Abstract: Sensors for use in sensing the level and temperature of a corrosive medium contained in a container. The sensors have particular use in the semiconductor manufacturing industry, however the sensors also have applications in the biotech, pharmaceutical, plating, chemical, petroleum, etc. industries. The sensors comprise first and second elongate, conductive sensor members, each of which has a longitudinal axis and is dimensioned to extend into the medium. The first and second sensor members each include a core that is made from a non-metallic, electrically resistive material having a plurality of non-metallic conductive fibers embedded therein. Each core has opposite ends and the fibers are oriented parallel to the longitudinal axis of the first and second sensor members and extend continuously substantially between the ends of the cores. Media level can be sensed by comparing the capacitance of the sensor members, which changes as the level of the media changes.

Abstract: An optical fiber coil assembly comprising two optically interconnected optical fiber coils or coil parts (22, 23) rigidly supported in predetermined positional relationship by respective rigid support means so constructed and arranged that static or quasi-static pressure (P) applied to the assembly produces a decrease in the path length of one of the coils or coil parts, and an increase in the path length of the other.

Abstract: An optical sensing system (e.g. hydrophone) includes a plurality of laser light sources for producing light signals of different frequencies which are combined by a Bragg cell and launched into a single optical fibre leading to an optical sensor array arrangement. This sensor array arrangement includes a plurality of optical sensors separated by redirecting means for redirecting light signals along an optical fibre in time displaced relationship to an optical detector.

Abstract: An optical phase modulator comprises a body 1 of a matrix material which supports a length of optical fiber 2, the said body including a polymer material having piezoelectric properties and being provided with spaced electrode areas 4 such that the application of an electrical potential between said areas will produce a mechanical strain in the body 1, the said strain affecting the said fiber 2 so as to control phase modulation of light when this is present in the fibre. This can give a device of inexpensive construction which is robust and has high sensitivity.

Abstract: Inertially insensitive optical fibre hydrophones are described, utilizing materials and configurations to obtain acceleration balanced designs suitable for underwater applications where acceleration is a problem. Balancing and/or insensitivity is obtained both in longitudinal and axially perpendicular directions. Acoustic sensitivity of a coil formed by the fibre is maintained by the properties of materials used to provide a rigid former, encapsulant material and secondary material which form the hydrophone.

Abstract: An optical sensing system comprising single light source and a series of phase shifting switching devices positioned linearly aligned with the light source. Each phase shifting device is driven by a driving device with pulses at different frequencies and sequentially from the most proximately located phase switching device to the most distant phase switching device so that light eventually passes through each of the phase switching devices. Fiber sensor arrays are aligned with each of the phase switching devices and light reflected from the fiber sensor arrays is detected by a plurality of photodetector devices each associated with a fiber sensor array.

Abstract: A multiplex optical sensing system comprises an optical fibre arranged to be subjected at the longest length to fibre deforming forces during operation of the system and means for producing a plurality of pulse trains of coherent light in which the frequency of frequencies of (F1+.DELTA.F1), (F2+.DELTA.F2), (F3+.DELTA.F3) of the pulses in respective pulse trains lie within a different frequency channel for transmission along said optical fibre.