Optics-Based Strain Sensing System

Abstract

An optics-based strain sensing system is being developed for quazi-distributed strain sensing in locations and environments that are not accessible to conventional strain sensors. The system comprises an Optical Interrogator that has been designed and constructed by Southern Photonics [1], and optical fibre coupled Bragg grating strain sensors. It has been tested using commercial fibre Bragg gratings [2] that were attached to 2 samples of 316 grade stainless steel and cycled in strain and temperature using an Instron mechanical testing machine and temperature controlled cabinet. The results have been compared to the performance of conventional electrical resistance strain gauges. Pairs of fibre Bragg gratings were simultaneously interrogated at 1540 and 1550 nm centre wavelengths to demonstrate the ability of the system to use multiple sensors for quazi-distributed sensing and temperature compensation. The Optical Interrogator resolution is approximately 4 microstrains, accounting for longer term temperature drift, and it is capable of resolving dynamic strains at rates of up to 90 Hz.

Characterisation of a fibre bragg grating system for strain and temperature sensing

“…The FBG's were connected in series and then attached to the Optical Interrogator via a FC/APC type connector. The Optical Interrogator [5,6] has a superluminescent light emitting diode light source to interrogate the FBG sensors where the central frequency was 1550 nm. A Fabry-Perot cavity was used to spectrally resolve the light reflected off the FBG's and it was continually scanned from 1520 nm and 1570 nm where the dual channel sweep rate is 2 Hz.…”

“…We have previously discussed the results from preliminary measurements using FBG's and a new optical interrogator [5] being developed by Southern Photonics [6]. In this report we present a more accurate characterisation in terms of the temperature and strain response.…”