A PCCP broken wire monitoring system and method based on distributed optical fiber sensing

Abstract

The present invention discloses a PCCP broken wire monitoring system and method based on distributed optical fiber sensing, relating to the field of optical fiber sensing technology. The PCCP broken wire monitoring system comprises: a Sagnac interferometer, a Φ-OTDR system, a two-way loopback system, and a signal processing system; the Sagnac interferometer comprises: a first laser, a first optical coupler, a first delay optical fiber, a Faraday rotator mirror, and a first photodetector; the Φ-OTDR system comprises: a second laser, a second optical coupler, an acousto-optic modulator, a circulator, a third optical coupler, and a second photodetector; and the two-way loopback system comprises: a wavelength division multiplexer and a second delay optical fiber. The present invention solves the problems of low positioning accuracy, limited frequency measurement range, detection dead zones, and high computational pressure in PCCP broken wire monitoring.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a PCCP broken wire monitoring system and method based on distributed optical fiber sensing. Background Art

[0002] Prestressed Concrete Cylinder Pipe (PCCP) is a pipe commonly used to transport water and other fluids. It is composed of a series of prestressed concrete cylinders. A PCCP wire breakage occurs when the prestressing steel in the pipe breaks, causing a portion of the pipe to lose prestress, potentially leading to cracking, deformation, and damage. PCCP wire breakage often has serious impacts on water conservancy facilities and the surrounding environment. Therefore, monitoring and maintenance of PCCP wire breakage events are crucial to ensure pipeline safety and reliability.

[0003] PCCP pipelines typically consist of multiple pipe sections approximately 4 to 5 meters in length. When a PCCP wire breaks, the resulting transient elastic wave signal frequency is primarily concentrated in the high-frequency range of 10 kHz to 20 kHz, and lasts only tens of milliseconds. Therefore, to effectively monitor PCCP wire breaks, the monitoring system's spatial positioning uncertainty must be less than ±2.5 meters, and its frequency measurement range must be greater than 20 kHz. Furthermore, the monitoring system must be capable of capturing and analyzing transient signals to accurately identify and locate PCCP wire breaks.

[0004] An interferometer is a precision measuring instrument based on the principle of optical interference, characterized by high measurement accuracy, a wide frequency range, and excellent stability. The Sagnac interferometer, among others, utilizes the Sagnac effect for measurement. This type of interferometer typically has a frequency range in the MHz range and can roughly locate vibration events, making it widely used in fields such as gyroscopes, inertial navigation, and seismology. However, its positioning accuracy is low when monitoring over long distances, and there are issues such as inaccurate vibration event location.

[0005] The Phase-Sensitive Optical Time Domain Reflectometer (Φ-OTDR) is a high-resolution fiber optic sensor based on the principle of optical phase change, a type of distributed fiber optic sensing. It utilizes a narrow-linewidth laser to emit continuous light, which is pulse-modulated and then transmitted through the sensing fiber. A photodetector analyzes the Rayleigh backscattered (RBS) signal generated by the sensing fiber, leveraging phase change and interference effects to monitor and locate subtle events and changes in the fiber. It enables full-time monitoring of the sensing fiber and has high application value and widespread potential. By deploying optical fibers within PCCP pipelines and leveraging Φ-OTDR technology's sensitivity to fiber length, bend, and deformation, real-time monitoring of the pipeline is possible. This technology offers wide monitoring range, excellent real-time performance, and high positioning accuracy, effectively improving the safety and reliability of PCCP pipelines. However, due to the limited frequency range of the Φ-OTDR technology, it is difficult to achieve a frequency range of 20 kHz in long-distance monitoring scenarios, resulting in a limited ability to capture transient signals. Furthermore, the system is affected by coherent fading noise, resulting in detection dead zones. Furthermore, accurately identifying PCCP broken wires and their locations within the massive amounts of data captured by the Φ-OTDR system is extremely difficult.

[0006] In summary, the existing distributed optical fiber sensing technology has problems such as low positioning accuracy, limited frequency measurement range, detection dead zone, and high computational pressure when performing PCCP broken wire monitoring. Summary of the Invention

[0007] Based on this, an embodiment of the present invention provides a PCCP broken wire monitoring system and method based on distributed optical fiber sensing, which integrates Sagnac interferometry and Φ-OTDR technology to solve the problems of low positioning accuracy, limited frequency measurement range, detection dead zone, and high computational pressure in PCCP broken wire monitoring.

[0008] To achieve the above objectives, the present invention provides the following solutions:

[0009] A PCCP broken wire monitoring system based on distributed optical fiber sensing is used to detect broken wires in a PCCP pipeline. The PCCP pipeline comprises a pipeline body and an optical cable arranged on the pipeline body. The optical cable comprises at least a first sensing optical fiber and a second sensing optical fiber.

[0010] The PCCP broken wire monitoring system includes: a Sagnac interferometer, a Φ-OTDR system, a dual-path loopback system, and a signal processing system;

[0011] The Sagnac interferometer includes: a first laser, a first optical coupler, a first delay fiber, a Faraday rotator mirror, and a first photodetector; the Φ-OTDR system includes: a second laser, a second optical coupler, an acousto-optic modulator, a circulator, a third optical coupler, and a second photodetector; the two-way loopback system includes: a wavelength division multiplexer and a second delay fiber;

[0012] The first laser is used to output a first laser; the first port of the first optical coupler is used to receive the first laser; the fourth port of the first optical coupler is used to transmit the first laser to the first delay fiber; the first delay fiber is used to delay the first laser to obtain a first delayed light; the Faraday rotator is used to rotate the polarization state of the first delayed light to obtain a first state-converted light, and return the first state-converted light to the first delay fiber; the first delay fiber is also used to delay the first state-converted light and return the obtained second delayed light to the first optical coupler; the sixth port of the first optical coupler is used to transmit the first laser to the wavelength division multiplexer;

[0013] The second laser is used to output a second laser, the spectral width of the first laser is greater than the spectral width of the second laser, and the correlation of the first laser is less than the correlation of the second laser; the second optical coupler is used to split the second laser into two paths, one path is a probe light, and the other path is a reference light; the acousto-optic modulator is used to modulate the probe light into a pulse light with a set frequency shift; the first port of the circulator is used to receive the pulse light, and the second port of the circulator is used to transmit the pulse light to the wavelength division multiplexer;

[0014] One end of the wavelength division multiplexer is connected to one end of the first sensing fiber, the other end of the first sensing fiber is connected to one end of the second delay fiber, the other end of the second delay fiber is connected to one end of the second sensing fiber, and the other end of the second sensing fiber is connected to the fifth port of the first optical coupler; the wavelength division multiplexer is used to transmit the first laser to the first sensing fiber, and the first laser generates a third delayed light after being transmitted through the first sensing fiber, the second delay fiber, and the second sensing fiber in sequence; the fifth port of the first optical coupler is used to receive the third delayed light; the wavelength division multiplexer is also used to transmit the pulsed light to the first sensing fiber; the pulsed light passes through the first sensing fiber, the second delay fiber, and the second sensing fiber in sequence, and generates back Rayleigh scattered light during the transmission process; the back Rayleigh scattered light passes through the wavelength division multiplexer and the second port of the circulator in sequence, and then enters the third optical coupler through the third port of the circulator;

[0015] The fifth port of the first optical coupler is further used to transmit the second delayed light to the second sensing fiber, and the second delayed light generates a first interference light signal after being transmitted through the second sensing fiber, the second delay fiber, and the first sensing fiber in sequence; the sixth port of the first optical coupler is further used to receive the first interference light signal;

[0016] The fourth port of the first optical coupler is further used to transmit the third delayed light to the first delay optical fiber; the first delay optical fiber is further used to delay the third delayed light to obtain a fourth delayed light; the Faraday rotator is used to rotate the polarization state of the fourth delayed light to obtain a second state-converted light, and return the second state-converted light to the first delay optical fiber; the first delay optical fiber is further used to delay the second state-converted light to obtain a second interference signal; the fourth port of the first optical coupler is further used to receive the second interference optical signal; the first interference optical signal and the second interference optical signal interfere with each other at the third port of the first optical coupler to form an interference signal;

[0017] The first photodetector is connected to the third port of the first optical coupler, and is configured to receive the interference signal and perform photoelectric conversion on the interference signal to obtain a first electrical signal;

[0018] The third optical coupler is used to couple the pulsed light and the Rayleigh backscattered light to form an intermediate frequency signal; the second photodetector is connected to the third optical coupler, and is used to receive the intermediate frequency signal and perform photoelectric conversion on the intermediate frequency signal to obtain a second electrical signal;

[0019] The signal processing system is connected to the first photodetector and the second photodetector respectively;

[0020] The signal processing system is used to:

[0021] performing phase demodulation on the first electrical signal to obtain a first time domain signal;

[0022] performing energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline, and performing time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected wire breakage event when the suspected wire breakage event occurs;

[0023] performing amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal;

[0024] Energy spectrum analysis and frequency spectrum analysis are performed on the second time domain signal to complete the screening of the preliminary position of the suspected wire breakage event, determine the final position of the suspected wire breakage event, and determine whether the suspected wire breakage event is a real wire breakage event.

[0025] Optionally, the Sagnac interferometer further includes: a first optical filter and a second optical filter;

[0026] The first optical filter is arranged between the sixth port of the first optical coupler and the wavelength division multiplexer; and the second optical filter is arranged between the second sensing fiber and the fifth port of the first optical coupler.

[0027] Optionally, the Φ-OTDR system further includes: an erbium-doped fiber amplifier;

[0028] The erbium-doped fiber amplifier is arranged between the acousto-optic modulator and the circulator.

[0029] Optionally, the Sagnac interferometer further includes: an optical isolator;

[0030] The optical isolator is disposed between the first laser and the first port of the first optical coupler.

[0031] Optionally, the signal processing system specifically includes: a data acquisition card and a computer;

[0032] The data acquisition card is connected to the first photoelectric detector, the second photoelectric detector and the computer respectively;

[0033] The data acquisition card is used to acquire the first electrical signal and the second electrical signal;

[0034] The computer comprises:

[0035] A first demodulation module, configured to perform phase demodulation on the first electrical signal to obtain a first time domain signal;

[0036] a preliminary broken wire location analysis module, configured to perform energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected broken wire event has occurred in the PCCP pipeline, and to perform time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected broken wire event when the suspected broken wire event occurs;

[0037] a second demodulation module, configured to perform amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal;

[0038] The broken wire position final analysis module is used to perform energy spectrum analysis and frequency spectrum analysis on the second time domain signal to complete the screening of the preliminary position of the suspected broken wire event, determine the final position of the suspected broken wire event, and determine whether the suspected broken wire event is a real broken wire event.

[0039] Optionally, the signal processing system further includes: an acousto-optic modulation driver;

[0040] The acousto-optic modulation driver is connected to the data acquisition card and the acousto-optic modulator respectively; the data acquisition card is also used to receive the clock carrier signal and the pulse trigger modulation signal sent by the computer; the acousto-optic modulation driver is used to output a high-level pulse modulation signal to the acousto-optic modulator according to the clock carrier signal and the pulse trigger modulation signal.

[0041] Optionally, the signal processing system further includes: an electrical filter;

[0042] The electrical filter is arranged between the second photodetector and the data acquisition card.

[0043] To achieve the above object, the present invention also provides the following solution:

[0044] A PCCP broken wire monitoring method based on distributed optical fiber sensing is used in the above-mentioned PCCP broken wire monitoring system; the method comprises:

[0045] Obtain a first electrical signal and a second electrical signal; the first electrical signal is obtained by photoelectric conversion of an interference signal; the first electrical signal is obtained by photoelectric conversion of an intermediate frequency signal; the interference signal is formed by the interference of the first interference light signal and the second interference light signal; the first interference light signal is formed after the first laser sequentially passes through the fourth port of the first optical coupler, the first delay fiber, the Faraday rotation mirror, the first delay fiber, the fourth port of the first optical coupler, the fifth port of the first optical coupler, the second sensing fiber, the second delay fiber, the first sensing fiber, the wavelength division multiplexer and the sixth port of the first optical coupler; the first interference light signal is formed after the first laser sequentially passes through the fourth port of the first optical coupler, the first delay fiber, the Faraday rotation mirror, the first delay fiber, the fourth port of the first optical coupler, the fifth port of the first optical coupler, the second sensing fiber, the second delay fiber, the first sensing fiber, the wavelength division multiplexer and the sixth port of the first optical coupler; The light-related signal is formed when the first laser passes through the sixth port of the first optical coupler, the wavelength division multiplexer, the first sensing fiber, the second delay fiber, the second sensing fiber, the fifth port of the first optical coupler, the fourth port of the first optical coupler, the first delay fiber, the Faraday rotator, the first delay fiber, and the fourth port of the first optical coupler in sequence; the intermediate frequency signal is obtained by coupling the pulse light in the second laser and the backscattered Rayleigh light; the backscattered Rayleigh light is the backlight generated during the transmission process when the detection light in the second laser passes through the acousto-optic modulator, the circulator, the wavelength division multiplexer, the first sensing fiber, the second delay fiber, and the second sensing fiber in sequence;

[0046] performing phase demodulation on the first electrical signal to obtain a first time domain signal;

[0047] performing energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline, and performing time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected wire breakage event when the suspected wire breakage event occurs;

[0048] performing amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal;

[0049] Energy spectrum analysis and frequency spectrum analysis are performed on the second time domain signal to complete the screening of the preliminary position of the suspected wire breakage event, determine the final position of the suspected wire breakage event, and determine whether the suspected wire breakage event is a real wire breakage event.

[0050] Optionally, performing energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline specifically includes:

[0051] performing energy spectrum analysis on the first time domain signal to determine a short-time energy spectrum of the first time domain signal;

[0052] comparing the short-time energy spectrum of the first time domain signal with a pre-stored short-time energy spectrum of the system background noise, and determining as an abnormal signal a first time domain signal whose difference between the short-time energy spectrum of the first time domain signal and the short-time energy spectrum of the system background noise exceeds a set energy spectrum difference range;

[0053] Performing spectrum analysis on the abnormal signal to obtain spectrum characteristics of the abnormal signal;

[0054] The spectrum characteristics of the abnormal signal are compared with the spectrum characteristics in the pre-stored PCCP broken wire database. If the spectrum characteristics of the abnormal signal are consistent with the spectrum characteristics in the PCCP broken wire database, it is determined that a suspected broken wire event has occurred in the PCCP pipeline.

[0055] Optionally, performing energy spectrum analysis and frequency spectrum analysis on the second time domain signal to complete screening of the preliminary position of the suspected broken wire event, determine the final position of the suspected broken wire event, and determine whether the suspected broken wire event is a true broken wire event, specifically including:

[0056] Performing coherent fading noise suppression on the second time domain signal using a fading noise suppression method to obtain a suppressed time domain signal;

[0057] Perform energy spectrum analysis on the suppressed time domain signal to determine the final location of the suspected broken wire event;

[0058] A spectrum analysis is performed on the time domain signal at the final position of the suspected wire breakage event. If the spectrum characteristics of the time domain signal at the final position of the suspected wire breakage event are consistent with the spectrum characteristics of the first time domain signal, the suspected wire breakage event is determined to be a true wire breakage event.

[0059] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0060] The embodiment of the present invention integrates a Sagnac interferometer and a Φ-OTDR system, multiplexing the optical signals of the Sagnac interferometer and the Φ-OTDR system into the same optical fiber through a wavelength division multiplexer, thereby increasing transmission capacity and reducing insertion loss. The Faraday rotator structure eliminates circular and linear birefringence, and by adjusting the delayed optical fiber length, the interference signals are prevented from canceling each other, ensuring that the PCCP broken wire monitoring system will not fail to detect and locate PCCP broken wire events. The dual-path loopback system significantly improves the system's detectability. The signal processing system uses Sagnac interferometry technology to perform qualitative analysis on PCCP broken wire events and provides a preliminary location of suspected broken wire events, and then uses Φ-OTDR technology to accurately locate them, enabling the system to identify PCCP broken wire events through qualitative analysis and precise positioning. Therefore, the embodiment of the present invention solves the problems of low positioning accuracy, limited frequency measurement range, detection dead zones, and high computational pressure in PCCP broken wire monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0062] Figure 1 A schematic diagram of the structure of a PCCP broken wire monitoring system based on distributed optical fiber sensing provided in an embodiment of the present invention;

[0063] Figure 2 A schematic diagram of the positional relationship between a PCCP pipeline and a PCCP broken wire monitoring system provided in an embodiment of the present invention;

[0064] Figure 3 A flow chart of the calibration process provided by an embodiment of the present invention;

[0065] Figure 4 A flow chart of the monitoring process provided by an embodiment of the present invention;

[0066] Figure 5 A schematic diagram of the frequency spectrum relationship of a PCCP wire breakage event provided by an embodiment of the present invention;

[0067] Figure 6 A flow chart of a dual-path loopback fading noise suppression method provided by an embodiment of the present invention;

[0068] Figure 7 This is a diagram showing the effect of dual-path loopback fading noise suppression provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0069] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0070] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0071] PCCP pipelines are common underground water pipelines. Due to the various stresses and environmental factors that affect them during transportation, installation, and use, prestressed steel bars are susceptible to breakage or corrosion. This can degrade pipeline performance and even lead to serious accidents such as pipeline rupture. Therefore, monitoring PCCP pipelines for broken wires is crucial. The following embodiment provides a PCCP broken wire monitoring system and method based on distributed fiber optic sensing, integrating Sagnac interferometry and Φ-OTDR technology.

[0072] Example 1

[0073] This embodiment provides a PCCP broken wire monitoring system based on distributed optical fiber sensing, which is used to detect broken wires in PCCP pipelines. The PCCP pipeline includes a pipeline body and an optical cable arranged on the pipeline body; the optical cable includes at least a first sensing optical fiber and a second sensing optical fiber.

[0074] See also Figure 1 The PCCP broken wire monitoring system includes: a Sagnac interferometer, a Φ-OTDR system, a dual-path loopback system and a signal processing system.

[0075] The Sagnac interferometer includes: a first laser, a first optical coupler, a first delay fiber 7, a Faraday Rotating Mirror 11 (Faraday Rotating Mirror, FRM) and a first photodetector; the Φ-OTDR system includes: a second laser, a second optical coupler 14, an acousto-optic modulator (AOM), a circulator 13, a third optical coupler 15 and a second photodetector; the two-way loop system includes: a wavelength division multiplexer (WDM) and a second delay fiber 17. The first sensing fiber 16, the second delay fiber 17 and the second sensing fiber 18 together constitute the overall sensing fiber. The positional relationship between the PCCP pipeline and the PCCP broken wire monitoring system is shown as follows: Figure 2 As shown, 19 represents the PCCP broken wire monitoring system, 20 represents the pipeline body, and 21 represents the optical cable.

[0076] The first laser is used to output a first laser, which is a broadband low-coherence continuous light. The first optical coupler is used to receive, couple, and transmit optical signals, wherein the second port 2 performs input and output work, and the first port 1 of the first optical coupler is used to receive the first laser. The fourth port 4 of the first optical coupler is used to transmit the first laser to the first delay fiber 7. The first delay fiber 7 transmits the optical signal between the fourth port 4 of the first optical coupler and the Faraday rotator 11. The optical signal takes time to pass through this position, so a certain time delay will be generated. The first delay fiber 7 can be used to delay the first laser to obtain a first delayed light. The Faraday rotator 11 is used to rotate the polarization state of the optical signal input by the first delay fiber 7 before outputting it to the first delay fiber 7, that is, the Faraday rotator 11 is used to rotate the polarization state of the first delayed light to obtain a first state-converted light, and return the first state-converted light to the first delay fiber 7. The first delay fiber 7 is also used to delay the first state-converted light and return the obtained second delayed light to the first optical coupler. The sixth port 6 of the first optical coupler is used to transmit the first laser to the wavelength division multiplexer.

[0077] The second laser is used to output a second laser, which is a continuous narrow-linewidth high-coherence laser. The spectral width of the first laser is greater than the spectral width of the second laser, and the correlation of the first laser is less than the correlation of the second laser. The second optical coupler 14 is used to split the second laser into two paths, one for detection light and the other for reference light. The detection light signal is output to an acousto-optic modulator, and the reference light is output to a third optical coupler 15. The acousto-optic modulator is used to modulate the detection light into a pulse light with a set frequency shift amount. The first port a of the circulator 13 is used to receive the pulse light, and the second port b of the circulator 13 is used to transmit the pulse light to the wavelength division multiplexer.

[0078] One end of the wavelength division multiplexer is connected to one end of the first sensing fiber 16, the other end of the first sensing fiber 16 is connected to one end of the second delay fiber 17, the other end of the second delay fiber 17 is connected to one end of the second sensing fiber 18, and the other end of the second sensing fiber 18 is connected to the fifth port 5 of the first optical coupler. The connection end between the wavelength division multiplexer and the first sensing fiber 16 is port 8, the connection end between the first sensing fiber 16, the second delay fiber 17, and the first sensing fiber 16 is port 9, and the connection end between the second delay fiber 17 and the first optical coupler is port 10. The first laser and the second laser use different central wavelengths and each occupies a different bandwidth. Therefore, the wavelength division multiplexer can be used to multiplex the optical signals of different wavelengths input from the first optical coupler and the second port b of the circulator 13 into the sensing fiber. The wavelength division multiplexer can also separate the input optical signals of different wavelengths to achieve bidirectional signal transmission. In the interferometer section, the wavelength division multiplexer is primarily used to transmit optical signals between the first optical coupler and the sensing fiber, while the interferometer section is primarily used to transmit optical signals input from ports 8 and 10. In the Φ-OTDR system, the wavelength division multiplexer is primarily used to transmit pulsed light input from the second port b of the circulator 13 to the sensing fiber and to output the returned Rayleigh backscattered light (RBS) signal to the second port b of the circulator 13.

[0079] Specifically, the wavelength division multiplexer is used to transmit the first laser to the first sensing fiber 16, and the first laser generates a third delayed light after being transmitted through the first sensing fiber 16, the second delay fiber 17 and the second sensing fiber 18 in sequence; the fifth port 5 of the first optical coupler is used to receive the third delayed light; the wavelength division multiplexer is also used to transmit the pulsed light to the first sensing fiber 16; the pulsed light passes through the first sensing fiber 16, the second delay fiber 17 and the second sensing fiber 18 in sequence, and generates back Rayleigh scattered light during the transmission process; the back Rayleigh scattered light passes through the wavelength division multiplexer and the second port b of the circulator 13 in sequence, and then enters the third optical coupler 15 from the third port c of the circulator 13.

[0080] The fifth port 5 of the first optical coupler is also used to transmit the second delayed light to the second sensing fiber 18. After the second delayed light is transmitted through the second sensing fiber 18, the second delay fiber 17 and the first sensing fiber 16 in sequence, a first interference light signal is generated. The sixth port 6 of the first optical coupler is also used to receive the first interference light signal.

[0081] The fourth port 4 of the first optical coupler is also used to transmit the third delayed light to the first delay fiber 7; the first delay fiber 7 is also used to delay the third delayed light to obtain a fourth delayed light; the Faraday rotator 11 is used to rotate the polarization state of the fourth delayed light to obtain a second state-converted light, and return the second state-converted light to the first delay fiber 7; the first delay fiber 7 is also used to delay the second state-converted light to obtain a second interference signal; the fourth port 4 of the first optical coupler is also used to receive the second interference light signal; the first interference light signal and the second interference light signal interfere with each other at the third port 3 of the first optical coupler to form an interference signal. The Sagnac interferometer section includes two interference paths. The path of the first interference optical signal is: first port 1 - fourth port 4 - first delay fiber 7 - FRM - first delay fiber 7 - fourth port 4 - fifth port 5 - port 10 - port 9 - port 8 - sixth port 6 - third port 3; the path of the second interference optical signal is: first port 1 - sixth port 6 - port 8 - port 9 - port 10 - fifth port 5 - fourth port 4 - first delay fiber 7 - FRM - first delay fiber 7 - fourth port 4 - third port 3. These two paths enter the first photodetector through the same optical fiber in different orders, with the same optical path, resulting in interference. However, due to the use of a broadband, low-coherence light source, optical signals entering the first photodetector via other paths do not interfere.

[0082] The first photodetector is connected to the third port 3 of the first optical coupler, and is configured to receive the interference signal and perform photoelectric conversion on the interference signal to obtain a first electrical signal.

[0083] The third optical coupler 15 is used to couple the pulse light and the backscattered Rayleigh light to form an intermediate frequency signal; the second photodetector is connected to the third optical coupler 15, and is used to receive the intermediate frequency signal and perform photoelectric conversion on the intermediate frequency signal to obtain a second electrical signal.

[0084] The signal processing system is connected to the first photodetector and the second photodetector, respectively. The signal processing system is configured to: perform phase demodulation on the first electrical signal to obtain a first time domain signal; perform energy spectrum analysis and spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event has occurred in the PCCP pipeline, and perform time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected wire breakage event when the suspected wire breakage event occurs; perform amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal; perform energy spectrum analysis and spectrum analysis on the second time domain signal to complete screening of the preliminary location of the suspected wire breakage event, determine the final location of the suspected wire breakage event, and determine whether the suspected wire breakage event is a true wire breakage event.

[0085] As an optional embodiment, the Sagnac interferometer further includes: a first optical filter and a second optical filter. The first optical filter is arranged between the sixth port 6 of the first optical coupler and the wavelength division multiplexer; the second optical filter is arranged between the second sensing fiber 18 and the fifth port 5 of the first optical coupler.

[0086] The first optical filter is used to transmit the optical signal between the first optical coupler and the wavelength division multiplexer, and perform optical bandpass filtering on it to filter out the optical signal input by the second laser, thereby preventing the optical signal input by the second laser from being output by the wavelength division multiplexer to the first optical coupler through the sixth port.

[0087] The second optical filter is used to transmit the optical signal between the first optical coupler and the sensing optical fiber, and perform optical bandpass filtering on it to filter out the optical signal input by the second laser, thereby preventing the optical signal input by the second laser from being input into the first optical coupler through the sensing optical fiber through the fifth port.

[0088] As an optional embodiment, the Φ-OTDR system further includes an erbium-doped fiber amplifier (EDFA) 12. The EDFA 12 is disposed between the AOM and the circulator 13. The EDFA 12 is configured to amplify the pulsed light input by the AOM and output it to the first port a of the circulator 13.

[0089] As an optional embodiment, the Sagnac interferometer further includes an optical isolator. The optical isolator is disposed between the first laser and the first port 1 of the first optical coupler. The optical isolator is used to transmit continuous light to the first port 1 of the first optical coupler. It also has a unidirectional transmission characteristic, preventing backward-transmitted light generated for various reasons from adversely affecting the stability of the second laser's output power.

[0090] As an optional implementation, the signal processing system specifically includes: a data acquisition card (DAC) and a computer (PC).

[0091] The data acquisition card is connected to the first photodetector, the second photodetector and the computer respectively, and is used to acquire the first electrical signal and the second electrical signal.

[0092] The computer comprises:

[0093] The first demodulation module is configured to perform phase demodulation on the first electrical signal to obtain a first time domain signal.

[0094] The module for preliminary analysis of the position of a broken wire is configured to perform energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected broken wire event has occurred in the PCCP pipeline, and to perform delay positioning calculation based on the first time domain signal to determine a preliminary position of the suspected broken wire event when the suspected broken wire event occurs.

[0095] The second demodulation module is used to perform amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal.

[0096] The broken wire position final analysis module is used to perform energy spectrum analysis and frequency spectrum analysis on the second time domain signal to complete the screening of the preliminary position of the suspected broken wire event, determine the final position of the suspected broken wire event, and determine whether the suspected broken wire event is a real broken wire event.

[0097] As an optional embodiment, the signal processing system further includes an acousto-optic modulation driver (AOMDriver). The AOM driver is connected to the data acquisition card and the AOM, respectively. The data acquisition card is also used to receive the clock carrier signal and pulse trigger modulation signal sent by the computer. The AOM driver is used to output a high-level pulse modulation signal to the AOM based on the clock carrier signal and the pulse trigger modulation signal. The computer is also used to control the operating state of the data acquisition card. The AOM, modulated by the AOM driver, modulates the continuous detection light input from the second optical coupler 14 into pulsed light, generates a fixed frequency shift, and outputs it to the erbium-doped fiber amplifier 12.

[0098] As an optional embodiment, the signal processing system further includes an electrical filter. The electrical filter is disposed between the second photodetector and the data acquisition card. The electrical filter is configured to filter the second electrical signal input by the second photodetector within a specific bandwidth and output the filtered signal to the data acquisition card for acquisition.

[0099] In practical applications, a specific implementation process of the PCCP broken wire monitoring system based on distributed optical fiber sensing in this embodiment is as follows:

[0100] 1) The first laser outputs a wide-spectrum, low-coherence continuous light (1530 nm, linewidth 10 nm) which enters the first optical coupler after passing through an optical isolator. The coupler can adopt a 3*3 optical coupler (splitting ratio of 1:1:1). The optical signal is evenly divided into three parts and output from the second port 2, the fourth port 4, and the sixth port 6 respectively. The light from the second port 2 is lost.

[0101] 2) The optical signal output from the sixth port 6 passes through the first optical filter (1530 nm, bandwidth 10 nm), the wavelength division multiplexer, the first sensing fiber 16, the second delay fiber 17, the second sensing fiber 18, and the second optical filter (1530 nm, bandwidth 10 nm) in sequence, and then is input into the first optical coupler from the fifth port 5. Part of the light is output from the fourth port 4 and passes through the first delay fiber 7, the Faraday rotator 11, and the first delay fiber 7 in sequence to enter the first optical coupler. This signal is called the first interference light signal.

[0102] 3) The optical signal output from the fourth port 4 passes through the first delay fiber 7, has its polarization adjusted by the Faraday rotator 11, and then passes through the first delay fiber 7 again into the first coupler. After being split into three equal parts, the light passes through the fifth port 5 and enters the second optical filter. It then passes through the second sensing fiber 18, the second delay fiber 17, the first sensing fiber 16, the wavelength division multiplexer, and the first optical filter in sequence before returning to the first optical coupler through the sixth port 6. This signal is referred to as the second interference optical signal.

[0103] 4) When the first and second interfering optical signals meet at the third port 3 of the first optical coupler, they interfere with each other due to their identical optical path lengths, forming an interference signal. This interference signal is ultimately received by the first photodetector, converted into an electrical signal, and analyzed and processed by a computer after analog-to-digital conversion by a data acquisition card. The first photodetector has an operating wavelength of 1550.12 nm, a detection bandwidth of 200 MHz, and a gain of 45 dB.

[0104] 5) While the first laser is operating, the second laser continuously outputs narrow-linewidth laser light to the second optical coupler 14. The second laser has a wavelength of 1550 nm, a linewidth of 100 Hz, and an output power of 9.82 dBm. The second optical coupler 14 uses a 1x2 optical coupler (splitting ratio of 90:10), with 90% of the light output as the detection light signal to the acousto-optic modulator and 10% of the light output as the reference light to the third optical coupler 15.

[0105] 6) The data acquisition card outputs a 10 MHz clock signal and a pulse modulation signal to the AOM driver. The AOM multiplies the 10 MHz clock signal to 200 MHz and then chops the pulse modulation signal to output a high-level pulse modulation signal to the AOM.

[0106] 7) The probe light is modulated into pulsed light by an acousto-optic modulator, generating a 200 MHz frequency shift. The peak-to-peak value of the probe light is then amplified to -10.38 dBm by an erbium-doped fiber amplifier 12. The probe light is then input to the first port a of the circulator 13 and output to the wavelength division multiplexer through the second port b of the circulator 13.

[0107] 8) The wavelength division multiplexer operates in the C-band (1530nm-1565nm), with an insertion loss of 0.25dB and an isolation of 50dB. It transmits the pulsed light input from the second port b of the circulator 13 to the sensing fiber and outputs the returned Rayleigh backscattered light (RBS) signal to the second port b of the circulator 13, preventing the light from the first laser source from entering the circulator 13.

[0108] 9) Due to the good coherence of the light source, the Rayleigh backscattered light (RBS) output from the third port c of the circulator 13 beats with the reference light within the third optical coupler 15, ultimately forming an intermediate frequency signal. The third optical coupler 15 is a 2x2 optical coupler (with a 50:50 splitting ratio).

[0109] 10) The intermediate frequency signal is detected by a second photodetector, which uses a balanced detector (BPD) with dual input ports. Its operating wavelength is 800 to 1700 nm and its detection bandwidth is 250 MHz. This balanced detector can suppress common-mode noise (with a suppression ratio of up to 25 dB) and reduce the system noise floor. The electrical signal output by the second photodetector is bandpass filtered by an electrical filter and then output to a data acquisition card for analog-to-digital conversion. It is finally analyzed and processed by a computer.

[0110] The PCCP broken wire monitoring system based on distributed optical fiber sensing has a whole monitoring process including calibration and monitoring, as follows:

[0111] Calibration part:

[0112] 1) Connect the two single-mode sensing fibers on the PCCP to the system. The terminals of the two single-mode fibers are connected via a second delay fiber, ensuring that the midpoint of the interference path falls on the second delay fiber 17. 2) The sensing fibers are spatially calibrated by phase demodulating the intermediate frequency signal collected by the data acquisition card. 3) The starting and ending points of the first sensing fiber 16 and the second sensing fiber 18 are determined, along with the total length of the sensing fibers. 4) In the absence of PCCP breakage, phase demodulate the interference signal collected by the data acquisition card to estimate its short-time energy spectrum, completing the system's background noise analysis of the interference signal. Once the system is calibrated, monitoring for PCCP breakage events can begin.

[0113] Monitoring part:

[0114] 1) After completing position calibration and system noise statistics, the system continuously monitors PCCP wire breakage events by collecting interference signals and performing phase demodulation analysis. The system only performs short-term data buffering on the intermediate frequency signal without performing any analysis or processing.

[0115] 2) The time domain signal is obtained by phase demodulating the interference signal, and its short-time energy spectrum is compared with the short-time energy spectrum of the system background noise. The energy anomaly moments are identified and marked as abnormal signals.

[0116] 3) Perform short-time spectrum analysis on the identified abnormal signal and compare it with the spectrum characteristics in the PCCP broken wire database. If the spectrum characteristics are consistent, it proves that a PCCP broken wire event has occurred at that moment.

[0117] 4) Obtain the PCCP wire break event and perform delayed positioning calculation to calculate the location of the suspected wire break event.

[0118] 5) Obtain the two-way loopback signal captured by the coherent detection type Φ-OTDR system corresponding to the location of the suspected broken wire event at that moment, and perform amplitude and phase demodulation.

[0119] 6) The coherent fading noise is suppressed by a dual-loop fading noise suppression method. After completing the coherent fading noise suppression, the short-time energy spectrum analysis of the demodulated time domain signal is performed to obtain the precise location of the suspected broken wire event.

[0120] 7) Perform short-time spectrum analysis on the time domain signal at the precise location of the suspected broken wire event and compare it with the short-time spectrum characteristics of the interferometer. If the shared characteristic frequencies are consistent, it is determined that a PCCP broken wire event has occurred at that location.

[0121] 8) Record and alarm the time, precise location and signal characteristics of wire breakage events.

[0122] The PCCP broken wire monitoring system based on distributed optical fiber sensing in this embodiment includes a Sagnac interferometer using a wide-spectrum, low-coherence light source and a coherent detection-type Φ-OTDR system using a narrow-linewidth, high-coherence light source. Their optical signals are multiplexed into the same optical fiber via a wavelength division multiplexer to increase transmission capacity and reduce insertion loss. The Faraday rotator 11 in the system eliminates circular and linear birefringence and, by adjusting the delay fiber length, prevents interference signals from canceling each other out, ensuring that the system will not fail to detect and locate PCCP broken wire events. The sensing fiber utilizes a dual-path loopback structure, significantly improving the system's detectability. Sagnac interferometry technology is used to qualitatively analyze PCCP broken wire events and determine the location of suspected broken wire events. The Φ-OTDR technology then accurately locates the event, enabling the system to identify PCCP broken wire events through qualitative analysis and precise positioning.

[0123] Example 2

[0124] In order to implement the system corresponding to the above-mentioned embodiment 1 and obtain corresponding functions and technical effects, a PCCP broken wire monitoring method based on distributed optical fiber sensing is provided below.

[0125] The method is used in the system of the above-mentioned embodiment 1, and the method includes:

[0126] Step 101: Obtain a first electrical signal and a second electrical signal; the first electrical signal is obtained by photoelectric conversion of an interference signal; the first electrical signal is obtained by photoelectric conversion of an intermediate frequency signal; the interference signal is formed by the interference of the first interference light signal and the second interference light signal; the first interference light signal is formed after the first laser passes through the fourth port of the first optical coupler, the first delay fiber 7, the Faraday rotation mirror 11, the first delay fiber 7, the fourth port of the first optical coupler, the fifth port of the first optical coupler, the second sensing fiber 18, the second delay fiber 17, the first sensing fiber 16, the wavelength division multiplexer and the sixth port of the first optical coupler in sequence ... The optical signal is formed when the first laser passes through the sixth port of the first optical coupler, the wavelength division multiplexer, the first sensing fiber 16, the second delay fiber 17, the second sensing fiber 18, the fifth port of the first optical coupler, the fourth port of the first optical coupler, the first delay fiber 7, the Faraday rotation mirror 11, the first delay fiber 7 and the fourth port of the first optical coupler in sequence; the intermediate frequency signal is obtained by coupling the pulse light in the second laser and the backscattered Rayleigh light; the backscattered Rayleigh light is the backlight generated during the transmission process when the detection light in the second laser passes through the acousto-optic modulator, the circulator 13, the wavelength division multiplexer, the first sensing fiber 16, the second delay fiber 17 and the second sensing fiber 18 in sequence.

[0127] Step 102: Perform phase demodulation on the first electrical signal to obtain a first time domain signal.

[0128] Step 103: Perform energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline, and perform delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected wire breakage event when the suspected wire breakage event occurs.

[0129] The process of determining whether a suspected wire breakage event occurs in the PCCP pipeline is as follows:

[0130] Perform energy spectrum analysis on the first time domain signal to determine a short-time energy spectrum of the first time domain signal.

[0131] Compare the short-time energy spectrum of the first time domain signal with the pre-stored short-time energy spectrum of the system background noise, and determine as an abnormal signal the first time domain signal whose difference between the short-time energy spectrum of the first time domain signal and the short-time energy spectrum of the system background noise exceeds the set energy spectrum difference range.

[0132] Performing spectrum analysis on the abnormal signal to obtain spectrum characteristics of the abnormal signal.

[0133] The spectrum characteristics of the abnormal signal are compared with the spectrum characteristics in the pre-stored PCCP broken wire database. If the spectrum characteristics of the abnormal signal are consistent with the spectrum characteristics in the PCCP broken wire database, it is determined that a suspected broken wire event has occurred in the PCCP pipeline.

[0134] Step 104: Perform amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal.

[0135] Step 105: Perform energy spectrum analysis and frequency spectrum analysis on the second time domain signal to complete the screening of the preliminary position of the suspected wire breakage event, determine the final position of the suspected wire breakage event, and determine whether the suspected wire breakage event is a real wire breakage event.

[0136] A fading noise suppression method is used to suppress coherent fading noise on the second time domain signal to obtain a suppressed time domain signal.

[0137] Perform energy spectrum analysis on the suppressed time domain signal to determine the final location of the suspected broken wire event.

[0138] A spectrum analysis is performed on the time domain signal at the final position of the suspected wire breakage event. If the spectrum characteristics of the time domain signal at the final position of the suspected wire breakage event are consistent with the spectrum characteristics of the first time domain signal, the suspected wire breakage event is determined to be a true wire breakage event.

[0139] A more specific implementation process of the PCCP broken wire monitoring method based on distributed optical fiber sensing is described below.

[0140] First, perform calibration, see Figure 3 , the calibration process is:

[0141] 1) Connect the two single-mode sensing fibers on the PCCP to the system, and connect the terminals of the two single-mode fibers through a second delay fiber to ensure that the midpoint of the interference path falls on the second delay fiber 17; 2) Phase demodulate the intermediate frequency signal collected by the data acquisition card to calibrate the spatial position of the sensing fiber part; 3) Obtain the starting and ending points of the first sensing fiber 16 and the second sensing fiber 18, and the total length of the sensing fiber; 4) In the absence of PCCP breakage, phase demodulate the interference signal collected by the data acquisition card to obtain its short-time energy spectrum estimation, completing the system's background noise statistics for the interference signal.

[0142] After completing the system calibration, you can start monitoring the PCCP broken wire event. Figure 4 , the monitoring process is:

[0143] 1) When a PCCP wire break occurs, the transient elastic wave signal generated is primarily concentrated in the high-frequency range of 10 to 20 kHz. Therefore, after completing position calibration and system noise statistics, the system continuously monitors the characteristics of the PCCP wire break by collecting interference signals and performing phase demodulation analysis. The system only performs short-term data buffering on the intermediate frequency signal without performing any analysis or processing.

[0144] 2) By demodulating the phase of the interference signal to obtain its time domain signal, its short-time energy spectrum is compared with the short-time energy spectrum of the system background noise, and the energy abnormal moment is identified and marked as an abnormal signal; the comparison effect is as follows Figure 5 shown.

[0145] 3) Perform short-time spectrum analysis on the identified abnormal signal and compare it with the spectrum characteristics in the PCCP broken wire database. If the spectrum characteristics are consistent, it proves that a PCCP broken wire event has occurred at that moment.

[0146] 4) Obtain the PCCP wire break event and perform delayed positioning calculation to calculate the location of the suspected wire break event.

[0147] Delay positioning calculation method:

[0148] The Sagnac interferometer in the system includes two paths for interfering optical signals. The signal light from these two paths passes through the PCCP broken filament event location at different times, but the total path length is equal, allowing interference to occur and be detected by the first photodetector. The output power of the first photodetector can be expressed as:

[0149]

[0150] Where P(t) is the output power of the first photodetector, A is a constant coefficient related to the optical transmission loss, I0 is the initial intensity of the two signal lights, is the optical phase value generated at a certain moment, and θ represents the initial phase of the entire system.

[0151] Since the PCCP wire breakage event is a broadband disturbance event with multiple vibration frequencies, The expression is:

[0152]

[0153] Where, is a constant related to the PCCP broken wire strength, m i is the amplitude of a certain vibration frequency, w i It is a certain vibration frequency.

[0154] When it is stationary on the interference path, the phase difference between the two optical signals is 0. When a PCCP wire break event occurs, it will change. The positions where the wire break events occur simultaneously are at the first sensing optical fiber 16 between port 8 and port 9, and at the second sensing optical fiber 18 between port 9 and port 10. Therefore, the following assumptions can be made: ① The propagation time of the optical signal between 8 and 10 is T; ② The propagation time of the optical signal between 3 and 8 is τ2; ③ The propagation time of the optical signal between the first port 1 and port 10 is τ1; ④ The propagation time of the optical signal between port 8 and the PCCP wire break event is t1; ⑤ The propagation time of the optical signal between port 10 and the PCCP wire break event is t1.

[0155] Since the total length of the sensing optical fibers (the first sensing optical fiber 16, the second delay optical fiber 17, and the second sensing optical fiber 18) is known, the time T is a known quantity, and its expression is:

[0156]

[0157] where n is the refractive index of the optical fiber, L is the length of the sensing optical fiber, and c is the speed of light.

[0158] The optical fiber lengths between the third port 3 - port 8 and the first port 1 - port 10 are constant. τ1 and τ2 are constants, and due to the introduction of the first delay optical fiber 7 for adjustment, τ1 ≠ τ2; and due to the introduction of the second delay optical fiber 17, 2t1 < T, and the expression of t1 is:

[0159] <00003…

[0160] l is the distance of the PCCP wire break event from the starting end of the sensing optical fiber 1.

[0161] Since both optical signals have experienced two-phase modulations, for path A at the two moments of t + τ1 + t1 and t + τ1 + T - t1, and for path B at the two moments of t + τ2 + t1 and t + τ2 + T - t1, then there is:

[0162]

[0163] represents the phase change amount, and after simplification, it can be obtained:

[0164]

[0165] From formula 4, it can be seen that when occurs, will be constantly 0, and in the frequency domain, it will show a corresponding ω i The perturbation frequency intensity will be significantly less than the intensity corresponding to the surrounding frequencies, and a "notch point" will appear. The notch point frequency is the PCCP wire break event frequency.

[0166] Since τ1≠τ2, only A notch point will be generated when

[0167]

[0168] Then a series of characteristic frequencies can be obtained:

[0169]

[0170] Substituting formula (3) and formula (4), we can get:

[0171]

[0172] Therefore, the computer only needs to perform a short-time Fourier transform on the demodulated time domain waveform signal of the interference signal to obtain a short-time frequency domain spectrum, and then find the characteristic frequency generated by the PCCP broken wire event, thereby realizing the suspected location of the PCCP broken wire.

[0173] 5) Obtain the two-way loopback signal captured by the coherent detection type Φ-OTDR system corresponding to the location of the suspected broken wire event at that moment, and perform amplitude and phase demodulation.

[0174] 6) The coherent fading noise is suppressed by the dual-path loop fading noise suppression method. The implementation method and the effect are compared. Figure 6 and Figure 7 As shown. Among them, Figure 7 Part (a) shows the time domain signal of the first sensing fiber, Figure 7 Part (b) shows the time domain signal of the second sensing fiber, Figure 7 Part (c) shows the amplitude signal-to-noise ratio, Figure 7 Part (d) shows the optimal result of dual-path loopback fading noise suppression. Figure 7 Part (e) shows the time domain waveform after dual-path loopback fading noise suppression. After completing coherent fading noise suppression, the demodulated time domain signal is subjected to short-time energy spectrum analysis to obtain the precise location of the suspected broken wire event.

[0175] The dual-path loopback fading noise suppression method is:

[0176] ① Taking the spatial position relationship of the first sensing optical fiber 16 as a standard, the spatial data of the second sensing optical fiber 18 is folded so that the starting point and the end point of the first sensing optical fiber 16 and the second sensing optical fiber 18 are spatially aligned.

[0177] ② The intermediate frequency signal collected by the coherent detection type Φ-OTDR system within a certain width before and after the suspected broken wire event is intercepted and IQ demodulated to obtain the amplitude and phase change information of the first sensing optical fiber 16 and the second sensing optical fiber 18 within the spatial range.

[0178] ③ Using the amplitude signal-to-noise ratio as the optimization criterion, the demodulated phase information is amplitude optimized or weighted averaged to suppress the fading noise.

[0179] 7) Perform short-time spectrum analysis on the time domain signal at the precise location of the suspected broken wire event and compare it with the short-time spectrum characteristics of the interferometer. If the shared characteristic frequencies are consistent, it is determined that a PCCP broken wire event has occurred at that location.

[0180] 8) Record and alarm the time, precise location and signal characteristics of wire breakage events.

[0181] All the above embodiments have the following advantages:

[0182] (1) The first laser in the Sagnac interferometer uses a wide-spectrum low-coherence continuous light, and the second laser in the Φ-OTDR system uses a narrow-linewidth high-coherence laser. The two different wavelengths of optical signals are multiplexed into the same optical fiber through a wavelength division multiplexer, which improves the transmission capacity of the sensor and reduces the insertion loss.

[0183] (2) The Faraday rotator mirror 11 structure can effectively eliminate the circular birefringence and linear birefringence phenomena in the Sagnac interferometer and avoid the influence of polarization fading noise.

[0184] (3) By adjusting the length of the first delay fiber 7, the sagnac interferometer part senses the PCCP wire break event in an asymmetric manner, avoiding the two interference signals being phase-modulated by the same PCCP wire break event at the same time without generating a phase difference, and the signals cancel each other out, resulting in a non-interference signal output.

[0185] (4) The sensing fiber section adopts a dual-path loopback structure. The first sensing fiber 16 and the second sensing fiber 18 are of the same length and are laid out on the same route. The same PCCP break event will be detected at two symmetrical locations on the sensing fiber, forming complementary signals. For the Sagnac interferometer section, the PCCP break event signal strength will be enhanced, improving the system's detection capability. For the coherent detection Φ-OTDR section, two independent detection signals can be obtained at the same PCCP location, providing a data source for suppressing coherent fading noise.

[0186] (5) By adjusting the length of the second delay fiber 17, the midpoint of the interference path of the Sagnac interferometer part falls on the second delay fiber 17, rather than on the first sensing fiber 16 or the second sensing fiber 18, thereby avoiding the failure of detection and positioning of the PCCP broken wire event.

[0187] (6) By integrating Sagnac interferometry and Φ-OTDR technology, the Sagnac interferometer can be used to qualitatively analyze PCCP broken wire events and give the suspected broken wire event location; the suspected broken wire event location can be accurately located using Φ-OTDR technology; this strategy can greatly reduce the computing pressure of the computer (PC) while ensuring the accuracy of PCCP broken wire event identification and high positioning accuracy.

[0188] (7) The coherent detection Φ-OTDR system can suppress coherent fading noise by optimizing the dual-path loopback signal, thereby improving the system signal-to-noise ratio and positioning accuracy.

[0189] It can be seen that the present invention combines wavelength division multiplexing technology, Faraday rotator 11, increased delay optical fiber structure and dual-path loop structure to achieve rapid capture and recognition of transient broadband signals, and has the advantages of high recognition accuracy, precise positioning and low false alarm rate.

[0190] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. The methods disclosed in the embodiments are described briefly because they correspond to the systems disclosed in the embodiments. For relevant parts, refer to the description of the systems.

[0191] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A PCCP broken wire monitoring system based on distributed optical fiber sensing, characterized in that: Used to detect broken wires in PCCP pipelines; The PCCP pipeline includes: a pipeline body and an optical cable arranged on the pipeline body; the optical cable includes at least: a first sensing optical fiber and a second sensing optical fiber; The PCCP broken wire monitoring system includes: a Sagnac interferometer, a Φ-OTDR system, a dual-path loopback system, and a signal processing system; The Sagnac interferometer includes: a first laser, a first optical coupler, a first delay fiber, a Faraday rotator mirror, and a first photodetector; the Φ-OTDR system includes: a second laser, a second optical coupler, an acousto-optic modulator, a circulator, a third optical coupler, and a second photodetector; the two-way loopback system includes: a wavelength division multiplexer and a second delay fiber; The first laser is used to output a first laser; the first port of the first optical coupler is used to receive the first laser; the fourth port of the first optical coupler is used to transmit the first laser to the first delay fiber; the first delay fiber is used to delay the first laser to obtain a first delayed light; the Faraday rotator is used to rotate the polarization state of the first delayed light to obtain a first state-converted light, and return the first state-converted light to the first delay fiber; the first delay fiber is also used to delay the first state-converted light and return the obtained second delayed light to the first optical coupler; the sixth port of the first optical coupler is used to transmit the first laser to the wavelength division multiplexer; The second laser is used to output a second laser, the spectral width of the first laser is greater than the spectral width of the second laser, and the correlation of the first laser is less than the correlation of the second laser; the second optical coupler is used to split the second laser into two paths, one path is a probe light, and the other path is a reference light; the acousto-optic modulator is used to modulate the probe light into a pulse light with a set frequency shift; the first port of the circulator is used to receive the pulse light, and the second port of the circulator is used to transmit the pulse light to the wavelength division multiplexer; One end of the wavelength division multiplexer is connected to one end of the first sensing fiber, the other end of the first sensing fiber is connected to one end of the second delay fiber, the other end of the second delay fiber is connected to one end of the second sensing fiber, and the other end of the second sensing fiber is connected to the fifth port of the first optical coupler; the wavelength division multiplexer is used to transmit the first laser to the first sensing fiber, and the first laser generates a third delayed light after being transmitted through the first sensing fiber, the second delay fiber, and the second sensing fiber in sequence; the fifth port of the first optical coupler is used to receive the third delayed light; the wavelength division multiplexer is also used to transmit the pulsed light to the first sensing fiber; the pulsed light passes through the first sensing fiber, the second delay fiber, and the second sensing fiber in sequence, and generates back Rayleigh scattered light during the transmission process; the back Rayleigh scattered light passes through the wavelength division multiplexer and the second port of the circulator in sequence, and then enters the third optical coupler through the third port of the circulator; The fifth port of the first optical coupler is further used to transmit the second delayed light to the second sensing fiber, and the second delayed light generates a first interference light signal after being transmitted through the second sensing fiber, the second delay fiber, and the first sensing fiber in sequence; the sixth port of the first optical coupler is further used to receive the first interference light signal; The fourth port of the first optical coupler is further used to transmit the third delayed light to the first delay optical fiber; the first delay optical fiber is further used to delay the third delayed light to obtain a fourth delayed light; the Faraday rotator is used to rotate the polarization state of the fourth delayed light to obtain a second state-converted light, and return the second state-converted light to the first delay optical fiber; the first delay optical fiber is further used to delay the second state-converted light to obtain a second interference light signal; the fourth port of the first optical coupler is further used to receive the second interference light signal; the first interference light signal and the second interference light signal interfere with each other at the third port of the first optical coupler to form an interference signal; The first photodetector is connected to the third port of the first optical coupler, and is configured to receive the interference signal and perform photoelectric conversion on the interference signal to obtain a first electrical signal; The third optical coupler is used to couple the reference light and the backscattered Rayleigh light to form an intermediate frequency signal; the second photodetector is connected to the third optical coupler, and is used to receive the intermediate frequency signal and perform photoelectric conversion on the intermediate frequency signal to obtain a second electrical signal; The signal processing system is connected to the first photodetector and the second photodetector respectively; The signal processing system is used to: performing phase demodulation on the first electrical signal to obtain a first time domain signal; performing energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline, and performing time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected wire breakage event when the suspected wire breakage event occurs; performing amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal; Energy spectrum analysis and frequency spectrum analysis are performed on the second time domain signal to complete the screening of the preliminary position of the suspected wire breakage event, determine the final position of the suspected wire breakage event, and determine whether the suspected wire breakage event is a real wire breakage event.

2. A PCCP broken wire monitoring system based on distributed optical fiber sensing according to claim 1, characterized in that: The Sagnac interferometer further includes: a first optical filter and a second optical filter; The first optical filter is arranged between the sixth port of the first optical coupler and the wavelength division multiplexer; and the second optical filter is arranged between the second sensing fiber and the fifth port of the first optical coupler.

3. The PCCP broken wire monitoring system based on distributed optical fiber sensing according to claim 1, characterized in that: The Φ-OTDR system further includes: an erbium-doped fiber amplifier; The erbium-doped fiber amplifier is arranged between the acousto-optic modulator and the circulator.

4. The PCCP broken wire monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The Sagnac interferometer further includes: an optical isolator; The optical isolator is disposed between the first laser and the first port of the first optical coupler.

5. The PCCP broken wire monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The signal processing system specifically includes: a data acquisition card and a computer; The data acquisition card is connected to the first photoelectric detector, the second photoelectric detector and the computer respectively; The data acquisition card is used to acquire the first electrical signal and the second electrical signal; The computer comprises: A first demodulation module, configured to perform phase demodulation on the first electrical signal to obtain a first time domain signal; a preliminary broken wire location analysis module, configured to perform energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected broken wire event has occurred in the PCCP pipeline, and to perform time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected broken wire event when the suspected broken wire event occurs; a second demodulation module, configured to perform amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal; The broken wire position final analysis module is used to perform energy spectrum analysis and frequency spectrum analysis on the second time domain signal to complete the screening of the preliminary position of the suspected broken wire event, determine the final position of the suspected broken wire event, and determine whether the suspected broken wire event is a real broken wire event.

6. The PCCP broken wire monitoring system based on distributed optical fiber sensing according to claim 5, characterized in that: The signal processing system further includes: an acousto-optic modulation driver; The acousto-optic modulation driver is connected to the data acquisition card and the acousto-optic modulator respectively; the data acquisition card is also used to receive the clock carrier signal and the pulse trigger modulation signal sent by the computer; the acousto-optic modulation driver is used to output a high-level pulse modulation signal to the acousto-optic modulator according to the clock carrier signal and the pulse trigger modulation signal.

7. The PCCP broken wire monitoring system based on distributed optical fiber sensing according to claim 5, characterized in that: The signal processing system further includes: an electrical filter; The electrical filter is arranged between the second photodetector and the data acquisition card.

8. A PCCP broken wire monitoring method based on distributed optical fiber sensing, characterized in that: A PCCP broken wire monitoring system according to any one of claims 1 to 7; the method comprising: Obtain a first electrical signal and a second electrical signal; the first electrical signal is obtained by photoelectric conversion of an interference signal; the second electrical signal is obtained by photoelectric conversion of an intermediate frequency signal; the interference signal is formed by the interference of the first interference light signal and the second interference light signal; the first interference light signal is formed after the first laser passes through the fourth port of the first optical coupler, the first delay fiber, the Faraday rotation mirror, the first delay fiber, the fourth port of the first optical coupler, the fifth port of the first optical coupler, the second sensing fiber, the second delay fiber, the first sensing fiber, the wavelength division multiplexer and the sixth port of the first optical coupler in sequence; the second interference light signal is formed after the first laser passes through the fourth port of the first optical coupler, the first delay fiber, the Faraday rotation mirror, the first delay fiber, the fourth port of the first optical coupler, the fifth port of the first optical coupler, the second sensing fiber, the second delay fiber, the first sensing fiber, the wavelength division multiplexer and the sixth port of the first optical coupler in sequence; The light-related signal is formed when the first laser passes through the sixth port of the first optical coupler, the wavelength division multiplexer, the first sensing fiber, the second delay fiber, the second sensing fiber, the fifth port of the first optical coupler, the fourth port of the first optical coupler, the first delay fiber, the Faraday rotator, the first delay fiber, and the fourth port of the first optical coupler in sequence; the intermediate frequency signal is obtained by coupling the reference light and the backscattered Rayleigh light in the second laser; and the backscattered Rayleigh light is the backlight generated during the transmission process when the probe light in the second laser passes through the acousto-optic modulator, the circulator, the wavelength division multiplexer, the first sensing fiber, the second delay fiber, and the second sensing fiber in sequence; performing phase demodulation on the first electrical signal to obtain a first time domain signal; performing energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline, and performing time delay positioning calculation based on the first time domain signal to determine a preliminary location of the suspected wire breakage event when the suspected wire breakage event occurs; performing amplitude and phase demodulation on the second electrical signal to obtain a second time domain signal; Energy spectrum analysis and frequency spectrum analysis are performed on the second time domain signal to complete the screening of the preliminary position of the suspected wire breakage event, determine the final position of the suspected wire breakage event, and determine whether the suspected wire breakage event is a real wire breakage event.

9. The PCCP broken wire monitoring method based on distributed optical fiber sensing according to claim 8, characterized in that: Performing energy spectrum analysis and frequency spectrum analysis on the first time domain signal to determine whether a suspected wire breakage event occurs in the PCCP pipeline specifically includes: performing energy spectrum analysis on the first time domain signal to determine a short-time energy spectrum of the first time domain signal; comparing the short-time energy spectrum of the first time domain signal with a pre-stored short-time energy spectrum of the system background noise, and determining as an abnormal signal a first time domain signal whose difference between the short-time energy spectrum of the first time domain signal and the short-time energy spectrum of the system background noise exceeds a set energy spectrum difference range; Performing spectrum analysis on the abnormal signal to obtain spectrum characteristics of the abnormal signal; The spectrum characteristics of the abnormal signal are compared with the spectrum characteristics in the pre-stored PCCP broken wire database. If the spectrum characteristics of the abnormal signal are consistent with the spectrum characteristics in the PCCP broken wire database, it is determined that a suspected broken wire event has occurred in the PCCP pipeline.

10. The PCCP broken wire monitoring method based on distributed optical fiber sensing according to claim 8, characterized in that: Performing energy spectrum analysis and frequency spectrum analysis on the second time domain signal to complete the screening of the preliminary location of the suspected broken wire event, determine the final location of the suspected broken wire event, and determine whether the suspected broken wire event is a true broken wire event, specifically including: Performing coherent fading noise suppression on the second time domain signal using a fading noise suppression method to obtain a suppressed time domain signal; Perform energy spectrum analysis on the suppressed time domain signal to determine the final location of the suspected broken wire event; A spectrum analysis is performed on the time domain signal at the final position of the suspected wire breakage event. If the spectrum characteristics of the time domain signal at the final position of the suspected wire breakage event are consistent with the spectrum characteristics of the first time domain signal, the suspected wire breakage event is determined to be a true wire breakage event.

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