Method for measuring coaxial cable length and terminal load

Abstract

The invention provides a coaxial cable length and terminal load measuring method, which comprises the following steps: determining a coaxial cable to be measured, injecting a high-frequency electromagnetic wave signal into one end of the coaxial cable, and collecting a standing wave at the other end of the coaxial cable; continuously changing the frequency of the high-frequency electromagnetic wave signal injected into the coaxial cable to enable the peak value of the standing wave to be at an incident port; when the peak value of the standing wave is the complete superposition of the incident wave and the reflected wave, calculating the length of the coaxial cable; after the length of the coaxial cable is determined, the load type and the load parameters are determined according to the movement of the phase. In cable length measurement, high-frequency electromagnetic waves are injected into one end of the coaxial cable, the cable length is calculated by using a standing wave phenomenon, and meanwhile, the load type is judged and load parameters are measured by observing phase movement, so that the measurement efficiency of the length and the load of the coaxial cable is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of cables, and in particular to a method for measuring the length and terminal load of a coaxial cable. Background Art

[0002] At present, the detection of coaxial cable length and terminal load is also of practical significance in today's society. For example, if a highway cable buried deep underground breaks, conventional inspection will take up a considerable amount of time. For the load detection of coaxial cables, the cables are in the power system, and the load detection of the coaxial cable terminals can be used to test the status and power consumption of the terminal equipment or load connected to the cable.

[0003] How to reduce the length of coaxial cables and the load calculation time has become an urgent problem to be solved. Summary of the invention

[0004] In view of this, the present invention proposes a method for measuring the length and terminal load of a coaxial cable, aiming to solve the problem of how to reduce the length and load calculation time of the coaxial cable.

[0005] In one aspect, the present invention provides a method for measuring the length and terminal load of a coaxial cable, comprising:

[0006] Determine a coaxial cable to be tested, inject a high-frequency electromagnetic wave signal into one end of the coaxial cable, and collect a standing wave at the other end of the coaxial cable;

[0007] Continuously changing the frequency of the high-frequency electromagnetic wave signal injected into the coaxial cable so that the peak of the standing wave is at the incident port;

[0008] When the peak value of the standing wave is the complete superposition of the incident wave and the reflected wave, calculating the length of the coaxial cable;

[0009] After determining the length of the coaxial cable, the load type and load parameters are determined according to the phase shift.

[0010] Furthermore, before calculating the length of the coaxial cable, the frequency corresponding to the length of the coaxial cable is first determined, including:

[0011] When the standing wave peak is the complete superposition state of the incident wave and the reflected wave, at this time, the output of the multiplier has the maximum amplitude after the AC is filtered out by the low-pass filter. At this time, the DDS frequency modulated by the MCU is n / 2 times the corresponding wavelength, where n is an integer. Suppose the output value of the multiplier is x, the incident wave amplitude is A, and the standing wave amplitude is B, then calculate x according to formula (1):

[0012] x=A sinωt×B sinωt (1)

[0013] Further deduction can be obtained:

[0014]

[0015] After the AC is filtered out by a low-pass filter,

[0016]

[0017] When x takes the maximum value x1, the corresponding frequency emitted by the DDS can be obtained.

[0018] Further, after obtaining the corresponding frequency emitted by the DDS, determining the length of the coaxial cable after processing the frequency includes:

[0019] When the frequency increases, the arrival of each wave peak marks the appearance of a frequency that is an integer multiple of the wavelength. Therefore, by measuring the frequency of the coaxial cable, the corresponding length λ can be obtained. λ is calculated according to formula (4):

[0020]

[0021] Where n is the number of times the wave peak is obtained, λ is the length of the coaxial cable, f is the frequency of the electromagnetic wave injected at one end of the coaxial cable, and ν c For electromagnetic waves.

[0022] Further, after the coaxial cable length λ is calculated, the following steps are performed:

[0023] Electromagnetic wave ν c The value is ν c =2.45×10 8 m / s, after simplifying formula (4), we get:

[0024]

[0025] At the same time, due to the existence of distribution parameters, a straight line is linearly fitted after using the difference method to obtain the value. The approximate value of λ is λ1, K and B are the coefficients of the first-order term, and we get:

[0026]

[0027] Further, after the length of the coaxial cable is calculated, the method further comprises:

[0028] After the length measurement of the corresponding coaxial cable is completed, the length of the coaxial cable is known, and after the load is connected, the capacitance and resistance are measured according to their respective physical parameters, where:

[0029] When the end of the coaxial cable is open circuit, the potential at the test location will remain constant because there is no current flowing, so there is no potential drop;

[0030] When the load is a resistor, the potential at the test location will show a significant drop, more than 60%, because of the voltage drop caused by the current passing through the resistor;

[0031] When the load is a capacitor, the potential change at the test location will produce a tiny falling edge due to the current change during the capacitor's passage or discharge process.

[0032] Compared with the prior art, the beneficial effect of the present invention is that in the measurement of cable length, the present invention injects high-frequency electromagnetic waves at one end of the coaxial cable, calculates the cable length by using the standing wave phenomenon, and at the same time, observes the phase shift to judge the load type and measure the load parameters, which greatly improves the measurement efficiency of the length and load of the coaxial cable. At the same time, the invention can quickly locate the location of the cable fault, reduce the maintenance time, improve the maintenance efficiency, and reduce economic losses. In the present invention, through load detection, the coaxial cable is in the power system, and the load detection of the coaxial cable terminal can be used to test the state and power consumption of the terminal device or load connected to the cable, which can assist in detecting potential faults or abnormalities and ensure the stability and reliability of the cable system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0034] Figure 1 A flow chart of a method for measuring the length and terminal load of a coaxial cable provided by an embodiment of the present invention;

[0035] Figure 2 Functional block diagram of a coaxial cable length and terminal load measurement system provided by an embodiment of the present invention;

[0036] Figure 3 A functional block diagram of an MCU controlling a DDS to generate sine waves of different frequencies provided in an embodiment of the present invention;

[0037] Figure 4 A functional block diagram of an MCU obtaining a DC voltage through an ADC provided in an embodiment of the present invention;

[0038] Figure 5 A filter circuit diagram on a signal processing board provided by an embodiment of the present invention;

[0039] Figure 6 A structural diagram of a DC-DC power supply module provided in an embodiment of the present invention;

[0040] Figure 7A program flow chart of a system for measuring the length and terminal load of a coaxial cable provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] See also Figure 1 As shown, an embodiment of the present invention provides a method for measuring the length and terminal load of a coaxial cable, which is characterized by comprising the following steps:

[0043] S100: determining a coaxial cable to be tested, injecting a high-frequency electromagnetic wave signal into one end of the coaxial cable, and collecting a standing wave at the other end of the coaxial cable;

[0044] S200: continuously changing the frequency of the high-frequency electromagnetic wave signal injected into the coaxial cable so that the peak of the standing wave is at the incident port;

[0045] S300: When the peak value of the standing wave is the complete superposition of the incident wave and the reflected wave, calculating the length of the coaxial cable;

[0046] S400: After determining the length of the coaxial cable, determine the load type and load parameters according to the phase shift.

[0047] In the cable length measurement of the above embodiment, high-frequency electromagnetic waves are injected into one end of the coaxial cable, the cable length is calculated using the standing wave phenomenon, and at the same time, the phase shift is observed to determine the load type and measure the load parameters, thereby greatly improving the measurement efficiency of the length and load of the coaxial cable. At the same time, the above embodiment can quickly locate the position of the cable fault, reduce the maintenance time, improve the maintenance efficiency, and reduce economic losses.

[0048] In the above embodiments, through load detection, the coaxial cable is in the power system, and the load detection of the coaxial cable terminal can be used to test the status and power consumption of the terminal device or load connected to the cable, which can assist in detecting potential faults or abnormalities and ensure the stability and reliability of the cable system.

[0049] Specifically, before calculating the length of the coaxial cable, the frequency corresponding to the length of the coaxial cable is first determined, including:

[0050] When the standing wave peak is the complete superposition state of the incident wave and the reflected wave, at this time, the output of the multiplier has the maximum amplitude after the AC is filtered out by the low-pass filter. At this time, the DDS frequency modulated by the MCU is n / 2 times the corresponding wavelength, where n is an integer. Suppose the output value of the multiplier is x, the incident wave amplitude is A, and the standing wave amplitude is B, then calculate x according to formula (1):

[0051] x=Asinωt×Bsinωt (1)

[0052] Further deduction can be obtained:

[0053]

[0054] After the AC is filtered out by a low-pass filter,

[0055]

[0056] When x takes the maximum value x1, the corresponding frequency emitted by the DDS can be obtained.

[0057] In the above embodiment, by injecting a high-frequency electromagnetic wave signal into one end of the coaxial cable, due to the sudden change in impedance at the other end, the incident wave and the reflected wave will be superimposed, that is, a standing wave. By continuously changing the frequency of the electromagnetic wave, the peak of the standing wave is exactly at the incident port. At this frequency, the path of signal transmission is an integer multiple of the signal wavelength. As the frequency increases, the arrival of each wave peak marks the length of the electromagnetic wave transmission path by another wavelength, thereby calculating the length of the cable.

[0058] When the coaxial cable length corresponds to the frequency, when the standing wave peak is the complete superposition of the incident wave and the reflected wave, that is, when the output of the multiplier is the maximum after the AC is filtered out by the low-pass filter, the DDS frequency modulated by the MCU is n / 2 times the corresponding wavelength (n is an integer). Suppose the output value of the multiplier is x, the incident wave amplitude is A, and the standing wave amplitude is B, then calculate x according to formula (1):

[0059] x=Asinωt×Bsinωt (1)

[0060] Further deduction can be obtained:

[0061]

[0062] After the AC is filtered out by a low-pass filter,

[0063]

[0064] When x takes the maximum value x1, the corresponding frequency emitted by the DDS can be obtained.

[0065] Specifically, the processing of frequency determines the length of the coaxial cable. As the frequency increases, the arrival of each wave peak marks the appearance of a frequency that is an integer multiple of the wavelength. From this, it is calculated that the corresponding length can be obtained by measuring the frequency of the coaxial cable, where n is the number of wave peaks, λ is the length of the coaxial cable, and f is the frequency of the electromagnetic wave injected at one end of the coaxial cable: ν c For electromagnetic waves.

[0066] Specifically, after obtaining the corresponding frequency emitted by the DDS, determining the length of the coaxial cable after processing the frequency includes:

[0067] When the frequency increases, the arrival of each wave peak marks the appearance of a frequency that is an integer multiple of the wavelength. Therefore, by measuring the frequency of the coaxial cable, the corresponding length λ can be obtained. λ is calculated according to formula (4):

[0068]

[0069] Where n is the number of times the wave peak is obtained, λ is the length of the coaxial cable, f is the frequency of the electromagnetic wave injected at one end of the coaxial cable, and ν c For electromagnetic waves.

[0070] Specifically, after the coaxial cable length λ is calculated, the following steps are performed:

[0071] Electromagnetic waves c The value is v c =2.45×10 8 m / s, after simplifying formula (4), we get:

[0072]

[0073] At the same time, due to the existence of distribution parameters, a straight line is linearly fitted after using the difference method to obtain the value. The approximate value of λ is λ1, K and B are the coefficients of the first-order term, and we get:

[0074]

[0075] Through experimental measurement, its accuracy reaches 1%.

[0076] Specifically, after the length of the coaxial cable is calculated, the following steps are performed:

[0077] After the length measurement of the corresponding coaxial cable is completed, the length of the coaxial cable is known, and after the load is connected, the capacitance and resistance are measured according to their respective physical parameters, where:

[0078] When the end of the coaxial cable is open circuit, the potential at the test location will remain constant because there is no current flowing, so there is no potential drop;

[0079] When the load is a resistor, the potential at the test location will show a significant drop, more than 60%, because of the voltage drop caused by the current passing through the resistor;

[0080] When the load is a capacitor, the potential change at the test location will produce a tiny falling edge due to the current change during the capacitor's passage or discharge process.

[0081] The above embodiment is implemented by a coaxial cable length and terminal load measurement system, see Figure 2 As shown, Figure 2 Functional block diagram of a coaxial cable length and terminal load measurement system.

[0082] The measurement system has the following functions: (1) The system can display the working status, cable length, load type, and load parameters in a specified format; (2) The system can complete the measurement of cables with a length between 10 m and 20 m within 5 seconds with a relative error not exceeding 5%; (3) The system can complete the determination of load type and load parameters within 5 seconds with a relative error not exceeding 10%; (4) The system can complete the measurement of cables with a length of less than 1 m within 5 seconds with a relative error not exceeding 1%.

[0083] In order to complete the functions and reduce errors as much as possible, first of all, for the first requirement, the LCD screen can be controlled by the MCU using the synchronous serial communication interface protocol (SPI) to complete the display of the specified format. If you want to complete the length measurement, you can inject a periodic function waveform at one end of the coaxial cable, analyze and process the injected incident waveform and the obtained reflected waveform to obtain the corresponding cable length. For the measurement of load type and load parameters, the phase shift can be observed on the basis of the length measurement, and the parameter value can be obtained according to the amplitude of the phase shift. In the measurement of shorter cable length, the incident frequency can also be increased to facilitate detection.

[0084] Specifically, combined Figure 3 As shown in the figure, the structure and design of the swept frequency signal source of the measurement system include:

[0085] Solution 1: Use AD9959, which is a DDS specifically used in the RF field, with an output frequency of up to 200MHz and an output amplitude of ±500mV. The theoretical verification basically meets expectations, but it is found that the amplitude is not high enough, and the amplitude may be seriously reduced when the frequency is close to 80MHZ, affecting the frequency judgment.

[0086] Solution 2: Use the AD9910 chip, which is a high-performance DDS chip with an output frequency of up to 400MHz, capable of generating sine waves, a DAC accuracy of 14 bits, and an output amplitude of ±760mV. In actual verification, the amplitude of its adjustable frequency range is severely reduced after 140MHZ, affecting the frequency judgment. It is significantly better than AD9959 and is conducive to improving the accuracy of the measured parameters.

[0087] It can be seen from the actual scheme verification that Scheme 2 has obvious advantages over Scheme 1, so Scheme 2 is selected.

[0088] Combination Figure 4 As shown, the signal detection and processing system structure and design of the measurement system include:

[0089] At one end of the coaxial cable, the incident wave and the reflected wave are superimposed. The standing wave generated by the superposition is the basis for signal detection. Generally speaking, there are two methods: AC search and DC search. However, at high frequencies, the above two methods have their limitations in both numerical accuracy and parameter measurement. Compared with these two methods, detection has higher accuracy and measurable width.

[0090] Solution 1: The two ends of the resistor are the incident wave and the reflected wave, respectively. The multiplier is used for synchronous detection and synchronous demodulation to obtain the product of the incident wave and the reflected wave. Therefore, AD835 is used as the multiplier, which has the characteristics of high bandwidth. The input bias current and input bias voltage are also very low, which helps to reduce input errors and enhance accuracy, and can also slightly increase gain.

[0091] Solution 2: Use diodes for detection. Use the unidirectional conductivity of diodes for detection. Only half of the sine wave above the x-axis is retained, and then the average value is calculated to obtain a DC voltage. Since it is a passive detection, it requires a relatively large signal power, and the required conduction voltage of the diode may cause the diode to fail to conduct when the amplitude is low. Therefore, Solution 2 has a greater disadvantage compared to Solution 1.

[0092] Solution 3: Use transistors for detection. Triode detection is a type of diode detection. Compared with diodes, it uses the critical conduction of the base of the transistor to connect a capacitor in series before the base, and gives a relatively small bias to the base, so that the base is basically maintained in a critical conduction state. If a sine wave is input, the base will enter and the emitter will output. The specific principle is similar to that of the diode, but it can also complete detection when the amplitude is low. However, compared with the multiplier, its performance at high frequencies is relatively poor.

[0093] By comparing the three solutions, it is found that Solution 1 has better performance.

[0094] Specifically, the system structure and circuit design of the measurement system include:

[0095] Sweep signal source (DDS) circuit

[0096] The DDS circuit design is to generate a signal with a specific frequency and phase in a digital way. The MCU provides the target control parameters to enable the AD9910 to generate the required frequency for DAC.

[0097] For output filtering (the analog signal generated by the DDS circuit needs to be filtered through a low-pass filter to remove the high-frequency noise introduced in the digital conversion) to smooth the output signal.

[0098] Signal processing structure design

[0099] Combination Figure 5 As shown, the two ends of the 75Ω resistor are connected to a multiplier for operation, and a second-order RC filter is connected to the output of the multiplier to filter out the AC component and obtain the DC component. At the same time, a first-order RC filter is connected to the electromagnetic wave injection end of the coaxial cable for load parameter detection.

[0100] Design of power module

[0101] Combination Figure 6 As shown in the figure, since the modules need different power levels, the main control board and the AD9910 signal transmitter board both need 5V power supply, and the multiplier needs ±5V voltage. Since the question requires only a single 6V power supply, the level conversion is completed through a DC-DC boost.

[0102] Combination Figure 7 As shown, after using MUC to control DDS to generate high-frequency signals, collect the DC signal output by the multiplier and find the peak of the signal. The DDS output frequency corresponding to the peak is the multiple of the coaxial cable wavelength. Use the formula l = 150 / w to calculate the length of the cable.

[0103] When measuring the load, the wavelength of the doubled frequency is output, and the voltage value drops significantly when the load is a resistor. When it is a capacitor, the change is small and easy to distinguish. For resistance measurement, the DC component can be directly used to measure the load voltage. For capacitance, DDS frequency conversion is used for fast scanning, and the resonance point frequency is collected to convert its capacitance value.

[0104] When the above-mentioned coaxial cable length and terminal load measurement system is implemented, the test data is recorded as follows:

[0105] Table 1 shows the data when the end of the coaxial cable is open:

[0106]

[0107] Table 2 shows the data when the coaxial cable is terminated with a resistor:

[0108] True / Ω 22.2 24.2 9.9 29.9 27.4 Measured value / Ω 22.5 24.2 9.7 29.4 27.3 error% 0.01 0 0.02 0.01 0.003

[0109] The above measurement system can complete the measurement of cables with a length of 10m to 20m within 5 seconds with a relative error of no more than 1%, and complete the judgment of load type and load parameters within 5 seconds with a relative error of no more than 10%. It realizes the function of the coaxial cable length and terminal load detection device. Except for the capacitance test, the other parameters have reached the requirements of the performance part.

[0110] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0111] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0112] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0113] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for measuring the length and terminal load of a coaxial cable, characterized in that: include: Determine a coaxial cable to be tested, inject a high-frequency electromagnetic wave signal into one end of the coaxial cable, and collect a standing wave at the other end of the coaxial cable; Continuously changing the frequency of the high-frequency electromagnetic wave signal injected into the coaxial cable so that the peak of the standing wave is at the incident port; When the peak value of the standing wave is the complete superposition of the incident wave and the reflected wave, calculating the length of the coaxial cable; After determining the length of the coaxial cable, the load type and load parameters are determined according to the phase shift.

2. The method for measuring the length and terminal load of a coaxial cable according to claim 1, characterized in that: Before calculating the length of the coaxial cable, firstly determine the frequency corresponding to the length of the coaxial cable, including: When the standing wave peak is the complete superposition state of the incident wave and the reflected wave, at this time, the output of the multiplier has the maximum amplitude after the AC is filtered out by the low-pass filter. At this time, the DDS frequency modulated by the MCU is n / 2 times the corresponding wavelength, where n is an integer. Suppose the output value of the multiplier is x, the incident wave amplitude is A, and the standing wave amplitude is B, then x is calculated according to formula (1): x=A sinωt×B sinωt (1) Further deduction can be obtained: After the AC is filtered out by a low-pass filter, When x takes the maximum value x1, the corresponding frequency emitted by the DDS can be obtained.

3. The method for measuring the length and terminal load of a coaxial cable according to claim 2, characterized in that: After obtaining the corresponding frequency emitted by the DDS, determining the length of the coaxial cable after processing the frequency includes: When the frequency increases, the arrival of each wave peak marks the appearance of a frequency that is an integer multiple of the wavelength. Therefore, by measuring the frequency of the coaxial cable, the corresponding length λ can be obtained. λ is calculated according to formula (4): Where n is the number of times the wave peak is obtained, λ is the length of the coaxial cable, f is the frequency of the electromagnetic wave injected at one end of the coaxial cable, and ν c For electromagnetic waves.

4. The method for measuring the length and terminal load of a coaxial cable according to claim 3, characterized in that: After the coaxial cable length λ is calculated, the following steps are performed: Electromagnetic wave ν c The value is ν c =2.45×10 8 m / s, after simplifying formula (4), we get: At the same time, due to the existence of distribution parameters, a straight line is linearly fitted after using the difference method to obtain the value. The approximate value of λ is λ1, K and B are the coefficients of the first-order term, and we get:

5. The method for measuring the length and terminal load of a coaxial cable according to claim 3, characterized in that: After the length of the coaxial cable is calculated, the following steps are included: After the length measurement of the corresponding coaxial cable is completed, the length of the coaxial cable is known, and after the load is connected, the capacitance and resistance are measured according to their respective physical parameters, where: When the end of the coaxial cable is open circuit, the potential at the test location will remain constant because there is no current flowing, so there is no potential drop; When the load is a resistor, the potential at the test location will show a significant drop, more than 60%, because of the voltage drop caused by the current passing through the resistor; When the load is a capacitor, the potential change at the test location will produce a tiny falling edge due to the current change during the capacitor's passage or discharge process.

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