Abstract: An embedded optical sensor has a plurality of layers 10-20 and an optical fiber 21 with a fiber grating 28, disposed between the layers 14,16. The layers 10-20 comprise filaments 22 and resin 24 which have different thermal expansion coefficients and the filaments 22 are oriented so as to create unequal transverse residual stresses that act through the geometry of a resin-rich region that surrounds on the grating 28 in the fiber 21. The unequal transverse residual stresses cause birefringence in the grating 28, thereby causing the grating 28 to reflect light 32 having two wavelengths with a predetermined separation, each along a different polarization axis. The wavelength separation and average wavelength between such separation have different sensitivities to temperature and strain, thereby allowing independent temperature and strain measurements using only a single grating.

Abstract: An optical strain measuring arrangement including an optical waveguide comprising first and second cores fixedly mounted with respect to a mechanical structure to be monitored, and a detection system for relating the contrast in light intensity emerging from said cores to a range of wavelengths to establish an indication of strain along the range of the optical waveguide.

Abstract: A sensor employs a laser to obtain a collimated light beam for transmission across the gas effluent of a catalytic cracking process. Particulate matter entrained in the gas flow forward scatters light energy to a collecting aperture which, in turn focuses the scattered light on a first photodetector. A second photodetector receives directly transmitted light energy. A ratio between the output signals of the two photodetectors is derived and presented to a threshold level detector. If the magnitude of the scatter exceeds a predetermined level it is concluded that a catalyst load dump has occurred. The optical system is carefully selected to ensure that only light energy scattered from a sample volume within the entrained gas flow reaches the first photodetector. This is important because it prevents particulate matter on the surfaces of the transparent windows from affecting the operating of the sensor.