Electromagnetic shielding effectiveness testing method for multi-branch multi-core cable

Abstract

The invention relates to a method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable. The method comprises the following steps: grounding a shielding layer of the multi-branch multi-core cable and selecting a plurality of wires to be tested; one end of a tested wire is selected as a signal injection end, the other end of the tested wire is selected as a signal detection end for testing, an adapter socket of the signal injection end of the tested wire is connected with a resistor, a signal generator injects a test signal at the signal injection end, and current noise and voltage noise are detected at the signal detection end through a frequency spectrograph; obtaining the shielding effectiveness according to the detected current noise and voltage noise; the signal injection end and the signal detection end are exchanged and tested, the shielding effectiveness is obtained, and the shielding effectiveness of the tested wire is determined according to the shielding effectiveness of the two tests; and measuring the shielding effectiveness of all the measured wires, and determining the electromagnetic shielding effectiveness of the multi-branch multi-core cable. According to the invention, the shielding effectiveness of the multi-branch multi-core cable can be tested and quantitatively evaluated.

Description

Technical Field

[0001] The invention belongs to the technical field of cable shielding effectiveness testing, and in particular relates to a method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable. Background Art

[0002] In many cases, due to the complexity of the interconnection system, the interconnection cable is composed of multi-branch multi-core transmission conductors. Due to the large number of branches, the processing of the shielding layer of this type of shielded cable is more complicated. Under the same process technology requirements, the shielding effect of the cable may vary greatly in different frequency ranges.

[0003] Currently, existing cable shielding effectiveness testing methods are mainly for cable bundles with single shielded conductors and one-to-one plugs, but are not applicable to quantitative testing of the electromagnetic shielding effectiveness of multi-branch and multi-core cables. For example, the 3-coaxial method uses standard test fixtures to test the electromagnetic shielding effectiveness. This method is more accurate for testing, but is only applicable to single conductors of fixed length, single-core coaxial type. The line injection method, current probe method, and power absorption clamp method can be used to test the electromagnetic shielding effectiveness of multi-core cable bundles, but are only applicable to cables with certain length requirements and one-to-one plugs. At the same time, the reverberation chamber method, GTEM chamber method, and darkroom radiation method use irradiation to test electromagnetic shielding, and the frequency range is applicable to above 400MHz.

[0004] In the prior art, there is no quantitative test method for objectively evaluating the electromagnetic shielding effectiveness of multi-branch and multi-core cables. Therefore, it is urgent to propose a quantitative test method for the electromagnetic shielding effectiveness of cables to avoid subjective judgment of the shielding effect of shielded cables. Summary of the Invention

[0005] The present invention provides a method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable. The method can test and quantitatively evaluate the shielding effectiveness of the multi-branch multi-core cable, thereby solving the technical problems mentioned in the background technology.

[0006] The technical solution of the present invention is as follows: A method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable, comprising: S10: Ground the shielding layer of the multi-branch multi-core cable, select multiple tested conductors from the multi-branch multi-core cable, connect both ends of each tested conductor to the adapter socket, and use all core wires in each tested conductor as signal transmission core wires; S20: Select one end of the measured wire as the signal injection end and the other end as the signal detection end to perform the first test. Connect the adapter socket of the signal injection end of the measured wire to a resistor. A signal generator injects a test signal at a preset frequency at the signal injection end through electromagnetic induction. Use a spectrum analyzer to detect current noise and voltage noise at the signal detection end. S30: Obtaining a first shielding effectiveness under a first test according to the detected current noise and voltage noise; S40: swapping the signal injection end and the signal detection end in S20, repeating the test process for a second test, obtaining a second shielding effectiveness under the second test, and determining the shielding effectiveness of the tested conductor based on the first shielding effectiveness and the second shielding effectiveness; S50: Repeat S20-S40 to measure the shielding effectiveness of all the tested conductors, and determine the electromagnetic shielding effectiveness of the multi-branch multi-core cable based on the shielding effectiveness of all the tested conductors.

[0007] Furthermore, the S20 includes: The signal generator is mounted on the measured conductor of the multi-branch multi-core cable through a current clamp and is close to the signal injection end; A spectrum analyzer for detecting current noise is mounted on the measured conductor of the multi-branch multi-core cable through a current clamp and is close to the signal detection end; A spectrum analyzer for detecting voltage noise is connected to a transfer socket at the signal detection end of the measured wire.

[0008] Furthermore, the adapter socket at the signal injection end of the measured wire is connected to a 50Ω resistor, and the adapter socket at the signal detection end of the measured wire is connected to a 50Ω impedance input end of the spectrum analyzer.

[0009] Furthermore, the calculation formula of the shielding effectiveness in S30 is as follows: , in, SE Indicates shielding effectiveness, V 2 represents the voltage noise, V 1 represents the current noise, Z Indicates the transfer coefficient of the current clamp.

[0010] Furthermore, the S10 includes: A typical transmission conductor in the multi-branch multi-core cable is selected as the conductor to be measured, and each branch of the multi-branch multi-core cable is covered during the selection, and the selection is carried out in sequence from the main branch to the secondary branch.

[0011] Furthermore, the preset frequency range of the test signal is 100kHz~100MHz.

[0012] Furthermore, the adapter socket is a BNC socket.

[0013] Furthermore, the measured conductor shielding effectiveness of the measured conductor is an average of the first shielding effectiveness and the second shielding effectiveness.

[0014] Furthermore, the electromagnetic shielding effectiveness of the multi-branch multi-core cable is an average of the shielding effectiveness of all tested conductors.

[0015] The present invention has the following beneficial effects: The present invention decomposes a complex multi-branch, multi-core cable and quantitatively tests the electromagnetic shielding effectiveness of the decomposed cables, thereby calculating the overall electromagnetic shielding effectiveness of the multi-branch, multi-core cable. The present invention has a simple testing method, requiring only a simple test fixture, current calipers, a signal generator, and a spectrum analyzer to complete the test. The present invention also offers flexible testing capabilities, allowing for the selection of frequency points of interest in a project, as well as the ability to conduct electromagnetic shielding effectiveness testing at custom frequencies through software development. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a flowchart of a method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable.

[0017] Figure 2 It is a schematic diagram of the electromagnetic shielding effectiveness testing method of the multi-branch multi-core cable of the present invention.

[0018] Figure 3 This is the schematic diagram of multi-core cable to BNC socket.

[0019] Figure 4 This is a terminal connection diagram of the injection end and the monitoring end.

[0020] Figure 5 This is an example of the electromagnetic shielding effectiveness test results of a certain type of cable.

[0021] Figure markings: 1-multi-branch multi-core cable, 2-signal generator, 3-current caliper, 4-spectrum analyzer, 5-test fixture, 6-cable socket, 7-shielding layer, 8-BNC socket, 9-BNC connector type 50 ohm resistor, 10-injection end BNC socket, 11-monitoring end BNC socket. DETAILED DESCRIPTION

[0022] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0023] In the technical solution of the present invention, Figure 1 This is a flow chart provided by a method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable according to the present invention, such as Figure 1 As shown, the present invention specifically includes: S10: Ground the shielding layer of the multi-branch multi-core cable, select multiple measured conductors in the multi-branch multi-core cable, connect both ends of each measured conductor to the adapter socket, and use all core wires in each measured conductor as signal transmission core wires.

[0024] Multi-branch multi-core cables have multiple branch lines at both ends, such as Figure 2 As shown, in the following description of the specific implementation process of the present invention, Figure 2 For example, Figure 2 The multi-branch multi-core cable has 3 branch cables on the left and 4 branch cables on the right. The ends of the left branch cables are A1, A2 and A3, and the ends of the right branch cables are B1, B2, B3 and B4. Figure 2 In the figure, 1 is a multi-branch multi-core cable, 2 is a signal generator, 3 is a current clamp, 4 is a spectrum analyzer, and 5 is a test fixture.

[0025] During the test, both ends of the multi-branch, multi-core cable are mounted on a test fixture. The test fixture is a bracket structure with cable sockets fixed at both ends corresponding to the cable plugs of the multi-branch, multi-core cable. The cable plugs are inserted into the cable sockets, and the shield of the multi-branch, multi-core cable is also connected to the cable sockets. The test fixture is equipped with a grounding conductor. The cable sockets form a complete ground loop with the ground plane through the ground conductor, thereby grounding the shield of the multi-branch, multi-core cable. After the multi-branch, multi-core cable is mounted on the test fixture, it is kept 5 cm above the ground plane.

[0026] A typical transmission conductor in the multi-branch multi-core cable is selected as the conductor to be measured, and each branch of the multi-branch multi-core cable is covered during the selection, and the selection is carried out in sequence from the main branch to the secondary branch.

[0027] by Figure 2 For example, according to the internal conductors of the cable, select A1-B1 as a shielded twisted pair, A2-B2 as a shielded twisted pair, A2-B3 as a shielded single-core wire, and A3-B4 as a shielded three-twisted wire, and use these four transmission wires as the measured wires.

[0028] Convert both ends of the tested wire to BNC plugs. Specifically, insert the cable plugs at both ends of the tested wire into the cable socket. Lead out all the core wires inside the tested wire from the back of the cable socket. Connect all the core wires from the back of the cable socket to the core wire connectors in the BNC socket. For twisted pair or triple twisted wire, the two cores or three cores of the wires should be led out from the back of the cable socket, interconnected, and then connected to the socket core of the BNC socket. The shielding layer should be connected to the test fixture. For the twisted pair connection diagram, see Figure 3 . Figure 3 In the figure, 5 is the test fixture, 6 is the cable socket, 7 is the shielding layer, and 8 is the BNC socket.

[0029] S20: Select one end of the measured wire as the signal injection end and the other end as the signal detection end to perform the first test. Connect the adapter socket of the signal injection end of the measured wire to a resistor. The signal generator injects a test signal at a preset frequency at the signal injection end through electromagnetic induction. Use a spectrum analyzer to detect current noise and voltage noise at the signal detection end.

[0030] Wherein, the signal generator is mounted on the measured conductor of the multi-branch multi-core cable through a current clamp and is close to the signal injection end; A spectrum analyzer for detecting current noise is mounted on the measured conductor of the multi-branch multi-core cable through a current clamp and is close to the signal detection end; A spectrum analyzer for detecting voltage noise is connected to a transfer socket at the signal detection end of the measured wire.

[0031] More specifically, the adapter socket at the signal injection end of the measured wire is connected to a 50Ω resistor, and the adapter socket at the signal detection end of the measured wire is connected to a 50Ω impedance input end of the spectrum analyzer.

[0032] More specifically, the preset frequency range of the test signal is 100 kHz to 100 MHz.

[0033] Use one end of the transmission line as the signal injection end and the other end as the signal monitoring end. Use a signal generator to inject a current of a certain frequency at the signal injection end through a current clamp. At the same time, use a spectrum analyzer to monitor the current noise at the branch of the transmission line monitoring end through the current clamp. At the same time, use a spectrum analyzer to test the voltage noise of the core line. Figure 2 The left side of the A1-B1 transmission line is the signal injection end, and the right side is the signal monitoring end. The BNC socket of the signal injection end of the measured line is terminated with a 50-ohm resistor, and the BNC socket of the monitoring end of the transmission line is connected to the 50-ohm impedance input end of the spectrum analyzer through a coaxial cable. Figure 4 . Figure 4 In the figure, 9 is a 50-ohm resistor with a BNC connector, 10 is a BNC socket for the injection end, and 11 is a BNC socket for the monitoring end.

[0034] S30: Obtaining a first shielding effectiveness under a first test according to the detected current noise and voltage noise.

[0035] Specifically, the calculation formula of the shielding effectiveness in S30 is as follows: , in, SE Indicates shielding effectiveness, V 2 represents the voltage noise, V 1 represents the current noise,Z Indicates the transfer coefficient of the current clamp.

[0036] The shielding effectiveness of the corresponding frequency can be calculated by the test values ​​of the two spectrum analyzers and the cable parameters. The test value of the monitoring current noise spectrum analyzer is recorded as V 1 (dBm), the voltage noise spectrum analyzer test value is recorded as V 2 (dBm), the transmission coefficient of the current clamp is recorded as Z , then the first shielding effectiveness of this test is recorded as SE11 The transmission coefficient of the current caliper is a set of data provided by the manufacturer of the current caliper along with the product, which is used for data calculation during testing.

[0037] S40: swapping the signal injection end and the signal detection end in S20, repeating the test process to perform a second test, and obtaining a second shielding effectiveness in the second test.

[0038] The measured conductor shielding effectiveness of the measured conductor is determined according to the first shielding effectiveness and the second shielding effectiveness.

[0039] The measured conductor shielding effectiveness of the measured conductor is an average of the first shielding effectiveness and the second shielding effectiveness.

[0040] The signal injection end and signal monitoring end of the transmission wire are swapped, and the current noise monitoring and voltage noise monitoring tests are performed again, and the second shielding effectiveness of the corresponding frequency is calculated. SE12 The average value of the first shielding effectiveness and the second shielding effectiveness is taken as the shielding effectiveness of the measured conductor. SE1=(SE11+SE12) / 2 .

[0041] S50: Repeat S20-S40 to measure the shielding effectiveness of all the tested conductors, and determine the electromagnetic shielding effectiveness of the multi-branch multi-core cable based on the shielding effectiveness of all the tested conductors.

[0042] The electromagnetic shielding effectiveness of the multi-branch multi-core cable is the average of the shielding effectiveness of all tested conductors.

[0043] Calculate the average value of the shielding effectiveness of the selected multiple tested conductors, which is the shielding effectiveness value of the multi-branch multi-core cable. SE=(SE1+SE2+SE3+SE4) / 4 .

[0044] In this embodiment, the electromagnetic shielding effectiveness test and evaluation is conducted on a certain type of multi-branch multi-core cable. The cable has a one-to-three bifurcated structure, and three shielded twisted pairs are selected as transmission conductors as the test objects. The test settings are performed according to the above steps. The length of the three transmission conductors is 2.6m, and the transmission coefficient of the current clamp at 1MHz is 10.6dB. The electromagnetic shielding effectiveness calculated by the test is SE11 =76.25dB, SE12 =72.63dB, SE21 =67.84dB, SE22 =69.25dB, SE31 =87.11dB, SE32 =84.55dB, so the quantitative evaluation value of electromagnetic shielding effectiveness of this type of multi-branch multi-core cable at 1MHz is SE 75.47dB. After testing at multiple frequency points, the test results are as follows Figure 5 shown.

[0045] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for testing the electromagnetic shielding effectiveness of a multi-branch multi-core cable, characterized in that: include: S10: Ground the shielding layer of the multi-branch multi-core cable, select multiple tested conductors from the multi-branch multi-core cable, connect both ends of each tested conductor to the adapter socket, and use all core wires in each tested conductor as signal transmission core wires; S20: Select one end of the measured wire as the signal injection end and the other end as the signal detection end to perform the first test. Connect the adapter socket of the signal injection end of the measured wire to a resistor. A signal generator injects a test signal at a preset frequency at the signal injection end through electromagnetic induction. Use a spectrum analyzer to detect current noise and voltage noise at the signal detection end. S30: Obtaining a first shielding effectiveness under a first test according to the detected current noise and voltage noise; S40: swapping the signal injection end and the signal detection end in S20, repeating the test process for a second test, obtaining a second shielding effectiveness under the second test, and determining the shielding effectiveness of the tested conductor based on the first shielding effectiveness and the second shielding effectiveness; S50: Repeat S20-S40 to measure the shielding effectiveness of all the tested conductors, and determine the electromagnetic shielding effectiveness of the multi-branch multi-core cable based on the shielding effectiveness of all the tested conductors.

2. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 1, wherein: The S20 includes: The signal generator is mounted on the measured conductor of the multi-branch multi-core cable through a current clamp and is close to the signal injection end; A spectrum analyzer for detecting current noise is mounted on the measured conductor of the multi-branch multi-core cable through a current clamp and is close to the signal detection end; A spectrum analyzer for detecting voltage noise is connected to a transfer socket at the signal detection end of the measured wire.

3. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 2, wherein: The adapter socket at the signal injection end of the measured wire is connected to a 50Ω resistor, and the adapter socket at the signal detection end of the measured wire is connected to a 50Ω impedance input end of the spectrum analyzer.

4. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 2, wherein: The calculation formula of the shielding effectiveness in S30 is as follows: ， in, SE Indicates shielding effectiveness, V 2 represents the voltage noise, V 1 represents the current noise, Z Indicates the transfer coefficient of the current clamp.

5. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 1, wherein: The S10 includes: A typical transmission conductor in the multi-branch multi-core cable is selected as the conductor to be measured, and each branch of the multi-branch multi-core cable is covered during the selection, and the selection is carried out in sequence from the main branch to the secondary branch.

6. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 1, wherein: The preset frequency range of the test signal is 100kHz~100MHz.

7. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 1, wherein: The adapter socket is a BNC socket.

8. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 1, wherein: The measured conductor shielding effectiveness of the measured conductor is an average of the first shielding effectiveness and the second shielding effectiveness.

9. The electromagnetic shielding effectiveness testing method of a multi-branch multi-core cable according to claim 1, wherein: The electromagnetic shielding effectiveness of the multi-branch multi-core cable is the average of the shielding effectiveness of all tested conductors.

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