Method and system for measuring direct current resistance of cable outer sheath, electronic equipment and medium

Abstract

This invention relates to the field of electrical measurement technology, and in particular to a method, system, electronic device, and medium for measuring the DC resistance of cable sheaths. The method includes: defining a sequentially connected induced current acquisition section, a measured resistance section, and a compensation injection section; extracting the frequency, phase, and amplitude reference parameters of the power frequency induced voltage signal; performing closed-loop dynamic adjustment based on a proportional-integral-differential algorithm until the residual power frequency interference voltage drops below a preset threshold; injecting a preset constant DC current into the measured resistance section and simultaneously acquiring the DC voltage drop signal across the measured resistance section; and calculating the DC resistance value of the measured resistance section based on the four-terminal test method. This method solves the technical problem of insufficient measurement accuracy of the DC resistance of cable sheaths in complex field environments with uninterrupted power supply and strong power frequency induced current, achieving high-precision, non-destructive, and portable measurement under such conditions.

Description

Technical Field

[0001] This invention relates to the field of electrical measurement technology, and in particular to a method, system, electronic device, and medium for measuring the DC resistance of cable outer sheath. Background Technology

[0002] With the accelerated progress of urban power grid undergrounding, high-voltage power cables have become the core carriers of power transmission in urban core areas. The cable outer sheath, as a crucial protective layer that blocks moisture and prevents electrochemical corrosion of the metal sheath, directly affects the long-term safe operation and service life of the cable line. Among these indicators, the DC resistance of the outer sheath is a key technical indicator characterizing the conductivity of its metal layer and determining whether the outer sheath has any damage or deterioration defects. Current power grid operation and maintenance regulations explicitly require periodic testing of the DC resistance of cable outer sheaths to assess their condition. However, under the conventional operating condition of multiple cables laid in the same trench (tunnel), adjacent live cables will induce a wide range of power frequency voltages (e.g., 0 to 20V) on the outer sheath of the cable under test, creating strong induced electrical interference. Traditional testing methods must be performed after a power outage, which not only requires complex power outage approval procedures, affecting power supply reliability, but also completely fails to meet the modern operation and maintenance needs for rapid and routine inspection of cable defects.

[0003] In the field of measuring the DC resistance of cable sheaths, existing methods face two main challenges. One category is the basic direct measurement method, including the two-terminal measurement method and the standard four-terminal measurement method. The two-terminal method cannot eliminate the contact resistance at the point where the test electrodes contact the cable, as well as the resistance of the test leads themselves, introducing inherent systematic errors and resulting in a low upper limit of measurement accuracy. While the standard four-terminal measurement method can theoretically eliminate these systematic errors and achieve high-precision measurement, in the aforementioned uninterrupted power supply environment with strong induced voltage, the induced voltage can saturate or severely distort the voltage sampling signal of the measuring instrument, rendering this method completely unusable. The other category consists of improved solutions for uninterrupted power supply conditions, which attempt to suppress or overcome induced electrical interference. For example, solutions using hardware filtering, passive shielding, or electrical isolation can only attenuate the interference signal that has already entered the measurement loop "afterward," failing to eliminate the interference at its root cause, thus having limited effectiveness. Furthermore, open-loop reverse voltage compensation schemes suffer from inaccurate acquisition of the induced electrical reference signal and uncontrollable compensation effects. Furthermore, existing technology (application publication number CN115236406A) discloses a method and device for measuring the insulation resistance of the outer sheath of high-voltage cables. This method calculates the insulation resistance value by measuring the voltage and current phasors at both ends of the aluminum sheath in the cross-interconnected section and performing calculations based on Kirchhoff's laws and Ohm's law, thus enabling insulation status judgment without cable interruption. However, this method has several limitations: First, it measures "insulation resistance," reflecting the insulation performance of the outer sheath to ground, which is a different physical quantity from the "DC resistance," characterizing the conductivity of the metal sheath conductor itself, and thus has different applications. Second, this method heavily relies on the cross-interconnected structure of high-voltage cables and is not applicable to the numerous non-cross-interconnected sections or single-circuit cables. Third, this method is an indirect calculation method based on multi-point electrical measurements; its accuracy depends on the measurement accuracy of multiple voltage and current transformers and the precision of the model calculations, rather than a direct measurement of the resistance section. Furthermore, and most importantly, this method does not address the direct interference of strong power frequency induced voltage on the measurement signal. In environments with particularly strong induced voltage, the accuracy of the voltage and current measurements upon which it relies may be affected by interference, thus limiting the accuracy of the final results. Meanwhile, some other improvement schemes employ a fixed online monitoring device installed along the entire cable line, which is extremely costly and lacks flexibility, failing to meet the mobility requirements of maintenance teams for temporary spot checks and fault location. Even worse, some schemes use puncture electrodes, which can damage the insulation integrity of the outer sheath, creating safety hazards. Therefore, existing technologies cannot simultaneously achieve high-precision measurement of the DC resistance of the cable outer sheath, non-destructive testing, portable maintenance adaptability, and reasonable cost control in complex field environments with uninterrupted power supply and strong power frequency induced voltage, forming a significant bottleneck restricting the improvement of the industry's maintenance technology level. Summary of the Invention

[0004] To address the aforementioned shortcomings or deficiencies, this invention provides a method, system, electronic device, and medium for measuring the DC resistance of cable outer sheaths. This solution addresses the technical problem of insufficient measurement accuracy of the DC resistance of cable outer sheaths in complex field environments with uninterrupted power supply and strong power frequency induced current.

[0005] This invention provides a method for measuring the DC resistance of a cable outer sheath, comprising: Perform electrode deployment operation to fix six measuring electrodes along the axial direction at preset intervals on the surface of the outer sheath of the cable under test in operation, defining the sequentially connected induced current acquisition section, measured resistance section and compensation injection section.

[0006] The power frequency induced voltage signal at both ends of the induced voltage acquisition section is obtained by performing the induced voltage acquisition operation, and the frequency, phase and amplitude reference parameters of the power frequency induced voltage signal are extracted.

[0007] The closed-loop compensation control operation is performed. Based on the reference parameters, a compensation voltage with the same frequency and opposite phase is injected into the conductor circuit containing the inductive current acquisition section, the measured resistance section and the compensation injection section. At the same time, the residual power frequency interference voltage at both ends of the measured resistance section is monitored, and the residual power frequency interference voltage is used as the feedback quantity to perform closed-loop dynamic adjustment based on the proportional-integral-derivative algorithm until the residual power frequency interference voltage drops below the preset threshold.

[0008] The DC excitation and sampling operation is performed. While maintaining the compensation voltage output, a preset constant DC current is injected into the measured resistor segment, and the DC voltage drop signal across the measured resistor segment is acquired simultaneously.

[0009] Perform resistance calculation operation, based on constant DC current and DC voltage drop signal, and calculate the DC resistance value of the measured resistor segment according to the principle of four-terminal test method.

[0010] According to a second aspect, the present invention provides a DC resistance measurement system for cable outer sheath, comprising: The electrode deployment module is used to fix six measuring electrodes along the axial direction at preset intervals on the surface of the outer sheath of the cable under test in operation, defining the sequentially connected inductive current acquisition section, measured resistance section and compensation injection section.

[0011] The induced voltage acquisition module is used to acquire the power frequency induced voltage signal at both ends of the induced voltage acquisition section by performing induced voltage acquisition operations, and to extract the frequency, phase and amplitude reference parameters of the power frequency induced voltage signal.

[0012] The closed-loop compensation control module is used to inject a compensation voltage of the same frequency and opposite phase into the conductor circuit containing the induced current acquisition section, the measured resistance section and the compensation injection section based on the reference parameters. At the same time, it monitors the residual power frequency interference voltage at both ends of the measured resistance section and uses the residual power frequency interference voltage as the feedback quantity to perform closed-loop dynamic adjustment based on the proportional-integral-derivative algorithm until the residual power frequency interference voltage drops below the preset threshold.

[0013] The DC excitation and sampling module is used to inject a preset constant DC current into the measured resistor segment while maintaining the compensation voltage output, and simultaneously acquire the DC voltage drop signal across the measured resistor segment.

[0014] The resistance calculation module is used to calculate the DC resistance value of the measured resistor segment based on the constant DC current and DC voltage drop signal, according to the principle of the four-terminal test method.

[0015] According to a third aspect, the present invention provides an electronic device comprising: At least one processor; and a memory communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor, which enables the at least one processor to perform any of the cable outer sheath DC resistance measurement methods in the embodiments of the present invention.

[0016] According to another aspect of the present invention, a non-transitory computer-readable storage medium storing computer instructions is provided, wherein the computer instructions are used to cause a computer to perform any of the cable outer sheath DC resistance measurement methods in the embodiments of the present invention.

[0017] The present invention provides a method for measuring the DC resistance of a cable outer sheath. This method is achieved through five core steps: electrode deployment, induced voltage acquisition, closed-loop compensation control, DC excitation and sampling, and resistance calculation. Specifically, during electrode deployment, six measuring electrodes are fixed at preset intervals on the surface of the cable outer sheath, defining an induced voltage acquisition segment, a measured resistance segment, and a compensation injection segment. This provides a clear physical segment basis for subsequent targeted signal processing and interference cancellation. The induced voltage acquisition operation obtains the pure power frequency induced voltage signal at both ends of the induced voltage acquisition segment and extracts its frequency, phase, and amplitude reference parameters, establishing synchronization and amplitude criteria for generating a precise reverse compensation signal. The closed-loop compensation control operation injects a compensation voltage of the same frequency but opposite phase into the conductor circuit based on the reference parameters, and calculates the resistance at both ends of the measured resistance segment. The residual power frequency interference voltage at the terminal is used as a feedback quantity. Closed-loop dynamic adjustment based on the proportional-integral-differential algorithm is performed to achieve active cancellation of the strong power frequency induced voltage at its source, reducing it to below the preset threshold. DC excitation and sampling operations are performed. While maintaining the above compensation effect, a constant DC current is injected into the measured resistance segment and the DC voltage drop signal at its two ends is collected simultaneously, ensuring excitation and measurement in an environment without severe power frequency interference. Resistance calculation operation is performed. Based on the current and voltage signals, the DC resistance value is calculated according to the principle of the four-terminal test method, and finally, the accurate measurement of the resistance of the cable outer sheath itself is achieved.

[0018] In this technical solution, the present invention addresses the accuracy problem described in the background art, where the standard four-terminal measurement method suffers from insufficient accuracy due to saturation distortion of the voltage sampling signal caused by strong power frequency induced electricity, rendering it completely unusable. By introducing induced voltage acquisition and closed-loop compensation control steps, an interference suppression mechanism combining "reference parameter extraction" and "dynamic feedback compensation" is constructed. This mechanism can directly acquire real-time interference signal characteristics from the tested circuit and drive the compensation module to generate a reverse voltage that is synchronous with the measured voltage in real time, with equal amplitude but opposite phase. This actively cancels the power frequency induced voltage difference to below the millivolt level in the measurement circuit, eliminating the main interference causing measurement signal distortion at its source. This allows the high-precision standard four-terminal test method to be reapplied even in environments with strong interference and no power outages. Therefore, the technical solution of this invention solves the technical problem of insufficient measurement accuracy of the DC resistance of the cable outer sheath in complex field environments with strong power frequency induced electricity and no power outages, achieving high-precision, non-destructive, portable measurement under such conditions. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for measuring the DC resistance of the outer sheath of a cable according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the hardware architecture of a DC resistance measurement system for cable outer sheath in another embodiment of the present invention; Figure 3 This is a schematic diagram of the core circuit principle structure in another embodiment of the present invention; Figure 4 This is an exploded view of the portable modular measuring electrode clamp according to another embodiment of the present invention; Figure 5 This is a schematic diagram of the functional unit architecture and data collaboration workflow inside the main control module in another embodiment of the present invention; Figure 6 This is a block diagram of a closed-loop negative feedback control system in another embodiment of the present invention; Figure 7 This is a standardized work process flowchart in another embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of a DC resistance measurement system for cable outer sheath according to an embodiment of the present invention; Figure 9 This is a block diagram of an electronic device used to implement embodiments of the present invention. Detailed Implementation

[0020] The following description, in conjunction with the accompanying drawings, illustrates exemplary embodiments of the present invention, including various details to aid understanding. These details should be considered merely exemplary. Therefore, those skilled in the art will recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope of the invention. Similarly, for clarity and brevity, descriptions of well-known functions and structures are omitted in the following description.

[0021] During the development of this invention, researchers, through extensive experiments and data analysis, revealed the intrinsic correlation between the power frequency voltages induced in adjacent sections along the axial direction of the cable sheath: on symmetrical and equal-length cable sections, the induced power frequency voltages have consistent amplitude and phase. Based on this relationship, this invention innovatively proposes this technical solution, utilizing an independent "induced voltage acquisition section" to obtain a clean power frequency interference reference. Through closed-loop feedback control, a compensation voltage with the same frequency, opposite phase, and equal amplitude is dynamically generated. Combined with the use of the standard four-terminal test method for DC excitation and sampling after compensation, high-precision measurement of the DC resistance of the cable sheath is achieved under strong interference conditions without power interruption, embodying the core concept of "actively canceling interference from the source to create conditions for accurate measurement."

[0022] Specifically, through comparative experiments, the invention team discovered that the traditional two-terminal method and the standard four-terminal method have technical defects that prevent them from working effectively in strong power frequency induced voltage environments: the two-terminal method is greatly affected by contact resistance and lead wire resistance, resulting in low accuracy; the standard four-terminal method becomes completely ineffective under strong induced voltage due to saturation and distortion of the voltage sampling signal. These technical defects make it impossible to perform routine, high-precision inspection of the DC resistance of the cable outer sheath under uninterrupted power supply conditions where multiple cables are laid in the same trench. The measurement method based on symmetrical segmentation and closed-loop cancellation proposed in this invention can improve environmental adaptability under a wide range of power frequency induced electrical interference from 0 volts (V) to 20V. Through induced current acquisition and software phase-locked loop tracking, the frequency, phase, and amplitude of the interference signal can be accurately locked. By executing incremental proportional-integral-derivative closed-loop regulation with residual interference voltage as feedback, the compensation voltage can be ensured to converge quickly and the power frequency interference of the measured section can be suppressed to below the millivolt threshold. After the interference is effectively suppressed, a constant DC is injected into the measured section and the voltage drop is measured. Combined with the four-terminal test method, the final DC resistance value can be ensured to eliminate both systematic errors and random strong interference, and the measurement result is accurate and reliable.

[0023] Therefore, this invention provides a method for measuring the DC resistance of cable sheaths according to the first aspect. This method can be applied to a cable sheath DC resistance measurement system (hereinafter referred to as the "system") based on a four-terminal testing method and segmented equipotential closed-loop cancellation. This system can run on its integrated main control module (such as an industrial-grade microcontroller) and supporting measurement hardware through embedded control software or algorithm programs to achieve high-precision measurement of the DC resistance of cable sheaths under strong power frequency induced electrical interference. Specifically, this system can be deployed in various hardware environments, including but not limited to: portable handheld measurement terminals, vehicle-mounted mobile inspection platforms, and online monitoring devices fixedly installed in cable tunnels or manholes. This flexible deployment architecture allows the system to meet the mobility and convenience requirements of power grid maintenance teams for on-site mobile inspections and fault diagnosis, while also adapting to the stability and continuity requirements for long-term, fixed-point, and automated status monitoring of critical cable sections.

[0024] like Figure 1 As shown, the method may include: Step S110, perform electrode deployment operation: fix six measuring electrodes along the axial direction at a preset interval on the surface of the outer sheath of the cable under test in the running state, and define the sequentially connected inductive current acquisition section, measured resistance section and compensation injection section.

[0025] Electrode deployment refers to the process by which on-site operators or automated equipment install and fix measuring electrodes onto the surface of the outer sheath of the cable under test according to a predetermined sequence and spacing; the induced voltage acquisition section refers to the cable outer sheath conductor section specifically used to acquire pure power frequency induced voltage; the measured resistance section refers to the cable outer sheath target conductor section whose DC resistance value is to be measured; and the compensation injection section refers to the cable outer sheath conductor section used to receive reverse compensation voltage and together with the induced voltage acquisition section to form a complete compensation circuit.

[0026] Specifically, the system can be used by operators to use portable insulating clamps or by using clamping fixtures mounted on automated robotic arms to sequentially position, attach, and fasten the six measuring electrodes along the cable axis.

[0027] For example, system operators use two-piece flame-retardant fiberglass clamps to sequentially install six electrodes on the outer sheath surface of high-voltage power cables with an outer diameter of 70 mm to 200 mm. Each clamp weighs no more than 200 grams and is pre-tightened via side bolts to ensure stable ohmic contact between the high-elasticity conductive silicone rubber layer inside the clamp and the cable surface, with a contact resistance not exceeding 50 milliohms. ).

[0028] Step S120: Perform induced voltage acquisition operation: acquire the power frequency induced voltage signal at both ends of the induced voltage acquisition section, and extract the frequency, phase and amplitude reference parameters of the power frequency induced voltage signal.

[0029] Among them, the induced voltage acquisition operation refers to the process of sampling and processing the voltage signal at both ends of a specified cable segment while disconnecting all external excitation current and compensation voltage circuits; the power frequency induced voltage signal refers to the AC voltage signal induced on the outer sheath of the cable with a frequency of power grid frequency (e.g., 50 Hz).

[0030] Specifically, the system can turn off the output of the DC constant current source module and the adaptive compensation module to put the induced current acquisition section in a passive state. Then, the first differential measurement channel continuously acquires the voltage at both ends of the section at a high sampling rate, and processes the acquired time-domain signal to extract the power frequency component parameters.

[0031] For example, the system's main control module controls the relevant modules to shut down and continuously acquires voltage data for 20 power frequency cycles (corresponding to 400 milliseconds, or 400 ms) through the first differential measurement channel at a sampling rate of 10 kHz. Subsequently, the data is processed based on a software phase-locked loop (SPLL) architecture to track and lock the frequency, phase, and amplitude of the induced voltage in real time, with the frequency tracking range covering 49.5 Hz to 50.5 Hz.

[0032] Step S130: Perform closed-loop compensation control operation: Inject a compensation voltage of the same frequency and opposite phase into the conductor circuit based on the reference parameters, while monitoring the residual power frequency interference voltage at both ends of the measured resistor segment, and using the residual power frequency interference voltage as the feedback quantity, perform closed-loop dynamic adjustment based on the proportional-integral-derivative algorithm until the residual power frequency interference voltage drops below the preset threshold.

[0033] Among them, closed-loop compensation control operation refers to the control process of dynamically adjusting the compensation output with residual interference as feedback, so that the interference voltage converges to the target range; residual power frequency interference voltage refers to the residual power frequency voltage component that still exists at both ends of the measured resistor segment after the reverse compensation voltage is applied.

[0034] Specifically, the system can synchronously acquire the voltage across the measured resistor segment through the second differential measurement channel and calculate the root mean square (RMS) value of the power frequency component in the voltage signal as the residual interference voltage feedback value. Subsequently, an incremental proportional-integral-derivative (PID) control algorithm is invoked. Based on the difference between the feedback value and a preset threshold, the control signal driving the adaptive compensation module is iteratively calculated and adjusted, thereby changing the amplitude and phase of the compensation voltage in the injection loop.

[0035] For example, after the system initializes compensation, it continuously monitors the residual interference voltage. An incremental PID algorithm is used, with a proportional gain... Integral coefficient Differential coefficients It can automatically switch according to the induced voltage intensity. The control objective is to ensure that the root mean square value of the residual interference voltage is below a preset threshold of 1 millivolt (mV) for 10 consecutive power frequency cycles, and then lock the compensation parameters.

[0036] Step S140: Perform DC excitation and sampling operation: While maintaining the compensation voltage output, inject a preset constant DC current into the measured resistor segment and simultaneously acquire the DC voltage drop signal across the measured resistor segment.

[0037] Among them, DC excitation and sampling operation refers to the process of applying DC test current to the target resistance section and simultaneously measuring the DC voltage drop across its two ends after the power frequency interference is effectively suppressed.

[0038] Specifically, while maintaining the output of the adaptive compensation module, the system enables the DC constant current source module, establishing a loop between the positive and negative terminals of the current excitation to inject a pre-set constant DC current into the measured resistor segment. Simultaneously, the system controls the second differential measurement channel to acquire the voltage signal across the measured resistor segment and performs multi-cycle synchronous sampling and averaging on this signal to extract the pure DC voltage drop component. For example, the system controls the DC constant current source module to output a constant DC current of 50 mA for 200 ms (10 power frequency cycles). During this period, the second differential measurement channel synchronously acquires the voltage at a high sampling rate and takes the arithmetic average of the sampled data from 10 consecutive power frequency cycles, ultimately obtaining a stable DC voltage drop measurement value, such as 2.5 mV.

[0039] In some embodiments, the system can perform multi-cycle synchronous sampling and averaging processing on the acquired voltage signal using the following formula (a1) to calculate the pure DC voltage drop average value. (a1) Formula (a1) is the formula for calculating the arithmetic mean of multi-cycle synchronous sampling. The value represents the average pure DC voltage drop across the measured resistor segment, expressed in volts (V). N is the total number of sampling points within a complete sampling window. In this embodiment, the sampling window is set to 10 power frequency cycles (corresponding to 200ms), and at a sampling rate of 10kHz, N=200. This represents the instantaneous value of the nth discrete voltage sampling point acquired by the second differential measurement channel, in units of V.

[0040] Next, in this embodiment, the system can also calculate the original measured value of the DC resistance of the measured resistance segment at the current ambient temperature using formula (b1) based on the principle of the four-terminal test method (Kelvin method). (b1) Formula (b1) is a formula for calculating DC resistance based on Ohm's law. This represents the original measured value of the DC resistance of the measured resistance segment, in ohms (Ω). ). This represents the constant DC measurement current output by the DC constant current source module and flowing through the measured resistor segment, measured in amperes. The preset value in this embodiment is... (i.e., 50mA). This formula eliminates the influence of test lead resistance and contact resistance by using independent voltage sampling terminals and current excitation terminals.

[0041] Furthermore, in this embodiment, the system can also perform temperature conversion on the original measured value of the DC resistance using formula (c1) to obtain the nominal value of the DC resistance at the standard temperature; (c1) Formula (c1) is a modified formula based on the linear temperature characteristics of conductor resistance. This indicates a correction to 20 degrees Celsius. The nominal value of DC resistance at the standard reference temperature, in units of α represents the temperature coefficient of resistance of the cable's outer sheath conductor material, expressed in degrees Celsius (°C). For common polyethylene sheath materials, take T represents the ambient temperature collected in real time by a temperature sensor, in units of... .

[0042] Furthermore, in this embodiment, the system can also calculate the length ratio coefficient when the actual layout length on site is inconsistent using formula (d1), in order to adapt to non-standard electrode deployment conditions. (d1) Among them, formula (d1) is the formula for calculating the length ratio coefficient. It is a dimensionless length proportionality coefficient. This indicates the actual length of the measured resistance segment on site, in meters (m). This indicates the actual length of the inductive current acquisition section on site, in meters. When... hour, .

[0043] Finally, in this embodiment, the system can also scale the induced electric reference amplitude according to the length scaling factor using formula (e1) to generate a compensation reference amplitude suitable for the measured resistance segment. (e1) Here, formula (e1) is the formula for scaling the amplitude of the induced voltage. This represents the amplitude of the compensation reference signal used for closed-loop compensation control, generated after scaling according to the length ratio, and is expressed in V. This represents the original induced voltage amplitude, measured and locked directly from the induced voltage acquisition section by the inductive phase-locked loop unit, in volts (V). Since the phase of the power frequency induced voltage is independent of the cable length, the phase parameter remains unchanged.

[0044] Therefore, by combining the above formulas (a1) to (e1), the system can construct a complete and adaptive high-precision data processing chain. This chain first (formula a1) extracts the pure DC measurement signal from the strong interference background; then (formula b1) calculates the original resistance value based on the four-terminal method principle; subsequently (formula c1) eliminates the influence of environmental variables through temperature conversion, outputting a standardized nominal resistance value. Simultaneously, to cope with complex on-site layout constraints, the system dynamically adjusts the interference suppression benchmark through (formulas d1 and e1), ensuring compensation accuracy under non-equal length conditions. This series of calculations ultimately achieves high-precision and high-reliability measurement of the DC resistance of the cable outer sheath in a complex environment with uninterrupted power supply and strong power frequency induced current.

[0045] Step S150: Perform resistance calculation operation: Based on the constant DC current and DC voltage drop signal, calculate the DC resistance value of the measured resistor segment according to the principle of the four-terminal test method.

[0046] The resistance calculation operation refers to the data processing process that calculates the resistance value from the applied current and the measured voltage drop according to Ohm's law, and makes necessary corrections (such as temperature correction).

[0047] Specifically, the system can, based on the four-terminal testing method, divide the measured DC voltage drop value obtained in step S140 by the constant DC measurement current value to obtain the original measured DC resistance value of the measured resistance segment at the measurement temperature. Furthermore, by combining the real-time acquired ambient temperature and the temperature coefficient of resistance of the cable outer sheath material, this original value can be converted to the nominal value at the standard temperature.

[0048] For example, the system calculates the original measured value of the DC resistance as 50 based on the measured DC voltage drop of 2.5mV and the injected current of 50mA. If the ambient temperature is 30 degrees Celsius... The temperature coefficient of resistance of the polyethylene sheath of the cable is 0.004. Then the original value will be converted to 20. The nominal DC resistance at standard temperature is approximately 47.6. .

[0049] In another embodiment, Table 1 below shows how the method of the present invention, under a wide range of power frequency induced voltage interference, can reduce the nominal value of a voltage of approximately 50. The results of a verification experiment on the DC resistance measurement of the outer sheath conductor of a cable were presented. This experiment aimed to verify the measurement accuracy and stability of the technical solution combining closed-loop compensation control and the four-terminal testing method in a real-world environment with strong interference.

[0050] The specific experimental setup is as follows: A section of intact cable of known length is selected, and the theoretical DC resistance of its outer sheath metal layer is calibrated to 50.00 Ω using precision instruments. During the experiment, an adjustable induced voltage generator was used to simulate a power frequency induced voltage ranging from 0 to 20V on the cable section under test, to simulate different levels of interference caused by multiple cables laid in the same trench. Subsequently, the electrode deployment, induced voltage acquisition, closed-loop compensation control, DC excitation and sampling, and resistance calculation were strictly performed according to the steps of this invention, and the measurement results under different induced voltage conditions were recorded. As shown in Table 1, in 10 independent tests, the simulated applied power frequency induced voltage covered a wide range from 0.51V to 13.12V. Although the interference voltage amplitude varied by more than 25 times, and the induced current fluctuated significantly accordingly, the DC resistance value of the cable outer sheath measured by the method of this invention (in the "Measured Resistance Value" column) remained stable at 50.05V. Up to 50.22 Between, and 50.00 The theoretical nominal values ​​are extremely close. The corresponding maximum single "measurement error" is 0.47%, and the minimum is 0.10%, all below 0.5%. The arithmetic mean of the measurement errors for all 10 sets of tests yields an "average measurement error" of 0.28%. This embodiment and the data in Table 1 demonstrate that the technical solution provided by this invention can effectively adapt to a wide range of power frequency induced voltage environments from 0 to 20V. Through precise closed-loop compensation control, the system successfully suppresses strong interference to below the millivolt level, creating pure conditions for high-precision four-terminal DC resistance measurement. Therefore, under interference of varying intensities, the system can achieve an error not exceeding [a certain value]. The high-precision measurement, with good repeatability and high stability, fully demonstrates the effectiveness and superiority of this method in solving the technical problem of "insufficient measurement accuracy under uninterrupted power supply and strong induced current environment".

[0051] Therefore, according to the above implementation method, the system achieves its function through five core steps: electrode deployment, induced voltage acquisition, closed-loop compensation control, DC excitation and sampling, and resistance calculation. Specifically, during electrode deployment, six measuring electrodes are fixed at preset intervals on the outer sheath of the operating cable, defining the induced voltage acquisition segment, the measured resistance segment, and the compensation injection segment, providing a clear physical segment basis for subsequent targeted signal processing and interference cancellation. The induced voltage acquisition operation obtains the pure power frequency induced voltage signal at both ends of the induced voltage acquisition segment and extracts its frequency, phase, and amplitude reference parameters, establishing synchronization and amplitude basis for generating a precise reverse compensation signal. The closed-loop compensation control operation injects a compensation voltage of the same frequency but opposite phase into the conductor circuit based on the reference parameters, and calculates the resistance at both ends of the measured resistance segment. The residual power frequency interference voltage at the terminal is used as a feedback quantity. Closed-loop dynamic adjustment based on the proportional-integral-differential algorithm is performed to achieve active cancellation of the strong power frequency induced voltage at its source, reducing it to below the preset threshold. DC excitation and sampling operations are performed. While maintaining the above compensation effect, a constant DC current is injected into the measured resistance segment and the DC voltage drop signal at its two ends is collected simultaneously, ensuring excitation and measurement in an environment without severe power frequency interference. Resistance calculation operation is performed. Based on the current and voltage signals, the DC resistance value is calculated according to the principle of the four-terminal test method, and finally, the accurate measurement of the resistance of the cable outer sheath itself is achieved.

[0052] Specifically, in this embodiment, addressing the issue of insufficient accuracy in the standard four-terminal measurement method due to saturation distortion of the voltage sampling signal caused by strong power frequency induced electricity, rendering it completely unusable, as described in the background art, an interference suppression mechanism combining "reference parameter extraction" and "dynamic feedback compensation" is constructed by introducing induced voltage acquisition and closed-loop compensation control steps. This mechanism can directly acquire real-time interference signal characteristics from the tested circuit and drive the compensation module to generate a reverse voltage that is synchronous with it in real time, with the same amplitude but opposite phase. This actively cancels the power frequency induced voltage difference to below the millivolt level in the measurement circuit, eliminating the main interference causing measurement signal distortion at its source. This allows the high-precision standard four-terminal test method to be restored and applied in a strong interference environment without power interruption. Therefore, the technical solution of this invention solves the technical problem of insufficient measurement accuracy of the DC resistance of the cable outer sheath in complex field environments with strong power frequency induced electricity without power interruption, realizing high-precision, non-destructive, portable measurement under such conditions.

[0053] In another embodiment, as follows: Figure 2 This diagram illustrates the hardware architecture of a cable sheath DC resistance measurement system according to a specific embodiment of the present invention. The diagram clearly shows the functional modules that implement the cable sheath DC resistance measurement method, their electrical connections, and data flow relationships, specifically illustrating how the measurement process is completed through hardware collaboration. Figure 2As shown, the system mainly includes a test electrode group, an induced current acquisition module, a differential voltage measurement module, a main control module, a DC constant current source module, an adaptive compensation module, a data storage unit, a human-machine interaction unit, and a lithium battery power supply unit. The test electrode group contains six measuring electrodes, labeled C (acquisition electrode), F+ (current excitation positive terminal), S+ (voltage sampling positive terminal), P (voltage sampling negative terminal), F- (current excitation negative terminal), and C (compensation electrode). These six electrodes are fixed to the surface of the cable's outer sheath in a preset order, physically defining the induced current acquisition section (between the two C electrodes), the measured resistance section (between the S+ and P electrodes), and the compensation injection section (between the F- and C electrodes). The test electrode group is the physical interface between the entire system and the cable under test. The input terminal of the induced current acquisition module is connected to the two C electrodes in the test electrode group, specifically used to acquire the voltage signal at both ends of the induced current acquisition section, i.e., a pure power frequency induced voltage signal, without external excitation. This module typically includes a high-impedance input buffer, a programmable gain amplifier, and an anti-aliasing filter circuit. Its output is a conditioned analog voltage signal, which is sent to the analog-to-digital converter inside the main control module for processing. The main control module is the core of the system's control and calculation, and can be implemented using a microcontroller or a digital signal processor. It receives digital signals from the induced voltage acquisition module and the differential voltage measurement module, runs embedded software, and executes all the operational steps in the above embodiments except for electrode deployment. Specifically, this includes: processing the induced voltage signal based on a software phase-locked loop to extract reference parameters; executing an incremental proportional-integral-derivative algorithm to achieve closed-loop compensation control; controlling the start, stop, and output of the DC constant current source module and the adaptive compensation module; calculating the sampled data to obtain the DC resistance value; and managing data storage and human-machine interaction processes. The adaptive compensation module operates under the control of the main control module. It receives digital control signals from the main control module, generated based on the compensation reference signal and closed-loop regulation results. Through internal digital-to-analog conversion, inverting amplification, and power drive circuitry, it generates a compensation voltage with the same frequency but opposite phase. This voltage is then injected into the compensation loop formed by the two C electrodes in the test electrode group to actively cancel the power frequency induced voltage. The DC constant current source module is also controlled by the main control module. After compensation stabilization, this module, according to the main control command, establishes a current excitation loop between the F+ and F- electrodes of the test electrode group, outputting a highly stable preset constant DC measurement current (e.g., 50mA) that flows through the measured resistance section. The differential voltage measurement module has two differential input channels. The first differential measurement channel, under the control of the main control module, can be selectively connected to the output of the induced voltage acquisition module or directly connected to relevant electrodes for high-precision measurement during the induced voltage acquisition stage. The second differential measurement channel is permanently connected to the S+ and P electrodes of the test electrode group, used to monitor residual power frequency interference voltage during the closed-loop compensation control stage and to synchronously acquire the DC voltage drop signal during the DC excitation and sampling stages.This module includes a precision instrumentation amplifier and a high-resolution analog-to-digital converter to ensure high accuracy and low noise in voltage measurements. A data storage unit (such as a flash memory chip or memory card) connects to the main control module to store measurement programs, system parameters, and measurement results (such as nominal DC resistance values, measurement timestamps, and ambient temperature). The human-machine interface typically includes an LCD screen and buttons / touchscreens, providing operators with an interface for parameter setting, measurement initiation, status display, and result viewing. The lithium battery power unit provides a stable and isolated power supply to all active modules in the system, ensuring portability and electrical safety in the field.

[0054] Workflow Summary: After the system is powered on, the operator initiates the measurement via the human-machine interface. The main control module first controls the relevant switches to connect the induced voltage acquisition module to the test electrode group, performing the induced voltage acquisition operation. Subsequently, the main control module generates reference parameters based on the acquired signal and controls the adaptive compensation module to start working. Simultaneously, it monitors residual interference through the second channel of the differential voltage measurement module and performs closed-loop adjustment. Once the compensation stabilizes, the main control module starts the DC constant current source module to inject DC current and simultaneously acquires the voltage drop signal through the second differential measurement channel. Finally, the main control module calculates the resistance value and displays the result through the human-machine interface. The data can also be optionally stored in the data storage unit.

[0055] therefore, Figure 2 The hardware system embodiment shown, through the precise coordination of the above-mentioned dedicated functional modules and the intelligent scheduling of the main control module, fully and efficiently realizes the DC resistance measurement method of the cable outer sheath of the present invention, providing a reliable physical carrier for high-precision and strong interference-resistant measurement.

[0056] In another embodiment, as follows: Figure 3 This diagram illustrates the core circuit principle structure upon which the DC resistance measurement method for cable outer sheaths of this invention is based. Using an abstract electrical connection, the diagram reveals the topological relationships, current paths, and signal measurement and injection points among the three functional segments (induced current acquisition segment, measured resistance segment, and compensation injection segment) defined in the above embodiments. This provides the foundation for understanding the technical solution of this invention from a circuit principle perspective.

[0057] like Figure 3As shown, a long horizontal conductor representing the outer sheath metal conductor of the cable runs through the entire diagram. Along the axial direction of this conductor, six key electrical connection terminals are defined from left to right and clearly labeled with vertical leads. These six terminals strictly correspond to the measuring electrodes in the following embodiment, and the entire measurement circuit is constructed based on this topology. The leftmost area corresponds to the induced voltage acquisition section. This section is defined by terminal "C" (acquisition electrode) and terminal "F+" (current excitation positive terminal). This area is clearly labeled as the "induced voltage acquisition section" in the diagram. In circuit principle, the function of this section is to provide a pure induced voltage sampling point. When the system is in the induced voltage acquisition operation phase, the first differential measurement channel connected between terminals C and F+ (the specific measurement circuit is not shown in the diagram, but is represented by an abstract measurement function) can measure the induced power frequency voltage at both ends of this section with high precision, without being disturbed by any excitation current or compensation current injected by the system itself, thereby obtaining a pure power frequency induced voltage signal. The middle area corresponds to the measured resistance section. This section is defined by terminals "S+" (positive voltage sampling terminal) and "S-" (negative voltage sampling terminal), and is clearly marked as "the section of resistance being measured" in the diagram. This section is the core target of the entire measurement, and its resistance value... (i.e., DC resistance value) to be determined. In circuit principle, terminals S+ and S- are connected to the high input impedance differential input terminal of the second differential measurement channel, specifically used to measure the potential difference across the target segment. Based on the four-terminal test method (Kelvin method), the measurement current flowing through this segment is provided by an external DC constant current source module through terminals F+ and F-, while voltage measurement is performed through independent terminals S+ and S-, thus completely eliminating the influence of test lead resistance and contact resistance on voltage measurement. This is the basis for achieving high-precision measurement. The rightmost area corresponds to the compensation injection segment. This segment is defined by terminal "F-" (current excitation negative terminal) and terminal "P" (compensation electrode), clearly marked as "compensation injection segment" in the diagram. In circuit principle, this segment has the same physical length as the induced current acquisition segment on the left and is symmetrically distributed around the measured resistance segment. Terminal P and terminal C on the left together form a compensation voltage injection loop. The compensation voltage output by the adaptive compensation module is applied between terminals C and P. Due to symmetry, when a compensation voltage with the same frequency but opposite phase as the induced voltage is injected between C and P, a potential difference that cancels it out can be generated across the measured resistance segment (S+ to S-), thereby suppressing power frequency interference. Working circuit explanation: Inductive voltage acquisition circuit: In step S120, the measurement is performed only between terminals C and F+, forming an independent high-impedance voltage measurement circuit.

[0058] Compensation current loop: In step S130, the compensation voltage is output from the adaptive compensation module and injected between terminals C and P. The current flow path is: C Inductive current acquisition section F+ The measured resistance section F- Compensation Injection Section P forms a complete power frequency compensation current loop.

[0059] DC current measurement loop: In step S140, the DC constant current source module outputs current, and the path is: F+ The measured resistance section F- forms an independent DC excitation loop. At this time, the DC voltage drop across the measured resistor segment is accurately acquired by the second differential measurement channel connected between S+ and S-.

[0060] therefore, Figure 3 The circuit principle structure embodiment shown demonstrates, from the most basic Ohm's law and circuit topology perspective, the core concept of this invention, which integrates "segmented equipotential closed-loop cancellation" and "four-terminal testing method". It clarifies the electrical function of each electrode, divides independent measurement and compensation loops, and reveals the physical basis for achieving interference acquisition and equivalence cancellation through a symmetrical structure, which is the fundamental basis of this patent's technical solution at the circuit principle level.

[0061] In another embodiment, as follows: Figure 4 This diagram shows an exploded view of the portable modular measuring electrode clamp, a key mechanical component used in the electrode deployment operation in the following embodiments. This clamp is part of the cable outer sheath DC resistance measurement system (corresponding to...). Figure 2 In the system architecture, a special device is used to quickly and reliably install six measuring electrodes on the surface of the running cable. Its design directly serves the core step of "fixing six measuring electrodes along the axial direction at a preset interval on the surface of the outer sheath of the cable under test in operation".

[0062] like Figure 4As shown, the portable modular measuring electrode clamp mainly consists of a main frame, conductive contact units, insulating positioning units, and a quick-locking mechanism. The main frame, shown in the blue shell, is made of high-strength insulating engineering plastic (such as polycarbonate), providing mechanical support and electrical insulation protection for the entire clamp. The shell is designed with a symmetrical opening and closing structure for easy cable wrapping. The bolt fixing devices on the left and right sides are part of the quick-locking mechanism. By rotating the handle or wrench, the internal screw can be driven, tightly clamping the clamp onto the cable sheath and providing sufficient clamping force to ensure stable electrical contact. The yellow circular area in the middle represents the highly elastic conductive silicone rubber unit, which is the core of the conductive contact unit. This unit is pre-embedded in the black annular part (i.e., the window of the insulating positioning unit). The yellow conductive silicone rubber undergoes radial deformation when the bolts are tightened, forming a large-area, low-contact-resistance ohmic connection with the cable's outer sheath metal layer, functioning equivalent to a "measuring electrode" (such as the acquisition electrode C, the current excitation positive terminal F+, etc.). Each independent clamp module encapsulates only one such conductive unit. The black ring-shaped section is an insulating positioning unit, typically made of abrasion-resistant nylon. It precisely defines the exposed area and position of the yellow conductive unit, ensuring it only contacts the target point on the cable outer sheath, while preventing short circuits between adjacent electrodes or between the electrode and the external environment. The circular holes at the top and bottom are standard interfaces and wiring channels. The top hole is for installing a standard banana plug or aviation connector, serving as the electrical lead interface for this electrode, facilitating connection to the system host (…). Figure 2 (As shown) Quick connection via test cable. The holes at the bottom are optional air pressure equalization or visual alignment holes.

[0063] Working principle and deployment process: In actual measurement, the operator will use six such independent fixture modules. First, the six electrodes are located along the cable axis using a measuring ruler. The installation position is then determined. At each predetermined position, a clamp module is snapped onto the cable, and the bolts on both sides are tightened until the clamp firmly holds the cable. At this point, the internal yellow conductive silicone rubber unit forms reliable electrical contact with the cable's outer sheath. Finally, the top interface of each clamp is connected to the corresponding terminal on the system host via a dedicated test cable. This modular design allows for precise control of the spacing between the six electrodes (i.e., defining the lengths of the induced current acquisition section, the measured resistance section, and the compensation injection section) through on-site measurement and positioning, thus flexibly adapting to cables of different diameters and varying measurement length requirements.

[0064] therefore, Figure 4The portable modular measuring electrode fixture embodiment shown illustrates the "performing electrode deployment operation" in the above embodiments from both mechanical structure and field operation perspectives. It provides a standardized, repeatable electrode installation solution with low contact resistance and no damage to the cable sheath, ensuring the reliability and convenience of electrical measurement loop construction. It is an indispensable field tool for achieving high-precision measurement methods.

[0065] In another embodiment, as follows: Figure 5 It means Figure 2 The diagram illustrates the functional unit architecture and data collaboration workflow within the main control module of the DC resistance measurement system for cable sheaths. This diagram focuses on the embedded software logic and core algorithm units of the main control module (typically implemented by a microcontroller or digital signal processor), revealing how the system precisely coordinates the five core operation steps in the aforementioned embodiments through a programmed and modular approach, thereby achieving a high-precision measurement intelligent control core.

[0066] like Figure 5 As shown, the main control module is internally divided into multiple logically independent but data-interconnected functional units, all under the unified control unit's scheduling and capable of calling external parameter settings and optimization algorithms. The inductive phase-locked loop (SPLL) unit is the foundation of signal processing. It receives the digitized "acquired inductive current" signal from the inductive current acquisition module. Based on a software SPLL architecture, this unit tracks and calculates the frequency, phase, and instantaneous amplitude of the input signal in real time, ultimately outputting precise "inductive current amplitude and phase" parameters. This is the source for generating all subsequent control references. The adaptive length matching unit receives the "inductive current amplitude and phase" parameters output from the inductive phase-locked loop unit. This unit matches the length of the inductive current acquisition segment (…) pre-input or set by the operator through the human-machine interface unit. ) and the length of the measured resistance segment ( The incremental PID closed-loop control unit intelligently scales the amplitude parameter of the induced voltage to generate a "reference signal" that perfectly matches the actual interference situation of the measured resistor segment. This "reference signal" is the accurate target for driving compensation. The incremental PID closed-loop control unit is the core algorithm module for achieving precise cancellation. This unit receives the "reference signal" from the adaptive length matching unit and simultaneously receives the "residual interference signal" (i.e., the feedback value of the residual power frequency interference voltage across the measured resistor segment) from the differential voltage measurement module in real time. This unit compares the "residual interference signal" with the ideal state (target is 0), generates an error, and uses the incremental proportional-integral-derivative algorithm for iterative calculation, dynamically outputting a "control signal". This "control signal" directly drives the adaptive compensation module, adjusting the amplitude and phase of its output compensation voltage, forming a closed-loop control system with residual interference as negative feedback. The time-division timing control unit is the "metronome" and "scheduler" of the entire measurement process. This unit, invoked by the control unit, strictly follows a preset, non-conflicting time sequence to send enable, disable, and sampling start commands to the induced voltage acquisition module, adaptive compensation module, DC constant current source module, and differential voltage measurement module. For example, it ensures that all excitation and compensation are disabled during the induced voltage acquisition phase; that the second channel of the adaptive compensation module and differential voltage measurement module is enabled during the closed-loop compensation phase; and that compensation is maintained, the DC constant current source is enabled, and sampling is performed synchronously during the DC measurement phase. It also sends a preset "current setpoint" to the DC constant current source module. The resistance calculation unit is responsible for the final data processing. After the DC measurement phase is completed, this unit receives the "DC voltage drop signal" from the differential voltage measurement module and calculates the original DC resistance value based on the four-terminal test method and the known "current setpoint." It can further call temperature sensor data to perform temperature conversion to obtain the nominal DC resistance value required for the final report. The control unit is the central scheduling center of the main control module, responsible for coordination. Figure 5 It ensures the orderly operation of all units and manages the interfaces for human-machine interaction and data storage. Parameter setting and optimization algorithms are optional, higher-level intelligent modules that can be used to dynamically optimize control parameters, such as those of incremental PID closed-loop control units. Alternatively, certain thresholds can be adaptively adjusted based on historical measurement data to achieve better convergence speed and stability.

[0067] therefore, Figure 5 The illustrated system block diagram, from the perspective of control logic and algorithm implementation, profoundly elucidates the "intelligent" core of the present invention's technical solution. It demonstrates how, through modular digital signal processing and closed-loop control algorithms, abstract steps such as "induced voltage acquisition," "closed-loop compensation control," "DC excitation sampling," and "resistance calculation" are transformed into programmable and precisely executable automated processes, ensuring high precision, high reliability, and strong environmental adaptability of the measurement method.

[0068] In another embodiment, as follows: Figure 6 This diagram illustrates the principle block diagram of the closed-loop negative feedback control system upon which the "execution of closed-loop compensation control operation" step in the above embodiment of the cable outer sheath DC resistance measurement method of the present invention is based. From the perspective of classical control theory, this diagram abstractly and clearly reveals the inherent logic of the closed-loop compensation control operation, the dynamic relationships between core functional modules, and the adjustment mechanism against external disturbances.

[0069] like Figure 6 As shown, the control system is a typical single-input single-output negative feedback closed loop. Its core control objective is to make the system output (i.e., the residual power frequency interference voltage at both ends of the tested cable segment) approach zero. The entire system is subject to an external disturbance input, namely the "external power frequency induced electrical disturbance," which simulates the power frequency voltage induced on the outer sheath of the tested cable by adjacent energized cables, with potentially varying amplitude and phase. The functional definitions of each module in the system are as follows: Inductive voltage reference: This module corresponds to the output of the step "extracting the frequency, phase, and amplitude reference parameters of the power frequency induced voltage signal" in the above embodiment. It provides the dynamic characteristics (frequency, phase, and amplitude) of the current external disturbance signal, serving as a given reference input or feedforward reference for the entire compensation system, and is the target basis for generating accurate reverse compensation signals.

[0070] Incremental PID controller: This is the "brain" of the closed-loop control, corresponding to the specific implementation unit of "performing closed-loop dynamic control based on the proportional-integral-derivative algorithm" in the above embodiment. It receives the error signal from the feedback channel and performs real-time calculations according to the incremental proportional-integral-derivative algorithm, outputting the control signal used to drive the actuator. Its "incremental" characteristic ensures the stability of the digital implementation and its resistance to integral saturation.

[0071] Adaptive Compensation Module: This is the "actuator" of the closed-loop system, corresponding to the functional entity of "injecting a compensation voltage of the same frequency but opposite phase" in the above embodiment. It receives the control signal from the incremental PID controller and generates a power frequency compensation voltage whose amplitude and phase can be dynamically adjusted, injecting this voltage into the measurement circuit.

[0072] The cable segment under test: This is the controlled object, specifically referring to the "resistance segment under test" defined in the above embodiment. The voltage across its two ends is the controlled variable of the system. It is simultaneously affected by both the "external power frequency induced electrical disturbance" and the compensation voltage output by the "adaptive compensation module".

[0073] Differential voltage measurement module: This is the system's "measurement feedback loop," corresponding to the hardware unit in the above embodiment that "monitors the residual power frequency interference voltage across the measured resistance segment." It continuously and accurately measures the voltage across the measured cable segment and calculates the effective value of its power frequency component (i.e., residual interference), sending it back as a feedback signal to the incremental PID controller.

[0074] System working principle and signal flow: Disturbance and reference: "External power frequency induced electrical disturbance" acts directly on "the cable section under test" and attempts to establish a power frequency interference voltage at both ends of the cable.

[0075] Feedback and Error Generation: The differential voltage measurement module measures the actual output voltage (i.e., residual interference) of the cable segment under test in real time and uses this measurement as a feedback signal. This value is compared with the ideal output value "0" (this comparison is implicitly performed within the incremental PID controller), generating an error signal. .

[0076] Control law operation: The incremental PID controller receives the error signal. Based on its proportional, integral, and derivative components, the increment of the control quantity is calculated in real time according to a preset algorithm. The controller also references the frequency and phase feedforward information provided by the "inductive reference" to ensure that its output control signal is dynamically synchronized with external disturbances.

[0077] Compensation output: The control signal drives the "adaptive compensation module" to generate a compensation voltage with the same frequency, opposite phase, and controlled amplitude as the external disturbance, which is also applied to the "cable segment under test".

[0078] Dynamic Balance: Under closed-loop regulation, the compensation voltage output by the "adaptive compensation module" cancels out the "external power frequency induced electrical disturbance" on the "tested cable segment". Through continuous feedback from the "differential voltage measurement module" and continuous correction by the "incremental PID controller", the system can dynamically track changes in external disturbances and stably suppress the residual power frequency interference voltage at both ends of the "tested cable segment" below a preset threshold, thereby achieving the technical effect of "closed-loop dynamic regulation until... it drops below the preset threshold".

[0079] therefore, Figure 6The illustrated block diagram of the closed-loop control system, from the perspective of automatic control theory, profoundly explains the scientific nature and superiority of the "closed-loop compensation control operation" in this invention. It demonstrates that this technical solution is not a simple open-loop cancellation, but an intelligent dynamic system with feedforward (reference), feedback (measurement), and powerful regulation capabilities (PID). It can effectively cope with a wide range of potentially fluctuating power frequency induced electrical interference in the field, which is the core mechanism by which this invention solves the problem of "insufficient measurement accuracy under strong induced electrical environments."

[0080] In another embodiment, as follows: Figure 7 This diagram illustrates a complete, standardized, and field-executable workflow for the DC resistance measurement method for cable outer sheaths provided by this invention. The diagram, presented in a step-by-step and sequential manner, details the core method of the aforementioned embodiments into a standardized operational process comprising six stages (S1 to S6), covering the entire process from on-site preparation to data archiving. This provides power grid maintenance teams with a clear, repeatable, and highly reliable on-site operational guide.

[0081] like Figure 7 As shown, the complete workflow strictly follows technical logic, breaking down the measurement task into six sequential steps that include conditional judgments: Step S1: Field Electrode Placement and System Initialization. This step corresponds to the field implementation of "performing electrode deployment operations" in the above embodiments. For example... Figure 7 In Chinese, the operator must first clean the surface of the cable outer sheath to ensure good electrical contact, and then fix the six measuring electrode clamps (corresponding to) sequentially along the axial direction at preset intervals. Figure 4 (Clamp), and reliably connect all electrode leads to the measuring host (corresponding to) Figure 2 The corresponding interface of the system. After powering on, key parameters such as the length of the measured resistance segment, the preset injection current value, and the ambient temperature are set through the human-machine interaction unit to complete the hardware connection and software configuration of the system.

[0082] Step S2: Inductive Voltage Acquisition and Parameter Locking. This step refines the "performing the induced voltage acquisition operation" in the above embodiment. The process is clear: First, the system automatically shuts down the DC constant current source and the output of the adaptive compensation module, putting the circuit in a "no external excitation state." Then, the induced voltage acquisition module starts working, continuously acquiring the induced voltage signal for 20 power frequency cycles (corresponding to 400ms). The phase-locked loop unit processes this signal in real time, accurately extracting the frequency, phase, and amplitude. If the arrangement is not of equal length, the amplitude is automatically scaled according to the length ratio, ultimately generating an accurate "compensation reference signal." This step establishes a precise reference for the entire compensation process.

[0083] Step S3: Adaptive Closed-Loop Compensation Locking. This step fully implements the "execution of closed-loop compensation control operation" in the above embodiment. The process is shown as a closed loop: First, the adaptive compensation module is turned on, injecting the initial compensation voltage; simultaneously, the differential voltage measurement module continuously monitors the residual interference across the measured resistor segment; the incremental proportional-integral-derivative closed-loop controller dynamically adjusts the amplitude and phase of the compensation voltage according to the residual interference. This adjustment cycle continues until the system determines that the strict condition of "residual interference being below 1mV for 10 consecutive cycles" is met, only then are the compensation parameters locked, indicating that the strong power frequency interference has been stably suppressed to below the millivolt level.

[0084] Step S4: Precise Measurement of DC Resistance. This step corresponds to the core parts of "performing DC excitation and sampling operations" and "performing resistance calculation operations" in the above embodiments. The process is clearly performed while maintaining the compensated output: turn on the DC constant current source and inject a preset DC current (e.g., 50mA); after the current stabilizes, the differential voltage measurement module synchronously acquires the DC voltage drop signal and uses the "multi-cycle synchronous sampling and averaging" technique to suppress noise; finally, the resistance value is calculated after temperature correction (calling the preset temperature coefficient) and displayed in real time.

[0085] Step S5: Residual Interference Verification and Data Storage. This step is an important quality control extension of the method described in the above embodiments. The process includes a decision branch: After obtaining the resistance value, the system first shuts off the DC constant current source and immediately re-detects the residual interference of the measured section. If the verification value is still below the 1mV threshold, the entire measurement is deemed valid, and the system automatically packages and stores key data such as measurement time, location information, resistance value, and ambient temperature. If the verification value is above the threshold, it indicates that the compensation may have failed during the measurement, and the process automatically returns to step S2 to re-execute the compensation and measurement, thereby ensuring the absolute reliability of the stored data.

[0086] Step S6: Inspection Completion and Data Export. This step involves on-site completion and data management after single-point measurement. This includes safely shutting down the equipment power, disassembling and storing the electrode clamps, and finally exporting the historical measurement data stored in the host to the backend operation and maintenance management system in batches via USB, Bluetooth, or 4G communication methods, completing the complete data archiving for this inspection task.

[0087] Field application example: A power supply company's work team is conducting an inspection of a 110kV cable tunnel. Upon arriving at the target cable joint, the maintenance personnel strictly follow... Figure 7 Procedure: First, execute S1, clean the cable surface, install six electrode clamps with a spacing of 0.5m, connect the host and set the parameters. Then, start automatic measurement. The system sequentially executes S2 (acquiring and locking induced current), S3 (completing closed-loop compensation locking within approximately 300ms), and S4 (injecting 50mA current, measuring and displaying a resistance value of 48.1). In step S5, if the system verification passes, the data for that point is automatically stored. After completing that point, personnel move to the next inspection point and repeat steps S1 to S5. After the daily inspection is completed, step S6 is executed, automatically uploading the resistance data of all measured points to the production management system via the 4G network and generating a cable outer sheath status report.

[0088] therefore, Figure 7 The complete workflow diagram shown in this embodiment transforms the technical solution of this invention into a standardized and procedural operating procedure from the perspective of field engineering practice. It not only clarifies the specific operations, judgment conditions, and sequence of each step, but also introduces important quality control (S5) and data management (S6) steps, ensuring reliable execution of the method in complex field environments and traceability of measurement results. This greatly enhances the operability of the technical solution and its practical value in routine power grid inspections.

[0089] In some embodiments, performing an electrode deployment operation includes: Six measuring electrodes are arranged sequentially along the cable axis in a preset order. The six measuring electrodes are, in order, the acquisition electrode, the positive terminal of the current excitation, the positive terminal of the voltage sampling, the negative terminal of the voltage sampling, the negative terminal of the current excitation, and the compensation electrode.

[0090] Specifically, the outer sheath conductor segment between the acquisition electrode and the positive terminal of the current excitation is defined as the induced current acquisition segment, the outer sheath conductor segment between the positive terminal of the voltage sampling and the negative terminal of the voltage sampling is defined as the measured resistance segment, and the outer sheath conductor segment between the negative terminal of the current excitation and the compensation electrode is defined as the compensation injection segment.

[0091] Specifically, six measuring electrodes are arranged in a straight line along the outer sheath of the cable, forming three functionally defined and electrically continuous conductor segments. The acquisition electrode and the positive current excitation terminal define the source segment of the induced signal; the positive and negative voltage sampling terminals define the target segment of the resistance under test and connect to the high-impedance measurement circuit; the negative current excitation terminal and the compensation electrode define the area where the compensation voltage applies. For example, in a standard measurement configuration, the axial distance between the positive and negative voltage sampling terminals is preset to 0.5m to define the resistance segment under test. The axial distances between the positive current excitation terminal and the positive voltage sampling terminal, and between the negative voltage sampling terminal and the negative current excitation terminal, are both preset to 0.15m. The axial distances between the acquisition electrode and the positive current excitation terminal, and between the negative current excitation terminal and the compensation electrode, are also preset to 0.5m. Accordingly, the total axial length of the entire electrode arrangement is 2.0m.

[0092] The physical lengths of the induced current acquisition section and the compensation injection section are equal, and they are symmetrically distributed with the measured resistance section as the center.

[0093] Specifically, symmetrical distribution means that the induced voltage acquisition section and the compensation injection section are located on opposite sides of the measured resistance section along its axial direction, and their geometric centers are symmetrical with respect to the geometric center of the measured resistance section. This equal-length symmetrical topology is designed based on the principle of uniform distribution of power frequency induced voltage along the axial direction of the cable sheath. It aims to ensure that the power frequency induced voltage signal acquired by the induced voltage acquisition section is consistent with the actual interference signal experienced by the measured resistance section in terms of amplitude and phase, providing an accurate reference for subsequent precise cancellation. For example, in standard configuration, the lengths of the induced voltage acquisition section, the measured resistance section, and the compensation injection section are all 0.5m, forming a strict symmetrical relationship. Under special on-site conditions, if the actual length of the induced voltage acquisition section is inconsistent with the length of the measured resistance section due to installation space limitations, the system's built-in adaptive length matching unit can linearly scale the acquired induced voltage amplitude reference according to the ratio of their actual lengths to generate a compensation reference signal adapted to the actual length of the measured resistance section, thereby ensuring effective compensation accuracy even under non-standard symmetrical arrangements.

[0094] Therefore, according to the above implementation method, the system can quickly construct the physical measurement architecture required by the four-terminal testing method and the closed-loop cancellation principle on site through a standardized electrode layout process. The equal-length and symmetrical electrode arrangement lays the physical foundation for the accurate acquisition and equal cancellation of induced electrical interference from a spatial structure perspective, while the clear definition of electrode functions and electrical connection relationships provide a clear hardware interface for the subsequent time-division multiplexing precise measurement and control process.

[0095] In some embodiments, performing an induced voltage acquisition operation includes: Without external excitation, the voltage signals at both ends of the induced voltage acquisition section are acquired through the first differential measurement channel to obtain a pure power frequency induced voltage signal.

[0096] Among them, the state without external excitation refers to the circuit condition in which neither the DC constant current source module nor the adaptive compensation module has power output; the first differential measurement channel refers to the high impedance and high common mode rejection ratio measurement circuit connected between the acquisition electrode and the positive terminal of the current excitation, which is dedicated to measuring the potential difference between the two ends of the induced current acquisition section.

[0097] Specifically, the system's main control module, through a time-division multiplexing timing control unit, shuts off the power output terminals of the DC constant current source module and the adaptive compensation module during the induced current acquisition phase, ensuring that no external current flows through the induced current acquisition section. At this time, the voltage across the induced current acquisition section is differentially sampled through the first differential measurement channel. The obtained signal is a pure power frequency induced voltage signal generated by the adjacent energized cable and not contaminated by signals injected by the measurement system itself. For example, the input impedance of the first differential measurement channel is not lower than... The sampling rate is set to 10kHz. Under this condition, voltage data is continuously acquired for 400ms (corresponding to 20 50Hz power frequency cycles), which can obtain a time-domain waveform containing complete power frequency fluctuation information.

[0098] The power frequency induced voltage signal is processed, and the frequency, phase and amplitude of the power frequency induced voltage signal are tracked and extracted in real time based on software phase-locked loop to generate induced voltage reference parameters.

[0099] Among them, the induced voltage reference parameters refer to three physical quantities used to characterize the core characteristics of the current interference signal, which are calculated in real time from the power frequency induced voltage signal: frequency ( Phase () ) and amplitude ( ).

[0100] Specifically, the inductive phase-locked loop unit built into the system's main control module uses a software phase-locked loop architecture based on a second-order generalized integrator to process the acquired discrete-time voltage signal sequence. The architecture generates in-phase components by constructing a quadrature signal generator. Orthogonal components Then, through digital computation, the instantaneous amplitude and phase of the signal are calculated in real time, and a proportional-integral regulator is used to track minute fluctuations in the grid frequency in a closed loop, ultimately locking and outputting the frequency, phase, and amplitude parameters. For example, the damping coefficient k of the software phase-locked loop is set to... Reference angular frequency Set as Radius per second (rad / s) (corresponding to 50Hz). This unit can adaptively track power grid frequency fluctuations within the range of 49.5Hz to 50.5Hz and output the frequency in real time. Phase and amplitude The phase tracking error is no greater than 0.5 degrees.

[0101] In some embodiments, the system can process the acquired discrete-time induced electrical signal using the following formula (1). The signal is processed to generate two signals, one in phase and one quadrature, to eliminate the influence of harmonic interference on parameter extraction. (1a) (1b) Equations (1a) and (1b) together define the continuous-domain transfer function of the second-order generalized integrator, used to construct a set of pure orthogonal basis signals with a 90-degree phase difference from noisy induced electrical signals. s is the Laplace operator in the complex frequency domain. The generated in-phase component of the induced electrical signal has a phase that is synchronized with the fundamental component of the input signal. The generated induced electrical signal is a quadrature component, lagging the in-phase component by 90 degrees. k is the damping coefficient of the SOGI (Second-Order Generalized Integrator), used to adjust the bandwidth and dynamic response speed of the filter. In this embodiment, k=2 is taken to achieve a balance between response speed and anti-interference performance. The rated angular frequency of the power grid corresponds to a 50Hz power frequency, and its value is... rad / s. s is the Laplace operator in the complex frequency domain.

[0102] Next, in this embodiment, the system can also use the above-mentioned orthogonal signals to calculate the amplitude and phase parameters of the induced electrical signal in real time using the instantaneous amplitude calculation method based on formula (2); (2a) (2b) Formula (2a) is used to calculate the instantaneous amplitude of the induced electrical signal. Formula (2b) is used to calculate the instantaneous phase of the induced electrical signal. ,function It is a four-quadrant arctangent function, which ensures that the phase value is continuous and without jumps within the range of 0 to 2π radians. n is the index number of the discrete time series.

[0103] Therefore, by combining the above formulas (1a) and (1b) with formulas (2a) and (2b), the system can extract the original induced voltage signal containing harmonics and noise. In this process, the amplitude, phase, and frequency (obtained by phase difference) of the pure power frequency component are accurately and in real time extracted as reference parameters, providing the necessary dynamic reference signal for the subsequent generation of accurate compensation voltage with the same frequency and opposite phase, thereby realizing the root characteristic locking of strong power frequency induced interference.

[0104] Perform a length matching judgment to identify whether the actual length of the induced current acquisition segment is consistent with the actual length of the measured resistance segment.

[0105] Among them, length matching judgment refers to comparing the lengths of the inductive current acquisition segments actually deployed on site. Length of the measured resistance segment This involves a logic operation to determine if the parameters are equal. This judgment is a prerequisite for deciding whether to scale the inductive reference parameters.

[0106] Specifically, the system receives the actual layout length on site from the operator through the human-computer interaction unit. and Or it can be automatically calculated from the preset standard length and electrode installation position. and The main control module compares these two values. If the difference is within a preset tolerance range (e.g., ...), ... If the values ​​match, the system is considered consistent; otherwise, it is considered inconsistent. For example, under standard operating conditions, and Both are preset to 0.5m, and the system judges them as consistent. However, in special locations such as narrow corners in tunnels, if the induced current acquisition section can only be set at 0.5m, while the measured resistance section needs to be measured at 0.25m due to space constraints, then... m, m, the system determines is inconsistent.

[0107] If the length matching judgment result is inconsistent, the amplitude in the inductive reference parameter is scaled proportionally according to the actual length ratio of the inductive current acquisition segment and the measured resistance segment to generate a compensation reference signal.

[0108] The compensation reference signal refers to the induced electrical parameters after length ratio correction, including the corrected amplitude. And the frequency and phase directly output by the phase-locked loop. This signal will serve as the final control reference for driving the adaptive compensation module.

[0109] Specifically, the system calls the adaptive length matching unit, which first calculates the length ratio coefficient. Subsequently, the amplitude in the induced current reference parameters was... Multiply by a coefficient The corrected amplitude is obtained. Since the phase of the power frequency induced voltage is independent of the cable length, the frequency and phase parameters remain constant. Ultimately, by , and Together, they constitute the compensation reference signal. For example, continuing the previous example, m, m, then If the amplitude of the induced voltage output by the phase-locked loop is... If it is 10V, then the corrected compensation reference amplitude is... .frequency (e.g., 50.1Hz) and phase It is then used directly to form the compensation reference signal.

[0110] Therefore, according to the above implementation method, the system can accurately acquire a clean power frequency inductive interference reference before measurement and precisely lock its dynamic parameters through a software phase-locked loop. Furthermore, through the built-in length matching and adaptive scaling mechanism, the system can flexibly adapt to various non-standard equal-length electrode arrangements in the field, ensuring that an accurate and suitable reference signal is provided for subsequent closed-loop compensation control, thereby expanding the adaptability of the measurement method to complex field environments.

[0111] In some embodiments, performing closed-loop compensation control operations includes: Based on the compensation reference signal, an initial reverse compensation control quantity is configured and output to drive the adaptive compensation module to inject an initial compensation voltage into the compensation loop formed by the acquisition electrode and the compensation electrode.

[0112] Among them, the reverse compensation control quantity refers to the digital control signal output by the digital-to-analog converter of the main control module, which is used to control the amplitude and phase of the output voltage of the adaptive compensation module; the compensation loop refers to the closed electrical path formed by the current flowing from the output of the adaptive compensation module, through the acquisition electrode, the outer sheath conductor of the cable, the compensation electrode, and then back to the input of the adaptive compensation module.

[0113] Specifically, the system's main control module uses the compensation reference signal (including frequency) as a basis. phase Amplitude The system generates an initial digital control sequence through its internal digital-to-analog converter. This sequence is then processed by the buffer, inverting amplification, and power follower circuitry within the adaptive compensation module, converting it into an AC voltage with the same frequency as the compensation reference signal, opposite initial phase, and proportional initial amplitude, which is then applied to the compensation circuit. For example, if the amplitude of the compensation reference signal... The voltage is 5V, the frequency is 50Hz, and the phase is 30 degrees. The main control module generates an initial control quantity, which drives the adaptive compensation module to output an initial compensation voltage with a frequency of 50Hz, a phase of 210 degrees (i.e., 30 degrees + 180 degrees), and an amplitude of approximately 5V.

[0114] The voltage signal across the two ends of the measured resistor segment is synchronously acquired through the second differential measurement channel, and the root mean square value of the power frequency component in the voltage signal across the two ends of the measured resistor segment is calculated as the residual interference voltage feedback value.

[0115] The residual interference voltage feedback value refers to the effective value of the power frequency voltage component that still exists across the measured resistor section after the compensation voltage is applied, denoted as... , where k represents the kth control cycle.

[0116] Specifically, while the adaptive compensation module outputs the compensation voltage, the system simultaneously acquires the voltage waveform between the positive and negative terminals of the voltage sampling via the second differential measurement channel at a high sampling rate. Subsequently, the voltage data for one complete power frequency cycle is subjected to a Fast Fourier Transform or digital filtering to extract the 50Hz power frequency component, and the root mean square value of this component is calculated as the feedback quantity for the current control cycle. For example, the second differential measurement channel acquires voltage at a sampling rate of 10kHz, processing 20ms (one power frequency cycle) of data per control cycle. The root mean square value of the current residual power frequency voltage is calculated through digital signal processing. For example, 150mV.

[0117] The difference between the residual interference voltage feedback value and the preset threshold is calculated to generate a closed-loop control error signal.

[0118] Among them, the closed-loop control error signal refers to the residual disturbance voltage feedback value. Compared with the system's preset interference suppression target threshold The algebraic difference between them is denoted as This error signal serves as the input for the subsequent proportional-integral-derivative (PDI) control algorithm.

[0119] Specifically, the system reads a preset threshold from memory. The real-time calculation results and Subtracting them gives the error value for the current control cycle. This error value reflects the deviation between the current compensation effect and the target effect. For example, the system's preset threshold. It is 1mV. If the current feedback value If the value is 150mV, then the error signal is calculated. .

[0120] Based on the closed-loop control error signal, the incremental proportional-integral-derivative control algorithm is invoked to iteratively calculate and output the amplitude adjustment and phase correction of the reverse compensation control quantity, so as to dynamically adjust the compensation voltage output by the adaptive compensation module.

[0121] The incremental proportional-integral-derivative (PI-DE) control algorithm is a discretized control algorithm whose output is the increment (change) of the control variable, rather than its absolute position. This algorithm achieves precise regulation of the controlled variable by combining the proportional term for rapid error response, the integral term for eliminating steady-state error, and the derivative term for predicting error trends. The amplitude adjustment and phase correction are two parameters output by the algorithm used for fine-tuning the reverse compensation control variable.

[0122] Specifically, the system will use the error signal Input an incremental proportional-integral-derivative controller. The controller adjusts the current error... Previous cycle error and the error of the previous cycle Combined with the preset proportional coefficient Integral coefficient Differential coefficients According to the formula Calculate the increment of the control quantity This increment It includes amplitude adjustment components and phase correction components. The system will use the current control quantity... Updated to and output new To drive the adaptive compensation module. For example, set Based on the current error of 149mV and historical error data, the control increment is calculated. This increment affects the output control quantity. The corresponding compensation voltage amplitude is slightly increased, and the phase is finely adjusted, so that the output compensation voltage is closer to the ideal reverse cancellation signal.

[0123] Repeatedly execute the steps of acquisition, solution, generation and iterative calculation to form a closed-loop regulation process, and determine whether the residual interference voltage feedback value is continuously lower than the preset threshold for multiple consecutive power frequency cycles.

[0124] Among them, the closed-loop control process refers to "collection and feedback". Calculation error Algorithm Adjustment Output control Affected The system repeats the feedback process. Multiple consecutive power frequency cycles are the convergence criteria set by the system to confirm that the compensation effect has reached a stable state.

[0125] Specifically, within each control cycle (e.g., 20ms), the system repeatedly performs the aforementioned feedback acquisition, error calculation, and incremental proportional-integral-derivative (PI-DI) operations. Simultaneously, in a separate monitoring thread, the system continuously checks each of the calculations obtained within the most recent N power frequency cycles. Are all values ​​less than the preset threshold? For example, the system is set to determine the residual interference voltage feedback value calculated for each of 10 consecutive power frequency cycles (corresponding to 200ms). All are below the preset threshold of 1mV .

[0126] When the judgment condition is met, the reverse compensation control quantity of the current iteration calculation output is locked to maintain a stable output of the compensation voltage.

[0127] Locking refers to the main control module stopping the control of the reverse compensation quantity. The iterative update will change the current control quantity. The value is fixed, and this value is continuously output to the drive circuit of the adaptive compensation module.

[0128] Specifically, once the system monitors 10 consecutive cycles of If the condition of less than 1mV is met, the main control module immediately exits the incremental proportional-integral-derivative control cycle. The digital-to-analog converter will maintain the output with the currently locked control value. The corresponding analog voltage causes the adaptive compensation module to output a compensation voltage with constant amplitude and phase, thereby maintaining an approximately zero power frequency interference voltage environment across the measured resistor segment. For example, after approximately 15 control cycles (300ms) of adjustment, The voltage remained stable at around 0.5mV for 10 consecutive cycles. The system determined that compensation was complete and locked the current control value. At this point, the adaptive compensation module continuously output a stable compensation voltage with an amplitude of 5.02V and a phase of 210.5 degrees.

[0129] Therefore, according to the above implementation method, the system can achieve dynamic, accurate, and rapid cancellation of power frequency induced voltages over a wide range of 0 to 20V through real-time feedback and incremental proportional-integral-derivative closed-loop control. This system suppresses residual interference to below the millivolt level, creating a clean electrical environment for subsequent high-precision DC resistance measurements, fundamentally solving the technical bottleneck that prevents the application of the standard four-terminal test method under strong induced electrical interference.

[0130] In some embodiments, the system can calculate the error input signal required for closed-loop control using the following formula (a): (a) Formula (a) is the formula for calculating the error input of the incremental proportional-integral-derivative control algorithm. This represents the closed-loop control error value calculated in the k-th control cycle, in units of V. This represents the root mean square value of the residual power frequency induced voltage of the measured resistor segment, which is acquired by the second channel of the differential voltage measurement module and calculated after signal processing during the k-th control cycle. It reflects the instantaneous state of the current compensation effect. In this embodiment, the residual interference voltage suppression target threshold is set as preset by the system. This threshold defines the target accuracy for compensation convergence.

[0131] Next, in this embodiment, the system can also calculate the adjustment increment of the compensation control quantity using formula (b): (b) Among them, formula (b) is the core recursive formula of the incremental proportional-integral-derivative control algorithm. It represents the increment of the control quantity calculated in the k-th control cycle, and is a dimensionless digital control signal. This is a proportionality coefficient used to amplify the rate of change between the current error and the error at the previous moment, thereby accelerating the system response speed. is the integral coefficient, used to accumulate historical errors, with the aim of eliminating the steady-state error of the system. These are the differential coefficients, used to predict the trend of error changes, and play a role in suppressing overshoot and enhancing system stability. and They represent the previous one (the first one) (the first) and the first two (the first) The error value obtained by calculating the control cycle (number of cycles) is the historical state necessary for the algorithm to perform recursive calculation.

[0132] Furthermore, in this embodiment, the system can also calculate the final control quantity output to the adaptive compensation module using formula (c): (c) Formula (c) is the update formula for the control quantity. This represents the final control quantity calculated in the k-th control cycle and which will be output to the digital-to-analog converter. Indicates the previous control cycle (the first cycle) The formula shows that the current control quantity is the control quantity from the previous moment, plus the increment calculated in this cycle. This "incremental" characteristic effectively avoids problems such as integral saturation, making the control process more stable.

[0133] Therefore, by combining the above formulas (a) to (c), the system can construct a complete incremental proportional-integral-derivative closed-loop control law. This control law is based on the deviation between the real-time measured residual disturbance voltage and the target threshold. Using the proportional, integral, and derivative functions as the sole input, a precise control increment is calculated by dynamically adjusting their contributions. Based on this, the final control commands are iteratively updated. .this After digital-to-analog conversion, the adaptive compensation module is driven to dynamically adjust the amplitude and phase of its output compensation voltage, thereby forming a negative feedback closed loop aimed at suppressing residual interference. This system can ensure that the power frequency induced voltage difference across the measured resistor segment converges quickly and stably to within a preset threshold of 1mV, fundamentally solving the technical defects of existing open-loop compensation schemes, such as uncontrollable compensation effect and poor anti-interference fluctuation capability.

[0134] In some embodiments, performing DC excitation and sampling operations includes: The adaptive compensation module is controlled to maintain the locked compensation voltage output, while the DC constant current source module is controlled to enter the enabled state.

[0135] The enabled state refers to the working mode in which the power output circuit of the DC constant current source module is activated and ready to output a constant current according to a preset value.

[0136] Specifically, after the closed-loop compensation control operation is completed and the compensation parameters are locked, the system's main control module, through a time-sharing control unit, first ensures that the control quantity sent to the digital-to-analog converter output channel of the adaptive compensation module remains unchanged, thereby maintaining the stability of its compensation voltage output. Subsequently, the main control module sends a high-level logic signal to the enable control terminal of the DC constant current source module through a general-purpose input / output port, activating the module's internal control loop and power output stage. For example, after confirming that the compensation is locked, the main control module controls the digital-to-analog converter of the adaptive compensation module to continuously output a fixed digital code value corresponding to the 5.02V compensation voltage. Simultaneously, the main control module's input / output port GPIO1 outputs a 3.3V high-level signal to the enable pin of the DC constant current source module, and the closed-loop system composed of the precision operational amplifier, metal-oxide-semiconductor field-effect transistor, and sampling resistor inside the module begins to operate.

[0137] The control DC constant current source module establishes a current excitation loop between the positive and negative terminals of the current excitation to inject a preset constant DC measurement current into the measured resistance segment.

[0138] In this context, the current excitation loop refers to the closed conductive path formed by current flowing from the positive output terminal of the DC constant current source module, through the test lead to the positive current excitation terminal, through the measured resistor section, and then back from the negative current excitation terminal to the negative output terminal of the DC constant current source module through the test lead. The constant DC measurement current refers to a DC current with stable amplitude and minimal ripple, denoted as . .

[0139] Specifically, the system's main control module generates a corresponding digital current setting based on a preset current value (e.g., 50mA) through internal calculation or table lookup, and sends it to the current reference setting terminal of the DC constant current source module via a digital-to-analog converter or direct digital control interface. Based on this setting, the DC constant current source module establishes and maintains a highly stable DC current between the positive and negative terminals of the current excitation through its internal closed-loop feedback control. For example, the main control module presets the measurement current... The current is set to 50mA. After receiving this setting, the DC constant current source module establishes a stable 50mA current between its output terminals. The current flows out from the positive terminal of the module, through a double-shielded test cable to the current excitation positive terminal clamp fixed on the cable, flows through a 0.5m long section of the resistor under test, and then flows back from the current excitation negative terminal clamp to the negative terminal of the module, forming a complete excitation circuit.

[0140] Control the second differential measurement channel to acquire the voltage signal between the positive and negative voltage sampling terminals.

[0141] Among them, voltage signal acquisition refers to the process of synchronously and continuously discretizing the potential difference between the positive and negative terminals of voltage sampling using a high-precision analog-to-digital converter during DC current injection.

[0142] Specifically, when the DC constant current source module outputs current and reaches a stable state (e.g., after 50ms), the system main control module controls the analog-to-digital converter (ADC) of the second differential measurement channel to start. The high-input-impedance differential amplifier of the second differential measurement channel amplifies and conditions the voltage between the positive and negative sampling terminals, and then the high-speed ADC digitizes this voltage at a fixed sampling rate. For example, 50ms after the DC current stabilizes, the main control module triggers the ADC of the second differential measurement channel to start working. This channel synchronously samples the voltage between the positive and negative sampling terminals at a sampling rate of 10kHz. The voltage signal acquired at this time includes the DC voltage drop component generated by the DC current, possibly residual minor power frequency interference components, and circuit background noise.

[0143] The second differential measurement channel is controlled to perform multi-cycle synchronous sampling of the voltage signal, and the average value of the sampled data is calculated to obtain the DC voltage drop measurement value across the measured resistor segment.

[0144] Multi-cycle synchronous sampling refers to continuous voltage sampling with time windows that are integer multiples of the power frequency cycle, ensuring that the sampling start point is synchronized with the power frequency cycle. This facilitates subsequent averaging and cancellation of periodic residual interference. The measured DC voltage drop value is the stable voltage value characterizing the DC potential difference across the measured resistor segment, obtained after multi-cycle averaging. It is denoted as... .

[0145] Specifically, the system's main control module controls the analog-to-digital converter of the second differential measurement channel to accurately acquire voltage data for N consecutive complete power frequency cycles. Then, the arithmetic mean of the instantaneous voltage values ​​at all sampling points within this time window is calculated. This averaging effectively cancels out periodic residual interference related to the power frequency cycle (due to the symmetry of its positive and negative half-cycles) and random white noise in the sampled data, thereby extracting the pure DC voltage component. For example, the system is set to a sampling window of 10 power frequency cycles (corresponding to 200ms). The second differential measurement channel collects 2000 points (10kHz * 0.2s) within 200ms. The main control module reads these 2000 voltage sample values. And calculate the measured value of DC voltage drop according to the following formula: Assuming the calculation result... The value is 2.5mV, which is the measured DC voltage drop across the resistor segment being measured.

[0146] Therefore, according to the above implementation method, the system can inject a highly stable DC test current into the target resistance segment in an electrical environment where strong power frequency interference is effectively suppressed, and simultaneously perform high-precision, interference-resistant voltage sampling. Through multi-cycle synchronous sampling and averaging data processing, the system can filter out residual periodic interference and random noise to the greatest extent, accurately extract the DC voltage drop signal determined by Ohm's law, and provide reliable and clean raw data for finally calculating the high-precision DC resistance value based on the four-terminal test method.

[0147] In some embodiments, performing a resistance calculation operation includes: Based on the principle of the four-terminal test method, the ratio of the measured DC voltage drop to the constant DC measuring current is calculated as the original measured DC resistance of the measured resistance segment.

[0148] The original measured value of DC resistance refers to the resistance value calculated directly from the measured voltage and current using Ohm's law at the ambient temperature of the measurement site, and is denoted as . This reflects the actual conductivity of the cable's outer sheath at the current temperature.

[0149] Specifically, the resistance calculation unit of the system's main control module reads the measured DC voltage drop value obtained from the DC excitation and sampling operation steps. and preset constant DC measurement current According to the principle of the four-terminal test method (Kelvin bridge method), the resistance value is equal to the ratio of the voltage drop across the measured segment to the current flowing through that segment. The system performs a division operation. This directly yields the raw measured value of DC resistance in ohms. For example, if the DC voltage drop measurement value 2.5mV, constant DC measurement current If the current is 50mA, then the calculated original measured value of the DC resistance is... ohm( ), that is, 50 .

[0150] Collect and measure the ambient temperature parameters at the measurement site.

[0151] The ambient temperature parameter refers to the temperature of the air surrounding the outer sheath of the cable being measured during the measurement, denoted as T, and usually measured in units of 1000 liters. This parameter is used to correct the resistance measurement for temperature, in order to eliminate the effect of ambient temperature changes on the conductor resistance.

[0152] Specifically, the system measures the ambient air temperature in real time using a temperature sensor integrated inside the main unit chassis or an external connection (such as the DS18B20 digital temperature sensor). The temperature sensor transmits the measured analog or digital temperature signal to the analog-to-digital converter or digital interface of the main control module. The main control module reads and analyzes the signal to obtain the current ambient temperature value T. For example, when measuring in a cable tunnel, the system measures the ambient temperature T as 30°C using the temperature sensor. The value 30 is then stored in the storage unit for subsequent calculations.

[0153] Based on the ambient temperature parameters and the preset temperature coefficient of resistance of the cable outer sheath material, the original measured value of DC resistance is converted by temperature to obtain the nominal value of DC resistance at the standard temperature.

[0154] The temperature coefficient of resistance refers to the ratio of the change in resistance of a conductor material with temperature, denoted as . The unit is usually 1 For materials commonly used in cable outer sheaths, such as polyethylene (PE) or polyvinyl chloride (PVC), this coefficient is a known physical constant. Temperature conversion refers to correcting and converting the resistance value measured at a certain temperature to a standard reference temperature (usually...) based on the temperature coefficient of resistance. The process of calculating the resistance value at a standard temperature (C60°C). The nominal DC resistance value refers to the resistance value obtained after temperature conversion at the standard temperature (C60°C). The reported value of the DC resistance of the cable outer sheath under ( ) is denoted as This value facilitates a unified comparison and condition assessment of cable resistance measured at different times and in different environments.

[0155] Specifically, the resistance calculation unit of the system's main control module reads the pre-stored temperature coefficient of resistance of the cable outer sheath material from the memory. Combined with the collected ambient temperature T and the calculated original DC resistance value According to the formula Perform the calculation. In the formula, T is the ambient temperature, and 20 is the standard reference temperature. This formula is based on the physical law that the resistance of a conductor changes linearly with temperature. Corrected to Equivalent resistance value under the condition For example, assuming the cable sheath is made of polyethylene, its temperature coefficient of resistance... The default value is 0.004. Ambient temperature at the site Original measured value of DC resistance Substitute into the formula to calculate: .

[0156] Therefore, the system calculates that in nominal DC resistance at standard temperature Approximately 48.08 .

[0157] In summary, based on the above implementation method, the system can first accurately calculate the original DC resistance value of the cable outer sheath at the instant of measurement using high-precision voltage and current data and the four-terminal testing method. Furthermore, by integrating temperature sensing and built-in material parameters, the system can automatically perform professional temperature conversion, uniformly correcting the original measured value to the industry standard temperature. The nominal value is obtained under the specified conditions. This process eliminates the systematic bias caused by environmental temperature fluctuations in the measurement results, making the measurement data obtained under different seasons and climatic conditions directly comparable, improving the accuracy and reliability of long-term monitoring and trend analysis, and providing normalized core data for the scientific assessment of cable condition.

[0158] In some embodiments, the above method further includes performing measurement result verification and data archiving operations, wherein performing measurement result verification and data archiving operations includes: After the nominal value of the DC resistance is calculated, the DC constant current source module is deactivated, and the voltage signal across the measured resistance segment is acquired again through the second differential measurement channel.

[0159] Measurement result verification refers to the quality control step of re-verifying the stability of the compensation environment after completing a full resistance measurement and calculation to confirm the validity of the measurement data. Data archiving refers to the process of formatting and storing the verified measurement results and their associated metadata.

[0160] Specifically, after obtaining the nominal value of the DC resistance Subsequently, the system's main control module first sends a low-level signal to the enable control terminal of the DC constant current source module through the general purpose input / output port, commanding it to shut down its power output. After the current excitation loop is disconnected, the system immediately controls the second differential measurement channel to perform a rapid acquisition of the voltage between the positive and negative voltage sampling terminals. For example, if the GPIO1 pin of the main control module outputs a 0V low level, the DC constant current source module will shut down its output within 5ms. Then, the main control module triggers the analog-to-digital converter of the second differential measurement channel to acquire a voltage signal for 20ms (corresponding to one power frequency cycle) at a sampling rate of 10kHz.

[0161] The root mean square value of the power frequency component in the re-acquired voltage signal is calculated and used as the residual interference voltage value for verification.

[0162] The residual interference voltage value used for verification refers to the effective value of the power frequency voltage obtained by sampling and calculating the voltage across the measured resistor immediately after the measurement cycle ends, denoted as . This value is used to determine whether the closed-loop compensation control was still effectively maintained during the DC measurement.

[0163] Specifically, the system performs the same signal processing procedure as the closed-loop compensation control stage on the newly acquired 20ms voltage data: extracting the 50Hz power frequency component through digital filtering or fast Fourier transform, and calculating the root mean square (RMS) value of this component. For example, processing the acquired 200 voltage sampling points yields the RMS value of their 50Hz components. It is 0.8mV.

[0164] The residual interference voltage value used for verification is compared with a preset threshold.

[0165] The comparison refers to comparing the calculated residual interference voltage value used for verification. Compared with the pre-stored threshold in the system used to determine whether the compensation has failed Logical operations for determining size relationships. Typically, Preset thresholds used in the closed-loop compensation control phase Same or similar.

[0166] Specifically, the system's main control module reads the preset verification threshold from the memory. (e.g., 1mV), and compare it with the real-time calculated value. Perform numerical comparisons. The purpose of the comparison is to generate a Boolean (true / false) logical result to drive subsequent process branches. For example, the system reads a preset verification threshold. It is 1mV. The calculated value is... When comparing mV with 1mV, since 0.8≤1, the comparison result is "not greater than the threshold".

[0167] If the comparison result shows that the residual interference voltage value for verification is not greater than the preset threshold, the current measurement cycle is determined to be valid, and the nominal value of DC resistance, the corresponding measurement timestamp, and the ambient temperature parameter are associated and stored.

[0168] The measurement timestamp refers to the precise time information, including year, month, day, hour, minute, and second, read from the real-time clock chip when the system determines that the measurement is valid. Associated storage refers to the process of packaging multiple related data items (such as resistance value, time, and temperature) from a single valid measurement into a single data record and writing it into non-volatile memory.

[0169] Specifically, when At this point, the system determines that the entire measurement cycle from electrode deployment to resistance calculation is valid, and the compensation environment remains stable throughout the DC measurement. Subsequently, the system obtains the current time from the real-time clock module and generates a measurement timestamp. Finally, the calculated nominal DC resistance value is... The timestamp, along with the previously collected ambient temperature parameter T, is combined into a complete record and written to the internal flash memory or external storage card. For example, if the system determines the measurement is valid, it reads the real-time clock to obtain the timestamp "2024-08-07 14:30:25". Subsequently, the nominal DC resistance value of 48.08 is... The timestamp and ambient temperature are 30 degrees Celsius. These three data items are combined in "CSV" (comma-separated values) format to form the record "48.08,2024-08-07 14:30:25,30", and appended to the "measurement_log.csv" file on the storage card.

[0170] If the comparison result shows that the residual interference voltage value for verification is greater than the preset threshold, the current measurement cycle is determined to be invalid, and the control flow jumps to perform the induced voltage acquisition operation to start a new measurement cycle.

[0171] In this context, "invalid measurement loop" means that the result of the recently completed measurement process is deemed unreliable due to a failed verification and should be discarded. "Process jump" means that the main control program no longer executes any subsequent operations related to the current measurement result, but instead directly resets the measurement state machine and returns to the beginning stage of the measurement process.

[0172] Specifically, when If the system determines that compensation may fail during DC measurement (e.g., due to sudden changes in induced voltage caused by the start-up or shutdown of large equipment on site), the measurement result will be invalid. The main control module will discard all intermediate data and the final result obtained from this calculation. No storage operation is performed. Simultaneously, by modifying the program counter or calling a function, the main program immediately jumps to "Step S120: Perform induced voltage acquisition operation," restarting a completely new measurement process. For example, assume the verification calculation yields... mV, greater than the 1mV threshold. The system determines this measurement is invalid. The main control module displays "Verification failed, remeasure" on the user interface and automatically calls the function to perform the induced voltage acquisition operation, starting a new round of induced electrical signal acquisition, closed-loop compensation, DC excitation and sampling process.

[0173] Therefore, according to the above implementation method, the system can automatically perform rigorous quality verification after each measurement. This mechanism effectively identifies compensation failures caused by sudden changes in the field environment by retesting residual interference, ensuring that every resistance value stored in the database is high-quality data measured under conditions where interference is reliably suppressed. Simultaneously, the automated invalid data removal and process retry functions improve adaptability to complex field conditions and the reliability of overall measurement results, avoiding the use of erroneous data in subsequent cable condition assessments and decisions.

[0174] Figure 8 This is a structural block diagram of a DC resistance measurement system for cable outer sheath according to an embodiment of the present invention.

[0175] like Figure 8 As shown, the DC resistance measurement system for the cable outer sheath includes: The electrode deployment module 210 is used to fix six measuring electrodes along the axial direction at a preset interval on the surface of the outer sheath of the cable under test in the running state, defining the sequentially connected inductive current acquisition section, measured resistance section and compensation injection section.

[0176] The induced voltage acquisition module 220 is used to acquire the power frequency induced voltage signal at both ends of the induced voltage acquisition section by performing induced voltage acquisition operation, and to extract the frequency, phase and amplitude reference parameters of the power frequency induced voltage signal.

[0177] The closed-loop compensation control module 230 is used to inject a compensation voltage of the same frequency and opposite phase into the conductor circuit containing the induced current acquisition section, the measured resistance section and the compensation injection section based on the reference parameters. At the same time, it monitors the residual power frequency interference voltage at both ends of the measured resistance section and uses the residual power frequency interference voltage as the feedback quantity to perform closed-loop dynamic adjustment based on the proportional-integral-derivative algorithm until the residual power frequency interference voltage drops below the preset threshold.

[0178] The DC excitation and sampling module 240 is used to inject a preset constant DC current into the measured resistor segment while maintaining the compensation voltage output, and simultaneously acquire the DC voltage drop signal across the measured resistor segment.

[0179] The resistance calculation module 250 is used to calculate the DC resistance value of the measured resistor segment based on the constant DC current and DC voltage drop signal, according to the principle of the four-terminal test method.

[0180] The specific functions and examples of each module and submodule of the device in this embodiment can be found in the relevant descriptions of the corresponding steps in the above method embodiments, and will not be repeated here.

[0181] According to embodiments of the present invention, the above-described method of the present invention can be applied to an electronic device and a readable storage medium.

[0182] Figure 9 A schematic block diagram of an electronic device 600 that can be used to implement embodiments of the present invention is shown. The electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device may also represent various forms of mobile devices, such as personal digital assistants, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely illustrative and are not intended to limit the implementation of the invention described and / or claimed herein.

[0183] like Figure 9 As shown, the electronic device 600 includes a computing unit 601, which can perform various appropriate actions and processes based on a computer program stored in a read-only memory (ROM) 602 or a computer program loaded from a storage unit 608 into a random access memory (RAM) 603. The RAM 603 may also store various programs and data required for the operation of the electronic device 600. The computing unit 601, ROM 602, and RAM 603 are interconnected via a bus 604. An input / output (I / O) interface 605 is also connected to the bus 604.

[0184] Multiple components in electronic device 600 are connected to I / O interface 605, including: input unit 606, such as keyboard, mouse, etc.; output unit 607, such as various types of displays, speakers, etc.; storage unit 608, such as disk, optical disk, etc.; and communication unit 609, such as network card, modem, wireless transceiver, etc. Communication unit 609 allows electronic device 600 to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0185] The computing unit 601 can be a variety of general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the computing unit 601 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various special-purpose artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, a digital signal processor (DSP), and any suitable processor, controller, microcontroller, etc. The computing unit 601 performs the various methods and processes described above, such as a method for measuring the DC resistance of a cable sheath. For example, in some embodiments, a method for measuring the DC resistance of a cable sheath can be implemented as a computer software program tangibly contained in a machine-readable medium, such as storage unit 608. In some embodiments, part or all of the computer program can be loaded and / or installed on the electronic device 600 via ROM 602 and / or communication unit 609. When the computer program is loaded into RAM 603 and executed by the computing unit 601, one or more steps of the method for measuring the DC resistance of a cable sheath described above can be performed. Alternatively, in other embodiments, the computing unit 601 may be configured by any other suitable means (e.g., by means of firmware) to perform a method for measuring the DC resistance of a cable sheath.

[0186] Various embodiments of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), application-specific standard products (ASSPs), systems-on-a-chip (SoCs), payload-programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include implementations in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a dedicated or general-purpose programmable processor, capable of receiving data and instructions from a storage system, at least one input device, and at least one output device, and transmitting data and instructions to the storage system, the at least one input device, and the at least one output device.

[0187] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0188] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0189] To provide interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device for displaying information to the user (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor); and a keyboard and pointing device (e.g., a mouse or trackball) through which the user provides input to the computer. Other types of devices can also be used to provide interaction with the user; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including sound input, voice input, or tactile input).

[0190] The systems and technologies described herein can be implemented in computing systems that include backend components (e.g., as a data server), or computing systems that include middleware components (e.g., an application server), or computing systems that include frontend components (e.g., a user computer with a graphical user interface or web browser through which a user can interact with implementations of the systems and technologies described herein), or any combination of such backend, middleware, or frontend components. The components of the system can be interconnected via digital data communication of any form or medium (e.g., a communication network). Examples of communication networks include local area networks (LANs), wide area networks (WANs), and the Internet.

[0191] Computer systems can include clients and servers. Clients and servers are generally located far apart and typically interact via communication networks. Client-server relationships are created by computer programs running on the respective computers and having a client-server relationship with each other. Servers can be cloud servers, servers in distributed systems, or servers incorporating blockchain technology.

[0192] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0193] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for measuring the DC resistance of a cable outer sheath, characterized in that, include: Six measuring electrodes are fixed along the axial direction at a preset interval on the surface of the outer sheath of the cable under test in operation, defining the sequentially connected induced current acquisition section, measured resistance section and compensation injection section. Acquire the power frequency induced voltage signal at both ends of the induced voltage acquisition section, and extract the frequency, phase and amplitude reference parameters of the power frequency induced voltage signal; Based on the reference parameters, a compensation voltage of the same frequency and opposite phase is injected into the conductor circuit. At the same time, the residual power frequency interference voltage at both ends of the measured resistor segment is monitored. The residual power frequency interference voltage is used as the feedback quantity to perform closed-loop dynamic adjustment based on the proportional-integral-derivative algorithm until the residual power frequency interference voltage drops below the preset threshold. While maintaining the output of the compensation voltage, a preset constant DC current is injected into the measured resistance segment, and the DC voltage drop signal across the measured resistance segment is acquired simultaneously. Based on the constant DC current and the DC voltage drop signal, the DC resistance value of the measured resistor segment is calculated according to the principle of the four-terminal test method.

2. The method according to claim 1, characterized in that, The method involves fixing six measuring electrodes along the axial direction at preset intervals on the surface of the outer sheath of the cable under test in operation, defining a sequentially connected induced current acquisition section, a measured resistance section, and a compensation injection section, including: Six measuring electrodes are arranged sequentially along the cable axis in a preset order. The six measuring electrodes are, in order, a data acquisition electrode, a current excitation positive terminal, a voltage sampling positive terminal, a voltage sampling negative terminal, a current excitation negative terminal, and a compensation electrode. Wherein, the outer sheath conductor segment between the acquisition electrode and the positive terminal of the current excitation is defined as the induced current acquisition segment, the outer sheath conductor segment between the positive terminal of the voltage sampling and the negative terminal of the voltage sampling is defined as the measured resistance segment, and the outer sheath conductor segment between the negative terminal of the current excitation and the compensation electrode is defined as the compensation injection segment; The physical lengths of the inductive current acquisition segment and the compensation injection segment are equal, and they are symmetrically distributed with the measured resistance segment as the center.

3. The method according to claim 1, characterized in that, The process of acquiring the power frequency induced voltage signal at both ends of the induced voltage acquisition section and extracting the frequency, phase, and amplitude reference parameters of the power frequency induced voltage signal includes: In the absence of external excitation, the voltage signal at both ends of the induced voltage acquisition section is acquired through the first differential measurement channel to obtain a pure power frequency induced voltage signal. The power frequency induced voltage signal is processed, and the frequency, phase and amplitude of the power frequency induced voltage signal are tracked and extracted in real time based on a software phase-locked loop to generate induced voltage reference parameters. Perform a length matching judgment to identify whether the actual length of the inductive current acquisition segment is consistent with the actual length of the measured resistance segment; If the length matching judgment result is inconsistent, the amplitude in the induced current reference parameter is scaled proportionally according to the actual length ratio of the induced current acquisition segment and the measured resistance segment to generate a compensation reference signal.

4. The method according to claim 1, characterized in that, The process involves injecting a compensation voltage of the same frequency but opposite phase into the conductor circuit based on the reference parameters, while simultaneously monitoring the residual power frequency interference voltage across the measured resistor segment. Using this residual power frequency interference voltage as feedback, a closed-loop dynamic adjustment based on a proportional-integral-differential algorithm is performed until the residual power frequency interference voltage drops below a preset threshold. This includes: Based on the compensation reference signal, an initial reverse compensation control quantity is configured and output to drive the adaptive compensation module to inject an initial compensation voltage into the compensation loop formed by the acquisition electrode and the compensation electrode. The voltage signal across the two ends of the measured resistor segment is synchronously acquired through the second differential measurement channel, and the root mean square value of the power frequency component in the voltage signal across the two ends of the measured resistor segment is calculated as the residual interference voltage feedback value. Calculate the difference between the residual interference voltage feedback value and the preset threshold to generate a closed-loop control error signal; Based on the closed-loop control error signal, the incremental proportional-integral-derivative control algorithm is invoked to iteratively calculate and output the amplitude adjustment and phase correction of the reverse compensation control quantity, so as to dynamically adjust the compensation voltage output by the adaptive compensation module. Repeat the acquisition, calculation, generation and iterative calculation steps to form a closed-loop regulation process, and determine whether the residual interference voltage feedback value is continuously lower than the preset threshold for multiple consecutive power frequency cycles; When the determination condition is met, the reverse compensation control quantity of the current iteration calculation output is locked to maintain the stable output of the compensation voltage.

5. The method according to claim 4, characterized in that, While maintaining the compensation voltage output, injecting a preset constant DC current into the measured resistance segment and simultaneously acquiring the DC voltage drop signal across the measured resistance segment includes: The adaptive compensation module is controlled to maintain the locked compensation voltage output, while the DC constant current source module is controlled to enter the enabled state. The DC constant current source module is controlled to establish a current excitation loop between the positive terminal of the current excitation and the negative terminal of the current excitation, so as to inject a preset constant DC measurement current into the measured resistance segment. Control the second differential measurement channel to acquire the voltage signal between the positive voltage sampling terminal and the negative voltage sampling terminal; The second differential measurement channel is controlled to perform multi-cycle synchronous sampling of the voltage signal, and the average value of the sampled data is calculated to obtain the DC voltage drop measurement value across the measured resistor segment.

6. The method according to claim 5, characterized in that, The calculation of the DC resistance value of the measured resistor segment based on the constant DC current and the DC voltage drop signal, according to the four-terminal test method principle, includes: Based on the principle of the four-terminal test method, the ratio of the measured DC voltage drop to the constant DC measurement current is calculated as the original measured DC resistance of the measured resistance segment. Collect and measure the ambient temperature parameters at the measurement site; Based on the ambient temperature parameters and the preset temperature coefficient of resistance of the cable outer sheath material, the original measured value of the DC resistance is converted to a temperature value to obtain the nominal value of the DC resistance at the standard temperature.

7. The method according to claim 6, characterized in that, The method further includes performing measurement result verification and data archiving operations, wherein performing measurement result verification and data archiving operations includes: After the nominal value of the DC resistance is calculated, the DC constant current source module is controlled to exit the enabled state, and the voltage signal across the measured resistance segment is collected again through the second differential measurement channel. Calculate the root mean square value of the power frequency component in the voltage signal that is acquired again, and use it as the residual interference voltage value for verification. The residual interference voltage value used for verification is compared with the preset threshold. If the comparison result shows that the residual interference voltage value used for verification is not greater than the preset threshold, then the current measurement cycle is determined to be valid, and the nominal value of the DC resistance, the corresponding measurement timestamp, and the ambient temperature parameter are associated and stored. If the comparison result shows that the residual interference voltage value used for verification is greater than the preset threshold, the current measurement cycle is determined to be invalid, and the control flow jumps to the operation of performing induced voltage acquisition to start a new measurement cycle.

8. A DC resistance measurement system for cable outer sheath, characterized in that, include: The electrode deployment module is used to fix six measuring electrodes along the axial direction at a preset interval on the surface of the outer sheath of the cable under test in operation, defining the sequentially connected inductive current acquisition section, measured resistance section and compensation injection section. The induced voltage acquisition module is used to acquire the power frequency induced voltage signal at both ends of the induced voltage acquisition section by performing induced voltage acquisition operation, and to extract the frequency, phase and amplitude reference parameters of the power frequency induced voltage signal; The closed-loop compensation control module is used to inject a compensation voltage of the same frequency and opposite phase into the conductor circuit containing the induced current acquisition section, the measured resistance section and the compensation injection section based on the reference parameters. At the same time, it monitors the residual power frequency interference voltage at both ends of the measured resistance section and uses the residual power frequency interference voltage as feedback to perform closed-loop dynamic adjustment based on the proportional-integral-derivative algorithm until the residual power frequency interference voltage drops below a preset threshold. The DC excitation and sampling module is used to inject a preset constant DC current into the measured resistor segment while maintaining the output of the compensation voltage, and simultaneously acquire the DC voltage drop signal across the measured resistor segment. The resistance calculation module is used to calculate the DC resistance value of the measured resistor segment based on the constant DC current and the DC voltage drop signal, according to the principle of the four-terminal test method.

9. An electronic device, characterized in that, include: At least one processor; and a memory that is communicatively connected to the at least one processor; The memory stores instructions that can be executed by the at least one processor to enable the at least one processor to perform the method of any one of claims 1-7.

10. A non-transitory computer-readable storage medium storing computer instructions, characterized in that, in, Computer instructions are used to cause a computer to perform the method according to any one of claims 1-7.

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