Collecting instrument for cathode protection of natural gas pipeline

Abstract

The invention relates to the technical field of natural gas pipeline protection, in particular to an acquisition instrument for cathode protection of a natural gas pipeline, which comprises a pile body, a solar panel is fixedly mounted at the top of the pile body, an equipment cavity is formed in the pile body, an acquisition instrument is mounted in the equipment cavity, and the acquisition instrument is electrically connected with an insulating wiring board. The input end of the insulation wiring board is connected with a polarization probe through an integrated wire set and further connected with a pipeline cable, and the other end of the pipeline cable is connected with a pipeline. The cathode protection circuit composed of an alternating-current potential test circuit, a direct-current potential test circuit and a relay group circuit can measure alternating-current interference voltage around the pipeline and measure the direct-current potential difference between the pipeline and a reference electrode, so that the comprehensive monitoring capability on the cathode protection condition of the pipeline is provided; and through an integrated signal processing algorithm and a resistivity compensation algorithm, the accuracy of acquired data can be improved, so that the real condition of the pipeline can be better reflected.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas pipeline protection, and in particular to a collector for cathodic protection of a natural gas pipeline. Background Art

[0002] The cathodic protection data acquisition device is used to measure and record the power-on potential, natural potential, power-off potential, pipe-to-ground AC voltage, pipeline AC current density, pipeline DC current density, sacrificial anode open circuit potential, and sacrificial anode protection current of pipeline cathodic protection in the field; by integrating multiple sensors, controllers, and communication modules, it can realize comprehensive monitoring of the status of the cathodic protection system, and use cloud computing and artificial intelligence technology to process and analyze data, accurately judge the corrosion status of the facilities, and provide a scientific basis for facility operation and maintenance; in recent years, with the rapid development of national modernization, the construction of ultra-high voltage transmission lines and towers, acid rain, urban rail transit 110KV transmission line modification, high-speed rail electrification tracks, signal base stations, highways and other facilities has caused buried steel pipelines to be greatly disturbed by AC and DC stray currents. Long-term interference corrosion of pipelines will cause hazards such as pipeline perforation and gas leakage.

[0003] At present, traditional test piles mainly rely on manual field multimeters to detect cathodic protection data. The collected data is single, inefficient, unreliable, and highly dangerous. The management and daily patrol of cathodic protection effects are extremely difficult, and it is difficult to meet the needs of more and more long-distance pipeline cathodic protection data monitoring. In view of this, a data collector for cathodic protection of natural gas pipelines is provided. Summary of the invention

[0004] The main purpose of the present invention is to provide a data collector for cathodic protection of natural gas pipelines, so as to solve the problem proposed in the related art that the current traditional test piles mainly rely on manual field multimeters to detect cathodic protection data, the collected data is single, the efficiency is low, the reliability is poor, the risk is high, the management of cathodic protection effects and daily patrols are extremely difficult, and it is difficult to meet the needs of more and more long-distance pipeline cathodic protection data monitoring.

[0005] In order to achieve the above-mentioned object, according to one aspect of the present invention, there is provided a collector for cathodic protection of a natural gas pipeline, comprising a pile body, a solar panel is fixedly mounted on the top of the pile body, an equipment cavity is opened in the pile body, a collector is mounted in the equipment cavity, the collector is electrically connected to an insulating wiring board, an input end of the insulating wiring board is connected to a polarization probe through an integrated wire group, the input end of the insulating wiring board is also connected to a pipeline cable, and the other end of the pipeline cable is connected to a pipeline;

[0006] Among them, the integrated wire group includes sacrificial anode wire, long-term reference wire, AC test wire, polarization test wire and self-corrosion test wire.

[0007] Furthermore, the collector comprises:

[0008] An AD data acquisition unit, the AD data acquisition unit is used to collect voltage information in a cathode protection circuit, the cathode protection circuit is composed of an AC potential test circuit, a DC potential test circuit and a relay group circuit;

[0009] A wireless transmission module, which is used to transmit the collected data to a remote monitoring center wirelessly;

[0010] A positioning module, which is used to determine the specific location of the monitoring point;

[0011] The microprocessor unit is used to process information between various unit modules and is integrated with a signal processing algorithm and a resistivity compensation algorithm to improve the accuracy of the collected data.

[0012] Furthermore, the AD data acquisition unit comprises:

[0013] A collection unit, the collection unit is used to transmit the cathode voltage on the gas pipeline to the cathode protection circuit;

[0014] A voltage sensor, wherein the voltage sensor receives the cathode voltage of the analog signal from the acquisition unit at a certain sampling time interval, converts the cathode voltage of the digital signal through the ADC, and sends the digital signal to the first input terminal of the comparator;

[0015] A voltage module, wherein the voltage module is used to send the received reference voltage to the second input terminal of the comparator;

[0016] A comparator, the comparator is used to compare the cathode voltage received at the first input terminal with the reference voltage received at the second input terminal, and if the cathode voltage is higher than the reference voltage, an alarm signal is sent through the output terminal; if the cathode voltage is equal to or lower than the reference voltage, the comparator waits for the next acquisition and comparison in a loop;

[0017] An alarm signal transmitter is used to send out an alarm signal wirelessly.

[0018] Furthermore, in the cathodic protection circuit:

[0019] The AC potential test circuit is used to measure the AC interference voltage in the soil around the pipeline;

[0020] The DC potential test circuit is used to measure the DC potential difference between the pipeline and the reference electrode;

[0021] The relay group circuit is used to control and switch different test modes or disconnect certain circuits when an abnormality is detected to protect the equipment from damage.

[0022] The relay group circuit changes state according to the instructions of the microprocessor unit, thereby adjusting the cathodic protection system or isolating the faulty part.

[0023] Furthermore, the AC potential test circuit includes an operational amplifier U64, wherein the input terminal VIN of the operational amplifier U64 is connected to a capacitor C234, a capacitor C235 and a resistor R328, wherein one end of the capacitor C234 is connected to the cathode of the diode D3, the anode of the diode D3 is connected to the -5V input voltage, one end of the capacitor C235 is connected to the anode of the diode D4, the cathode of the diode D4 is connected to the +5V input voltage, the common node of the capacitors C234 and C235 is used as an input terminal for receiving a current test signal, the other end of the capacitor C234 shares a node with C235 and is connected to the input terminal VIN of the operational amplifier; a clamping circuit is formed by diodes D3 and D4 to protect the input terminal of the operational amplifier U64, and the common node of C234 and C235 is used to receive a current test signal.

[0024] The OUTPUT end of the operational amplifier U64 is connected to a resistor R329 and a capacitor C238, the other end of the capacitor C238 is grounded, and a common node of the resistor R329 and the capacitor C238 is used as an AC potential output;

[0025] Resistor R329 acts as a load resistor to convert the output signal of operational amplifier U64 into a voltage signal for adjusting the amplitude and impedance matching of the output signal. Capacitor C238 provides a high-frequency bypass at the output of operational amplifier U64 to improve the quality and stability of the output signal. It helps to eliminate high-frequency noise and ensure the accuracy of the output signal.

[0026] The -VS terminal of the operational amplifier U64 is connected to a capacitor C239, the other end of the capacitor C239 is grounded, and a capacitor C241 is connected to a common node between the capacitor C239 and the -VS terminal, the other end of the capacitor C241 is connected to the CAV terminal of the operational amplifier U64, and the negative electrode of the capacitor C241 is connected to a -5V input voltage;

[0027] Capacitor C239 is used to provide power decoupling to reduce noise and ripple on the power line and ensure the stable power supply required for the normal operation of the operational amplifier. The other end of capacitor C239 is grounded, which can absorb high-frequency noise from the power supply and prevent such noise from interfering with the internal operation of the operational amplifier.

[0028] The other end of capacitor C241 is connected to the -5V input voltage. Capacitor C241 is used to further stabilize the power supply and also to suppress the noise of the internal circuit of the operational amplifier. The CAV terminal represents the bias voltage of the operational amplifier. The voltage of this port determines the operating point of the operational amplifier.

[0029] The negative terminal of capacitor C241 is connected to the -5V input voltage, which means that the -VS terminal of operational amplifier U64 requires a stable -5V power supply to work properly;

[0030] The +VS terminal of the operational amplifier U64 is connected to a capacitor C236, the other end of the capacitor C236 is connected to the COM terminal of the operational amplifier U64, and the common node of the COM terminal and the capacitor C236 is grounded, and the common node of the capacitor C236 and the +VS terminal is connected to a +5V input voltage;

[0031] Capacitor C236 is used to provide power decoupling to reduce noise and ripples on the power line and ensure the stable power supply required for the normal operation of the operational amplifier. The common node of capacitor C236 and the COM terminal is grounded, which helps to absorb high-frequency noise from the power supply and prevent such noise from interfering with the internal circuit of the operational amplifier. The common node of capacitor C236 and the +VS terminal is connected to the +5V input voltage, which requires a stable +5V power supply for the +VS terminal of the operational amplifier U64.

[0032] The Cc terminal of the operational amplifier U64 is connected to a capacitor C242, and the other end of the capacitor C242 is grounded.

[0033] Further, the DC potential test circuit includes a dual operational amplifier LM324, wherein the -IN terminal of the dual operational amplifier LM324 is connected to a pipeline, and the +IN terminal of the dual operational amplifier LM324 is connected to a current test signal;

[0034] The OUT terminal of the dual operational amplifier LM324 is connected to a resistor R327, and the other end of the resistor R327 serves as an output terminal of a current-to-potential signal;

[0035] The VS terminal of the dual operational amplifier LM324 is connected to a capacitor C231, a common node between one end of the capacitor C231 and the VS terminal is connected to a capacitor C233, and a +5V input voltage is connected to the common node between the capacitor C231 and the VS terminal, and the other end of the capacitor C231 and the other end of the capacitor C233 are grounded together;

[0036] The OFFSET end of the dual operational amplifier LM324 is connected to a resistor R301, the other end of the resistor 301 is connected to a +5V input voltage, and a common node between the OFFSET end and the resistor R301 is connected to a resistor R331, a common node between the resistor R331 and the resistor R301 is connected to a capacitor C243, and the other end of the capacitor C243 is connected to the resistor R331 and is grounded together;

[0037] The GND terminal, A1 terminal and A2 terminal of the dual operational amplifier LM324 are grounded together.

[0038] Further, the relay group circuit includes a current test signal output circuit and a potential test signal output circuit;

[0039] Wherein, the current test signal output circuit includes relay K1, relay K1 and relay K3;

[0040] The contact 3 of the relay K1 is connected to a resistor R1, the other end of the resistor R1 is connected to a resistor R2, the other end of the resistor R2 is connected to the contact 5 of the relay K1, and the common node of the resistors R1 and R2 is connected to the pipeline; the purpose of connecting the common node of the resistors R1 and R2 to the natural gas pipeline is to measure the AC interference voltage around the pipeline. The resistors R1 and R2 form a voltage divider, which is used to limit the current flowing into the pipeline to prevent excessive current from damaging the circuit or affecting the normal operation of the pipeline. At the same time, this voltage divider also allows weak AC signals to pass through, so that the measuring equipment can capture the changes in the AC potential. When the contacts of the K1 relay are closed, the voltage divider is connected to the circuit, thereby realizing the measurement function of the AC potential.

[0041] The contact 4 of the relay K1 is connected to the contact 4 of the relay K3, and the contact 5 of the relay K3 is connected to the sacrificial anode, and the contact 3 of the relay K3 is connected to the contact 4 of the relay K2;

[0042] The contact 5 of the relay K2 is connected to the polarization test piece, and the contact 3 of the relay K2 is connected to the AC test piece.

[0043] Polarization test pieces and AC test pieces are important components for monitoring and evaluating the anti-corrosion performance of natural gas pipelines. Polarization test pieces simulate pipeline materials and are used to measure their electrochemical reactions under specific conditions, especially the extent of redox reactions, so as to understand whether the pipeline is in a good anti-corrosion state. AC test pieces are used to detect the presence and intensity of AC interference voltage, because AC interference may affect the effectiveness of anti-corrosion protection;

[0044] Relay K3 and relay K2 act as switches in the circuit. They can selectively connect or disconnect the polarization test strip and AC test strip, as well as the sacrificial anode, as needed. The sacrificial anode is a commonly used anti-corrosion method that protects the pipeline itself by allowing another metal (such as magnesium or zinc) to replace the pipeline as the target of corrosion. When contact 5 of relay K3 is connected to the sacrificial anode, it can monitor the working status of the sacrificial anode to ensure that it effectively consumes itself to protect the pipeline. Relay K2 is responsible for connecting the polarization test strip and the AC test strip for related tests;

[0045] The relay group circuit can change state according to the instructions of the microprocessor unit, so as to realize fast switching between different test modes, or disconnect certain circuits when abnormalities are detected to protect the equipment from damage.

[0046] Further, the potential test signal output circuit includes relay K4, relay K5, relay K6, relay K7, relay K8 and relay K9;

[0047] Wherein, the contact 4 of the relay K4 is connected to the pipeline, the contact 4 of the relay K5 is connected to the polarized test piece, the contact 4 of the relay K6 is connected to the sacrificial anode, the contact 4 of the relay K7 is connected to the natural test piece, and the contacts 3 of the relay K4, the relay K5 and the relay K6 are connected in parallel;

[0048] The contacts 5 of the relays K4, K5, K6 and K7 are connected in parallel, and the parallel common node of the contacts 5 is connected to the contact 5 of the relay K8, and the contact 3 of the relay K8 serves as the output end of the current-to-potential signal;

[0049] The contact 4 of the relay K8 is connected to a resistor R3, the other end of the resistor R3 is connected to the contact 4 of the relay K9, the common node of the resistor R3 and the contact 4 of the relay K8 is connected to the contact 3 of the relay K9, and the contact 4 of the relay K9 serves as the output end of the potential test signal;

[0050] A common node between the resistor R3 and the contact 4 of the relay K9 is connected to a resistor R4, and the other end of the resistor R4 is grounded.

[0051] Furthermore, the microprocessor unit receives the digital signal converted from the ADC, and uses a signal processing algorithm to identify and remove AC and DC stray current interference, and calibrates the effect of soil resistivity changes with temperature on the signal through a resistivity compensation algorithm;

[0052] The specific steps involved in the signal processing algorithm to remove AC stray current interference are:

[0053] The voltage signal in the cathodic protection circuit is collected for T seconds, and the sampling frequency is f sHz, the total number of sampling points is N;

[0054] Perform discrete Fourier transform on the collected voltage signal x[n] to obtain the frequency domain signal X[k];

[0055]

[0056] Calculate the amplitude of the spectrum |X[k]| to identify the interference frequency in the voltage signal;

[0057]

[0058] Where X[k] represents the kth component of the frequency domain signal, which is the spectral component of the discrete time signal x[n] at frequency k; k represents the frequency index; x[n] represents the nth sampling point of the time domain signal; n represents the time index; e -j2πkn / N represents a complex exponential function, represents a complex rotation factor at frequency k; j represents an imaginary unit, and j 2 =-1; |X[k]| represents the amplitude of the frequency domain signal X[k]; Re(X[k]) represents the real part of the frequency domain signal X[k]; Im(X[k]) represents the imaginary part of the frequency domain signal X[k];

[0059] A second-order band-stop filter is designed and applied to the original signal to remove the identified interference frequency, wherein the transfer function of the second-order band-stop filter is specifically:

[0060]

[0061] In the formula, ω 0 =2πf 0 represents the center angular frequency, f 0 is the center frequency; Q is the quality factor, which determines the bandwidth and selectivity of the filter; ζ is the damping ratio; s is the Laplace transform variable, which is used to describe the frequency characteristics of the filter.

[0062] Furthermore, the influence of soil resistivity changing with temperature on the signal is calibrated by the resistivity compensation algorithm, and the specific expression involved is:

[0063] ρ(T)=ρ 0 ·[1+α·(TT 0 )];

[0064] Where ρ(T) represents the soil resistivity at temperature T; ρ 0 Indicates the reference temperature t 0 The soil resistivity under the condition of α is the temperature coefficient of soil resistivity; T 0 represents the reference temperature; T represents the currently measured soil temperature;

[0065] At the same time, considering the influence of humidity H and salinity S on soil resistivity, the calibrated soil resistivity ρ is obtained eff :

[0066] ρ eff =ρ 0 ·[1+α·(TT 0 )+β·(HH 0 )+γ·(SS 0 )];

[0067] In the formula, β represents the humidity coefficient; γ represents the salinity coefficient; H 0 Indicates reference humidity; H indicates the currently measured soil humidity; S 0 represents the reference salinity; S represents the currently measured soil salinity;

[0068] And use the outlier detection method to calculate the invalid interference term Δρ eff , the final soil resistivity ρ(T, H, S) is obtained by removing the invalid interference terms:

[0069] ρ(T,H,S)=ρ eff -Δρ eff ;

[0070] ρ(T,H,S)=ρ 0 ·[1+α·(TT 0 )+β·(HH 0 )+γ·(SS 0 )]-Δρ eff .

[0071] The microprocessor unit reads the current temperature T, humidity H and salinity S and the measured soil resistivity ρ(T, H, S), and then uses the resistivity compensation algorithm to calculate the corrected soil resistivity ρ(T, H, S). The values ​​of α, β and γ depend on the specific composition of the soil and other environmental factors. Therefore, in practical applications, α, β and γ need to be determined through experimental data.

[0072] By calculating the corrected soil resistivity ρ(T, H, S), any changes or failures in the cathodic protection system, such as insufficient or over-protection protection current, can be discovered in a timely manner, so that necessary measures can be taken to make adjustments; accurate soil resistivity data helps maintain an effective cathodic protection level, avoid corrosion due to insufficient protection or material loss due to excessive protection, and thus extend the service life of the natural gas pipeline.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] 1. In the collector for cathodic protection of natural gas pipelines, the online monitoring of cathodic protection of gas pipelines realizes real-time and wireless data transmission between each monitoring point and the monitoring center; intensively collects cathodic protection parameter data, and the collected data is uploaded to the monitoring center via 4G wireless transmission. The monitoring center receives the data and analyzes and processes the data, thereby realizing real-time monitoring and prediction of the corrosion status of the gas pipeline and improving the reliability and efficiency of the cathodic protection system.

[0075] 2. In the collector for cathodic protection of natural gas pipelines, a cathodic protection circuit consisting of an AC potential test circuit, a DC potential test circuit and a relay group circuit is provided, which can measure the AC interference voltage around the pipeline (AC potential test circuit) and measure the DC potential difference between the pipeline and the reference electrode (DC potential test circuit), thereby providing a comprehensive monitoring capability for the cathodic protection status of the pipeline;

[0076] Through the integrated signal processing algorithm and resistivity compensation algorithm, the accuracy of the collected data can be improved, thereby better reflecting the actual condition of the pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 This is a schematic diagram of the overall structure of a collector in a preferred embodiment of the present invention;

[0078] Figure 2 This is a schematic diagram of the module of the collector system in a preferred embodiment of the present invention;

[0079] Figure 3 A schematic diagram of an AC potential test circuit in a preferred embodiment of the present invention;

[0080] Figure 4 A schematic diagram of a DC potential test circuit in a preferred embodiment of the present invention;

[0081] Figure 5 Schematic diagram of the relay group circuit in the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0082] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0083] See also Figure 1-Figure 5As shown, the purpose of this embodiment is to provide a collector for cathodic protection of a natural gas pipeline, comprising a pile body 1, a solar panel 2 is fixedly installed on the top of the pile body 1, the solar panel 2 is used to power a collector 3, the device for the solar panel 2 to power the collector 3 also includes at least a battery, the solar panel power is ≥5W, and the solar battery capacity is ≥20Wh; an equipment cavity is opened in the pile body 1, the collector 3 is installed in the equipment cavity, the collector 3 is electrically connected to an insulating wiring board 4, the input end of the insulating wiring board 4 is connected to a polarization probe 5 through an integrated wire group 41, the input end of the insulating wiring board 4 is also connected to a pipeline cable, and the other end of the pipeline cable is connected to a pipeline 6;

[0084] The integrated wire group 41 includes a sacrificial anode wire, a long-term reference wire, an AC test wire, a polarization test wire and a self-corrosion test wire, and the polarization probe 5 is buried around the pipeline;

[0085] The polarization probe 5 is provided with a polarization test piece, an AC test piece, a sacrificial anode test piece, a long-term reference test piece and a self-corrosion test piece, respectively, and the test pieces are buried in the soil around the pipeline 6;

[0086] Among them, the sacrificial anode wire is connected to the polarization test piece; the long-term reference wire is connected to the long-term reference test piece; the AC test piece wire is connected to the AC test piece; the polarization test piece wire is connected to the polarization test piece; and the self-corrosion test piece wire is connected to the self-corrosion test piece.

[0087] In soil or freshwater environments, it is advisable to use a copper-saturated copper sulfate reference electrode (hereinafter referred to as a saturated copper sulfate reference electrode, abbreviated as CSE); in soil environments, a high-purity zinc reference electrode (abbreviated as: ZRE, purity not less than 99.995%) can also be used. When using this reference electrode, it needs to be coated with 75% gypsum, 20% bentonite and 5% sodium sulfate backfill. The potential relative to the copper sulfate electrode -850mV is: +250mV (25℃), and the operating temperature should not be greater than 60℃; in seawater environments, a silver-silver chloride reference electrode (abbreviated as SSC) is advisable;

[0088] In this embodiment, the cross-sectional area of ​​the AC test wire, long-term reference wire, pipeline cable, polarization test wire and solar panel 2 power supply cable should be ≥2.5mm 2 The standard length is 5 meters, which is convenient for welding and installation;

[0089] The collector 3 includes:

[0090] AD data acquisition unit, the AD data acquisition unit is used to collect voltage information in the cathode protection circuit, the cathode protection circuit is composed of an AC potential test circuit, a DC potential test circuit and a relay group circuit;

[0091] During long-term use, oil and gas pipelines are prone to corrosion due to environmental factors such as soil, moisture, and oxygen. Therefore, by applying electric current, a protective film is formed on the surface of the pipeline to prevent corrosion.

[0092] In the cathodic protection circuit, the long-term reference test piece uses a pre-packaged long-term copper sulfate reference electrode. The long-term reference electrode should be installed as close to the pipeline as possible, 0.1m away from the exposed surface of the test piece, and 0.20-0.3m away from the pipe wall; before burying, the long-term reference electrode body should be soaked in clean water for more than 12 hours to ensure that the long-term reference electrode is fully moistened and in good contact with the soil. The long-term reference electrode should be handled with care during installation and should not cause the long-term reference electrode shell to rupture.

[0093] Specifically, the sacrificial anode test piece and the long-term reference test piece are buried at the same depth of the pipeline, 45 cm laterally along the pipeline, and the distance between the sacrificial anode test piece and the long-term reference test piece is 2-3 meters;

[0094] The AC test piece, polarization test piece, and self-corrosion test piece are placed about 10-20 cm around the long-term reference test piece, and the test pieces are spaced about 10-20 cm apart.

[0095] The pile body 1 is buried above the long-term reference test piece, and the burial depth is 1 meter.

[0096] The AD data acquisition unit includes a cathodic protection test probe, including basic components such as a test piece and a reference electrode. The exposed area of ​​the test piece should be 1 to 50 cm 2 ; When the AC and DC stray current interference is low, the test piece area used to evaluate the effectiveness of cathodic protection can be selected according to the type of anti-corrosion layer; when evaluating the AC and DC interference level or evaluating the effectiveness of cathodic protection in the presence of AC and DC stray current interference, the test piece area should be 1cm 2 ; The area of ​​the self-corrosion test piece can be selected from 6.5 to 50 cm 2 ; Except for the exposed surface, the rest of the test piece should be well insulated for corrosion protection; The area and number of the selected test pieces should not affect the output current of the cathodic protection system;

[0097] A wireless transmission module, which is used to transmit the collected data to a remote monitoring center wirelessly, preferably using 4G full-network communication and TCP / IP communication protocol;

[0098] A positioning module, which is used to determine the specific location of the monitoring point using GPS or other positioning technologies;

[0099] A microprocessor unit, which is used to process information between various unit modules and is integrated with a signal processing algorithm and a resistivity compensation algorithm to improve the accuracy of the collected data;

[0100] When the AC voltage is higher than 4V, it is considered to be interference, and a solid-state decoupler should be installed for drainage.

[0101] Wherein, the AD data acquisition unit comprises:

[0102] A collection unit, the collection unit is used to transmit the cathode voltage on the gas pipeline to the cathode protection circuit, and the collection unit is electrically connected to the gas pipeline through a cathode protection cable;

[0103] A voltage sensor, wherein the voltage sensor receives the cathode voltage of the analog signal from the acquisition unit at a certain sampling time interval, converts the cathode voltage of the digital signal through the ADC, and sends the digital signal to the first input terminal of the comparator;

[0104] A voltage module, wherein the voltage module is used to send the received reference voltage to the second input terminal of the comparator;

[0105] A comparator, the comparator is used to compare the cathode voltage received at the first input terminal with the reference voltage received at the second input terminal, and if the cathode voltage is higher than the reference voltage, an alarm signal is sent through the output terminal; if the cathode voltage is equal to or lower than the reference voltage, the comparator waits for the next acquisition and comparison in a loop;

[0106] The alarm signal transmitter is used to send out the alarm signal in a wireless form. The alarm signal transmitter is specifically a wireless transmitting device such as an RF antenna.

[0107] In this embodiment, in the cathode protection circuit:

[0108] The AC potential test circuit is used to measure the AC interference voltage in the soil around the pipeline;

[0109] The DC potential test circuit is used to measure the DC potential difference between the pipeline and the reference electrode;

[0110] The relay group circuit is used to control and switch different test modes or disconnect certain circuits when an abnormality is detected to protect the equipment from damage.

[0111] The relay group circuit changes state according to the instructions of the microprocessor unit, thereby adjusting the cathodic protection system or isolating the faulty part.

[0112] In this embodiment, in the cathode protection circuit:

[0113] The microprocessor unit triggers the AC potential test circuit and the DC potential test circuit to perform measurements according to a predetermined schedule or condition;

[0114] After the test circuit completes the measurement, it transmits the data back to the microprocessor unit for processing;

[0115] The microprocessor unit analyses the received data and determines whether the cathodic protection system is functioning properly based on preset criteria;

[0116] If an anomaly is detected, such as low or high cathode voltage, the microprocessor unit sends instructions to the relay bank circuit to adjust the settings of the cathodic protection system or, if necessary, shut down the system to prevent further damage;

[0117] At the same time, if the alarm condition is triggered, the alarm signal transmitter will start and send an alarm signal to the remote monitoring center.

[0118] In this embodiment, the AC potential test circuit includes an operational amplifier U64, wherein the input terminal VIN of the operational amplifier U64 is connected to a capacitor C234, a capacitor C235 and a resistor R328, wherein one end of the capacitor C234 is connected to the cathode of the diode D3, and the anode of the diode D3 is connected to the -5V input voltage, one end of the capacitor C235 is connected to the anode of the diode D4, and the cathode of the diode D4 is connected to the +5V input voltage, and the common node of the capacitors C234 and C235 is used as an input terminal for receiving a current test signal, and the other end of the capacitor C234 shares a node with C235 and is connected to the input terminal VIN of the operational amplifier; a clamping circuit is formed by diodes D3 and D4 to protect the input terminal of the operational amplifier U64, and the common node of C234 and C235 is used to receive a current test signal.

[0119] The OUTPUT end of the operational amplifier U64 is connected to a resistor R329 and a capacitor C238, the other end of the capacitor C238 is grounded, and a common node of the resistor R329 and the capacitor C238 is used as an AC potential output;

[0120] Resistor R329 acts as a load resistor to convert the output signal of operational amplifier U64 into a voltage signal for adjusting the amplitude and impedance matching of the output signal. Capacitor C238 provides a high-frequency bypass at the output end of operational amplifier U64 to improve the quality and stability of the output signal, help eliminate high-frequency noise, and ensure the accuracy of the output signal.

[0121] The -VS terminal of the operational amplifier U64 is connected to a capacitor C239, the other end of the capacitor C239 is grounded, and a capacitor C241 is connected to a common node between the capacitor C239 and the -VS terminal, the other end of the capacitor C241 is connected to the CAV terminal of the operational amplifier U64, and the negative electrode of the capacitor C241 is connected to a -5V input voltage;

[0122] Capacitor C239 is used to provide power decoupling to reduce noise and ripple on the power line and ensure the stable power supply required for the normal operation of the operational amplifier. The other end of capacitor C239 is grounded, which can absorb high-frequency noise from the power supply and prevent such noise from interfering with the internal operation of the operational amplifier.

[0123] The other end of capacitor C241 is connected to the -5V input voltage. Capacitor C241 is used to further stabilize the power supply and also to suppress the noise of the internal circuit of the operational amplifier. The CAV terminal represents the bias voltage of the operational amplifier. The voltage of this port determines the operating point of the operational amplifier.

[0124] The negative terminal of capacitor C241 is connected to the -5V input voltage, which means that the -VS terminal of operational amplifier U64 requires a stable -5V power supply to work properly;

[0125] The +VS terminal of the operational amplifier U64 is connected to a capacitor C236, the other end of the capacitor C236 is connected to the COM terminal of the operational amplifier U64, and the common node of the COM terminal and the capacitor C236 is grounded, and the common node of the capacitor C236 and the +VS terminal is connected to a +5V input voltage;

[0126] Capacitor C236 is used to provide power decoupling to reduce noise and ripples on the power line and ensure the stable power supply required for the normal operation of the operational amplifier. The common node of capacitor C236 and the COM terminal is grounded, which helps to absorb high-frequency noise from the power supply and prevent such noise from interfering with the internal circuit of the operational amplifier. The common node of capacitor C236 and the +VS terminal is connected to the +5V input voltage, which requires a stable +5V power supply for the +VS terminal of the operational amplifier U64.

[0127] The Cc terminal of the operational amplifier U64 is connected to a capacitor C242, and the other end of the capacitor C242 is grounded.

[0128] The DC potential test circuit includes a dual operational amplifier LM324, wherein the -IN terminal of the dual operational amplifier LM324 is connected to a pipeline, and the +IN terminal of the dual operational amplifier LM324 is connected to a current test signal;

[0129] The OUT terminal of the dual operational amplifier LM324 is connected to a resistor R327, and the other end of the resistor R327 serves as an output terminal of a current-to-potential signal;

[0130] The VS terminal of the dual operational amplifier LM324 is connected to a capacitor C231, a common node between one end of the capacitor C231 and the VS terminal is connected to a capacitor C233, and a +5V input voltage is connected to the common node between the capacitor C231 and the VS terminal, and the other end of the capacitor C231 and the other end of the capacitor C233 are grounded together;

[0131] The OFFSET end of the dual operational amplifier LM324 is connected to a resistor R301, the other end of the resistor 301 is connected to a +5V input voltage, and a common node between the OFFSET end and the resistor R301 is connected to a resistor R331, a common node between the resistor R331 and the resistor R301 is connected to a capacitor C243, and the other end of the capacitor C243 is connected to the resistor R331 and is grounded together;

[0132] The GND terminal, A1 terminal and A2 terminal of the dual operational amplifier LM324 are grounded together.

[0133] The DC potential test circuit can accurately evaluate the effectiveness of cathodic protection by directly measuring the DC potential difference between the pipeline and the reference electrode, thereby ensuring that the pipeline is in the best anti-corrosion protection state. The DC potential test circuit is not affected by AC interference, so its measurement results are more reliable.

[0134] In this embodiment, the relay group circuit includes a current test signal output circuit and a potential test signal output circuit;

[0135] Wherein, the current test signal output circuit includes relay K1, relay K1 and relay K3;

[0136] The contact 3 of the relay K1 is connected to a resistor R1, the other end of the resistor R1 is connected to a resistor R2, the other end of the resistor R2 is connected to the contact 5 of the relay K1, and the common node of the resistors R1 and R2 is connected to the pipeline; the purpose of connecting the common node of the resistors R1 and R2 to the natural gas pipeline is to measure the AC interference voltage around the pipeline. The resistors R1 and R2 form a voltage divider, which is used to limit the current flowing into the pipeline to prevent excessive current from damaging the circuit or affecting the normal operation of the pipeline. At the same time, this voltage divider also allows weak AC signals to pass through, so that the measuring equipment can capture the changes in the AC potential. When the contacts of the K1 relay are closed, the voltage divider is connected to the circuit, thereby realizing the measurement function of the AC potential.

[0137] The contact 4 of the relay K1 is connected to the contact 4 of the relay K3, and the contact 5 of the relay K3 is connected to the sacrificial anode, and the contact 3 of the relay K3 is connected to the contact 4 of the relay K2;

[0138] The contact 5 of the relay K2 is connected to the polarization test piece, and the contact 3 of the relay K2 is connected to the AC test piece.

[0139] Polarization test pieces and AC test pieces are important components for monitoring and evaluating the anti-corrosion performance of natural gas pipelines. Polarization test pieces simulate pipeline materials and are used to measure their electrochemical reactions under specific conditions, especially the extent of redox reactions, so as to understand whether the pipeline is in a good anti-corrosion state. AC test pieces are used to detect the presence and intensity of AC interference voltage, because AC interference may affect the effectiveness of anti-corrosion protection;

[0140] Relay K3 and relay K2 act as switches in the circuit. They can selectively connect or disconnect the polarization test strip and AC test strip, as well as the sacrificial anode, as needed. The sacrificial anode is a commonly used anti-corrosion method that protects the pipeline itself by allowing another metal (such as magnesium or zinc) to replace the pipeline as the target of corrosion. When contact 5 of relay K3 is connected to the sacrificial anode, it can monitor the working status of the sacrificial anode to ensure that it effectively consumes itself to protect the pipeline. Relay K2 is responsible for connecting the polarization test strip and the AC test strip for related tests;

[0141] The relay group circuit can change state according to the instructions of the microprocessor unit, so as to realize fast switching between different test modes, or disconnect certain circuits when abnormalities are detected to protect the equipment from damage.

[0142] In this embodiment, the potential test signal output circuit includes relay K4, relay K5, relay K6, relay K7, relay K8 and relay K9;

[0143] Wherein, the contact 4 of the relay K4 is connected to the pipeline, the contact 4 of the relay K5 is connected to the polarized test piece, the contact 4 of the relay K6 is connected to the sacrificial anode, the contact 4 of the relay K7 is connected to the natural test piece, and the contacts 3 of the relay K4, the relay K5 and the relay K6 are connected in parallel;

[0144] The contacts 5 of the relays K4, K5, K6 and K7 are connected in parallel, and the parallel common node of the contacts 5 is connected to the contact 5 of the relay K8, and the contact 3 of the relay K8 serves as the output end of the current-to-potential signal;

[0145] The contact 4 of the relay K8 is connected to a resistor R3, the other end of the resistor R3 is connected to the contact 4 of the relay K9, the common node of the resistor R3 and the contact 4 of the relay K8 is connected to the contact 3 of the relay K9, and the contact 4 of the relay K9 serves as the output end of the potential test signal;

[0146] A common node between the resistor R3 and the contact 4 of the relay K9 is connected to a resistor R4, and the other end of the resistor R4 is grounded.

[0147] Specifically, the specific functions of the microprocessor unit are:

[0148] It is responsible for starting the AD data acquisition unit and controlling the acquisition time interval;

[0149] Used to trigger the voltage sensor for sampling;

[0150] It is used to receive the digital signal converted from the ADC and use the signal processing algorithm to identify and remove the AC interference source. The signal processing algorithm can quickly identify abnormal signals and trigger the alarm mechanism. The microprocessor unit can trigger the alarm mechanism according to the pre-programmed logic, and promptly notify the maintenance personnel to check and repair, avoiding the expansion of problems caused by delays. Since the signal processing algorithm can effectively remove the interference signal, it reduces the false alarm caused by interference and improves the stability and reliability of the system; and the resistivity compensation algorithm is used to calibrate the impact of soil resistivity changes with temperature on the signal;

[0151] Used to perform mathematical operations on the collected data, such as average value calculation, maximum and minimum value detection, etc., to obtain more accurate measurement results;

[0152] Used to determine whether the cathodic protection status is normal and identify potential problems by comparing the actual voltage with the preset threshold;

[0153] When the cathode voltage is detected to be above or below a predetermined safety range, the microprocessor unit triggers an alarm mechanism according to pre-programmed logic;

[0154] Control the alarm signal transmitter to send alarm signals and record the occurrence time and related data of the alarm event;

[0155] Receive commands from the remote monitoring center and perform corresponding operations according to the instructions, such as changing the sampling frequency and adjusting the alarm threshold.

[0156] Furthermore, the microprocessor unit receives the digital signal converted from the ADC, and uses a signal processing algorithm to identify and remove AC and DC stray current interference, and calibrates the effect of soil resistivity changes with temperature on the (current or voltage) signal through a resistivity compensation algorithm. In a cathodic protection system, the potential (voltage) of the structure relative to the reference electrode is usually measured to evaluate the effect of cathodic protection, because the potential can intuitively reflect whether the metal surface is in an appropriate protection state; if a current signal is used, an additional step may be required to convert it into potential information in order to evaluate the protection state;

[0157] The specific steps involved in the signal processing algorithm to remove AC stray current interference are:

[0158] The voltage signal in the cathodic protection circuit is collected for T seconds, and the sampling frequency is f s Hz, the total number of sampling points is N;

[0159] Perform discrete Fourier transform on the collected voltage signal x[n] to obtain the frequency domain signal X[k];

[0160]

[0161] Calculate the amplitude of the spectrum |X[k]|, and set a threshold to identify the frequency points whose amplitudes are significantly higher than the background noise. These frequency points are interference frequencies, and then identify the interference frequencies in the voltage signal.

[0162]

[0163] Where X[k] represents the kth component of the frequency domain signal, which is the spectral component of the discrete time signal x[n] at frequency k; k represents the frequency index; x[n] represents the nth sampling point of the time domain signal; n represents the time index; e -j2πkn / N represents a complex exponential function, represents a complex rotation factor at frequency k; j represents an imaginary unit, and j 2 =-1; |X[k]| represents the amplitude of the frequency domain signal X[k]; Re(X[k]) represents the real part of the frequency domain signal X[k]; Im(X[k]) represents the imaginary part of the frequency domain signal X[k];

[0164] A second-order band-stop filter is designed and applied to the original signal to remove the identified interference frequency, wherein the transfer function of the second-order band-stop filter is specifically:

[0165]

[0166] In the formula, ω 0 =2πf 0 represents the center angular frequency, f 0 is the center frequency; Q is the quality factor, which determines the bandwidth and selectivity of the filter; ζ is the damping ratio; s is the Laplace transform variable, which is used to describe the frequency characteristics of the filter;

[0167] The transfer function of a second-order band-stop filter describes how the filter alters the input signal to produce the output signal.

[0168] Band-stop filters are mainly used to remove specific frequency components in signals, such as the grid frequency (usually 50Hz or 60Hz) and its harmonics. In cathodic protection systems, if such AC interference exists, a second-order band-stop filter is used to help remove these unwanted frequency components, thereby improving the accuracy of data acquisition.

[0169] The signal processing algorithm converts the time domain signal into the frequency domain signal through discrete Fourier transform, which can intuitively see which frequency components dominate the signal. Due to the AC interference in the cathodic protection circuit, these interference components will appear as peaks in the frequency domain signal. By calculating the amplitude of the spectrum, these interference frequency components can be identified and appropriate filters can be designed to remove them. After using a second-order band-stop filter to remove the interference frequency components, the purity of the signal can be significantly improved, that is, the DC signal related to the cathodic protection is retained, while the unnecessary AC interference components are removed. This makes the subsequent signal processing and data analysis more accurate;

[0170] By removing AC interference, the actual effect of cathodic protection can be observed more clearly. For example, when the cathode voltage is too low or too high, it can be identified more accurately and the cathodic protection system settings can be adjusted in time to ensure the anti-corrosion effect of the pipeline.

[0171] The soil resistivity is measured using the equidistant method test;

[0172] Furthermore, the resistivity compensation algorithm is used to calibrate the effect of soil resistivity changing with temperature on the current signal. The specific expression involved is:

[0173] ρ(T)=ρ 0 ·[1+α·(TT 0 )];

[0174] Where ρ(T) represents the soil resistivity at temperature T; ρ 0 Indicates the reference temperature T 0 The soil resistivity under the condition of α is the temperature coefficient of soil resistivity; T 0 represents the reference temperature; T represents the currently measured soil temperature;

[0175] At the same time, considering the influence of humidity H and salinity S on soil resistivity, the calibrated soil resistivity ρ is obtained eff :

[0176] ρ eff =ρ 0 ·[1+α·(TT 0 )+β·(HH 0 )+γ·(SS 0 )];

[0177] In the formula, β represents the humidity coefficient; γ represents the salinity coefficient; H 0 Indicates reference humidity; H indicates the currently measured soil humidity; S 0 represents the reference salinity; S represents the currently measured soil salinity;

[0178] And use the outlier detection method to calculate the invalid interference term Δρeff , the final soil resistivity ρ(T, H, S) is obtained by removing the invalid interference terms:

[0179] ρ(T,H,S)=ρ eff -Δρ eff ;

[0180] ρ(T,H,S)=ρ 0 ·[1+α·(TT 0 )+β·(HH 0 )+γ·(SS 0 )]-Δρ eff .

[0181] Specifically, the invalid interference term Δρ eff Indicates measurement deviation due to equipment defects, measurement errors, external noise, etc.;

[0182] When calibrating soil resistivity, the reason for removing invalid interference items instead of adding them is that invalid interference items represent deviations caused by equipment defects, external noise, measurement errors, etc. These deviations are not a true reflection of the characteristics of the soil itself. Therefore, in order to obtain more accurate soil resistivity measurements, these deviations need to be removed. Removing invalid interference items can help formulate more reasonable equipment maintenance plans and avoid the impact of measurement errors caused by equipment failures on decision-making;

[0183] Among them, get the invalid interference term Δρ eff The specific method is:

[0184] First, soil resistivity data is collected over a period of time;

[0185] Calculate the mean μ and standard deviation σ of the resistivity data during this period;

[0186] Set a threshold. Usually, data points outside μ±kσ are considered outliers, and k is usually 3 (i.e., the 3σ principle).

[0187] Any data point beyond μ ± 3σ is considered an outlier;

[0188] The average deviation of outliers is taken as the invalid interference term Δρ eff ;

[0189] The microprocessor unit reads the current temperature T, humidity H and salinity S and the measured soil resistivity ρ eff , and then use the resistivity compensation algorithm to calculate the corrected soil resistivity ρ(T, H, S). The values ​​of α, β, and γ depend on the specific composition of the soil and other environmental factors. Therefore, in practical applications, α, β, and γ all need to be determined by experimental data;

[0190] By calculating the corrected soil resistivity ρ(T, H, S), any changes or failures in the cathodic protection system, such as insufficient or over-protection protection current, can be discovered in a timely manner, so that necessary measures can be taken to make adjustments; accurate soil resistivity data helps maintain an effective cathodic protection level, avoid corrosion due to insufficient protection or material loss due to excessive protection, and thus extend the service life of the natural gas pipeline.

[0191] The application of resistivity compensation algorithm simplifies maintenance work. Maintenance personnel can quickly determine the system status based on the corrected data and make corresponding adjustments. There is no need for frequent on-site testing and adjustments, which reduces the difficulty of maintenance.

[0192] In this embodiment, the specific steps involved in removing DC stray current interference by using a signal processing algorithm are:

[0193] Define a fixed-size sliding window w, the window size is W, and usually a window size large enough to contain enough data points to estimate the DC offset;

[0194] Collect a section of signal data containing DC offset, let this section of data be x 直 [n],x 直 Represents a signal containing a DC offset, n is the index of the sampling point, representing each sampling point in the time series. In the signal processing of the cathodic protection system, the DC offset part of the signal needs to be removed to avoid these offsets affecting subsequent data analysis and processing. Therefore, it is necessary to first collect a section of signal data containing a DC offset, and then process the data to remove the DC component;

[0195] And the sampling length is T 直 seconds, the sampling frequency is f s直 Hz, the total number of sampling points is N 直 ;

[0196] Calculate the average value of all sampling points as the DC component V dc :

[0197]

[0198] In the formula, i represents the starting point of the sliding window;

[0199] Subtract the mean value V from each sample point dc , and obtain the signal y[n] after removing the DC component;

[0200] y[n]=x 直 [n]-V i dc ;

[0201] Whenever a new data point x直 When [n] arrives, update the position of the sliding window, that is, move forward one sampling point, and recalculate the new DC component V i+1 dc ;

[0202]

[0203] At the same time, the signal y[n] after removing the DC component is updated. When processing a signal containing a DC offset, the DC component refers to the constant part of the signal, which does not change over time. In many application scenarios, this constant part is unnecessary and may even interfere with the results of subsequent processing or analysis. In the cathodic protection system, DC stray currents may interfere with the effectiveness evaluation of the cathodic protection. By removing these interferences, the status of the cathodic protection can be more accurately monitored and evaluated. Specifically, by subtracting the average value from each sampling point, a new signal without a DC component can be obtained. This new signal is more suitable for subsequent analysis and processing, such as evaluating the effectiveness of the cathodic protection circuit.

[0204] Over time, the above process is repeated to keep the sliding window always covering the latest data points and update the DC component in real time, thereby reducing the cumulative error. Removing the DC component can improve the quality of the signal and make subsequent processing easier. For example, when performing spectrum analysis, the DC component may mask other important frequency components.

[0205] In the case of a slowly changing DC offset, the removal of a fixed DC component will lead to error accumulation. Therefore, the sliding window method is introduced to continuously update the DC component to reduce the accumulated error, thereby improving the accuracy of the final signal processing;

[0206] In the cathodic protection system, soil resistivity will change with the changes of temperature, humidity and other factors, resulting in DC offset. The sliding window method can help adjust these changes in real time, ensure the accuracy of the measurement, and reduce invalid interference caused by equipment defects, measurement errors and other factors.

[0207] Therefore, the estimated value of the DC component V is calibrated again to take into account the change in soil resistivity. i′ dc The specific steps involved are:

[0208] Use the soil resistivity calibration formula to calculate the final soil resistivity ρ(T, H, S), and update the soil resistivity corresponding to the data in the sliding window;

[0209] The estimated value of the DC component V is recalibrated by incorporating the change in soil resistivity i′ dc ;

[0210]

[0211] The estimated value of the DC component is subtracted from the invalid interference term in proportion, so that the DC component is closer to the true value, better adapts to the change of soil resistivity during signal processing, and removes the invalid interference term, thereby improving the reliability and accuracy of the cathodic protection system.

[0212] The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed as above in the form of preferred embodiments, it is not intended to limit the present invention. Any technical personnel in the field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A collector for cathodic protection of natural gas pipelines, characterized in that: The invention comprises a pile body (1), a solar panel (2) is fixedly mounted on the top of the pile body (1), an equipment cavity is opened in the pile body (1), a collector (3) is mounted in the equipment cavity, the collector (3) is electrically connected to an insulating wiring board (4), an input end of the insulating wiring board (4) is connected to a polarization probe (5) through an integrated wire group (41), the input end of the insulating wiring board (4) is also connected to a pipeline cable, and the other end of the pipeline cable is connected to a pipeline (6); The integrated wire group (41) includes a sacrificial anode wire, a long-acting reference wire, an AC test wire, a polarization test wire and a self-corrosion test wire.

2. The collector for cathodic protection of natural gas pipeline according to claim 1, characterized in that: The collector (3) comprises: An AD data acquisition unit, wherein the AD data acquisition unit is used to collect voltage information in a cathode protection circuit, wherein the cathode protection circuit is composed of an AC potential test circuit, a DC potential test circuit and a relay group circuit; A wireless transmission module, which is used to transmit the collected data to a remote monitoring center wirelessly; A positioning module, which is used to determine the specific location of the monitoring point; The microprocessor unit is used to process information between various unit modules and is integrated with a signal processing algorithm and a resistivity compensation algorithm to improve the accuracy of the collected data.

3. The collector for cathodic protection of natural gas pipeline according to claim 1, characterized in that: The AD data acquisition unit comprises: A collection unit, the collection unit is used to transmit the cathode voltage on the gas pipeline to the cathode protection circuit; A voltage sensor, wherein the voltage sensor receives the cathode voltage of the analog signal from the acquisition unit at a certain sampling time interval, converts the cathode voltage of the digital signal through the ADC, and sends the digital signal to the first input terminal of the comparator; A voltage module, wherein the voltage module is used to send the received reference voltage to the second input terminal of the comparator; A comparator, the comparator is used to compare the cathode voltage received at the first input terminal with the reference voltage received at the second input terminal, and if the cathode voltage is higher than the reference voltage, an alarm signal is sent through the output terminal; if the cathode voltage is equal to or lower than the reference voltage, the comparator waits for the next acquisition and comparison in a loop; An alarm signal transmitter is used to send out an alarm signal wirelessly.

4. The collector for cathodic protection of natural gas pipeline according to claim 1, characterized in that: In the cathodic protection circuit: The AC potential test circuit is used to measure the AC interference voltage in the soil around the pipeline; The DC potential test circuit is used to measure the DC potential difference between the pipeline and the reference electrode; The relay group circuit is used to control and switch different test modes.

5. The collector for cathodic protection of natural gas pipeline according to claim 3, characterized in that: The AC potential test circuit includes an operational amplifier U64, wherein an input terminal VIN of the operational amplifier U64 is connected with a capacitor C234, a capacitor C235 and a resistor R328, wherein one end of the capacitor C234 is connected to the cathode of the diode D3, and the anode of the diode D3 is connected to a -5V input voltage, one end of the capacitor C235 is connected to the anode of the diode D4, and the cathode of the diode D4 is connected to a +5V input voltage, and a common node of the capacitors C234 and C235 is used as an input terminal for receiving a current test signal, and the other end of the capacitor C234 shares a node with C235 and is connected to the input terminal VIN of the operational amplifier; The OUTPUT end of the operational amplifier U64 is connected to a resistor R329 and a capacitor C238, the other end of the capacitor C238 is grounded, and a common node of the resistor R329 and the capacitor C238 is used as an AC potential output; The -VS terminal of the operational amplifier U64 is connected to a capacitor C239, the other end of the capacitor C239 is grounded, and a capacitor C241 is connected to a common node between the capacitor C239 and the -VS terminal, the other end of the capacitor C241 is connected to the CAV terminal of the operational amplifier U64, and the negative electrode of the capacitor C241 is connected to a -5V input voltage; The +VS terminal of the operational amplifier U64 is connected to a capacitor C236, the other end of the capacitor C236 is connected to the COM terminal of the operational amplifier U64, and the common node of the COM terminal and the capacitor C236 is grounded, and the common node of the capacitor C236 and the +VS terminal is connected to a +5V input voltage; The Cc terminal of the operational amplifier U64 is connected to a capacitor C242, and the other end of the capacitor C242 is grounded.

6. The collector for cathodic protection of natural gas pipeline according to claim 4, characterized in that: The DC potential test circuit comprises a dual operational amplifier LM324, wherein the -IN terminal of the dual operational amplifier LM324 is connected to a pipeline, and the +IN terminal of the dual operational amplifier LM324 is connected to a current test signal; The OUT terminal of the dual operational amplifier LM324 is connected to a resistor R327, and the other end of the resistor R327 serves as an output terminal of a current-to-potential signal; The VS terminal of the dual operational amplifier LM324 is connected to a capacitor C231, a common node between one end of the capacitor C231 and the VS terminal is connected to a capacitor C233, and a +5V input voltage is connected to the common node between the capacitor C231 and the VS terminal, and the other end of the capacitor C231 and the other end of the capacitor C233 are grounded together; The OFFSET end of the dual operational amplifier LM324 is connected to a resistor R301, the other end of the resistor 301 is connected to a +5V input voltage, and a common node between the OFFSET end and the resistor R301 is connected to a resistor R331, a common node between the resistor R331 and the resistor R301 is connected to a capacitor C243, and the other end of the capacitor C243 is connected to the resistor R331 and is grounded together; The GND terminal, A1 terminal and A2 terminal of the dual operational amplifier LM324 are grounded together.

7. The collector for cathodic protection of natural gas pipeline according to claim 4, characterized in that: The relay group circuit includes a current test signal output circuit and a potential test signal output circuit; Wherein, the current test signal output circuit includes relay K1, relay K1 and relay K3; The contact 3 of the relay K1 is connected to a resistor R1, the other end of the resistor R1 is connected to a resistor R2, the other end of the resistor R2 is connected to the contact 5 of the relay K1, and the common node of the resistor R1 and the resistor R2 is connected to the pipeline; The contact 4 of the relay K1 is connected to the contact 4 of the relay K3, and the contact 5 of the relay K3 is connected to the sacrificial anode, and the contact 3 of the relay K3 is connected to the contact 4 of the relay K2; The contact 5 of the relay K2 is connected to the polarization test piece, and the contact 3 of the relay K2 is connected to the AC test piece.

8. The collector for cathodic protection of natural gas pipeline according to claim 7, characterized in that: The potential test signal output circuit includes relay K4, relay K5, relay K6, relay K7, relay K8 and relay K9; Wherein, the contact 4 of the relay K4 is connected to the pipeline, the contact 4 of the relay K5 is connected to the polarized test piece, the contact 4 of the relay K6 is connected to the sacrificial anode, the contact 4 of the relay K7 is connected to the natural test piece, and the contacts 3 of the relay K4, the relay K5 and the relay K6 are connected in parallel; The contacts 5 of the relays K4, K5, K6 and K7 are connected in parallel, and the parallel common node of the contacts 5 is connected to the contact 5 of the relay K8, and the contact 3 of the relay K8 serves as the output end of the current-to-potential signal; The contact 4 of the relay K8 is connected to a resistor R3, the other end of the resistor R3 is connected to the contact 4 of the relay K9, the common node of the resistor R3 and the contact 4 of the relay K8 is connected to the contact 3 of the relay K9, and the contact 4 of the relay K9 serves as the output end of the potential test signal; A common node between the resistor R3 and the contact 4 of the relay K9 is connected to a resistor R4, and the other end of the resistor R4 is grounded.

9. The collector for cathodic protection of natural gas pipeline according to claim 2, characterized in that: The microprocessor unit receives the digital signal converted from the ADC, and uses a signal processing algorithm to identify and remove AC and DC stray current interference, and calibrates the effect of soil resistivity changes with temperature on the signal through a resistivity compensation algorithm; The specific steps involved in the signal processing algorithm to remove AC stray current interference are: The voltage signal in the cathodic protection circuit is collected for T seconds, and the sampling frequency is f s Hz, the total number of sampling points is N; Perform discrete Fourier transform on the collected voltage signal x[n] to obtain the frequency domain signal X[k]; Calculate the amplitude of the spectrum |X[k]| to identify the interference frequency in the voltage signal; In the formula, X[k] represents the kth component of the frequency domain signal; k represents the frequency index; x[n] represents the nth sampling point of the time domain signal; n represents the time index; e- j2πkn / N represents a complex exponential function; j represents an imaginary unit, and j 2 =-1; |X[k]| represents the amplitude of the frequency domain signal X[k]; Re(X[k]) represents the real part of the frequency domain signal X[k]; Im(X[k]) represents the imaginary part of the frequency domain signal X[k]; A second-order band-stop filter is designed and applied to the original signal to remove the identified interference frequency, wherein the transfer function of the second-order band-stop filter is specifically: Wherein, ω0=2πf0 represents the center angular frequency, f0 represents the center frequency; Q represents the quality factor; ζ represents the damping ratio; s represents the Laplace transform variable.

10. The collector for cathodic protection of natural gas pipeline according to claim 2, characterized in that: The resistivity compensation algorithm is used to calibrate the effect of soil resistivity changing with temperature on the signal. The specific expression involved is: ρ(T)=ρ0·[1+α·(T-T0)]; Wherein, ρ(T) represents the soil resistivity at temperature T; ρ0 represents the soil resistivity at reference temperature T0; α represents the temperature coefficient of soil resistivity; T0 represents the reference temperature; T represents the currently measured soil temperature; At the same time, considering the influence of humidity H and salinity S on soil resistivity, the calibrated soil resistivity ρe is obtained ff : r eff =ρ0·[1+α·(T-T0)+β·(H-H0)+γ·(S- S0 )]; In the formula, β represents the humidity coefficient; γ represents the salinity coefficient; H0 represents the reference humidity; H represents the currently measured soil humidity; S0 represents the reference salinity; S represents the currently measured soil salinity; And use the outlier detection method to calculate the invalid interference term Δρ eff , the final soil resistivity ρ(T, H, S) is obtained by removing the invalid interference terms: ρ(T, H, S)=ρe ff -Dr. ff ; ρ(T, H, S)=ρ0·[1+α·(T-T0)+β·(H-H0)+γ·(S-S0)]-Δρ eff 。

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