PCCP broken wire monitoring and positioning system and method based on double-fiber same-point locking

Abstract

The invention discloses a PCCP broken wire monitoring and positioning system and method based on double-fiber same-point locking. The system comprises a laser, an optical isolator, two sensing optical fibers, two delay optical fibers, two optical couplers, a polarization controller, three photoelectric detectors, a data acquisition card and an upper computer. According to the method, the signal propagation time delay of the same spatial position on the two tightly attached single-mode sensing optical fibers is utilized to accurately calculate the occurrence position of the PCCP wire breaking event in an optical path, and the calibration information of the spatial position of the sensing optical fibers is combined, so that high precision and high sensitivity of positioning of the PCCP wire breaking event are ensured, and the positioning accuracy of the PCCP wire breaking event is improved. Meanwhile, precise capture and rapid identification of high-frequency transient signals are achieved in combination with an interference structure, the problems that in the existing interferometer technology, when PCCP broken wire monitoring is conducted, the positioning precision is low, and a detection dead zone exists are solved, and the advantages of being high in positioning precision, large in frequency measurement range, high in identification capacity, free of the detection dead zone and the like are achieved.

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 and positioning system and method based on dual-fiber same-point locking. Background Art

[0002] Prestressed Concrete Cylinder Pipe (PCCP) is a high-performance pipe widely used in water conservancy projects, urban water supply, drainage systems and industrial water supply. PCCP pipes combine the compressive properties of concrete and the tensile properties of steel. They have the advantages of high strength, good durability and strong impermeability. Therefore, they are widely used in long-distance water supply projects. Although its multi-layer composite structure (steel cylinder + prestressed steel wire + concrete) gives it high strength characteristics, the problem of internal steel wire breakage (broken wire) is becoming increasingly prominent. A single broken wire can cause a chain breakage of adjacent steel wires, resulting in cracking of the pipe concrete or even bursting of the pipe, causing an average daily leakage of 10,000 tons of water resources, which has become a major hidden danger threatening water supply safety.

[0003] PCCP wire breakage is concealed (deeply buried underground) and sudden (instantaneous breakage after stress accumulation), and its hazards present multi-dimensional characteristics. At the moment when the PCCP wire breaks, the short-term elastic stress wave it triggers presents a high-frequency characteristic of 15 to 25 kHz in the frequency domain, and the duration of the signal is in the order of tens of milliseconds, that is, it has a high-frequency instantaneous characteristic.

[0004] In the existing technology, the traditional PCCP broken wire detection methods mainly include: manual tapping method, electromagnetic induction method (ECT), acoustic emission technology (AE) and internal video detection (CCTV) technology. Among them, the manual tapping method has a high error rate and a long detection time, ECT is easily interfered by surrounding metal structures and cannot be monitored in real time, AE has serious signal attenuation and a high false alarm rate, and CCTV has limited applicability and cannot quantify damage.

[0005] Interferometer is a high-precision measuring device based on the interference phenomenon of light. With its high sensitivity, wide-band response and anti-interference ability, interferometer has become one of the ideal technical means for monitoring PCCP broken wires. For example, the frequency measurement range of Sagnac Interferometer (SI) is usually much larger than the kHz level. By capturing high-frequency transient elastic waves and analyzing their characteristics, it can achieve early warning of broken wires and risk assessment, and can achieve rough positioning of vibration events, significantly improving the safety and operation and maintenance efficiency of water supply networks. However, although interferometer has many advantages in the application of PCCP broken wire detection, its positioning accuracy is very low when performing long-distance detection, which cannot meet the high positioning accuracy requirements of the detection system (accuracy ≤ 2m), and there are also many problems such as inaccurate positioning. Summary of the invention

[0006] In view of the problems of low positioning accuracy and detection dead zones existing in the existing interferometer technology when monitoring the broken wires of PCCP, the present invention proposes a PCCP broken wire monitoring and positioning system and method based on double-fiber same-point locking. Combining with the interferometer structure, it realizes the precise capture and rapid identification of high-frequency transient signals.

[0007] The present invention adopts the following technical solutions: A PCCP broken wire monitoring and positioning system based on double-fiber same-point locking, comprising: a laser, an optical isolator, a first sensing optical fiber, a first delay optical fiber, a second sensing optical fiber, a first optical coupler, a second delay optical fiber, a polarization controller, a second optical coupler, three photodetectors, a data acquisition card, and a host computer.

[0008] The laser is used to output a continuous optical signal to the optical isolator, and the optical isolator transmits the continuous optical signal to the first sensing optical fiber and enters the second sensing optical fiber after passing through the first delay optical fiber;

[0009] The optical signal output by the second sensing optical fiber is divided into two optical signals A and B of equal intensity after passing through the first optical coupler. The optical signal of path A is output to the second optical coupler through the second delay optical fiber, and the optical signal of path B is output to the second optical coupler through the polarization controller;

[0010] The second optical coupler outputs three interference signals, which respectively enter the three photodetectors, are converted into electrical signals, and then are transmitted to the host computer for signal processing after analog-to-digital conversion and acquisition by the data acquisition card.

[0011] Preferably, the optical signals of paths A and B enter the second optical coupler through two optical fibers of different lengths, and different propagation times are formed by the unequal-length optical paths, and interference occurs in the second optical coupler.

[0012] Preferably, the second optical coupler is a 3×3 optical coupler with a splitting ratio of 33:33:33. The three output ports are respectively connected to the input ends of the first photodetector, the second photodetector, and the third photodetector. The interference signals formed by coupling the optical signals of paths A and B are respectively output through the three output ports by the three-port phase discrimination structure.

[0013] Preferably, both the first sensing optical fiber and the second sensing optical fiber are single-mode optical fibers, adopting a double-fiber same-point structure and connected by the first delay optical fiber; the distance between the first sensing optical fiber and the second sensing optical fiber is less than the wavelength of the broken wire signal to be measured, so that the two vibration signals received by the first and second sensing optical fibers at the same spatial position are the same when a broken wire event occurs.

[0014] Preferably, the polarization controller is used to adjust the polarization state to make the polarization states of the optical signals of paths A and B match, and stable interference signal fringes are generated through the second optical coupler.

[0015] The technical solution of the present invention also provides: a method for monitoring and positioning broken wires of PCCP based on double-fiber same-point locking. Any of the above PCCP broken wire monitoring and positioning systems is used to monitor PCCP broken wire events and determine the location where the broken wire occurs. The specific steps are as follows:

[0016] Step 1, calibration step: used to define the fiber laying method, calculate the system background noise, and make the fiber length and spatial position correspond and match;

[0017] Step 2, monitoring step: used to monitor the process of PCCP broken wire signals, collect and demodulate the phase change caused by the change in the refractive index or length of the fiber due to the broken wire signal, and restore the real vibration signal;

[0018] Step 3, positioning step: use the double-fiber same-point locking method, combined with the calibration information, to determine the location where the broken wire signal occurs.

[0019] Preferably, the calibration step is specifically as follows:

[0020] Step 1.1: Closely attach the first sensing fiber and the second sensing fiber on the PCCP pipe wall. One end of the first sensing fiber and the second sensing fiber is connected through the first delay fiber;

[0021] Step 1.2: Demodulate the phase of the interference signal collected by the data acquisition card, and calibrate the spatial positions of the first sensing fiber and the second sensing fiber, so that the spatial position and the fiber length correspond and match;

[0022] Step 1.3: Obtain the positions of both ends of the first sensing fiber and the second sensing fiber, and determine the total length of the first sensing fiber and the second sensing fiber;

[0023] Step 1.4: Calculate the system background noise in the case of no PCCP broken wire event.

[0024] Preferably, the monitoring step is specifically as follows:

[0025] Step 2.1: When a PCCP broken wire event occurs, the vibration causes a change in the refractive index or length of the fiber, resulting in phase modulation. The phase change is:

[0026] φ(t) = βsin(ωt)

[0027] Where β is the phase modulation amplitude and the vibration frequency is ω;

[0028] Step 2.2: When the vibration signal reaches the first optical coupler, it is divided into two optical signals, A and B. The A optical signal passes through the second delay fiber and reaches the second optical coupler; the B optical signal directly reaches the second optical coupler through the polarization controller;

[0029] The phase of the optical signal on path A is φ(t), and the phase of the optical signal on path B is φ(t - τ):

[0030]

[0031] Where n is the refractive index of the optical fiber, R is the length of the second delay optical fiber, and C is the speed of light in a vacuum.

[0032] The phase difference between the optical signals on paths A and B is Δφ(t):

[0033]

[0034] Step 2.3: The optical signals on paths A and B interfere at the second optical coupler, and the interference light intensities received by the first photodetector, the second photodetector, and the third photodetector are I1(t), I2(t), and I3(t) respectively:

[0035] I1(t) = D1 + A1 cos[Δφ(t)]

[0036]

[0037] Where D1 is the DC component of the interference light intensity I1, A1 is the AC component of the interference light intensity I1; D2 is the DC component of the interference light intensity I2, A2 is the AC component of the interference light intensity I2; D3 is the DC component of the interference light intensity I3, A3 is the AC component of the interference light intensity I3;

[0038] Step 2.4: The three interference optical signals are received by three photodetectors and then transmitted to a data acquisition card, and the data acquisition card transmits them to a host computer for signal demodulation to restore the vibration signal.

[0039] Preferably, the positioning step is as follows:

[0040] Step 3.1: When a PCCP wire break event occurs, the first sensing optical fiber and the second sensing optical fiber simultaneously receive high-frequency vibration signals caused by the wire break at the same spatial position;

[0041] Step 3.2: Restore the high-frequency vibration signals at the same spatial position, draw the time-domain diagrams of the two signals, determine the time delay Δt between the two high-frequency vibration signals at the same spatial position, and calculate the spacing L between the two high-frequency vibration signals on the optical path:

[0042]

[0043] Where υ is the speed of light in the optical fiber;

[0044] Step 3.3: Determine the length l from the same spatial position to the first delay optical fiber according to the spacing L and the length S of the first delay optical fiber.

[0045] L = S + 2l

[0046] Wherein, the length S of the first delay optical fiber is a fixed value;

[0047] Step 3.4. Determine the occurrence position of the PCCP wire break event according to the calibration information.

[0048] Furthermore, the length S of the first delay optical fiber is related to the frequency of the PCCP wire break event. The length S of the first delay optical fiber determines the time delay length between the two high-frequency vibration signals received by the first sensing optical fiber and the second sensing optical fiber at the same spatial position. The time delay length is used to accurately calculate the time delay Δt according to the time domain diagrams of the two signals.

[0049] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects:

[0050] 1. By adopting the PCCP wire break monitoring and positioning method of double-fiber same-point locking, the present invention accurately calculates the occurrence position of the wire break event in the optical path by using the signal propagation time delay at the same spatial position on two closely attached single-mode sensing optical fibers, and combines the calibration information of the spatial position of the sensing optical fiber to ensure high precision and high sensitivity in the positioning of the PCCP wire break event, having advantages such as a large frequency measurement range, strong recognition ability, and no detection dead zone.

[0051] 2. The PCCP wire break monitoring and positioning system of the present invention adopts a three-port phase discrimination structure, which can effectively suppress the common-mode noise, complete the unambiguous phase demodulation, and achieve a linear response in the full dynamic range.

[0052] 3. The PCCP wire break monitoring and positioning system of the present invention accesses a polarization controller in the optical path to adjust the polarization state, so that the polarization states of the two optical signals always remain matched, which can effectively avoid the negative impacts caused by polarization fading noise and contrast reduction, and maximize the visibility of the high-frequency transient vibration signal to be measured, thereby improving the detection sensitivity and stability. Description of the Drawings

[0053] Figure 1 is the structure diagram of the PCCP wire break monitoring and positioning system of the present invention;

[0054] Figure 2 is the calibration flow chart of the PCCP wire break monitoring and positioning method of the present invention;

[0055] Figure 3 is the installation schematic diagram of the PCCP wire break monitoring and positioning system of the present invention;

[0056] Figure 4 is the flow chart of the PCCP wire break monitoring and positioning method of the present invention;

[0057] Figure 5 It is a comparison diagram of the monitored PCCP wire break signal and background noise of the present invention;

[0058] Figure 6 It is a schematic diagram of calculating the time delay by the double-fiber same-point locking method of the present invention. Specific embodiments

[0059] In order to make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the application will be further elaborated in detail below with reference to the accompanying drawings. The described embodiments are only a part of the embodiments involved in the present invention. All non-innovative embodiments made by other researchers in the field based on this embodiment fall within the protection scope of the present invention. At the same time, for the step numbers in the embodiments of the present invention, they are only set for the convenience of elaboration and explanation, and no limitation is imposed on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0060] Embodiment 1:

[0061] In an embodiment of the present invention, a PCCP wire break monitoring and positioning system based on double-fiber same-point locking has a structural diagram as Figure 1 shown, including: a laser, an optical isolator, a sensing optical fiber, a first delay optical fiber, a first optical coupler, a second delay optical fiber, a polarization controller, a second optical coupler, a first photodetector, a second photodetector, a third photodetector, a data acquisition card (DAQ) and a host computer (PC).

[0062] Specifically, in this embodiment, the functions and selection strategies of each device in the system are as follows:

[0063] Laser: It is used to output continuous light to the optical isolator. When selecting, a light source with a wide spectrum (>10nm), low coherence, and stable power (<1dB) is selected.

[0064] Optical isolator: It is used to transmit continuous light to the sensing optical fiber. At the same time, it has a unidirectional transmission characteristic, which can prevent the back-propagating light generated due to various reasons from having an adverse effect on the output power stability of the first laser. When selecting, a polarization-independent optical isolator with an isolation degree >30dB should be selected, and the selected optical isolator needs to cover the output wavelength band of the laser. The optical isolator receives the continuous light output by the laser from port 1 and outputs it to the first sensing optical fiber from port 2.

[0065] Sensing optical fiber: It consists of a first sensing optical fiber connecting the optical isolator and the first delay optical fiber, and a second sensing optical fiber connecting the first delay optical fiber and the first optical coupler, which are respectively used to transmit the optical signals input from port 2 and port 4. When selecting, a common single-mode optical fiber is selected.

[0066] The first delay optical fiber: It is used to transmit the optical signal between the first sensing optical fiber and the second sensing optical fiber. Since it takes time for the optical signal to pass through this position, a certain time delay will be generated. When selecting the type, an ordinary single-mode optical fiber is chosen. The optical signal is input from port 3 through the first sensing optical fiber into the first delay optical fiber and output from port 4 to the second delay optical fiber.

[0067] The first optical coupler: After the optical signal output from the second sensing optical fiber passes through port 5, it is input from port 6 into the first optical coupler. After passing through the first optical coupler, it is output from ports 7 and 8 respectively. When selecting the type, a 1×2 optical coupler with a splitting ratio of 50:50 is chosen.

[0068] The second delay optical fiber: It is used to receive the optical signal output from port 7 of the first optical coupler and then transmit it to port 9 of the second optical coupler. Since it takes time for the optical signal to pass through this position, a certain time delay will be generated. When selecting the type, an ordinary single-mode optical fiber can be chosen.

[0069] The polarization controller: It receives the optical signal output from port 8 of the first optical coupler and then transmits it to port 10 of the second optical coupler. It is used to ensure the consistency of the polarization state of the light and ensure the generation of stable interference fringes. When selecting the type, a broadband polarization controller that matches the working wavelength of the laser should be chosen;

[0070] The second optical coupler: It is used to receive the optical signal transmitted to port 9 by the second delay optical fiber and the optical signal transmitted to port 10 by the polarization controller. After coupling the two paths of light, it is output from ports 11, 12, and 13 of the second optical coupler to the first, second, and third photodetectors respectively. When selecting the type, a 3×3 optical coupler with a splitting ratio of 33:33:33 should be chosen.

[0071] The first photodetector: It is used to receive the optical signal output from port 11 of the second optical coupler, convert it into an electrical signal and transmit it to the data acquisition card. When selecting the type, a photodetector that is strictly matched with the light source wavelength and has high sensitivity should be chosen. At the same time, its bandwidth should be greater than 10 MHz and the response time should be less than 10 ns to avoid phase distortion.

[0072] The second photodetector: It is used to receive the optical signal output from port 12 of the second optical coupler, convert it into an electrical signal and transmit it to the data acquisition card. When selecting the type, a photodetector that is strictly matched with the light source wavelength and has high sensitivity should be chosen. At the same time, its bandwidth should be greater than 10 MHz and the response time should be less than 10 ns to avoid phase distortion.

[0073] Third photodetector: It is used to receive the optical signal output from port 13 of the second optical coupler, convert it into an electrical signal and transmit it to the data acquisition card. When selecting the type, a photodetector that is strictly matched with the light source wavelength and has high sensitivity should be selected. At the same time, its bandwidth should be greater than 10 MHz and the response time should be less than 10 ns to avoid phase distortion.

[0074] Data Acquisition Card (DAQ): Controlled by the host computer (PC), it is used to collect the electrical signals input by the first photodetector, the second photodetector and the third photodetector, and output the collected digital signals to the host computer (PC);

[0075] Host computer (PC): It is used to control the working state of the data acquisition card (DAQ) and can analyze and process the digital signals collected by the data acquisition card (DAQ).

[0076] In the system of this embodiment, two interference paths are formed. The first optical signal transmission path is: port 1 - port 2 - port 3 - port 4 - port 5 - port 6 - port 7 - port 9, and the second optical signal transmission path is: port 1 - port 2 - port 3 - port 4 - port 5 - port 6 - port 8 - port 10. The two interference paths pass through two optical fibers with different lengths. Through the second optical coupler, they enter the first photodetector, the second photodetector and the third photodetector, and different propagation times are formed by the unequal-length optical paths to form interference.

[0077] Among them, the interval between the first sensing optical fiber and the second sensing optical fiber should be much smaller than the wavelength of the wire break signal to be measured, so that when a wire break event occurs, the two vibration signals received by the first sensing optical fiber and the second sensing optical fiber at the same spatial position are consistent.

[0078] Furthermore, the length of the first delay optical fiber is related to the frequency of the wire break event. The length of the first delay optical fiber determines the time delay length between the two vibration signals received by the first sensing optical fiber and the second sensing optical fiber at the same spatial position. In order to meet the positioning conditions, the time delay length should ensure that the time delay Δt can be accurately calculated according to the time-domain diagrams of the two signals.

[0079] Furthermore, the system of this embodiment adjusts the polarization state through a polarization controller so that the polarization states of the two optical signals always remain matched, thereby effectively avoiding the negative impacts caused by polarization fading noise and contrast reduction, maximizing the visibility of the high-frequency transient vibration signal to be measured, and thus improving the detection sensitivity and stability; at the same time, a three-port phase discrimination structure is adopted to efficiently suppress the common-mode noise, complete the non-ambiguous phase demodulation, and achieve a full dynamic range linear response.

[0080] When in use, the working process of the PCCP wire break monitoring and positioning system of this embodiment includes the following steps:

[0081] First, the laser outputs a wide-spectrum and low-coherence continuous light (1530 nm, line width 10 nm). After passing through the optical isolator, it enters the first sensing optical fiber, and then enters the second sensing optical fiber through the first delay optical fiber.

[0082] Then, the optical signal output from the second sensing optical fiber passes through the first optical coupler (splitting ratio 50:50). The optical signal is evenly divided into two paths and output from ports 7 and 8 respectively; among them, the optical signal at port 7 is output to the second delay optical fiber, and the optical signal at port 8 is output to the polarization controller.

[0083] Next, the second delay optical fiber is connected to port 9 of the second optical coupler, and the polarization controller is connected to port 10 of the second optical coupler. The two optical signals are coupled at the second optical coupler. This coupler can use a 3*3 optical coupler (splitting ratio 33:33:33). The optical signal is evenly divided into three paths and output from ports 11, 12, and 13 respectively, forming three interference signals with a fixed phase difference.

[0084] Finally, the three interference signals are respectively received by the first photodetector, the second photodetector, and the third photodetector, and converted into electrical signals. After the analog-to-digital conversion and acquisition by the data acquisition card, they are transmitted to the upper computer for signal processing work.

[0085] In particular, in this embodiment, the first photodetector, the second photodetector, and the third photodetector all select photodetectors with a working wavelength of 1550 nm, a gain of 45 dB, and a detection bandwidth of 200 MHz.

[0086] Embodiment 2:

[0087] In an embodiment of the present invention, a method for monitoring and positioning broken wires of PCCP based on double-fiber same-point locking specifically includes calibration, monitoring, and positioning steps.

[0088] Among them, the calibration step defines the optical fiber layout method, calculates the system background noise, and makes the optical fiber length and spatial position correspond and match;

[0089] The monitoring step completes the monitoring process of the PCCP broken wire signal by the system. By collecting and demodulating the phase change caused by the change in the refractive index or length of the optical fiber due to the broken wire signal, the real vibration signal is restored;

[0090] The positioning step uses the double-fiber same-point locking method and combines the calibration information to determine the position where the broken wire signal occurs.

[0091] Specifically, in this embodiment, the system calibration process is as Figure 2 shown, and the sub-steps are as follows:

[0092] Step 1.1: Install the PCCP broken wire monitoring and positioning as Figure 3 shown. Press two single-mode sensing optical fibers on the wall of the PCCP pipeline tightly (spacing < 5 mm). Connect the ports 3 and 4 of the two single-mode optical fibers through the first delay optical fiber;

[0093] Step 1.2: Through phase demodulation of the interference signal collected by the data acquisition card, calibrate the spatial position of the sensing optical fiber part to make the spatial position and the optical fiber length correspond and match;

[0094] Step 1.3: Obtain the positions of the ports 2, 3, 4, and 5 of the sensing optical fiber and determine the total length of the sensing optical fiber;

[0095] Step 1.4: Calculate the system background noise when no PCCP broken wire event occurs.

[0096] After completing the system calibration, start monitoring and positioning the PCCP broken wire event. The monitoring process is as Figure 4 shown. The specific sub-steps are as follows:

[0097] Step 2.1: When a PCCP broken wire event occurs, vibration signals caused by the broken wire are received simultaneously at the same spatial position on the first sensing optical fiber and the second sensing optical fiber;

[0098] Step 2.2: After the vibration signal reaches the first optical coupler, it is divided into two optical signals, A and B. The optical signal A reaches the second optical coupler through the second delay optical fiber; the optical signal B reaches the second optical coupler directly through the polarization controller; the two optical signals A and B interfere at the second optical coupler. The system can collect two identical interference signals, and there is a time delay between these two interference signals.

[0099] Step 2.3: Perform phase demodulation on the two collected interference signals to obtain the time-domain information corresponding to the broken wire vibration signal, and compare it with the background noise to determine it as an abnormal high-frequency signal. The comparison result is as Figure 5 shown.

[0100] Step 2.4: The three interference optical signals are received by three photodetectors and then transmitted to the data acquisition card, and are transmitted by the data acquisition card to the upper computer for signal demodulation to restore the vibration signal.

[0101] Furthermore, determine the occurrence position of the broken wire signal. The specific sub-steps of the positioning process are as follows:

[0102] Step 3.1: When a PCCP broken wire event occurs, high-frequency vibration signals caused by the broken wire are received simultaneously at the same spatial position on the first sensing optical fiber and the second sensing optical fiber;

[0103] Step 3.2: Adopt the double-fiber same-point locking method to integrate the time-domain information of the two broken-wire vibration signals and draw the time-domain diagrams of the two signals, as shown in Figure 6 shown.

[0104] The time delay Δt between the two signals can be determined from the figure, and thus the distance L between the two events on the optical path can be known.

[0105] Step 3.3: According to the calibration information and combined with the length (fixed value) of the first delay optical fiber, the accurate spatial position where the PCCP broken-wire event occurs can be accurately located.

[0106] Specifically, the distance L between the two events on the optical path is the sum of the length S of the first delay optical fiber and twice the length l from this position to the first delay optical fiber. Among them, the length S of the first delay optical fiber is a fixed value, so the length l from this position to the first delay optical fiber can be determined, and the occurrence position of the broken-wire event can be determined according to the calibration information.

[0107] In summary, the PCCP broken-wire monitoring and positioning method of the present invention using double-fiber same-point locking can ensure high precision and high sensitivity in the positioning of PCCP broken-wire events by accurately calculating the occurrence position of the broken-wire event in the optical path and combining the calibration information of the spatial position of the sensing optical fiber.

[0108] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A PCCP broken wire monitoring and positioning system based on double-fiber same-point locking, characterized in that, Comprising: A laser, an optical isolator, a first sensing optical fiber, a first delay optical fiber, a second sensing optical fiber, a first optical coupler, a second delay optical fiber, a polarization controller, a second optical coupler, three photodetectors, a data acquisition card and a host computer; The laser is used to output a continuous optical signal to the optical isolator, and the optical isolator transmits the continuous optical signal to the first sensing optical fiber, which enters the second sensing optical fiber after passing through the first delay optical fiber; The optical signal output by the second sensing optical fiber is divided into two optical signals A and B after passing through the first optical coupler and then output. The optical signal of path A is output to the second optical coupler through the second delay optical fiber, and the optical signal of path B is output to the second optical coupler through the polarization controller; The second optical coupler outputs three interference signals, which respectively enter the three photodetectors, are converted into electrical signals, and then are transmitted to the host computer for signal processing after analog-to-digital conversion and acquisition by the data acquisition card.

2. The PCCP broken wire monitoring and positioning system based on dual-fiber same-point locking according to claim 1, characterized in that, The optical signals of paths A and B enter the second optical coupler through two optical fibers of different lengths, and different propagation times are formed by the unequal-length optical paths, and interference occurs at the second optical coupler.

3. The PCCP wire break monitoring and positioning system based on dual-fiber same-point locking according to claim 2, characterized in that, The second optical coupler is a 3×3 optical coupler with a splitting ratio of 33:33:

33. The three output ports are respectively connected to the input ends of the first photodetector, the second photodetector and the third photodetector, and the interference signals formed by coupling the optical signals of paths A and B are respectively output through the three output ports by the three-port phase discrimination structure.

4. The PCCP broken wire monitoring and positioning system based on dual-fiber same-point locking according to claim 2, characterized in that, Both the first sensing optical fiber and the second sensing optical fiber are single-mode optical fibers, adopting a double-fiber same-point structure and connected by the first delay optical fiber; the distance between the first sensing optical fiber and the second sensing optical fiber is less than the wavelength of the broken wire signal to be measured, so that when a broken wire event occurs, the two vibration signals received by the first and second sensing optical fibers at the same spatial position are consistent.

5. The PCCP broken wire monitoring and positioning system based on dual-fiber same-point locking according to claim 1, characterized in that, The polarization controller is used to adjust the polarization state to make the polarization states of the optical signals of paths A and B match, and stable interference signal fringes are generated through the second optical coupler.

6. A method for monitoring and locating broken wires of PCCP based on double-fiber same-point locking, which is applied to the PCCP broken wire monitoring and locating system according to any one of claims 1 to 5, monitors the PCCP broken wire event and determines the position where the broken wire occurs; characterized in that, Including the following steps: Step 1, Calibration step: Used to define the optical fiber layout method, calculate the system background noise, and make the optical fiber length and spatial position correspond and match; Step 2, Monitoring step: Used to monitor the process of the PCCP broken wire signal, collect and demodulate the phase change caused by the change of the refractive index or length of the optical fiber caused by the broken wire signal, and restore the real vibration signal; Step 3, Positioning step: Use the double-fiber same-point locking method, combined with the calibration information, to determine the position where the broken wire signal occurs.

7. The method for monitoring and positioning broken wires of PCCP based on double-fiber same-point locking according to claim 6, characterized in that The calibration step is specifically as follows: Step 1.1, Closely attach the first sensing optical fiber and the second sensing optical fiber on the PCCP pipeline wall, and one end of the first sensing optical fiber and the second sensing optical fiber is connected by the first delay optical fiber; Step 1.2, Demodulate the phase of the interference signal collected by the data acquisition card, and calibrate the spatial positions of the first sensing optical fiber and the second sensing optical fiber, so that the spatial position and the optical fiber length correspond and match; Step 1.3, Obtain the positions of both ends of the first sensing optical fiber and the second sensing optical fiber, and determine the total length of the first sensing optical fiber and the second sensing optical fiber; Step 1.4: Calculate the system background noise in the case of no PCCP wire break event.

8. The method for monitoring and positioning broken wires of PCCP based on double-fiber same-point locking according to claim 6, characterized in that, The monitoring steps are as follows: Step 2.1: When a PCCP wire break event occurs, the vibration causes changes in the refractive index or length of the optical fiber, resulting in phase modulation. The phase change is: φ(t) = βsin(ωt) where β is the phase modulation amplitude and ω is the vibration frequency; Step 2.2: When the vibration signal reaches the first optical coupler, it is divided into two optical signals, A and B. The optical signal of path A reaches the second optical coupler through the second delay optical fiber; the optical signal of path B directly reaches the second optical coupler through the polarization controller; The phase of the optical signal of path A is φ(t), and the phase of the optical signal of path B is φ(t - τ): where n is the refractive index of the optical fiber, R is the length of the second delay optical fiber, and C is the speed of light in a vacuum; The phase difference between the optical signals of paths A and B is Δφ(t): Step 2.3: The optical signals of paths A and B interfere at the second optical coupler. The interference light intensities received by the first photodetector, the second photodetector, and the third photodetector are I1(t), I2(t), and I3(t) respectively: I1(t) = D1 + A1cos[Δφ(t)] where D1 is the DC component of the interference light intensity I1, A1 is the AC component of the interference light intensity I1; D2 is the DC component of the interference light intensity I2, A2 is the AC component of the interference light intensity I2; D3 is the DC component of the interference light intensity I3, A3 is the AC component of the interference light intensity I3; Step 2.4: The three interference optical signals are received by three photodetectors and then transmitted to the data acquisition card, and then transmitted by the data acquisition card to the upper computer for signal demodulation to restore the vibration signal.

9. The method for monitoring and positioning broken wires of PCCP based on double-fiber same-point locking according to claim 8, wherein, The positioning steps are as follows: Step 3.1: When a PCCP wire break event occurs, the first sensing optical fiber and the second sensing optical fiber simultaneously receive the high-frequency vibration signals caused by the wire break at the same spatial position; Step 3.2: Restore the high-frequency vibration signals at the same spatial position, draw the time-domain diagrams of the two signals, determine the time delay Δt between the two high-frequency vibration signals at the same spatial position, and calculate the distance L between the two high-frequency vibration signals on the optical path: where υ is the speed of light in the optical fiber; Step 3.3: Determine the length l from the same spatial position to the first delay optical fiber according to the distance L and the length S of the first delay optical fiber: L = S + 2l where the length S of the first delay optical fiber is a fixed value; Step 3.4: Determine the occurrence position of the PCCP wire break event according to the calibration information.

10. The method for monitoring and positioning broken wires of PCCP based on double-fiber same-point locking according to claim 8, wherein The length S of the first delay optical fiber is related to the frequency of the PCCP wire break event. The length S of the first delay optical fiber determines the time delay length between the two high-frequency vibration signals received by the first sensing optical fiber and the second sensing optical fiber at the same spatial position. The time delay length is used to accurately calculate the time delay Δt according to the time-domain diagrams of the two signals.

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