CN-121994329-A - Dual-mode OTDR liquid level measurement method based on interference signal enhancement

CN121994329ACN 121994329 ACN121994329 ACN 121994329ACN-121994329-A

Abstract

The invention relates to a dual-mode OTDR liquid level measurement method based on interference signal enhancement. The method comprises the steps of constructing an optical path system comprising double transmission channels, acquiring a switchable first OTDR optical path and a switchable second OTDR optical path, acquiring initial position information of a liquid level by acquiring reflected light signals of the end face of a probe, acquiring modulated detection light by a laser frequency modulation device, utilizing the reflected light of the end face of the probe and the reflected light of the liquid level to form beat frequency interference signals, analyzing to obtain beat frequency values, calculating the distance between the probe and the liquid level, acquiring parallel emergent light and stable light spots by a spherical probe to obtain reflected light signals with stable amplitude, acquiring a compliance beat frequency interference signal, acquiring distance data, circularly switching the double optical paths to acquire positioning signals and distance signals, judging the fluctuation state of the liquid level, generating early warning signals, regulating sampling frequency according to the early warning signals, acquiring distance monitoring data, and updating a liquid level position change curve in real time. The dual mode OTDR level measurement is achieved.

Inventors

CUI HUAIJUN
ZHU TIANFENG

Assignees

上海嘉慧光电子技术有限公司

Dates

Publication Date: 20260508
Application Date: 20260203

Claims (12)

1. A dual mode OTDR level measurement method based on interference signal enhancement, comprising: S1, acquiring a switchable first OTDR optical path and a switchable second OTDR optical path, switching a channel to the first OTDR optical path to acquire a probe end face reflected light signal, identifying the instant moment when an optical fiber probe enters a liquid level, and acquiring preliminary position information of the liquid level by combining the motor motion parameters of the probe; S2, switching a second OTDR optical path by an optical switch based on the preliminary position information of the liquid level, and carrying out frequency modulation on a light source through a laser frequency modulation device to obtain modulated detection light, obtaining a beat frequency interference signal, obtaining a beat frequency value through analyzing the beat frequency interference signal, and calculating corresponding parameters to obtain the distance between an optical fiber probe and the liquid level; S3, acquiring distance data between an optical fiber probe and the liquid surface based on the compliant beat frequency interference signal, circularly switching corresponding channels through an optical switch, acquiring a liquid level positioning signal of the OTDR and a distance signal of the OTDR, acquiring a fluctuation early warning signal by judging a liquid level fluctuation state, regulating and controlling the signal sampling frequency of the OTDR based on the fluctuation early warning signal, acquiring distance monitoring data, updating a liquid level position change curve in real time, and dynamically tracking and monitoring the liquid level position.
2. The method of claim 1 wherein the step of obtaining the switchable first and second OTDR optical paths includes obtaining a switchable optical path infrastructure by constructing an integrated optical path of the first and second dual transmission channels, configuring the first channel as a typical OTDR optical path and configuring the second channel as an improved OTDR optical path in series with a laser frequency modulation device to obtain the first and second OTDR optical paths, and switching the optical paths between the first and second OTDR optical paths by a channel switching command of the optical switch.
3. The method of claim 1, wherein the specific process of obtaining the preliminary position information of the liquid level comprises the steps of transmitting pulse light emitted by a light source to an optical fiber probe through a coupler and a circulator based on the transmission characteristic of a first OTDR light path to obtain a reflected light signal of an emergent end face of the optical fiber probe, comparing the reflectivity difference of the optical fiber probe in air and liquid to obtain a reflected light amplitude abrupt change signal, capturing the instant moment when the optical fiber probe enters the liquid level, and calculating the preliminary position information of the liquid level by combining the movement speed and the travel parameter of a motor connected with the probe.
4. The method of claim 1, wherein the frequency modulating the light source by the laser frequency modulating device comprises connecting the laser frequency modulating device in series between the light source and the coupler based on the structural design of the second OTDR optical path to obtain a frequency-adjustable optical transmission path; And the working parameters of the modulating device are calibrated in real time to obtain the modulated detection light with the frequency linearly changed.
5. The method of claim 1, wherein the specific process of obtaining the beat frequency value by analyzing the beat frequency interference signal comprises the steps of extracting time domain intensity change data of the beat frequency interference signal based on the second OTDR optical path to obtain an original time domain signal, converting the original time domain signal into a frequency domain signal through Fourier transformation to obtain a frequency domain spectrogram, positioning a peak position corresponding to the beat frequency based on the frequency domain spectrogram by using a peak identification algorithm, and analyzing by combining frequency resolution parameters of the spectrogram to obtain the beat frequency value.
6. The method of claim 1, wherein the obtaining parallel emergent light comprises performing spherical surface treatment on an optical fiber end face to obtain an optical fiber probe, performing total reflection transmission on light emitted by a light source in the optical fiber probe to obtain quasi-parallel light, and optimizing curvature radius parameters of the spherical end face to obtain parallel emergent light.
7. The method of claim 1, wherein the obtaining the reflected light signal comprises obtaining liquid surface reflected light based on a transmission characteristic of parallel emergent light, adjusting output power of a light source by using matching property of the liquid surface reflected light and reflected light of an end face of a probe to obtain double-beam reflected light, and obtaining the reflected light signal with amplitude fluctuation smaller than a preset threshold value by filtering an external light interference signal.
8. The method of claim 1, wherein the specific process of obtaining the compliant beat frequency interference signal comprises obtaining an initial interference signal based on the large receiving angle characteristic of the spherical probe, performing signal-to-noise ratio analysis by using the initial interference signal to obtain a primary interference signal with a compliant signal-to-noise ratio, and calibrating phase offset caused by optical path difference to obtain the compliant beat frequency interference signal.
9. The method of claim 1, wherein the specific process of obtaining the distance data between the optical fiber probe and the liquid level comprises the steps of calling a preset distance calculation formula to obtain an original calculation value of the liquid level distance based on a beat frequency value obtained by analyzing the compliance beat frequency interference signal, correcting an environment influence parameter of a measurement error of a medium refractive index and a light speed based on the original calculation value to obtain a distance correction value, and verifying the rationality of a calculation result based on the comparison of the distance correction value and the preliminary position information of the liquid level to obtain the distance data between the optical fiber probe and the liquid level.
10. The method according to claim 1, wherein the specific process of circularly switching the corresponding channels through the optical switch comprises presetting a cycle switching period of the optical switch based on the distance data, obtaining a time interval parameter of channel switching, controlling the optical switch to alternately switch between the first channel and the second channel, obtaining a real-time distance signal of a liquid level positioning verification signal of a first OTDR and a second OTDR, performing time sequence alignment processing on the liquid level positioning verification signal and the real-time distance signal, correspondingly identifying a positioning verification signal and a real-time distance signal according to time stamps, and obtaining a time sequence synchronous dual-mode monitoring signal.
11. The method according to claim 1, wherein the specific process of acquiring the distance monitoring data comprises analyzing the fluctuation amplitude of the real-time distance signal based on the dual-mode monitoring signal, judging the stable state of the liquid level to obtain a liquid level fluctuation state judgment result, and based on the sampling frequency lifting instruction, increasing the sampling density of the signal to a preset multiple to acquire the distance monitoring data and capturing the fluctuation period.
12. The method of claim 1, wherein the specific process of dynamically tracking and monitoring the liquid level position comprises the steps of constructing a liquid level position change data set according to time sequence based on distance monitoring data, obtaining time sequence change information of the liquid level position, generating a liquid level position change curve by adopting a data fitting algorithm to obtain dynamic change trend of the liquid level, updating curve parameters in real time and setting an abnormal threshold value, and tracking and monitoring the liquid level position.

Description

Dual-mode OTDR liquid level measurement method based on interference signal enhancement Technical Field The invention belongs to the technical field of liquid level measurement, and particularly relates to a dual-mode OTDR liquid level measurement method based on interference signal enhancement. Background The current level measurement technology still has the following to be improved: In the fields of modern industrial production, energy management, chemical storage and the like, accurate and real-time monitoring of the liquid level position is a key link for guaranteeing production safety and optimizing resource allocation. The current mainstream liquid level measurement technology can be divided into contact type and non-contact type, but has obvious technical bottlenecks, and is difficult to simultaneously meet the comprehensive requirements of low cost, high precision, wide adaptation, stability and reliability. The contact type measuring method (such as floating ball type, capacitance type and static pressure type) needs to be in direct contact with the measured liquid, and when the measuring is carried out on the highly corrosive, high-viscosity or easily polluted liquid, the problems of probe corrosion, scaling, polluted liquid and the like are easy to occur, so that the service life of equipment is shortened, the measuring accuracy and the production safety are possibly influenced, and the application scene is greatly limited. In the non-contact measurement technology, the conventional OTDR (optical time domain reflectometer) method is applied to a certain extent by virtue of the advantages of simple structure, low cost, convenience in operation and the like, and the core of the method is to position the liquid level by detecting the difference of the reflectivity of an optical fiber probe in air and liquid, but the method is limited by pulse light transmission characteristics and signal analysis precision, and the measurement precision can only reach the meter level and cannot meet the millimeter-level monitoring requirement in a precise industrial scene. Although the OFDR (optical frequency domain reflectometer) technology capable of realizing high-precision measurement has higher spatial resolution, the technology relies on an expensive narrow bandwidth sweep-frequency light source, a double-interference light path and a balance detector, so that the technology has the advantages of complex hardware structure, high manufacturing cost, high debugging difficulty and high maintenance cost, and is difficult to realize large-scale mass production and wide popularization and application. Meanwhile, the traditional optical fiber probe for non-contact measurement generally adopts a plane emergent end face design, so that the divergence angle of the emergent light signal emitted by the light source is large, the size of a light spot and the density of optical power formed on the liquid level are easy to severely fluctuate along with the change of the distance between the probe and the liquid level, and further the reflected light receiving quantity of the liquid level is small and the signal amplitude is unstable. In addition, the receiving angle of the plane probe is limited, liquid level reflected light is difficult to collect effectively, so that the signal-to-noise ratio of interference signals formed by the probe end face reflected light and the liquid level reflected light is low, amplitude fluctuation exceeds a practical threshold value, and analysis accuracy of the interference signals and reliability of measurement results are seriously affected. On the other hand, the existing liquid level measurement technology adopts a single measurement mode, and cannot meet the dual requirements of quick positioning and accurate monitoring, namely the technology with the quick positioning function is insufficient in precision, the positioning efficiency is low only by pursuing the technology with high precision, and when facing a liquid level fluctuation scene, a dynamic adaptation mechanism is lacking, a sampling strategy cannot be adjusted according to the liquid level stability, the problem that critical data are missed to be measured or redundant data are too much easily occurs, and the practicability and the suitability of the measurement technology under complex working conditions are further limited. In summary, the existing liquid level measurement technology has many shortcomings in measurement accuracy, cost control, scene suitability, signal stability and the like, and a novel measurement method capable of integrating low-cost rapid positioning, high-accuracy real-time monitoring, optical path design optimization and signal processing logic is needed to break through the bottleneck of the prior art. Disclosure of Invention In order to solve the problems in the prior art, the invention provides a dual-mode OTDR liquid level measurement method based on interference signal enhancement; the aim of th