A pre-branching cable localizing optical fiber acoustic emission sensor and monitoring system

Abstract

The present application belongs to the technical field of power cable monitoring, and particularly relates to a pre-branch cable partial discharge optical fiber acoustic emission sensor and a monitoring system. The sensor comprises a shell, a wire clamp and a fused taper sensing unit. The sensing unit adopts a single optical fiber backfold reflection structure and does not contain electronic devices inside, and converts partial discharge sound waves into optical signals through the acousto-optic modulation effect. The back of the wire clamp is bonded with the shell through an ultrathin epoxy resin, realizing efficient conduction of sound waves. The monitoring system comprises a laser, an optical fiber circulator, an optical-electric converter and an upper computer. The optical-electric converter integrates a transimpedance amplification module, a second-order filter module and a radio frequency matching module to demodulate optical signals. The upper computer intelligently identifies and saves abnormal discharge data through continuous sampling combined with a dynamic threshold triggering algorithm, and draws a trend chart. The present application solves the problems of traditional sensors, such as being easily affected by electromagnetic interference and poor long-term stability, and realizes high-sensitivity and anti-interference in-situ monitoring of the branch points of pre-branch cables.

Description

Technical Field

[0001] This invention belongs to the field of power cable monitoring technology, specifically relating to a fiber optic acoustic emission sensor and monitoring system for partial discharge of pre-branched cables. Background Technology

[0002] Partial discharge monitoring technology for pre-branched cables has been widely used in power systems both domestically and internationally. Its technical methods are becoming increasingly mature, allowing for the acquisition of insulation status information from critical components such as the cable body, connectors, and pre-branched sections using partial discharge sensors. Partial discharge detection methods mainly fall into four categories: ultra-high frequency (UHF), transient ground voltage (TEV), acoustic emission (AE), and high-frequency current (HFCT). Among these, high-frequency current sensors are primarily divided into Rogowski coil type and clamp-on magnetic core type, with installation methods including snap-fit, wound, and fixed types.

[0003] The aforementioned partial discharge sensors generally suffer from the following problems in practical applications: 1. Limited anti-interference capability: UHF, TEV and HFCT are based on the principle of electrical signal detection, which is extremely susceptible to the complex electromagnetic noise interference of substations; although traditional AE sensors detect sound waves, they contain electronic components and are easily affected by the environmental electromagnetic field, resulting in false alarms.

[0004] 2. Insufficient long-term stability: The electronic components inside the sensor (such as piezoelectric ceramics and operational amplifier chips) are prone to aging during long-term operation, which can cause zero-point drift or gain changes, resulting in distorted monitoring data.

[0005] 3. Accumulation of minute errors: In long-term continuous monitoring, the minute errors caused by temperature drift and time drift of existing sensors will accumulate over time, resulting in trend distortion and reducing the reliability of early warning.

[0006] 4. Sensitive to on-site installation conditions: Different sensors have different requirements for coupling medium and grounding, resulting in poor installation consistency and making it difficult to establish a unified discharge quantity criterion.

[0007] 5. Loose coupling: The sensor is not tightly coupled with the cable structure at the partial discharge location, resulting in high acoustic wave transmission loss and reduced monitoring sensitivity and accuracy.

[0008] 6. Lack of effective monitoring methods: The branching point of high-voltage level intelligent green pre-branched optical-electric composite cable is a core component. Especially in scenarios of 35kV and below, the local electric field is concentrated at the branching point, which is prone to partial discharge and thermal damage. In addition, the embedded optical fiber is prone to stress concentration under mechanical load, and there is currently a lack of effective means for in-situ monitoring of electric field changes in this critical part. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a pre-branched cable partial discharge fiber optic acoustic emission sensor and monitoring system.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A pre-branched cable partial discharge fiber optic acoustic emission sensor includes a housing, a wire clamp, an outer cover, and a fused tapered sensing unit fixedly disposed in the inner cavity of the housing. The wire clamp is located on the back of the housing and is used to clamp and fix the main cable and branch cable, and to conduct the sound waves generated by partial discharge to the housing; The side wall along the length direction of the housing is provided with a groove A for a multi-core optical cable to pass through and enter the inner cavity of the housing; The fused tapered sensing unit includes an optical fiber and an optical fiber heat shrink tubing. The optical fiber is bent inside the optical fiber heat shrink tubing to form a foldback point, which constitutes a light-reflecting end face. The optical fiber forms two parallel optical fiber segments inside the optical fiber heat shrink tubing. The two parallel optical fiber segments are fused tapered to form a double-cone fused coupling region, which is located at the axial center of the optical fiber heat shrink tubing. The fused tapered sensing unit is a single-fiber foldback reflective structure. The optical signal is injected through the optical fiber, transmitted to the optical reflection end face, reflected, and returns along the original path. The optical fiber in the multi-core optical cable is connected to the fused tapered sensing unit; The outer cover is provided at the opening of the housing for encapsulating a portion of the multi-core optical cable and the fused tapered sensing unit located inside the housing within the inner cavity of the housing.

[0011] Furthermore, the splitting ratio of the biconical molten coupling region is in the range of 45%-55%, and the additional loss is less than 0.5dB; The preparation parameters corresponding to the double-cone molten coupling region include: the molten tapering process undergoes 70-80 spectrophotometric oscillation cycles.

[0012] Furthermore, the conical region of the double-cone molten coupling region constitutes a strain concentration structure, which is used to change the phase and intensity of the transmitted light through the acousto-optic modulation effect when the sound field acts on the coupling region through the shell; the narrow waist region of the double-cone molten coupling region has a strain amplification effect on the incident sound wave.

[0013] Furthermore, the wire clamp is a C-type wire clamp and also includes a wire clamp fixing arm integrally connected to the wire clamp; the two ends of the wire clamp fixing arm are provided with first screw holes, and the bottom plate of the housing is provided with corresponding second screw holes; the housing and the wire clamp are connected and fixed by fastening screws passing through the first screw holes and the second screw holes, so that the back of the housing is in close contact with the back of the wire clamp.

[0014] Furthermore, the back of the housing and the back of the wire clamp are bonded together by a two-component epoxy resin adhesive, wherein the thickness of the two-component epoxy resin adhesive layer is 0.02 mm to 0.1 mm. Before bonding, the back of the housing and the corresponding contact area of ​​the wire clamp are degreased and roughened respectively.

[0015] Furthermore, the interior of the housing is sequentially fixed with a recess, multiple fiber optic partitions, and a main partition along the extension direction of the multi-core optical cable; the main partition is provided with a groove B, and the recess is provided with a groove C. The groove C, the groove B, the groove A, and the top surface of the fiber optic partition work together to support the multi-core optical cable. The outer cover has a V-shaped groove at the position corresponding to the groove A. The V-shaped groove is arranged opposite to the groove A and is used to clamp and fix the multi-core optical cable.

[0016] Furthermore, inside the housing, along a direction perpendicular to the length, a secondary partition is provided at intervals from the main partition; a spacer area for placing the molten tapered sensing unit is formed between the main partition and the secondary partition, and the spacer area is filled with silicone grease; The molten tapered sensing unit is fixed in the interval area and tightly adhered to the bottom surface of the housing by high-temperature resistant epoxy resin adhesive; an inner cover plate is detachably provided above the interval area, and the inner cover plate is sealed to the end of the molten tapered sensing unit by high-temperature resistant epoxy resin adhesive.

[0017] Furthermore, multiple fiber-coil separators are arranged sequentially at intervals along the extension direction of the multi-core optical cable. The top surface of the fiber-coil separator is used as a fulcrum for coiling single-core optical fibers branched from the multi-core optical cable, so as to reserve excess fiber length.

[0018] A pre-branched cable partial discharge monitoring system includes a power supply, a laser, a coupler, a photoelectric converter, a synchronous data acquisition card, a host computer, an optical fiber circulator, and the pre-branched cable partial discharge optical fiber acoustic emission sensor as described above. The power supply is used to power the laser; The laser's output port is connected to the input end of the coupler, and the coupler's output end is connected to the first port of the fiber optic circulator; The second port of the fiber optic circulator is connected to the fused tapered sensing unit in the pre-branched cable partial discharge fiber optic acoustic emission sensor via a single-core fiber optic cable. The third port of the fiber optic circulator is connected to the input end of the photoelectric converter via a transmission fiber, and is used to receive optical signals carrying acoustic wave information. The output terminal of the photoelectric converter is connected to the synchronous data acquisition card, and the synchronous data acquisition card is connected to the host computer. The synchronous data acquisition card is configured to perform multi-channel parallel synchronous acquisition using a sampling frequency of not less than 1 MHz, and transmit the acquired real-time data stream to the host computer. The host computer is configured to: receive the real-time data stream and perform real-time processing using a continuous sampling combined with program-triggered saving mode; specifically, it includes: using a 1-second time window, calculating the absolute maximum amplitude and arithmetic mean of the data within the window in real time; when the absolute maximum amplitude is greater than 5 times the arithmetic mean, it is determined to be abnormal and the saving mechanism is automatically triggered to store the data as a file; at the same time, it performs time-domain parameter extraction, spectrum analysis, and time-frequency graph generation on the data to identify abnormal signals.

[0019] Furthermore, the photoelectric converter includes a photoelectric conversion module, an active filter module, and a radio frequency impedance matching module that are connected in sequence. The photoelectric conversion module includes a photodiode M2 ​​and a transimpedance amplifier; the anode of the photodiode M2 ​​is grounded, and the cathode is connected to the inverting input terminal of the transimpedance amplifier; the non-inverting input terminal of the transimpedance amplifier is connected to a first voltage divider network, which is connected between the +5V power supply and ground to provide a DC bias level; a feedback resistor branch is connected in series between the inverting input terminal and the output terminal of the transimpedance amplifier, and a compensation capacitor is connected in parallel across the two ends of the feedback resistor branch; the positive power supply terminal of the transimpedance amplifier is connected to a first power supply filter circuit. The active filter module has an input RC network connected to its input terminal, which includes an input resistor R2 connected in series and an input capacitor C1 with one end grounded. The active filter module includes an audio operational amplifier and a second-order low-pass filter circuit built around the audio operational amplifier. The second-order low-pass filter circuit includes a first voltage divider resistor R7 connected between the output node of the input RC network and the inverting input terminal of the audio operational amplifier, and a feedback resistor R4 connected between the output node of the input RC network and the output terminal of the audio operational amplifier. A feedback capacitor C2 is also connected between the inverting input terminal and the output terminal of the audio operational amplifier. A second voltage divider network is connected to the non-inverting input terminal of the audio operational amplifier, and this second voltage divider network is connected between the +5V power supply and ground. A second power supply filter circuit is connected to the positive power supply terminal of the audio operational amplifier. The RF impedance matching module includes a matching resistor R3 connected in series on the signal transmission line and an RF connector RF1; the matching resistor R3 has a resistance of 50Ω, its input is connected to the output of the audio operational amplifier, and its output is connected to the signal pin of the RF connector RF1, which is used to achieve 50Ω impedance matching to reduce high-frequency signal reflection loss; the ground terminal of the RF connector RF1 is grounded.

[0020] Compared with the prior art, the present invention has the following significant advantages: 1. This invention completely solves the problem of electromagnetic noise interference through an all-fiber passive design. The sensing unit, fabricated using fiber optic fused biconical tape (FBT) technology, contains no electronic components and requires no power supply. The sensor is only sensitive to the acoustic emission (AE) field generated by partial discharge, and is completely insensitive to the electric field in a high-voltage environment. This inherent anti-interference characteristic effectively solves the problem of traditional UHF, TEV, and HFCT sensors being susceptible to electromagnetic noise, enabling accurate monitoring in strong electromagnetic environments.

[0021] 2. This invention eliminates the effects of electronic component aging through a passive optical fiber structure. The core sensing element of this invention is made of optical fiber made of silicon dioxide, eliminating the zero-point drift or gain changes inherent in electronic components. During long-term monitoring, the optical fiber characteristics remain extremely stable, preventing the accumulation of minute errors due to aging, thus ensuring the long-term accuracy of the monitoring data and resolving the problems of trend distortion and decreased early warning reliability.

[0022] 3. This invention achieves uniformity in installation through a standardized mechanical coupling design. The invention features a C-shaped copper wire clamp structure with a long arm, coupled with standardized screw hole connections, establishing a fixed installation force and coupling path. This design eliminates measurement deviations caused by human installation factors (such as differences in winding tightness and contact pressure), ensuring consistency in measurements from different sensors at different installation points, and facilitating the establishment of unified partial discharge criteria.

[0023] 4. This invention significantly improves monitoring accuracy through a multi-level tightly coupled structure. Structurally, this invention achieves three layers of tight coupling: the first layer is the tight fit between the C-type copper wire clamp and the cable; the second layer is the seamless bonding between the back of the wire clamp and the back of the housing through a 0.02-0.1mm epoxy resin layer; the third layer is the acoustic impedance matching between the sensing unit inside the housing and the silicone grease. This design transmits partial discharge acoustic waves losslessly to the sensing optical fiber, greatly reducing transmission loss and significantly improving monitoring sensitivity and accuracy.

[0024] 5. This invention provides a highly sensitive in-situ monitoring solution for branch points. The molten tapered sensing unit of this invention possesses extremely high strain sensitivity (achieved by controlling a tapering process with 70-80 oscillation cycles). This sensor can be directly installed at the branch node of a pre-branched cable, capturing the weak acoustic emission signal at the branch point to invert internal electric field changes and insulation status, filling the gap in partial discharge monitoring at branch points in voltage scenarios of 35kV and below.

[0025] 6. This invention protects optical fiber performance through a layered encapsulation and buffering structure. The invention features a unique layered structure within the housing: the lower layer uses silicone grease and an inner cover plate to flexibly seal and buffer the sensitive fusion tapered area; the upper layer has a groove A and a fiber optic disc, which not only secures the multi-core optical cable but also provides excess length for single-core fiber splicing. This structure effectively absorbs stress caused by mechanical loads and thermal expansion differences, preventing single-core fiber breakage or performance degradation, and extending the system's lifespan. Attached Figure Description

[0026] Figure 1 This is a perspective view of the partial discharge sensor in an embodiment of the present invention.

[0027] Figure 2 This is a perspective view of the outer cover in an embodiment of the present invention.

[0028] Figure 3 This is a perspective view of the partial discharge sensor in an embodiment of the present invention (with the outer cover removed).

[0029] Figure 4 This is a schematic diagram of the state of the molten tapered sensing unit in this embodiment of the invention before the molten tapered process is implemented.

[0030] Figure 5 This is a schematic diagram of the state of the molten tapered sensing unit in this embodiment of the invention before the molten tapered process is implemented.

[0031] Figure 6 This is a schematic diagram of the monitoring system in an embodiment of the present invention.

[0032] Figure 7 This is a schematic diagram illustrating the use of the partial discharge sensor in an embodiment of the present invention.

[0033] Figure 8 This is a circuit diagram of the photoelectric conversion module in an embodiment of the present invention.

[0034] Figure 9 This is a circuit diagram of the active filter module in an embodiment of the present invention.

[0035] Figure 10 This is a circuit diagram of the radio frequency impedance matching module in an embodiment of the present invention.

[0036] Figure 11 This is a circuit diagram of the photoelectric converter in an embodiment of the present invention.

[0037] In the diagram: 2-Outer cover, 3-Housing shell, 4-Cable clamp fixing arm, 5-Cable clamp, 6-First screw hole, 7-V-groove, 8-Third screw hole, 9-Fourth screw hole, 10-Fiber coil partition, 11-Groove A, 12-Concave block, 13-Optical cable branch point, 14-Second screw hole, 15-Fused tapered sensing unit, 16-Groove B, 17-Inner cover plate, 18-Mounting hole, 19-Main partition, 20-Secondary partition; 21-Power supply, 22-Laser, 23-Coupler, 24-Fiber circulator, 241-First port, 242-Second port, 243-Third port. 25-Partial discharge fiber optic acoustic emission sensor; 26-Photoelectric converter; 27-Data acquisition card; 28-Host computer; 29-Transmission fiber optic cable; 30-First fiber segment; 31-Second fiber segment; 32-Foldback point; 33-Third fiber segment; 34-Fiber optic heat shrink tubing; 36-Slit; 37-Multi-core optical cable; 371-Single-core optical cable CI; 372-Single-core optical cable CI; 373-Single-core optical cable CI; 374-Single-core optical cable CI; 38-Main cable; 391-Branch cable I; 392-Branch cable II; 393-Branch cable III; 394-Branch cable IV. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] Example 1: Pre-branched cable partial discharge fiber optic acoustic emission sensor like Figure 1 , Figure 2 and Figure 3 As shown, this embodiment provides a pre-branched cable partial discharge fiber optic acoustic emission sensor, which is mainly used to be fixed at the branch connection of the pre-branched cable (such as the branch box or pre-branch joint position) to detect the acoustic wave signal generated by the partial discharge inside the cable.

[0040] The partial discharge fiber optic acoustic emission sensor mainly includes a housing 3, a wire clamp 5, an outer cover 2, and a fused tapered sensing unit 15 fixedly installed in the inner cavity of the housing 3.

[0041] 1. Mechanical coupling structure between the housing and the wire clamp like Figure 1 and Figure 3 As shown, the housing 3 serves as the main supporting structure of the sensor. Its material is preferably a high-strength insulating material such as PEEK (polyether ether ketone) or PPS (polyphenylene sulfide), which has good high temperature resistance, corrosion resistance and insulation properties.

[0042] The wire clamp 5 is located on the back of the housing 3. Specifically, the wire clamp 5 is a C-type connector, preferably made of copper or aluminum alloy to ensure good sound conduction performance. The wire clamp 5 also includes a wire clamp fixing arm 4 integrally connected to the wire clamp, extending to both sides. The two ends of the wire clamp fixing arm 4 are provided with first screw holes 6, and the bottom plate of the housing 3 is provided with corresponding second screw holes 14. The housing 3 and the wire clamp 5 are connected and fixed by fastening screws passing through the first screw holes 6 and the second screw holes 14, so that the back of the housing 3 fits tightly against the back of the wire clamp 5.

[0043] To further reduce acoustic wave transmission loss and improve connection reliability, the back of housing 3 and the back of wire clamp 5 are bonded together using a two-component epoxy resin adhesive. The thickness of the two-component epoxy resin adhesive layer is controlled between 0.02mm and 0.1mm (an excessively thick adhesive layer will affect the sensor's sensitivity). Before bonding, the corresponding contact areas on the back of housing 3 and the back of wire clamp 5 are degreased and roughened to remove the oxide layer, increase surface roughness, and enhance bonding strength, and then cleaned with alcohol. During bonding, excess adhesive and air bubbles are gently rotated or squeezed out, and then clamped or weighed down with a weight, and cured at room temperature for more than 24 hours to ensure bonding strength.

[0044] In practical use, the outer sheath and sleeve of the cable are cut open at the designed pre-branching point to expose the inner copper core, such as... Figure 7 As shown, a clamp 5 is used to hold and fix the main cable 38 and the pre-branch cable (one of the branch cable I 391, branch cable II 392, branch cable III 393, and branch cable IV 394) to conduct the sound waves generated by the partial discharge of the pre-branch cable to the housing 3, thereby achieving tight acoustic coupling between the sensor and the cable under test.

[0045] 2. Optical cable entry and layered encapsulation structure like Figure 3 As shown, to adapt to the complex wiring environment on site, the side wall of the housing 3 along its length is provided with a groove A11 for the multi-core optical cable 37 to pass through and enter the inner cavity of the housing 3. The outer cover 2 has a V-shaped groove 7 corresponding to the groove A11. When the outer cover 2 is closed, the V-shaped groove 7 and the groove A11 are positioned opposite each other, jointly clamping and fixing the multi-core optical cable 37 to prevent it from loosening. The outer cover 2 has several third screw holes 8, and the housing 3 has several fourth screw holes 9. The outer cover 2 and the housing 3 are connected and fixed by fastening screws passing through the third screw holes 8 and the fourth screw holes 9.

[0046] Inside the housing 3, a recess 12, multiple fiber optic partitions 10, and a main partition 19 are sequentially fixed along the extension direction of the multi-core optical cable 37.

[0047] The recessed block 12 has a groove C, and the main partition plate 19 has a groove B16. The grooves C, B16, and A11, together with the top surface of the fiber optic partition plate 10, form a continuous support channel for supporting the multi-core optical cable 37.

[0048] Multiple fiber optic partitions 10 are sequentially spaced along the extension direction of the multi-core optical cable 37. During actual construction, it is necessary to separate single-core optical fibers (i.e., sensing fibers, such as...) from the multi-core optical cable 37. Figure 7 The single-core optical cables CⅠ371, CⅡ372, CⅢ373, and CⅣ374 shown are connected to the fused taper sensing unit 15. The top surface of the fiber optic spool 10 serves as a fulcrum for coiling the split single-core optical fiber, reserving excess fiber length and preventing the fiber from being subjected to direct mechanical tension.

[0049] The method for connecting a single-core optical fiber branched from the multi-core optical cable 37 to the fused tapered sensing unit 15 is as follows: at a distance of approximately 40cm from the front of the housing 3 (e.g., ... Figure 3 (L=40cm), cut the multi-core optical cable 37 with slit 36, and cut the single-core optical fiber to be separated. The end closest to the shell 3 is the connection end (e.g. Figure 7 (as shown in CKⅠ, CKⅡ, CKⅢ, CKⅣ); the multi-core optical cable 37 located between the concave block 12 and the main partition 19 is cut to form an optical cable branch point 13. The connection end of the single-core optical fiber is extracted from the optical cable branch point 13 and connected to the fused tapered sensing unit 15 after being coiled.

[0050] 3. Packaging and protection of fused taper sensor units like Figure 3 As shown, a secondary partition 20 is disposed inside the housing 3 along a direction perpendicular to its length, spaced apart from the main partition 19. A spacer area is formed between the main partition 19 and the secondary partition 20 for placing the molten tapered sensing unit 15. This spacer area is filled with silicone grease for acoustic impedance matching and buffer protection.

[0051] The fused tapered sensing unit 15 is fixed to the spacer area and tightly adhered to the bottom surface of the housing 3 using high-temperature resistant epoxy resin. An inner cover plate 17 is detachably provided above the spacer area. The inner cover plate 17 has several mounting holes 18, and its two ends are fixedly connected to the main partition plate 19 and the secondary partition plate 20 respectively using screws and mounting holes 18. The inner cover plate 17 is sealed to the ends of the fused tapered sensing unit 15 using high-temperature resistant epoxy resin to prevent leakage of internal silicone grease and protect the sensing unit from moisture and dust corrosion.

[0052] 4. Specific structure of the fused tapered sensing unit Combination Figure 4 and Figure 5As shown, the fused taper sensing unit 15 is the core sensing element. It includes an optical fiber (preferably a single-mode optical fiber) and an optical fiber heat shrink tubing 34, with the optical fiber bent inside the optical fiber heat shrink tubing 34 to form a foldback point 32.

[0053] The specific manufacturing process is as follows: Take an optical fiber, insert one section into an optical fiber heat shrink tubing 34, bend the fiber 180 degrees outside the tubing to form a fold point 32, and then thread the end back through the same end of the optical fiber heat shrink tubing 34. Adjust the position of the optical fiber so that the fold point 32 is located at the axial center of the optical fiber heat shrink tubing 34. At this time, two closely fitted parallel optical fiber segments (i.e., the second optical fiber segment 31 and the third optical fiber segment 33) are formed inside the tubing. The segment outside the tubing is the first optical fiber segment 30, which serves as the optical signal input / output end. The end face of the fold point 32 is processed to form a light-reflecting end face.

[0054] Subsequently, the structure after fiber threading undergoes a fused tapering process. The fiber heat shrink tubing 34 is fixed to the fused tapering machine fixture, aligning the two parallel fiber segments inside the tubing in the heating zone. Heating and stretching are then performed on the central region of the fiber heat shrink tubing 34. During stretching, the two parallel fiber segments gradually fuse to form a biconical fused coupling zone. By real-time monitoring of the splitting ratio, heating and stretching are stopped when the splitting ratio reaches a preset value (e.g., 50%) and after 70-80 splitting ratio oscillation cycles. Finally, the fiber heat shrink tubing 34 is heated to shrink, tightly wrapping and fixing the internal biconical fused coupling zone, thus obtaining the fused tapered sensing unit 15.

[0055] The biconical fused coupling region is a critical sensing area. Its conical shape constitutes a strain concentration structure. When the acoustic field generated by partial discharge from the pre-branched cable acts on the coupling region via the housing 3, the acoustic wave propagates along the coupling region, causing strain field disturbances. In particular, the narrowest part (the thinnest part) of the biconical fused coupling region has a significant strain amplification effect on the incident acoustic wave. Through the acousto-optic modulation effect, the phase and intensity of the light transmitted in the optical fiber change with strain.

[0056] During operation, the optical signal enters through the first optical fiber segment 30, is reflected at the foldback point 32, and returns along the original path, thus forming a single-end reflective optical path interface. The single-core optical fiber (i.e., the sensing fiber) in the multi-core optical cable 37 is fused to the first optical fiber segment 30 to realize the transmission of the optical signal.

[0057] Injection molding protection and heat insulation after sensor installation: After the pre-branched cable and sensor are installed, an insulation layer needs to be wrapped around the entire sensor. For medium- and high-voltage cables, injection molding is typically used to integrate and protect the pre-branched cable connection and the sensor. The temperature during injection molding can reach 170-180℃. To prevent this high temperature from causing aging of the internal electronic components, failure of the adhesive layer, or damage to the optical fiber, the sensor must be heat-insulated before injection molding.

[0058] Specifically, polyvinyl chloride (PVC) insulation material is used as the insulation material, and a layer of insulation material with a thickness greater than 2mm is tightly wrapped around the outside of the sensor and the copper core of the pre-branched cable to ensure complete coverage; at the same time, all exposed optical cables at the pre-branching point are also wrapped. This insulation layer can effectively isolate the high temperature during injection molding, prevent the high temperature from causing thermal damage to the optical cable and the internal structure of the sensor, and ensure the sensor's performance is intact after injection molding and encapsulation.

[0059] Example 2: Partial Discharge Monitoring System for Pre-branched Cables like Figure 6 As shown, this embodiment provides a partial discharge monitoring system for pre-branched cables that utilizes the aforementioned sensor.

[0060] The system includes a power supply 21, a laser 22, a coupler 23, an optical fiber circulator 24, a photoelectric converter 26, a synchronous data acquisition card 27, a host computer 28, and a pre-branched cable partial discharge optical fiber acoustic emission sensor 25 as in Embodiment 1.

[0061] System connection relationships: Power supply 21 is used to power laser 22.

[0062] The output port of laser 22 is connected to the input end of coupler 23, and the output end of coupler 23 is connected to the first port 241 of fiber optic circulator 24.

[0063] The second port 242 of the fiber optic circulator 24 is connected to the pre-branched cable partial discharge fiber optic acoustic emission sensor 25 via a single-core fiber, specifically to the first fiber segment 30 of the fused taper sensing unit 15 in the sensor 25.

[0064] The third port 243 of the fiber optic circulator 24 is connected to the input of the photoelectric converter 26 via the transmission fiber 29, and is used to receive the light signal carrying the acoustic wave information reflected back from the sensor.

[0065] Circuit demodulation and data acquisition: like Figure 11 As shown, the photoelectric converter 26 includes a photoelectric conversion module, an active filter module, and an RF impedance matching module that are connected in sequence.

[0066] 1. Specific circuit and parameter selection for photoelectric conversion modules like Figure 8 As shown, the photoelectric conversion module mainly consists of a 1550nm photodiode (M2) with a pigtail and an OPA380AIDGKR transimpedance amplifier. The pigtail of photodiode M2 ​​is connected to the end of the photodiode for receiving and transmitting optical signals to the photosensitive surface of the photodiode.

[0067] The specific circuit connection is as follows: The anode of photodiode M2 ​​is connected to system ground (GND), and the cathode is connected to the inverting input terminal (-In) of OPA380.

[0068] Resistors R5 and R6 form the first voltage divider network. Specifically, the upper end of R5 is connected to a +5V power supply, and the lower end of R5 is connected to the upper end of R6 to form node A. Node A is directly connected to the non-inverting input terminal (+In) of the OPA380. The lower end of R6 is grounded.

[0069] Parameter selection and effect analysis: R5 is selected as 90kΩ and R6 as 10kΩ. Their series connection provides a 0.5V DC bias voltage to the non-inverting input port 3 of the OPA380 transimpedance amplifier. Resistors R5 and R6 are selected according to a 9:1 resistance ratio. While maintaining the voltage division ratio, the overall values ​​of the two resistors are controlled within the 10-100kΩ range to prevent the overall resistance from being too small, which would increase the circuit's static power consumption, and too large, which would introduce significant Johnson noise.

[0070] Power supply filtering section: Capacitors C5 and C6 are connected in parallel. One end of C5 and C6 is connected to the positive power supply terminal (V+) of the OPA380, and the other end is connected to the system ground GND, forming the first power supply filtering circuit. C5 is selected as 1μF and C6 is selected as 100nF, and their parallel configuration achieves wide-band power supply filtering. The large-capacity 1μF electrolytic capacitor filters out low-frequency power fluctuations, and the small-capacity 100nF ceramic capacitor suppresses high-frequency switching noise. The combination of high and low capacitance values ​​covers interference across the entire frequency band.

[0071] Feedback branch: One end of fixed resistor R1 is connected to the inverting input (-In) of OPA380, and the other end is connected to one end of potentiometer R11. R1 and R11 are connected in series. The other end of R11 is connected to the output (out) of OPA380, forming the feedback resistor branch. One end of compensation capacitor C4 is connected to the inverting input (-In) of OPA380, and the other end is connected to the output (out) of OPA380. C4 is connected in parallel across the series branch of R1 and R11.

[0072] Parameter Selection and Effect Analysis: The feedback branch of the OPA380AIDGKR transimpedance amplifier uses a 470Ω fixed resistor R1 in series with a 20kΩ potentiometer R11. The total feedback resistance adjustment range is 470Ω-20.47kΩ, thus achieving continuously adjustable transimpedance gain. Limiting the feedback resistance to the 470Ω-20.47kΩ range is crucial; an excessively large value will exacerbate thermal noise, while a value that is too small will reduce the overall voltage gain, failing to amplify the weak photocurrent to a suitable level. A 10pF surface-mount capacitor C4 is used for phase and frequency compensation of the transimpedance amplifier. If this capacitance is too small, it will not provide sufficient phase margin at the high-gain setting (20.47kΩ) of the feedback branch, failing to effectively compensate for the poles introduced by the photodiode junction capacitance and PCB parasitic capacitance, easily causing self-oscillation in the OPA380. If it is too large, although stability is guaranteed, it will severely reduce the bandwidth of the preceding stage, causing useful signals below 310kHz to attenuate prematurely. The negative power supply terminal (V-) of the OPA380 is connected to system ground GND.

[0073] 2. Specific circuit and parameter selection for active filter modules like Figure 9 As shown, the active filtering module uses the OPA1656ID as an audio operational amplifier to construct an active second-order Butterworth low-pass filter.

[0074] The specific circuit connection is as follows: The left end of the input resistor R2 is the signal input terminal, and the right end is connected to node G; one end of the input capacitor C1 is connected to node G, and the other end is grounded. R2 and C1 together form the input RC network. The left end of the first voltage divider resistor R7 is connected to node G, and the right end is connected to the inverting input terminal (-In) of the OPA1656ID; the feedback resistor R4 is connected between node G and the output terminal (out) of the OPA1656ID; the two ends of the feedback capacitor C2 are connected to the inverting input terminal (-In) and the output terminal (out) of the OPA1656ID, respectively. R4, R7, C2 and the operational amplifier constitute a second-order low-pass filter circuit (MFB multi-channel negative feedback topology).

[0075] The upper end of resistor R9 is connected to +5V, and its lower end, along with the upper end of resistor R8, is connected to the non-inverting input (+In) of the OPA1656ID. The lower end of R8 is grounded. R8 and R9 form the second voltage divider network. Capacitors C3 and C7 are connected in parallel, with one end connected to the positive power supply terminal (V+) of the OPA1656ID and the other end grounded, forming the second power supply filter circuit. The negative power supply terminal (V-) of the OPA1656ID is connected to GND.

[0076] Parameter Selection and Performance Analysis: Resistors R8 and R9 (90kΩ and 10kΩ) are selected according to a 9:1 resistance ratio to provide a 0.5V DC bias voltage to the non-inverting input (pin 3) of the OPA1656. While maintaining the voltage divider ratio, the overall values ​​of the two resistors are controlled within the 10kΩ-100kΩ range, balancing noise level and power consumption. Capacitors C3 (1μF) and C7 (100nF) are selected, employing the classic design approach of combining large and small capacitance capacitors. The 1μF capacitor filters out low-frequency power supply fluctuations, while the 100nF ceramic capacitor suppresses high-frequency switching noise.

[0077] The filter circuit parameters are set as follows: R2=3.63kΩ, C1=400pF, R7=1.82kΩ, R4=3.63kΩ, and C2=100pF together form a standard second-order Butterworth low-pass filter circuit. The topology requires a gain A=-R4 / R2, so R2 and R4 are both selected as 3.63kΩ; R7 is selected as 1.82kΩ. The circuit quality factor and cutoff frequency are determined in conjunction with the filter capacitors. Considering the output load constraints of the preamplifier OPA380 and the resistor Johnson noise level, R2, R4, and R7 are limited to the 1kΩ-5kΩ range. Resistance values ​​greater than 10kΩ will introduce significant resistor thermal noise, while resistance values ​​less than 500Ω will increase the output current of the preamplifier OPA380, increasing the load pressure on the preamplifier. Both input capacitor C1 and feedback capacitor C2 are pF-level ceramic capacitors. For the -3dB cutoff frequency of 310kHz in this design, the reasonable value range for this type of filter capacitor is 100-1000pF; compared with nF and uF level capacitors, it has lower parasitic inductance and is suitable for high-frequency signal filtering scenarios. Parameter calculations are performed using the theoretical formulas of a second-order Butterworth filter under the MFB topology, including the cutoff frequency formula. Quality factor With R2=R4=3.63kΩ pre-set, and to meet the Butterworth filter design condition of Q≈0.71, R7=1.82kΩ was calculated. The -3dB cutoff frequency fc=310kHz was set, and considering the capacitor value range constraints, C1=400pF and C2=100pF were finally determined. This circuit, with a -3dB cutoff frequency of 310kHz, passband gain |A|=1, and quality factor Q≈0.71, meets the Butterworth filter design requirements. The OPA1656 achieves DC negative feedback through R4, while C2 only participates in high-frequency feedback. The op-amp's closed-loop operating mode significantly improves the circuit's load-driving capacity, reduces the disturbance of the output amplitude by the external load, and ensures stable output waveform.

[0078] 3. Specific circuit and parameter selection for the emitter impedance matching module like Figure 10As shown, the RF impedance matching module includes an RF connector RF1 and a matching resistor R3. The RF connector RF1 is a BNC RF connector. The signal after second-order filtering is connected in series to the matching resistor R3, which has a resistance of 50Ω. The output of R3 is connected to the center signal pin of the RF connector RF1, and the ground terminal of RF1 is connected to ground.

[0079] Parameter selection and effect analysis: R3 strictly selects the standard RF 50Ω resistance value to match the characteristic impedance of the coaxial cable and suppress signal reflection problems during long-distance transmission; the conditioned analog signal is sent to the RF connector RF1 and then transmitted to the synchronous data acquisition card 27.

[0080] Overall system workflow: The output end of the photoelectric converter 26 (i.e., the radio frequency connector RF1) is connected to the synchronous data acquisition card 27, and the synchronous data acquisition card 27 is connected to the host computer 28.

[0081] The synchronous data acquisition card 27 is configured to perform multi-channel parallel synchronous acquisition using a sampling frequency of not less than 1 MHz, and continuously transmit the acquired real-time data stream to the host computer via the PCIe bus.

[0082] The host computer 28 is configured to: receive the real-time data stream and perform real-time processing using a continuous sampling combined with program-triggered saving mode; specifically, it includes: using a 1-second time window, calculating the absolute maximum amplitude and arithmetic mean of the data within the window in real time; when the absolute maximum amplitude is greater than 5 times the arithmetic mean, it is determined to be a discharge event and the saving mechanism is automatically triggered to store the data as a file; at the same time, the host computer is also configured to perform time-domain parameter extraction (such as amplitude, pulse number), spectrum analysis (FFT transform), and time-frequency graph generation on the saved data to identify abnormal signals hidden in noise, thereby determining whether there is a partial discharge fault in the pre-branched cable.

[0083] The specific monitoring steps are as follows: Step 1: When the cable is in normal operation and no partial discharge defects are observed, the power supply module 21 continuously provides a stable operating voltage to the 1550nm laser 22. The laser emits continuous probe light with a wavelength of approximately 1550nm. The beam is coupled through the light source coupler 23 and then sent into the fiber optic circulator 24, eventually reaching the internal particulate discharge acoustic emission sensor 25. At this time, the reference reflected light inside the fiber optic cable travels back along the original path, is directionally input to the back-end photoelectric converter 26 through the fiber optic circulator 24, and the photoelectric converter module outputs a stable DC voltage signal, which is finally transmitted to the host computer by the synchronous acquisition card 27 as the baseline reference signal of the system.

[0084] Step 2: When the cable insulation layer is damaged and a partial discharge fault occurs, the partial discharge phenomenon will excite a high-frequency elastic stress wave; the partial discharge acoustic emission sensor 25 captures the mechanical stress wave, and the stress wave acts on the sensing optical fiber, causing it to undergo micro-bending deformation. The light beam transmitted inside the optical fiber is subjected to intensity modulation, and the light intensity changes with the acoustic emission time-domain characteristics, thereby generating a modulated optical signal carrying the partial discharge characteristic information of the cable; the modulated reflected light is sent to the photoelectric converter 26 after being isolated by the circulator 24, completing the optical signal return process.

[0085] Step 3: The incident light carrying partial discharge information shines on the 1550nm photodiode. The photoelectric effect converts the light signal with varying intensity into a weak alternating photocurrent signal. This current amplitude is only in the nA range and cannot be directly recognized by the acquisition device, requiring subsequent signal conditioning. The weak photocurrent is fed into the OPA380AIDGKR transimpedance amplifier unit. The circuit uses a fixed resistor R1 and a 20kΩ potentiometer R11 connected in series to form an adjustable feedback branch. Relying on the transimpedance amplification principle, the photocurrent is converted into a voltage signal. By adjusting the potentiometer, the overall transimpedance gain can be changed to adapt to partial discharge signals of different intensities. At the same time, a 10pF compensation capacitor C4 performs phase compensation, improves the phase margin of the op-amp, avoids the high-frequency self-oscillation problem of the OPA380 chip, and outputs an amplified voltage signal with excellent signal-to-noise ratio.

[0086] Step 4: The amplified voltage signal is input into a second-order Butterworth low-pass filter circuit built with an OPA1656ID operational amplifier. Based on the selection of the parameters of components R2, R4, R7, C1, and C2, high-frequency noise caused by environmental electromagnetic interference and 50Hz power frequency coupling noise are filtered out. At the same time, R9 and R8 provide 0.5V DC bias to ensure that the operational amplifier operates in the linear range, eliminate signal distortion problems, and output a filtered voltage signal with a flat waveform and low noise level, thus completing signal noise reduction and waveform optimization.

[0087] Step 5: The filtered voltage signal is output via a 50Ω matching resistor R3 and then sent to the synchronous acquisition card 27. The acquisition card transmits the acquired filtered voltage signal to the host computer in real time via the PCIe bus for subsequent processing by the partial discharge monitoring and analysis software. The software adopts a continuous sampling combined with program-triggered saving mode: it reads data from the acquisition card at 1-second intervals, and the program calculates the absolute maximum amplitude and arithmetic mean of the data segment; when the absolute maximum amplitude is greater than 5 times the arithmetic mean, the program automatically triggers the saving mechanism, marking the filtered voltage signal acquired within 1 second as a discharge event and storing it as a .csv format file to ensure effective capture of abnormal events.

[0088] Step 6: During the automatic monitoring process, the software automatically counts the absolute maximum value and the number of occurrences of each discharge event daily, and plots line graphs showing the trends of maximum value-time and number of occurrences-time. This allows maintenance personnel to observe the evolution of partial discharge behavior over time, determine whether there is an accelerated deterioration trend in the insulation defects of the pre-branched cable, and provide a basis for subsequent maintenance decisions.

[0089] Through the above system design, the present invention realizes non-electrical, anti-interference, and highly sensitive online monitoring of key parts of pre-branched cables.

[0090] In the description of this invention, terms such as "inner," "outer," "upper," "lower," "front," and "rear," which indicate orientation or positional relationship, are used only for the convenience of describing this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0091] The above description is only one embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A pre-branched cable partial discharge fiber optic acoustic emission sensor, characterized in that, It includes a housing (3), a wire clamp (5), an outer cover (2), and a molten tapered sensing unit (15) fixedly disposed in the inner cavity of the housing (3); The wire clamp (5) is located on the back of the housing (3) and is used to clamp and fix the main cable (38) and the branch cable, and to transmit the sound waves generated by partial discharge to the housing (3). The housing (3) has a groove A (11) on its side wall along the length direction for allowing a multi-core optical cable (37) to pass through and enter the inner cavity of the housing (3); The fused tapered sensing unit (15) includes an optical fiber and an optical fiber heat shrink tube (34). The optical fiber is bent inside the optical fiber heat shrink tube (34) to form a fold point (32), and the fold point (32) constitutes a light reflection end face. The optical fiber forms two parallel optical fiber segments inside the optical fiber heat shrink tube (34). The two parallel optical fiber segments are fused tapered to form a double cone fused coupling region. The double cone fused coupling region is located at the axial center of the optical fiber heat shrink tube (34). The fused tapered sensing unit (15) is a single-fiber foldback reflective structure. The optical signal is injected through the optical fiber, transmitted to the optical reflection end face, reflected, and returns along the original path. The optical fiber in the multi-core optical cable (37) is connected to the fused tapered sensing unit (15); The outer cover (2) is provided at the opening of the housing (3) for encapsulating a portion of the multi-core optical cable (37) and the fused tapered sensing unit (15) located inside the housing (3) in the inner cavity of the housing (3).

2. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 1, characterized in that, The splitting ratio of the biconical molten coupling region is in the range of 45%-55%, and the additional loss is less than 0.5dB; The preparation parameters corresponding to the double-cone molten coupling region include: the molten tapering process undergoes 70-80 spectrophotometric oscillation cycles.

3. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 1, characterized in that, The conical region of the double-cone molten coupling zone forms a strain concentration structure, which is used to change the phase and intensity of the transmitted light through the acousto-optic modulation effect when the sound field acts on the coupling zone through the shell (3); the narrow waist region of the double-cone molten coupling zone has a strain amplification effect on the incident sound wave.

4. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 1, characterized in that, The wire clamp (5) is a C-type wire clamp and also includes a wire clamp fixing arm (4) integrally connected to the wire clamp; the two ends of the wire clamp fixing arm (4) are provided with first screw holes (6), and the bottom plate of the housing (3) is provided with corresponding second screw holes (14); the housing (3) and the wire clamp (5) are connected and fixed by fastening screws passing through the first screw holes (6) and the second screw holes (14), so that the back of the housing (3) is in close contact with the back of the wire clamp (5).

5. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 1, characterized in that, The back of the housing (3) and the back of the wire clamp (5) are bonded together by a two-component epoxy resin adhesive, wherein the thickness of the two-component epoxy resin adhesive layer is 0.02 mm to 0.1 mm. Before bonding, the back of the housing (3) and the corresponding contact area of ​​the back of the wire clamp (5) are respectively degreased and roughened.

6. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 1, characterized in that, Inside the housing (3) along the extension direction of the multi-core optical cable (37), a recess (12), multiple fiber optic partitions (10), and a main partition (19) are fixedly provided in sequence; the main partition (19) is provided with a groove B (16), the recess (12) is provided with a groove C, and the groove C, the groove B (16), the groove A (11), and the top surface of the fiber optic partition (10) cooperate to support the multi-core optical cable (37). The outer cover (2) is provided with a V-shaped groove (7) corresponding to the groove A (11). The V-shaped groove (7) is arranged opposite to the groove A (11) and is used to clamp and fix the multi-core optical cable (37).

7. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 6, characterized in that, Inside the housing (3), along the direction perpendicular to the length, there is a secondary partition (20) spaced apart from the main partition (19); a spacer area for placing the molten tapered sensing unit (15) is formed between the main partition (19) and the secondary partition (20), and the spacer area is filled with silicone grease; The molten tapered sensing unit (15) is fixed in the interval area by high-temperature resistant epoxy resin and closely adheres to the bottom surface of the housing (3); an inner cover plate (17) is detachably provided above the interval area, and the inner cover plate (17) and the end of the molten tapered sensing unit (15) are sealed by high-temperature resistant epoxy resin.

8. The pre-branched cable partial discharge fiber optic acoustic emission sensor according to claim 6, characterized in that, Multiple fiber optic partitions (10) are arranged sequentially at intervals along the extension direction of the multi-core optical cable (37). The top surface of the fiber optic partition (10) is used as a fulcrum for coiling single-core optical fibers branched from the multi-core optical cable (37) to reserve excess fiber length.

9. A partial discharge monitoring system for pre-branched cables, characterized in that, It includes a power supply (21), a laser (22), a coupler (23), a photoelectric converter (26), a synchronous data acquisition card (27), a host computer (28), and also includes an optical fiber circulator (24) and a pre-branched cable partial discharge optical fiber acoustic emission sensor (25) as described in any one of claims 1-8. The power supply (21) is used to power the laser (22); The output port of the laser (22) is connected to the input end of the coupler (23), and the output end of the coupler (23) is connected to the first port (241) of the fiber optic circulator (24). The second port (242) of the fiber optic circulator (24) is connected to the fused tapered sensing unit (15) in the pre-branched cable partial discharge fiber optic acoustic emission sensor (25) via a single-core fiber. The third port (243) of the fiber optic circulator (24) is connected to the input end of the photoelectric converter (26) via a transmission fiber (29) to receive optical signals carrying acoustic wave information. The output end of the photoelectric converter (26) is connected to the synchronous data acquisition card (27), and the synchronous data acquisition card (27) is connected to the host computer (28); The synchronous data acquisition card (27) is configured to: perform multi-channel parallel synchronous acquisition using a sampling frequency of not less than 1 MHz, and transmit the acquired real-time data stream to the host computer; The host computer (28) is configured to: receive the real-time data stream and perform real-time processing using a continuous sampling combined with program-triggered saving working mode; specifically including: using a 1-second time window, calculating the absolute maximum amplitude and arithmetic mean of the data within the window in real time; when the absolute maximum amplitude is greater than 5 times the arithmetic mean, it is determined to be abnormal and the saving mechanism is automatically triggered to store the data as a file; at the same time, the data is subjected to time domain parameter extraction, spectrum analysis and time-frequency diagram generation to identify abnormal signals.

10. The pre-branched cable partial discharge monitoring system according to claim 9, characterized in that, The photoelectric converter (26) includes a photoelectric conversion module, an active filter module and a radio frequency impedance matching module connected in sequence; The photoelectric conversion module includes a photodiode M2 ​​and a transimpedance amplifier; the anode of the photodiode M2 ​​is grounded, and the cathode is connected to the inverting input terminal of the transimpedance amplifier; the non-inverting input terminal of the transimpedance amplifier is connected to a first voltage divider network, which is connected between the +5V power supply and ground to provide a DC bias level; a feedback resistor branch is connected in series between the inverting input terminal and the output terminal of the transimpedance amplifier, and a compensation capacitor is connected in parallel across the two ends of the feedback resistor branch; the positive power supply terminal of the transimpedance amplifier is connected to a first power supply filter circuit. The active filter module has an input RC network connected to its input terminal, which includes an input resistor R2 connected in series and an input capacitor C1 with one end grounded. The active filter module includes an audio operational amplifier and a second-order low-pass filter circuit built around the audio operational amplifier. The second-order low-pass filter circuit includes a first voltage divider resistor R7 connected between the output node of the input RC network and the inverting input terminal of the audio operational amplifier, and a feedback resistor R4 connected between the output node of the input RC network and the output terminal of the audio operational amplifier. A feedback capacitor C2 is also connected between the inverting input terminal and the output terminal of the audio operational amplifier. A second voltage divider network is connected to the non-inverting input terminal of the audio operational amplifier, and this second voltage divider network is connected between the +5V power supply and ground. A second power supply filter circuit is connected to the positive power supply terminal of the audio operational amplifier. The RF impedance matching module includes a matching resistor R3 connected in series on the signal transmission line and an RF connector RF1; the matching resistor R3 has a resistance of 50Ω, its input is connected to the output of the audio operational amplifier, and its output is connected to the signal pin of the RF connector RF1, which is used to achieve 50Ω impedance matching to reduce high-frequency signal reflection loss; the ground terminal of the RF connector RF1 is grounded.

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