Fiber Optic Gyroscope with Wide Dynamic Range Analog Phase Tracker.
Patent Application, Filed 26 Jul 91,
DEPARTMENT OF THE NAVY WASHINGTON DC
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A simple analog phase tracking circuit used with an open-loop fiber gyroscope that imitates the operation of a true closed-loop gyroscope, by electronically generating a sinusoidal output which nulls the Sagnac phase shift. The nulling or tracking technique is based on the generation of sine and cosine dependent interferometric outputs from an open-loop gyroscope using dynamic phase modulation. Cross-multiplication of the outputs with electronically generated phase shift components and combining these signals obtained from the cross multiplication process produces a component which is dependent on the difference between the Sagnac phase shift and the electronically generated phase. By controlling the electronic phase shift, the output can be nulled. In this way, the phase tracking approach imitates the operation of a true closed-loop gyroscope and uses the simple structure of open-loop gyroscope. The scheme has a wide dynamic range, relatively low drift and short term noise. The analog phase tracker significantly increases dynamic range, as a large number of 2 pi phase excursions could be accommodated with digital tracking. The electronics are very simple and are low in cost.
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