Fibre optic sensing device and method

Claim 1

Detector apparatus including a fibre optic sensor comprising: a length of optical fibre having a core and a sheath respectively comprising materials the refractive indices of which vary differentially in accordance with a physical variable to be sensed and which causes corresponding changes in the back-scattering of radiation injected into the optical fibre, optical pulse supply means for supplying to said length of optical fibre a pulse of electromagnetic radiation at wavelengths in a range including visible, ultraviolet and infrared wavelengths, mode filter means for rendering said detector apparatus substantially insensitive to changes in a numerical aperture of said fibre core; radiation sensing means positioned to receive optical radiation back-scattered by the length of optical fibre, detector means responsive to said radiation sensing means to provide an output signal dependent on the intensity of the back-scattered radiation, processor means coupled to said detector means for deriving from said output signal a control signal dependent on sensor variations in said physical variable comparator means to compare changes in said control signal with a predetermined algorithm, and output means responsive to said control signal for providing an output signal dependent on said sensor variations.