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We propose the application of Distributed Acoustic Sensing (DAS) based on Rayleigh Coherent Optical Time-Domain Reflectometry (C-OTDR) to unconventional sensing tasks in industrial condition monitoring. As examples we present results on the way to fibre-optic remote sensing of dielectric damage processes in high voltage cable joints as well as to condition monitoring of passive rollers in large industrial belt conveyor systems.
We present results demonstrating several beneficial effects on distributed fiber optic vibration sensing (DVS) functionality and performance resulting from utilizing standard single mode optical fiber (SMF) with femtosecond laser-inscribed equally-spaced simple scattering dots. This modification is particularly useful when using traditional single-wavelength amplitude-based coherent optical time domain reflectometry (C-OTDR) as sensing method. Local sensitivity is increased in quasi-distributed interferometric sensing zones which are formed by the fiber segments between subsequent pairs of the scattering dots. The otherwise nonlinear transfer function is overwritten with that of an ordinary two-beam interferometer. This linearizes the phase response to monotonous temperature variations. Furthermore, sensitivity fading is mitigated and the demodulation of low-frequency signals is enabled. The modification also allows for the quantitative determination of local temperature gradients directly from the C-OTDR intensity traces. The dots’ reflectivities and thus the induced attenuation can be tuned via the inscription process parameters. Our approach is a simple, robust and cost-effective way to gain these sensing improvements without the need for more sophisticated interrogator technology or more complex fiber structuring, e.g., based on ultra-weak FBG arrays. Our claims are substantiated by experimental evidence.
Distributed Fibre Optic Acoustic and Vibration Sensors for Industrial Monitoring Applications
(2017)
We investigate the usability of distributed fibre optic acoustic sensing (DAS) for innovative and advanced monitoring applications in industrial and civil infrastructure installations. In this paper, we report on our ongoing application-oriented research activities regarding the utilization of DAS based on coherent optical time-domain reflectometry (C-OTDR) for condition monitoring of a variety of infrastructures. Specifically, our research presented here aims at acoustic condition monitoring of and fault detection in pipelines and industrial piping systems, at acoustic condition monitoring of rollers in industrial conveyor belt installations, and at acoustic condition monitoring of and threat detection in extensive submarine power cables, respectively. Furthermore, we show a method to mitigate the effect of sensitivity fading of C-OTDR based DAS due to unstable environmental conditions via the modification of the sensor fibre. This can help to provide a continuous adequate sensor functionality for a number of different industrial monitoring applications.
Distributed vibration sensing (DVS) based on Rayleigh single pulse optical time-domain reflectometry (C-OTDR) is an attractive and robust method for a variety of sensing applications including geosensing. A key issue for the usability of DVS systems is the signal-to-noise ratio (SNR) and thus the feasibility to demodulate a measured signal, especially in the case of small dynamic strain amplitudes. We present a simple method to locally boost the sensitivity of DVS using pairs of fs-laser-written strongly scattering fiber segments.
Distributed vibration sensing (DVS) based on Rayleigh single pulse optical time-domain reflectometry (C-OTDR) is an attractive and robust method for a variety of sensing applications including geosensing. A key issue for the usability of DVS systems is the signal-to-noise ratio (SNR) and thus the feasibility to demodulate a measured signal, especially in the case of small dynamic strain amplitudes. We present a simple method to locally boost the sensitivity of DVS using pairs of fs-laser-written strongly scattering fiber segments.