Closed loop fiber optic gyroscope with reduced sensitivity to electronic drift

摘要

A closed loop fiber optic gyro features signal processing wherein square wave phase modulation is added to a modulation drive signal after overflow logic so that the square wave modulation will not cause a phase modulation ramp to exceed overflow/underflow logic limits. The arrangement is such that the phase modulation causes a retrace with each modulation period when the amplitude of the ramp is within predetermined limits. A variable time constant in a retrace correction loop gives better retrace limit correction performance when the gyro is first turned on as during a "warm-up" period. The amplitude of the gyro square wave output is determined by taking the difference between the output of the first half cycle of the square wave modulation and the average of adjacent second half cycles thereof. An error signal for a retrace limit is developed by considering changes in the square wave amplitude and not the square wave amplitude itself. Corrections in the retrace limit are implemented via a variable digital retrace point. These features are effective for reducing gyro sensitivity to electronic drift.