Method for simultaneously measuring distributed type temperatures and strain

Abstract

The invention provides a method for simultaneously measuring distributed type temperatures and strain. A brillouin optical time domain reflectometer and a coherent light time domain reflectometer share the same optical path system and the same circuit system and serve as a sensing measurement system. The sensing measurement system works in a BOTDR mode and a COTDR mode in an alternate mode to measure a brillouin scattering spectrum and a Rayleigh scattering spectrum which are distributed along a single single-mode sensing optical fiber and detect the frequency shift of the brillouin scattering spectrum and the frequency shift of the Rayleigh scattering spectrum, a linear equation set in two unknowns about the temperature and the strain is set up according to the characteristic that the frequency shift of the two scattering spectra is in the linear relationship with the temperature and the strain, and the temperature and the strain of each position of the sensing optical fiber can be obtained by solving the equation set, and then the temperatures and the strain distributed along the whole sensing optical fiber can be obtained. According to the method, the complexity and the manufacturing cost of the system are greatly reduced, no special requirement for the brillouin frequency shift coefficient of the optical fiber exists, and the application range of the measurement system is enlarged.

Description

technical field [0001] The invention relates to a method for realizing simultaneous measurement of distributed temperature and strain by using a single optical fiber, belonging to the technical field of measurement. Background technique [0002] Due to the advantages of strong anti-electromagnetic interference, easy installation of equipment, good insulation, and high sensitivity, optical fiber sensing technology has received more and more attention in the fields of electric power, construction, and civil engineering. BOTDR (Brillouin Optical Time Domain Reflectometry, Brillouin Optical Time Domain Reflectometry) measures the temperature and strain by measuring the frequency shift of the Brillouin scattering spectrum of the incident light pulse in the optical fiber, but the temperature with Brillouin frequency shift And strain cross-sensitivity issues, resulting in indistinguishable temperature and strain, limit the application of this technique. COTDR (Coherent Optical Tim...

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Problems solved by technology

[0004] At present, when using optical fiber sensing technology to measure distributed temperature and strain at the same time, the dual-fiber method is usually used. There are two schemes for this method. One scheme is that two optical fibers are laid in parallel, and the temperature of the Brillouin frequency shift of the two optical fibers , different strain coefficients, measure the Brillouin frequency shift of two optical fibers, and solve the temperature and strain through simultaneous equations. This method is only applicable to special customized optical fibers, and cannot be applied to communication optical cables or photoelectric composite cables.

Another dual-fiber solution is also to lay two optical fibers in parallel, one of which is only affected by temperature, and the other is affected by temperature and strain at the same time, and the Brillouin frequency shift of the two optical fibers is measured, through the simultaneous equations Solving for temperature and strain, this solution is also not suitable for already laid communication optical cables or photoelectric composite cables

In addition, the measurement method combining Raman optical fiber distributed temperature measurement technology with Brillouin technology can be applied to a single optical fiber, but this method requires two sets of optical path systems, the system structure is complex, the cost is high, and it is difficult to apply single mode fiber

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