DESIGN AND SIGNAL PROCESSING OF FIBER OPTICS ROLL SENSOR

Abstract

DESIGN AND SIGNAL PROCESSING OF FIBER OPTICS ROLL SENSOR By Rana Fayyaz Ahmad Fiber Optics based rotation rate sensors can be considered an important technology for the future applications related to guidance and control. Its “Solid state/static” configuration has the advantages over the previous approaches using spinning wheels or gas ring laser based rate sensors. It has greater reliability and longer life. The fiber optics rotation rate sensors requires a multidisciplinary approach involving physics, opto-electronic technology, signal processing theory and electronic design. The fiber optics rotation rate sensor is based on the Sagnac effect which explains that it is possible to detect the rotation w.r.t inertial space with an optical system having no moving parts. The fiber optics gyros developed mostly used in the application where the bias drift requirement is less than 0.1 deg/hr. For this kind of design, the maximum achievable rate is up to 400 deg/sec (Open Loop Configuration). To detect the higher rotation rates more than 1000 deg/sec, a new optical design as well as a signal processing scheme is required. To measure the higher roll, a scheme is developed which is able to detect the higher rates or roll. The open loop scheme is followed for this due to lower cost of the optical components than others available. The optical sensor is modulated at 74 KHz .Multiple Harmonics are received at the detector output. The signal conditioning is carried out by designing low noise electronics. Direct digital processing is used. The signal is sampled at 1 M Samples/sec. A signal processing scheme based on the state space RLS concept is developed. The SSRLS filter places the nulls on the undesired frequency components .This SSRLS filter has the capability to suppress multiple harmonics of the fundamental frequency as well as any other sub harmonics . Sagnac phase shift is calculated from the first and second harmonics. This phase is directly proportional to the rate and after integration the roll can be calculated.