Cable shielding performance testing device and method based on line injection method

Abstract

The invention relates to a cable shielding performance testing device and method based on a line injection method, and the device comprises a network analyzer, an injection line, a terminal matching shielding box, a first metal fixing clamp, a second metal fixing clamp, and a plurality of non-metal movable clamps. The near ends of the injection line and the detected cable are both installed in the first metal fixing clamp, the far ends of the injection line and the detected cable are both installed in the second metal fixing clamp, and the injection line is communicated with the shielding layer conductor through the metal fixing clamp. The nonmetal movable clamp comprises a clamp body, a position indicating structure and an adjusting bolt, a clamp cavity is formed in the clamp body, the adjusting bolt is installed in the clamp body and extends into the clamp cavity, the adjusting bolt can move in the clamp body, and the position indicating structure can indicate the position of the adjusting bolt; the nonmetal movable clamps are installed on the coupling section, the injection line and the tested cable are both located in the clamp cavity, and the adjusting bolt can be tightly pressed on the side, away from the tested cable, of the injection line.

Description

Technical Field

[0001] The present invention relates to the technical field of cable performance detection, and in particular to a cable shielding performance testing device and method based on a line injection method. Background Art

[0002] With the development and application of new energy technologies, the shielding performance of power cables has gradually attracted attention. There are two difficulties in testing the shielding performance of power cables. First, the outer diameters of the conductor and the cable are large, which makes it difficult to prepare the sample and the cutoff frequency in the test is not high; second, the power cable does not have a standardized characteristic impedance value, which leads to a large reflected wave and affects the test data. At present, the shielding performance test methods at home and abroad include the absorption clamp method, the triaxial method, and the line injection method. Among them, the absorption clamp method cannot meet the test requirements of cables with large outer diameters because the specifications of the commercially available absorption clamps are only 30MHz~3GHz and the maximum wire diameter is only 14mm. The triaxial method cannot test cables with large outer diameters because the lower limit cutoff frequency is high and the test results do not include coupling admittance. Although the line injection method is in principle compliant and can be used for testing large-diameter cables, it has the problems of complex testing and poor repeatability. The method and principle of the line injection method are described in the 1993 revised version of the standard IEC 62153-4-6 and the standard IEC96-1. When using the existing line injection method for testing, a section of the injection line is attached to the cable under test by pasting or binding, and the part of the injection line that is attached to the cable under test constitutes a coupling section. The injection line and the shielding layer of the cable under test form an output line as an injection circuit, and the inner loop is composed of the core wire and shielding layer of the cable under test. During the test, the effective distance between the injection line and the cable under test is difficult to control, and a slight change in the distance will cause a change in the test conditions. Therefore, the repeatability of each measurement is poor, the test is complicated, and it is difficult to ensure the measurement accuracy. Summary of the invention

[0003] In view of the above-mentioned shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a cable shielding performance test device and method based on the line injection method, which has good measurement repeatability and high test accuracy.

[0004] To achieve the above-mentioned purpose, the present invention provides a cable shielding performance testing device based on a line injection method, which is used to test the shielding performance of a tested cable, and comprises a network analyzer, an injection line and a terminal matching shielding box, wherein the proximal end of the injection line is connected to the transmitting end of the network analyzer, and the distal end is connected to the terminal matching shielding box, the proximal end of the tested cable is connected to the terminal matching shielding box, and the distal end is connected to the input end of the network analyzer, and further comprises a first metal fixing fixture, a second metal fixing fixture and a plurality of non-metallic movable fixtures, the proximal end of the injection line and the proximal end of the tested cable are both installed in the first metal fixing fixture, and the injection line is connected to the shielding layer conductor of the tested cable through the first metal fixing fixture, the distal end of the injection line and the distal end of the tested cable are both installed in the second metal fixing fixture, and The injection line is connected to the shielding layer conductor of the cable under test through the second metal fixing clamp, and the injection line and the cable under test have a coupling section between the two first metal fixing clamps and the second metal fixing clamp; the non-metallic movable clamp includes a clamp body, a position indicating structure and an adjusting bolt, and the clamp body is provided with a clamp cavity for accommodating the injection line and the cable under test, the adjusting bolt is installed in the clamp body and its inner end extends into the clamp cavity, the adjusting bolt can be moved in the clamp body to extend into or exit the clamp cavity, and the position indicating structure can indicate the position of the adjusting bolt; multiple non-metallic movable clamps are installed at different positions of the coupling section, and the injection line and the cable under test are both located in the clamp cavity, and the inner end of the adjusting bolt can be pressed against the side of the injection line away from the cable under test.

[0005] Furthermore, the adjusting bolt of the non-metallic movable clamp is screwed into the clamp body, and the position indicating structure can indicate the axial position of the adjusting bolt.

[0006] Furthermore, the position indicating structure includes a scale, and the scale is parallel to the axial direction of the adjusting bolt.

[0007] Furthermore, the scale is a millimeter scale.

[0008] Furthermore, the clamp body of the non-metallic movable clamp includes a first clamp block, a second clamp block and a locking structure, the first clamp block and the second clamp block are hinged, the first clamp block is provided with a first cavity portion, the second clamp block is provided with a second cavity portion, the first clamp block and the second clamp block can be relatively rotated to separate or close, and when closed, the first cavity portion and the second cavity portion are connected to form a clamp cavity, and the locking structure can lock the first clamp block and the second clamp block in a closed state.

[0009] Furthermore, the fixture cavity in the fixture body of the non-metallic movable fixture is cylindrical, and its diameter is larger than the sum of the diameter of the measured cable and the diameter of the injection line.

[0010] Furthermore, it also includes a time domain reflectometer and a switching switch. The far end of the cable under test, the input end of the network analyzer and the input end of the time domain reflectometer are respectively connected to the switching switch through leads, and the switching switch can control the cable under test to be connected to the network analyzer or to the time domain reflectometer.

[0011] The present invention also provides a cable shielding performance test method based on the line injection method, which is performed using the above-mentioned cable shielding performance test device and includes the following steps:

[0012] Step 1: Install the cable shielding performance test device and the tested cable, and adjust the position of the adjustment bolt in the non-metallic movable fixture so that its inner end abuts against the injection line;

[0013] Step 2, switch the switch to a state where the far end of the cable under test is connected to the input end of the time domain reflectometer, the network analyzer transmits a signal, obtains the reflection data of the injection circuit through the reflection graph of the time domain reflectometer, monitors the characteristic impedance and reflection loss, and adjusts the compression degree of the injection line by adjusting the adjustment bolt of the non-metallic movable clamp to adjust the effective distance between the injected line and the cable under test, so that the characteristic impedance is maintained at a specified value and the reflection loss meets the specified value requirements;

[0014] Step 3: Switch the switch to a state where the far end of the cable under test is connected to the input end of the network analyzer. The network analyzer transmits a signal and reads the through parameter of the network analyzer, which is the shielding performance value of the cable under test.

[0015] Furthermore, in step S2, the characteristic impedance is maintained at 50Ω and the reflection loss is greater than 20dB.

[0016] As described above, the cable shielding performance testing device and method according to the present invention have the following beneficial effects:

[0017] 1. It can flexibly adjust the effective distance between the tested cable and the injection line in the coupling section during measurement, ensuring that the characteristic impedance and reflection loss are in the same state during the test, with good test repeatability, high test accuracy and flexible use. It can test the transfer impedance at a frequency of 10kHz to 1GHz, with high upper and lower edges of the test frequency. The test results include the coupling admittance of the cable, making the test results of sparsely braided shielded cables more accurate.

[0018] 2. By setting up a time domain reflectometer and a switching switch, the characteristic impedance and reflection loss can be monitored during the test. After they meet the specified requirements, the shielding performance value of the cable can be obtained through a network analyzer to ensure test accuracy.

[0019] 3. Compared with conventional on-site measuring devices, the device in the present invention has a simple configuration, low investment, small footprint, can be flexibly and freely placed, is light in weight, and is easy to move. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of a cable shielding performance testing device of the present invention.

[0021] Figure 2 It is a schematic structural diagram of the non-metallic active fixture in the present invention.

[0022] Figure 3 The figure is a working schematic diagram of the non-metallic movable clamp of the present invention when clamping the tested cable and the injection line.

[0023] Description of Figure Numbers

[0024] 1 Cable under test

[0025] 2 Network Analyzer

[0026] 3 Injection line

[0027] 4 Terminal matching shielding box

[0028] 5. First metal fixing fixture

[0029] 6 Second metal fixing fixture

[0030] 7 Non-metallic movable fixture

[0031] 71 fixture body

[0032] 711 First clamp

[0033] 712 Second clamp

[0034] 713 Hinge

[0035] 72 fixture cavity

[0036] 721 First cavity

[0037] 722 Second cavity

[0038] 73 Adjustment pin

[0039] 74 ruler

[0040] 8 Time Domain Reflectometry

[0041] 9 Toggle Switch

[0042] 10 Lead

[0043] 11. Base DETAILED DESCRIPTION

[0044] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0045] It should be noted that the structures, proportions, sizes, etc. drawn in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportional relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and so on quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0046] See also Figures 1 to 3 The present invention provides a cable shielding performance test device based on the line injection method, which is used to test the shielding performance of the tested cable 1, including a network analyzer 2, an injection line 3 and a terminal matching shielding box 4, wherein the proximal end of the injection line 3 is connected to the transmitting end of the network analyzer 2, and the distal end is connected to the terminal matching shielding box 4, and the proximal end of the tested cable 1 is connected to the terminal matching shielding box 4, and the distal end is connected to the input end of the network analyzer 2. Among them, the terminal matching shielding box 4 plays a shielding role, the network analyzer 2 can transmit and receive signals, and the network analyzer 2, the injection line 3 and the terminal matching shielding box 4 are conventional mechanisms in the existing line injection method, so their specific structures and principles are not described in detail.

[0047] In the present invention, the cable shielding performance test device also includes a first metal fixing fixture 5, a second metal fixing fixture 6 and a plurality of non-metallic movable fixtures 7, the proximal end of the injection line 3 and the proximal end of the tested cable 1 are both installed in the first metal fixing fixture 5, and the injection line 3 is connected to the shielding layer conductor of the tested cable 1 through the first metal fixing fixture 5, the distal end of the injection line 3 and the distal end of the tested cable 1 are both installed in the second metal fixing fixture 6, and the injection line 3 is connected to the shielding layer conductor of the tested cable 1 through the second metal fixing fixture 6, and the injection line 3 and the tested cable 1 have a coupling section between the two first metal fixing fixtures 5 and the second metal fixing fixture 6; the non-metallic movable fixture 7 includes a clamp The clamp body 71 includes a position indicating structure and an adjusting bolt 73. The clamp body 71 is provided with a clamp cavity 72 for accommodating the injection line 3 and the cable 1 under test. The adjusting bolt 73 is installed in the clamp body 71 and its inner end extends into the clamp cavity 72. The adjusting bolt 73 can move in the clamp body 71 to extend into or exit the clamp cavity 72. The position indicating structure can indicate the position of the adjusting bolt 73. A plurality of non-metallic movable clamps 7 are installed at different positions of the coupling section, and the injection line 3 and the cable 1 under test are both located in the clamp cavity 72. The inner end of the adjusting bolt 73 can be pressed against the side of the injection line 3 away from the cable 1 under test, that is, at this time, the cable 1 under test and the adjusting bolt 73 are respectively located on the opposite sides of the injection line 3.

[0048] The basic working principle of the cable shielding performance testing device involved in the present invention is: during installation, first install the proximal end and distal end of the tested cable 1 and the injection line 3 in the first metal fixing fixture 5 and the second metal fixing fixture 6 respectively. After the tested cable 1 and the injection line 3 are installed and fixed, the two can remain parallel and close. The proximal end of the injection line 3 is connected to the transmitting end of the network analyzer 2, and the proximal end is equipped with a terminal matching shielding box 4. The proximal end of the tested cable 1 is equipped with a terminal matching shielding box 4, and the distal end is connected to the input end of the network analyzer 2. Then install a plurality of non-metallic movable fixtures 7 at appropriate positions at the coupling section, and use the adjustment bolts 73 in the non-metallic movable fixtures 7 to press the injection line 3 onto the tested cable 1, see Figure 3, the positions of the tested cable 1 and the injection line 3 in the non-metallic movable fixture 7 are fixed. During measurement, a signal is transmitted through the transmitting end of the network analyzer 2, and is received by the network analyzer 2 after passing through the tested cable 1 and the injection line 3, and the corresponding parameters are read from the network analyzer 2. The measurement principle here is the same as the measurement principle of the existing line injection method, and will not be described in detail. In the present invention, the improvement is that during measurement, the effective distance between the tested cable 1 and the injection line 3 in the coupling section can be adjusted by the non-metallic movable fixture 7. The effective distance between the tested cable 1 and the injection line 3 is the distance from the center of the injection line 3 to the shielding layer of the tested cable 1. Specifically, by adjusting the degree of compression of the injection line 3 by the adjustment bolt 73 in the non-metallic movable fixture 7, the effective distance changes. When measuring by the online injection method, a slight change in the effective distance can cause a change in the reflection loss. Therefore, the reflection loss can meet the standard requirement of ≥20dB by adjusting the non-metallic movable fixture 7, and then read the through parameter of the network analyzer 2, specifically the S21 parameter of the network analyzer 2, which is the shielding performance value of the tested cable 1. And when adjusting, the required effective distance can be obtained through corresponding calculations, and then the displacement of the adjustment bolt 73 when it moves can be determined through the position indication structure, so as to better optimize the reflection loss. When performing multiple measurements, it can be ensured that each measurement is under the same measurement conditions (that is, the characteristic impedance and reflection loss are the same), the test work has good repeatability, high test accuracy, and easy operation.

[0049] In this embodiment, see Figure 2 and Figure 3 As a preferred design, the adjusting bolt 73 of the non-metallic movable clamp 7 is screwed into the clamp body 71, and the adjusting bolt 73 is a bolt. The position indicating structure can indicate the axial position of the adjusting bolt 73, wherein the position indicating structure includes a scale 74, and the scale of the scale 74 is parallel to the axial direction of the adjusting bolt 73, and the scale 74 is preferably a millimeter scale, that is, the minimum scale is 1mm. When in use, the adjusting bolt 73 can be moved along its axial straight line by rotating the adjusting bolt 73, so as to adjust the degree of its compression on the injection line 3, and the position of the adjusting bolt 73 is stable. By adjusting the outer end of the adjusting bolt 73 corresponding to the position on the scale 74, the moving distance of the adjusting bolt 73 can be determined, so as to calculate the adjustment amount of the effective distance between the measured cable 1 and the injection line 3. Of course, in other embodiments, the installation and movement form of the adjusting bolt 73 can also adopt other appropriate forms, and the position indicating structure can also adopt other existing structures that can measure position quantities, such as position sensors.

[0050] In this embodiment, see Figure 2 and Figure 3As a preferred design, the clamp body 71 of the non-metallic movable clamp 7 includes a first clamp block 711, a second clamp block 712 and a locking structure (not shown in the drawings). The first clamp block 711 and one side of the second clamp block 712 are hingedly connected by the hinge 713. The first clamp block 711 is provided with a first cavity 721, and the second clamp block 712 is provided with a second cavity 722. The first clamp block 711 and the second clamp block 712 can rotate relative to each other to separate or close, and when closed, the first cavity 721 and the second cavity 722 are connected to each other to form the clamp cavity 72, and the locking structure can lock the first clamp block 711 and the second clamp block 712 in a closed state. When in use, first rotate the first clamp block 711 and the second clamp block 712 apart, and then install them on the injection line 3 and the cable under test 1 of the coupling section, the injection line 3 and the cable under test 1 are located in the first cavity 721 and the second cavity 722, and then rotate the first clamp block 711 and the second clamp block 712 together, so that the injection line 3 and the cable under test 1 are both located in the clamping cavity, and then lock the first clamp block 711 and the second clamp block 712 through the locking structure and keep them stable. The installation and disassembly are very convenient and the use is flexible. At the same time, it is convenient to adjust the position of the non-metallic movable clamp 7 in the length direction of the coupling section.

[0051] In this embodiment, see Figure 2 and Figure 3 Furthermore, the fixture cavity 72 in the fixture body 71 of the non-metallic movable fixture 7 is cylindrical, and its diameter D3 is larger than the sum of the diameter D1 of the measured cable 1 and the diameter D2 of the injection line 3, that is, D3>D1+D2. After the non-metallic movable fixture 7 is installed, see Figure 3 , from the cross section of the cable 1 under test, the adjustment bolt 73 is located on the connecting line between the center of the cable 1 under test and the center of the injection line 3. The diameter D3 of the clamp cavity 72 preferably adopts a relatively large value, which can accommodate cables 1 under test of various sizes. When the diameter of the cable 1 under test is relatively small relative to the diameter of the clamp cavity 72, the adjustment bolt 73 extends into the clamp cavity 72 for a longer distance to abut against the injection line 3. The position of the cable 1 under test in the clamp cavity 72 can be fixed, and it can also be achieved by setting a suitable auxiliary structure, such as a binding rope, an elastic strip, etc., to better stabilize the position of the cable 1 under test. The above method can enable the non-metallic movable clamp 7 to meet the testing needs of cables of different sizes and has a wide range of applications.

[0052] In this embodiment, see Figure 1As a preferred design, it also includes an insulating base 11, which can be made of wood or other insulating materials. The first metal fixing fixture 5 and the second metal fixing fixture 6 are both detachably mounted on the insulating base 11. The first metal fixing fixture 5 and the second metal fixing fixture 6 in the cable shielding performance test device can be set to a plurality of different sizes, which can clamp cables of different diameters. When measuring, the corresponding first metal fixing fixture 5 and the second metal fixing fixture 6 are replaced according to the size of the object to be measured. Of course, the first metal fixing fixture 5 and the second metal fixing fixture 6 can also be fixtures with a certain clamping range, which can clamp cables of various diameters.

[0053] In this embodiment, see Figure 1 As a preferred design, the cable shielding performance test device also includes a time domain reflectometer 8 and a switch 9. The far end of the tested cable 1, the input end of the network analyzer 2 and the input end of the time domain reflectometer 8 are respectively connected to the switch 9 through a lead 10. The switch 9 can control the tested cable 1 to be connected to the network analyzer 2 or to the time domain reflectometer 8. The time domain reflectometer 8 is used to monitor and display the characteristic impedance of the injection circuit to further optimize the reflected wave and make the test result true and reliable.

[0054] The present invention also provides a cable shielding performance test method based on the line injection method, which is performed using the above-mentioned cable shielding performance test device and includes the following steps:

[0055] Step 1: Install the cable shielding performance test device and the tested cable 1, and adjust the position of the adjustment bolt 73 in the non-metallic movable fixture 7 so that its inner end abuts against the injection line 3. Among them, multiple non-metallic movable fixtures 7 are at different positions in the length direction of the coupling section, and the specific positions are determined according to needs, preferably evenly arranged. After installation, the injection line 3 and the shielding layer of the tested cable 1 form an injection circuit.

[0056] Step 2, switch the switch 9 to a state where the far end of the cable 1 under test is connected to the input end of the time domain reflectometer 8, the network analyzer 2 transmits a signal, obtains the reflection data of the injection circuit through the reflection pattern of the time domain reflectometer 8, monitors the characteristic impedance and reflection loss, and adjusts the position of the adjustment bolt 73 of the non-metallic movable fixture 7 to adjust the degree of compression of the injection line 3, thereby adjusting the effective distance between the injected line 3 and the cable 1 under test, so that the characteristic impedance is maintained at a specified value, and the reflection loss meets the specified value requirements. Preferably, during the test, the characteristic impedance is maintained at 50Ω and the reflection loss is greater than 20dB. Specifically, through the reflection pattern of the time domain reflectometer 8, it can be determined which position of the coupling section needs to adjust the effective distance, and then the corresponding non-metallic movable fixture 7 is adjusted to ensure that the characteristic impedance and reflection loss meet the above requirements.

[0057] Step 3, switch the switch 9 to a state where the far end of the cable 1 under test is connected to the input end of the network analyzer 2, the network analyzer 2 transmits a signal, and reads the through parameter of the network analyzer 2, that is, the S21 parameter in the network analyzer 2. At this time, the through parameter is obtained when the characteristic impedance is maintained at 50Ω and the reflection loss is greater than 20dB, which is the shielding performance value of the cable 1 under test.

[0058] During repeated test adjustments, the effective distance required for the 50Ω characteristic impedance can be calculated to guide the adjustment of the position of the adjustment pin 73 in the non-metallic movable fixture to ensure that the characteristic impedance is 50Ω when connected to the network analyzer.

[0059] As can be seen from the above, the cable shielding performance testing device and method based on the line injection method of the present invention have the following technical effects:

[0060] 1. It can flexibly adjust the effective distance between the tested cable 1 and the injection line 3 in the coupling section during measurement, ensuring that the characteristic impedance and reflection loss are in the same state during the test. The test has good repeatability, high test accuracy and is flexible to use. The transfer impedance at a frequency of 10kHz to 1GHz can be tested, and the upper and lower edges of the test frequency are very high. The test results include the coupling admittance of the cable, making the test results of sparsely braided shielded cables more accurate.

[0061] 2. By setting up a time domain reflectometer 8 and a switching switch 9, the characteristic impedance and reflection loss can be monitored during the test. After they meet the specified requirements, the shielding performance value of the cable can be obtained through the network analyzer 2 to ensure the test accuracy.

[0062] 3. Compared with conventional on-site measuring devices, the device in the present invention has a simple configuration, low investment, small footprint, can be flexibly and freely placed, is light in weight, and is easy to move.

[0063] In summary, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0064] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A cable shielding performance test device based on a line injection method, used for testing the shielding performance of a tested cable (1), comprising a network analyzer (2), an injection line (3) and a terminal matching shielding box (4), wherein the proximal end of the injection line (3) is connected to the transmitting end of the network analyzer (2), and the distal end is connected to the terminal matching shielding box (4), the proximal end of the tested cable (1) is connected to the terminal matching shielding box (4), and the distal end is connected to the input end of the network analyzer (2), characterized in that: The invention also comprises a first metal fixing fixture (5), a second metal fixing fixture (6) and a plurality of non-metal movable fixtures (7); the proximal end of the injection line (3) and the proximal end of the measured cable (1) are both mounted in the first metal fixing fixture (5), and the injection line (3) is connected to the shielding conductor of the measured cable (1) through the first metal fixing fixture (5); the distal end of the injection line (3) and the distal end of the measured cable (1) are both mounted in the second metal fixing fixture (6), and the injection line (3) is connected to the shielding conductor of the measured cable (1) through the second metal fixing fixture (6); the injection line (3) and the measured cable (1) have a coupling section between the two first metal fixing fixtures (5) and the second metal fixing fixture (6); the non-metal movable fixture (7) is a plurality of non-metal movable fixtures (7); the proximal end of the injection line (3) and the proximal end of the measured cable (1) are both mounted in the second metal fixing fixture (6), and the injection line (3) is connected to the shielding conductor of the measured cable (1) through the second metal fixing fixture (6); (7) comprises a fixture body (71), a position indicating structure and an adjusting bolt (73); the fixture body (71) is provided with a fixture cavity (72) for accommodating an injection line (3) and a cable under test (1); the adjusting bolt (73) is installed in the fixture body (71) and its inner side end extends into the fixture cavity (72); the adjusting bolt (73) can move in the fixture body (71) to extend into or exit the fixture cavity (72); the position indicating structure can indicate the position of the adjusting bolt (73); a plurality of non-metallic movable fixtures (7) are installed at different positions of the coupling section, and the injection line (3) and the cable under test (1) are both located in the fixture cavity (72); the inner side end of the adjusting bolt (73) can be pressed against a side of the injection line (3) away from the cable under test (1).

2. The cable shielding performance testing device according to claim 1, characterized in that: The adjusting bolt (73) of the non-metallic movable clamp (7) is screwed into the clamp body (71), and the position indicating structure can indicate the axial position of the adjusting bolt (73).

3. The cable shielding performance testing device according to claim 2, characterized in that: The position indicating structure comprises a scale (74), and the scale of the scale (74) is parallel to the axial direction of the adjusting bolt (73).

4. The cable shielding performance testing device according to claim 3, characterized in that: The scale (74) is a millimeter scale.

5. The cable shielding performance testing device according to claim 1, characterized in that: The clamp body (71) of the non-metallic movable clamp (7) comprises a first clamp block (711), a second clamp block (712) and a locking structure. The first clamp block (711) and the second clamp block (712) are hinged to each other. A first cavity (721) is provided in the first clamp block (711), and a second cavity (722) is provided in the second clamp block (712). The first clamp block (711) and the second clamp block (712) can rotate relative to each other to be separated or closed, and when closed, the first cavity (721) and the second cavity (722) are connected to each other to form a clamp cavity (72). The locking structure can lock the first clamp block (711) and the second clamp block (712) in a closed state.

6. The cable shielding performance testing device according to claim 1, characterized in that: The fixture cavity (72) in the fixture body (71) of the non-metallic movable fixture (7) is cylindrical, and its diameter is greater than the sum of the diameter of the measured cable (1) and the diameter of the injection line (3).

7. The cable shielding performance testing device according to claim 1, characterized in that: It also comprises an insulating base (11), and the first metal fixing clamp (5) and the second metal fixing clamp (6) are both detachably mounted on the insulating base (11).

8. The cable shielding performance testing device according to claim 1, characterized in that: The device also comprises a time domain reflectometer (8) and a switching switch (9); the remote end of the tested cable (1), the input end of the network analyzer (2) and the input end of the time domain reflectometer (8) are respectively connected to the switching switch (9) via a lead wire (10); the switching switch (9) can control the tested cable (1) to be connected to the network analyzer (2) or to be connected to the time domain reflectometer (8).

9. A cable shielding performance testing method based on line injection method, characterized in that: The cable shielding performance test device according to claim 8 is used, comprising the following steps: Step 1: Install the cable shielding performance test device and the tested cable (1), and adjust the position of the adjustment bolt (73) in the non-metallic movable fixture (7) so that its inner end abuts against the injection line (3); Step 2, switching the switch (9) to a state where the far end of the tested cable (1) is connected to the input end of the time domain reflectometer (8), the network analyzer (2) transmits a signal, and the reflection data of the injection circuit is obtained through the reflection pattern of the time domain reflectometer (8), and the characteristic impedance and reflection loss are monitored. By adjusting the degree of compression of the injection line (3) by the adjustment bolt (73) of the non-metallic movable clamp (7), the effective distance between the injected line (3) and the tested cable (1) is adjusted, so that the characteristic impedance is maintained at a specified value and the reflection loss meets the specified value requirements; Step 3, switch the switch (9) to a state where the far end of the tested cable (1) is connected to the input end of the network analyzer (2), the network analyzer (2) transmits a signal, and the through parameter of the network analyzer (2) is read, which is the shielding performance value of the tested cable (1).

10. The cable shielding performance testing method according to claim 9, characterized in that: In the step S2, the characteristic impedance is maintained at 50Ω and the reflection loss is greater than 20dB.

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