A single-ended grounding voltage acquisition circuit and acquisition method for the outer metal sheath of a cable

Abstract

The present invention discloses a single-ended grounding voltage acquisition circuit and acquisition method for the outer metal sheath of a cable. The acquisition circuit includes a filtering module, a signal isolation module and a signal amplification module. The filtering module can filter out interference signals greater than 20Hz through a specific combination of resistors and capacitors, providing a purer input signal for subsequent signal processing. The signal isolation module implements power supply isolation and conversion through a power conversion chip and a DC-DC conversion chip, while utilizing an isolated operational amplifier chip to isolate and amplify the signal, thereby improving the signal quality and stability. The signal amplification module reduces noise and amplifies weak signals through two-stage amplification to obtain a higher voltage gain, and finally converts the signal into a digital signal to meet the MCU's requirements for signal analysis, processing and storage. The acquisition circuit has high practicality and economy, and can operate stably in complex electromagnetic environments. The acquisition method can effectively solve the problems existing in the prior art.

Description

Technical Field

[0001] The present invention relates to the field of power engineering, and more specifically to a voltage acquisition circuit and method for a single-ended grounding system for a cable's outer metal sheath. This invention has important applications in power transmission and distribution, cable operating status monitoring, fault diagnosis, and power system maintenance. It is particularly suitable for accurately acquiring weak voltage signals in high-noise, complex electromagnetic environments. Background Art

[0002] In the field of power engineering, accurately measuring and monitoring various electrical parameters is crucial for ensuring the safe and stable operation of power systems. In particular, voltage acquisition in single-ended grounding systems of cable sheaths is crucial for understanding cable operating conditions, preventing faults, and optimizing power equipment operation. However, existing technologies have numerous challenges in processing weak voltage signals from cable sheaths, making them difficult to meet the requirements for high-precision acquisition.

[0003] Weak signals typically refer to signals with relatively low amplitude and input impedance. In practical applications, these signals are highly susceptible to interference, resulting in poor signal quality and difficulty in accurately capturing effective information. Furthermore, existing amplifiers commonly exhibit input offset voltage. Even if zero-point adjustment temporarily meets measurement requirements, the offset voltage drift problem remains difficult to resolve, seriously impacting the precise measurement of weak signals.

[0004] When processing weak signals from the cable's outer metal sheath, current technologies rely solely on simple amplification circuits, unable to effectively filter out interference signals, accurately amplify signals, and reliably acquire them. Existing acquisition methods and circuits struggle to meet the requirements for precise acquisition in complex electromagnetic environments and weak signal detection. This results in inaccurate voltage data collection for single-ended grounding systems of the cable's outer metal sheath, making it impossible to provide a reliable basis for assessing the cable system's operating status, thereby impacting the safe and stable operation of the power system. Summary of the Invention

[0005] To address the above issues, the present invention provides a circuit and method for collecting the voltage of a cable's outer metal sheath on a single-ended ground. These circuits can accurately capture weak voltage signals in a single-ended grounding system, providing reliable support for accurate assessment of the system's operating status. This circuit features a compact structure, low cost, high practicality and affordability, and can operate stably in complex electromagnetic environments, effectively resolving the challenges of existing technologies.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A single-ended ground voltage acquisition circuit for the outer metal sheath of a cable includes the following modules: a filtering module, a signal isolation module, and a signal amplification module. The functions and specific circuit designs of each module are as follows:

[0008] The filter module is composed of resistors and capacitors. The filter module is a low-pass filter. Its main function is to effectively filter out interference signals above 20Hz in the circuit, making the useful signal purer. Through a specific combination of resistors and capacitors, the filter module can effectively suppress high-frequency interference signals while reducing the impact of low-frequency noise, providing a purer input signal for subsequent signal processing.

[0009] The signal isolation module includes a first signal preprocessing circuit, a power conversion chip U1, a DC-DC converter chip U2, an isolated op amp chip U3, resistors R301 and R302, and a capacitor C301. This module primarily isolates and converts power and amplifies signals, preventing electromagnetic interference from the measurement system and protecting the back-end acquisition circuit from spikes. The module uses the power conversion chip and DC-DC converter chip to isolate and convert power, while also utilizing the isolated op amp chip to isolate and amplify the signal, effectively improving signal quality and stability.

[0010] The signal amplification module includes a second signal preprocessing circuit, an isolated op amp chip U4, an instrumentation amplifier chip U5, and resistor R501. This module further amplifies the filtered and isolated signal. The amplified analog signal is converted to a digital signal via an analog-to-digital converter (ADC) and output to the MCU for analysis, processing, and storage. Through two stages of amplification (an isolated op amp chip and an instrumentation amplifier chip), the module reduces noise and amplifies weak signals, achieving a high voltage gain to facilitate subsequent circuit processing.

[0011] A further improvement of the present invention is that the filter module is composed of resistors and capacitors, specifically including resistors R001, R002, R003, R004, R005, R006, R007, R008, and capacitors C001, C002, C003, and C004; and the connection method thereof is as follows:

[0012] Resistor R001, resistor R003, resistor R005, and resistor R007 are connected in series in sequence; resistor R002, resistor R004, resistor R006, and resistor R008 are connected in series in sequence;

[0013] One end of capacitor C001 is connected to the node between resistor R001 and resistor R003, and the other end of capacitor C001 is connected to the node between resistor R002 and resistor R004; one end of capacitor C002 is connected to the node between resistor R003 and resistor R005, and the other end of capacitor C002 is connected to the node between resistor R004 and resistor R006; one end of capacitor C003 is connected to the node between resistor R005 and resistor R007, and the other end of capacitor C003 is connected to the node between resistor R006 and resistor R008; one end of capacitor C004 is connected to the other end of resistor R007, and the other end of capacitor C004 is connected to the other end of R008; one end of grounding resistor R000 is connected to the other end of resistor R001, and the other end of grounding resistor R000 is connected to the other end of R002, and varistor D is connected in parallel with grounding resistor R000.

[0014] A further improvement of the present invention is that the specific circuit connection of the signal isolation module is as follows:

[0015] The first signal preprocessing circuit includes a resistor R009, a resistor R010, a resistor R011 and a capacitor C005; the resistor R009 is connected in parallel with the capacitor C004, one end of the resistor R010 is connected to one end of the resistor R009, and the other end of the resistor R010 is connected to the differential input positive terminal pin VINP of the isolated operational amplifier chip U3; one end of the resistor R011 is connected to the other end of the resistor R009, and the other end of the resistor R011 is connected to the differential input negative terminal pin VINN of U3; one end of the capacitor C005 is connected to the differential input negative terminal of the isolated operational amplifier chip U3, and the other end of the capacitor C005 is connected to the differential input positive terminal of the isolated operational amplifier chip U3;

[0016] The input pin VIN of the power conversion chip U1 is connected to the BAT_+12V power supply, and the ground pin GND is connected to the ground pin GNDP of the DC-DC conversion chip U2; the output pin +VO of U1 is connected to the enable pin EN and the input pin VINP of the DC-DC conversion chip U2 respectively; the isolated voltage output pin VISO of the DC-DC conversion chip U2 is connected to the pin VDD1 of the signal isolation op amp chip U3;

[0017] One end of the resistor R301 is connected to the positive voltage output terminal VOUTP of the isolated operational amplifier chip U3, and the other end of the resistor R301 is connected to one end of the capacitor C301; one end of the resistor R302 is connected to the negative voltage output pin VOUTN of the signal isolation amplifier, and the other end of the resistor R302 is connected to the other end of the capacitor C301.

[0018] A further improvement of the present invention is that the specific circuit connection of the signal amplification module is as follows:

[0019] The second signal preprocessing circuit includes a resistor R3901, a resistor R3902, a capacitor C401, and a capacitor C402, wherein one end of the capacitor C401 is connected to one end of the capacitor C301, and the other end of the capacitor C401 is connected to the positive input pin +IN of the isolated operational amplifier chip U4; one end of the capacitor C402 is connected to one end of the capacitor C301, and the other end of the capacitor C402 is connected to the negative input pin -IN of the isolated operational amplifier chip U4; the resistor R3901 and the resistor R3902 are connected in series, the other end of the resistor R3901 is connected to the other end of the capacitor C401, the other end of the resistor R3902 is connected to the other end of the capacitor C402, and the endpoint between the resistor R3901 and the resistor R3902 is grounded;

[0020] The positive input pin of the instrumentation amplifier chip U5 is connected to the output pin OUT of the isolation operational amplifier chip U4, one end of the resistor R501 is connected to the output pin OUT of the instrumentation amplifier chip U5, and the other end of the resistor R501 is connected to ADC1 / 2 / 3_V.

[0021] A method for collecting the single-ended ground voltage of a cable outer metal sheath is provided, and the specific steps are as follows:

[0022] A. Measure the voltage signal of the sampling resistor and accurately collect the voltage waveform at both ends of the sampling resistor;

[0023] B. The influence of interference signals greater than 20Hz on the real signal is filtered out through a filter module composed of resistors and filter capacitors;

[0024] C. The signal enters the first pre-processing unit for filtering. At the same time, the power conversion chip converts the +12V power supply into a +5V power supply. The DC-DC conversion chip and the isolation amplifier chip isolate and amplify the output power signal and voltage signal respectively.

[0025] D. Enter the second signal pre-processing unit for capacitor filtering and resistor voltage division, and process the signal again. Use an isolated operational amplifier chip and an instrumentation amplifier chip to perform corresponding noise reduction and amplification on the tiny signal through two-stage amplification, and obtain a higher voltage gain. After the above series of processing, an accurate voltage signal is finally obtained and output to the MCU for analysis, processing and storage.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] This invention can accurately collect weak voltage signals in a single-ended grounding system of a cable's outer metal sheath, providing reliable support for accurate assessment of the system's operating status. The acquisition circuit in this invention is compact, low-cost, highly practical and economical, and can operate stably in complex electromagnetic environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : A circuit diagram for collecting the single-ended grounding voltage waveform of the cable outer metal sheath provided in an embodiment of the present invention shows the connection relationship between the filtering module, signal isolation module, and signal amplification module, as well as the connection method with other circuit elements, which helps to understand the architecture and workflow of the entire circuit.

[0029] Figure 2 : A flow chart of a method for collecting the single-ended grounding voltage of the outer metal sheath of a cable provided in an embodiment of the present invention, presenting the various steps and their sequence of the voltage collection process.

[0030] Figure 3 :Provided by the embodiment of the present invention Figure 1 The voltage waveform between points T1+ and T1- is used to show the voltage signal before processing by the filtering module. The noise and interference components in the original signal can be seen, providing a benchmark for comparing subsequent filtering effects.

[0031] Figure 4 :Provided by the embodiment of the present invention Figure 1 The voltage waveform between T2+ and T2- reflects the voltage waveform change after filtering and the first signal preprocessing circuit. Figure 3 By comparison, we can show the optimization effect of filtering and preprocessing on the signal.

[0032] Figure 5 :Provided by the embodiment of the present invention Figure 1 The voltage waveform between points T3+ and T3- ​​shows the waveform after being processed by the isolation amplifier module, reflecting the role of the isolation amplifier module in suppressing interference, improving signal quality, and improving the signal waveform.

[0033] Figure 6 :Provided by the embodiment of the present invention Figure 1 The voltage waveform between the T4+ point and the T4- point shows the voltage waveform after being processed by the second preprocessing unit, which illustrates the contribution of the second preprocessing unit in the signal optimization process.

[0034] Figure 7 :Provided by the embodiment of the present invention Figure 1 The voltage waveform at point T5 shows the voltage waveform after being processed by the isolated operational amplifier chip U4.

[0035] Figure 8 :Provided by the embodiment of the present invention Figure 1 The voltage waveform at point T6 shows the final voltage waveform after being processed by the voltage acquisition module. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The elements and features described in one embodiment of the present invention may be combined with the elements and features shown in one or more other embodiments. It should be noted that for the purpose of clarity, the representation and description of components and processes that are not related to the present invention and are known to those of ordinary skill in the art are omitted in the description. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0037] like Figure 1-Figure 2 As shown, the cable outer metal sheath single-ended grounding voltage acquisition circuit disclosed in the present invention achieves accurate acquisition of the voltage of the cable outer metal sheath single-ended grounding system through the coordinated operation of various modules. The circuit structure and acquisition method of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] The single-ended ground voltage acquisition system for the cable outer metal sheath includes the following modules: filtering module, signal isolation module, and signal amplification module. The functions and specific circuit designs of each module are as follows:

[0039] The filter module is composed of resistors and capacitors. The filter module is a low-pass filter used to filter out interference signals above 20Hz;

[0040] The signal isolation module includes a first signal preprocessing circuit, a power conversion chip U1, a DC-DC conversion chip U2, an isolated operational amplifier chip U3, a resistor R301, a resistor R302, and a capacitor C301; the main function of the signal isolation module is to realize power isolation conversion and signal isolation amplification, avoid electromagnetic interference introduced into the measurement system, and protect the back-end acquisition circuit from the influence of peak electromagnetic pulses.

[0041] The signal amplification module includes a second signal preprocessing circuit, an isolated operational amplifier chip U4, an instrumentation amplifier chip U5, and a resistor R501. The main function of the signal amplification module is to further amplify the signal after filtering and isolation processing. The amplified analog signal is converted into a digital signal by an analog-to-digital converter (ADC) and output to the MCU for analysis, processing, and storage.

[0042] The three modules are as follows:

[0043] 1. Filter module

[0044] The filtering module plays a crucial role in the entire circuit. Because the microvolt-level DC voltage signals to be detected are extremely weak and contain a large amount of noise, the inherent noise of the measurement circuit, instrument amplifier circuit, and related components, as well as external interference signals, are often much larger than the amplitude of the target signal. Simply amplifying the signal is insufficient to measure such tiny microvolt-level signals. The filtering module designed in this invention, through a specific combination of resistors and capacitors, effectively filters out interference signals, facilitating the circuit's ability to measure small millivolt-level signals.

[0045] by Figure 3 shown Figure 1 Taking the voltage waveform between points T1+ and T1- as an example, the present invention implements a 10V peak sine wave with a -10mV DC offset to extract a weak offset from the voltage signal. After processing by the filtering module, it can better highlight the useful signal and reduce interference signals. Specifically, the combination of resistors R001-R008 and capacitors C001-C004 forms a multi-stage filtering circuit. By rationally selecting the parameter values ​​of the resistors and capacitors, it achieves the filtering of interference signals. Among them, resistors R001, R003, R005, and R007 are connected in series, and resistors R002, R004, R006, and R008 are connected in series. This series structure helps increase the input impedance of the circuit and reduce the impact of the signal source on the circuit. Capacitors C001-C004 are connected between different nodes, respectively, utilizing the DC-blocking and AC-passing properties of the capacitors to filter out interference components in the signal. At the same time, the parallel connection of the grounding resistor and the varistor improves the anti-interference ability of the circuit and ensures the stability of the filtering effect.

[0046] 2. Signal Isolation Module

[0047] Anti-interference is an unavoidable issue during the amplification and measurement of millivolt-level DC voltage signals. Without signal isolation, the measurement system will introduce various electromagnetic interferences, which will be mixed into the target signal. This will not only reduce measurement accuracy, but also cause spikes in electromagnetic pulses to damage the back-end acquisition circuitry. The signal isolation module in this invention is used to prevent the measurement system from introducing various electromagnetic interferences and to prevent spikes in electromagnetic pulses from damaging the back-end acquisition circuitry, thereby improving measurement accuracy.

[0048] from Figure 4 and Figure 5It can be seen that after the signal is processed by the isolation module, the waveform is improved and interference signals are suppressed. Specifically, the first signal preprocessing circuit performs preliminary filtering and preprocessing of the signal through resistors R009–R011 and capacitor C005. Power conversion chip U1 converts the +12V power supply to +5V, providing stable power support for subsequent circuits. DC-DC converter chip U2 and isolated op amp chip U3 jointly implement signal isolation and amplification. Isolation technology isolates the signal from the power supply, preventing interference from power supply noise. The connection method of resistors R301, R302, and capacitor C301 further optimizes the signal output characteristics and ensures signal stability.

[0049] 3. Signal Amplification Module

[0050] The signal amplification module uses an isolated operational amplifier chip and an instrumentation amplifier chip to obtain a higher voltage gain by performing two-stage amplification on tiny signals. Figure 6 、 Figure 7 and Figure 8 It can be seen that after being processed by the signal amplification module, the weak voltage signal is gradually amplified, and can eventually meet the MCU's requirements for signal analysis, processing and storage, and realize the accurate acquisition of the waveform signal.

[0051] Specifically, the second signal preprocessing circuit filters and preprocesses the signal using resistors R3901 and R3902 and capacitors C401 and C402. It also divides the signal voltage to meet the input requirements of the subsequent amplification circuit. The isolated op amp chip U4 and the instrumentation amplifier chip U5 form a two-stage amplification circuit. The first stage uses the isolated op amp chip U4 to initially amplify the signal, while also isolating the signal and preventing interference during transmission. The second stage uses the instrumentation amplifier chip U5 to amplify the signal, achieving a high voltage gain and meeting the MCU's signal amplitude requirements. The connection of resistor R501 ensures that the signal's output impedance matches the MCU's input impedance, improving signal transmission efficiency and quality.

[0052] The voltage acquisition method is as follows:

[0053] In practical applications, the method for collecting the single-ended grounding voltage of the outer metal sheath of a cable according to the present invention is performed in the following steps:

[0054] 1. Measure the voltage signal across the sampling resistor to ensure accurate acquisition of the voltage waveform across the resistor. During the measurement process, select a suitable sampling resistor with stable resistance and high accuracy. Also, pay attention to the grounding of the measurement circuit to avoid introducing additional interference signals.

[0055] 2. The filtering module, consisting of resistors and capacitors, suppresses interference signals, laying the foundation for subsequent accurate processing of useful signals. During the filtering process, the parameter values ​​of the filter resistors and capacitors should be selected based on the actual electromagnetic environment and the characteristics of the interference signal to achieve the best filtering effect.

[0056] 3. The signal enters the first preprocessing unit for filtering. Simultaneously, the power conversion chip converts the +12V power supply to +5V. The DC-DC converter chip isolates the power supply, and the isolation amplifier chip amplifies the voltage signal. This step achieves power conversion and initial signal amplification and isolation, improving signal quality and stability.

[0057] 4. The signal enters the second signal preprocessing unit for capacitive filtering and resistive voltage division. An isolated op amp and an instrumentation amplifier chip are used to amplify the tiny signal in two stages, achieving high voltage gain. After this series of processing, a precise voltage signal is ultimately generated and output to the MCU for analysis, processing, and storage. During signal amplification, the amplifier gain and bandwidth must be appropriately selected based on the signal's amplitude and frequency characteristics. Attention must also be paid to the effects of amplifier nonlinear distortion and noise on the signal to ensure signal accuracy.

[0058] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be clear that the above is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. The present invention effectively solves the problem of difficulty in collecting weak signals in the prior art through innovative circuit design and acquisition methods, and provides a reliable and efficient solution for voltage acquisition in the field of power engineering, which has broad application prospects and promotion value.

[0059] Finally, it should be noted that although the present invention and its advantages have been described in detail above, it should be understood that various changes, substitutions, and modifications may be made without departing from the spirit and scope of the present invention as defined by the appended claims. Moreover, the scope of the present invention is not limited to the specific embodiments of the processes, devices, means, methods, and steps described in the specification. A person of ordinary skill in the art will readily understand from the disclosure of the present invention that existing and future developed processes, devices, means, methods, or steps that perform substantially the same functions or achieve substantially the same results as the corresponding embodiments described herein may be used according to the present invention. Therefore, the appended claims are intended to include within their scope such processes, devices, means, methods, or steps.

Claims

1. A single-ended ground voltage acquisition circuit for a cable outer metal sheath, characterized in that: It includes the following modules: filtering module, signal isolation module and signal amplification module; the functions and specific circuit designs of each module are as follows: The filter module is composed of resistors and capacitors. The filter module is a low-pass filter used to filter out interference signals above 20Hz; The signal isolation module includes a first signal preprocessing circuit, a power conversion chip U1, a DC-DC conversion chip U2, an isolated operational amplifier chip U3, resistors R301 and R302, and a capacitor C301. The main function of the signal isolation module is to achieve power isolation conversion and signal isolation amplification, avoid electromagnetic interference introduced into the measurement system, and protect the back-end acquisition circuit from the impact of spike electromagnetic pulses. The signal amplification module includes a second signal preprocessing circuit, an isolated operational amplifier chip U4, an instrumentation amplifier chip U5, and a resistor R501; the main function of the signal amplification module is to further amplify the signal after filtering and isolation processing. The amplified analog signal is converted into a digital signal through an analog-to-digital converter and output to the MCU for analysis, processing and storage.

2. The cable outer metal sheath single-ended ground voltage acquisition circuit according to claim 1, characterized in that: The filter module is composed of resistors and capacitors, including resistors R001, R002, R003, R004, R005, R006, R007, R008, and capacitors C001, C002, C003, and C004. The connection method is as follows: Resistor R001, resistor R003, resistor R005, and resistor R007 are connected in series in sequence; resistor R002, resistor R004, resistor R006, and resistor R008 are connected in series in sequence; One end of the capacitor C001 is connected to a node between the resistor R001 and the resistor R003, and the other end of the capacitor C001 is connected to a node between the resistor R002 and the resistor R004; One end of capacitor C002 is connected to a node between resistor R003 and resistor R005, and the other end of capacitor C002 is connected to a node between resistor R004 and resistor R006; one end of capacitor C003 is connected to a node between resistor R005 and resistor R007, and the other end of capacitor C003 is connected to a node between resistor R006 and resistor R008; One end of the capacitor C004 is connected to the other end of the resistor R007, and the other end of the capacitor C004 is connected to the other end of R008; One end of the grounding resistor R000 is connected to the other end of the resistor R001 , the other end of the grounding resistor R000 is connected to the other end of R002 , and the varistor D is connected in parallel with the grounding resistor R000 .

3. The cable outer metal sheath single-ended ground voltage acquisition circuit according to claim 1, characterized in that: The specific circuit connection of the signal isolation module is as follows: The first signal preprocessing circuit includes a resistor R009, a resistor R010, a resistor R011 and a capacitor C005; the resistor R009 is connected in parallel with the capacitor C004, one end of the resistor R010 is connected to one end of the resistor R009, and the other end of the resistor R010 is connected to the differential input negative terminal pin VINN of the isolated operational amplifier chip U3; one end of the resistor R011 is connected to the other end of the resistor R009, and the other end of the resistor R011 is connected to the differential input positive terminal pin VINP of U3; one end of the capacitor C005 is connected to the differential input negative terminal of the isolated operational amplifier chip U3, and the other end of the capacitor C005 is connected to the differential input positive terminal of the isolated operational amplifier chip U3; The input pin VIN of the power conversion chip U1 is connected to the BAT_+12V power supply, and the ground pin GND is connected to the ground pin GNDP of the DC-DC conversion chip U2; the output pin +VO of U1 is connected to the enable pin EN and the input pin VINP of the DC-DC conversion chip U2 respectively; the isolated voltage output pin VISO of the DC-DC conversion chip U2 is connected to the pin VDD1 of the signal isolation op amp chip U3; One end of the resistor R301 is connected to the positive voltage output terminal VOUTP of the isolated operational amplifier chip U3, and the other end of the resistor R301 is connected to one end of the capacitor C301; one end of the resistor R302 is connected to the negative voltage output pin VOUTN of the signal isolation amplifier, and the other end of the resistor R302 is connected to the other end of the capacitor C301.

4. The cable outer metal sheath single-ended ground voltage acquisition circuit according to claim 1, characterized in that: The specific circuit connection of the signal amplification module is as follows: The second signal preprocessing circuit includes a resistor R3901, a resistor R3902, a capacitor C401, and a capacitor C402, wherein one end of the capacitor C401 is connected to one end of the capacitor C301, and the negative electrode of the capacitor C401 is connected to the positive input pin +IN of the isolated operational amplifier chip U4; the positive electrode of the capacitor C402 is connected to the negative electrode of the capacitor C301, and the other end of the capacitor C402 is connected to the negative input pin -IN of the isolated operational amplifier chip U4; the resistor R3901 and the resistor R3902 are connected in series, the other end of the resistor R3901 is connected to the other end of the capacitor C401, the other end of the resistor R3902 is connected to the other end of the capacitor C402, and the endpoint between the resistor R3901 and the resistor R3902 is grounded; The positive input pin of the instrumentation amplifier chip U5 is connected to the output pin OUT of the isolation operational amplifier chip U4, one end of the resistor R501 is connected to the output pin OUT of the instrumentation amplifier chip U5, and the other end of the resistor R501 is connected to ADC1 / 2 / 3_V, which is connected to the ADC.

5. A method for collecting the voltage of a single-ended grounding circuit of a cable outer metal sheath, characterized in that: The specific steps are as follows: A. Measure the voltage signal of the sampling resistor and accurately collect the voltage waveform at both ends of the sampling resistor; B. The influence of interference signals greater than 20Hz on the real signal is filtered out through a filter module composed of resistors and filter capacitors; C. The signal enters the first pre-processing unit for filtering. At the same time, the power conversion chip converts the +12V power supply into a +5V power supply. The DC-DC conversion chip and the isolation amplifier chip isolate and amplify the output power signal and voltage signal respectively. D. Enter the second signal pre-processing unit for capacitor filtering and resistor voltage division, and process the signal again. Use an isolated op amp chip and an instrumentation amplifier chip to reduce noise and amplify the tiny signal through two-stage amplification, and obtain voltage gain. After the above series of processing, an accurate voltage signal is finally obtained and output to the MCU for analysis, processing and storage.

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