A method for ultrasonically detecting the pressure of liquid medium in a pipeline

Abstract

The present invention relates to the technical field of optical fiber sensing pressure measurement, and specifically to a method for ultrasonically detecting the pressure of a liquid medium in a pipeline. The method comprises the following steps: a pressure detection system directly adheres an elastic strain diaphragm to the outer wall of a monitored pipe using reflective optical fiber technology; a pulse command is issued, and light emitted by a laser semiconductor light source is coupled to an incident optical fiber, which directs the light from the light source to the surface of the elastic strain diaphragm. The elastic strain diaphragm receives the light beam from the laser semiconductor light source through the incident optical fiber. After the light is reflected by the surface of the elastic strain diaphragm, the light senses the pressure of the pipeline liquid from the diaphragm surface, causing the pipeline to generate a deformation reflecting the measured pressure. Based on the pressure generated by the liquid medium on the metal pipe wall, the deformation of the outer diameter of the pipeline is detected to obtain a displacement measurement parameter. The present invention has a simple structure, is easy to install, and is low in cost. No detection interface needs to be reserved, and the working status of a hydraulic system can be conveniently detected. The invention is also convenient to carry, simple to operate, and easy to use on site.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing pressure measurement, in particular to a method for ultrasonically detecting the pressure of a liquid medium in a pipeline. Background Art

[0002] With the development of industrialization, pipelines are ubiquitous in our daily lives, including water supply and drainage pipes, fire protection pipes, tap water pipes, heating pipes, and specialized industrial piping systems. Consequently, the demand for pipeline pressure monitoring is increasing. Compared to mechanical transmission, hydraulic transmission technology is more difficult to monitor and diagnose, and compared to electric transmission, its state parameters are more difficult to extract. Accurately monitoring pipeline pressure and issuing alarms when anomalies occur are urgent issues. Hydraulic system pressure is a key parameter reflecting the operating status of the pipeline system. Implementing pressure testing is essential to ensure safe system operation. Pressure testing inside gas or liquid pipelines is a primary method and means of monitoring pipeline system operation and diagnosing pipeline faults. The most challenging aspect of on-site pipeline fault diagnosis and resolution is obtaining information closely related to pipeline performance, such as acceleration, stress, and pressure. Pressure is the most challenging parameter to obtain. Traditional pressure testing methods, such as mechanical, pressure-sensitive, and pressure gauges, are mostly invasive and require contact with the medium being measured. These methods make it difficult to change the pressure measurement point and damage the integrity of the pipeline structure, especially under high-pressure conditions, which can easily lead to safety hazards. Pressure testing within gas or liquid pipelines in hydraulic systems, such as oil pipelines, water pipelines, and natural gas pipelines, is a crucial method for ensuring the proper functioning of pipeline systems and diagnosing pipeline faults. For a long time, the main measurement method used was invasive. Intrusive testing generally requires drilling a hole in the vessel being tested, then installing a stop valve at the hole to divert the measured medium to the sensitive element of the pressure measuring instrument, where the pressure is measured. Drilling a hole in the pipeline to install an invasive sensor compromises the integrity of the pipeline. This invasive testing method, which involves drilling holes in the pipe, not only compromises the integrity of the pipeline but also causes stress concentration, reducing pipeline strength and compromising system safety. Installing testing equipment in complex pressure piping systems is particularly difficult, and in some cases, even prohibited. This makes invasive pressure testing in pipeline systems difficult to implement in practice. These methods either pre-wire pressure instruments or pressure sensors at specific locations in the pipeline, or perform stress and strain measurements outside the pipe. The advantages of these testing methods are mature measurement theory and technology, low equipment cost, high reliability, and high measurement accuracy. However, there are some drawbacks. For example, the pressure measurement location must be predetermined during the pipeline system design, making it difficult to modify once installed. This approach often disrupts the overall characteristics of the pipeline system, making high-pressure pipelines particularly prone to accidents. Furthermore, in some applications, installing an intrusive measurement system is simply not feasible. In industries like oil and natural gas, due to their flammability, explosiveness, and strong corrosiveness, non-contact pressure measurement is essential. Existing intrusive pressure measurement methods, which require contact with the medium, cannot meet these requirements. Therefore, the search for non-intrusive or contactless pipeline pressure measurement methods is necessary.In this context, the detection media for non-contact pressure measurement methods can include ultrasound, various radiation, heat, electromagnetic waves, and lasers. Their common characteristic is that the detection source can be mounted on the outer wall of the pipe, using the detection medium provided to indirectly sense the liquid flow signal. Non-invasive pipeline pressure measurement theories and methods typically employ ultrasound as a pipeline pressure test. This is based on the sensitivity of ultrasonic propagation parameters (such as attenuation coefficient and sound velocity) in liquids to pressure changes. However, the acoustic attenuation coefficient exhibits numerous uncertainties during the measurement process and is susceptible to interference from external conditions. The shortcomings of existing non-invasive ultrasonic pipeline pressure measurement methods primarily include poor adaptability to measuring pressure in pipes of varying materials and diameters; large errors in low-pressure measurements; and significant impacts of temperature and flow velocity fluctuations on measurement accuracy caused by the elastic strain diaphragm. Currently, research into non-contact pressure measurement methods has been extensive and arduous, resulting in the launch of numerous products. For example, a non-contact hydraulic detection method based on elastic deformation of pipelines is one such achievement. This method utilizes the basic principle of using a liquid medium to exert pressure on the metal pipe wall, thereby causing radial elastic deformation of the pipe. The internal pressure of the pipe is calculated by detecting minute deformations of the pipe's outer diameter. Whether this method utilizes an LVDT elastic strain diaphragm displacement sensor or a capacitive sensor, a dedicated fixture is required for securement. Installation is cumbersome, and the fixture is bulky. This limits the application of elastic strain diaphragms when pipes are densely arranged.

[0003] Modern hydraulic equipment is becoming increasingly sophisticated and complex, and the resulting losses from system failures are also increasing. Only by accurately diagnosing the fault location and promptly repairing it in the shortest possible time can losses be minimized. Fault location in hydraulic systems requires pressure readings at numerous locations to scientifically diagnose the failed component. To measure the pressure of liquids and gases within known pipelines, existing fiber optic pressure sensors wind an optical fiber into a coil around the pipeline, distribute Bragg gratings along the fiber, and measure pressure changes within the pipeline by measuring changes in the fiber length. However, the need to wrap the fiber around the pipeline makes installation difficult and costly, resulting in limited practical application. If a rigid frame is added to the pipe wall, with the piezoelectric sensor positioned between the frame and the pipeline, the initial value can be set using an adjustable nut. The disadvantage of this approach is the complex structure, the elastic strain gauge, and the high rigidity requirements of the frame. This results in a bulky and inconvenient frame, while using high-rigidity, lightweight materials would also result in high costs.

[0004] While a wide variety of hydraulic measurement methods exist, the aforementioned methods present significant challenges in hydraulic system fault diagnosis. This is because during fault location, pressure often requires temporary monitoring at numerous locations, and installing pressure gauges or pressure sensors in these locations is difficult or even impractical. This delays repairs and results in greater losses. Traditional methods for measuring power require instrumentation installed in pipelines, which presents significant challenges in engineering implementation. Power is the product of pressure and flow rate, and conventional methods for measuring pressure, especially flow rate, significantly impact fluid flow, prohibiting this approach in most precision systems. This intrusive measurement method increases initial system installation costs and reduces reliability, while also increasing system size and efficiency. In particular, it lacks the ability to output an electrical signal proportional to the measured quantity. Therefore, the development of an efficient and cost-effective signal demodulation system is crucial for practical application. This method requires complex light sources and signal demodulation, making post-data acquisition computations difficult. Furthermore, it suffers from poor dynamic characteristics, which remain to be addressed. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a method for ultrasonically detecting the pressure of a liquid medium in a pipeline with a simple structure, easy installation, low cost, high reliability, strong anti-electromagnetic interference ability and a wide dynamic measurement range.

[0006] To achieve the above technical effects, the technical solutions of this application are as follows:

[0007] A method for ultrasonically detecting the pressure of a liquid medium in a pipeline comprises the following steps:

[0008] The non-invasive pressure detection system based on fiber optic reflection technology uses reflective fiber optic technology to directly attach the elastic strain diaphragm to the outer wall of the monitored pipe. The pressure detection system sends a pulse command, and the light emitted by the laser semiconductor (LD) light source is coupled to the incident fiber optic. The incident fiber optic transmits the light of the light source to the surface of the elastic strain diaphragm. The elastic strain diaphragm receives the light beam of the laser semiconductor light source through the incident fiber optic. After the light is reflected by the surface of the elastic strain diaphragm, the light senses the pressure of the pipeline liquid from the diaphragm surface, causing the pipeline to produce a certain deformation reflecting the measured pressure. According to the pressure generated by the liquid medium on the metal pipe wall, the tiny deformation of the outer diameter of the pipe is detected, and the corresponding displacement measurement parameters are obtained. The displacement / light intensity conversion is realized and reflected to another reflective fiber. After the reflective fiber receives it, the reflected light is coupled through the reflective fiber and transmitted to the receiver at the end of the reflective fiber. The receiver detects the intensity of the received light signal based on the collected reflected light power, calculates the size of the measured signal, and infers the pipe wall based on the intensity of the reflected light signal. The deformation that changes with the measured signal size is obtained as the distance d between the elastic modulus surface and the optical fiber is calculated, and then the pressure change value of the liquid in the pipeline is calculated based on Hooke's law of the deformation of the pipe wall. After completing the measurement of the pressure change of the pipeline liquid, the receiver uses the deformation of the elastic strain diaphragm under the action of pressure to modulate the reflected light power signal to obtain the required measured information, and converts the light intensity signal into an electrical signal. The operational amplifier then performs signal amplification, detection, and filtering. The measured analog signal is converted into an analog-to-digital (A / D) conversion and converted into a digital signal that can be recognized by the single-chip microcomputer. The dynamic pressure value and dynamic flow rate of the pipeline liquid are calculated. The emission light intensity coupling efficiency and relative position relationship between the incident optical fiber and the reflected optical fiber are used to reflect the change in the measured displacement. The momentum impulse and volumetric fluid oscillation principles are used to determine the coupling coefficient of the liquid structure, evaluate the impact of fluid pulsation on pipeline performance, and achieve non-invasive dynamic measurement of pipeline liquid pressure and flow changes with the stress value in the pipeline equal to the pressure value in the pipeline.

[0009] Furthermore, the light from the light source propagates from the A end of the incident optical fiber to the B end of the incident optical fiber. The light reaches the surface of the elastic strain diaphragm, is reflected by the surface to the C end of the reflecting optical fiber, and is received by the receiver at the D end of the reflecting optical fiber. The received light signal is then processed. The receiver causes a certain amount of deformation in the pipeline according to the pressure of the pipeline liquid. The change in deformation affects the optical power received by the optical fiber. In turn, the deformation of the pipeline wall is calculated based on the collected reflected light power. Based on the deformation of the pipeline wall, the pressure change of the liquid in the pipeline is inferred. The relationship between the stress and strain of the liquid in the pipeline is obtained through the generalized Hooke's law:

[0010]

[0011] And the stress value in the pipeline is equal to the pressure value in the pipeline, thus completing the pressure change measurement of the pipeline liquid. In the formula, E represents the elastic modulus of the pipe material, εx is the linear strain in the x direction, ε y is the linear strain in the y direction, ε z is the linear strain in the z direction, σ x is the stress in the x direction, σ y is the stress in the y direction, σ z is the stress in the z direction, and v is the Poisson's ratio.

[0012] Furthermore, when the pressure detection system is started, the pulse signal generated by the laser semiconductor transmits data through the incident optical fiber, outputs the main control pulse to the transmitting unit, and the reflected optical fiber undergoes photoelectric conversion through the optical fiber photoelectric converter, and is filtered, detected and analog-to-digital A / D converted and sent to the single-chip microcomputer unit.

[0013] Furthermore, the single-chip microcomputer unit controls the generation of laser semiconductor pulses, performs signal detection, digital filtering, parameter preset, sound speed calculation and transmission functions on the time signal output by the receiving unit, obtains the sound speed after calculation, is connected to the keyboard through a parallel interface, receives commands and parameters and sends them to the data processing computer through the communication interface for processing to obtain the pressure value, and the preset parameters are displayed on the display module.

[0014] Furthermore, the elastic deformation and strain generated by the pipe wall will cause the distance d between the elastic strain diaphragm and the B end of the incident optical fiber and the C end of the reflecting optical fiber to change, which in turn causes the intensity of the received reflected light to change. The receiver calculates the change in light intensity and the measurement results based on the measured light intensity change, and thus calculates the change in pipe wall pressure.

[0015] Furthermore, the distance d between the elastic strain diaphragm and the B end of the incident optical fiber and the C end of the reflected optical fiber forms a rectangular coordinate empirical distribution curve with the received light intensity M. When the total number n of measured values ​​is large and the interval between each group of measured values ​​is very small, the obtained empirical distribution curve approaches a smooth curve, that is, a theoretical distribution curve. From the shape of the curve, when d < d0, the receiving optical fiber cannot receive light, and this area is a dead zone; when d > d1, the slope of the curve is negative and gradually decreases, and the sensitivity is relatively poor. When the initial distance d0 < d < d1, when d is in this part of the area, the received light intensity M is almost linearly related to the distance d. d0 is the initial distance, and d1 represents the distance between d0 and the peak of the empirical distribution curve.

[0016] Furthermore, the pressure detection system uses the acoustic time t=t1-t2 of ultrasonic wave propagation in liquid, the pressure P and the acoustic velocity C of ultrasonic wave propagation in liquid to form a nonlinear functional relationship, and uses the least square method to statistically calibrate the data. After the mathematical model is processed and the curve is fitted, the polynomial regression equation is obtained: P=∑k(CC n );

[0017] Where t1 is the time interval between transmitting the pulse and receiving the echo, t2 is the time interval between transmitting the pulse and receiving the penetrating wave, and C n is the initial sound velocity corresponding to zero pressure, and the coefficient k is determined by the least squares method.

[0018] Furthermore, when the distance d is d0<d<d1, the wave velocity a is measured by the on-site measurement method. After calculation, the initial distance d0=a / 2T, d1=(a+2r) / 2T, T=tan(sin -1 NA), the percentage of the surface of the reflecting fiber end face illuminated by the fiber light cone is:

[0019]

[0020]

[0021] The percentage of incident light power received by the reflecting fiber is:

[0022]

[0023] R=r+2dI

[0024] Where d1 represents the distance from d0 to the peak of the empirical distribution curve, N is the working characteristic reflecting the ability of the strain gauge to measure dynamic strain, A represents a monotonically decreasing function of x within the domain of definition, δ represents the strain coefficient, r represents the inner diameter of the measured pipe, and P n represents the reflected light power, P1 represents the incident light power, F is the coupling efficiency, dT represents the derivative of the propagating acoustic time t, and NA stands for numerical aperture, which is a parameter used to describe the ability of optical devices such as optical fibers or lenses to collect and focus light.

[0025] Furthermore, first, the measured pipeline is taken, the surface of the measured point of the measured pipeline is cleaned, and a protective film layer is coated on the outside of the optical fiber. The protective film is a carbon coating or a polyimide coating; the elastic strain diaphragm is evenly and flatly attached to the pipe wall, the incident optical fiber and the reflection optical fiber are installed on the outside of the protective film, and the optical fiber and the elastic strain diaphragm are adjusted to a suitable distance d0<d<d1. The two optical fiber installation points are installed horizontally with the center line of the pipeline. Secondly, when the pressure value in the measured pipeline is known, based on the received optical signal, the pressure detection system calculates the distance d between the incident and reflection optical fibers and the elastic strain diaphragm surface according to formulas (2) to (4). The difference between d and the distance when the pipeline is not pressurized is recorded as d0, that is, as the compressive deformation of the pipe wall. According to formula (1), the pressure in the pipeline is finally calculated. This part is automatically calculated by the pressure detection system. The pipeline liquid pressure value is compared with the known pressure value to check the error range.

[0026] Furthermore, the pressure detection system uses artificial neural networks to comprehensively correct the ultrasonic sound velocity pressure measurement system based on the changes in liquid sound velocity caused by changes in hydraulic system pressure. It simulates the parallel processing network of the structural characteristics and functional characteristics of biological neural networks, selects a three-layer BP network, takes sound velocity and density as input, and pressure as output, and uses sparse component decomposition technology to solve the ultrasonic echo delay. The ultrasonic echo delay is calculated, and by determining the number of hidden layer nodes and the weight of the network, the network is trained using the artificial neural network training set to obtain a model of the relationship between pressure and ultrasonic delay characteristics. Then, when online, the forward propagation function of the network is used to obtain the corrected pressure value.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention adopts reflective optical fiber technology to directly adhere the elastic strain diaphragm to the outer wall of the monitored pipe according to the pipe shape and process parameters. It has a simple structure, is easy to install, and has low cost. It does not require a reserved detection interface, and can conveniently detect the working status of the hydraulic system. It is also easy to carry, simple to operate, and convenient for on-site use. The surface of the diaphragm is plated with a metal coating (aluminum or gold, etc.), which can reflect light well. By utilizing the principle that the elastic strain diaphragm deforms under pressure to modulate the reflected light power signal, and that the pressure is related to the intensity of the emitted light, non-invasive measurement of pipeline liquid pressure changes can be achieved, which can accurately reflect the amplitude and frequency characteristics. The advantage of this method is that the position of the pressure measurement point can be easily changed, rather than just targeting a fixed pipe section. Not only is the pressure measurement accuracy high and easy to debug, but it also avoids damaging the integrity of the pipeline and the problem of inconvenient measurement position of the pressure probe.

[0029] Based on the physical property that changes in the hydraulic system cause changes in the oil's sound velocity, this invention, designed for ordinary steel hydraulic pipelines, uses light emitted by a laser diode (LD) light source coupled to an incident optical fiber. This fundamentally addresses the challenges of conventional fiber optic sensors, such as light source fluctuations affecting measurement accuracy, as well as temperature and time drift. The light source's transmitting circuit utilizes a differential design, reducing common-mode interference in the electronic circuitry. This effectively suppresses interference from non-measured signals and prevents crosstalk from multiple parallel signals. The incident optical fiber directs light from the light source onto the surface of an elastic strain diaphragm, which receives the laser diode light beam through the incident optical fiber. The core optical fiber component is highly sensitive, heat-resistant, explosion-proof, corrosion-resistant, and water-resistant, making it safe and reliable, making it suitable for use in harsh environments. The concept is to convert pressure into deformation, which is then converted into light transmission, which is then converted into an electrical signal, and ultimately, pressure changes are inferred through electrical signal processing. Essentially, this method measures pressure changes, rather than directly measuring the pipeline fluid pressure. Dynamic changes in pipe wall pressure can be directly observed. The research results show that the ratio of the output signals of the incident optical fiber and the reflected optical fiber of the elastic strain diaphragm has a good linear relationship with the change of the measurement distance, and can significantly reduce the influence of the fluctuation of the light source luminous intensity and the roughness of the measured surface on the displacement measurement results. The elastic strain diaphragm uses the correspondence between the dual-path signal intensity ratio and the displacement to perform measurement, which is beneficial to improving the anti-interference ability and measurement accuracy.

[0030] In this invention, after light is reflected from the surface of the elastic strain diaphragm, it senses the pressure of the pipeline liquid from the diaphragm surface, causing the pipeline to produce a certain deformation reflecting the measured pressure. Based on the pressure exerted by the liquid medium on the metal pipe wall, the microscopic deformation of the pipe's outer diameter is detected, and the corresponding displacement measurement parameter is obtained. This displacement / light intensity conversion is achieved and reflected to another reflective optical fiber, which receives the reflected light. The reflected light is then coupled through the reflective fiber and transmitted to a receiver at the end of the reflective fiber. The receiver detects the intensity of the received light signal based on the collected reflected light power, and calculates the magnitude of the measured signal. This method has high reliability. The pipeline liquid pressure causes a certain amount of deformation in the pipeline, and changes in this deformation affect the light power received by the optical fiber. Conversely, the collected reflected light power can be used to infer the deformation of the pipe wall, and based on this deformation, the pressure change of the pipeline liquid can be inferred, thereby achieving pressure change measurement of the pipeline liquid. The output is proportional to the amount of reflected light. The output signal is much more sensitive to changes in light intensity than to changes in displacement, eliminating capacity issues. Furthermore, the radiation density is moderate, the emission spectrum is uniform and narrow, and is less affected by ambient light.

[0031] After completing the measurement of the pressure change of the pipeline liquid, the present invention uses the elastic strain diaphragm to deform under the action of pressure to modulate the reflected light power signal, and demodulates the light intensity modulation, polarization modulation, frequency modulation or phase modulation to obtain the required measured information. The light intensity signal is converted into an electrical signal, and then the operational amplifier is used to amplify, detect and filter the signal. The measured analog signal is converted into an analog-to-digital (A / D) conversion and converted into a digital signal that can be recognized by a single-chip microcomputer. The dynamic pressure value and dynamic flow rate of the pipeline liquid are calculated. The dynamic measurement range is wide, which solves the problem that the traditional single-ended output Y-branch structure reflective optical fiber sensor is easily affected by factors such as changes in incident light intensity and different measured surface morphologies.

[0032] This method uses the coupling efficiency and relative position of the emitted light intensity between the incident and reflecting optical fibers to reflect the magnitude of the measured displacement change. It then utilizes the principles of momentum-impulse and volumetric fluid oscillation to determine the coupling coefficient of the liquid structure and assess the impact of liquid pulsation on pipeline performance. This method enables non-invasive dynamic measurement of pipeline fluid pressure and flow changes, ensuring that the stress value in the downstream channel is equal to the pressure value within the pipeline. This method offers high accuracy and high response frequency, completely overcoming the influence of pipeline wall thickness and effectively eliminating inherent acoustic and electrical delay errors.

[0033] The present invention comprehensively utilizes the important characteristics of ultrasound, such as good directionality, high energy, strong penetrating ability, and reflection and refraction at interfaces, from both dynamic and static characteristics. This fundamentally breaks through the limitation that the sensing pressure element of traditional pressure testing instruments must be in contact with the liquid. This facilitates the external measurement of internal pressures in multiple parts of a closed hydraulic system. Based on measurement requirements, on-site non-invasive pipeline pressure testing services can be provided using real-time measurement results; as long as the liquid can be transmitted, it can be measured using this method. It is particularly suitable for measuring the flow of corrosive liquids, high-viscosity liquids, non-conductive liquids or gases. In engineering, the working status of the hydraulic system can be easily detected, and the working status of the system can be judged, providing technical means for realizing condition-based maintenance of the hydraulic system, and providing certain help in improving the reliability and maintainability of the hydraulic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the pressure measurement principle of the pressure detection system of the present invention.

[0035] Figure 2 yes Figure 1 Schematic diagram of the signal control principle.

[0036] Figure 3 It is a schematic diagram of the optical path of the elastic strain diaphragm reflecting optical fiber and the movable reflecting surface.

[0037] Figure 4It is a schematic diagram for calculating the change in pipe wall pressure based on the elastic deformation of the pipe wall.

[0038] Figure 5 It is a schematic diagram of the rectangular coordinate empirical distribution curve;

[0039] In the figure: 1-pipe, 2-elastic strain diaphragm, 3-laser semiconductor light source, 4-incident optical fiber, 5-reflecting optical fiber, 6-receiver. DETAILED DESCRIPTION

[0040] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process. However, the protection scope of the present invention is not limited to the following embodiment.

[0041] It should be pointed out that all directional indications in the embodiments of the present invention (such as both sides, edges, up, down, left, right, front, back, middle, top, bottom, tail, axial, radial...) are only used to explain the relative position relationship, movement state, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0042] Example 1

[0043] A method for ultrasonically detecting the pressure of a liquid medium in a pipeline comprises the following steps:

[0044] The non-invasive pressure detection system based on fiber optic reflection technology uses reflective fiber optic technology to directly attach the elastic strain diaphragm to the outer wall of the monitored pipe. The pressure detection system sends a pulse command, and the light emitted by the laser semiconductor (LD) light source is coupled to the incident fiber optic. The incident fiber optic transmits the light of the light source to the surface of the elastic strain diaphragm. The elastic strain diaphragm receives the light beam of the laser semiconductor light source through the incident fiber optic. After the light is reflected by the surface of the elastic strain diaphragm, the light senses the pressure of the pipeline liquid from the diaphragm surface, causing the pipeline to produce a certain deformation reflecting the measured pressure. According to the pressure generated by the liquid medium on the metal pipe wall, the tiny deformation of the outer diameter of the pipe is detected, and the corresponding displacement measurement parameters are obtained. The displacement / light intensity conversion is realized and reflected to another reflective fiber. After the reflective fiber receives it, the reflected light is coupled through the reflective fiber and transmitted to the receiver at the end of the reflective fiber. The receiver detects the intensity of the received light signal based on the collected reflected light power, calculates the size of the measured signal, and infers the pipe wall based on the intensity of the reflected light signal. The deformation that changes with the measured signal size is obtained as the distance d between the elastic modulus surface and the optical fiber is calculated, and then the pressure change value of the liquid in the pipeline is calculated based on Hooke's law of the deformation of the pipe wall. After completing the measurement of the pressure change of the pipeline liquid, the receiver uses the deformation of the elastic strain diaphragm under the action of pressure to modulate the reflected light power signal to obtain the required measured information, and converts the light intensity signal into an electrical signal. The operational amplifier then performs signal amplification, detection, and filtering. The measured analog signal is converted into an analog-to-digital (A / D) conversion and converted into a digital signal that can be recognized by the single-chip microcomputer. The dynamic pressure value and dynamic flow rate of the pipeline liquid are calculated. The emission light intensity coupling efficiency and relative position relationship between the incident optical fiber and the reflected optical fiber are used to reflect the change in the measured displacement. The momentum impulse and volumetric fluid oscillation principles are used to determine the coupling coefficient of the liquid structure, evaluate the impact of fluid pulsation on pipeline performance, and achieve non-invasive dynamic measurement of pipeline liquid pressure and flow changes with the stress value in the pipeline equal to the pressure value in the pipeline.

[0045] The present invention adopts reflective optical fiber technology to directly adhere the elastic strain diaphragm to the outer wall of the monitored pipe according to the pipe shape and process parameters. It has a simple structure, is easy to install, and has low cost. It does not require a reserved detection interface, and can conveniently detect the working status of the hydraulic system. It is also easy to carry, simple to operate, and convenient for on-site use. The surface of the diaphragm is plated with a metal coating (aluminum or gold, etc.), which can reflect light well. By utilizing the principle that the elastic strain diaphragm deforms under pressure to modulate the reflected light power signal, and that the pressure is related to the intensity of the emitted light, non-invasive measurement of pipeline liquid pressure changes can be achieved, which can accurately reflect the amplitude and frequency characteristics. The advantage of this method is that the position of the pressure measurement point can be easily changed, rather than just targeting a fixed pipe section. Not only is the pressure measurement accuracy high and easy to debug, but it also avoids damaging the integrity of the pipeline and the problem of inconvenient measurement position of the pressure probe.

[0046] Example 2

[0047] See Figure 1 、 Figure 2 According to the present invention, a non-invasive pressure detection system based on fiber optic reflection technology is implemented. The pressure detection system uses reflective fiber optic technology to directly attach an elastic strain diaphragm 2 to the outer wall of the pressure pipe 1 to be detected. The pressure detection system sends a pulse command, and the light emitted by the laser semiconductor light source 3 is coupled to the incident fiber 4. The incident fiber 4 transmits the light of the light source 3 to the surface of the elastic strain diaphragm 2. The elastic strain diaphragm 2 receives the light beam of the laser semiconductor light source 3 through the incident fiber 4. After the light is reflected by the surface of the elastic strain diaphragm 2, the light senses the pressure of the pipeline liquid from the diaphragm surface, causing the pipeline to produce a certain deformation reflecting the measured pressure. According to the pressure generated by the liquid medium on the metal pipe wall, the micro deformation of the outer diameter of the pipeline is detected, and the corresponding displacement measurement parameter is obtained, realizing the displacement / light intensity conversion and reflecting it to another reflective fiber 5. The reflective fiber 5 receives the reflected light, and the reflected light is coupled through the reflective fiber and transmitted to the receiver 6 at the end of the reflective fiber. The receiver 6 detects the intensity of the received light signal based on the collected reflected light power, and obtains the magnitude of the measured signal. The measured signal is small, and the deformation of the pipe wall as the distance d between the elastic modulus surface and the optical fiber is calculated based on the intensity of the reflected light signal, which changes with the magnitude of the measured signal. Then, the pressure change of the liquid in the pipe is calculated based on Hooke's law of the pipe wall deformation. After completing the measurement of the pressure change of the pipeline liquid, the receiver uses the deformation of the elastic strain diaphragm under the action of pressure to modulate the reflected light power signal to obtain the required measured information. The light intensity signal is converted into an electrical signal, which is then amplified, detected, and filtered by an operational amplifier. The measured analog signal is converted into an analog-to-digital (A / D) signal and converted into a digital signal that can be recognized by a single-chip microcomputer. The dynamic pressure and dynamic flow of the pipeline liquid are calculated. The coupling efficiency of the emitted light intensity and the relative position relationship between the incident optical fiber and the reflecting optical fiber are used to reflect the magnitude of the measured displacement change. The momentum impulse and volumetric fluid oscillation principles are used to determine the coupling coefficient of the liquid structure, evaluate the impact of fluid pulsation on pipeline performance, and achieve non-invasive dynamic measurement of pipeline liquid pressure and flow changes with the stress value in the pipeline equal to the pressure value in the pipeline.

[0048] The light from the light source propagates from the incident optical fiber end A to the end B, reaches the surface of the elastic strain diaphragm, is reflected by the surface to the reflecting optical fiber end C, and is received by the receiver at the end D. The received optical signal is then processed. The receiver causes a certain amount of deformation in the pipeline according to the pressure of the pipeline liquid. The change in deformation affects the optical power received by the optical fiber. Conversely, the deformation of the pipeline wall is calculated based on the collected reflected light power. Based on the deformation of the pipeline wall, the pressure change of the liquid in the pipeline is inferred. The relationship between the stress and strain of the liquid in the pipeline is obtained through the generalized Hooke's law:

[0049]

[0050] And the stress value in the pipeline is equal to the pressure value in the pipeline, thus completing the pressure change measurement of the pipeline liquid. In the formula, E represents the elastic modulus of the pipe material, ε x is the linear strain in the x direction, ε y is the linear strain in the y direction, ε z is the linear strain in the z direction, σ x is the stress in the x direction, σ y is the stress in the y direction, σ z is the stress in the z direction, and v is the Poisson's ratio.

[0051] When the pressure detection system is activated, the pulse signal generated by the laser semiconductor transmits data through the incident optical fiber, outputting the main control pulse to the transmitting unit. The reflected optical fiber undergoes photoelectric conversion through the optical fiber photoelectric converter, filtering, detection, and analog-to-digital A / D conversion before being sent to the single-chip microcomputer unit. This single-chip microcomputer unit controls the generation of the laser semiconductor pulse, performs signal detection, digital filtering, parameter presets, sound velocity calculation, and transmission functions on the time signal output by the receiving unit. The sound velocity is calculated and connected to the keyboard via a parallel interface. The received commands and parameters are sent to the data processing computer through the communication interface for processing to obtain the pressure value. For preset parameters, the display module displays them on the monitor.

[0052] See Figure 3 and Figure 4 Due to the change in pressure in the pipeline, the pipeline wall undergoes elastic deformation. Considering the change in the elastic modulus E of the elastic strain diaphragm within a large range, the parameter change range in the system when it changes between the maximum and minimum values ​​is given. A certain value or a certain functional relationship cannot be used to set the elastic modulus for calculation and design. The dynamic characteristics calculation of the pipeline must take into account the change in the elastic modulus of the hydraulic medium, otherwise the calculation result will have a large error. If you want to obtain a result that can be applied in engineering, you must use the real-time measurement results for calculation. In this embodiment, for the elastic deformation of the pipeline wall, when the pressure in the pipeline reaches a certain value, it will cause plastic deformation, and the numerical relationship needs to be adjusted. The pipeline wall produces strain, which will cause the distance d between the elastic strain diaphragm and the incident optical fiber B end and the reflecting optical fiber C end to change, which in turn causes the intensity of the received reflected light to change. The receiver, in turn, calculates the change based on the measured light intensity change and the real-time measurement results to deduce the change, thereby deducing the change in pipe wall pressure.

[0053] In an optional embodiment, the wave velocity a of the pipe wall cross-sectional area is measured by an on-site measurement method. After calculation, the initial distance d0 = a / 2T, = d1 = (a+2r) / 2T, T = tan(sin -1 NA), the percentage of the surface of the reflecting fiber end face illuminated by the fiber light cone is:

[0054]

[0055]

[0056] The percentage of incident light power received by the reflecting fiber is:

[0057]

[0058] R=r+2dT

[0059] Where d1 represents the distance from d0 to the peak of the empirical distribution curve, N is the working characteristic reflecting the strain gauge's ability to measure dynamic strain, A represents a monotonically decreasing function of x within the domain, δ represents the gauge factor, r represents the inner diameter of the measured pipe, P0 represents the reflected light power, P1 represents the incident light power, F is the coupling efficiency, dT represents the derivative of the propagating acoustic time t, and NA represents the numerical aperture, a parameter used to describe the ability of optical devices such as optical fibers or lenses to collect and focus light.

[0060] In an optional embodiment, the diameters of the incident and reflected optical fibers are 200 μm, the a value is 100 μm, the NA value is 0.5, the distance d between the optical fibers is the closest value between the edges of the two optical fibers, the optical coupling efficiency is 3.6%, and the d value is calculated to be 200 μm. When the optical coupling efficiency is 7.2%, the d value is 320 μm. It can be seen that the change in d is 120 μm. According to Hooke's law, the change in the liquid pressure in the tube can be calculated by the controller.

[0061] See Figure 5 The distance d between the elastic strain diaphragm and the incident fiber B and the reflected fiber C forms the following relationship with the received light intensity M: Figure 5 The rectangular coordinate empirical distribution curve shown in the figure approaches a smooth curve, i.e., the theoretical distribution curve, when the total number of measured values ​​n is large and the spacing between each group of measured values ​​is small. The shape of the curve shows that when d < d0, the receiving fiber cannot receive light, and this area is a dead zone. When d > d1, the slope of the curve is negative and gradually decreases, indicating relatively poor sensitivity. When the initial distance d0 < d < d1, when d is within this region, the received light intensity M is almost linearly related to the distance d. d0 represents the initial distance, and d1 represents the distance from d0 to the peak of the empirical distribution curve. This also results in relatively good sensitivity. Therefore, when the distance d is d0 < d < d1, the measurement effect is ideal.

[0062] The pressure detection system is based on the nonlinear functional relationship between the pressure P and the propagation speed of the ultrasonic wave in the liquid at t = t1-t2. The least square method is used to statistically calibrate the data. After the mathematical model is processed and the curve is fitted, the polynomial regression equation is obtained: P = ∑k(CC n )

[0063] Where t1 is the time interval between transmitting the pulse and receiving the echo, t2 is the time interval between transmitting the pulse and receiving the penetrating wave, and C o is the initial sound velocity corresponding to zero pressure, and the coefficient k is determined by the least squares method.

[0064] In this embodiment, first, the measured pipeline is taken, the surface of the measured point of the measured pipeline is cleaned, and a protective film layer is coated on the outside of the optical fiber. The protective film is a carbon coating, a polyimide coating, etc.; the elastic strain diaphragm is evenly and flatly attached to the pipeline wall, the incident optical fiber and the reflection optical fiber are installed on the outside of the film, and the optical fiber and the elastic strain diaphragm are adjusted to a suitable distance (d0 < d < d1). The two optical fiber installation points are installed horizontally with the center line of the pipeline. Secondly, when the pressure value in the measured pipeline is known, based on the received optical signal, the pressure detection system calculates the distance d between the incident and reflection optical fibers and the elastic strain diaphragm surface according to formulas (2) to (4). The difference between d and the distance when the pipeline is not pressurized is recorded as d0, that is, the compressive deformation of the pipeline wall. Finally, according to formula (1), the pressure in the pipeline is calculated. This part is automatically calculated by the pressure detection system. The pipeline liquid pressure value is compared with the known pressure value to verify the error range of the present invention. After the system passes the inspection, the system can be used to perform non-contact pressure measurement on the pipeline. It is difficult to establish a comprehensive correction model using traditional mathematical methods. Therefore, the pressure detection system is based on the change of liquid sound velocity caused by the pressure change of the hydraulic system, and uses artificial neural networks to comprehensively correct the ultrasonic sound velocity pressure measurement system. A parallel processing network that simulates the structural characteristics and functional characteristics of biological neural networks is selected. A three-layer BP network is selected, with sound velocity and density as input and pressure as output. The sparse component decomposition technology is used to solve the ultrasonic echo delay and calculate the ultrasonic echo delay. By determining the number of hidden layer nodes and the weight of the network, the artificial neural network training set is used to train the network to obtain a model of the relationship between pressure and ultrasonic delay characteristics. Then, when online, the forward propagation function of the network is used to obtain the corrected pressure value.

[0065] The embodiments of the present invention are described in detail above. Specific implementation methods are used herein to illustrate the present invention. The description of the above embodiments is only used to help understand the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there may be changes in the specific implementation methods and application scope. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for ultrasonically detecting the pressure of a liquid medium in a pipeline, characterized by: The steps include: The pressure detection system uses reflective fiber optic technology to directly attach the elastic strain diaphragm to the outer wall of the monitored pipe. The pressure detection system sends a pulse command, and the light emitted by the laser semiconductor light source is coupled to the incident optical fiber. The incident optical fiber directs the light of the light source to the surface of the elastic strain diaphragm. The elastic strain diaphragm receives the light beam of the laser semiconductor light source through the incident optical fiber. After the light is reflected by the surface of the elastic strain diaphragm, the light senses the liquid pressure in the pipeline from the surface of the diaphragm, causing the pipeline to produce a deformation reflecting the measured pressure. According to the pressure generated by the liquid medium on the metal pipe wall, the tiny deformation of the outer diameter of the pipeline is detected, and the displacement measurement parameters are obtained. The displacement / light intensity conversion is realized and reflected to another reflective optical fiber. After the reflective optical fiber receives it, the reflected light is coupled through the reflective optical fiber and transmitted to the receiver at the end of the reflective optical fiber. The receiver detects the intensity of the received light signal based on the collected reflected light power, calculates the size of the measured signal, and calculates the distance between the elastic mold surface and the optical fiber based on the intensity of the reflected light signal. The deformation amount that changes with the size of the measured signal is obtained from d, and then the pressure change value of the liquid in the pipeline is calculated according to Hooke's law of the deformation of the pipe wall. After completing the measurement of the pressure change of the pipeline liquid, the receiver uses the deformation of the elastic strain diaphragm under the action of pressure to modulate the reflected light power signal to obtain the required measured information, and converts the light intensity signal into an electrical signal. The operational amplifier then performs signal amplification, detection, and filtering, and performs analog-to-digital A / D conversion on the measured analog signal to convert it into a digital signal that can be recognized by the single-chip microcomputer. The dynamic pressure value and dynamic flow rate of the pipeline liquid are calculated, and the emission light intensity coupling efficiency and relative position relationship between the incident optical fiber and the reflected optical fiber are used to reflect the change in the measured displacement. The momentum impulse and volumetric fluid oscillation principles are used to determine the coupling coefficient of the liquid structure, evaluate the impact of fluid pulsation on pipeline performance, and achieve non-invasive dynamic measurement of pipeline liquid pressure and flow changes with the stress value in the pipeline equal to the pressure value in the pipeline.

2. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 1, wherein: The light from the light source propagates from the A end of the incident optical fiber to the B end of the incident optical fiber. The light reaches the surface of the elastic strain diaphragm and is reflected by the surface to the C end of the reflecting optical fiber. It is received by the receiver at the D end of the reflecting optical fiber and then processes the received light signal. The receiver causes the pipe to deform according to the pressure of the pipeline liquid. The change in deformation affects the optical power received by the optical fiber. The deformation of the pipeline wall is calculated based on the collected reflected light power. Based on the deformation of the pipeline wall, the pressure change of the liquid in the pipeline is inferred. The relationship between the stress and strain of the liquid in the pipeline is obtained by the generalized Hooke's law: （1） And the stress value in the pipeline is equal to the pressure value in the pipeline, thus completing the pressure change measurement of the pipeline liquid. In the formula, E represents the elastic modulus of the pipe material, ε x is the linear strain in the x direction, ε y is the linear strain in the y direction, ε z is the linear strain in the z direction, σ x is the stress in the x direction, σ y is the stress in the y direction, σ z is the stress in the z direction, υ is Poisson's ratio.

3. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 2, characterized in that: When the pressure detection system is started, the pulse signal generated by the laser semiconductor transmits data through the incident optical fiber, outputs the main control pulse to the transmitting unit, and the reflected optical fiber undergoes photoelectric conversion through the optical fiber photoelectric converter, and is filtered, detected and analog-to-digital A / D converted and sent to the microcontroller unit.

4. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 3, characterized in that: The single-chip microcomputer unit controls the generation of laser semiconductor pulses, performs signal detection, digital filtering, parameter presetting, sound velocity calculation and transmission functions on the time signal output by the receiving unit. After calculation, the sound velocity is obtained and connected to the keyboard through a parallel interface. The received commands and parameters are sent to the data processing computer through the communication interface for processing to obtain the pressure value. The preset parameters are displayed on the display module on the display.

5. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 4, characterized in that: Regarding the elastic deformation and strain generation of the pipeline wall, the distance d between the elastic strain diaphragm and the B end of the incident optical fiber and the C end of the reflected optical fiber will change, and then the intensity of the received reflected light will change. The receiver performs calculations based on the measured light intensity change and the real-time measurement results to deduce the change amount, and thus deduce the change in the pipeline wall pressure.

6. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 5, characterized in that: The distance d between the elastic strain diaphragm and the B end of the incident optical fiber and the C end of the reflected optical fiber forms a right-angle coordinate empirical distribution curve with the received light intensity M. When the total number n of measured values is very large and the interval between each group of measured values is very small, the obtained empirical distribution curve approaches a smooth curve. When d < d0, the receiving optical fiber cannot receive light, and this area is the dead zone; when d > d1, the slope of the curve is negative and gradually decreases, and the sensitivity is relatively poor. When the initial distance d0 < d < d1 and d is in this part of the area, the received light intensity M and the distance d are almost linearly related. d0 is the initial distance, and d1 represents the distance between d0 and the peak of the empirical distribution curve.

7. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 1, characterized in that: The pressure detection system uses the acoustic time t=t1-t2 of ultrasonic wave propagation in liquid, the pressure P and the acoustic velocity C of ultrasonic wave propagation in liquid to form a nonlinear functional relationship. The least square method is used to statistically calibrate the data. After the mathematical model is processed and the curve is fitted, the polynomial regression equation is obtained: P=∑k(CC o ); Where t1 is the time interval between transmitting the pulse and receiving the echo, t2 is the time interval between transmitting the pulse and receiving the penetrating wave, and C o is the initial sound velocity corresponding to zero pressure, and the coefficient k is determined by the least squares method.

8. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 2, wherein: When the distance d satisfies d0 < d < d1, the wave velocity a is measured by on-site measurement. After calculation, the initial distance , , T = tan(sin -1 NA), the percentage of the surface of the reflecting fiber end face irradiated by the fiber optical cone α is as follows: （2） （3） The percentage of the incident optical power received by the reflected optical fiber is: （4） R = r + 2dT Where d1 represents the distance from d0 to the peak of the empirical distribution curve, N is the working characteristic reflecting the ability of the elastic strain diaphragm to measure dynamic strain, and A represents a monotonically decreasing function of x within the domain of definition. δ represents the gauge factor, r represents the inner diameter of the measured pipe, P0 represents the reflected light power, P i represents the incident light power, F is the coupling efficiency, dT represents the derivative of the propagating acoustic time t, and NA stands for numerical aperture, which is a parameter used to describe the ability of an optical fiber or lens to collect and focus light.

9. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 8, characterized in that: First, take the pipeline to be measured and clean the surface of the measurement point of the pipeline to be measured. The outer part of the optical fiber is coated with a protective film layer, and the protective film is a carbon coating or a polyimide coating; evenly and flatly stick the elastic strain diaphragm on the pipeline wall, install the incident optical fiber and the reflected optical fiber outside the protective film, and adjust the distance between the optical fiber and the elastic strain diaphragm to be an appropriate distance d0 < d < d1. The installation points of the two optical fibers are horizontally installed with respect to the center line of the pipeline. Secondly, when the pressurization value in the pipeline to be measured is known, according to the received optical signal, the pressure detection system calculates the distance d between the incident and reflected optical fibers and the surface of the elastic strain diaphragm according to formulas (2) to (4). The difference between d and the distance d0 when the pipeline is not pressurized is used as the deformation amount of the pipeline wall under pressure. According to formula (1), finally, the pressure in the pipeline is calculated. This part automatically calculates the pipeline liquid pressure value by the pressure detection system and compares it with the known pressurization value to check the error range.

10. The method for ultrasonically detecting the pressure of a liquid medium in a pipeline according to claim 9, characterized in that: The pressure detection system is based on the change in the sound velocity of the liquid caused by the change in the pressure of the hydraulic system. It uses an artificial neural network to comprehensively correct the ultrasonic sound velocity pressure measurement system. It is a parallel processing network that simulates the structural and functional characteristics of the biological neural network. Select a three-layer BP network, with the sound velocity and density as inputs and the pressure as the output. Use the sparse component decomposition technology to solve the ultrasonic echo time delay, calculate the ultrasonic echo time delay, determine the number of hidden layer nodes and the weights of the network, and use the artificial neural network training set to train the network to obtain the relationship model between the pressure and the ultrasonic time delay characteristics. Then, in the online situation, use the forward propagation function of the network to obtain the corrected pressure value.

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