Abstract: To provide a polarization-diverse, heterodyne optical receiving system, a light signal is transmitted into an optical fiber having a plurality of optical sensors that are distinguishable using a multiplexing arrangement. A return light signal from the optical fiber is mixed with an optical local oscillator light signal, where the mixing outputs plural output signal portions having different polarizations. A birefringence of a particular optical sensor is determined based on the plural signal portions.

Abstract: To provide a polarization-diverse, heterodyne optical receiving system, a light signal is transmitted into an optical fiber having a plurality of optical sensors that are distinguishable using a multiplexing arrangement. A return light signal from the optical fiber is mixed with an optical local oscillator light signal, where the mixing outputs plural output signal portions having different polarizations. A birefringence of a particular optical sensor is determined based on the plural signal portions.

Abstract: A method and apparatus for receiving measurements from an interferometer transducer (22) uses a broad band light beam (19A), reflected from the transducer (22), and compares it with the amplitudes of narrow band beams, derived from the reflected broad band light beam (19A), by filters (23A-23D) on different frequencies. The narrow band light beams and the broad band light beam (19A) are measured on photo detectors (22A, 21B-21E). Microprocessor (57) compares outputs of the photo detectors to interpret phase differences between signals (25, 27, 29) from the narrow band beams. A periodically operable shutter and a single photo detector (21) can also be used. Other embodiments modulate (12) the light source (10) to produce very short broad band pulses of light (36, 40) which are reflected from the transducer (22).

Abstract: An apparatus for sensing data from a remote optical sensor 16 has its frequency stabilised by balancing the outputs of narrow band filter 28 30, spaced about a desired frequency 36 positioned at about the 3 db down points 40 of a broad band light source 10 using voltage control, current control or temperature control to vary the frequency of the wide band light source 10. Difference between the outputs through the two narrow band filters 28 30 can be used to drive an amplifier 48 to correct the frequency of the broad band light source. The outputs through the two narrow band filters 28 30 can be converted 52 to binary numbers and fed to a microprocessor 56 which is used, via analog conversion 60, to drive the amplifier 48. The broad band light source 10 can be pulse modulated 68 to provide temporally separate light pulses 92 94 through each of the narrow band filters 28 30, measured at separate times.

Abstract: A method and apparatus for use when measuring pressure in hydrocarbon wells. A sensor, an interferometric optical pressure transducer, at the end of a fibre optic line is illuminated by broadband light pulses. Measuring equipment output drives a display indicating the pressure at the sensor. The transducer is modelled by subjecting it to known pressures. The measuring equipment is modelled by applying test signals. The models are combined and a display output C is assumed. A mathematical model is used to calculate an estimation B of the actual output A from the sensor. B is compared with A and the value of C changed until the closest match is found between A and B. This value of C is taken as the output representing the pressure at the sensor. Different models and compensation factors allow for interchange of sensors and sensor types and measuring equipment and measuring equipment types.

Abstract: An apparatus for tracking a rotating blade to determine parameters associated with the rotation of that blade. In one embodiment, the apparatus includes a detector in which at least two sensing photodiodes define substantially fan shaped detector planes and are arranged to sense an illuminated point at a known location on the blade passing through these planes. The time taken for the point on the blade to pass between the planes is measured and parameters associated with the rotation of the blade are calculated therefrom. In another embodiment, the detector defines at least two divergent detector fields, and a reactive radiation source responsive to the passage of the blade through the detector fields is provided on the blade. The reactive radiation source is arranged to radiate a signal such as a light signal which is detected by the detector.

Abstract: This invention relates to apparatus for producing a periodic output signal having a predetermined period ratio (a/b) relative to a periodic input signal.Signals from a tachometer on a gearbox are received by a counter timer unit, the counter timer unit evaluates the number of clock pulses k.sup.o received from a clock within each period of the tacho signal. A control unit receives values of k.sup.o from the counter timer and employs an algorithm based on the following equation to calculate a count value n.sup.o to be loaded into a register for the next tacho period. ##EQU1## where dK represents k.sup.-1 -k.sup.o. An accumulator is connected via an adder to the register and at receipt of each clock pulse from the clock adds the count stored in register into the accumulator. An output is produced on line when the accumulator overflows.