtained, the degradation degree evaluation result of the single-core cable 105 to be measured can be obtained according to the corresponding relationship between the characteristic impedance and the degradation degree of the single-core cable 105 to be measured.
The measuring method applied to the single-core cable characteristic impedance measuring system provided by the invention realizes the overall health state degradation monitoring of the single-core cable.
The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The single-core cable characteristic impedance measuring clamp is characterized by comprising an inner conductor, an outer conductor and an SMA connector;
the inner conductor and the outer conductor form a horn-shaped coaxial structure, a preset gap is reserved between the inner conductor and the outer conductor, and an insulating medium is filled in the preset gap;
the inner conductor comprises a connecting column, a horn-shaped inner core and an inner bayonet used for clamping the cable core in a clearance fit mode, which are integrally and sequentially connected;
the outer conductor comprises an integrally connected shell and an outer clamping opening for clamping the cable shielding layer in a clearance fit manner;
the tail end of one end of the horn-shaped coaxial structure, which is far away from the opening of the horn, is connected with an SMA connector, and the needle core of the SMA connector and the connecting column are on the same horizontal line;
the connecting column of the inner conductor and the connecting position of the horn-shaped inner core form a 135-degree transition angle.
2. The single core cable characteristic impedance measurement clamp according to claim 1, wherein the inner bayonet is clearance fit with the cable core at a thickness of 1mm tolerance, and the outer bayonet is clearance fit with the cable shield at a thickness of 2mm tolerance.
3. The single-core cable characteristic impedance measurement jig according to claim 1, wherein the inner conductor and the outer conductor are made of copper material.
4. The single-core cable characteristic impedance measurement fixture according to claim 1, wherein the SMA joint is a 50Ω SMA joint.
5. The single-core cable characteristic impedance measurement clamp according to claim 1, wherein the insulating medium is polyvinyl chloride.
6. A single-core cable characteristic impedance measurement system, which is characterized by comprising the single-core cable characteristic impedance measurement clamp as claimed in any one of claims 1-5, and further comprising a signal generating device, a signal measuring device, an upper computer and a single-core cable to be measured;
the upper computer is connected with the signal generating device and the signal measuring device;
the output end of the signal generating device is connected with the first port of the T-shaped connector through a first signal cable, the input end of the signal measuring device is connected with the second port of the T-shaped connector through a second signal cable, the third port of the T-shaped connector is connected with the SMA connector of the single-core cable characteristic impedance measuring clamp through a third signal cable, and the single-core cable characteristic impedance measuring clamp is connected with the single-core cable to be measured.
7. The single-core cable characteristic impedance measurement system according to claim 6, wherein the first signal cable and the second signal cable are 50Ω signal cables of 1m length, and the third signal cable is 50Ω signal cable of 5m length.
8. The single-core cable characteristic impedance measurement system according to claim 7, wherein the signal generator is configured to generate the excitation signal having an amplitude of 1V.
9. The single-core cable characteristic impedance measurement system according to claim 6, wherein the signal measurement device is configured to measure a reflection coefficient of the single-core cable under measurement;
the upper computer is used for calculating the characteristic impedance of the single-core cable to be measured according to the reflection coefficient measured by the signal measuring device, and the characteristic impedance calculation formula is as follows:
；
wherein,,is characteristic impedance->Is the reflection coefficient.
10. A measurement method applied to the single-core cable characteristic impedance measurement system according to any one of claims 6 to 9, comprising:
connecting an upper computer with a signal generating device and a signal measuring device, connecting the signal generating device and the signal measuring device with a single-core cable characteristic impedance measuring clamp through a T-shaped connector, and connecting the single-core cable characteristic impedance measuring clamp with a single-core cable to be measured;
generating an excitation signal by an upper computer control signal generating device, and acquiring the reflection coefficient measured by a signal measuring device;
and the upper computer calculates the characteristic impedance of the single-core cable to be tested according to the reflection coefficient, and evaluates the degradation degree of the single-core cable to be tested according to the characteristic impedance calculation result of the single-core cable to be tested.
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