OFDR (optical frequency domain reflection)-based hollow optical fiber continuous liquid level sensing device and measurement method

Abstract

The invention discloses an OFDR (optical frequency domain reflection)-based hollow optical fiber continuous liquid level sensing device and a measurement method. The sensing device comprises a linear swept laser, an optical fiber beam splitter, an optical fiber circulator, a hollow optical fiber, an optical fiber coupler, a photoelectrical detector, a data acquisition card and a computer. Swept laser is split into signal light and reference light by the optical fiber beam splitter; the signal light enters the optical fiber circulator while the reference light enters the optical fiber coupler; the signal light enters the hollow optical fiber through a single-mode optical fiber; retroreflection signal light in the single-mode optical fiber is guided into the optical fiber coupler by the optical fiber circulator and subjected to beat-frequency interference with the reference light at the optical fiber coupler; the photoelectrical detector converts beat-frequency interference signals into electrical signals; the data acquisition card acquires the beat-frequency interference signals in the electrical signals; the computer controls the linear swept laser and the data acquisition card, analytically processes the beat-frequency interference signals and sends data to a lower computer.

Description

technical field [0001] The invention relates to the technical field of optical fiber sensing, more specifically, to a hollow fiber continuous liquid level sensing device and measurement method based on OFDR (optical frequency domain reflection technology). Background technique [0002] The invention is mainly applied to continuous liquid level measurement in petrochemical industry, aircraft oil storage tanks and other flammable and explosive applications. Traditional electronic or mechanical liquid level sensors are limited in liquid level monitoring in flammable and explosive environments. Optical fiber liquid level sensors have the advantages of flame and explosion protection and are more suitable for liquid level monitoring in petrochemical and aircraft fuel. [0003] At present, there are mainly four types of optical fiber continuous liquid level sensors: optical fiber liquid level sensors based on all-fiber interferometers, which realize liquid level measurement by demo...

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Problems solved by technology

[0003] At present, there are mainly four types of optical fiber continuous liquid level sensors: optical fiber liquid level sensors based on all-fiber interferometers, which realize liquid level measurement by demodulating the internal interference spectrum of the sensing structure when the liquid to be measured is immersed in the sensing structure. The accuracy is high, but the repeatability is not high, and the measurement range is very limited, usually only a few centimeters; based on the wavelength adjustment method of the sensing structure such as fiber grating, the grating is fixed on a structure such as a mechanical float, and the rise of the liquid level causes the mechanical float to occur. Deform and act on the fiber grating, so that the wavelength reflected by the fiber grating changes, so as to realize the liquid level monitoring by wavelength demodulation. This method requires an external mechanical structure, and the reliability of the measurement result is not high; based on reflection or transmission intensity demodulation The optical fiber liquid level sensor, by making some special structures, makes the reflected light or transmitted light change when the liquid to be measured acts on the structure, so as to realize the liquid level monitoring

The accuracy of this method is not high, the measuring range is limited, and the measurement result is inaccurate due to the unstable sensing structure; the optical fiber liquid level sensor that detects the back reflection signal, such as the optical fiber liquid level sensor based on OTDR (Optical Time Domain Reflectometry)

Since the OTDR can locate and measure the loss along the optical fiber, when the liquid to be measured acts on the optical fiber, it will change the light back reflection signal at this position, and the liquid level monitoring can be realized by detecting the reflected signal. The measurement of this method The range is large, but the accuracy is very low, generally at the meter level

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