Method and apparatus for distortion free measurements

Claim 1

In a ring laser angular rate sensor of the class wherein two waves propagate in opposite directions along a closed-loop path, wherein the frequency of each of said waves is a function of the rate of rotation of said closed-loop path, said waves establishing a phase difference therebetween, wherein the sensor provides an output signal indicative of the rotation of said closed-loop path, wherein said sensor is provided with a biasing means for introducing a frequency bias in at least one of said waves for preventing said waves from locking in to a common frequency for at least a majority of the time, the sensor comprising: signal means responsive to said waves capable of providing a measurement value related to said phase difference between said waves, said signal means providing said measurement value for occurrences of selected values of the first derivative of said phase difference; means coupled to said sensor for selectively causing said phase difference to take on a substantially random value at selected occurrences of said selected values of the first derivative thereby defining random phase measurement values; first function generating means for generating an empirical probability density function based on said random phase measurement values, said empirical probability density function establishing an empirical probability density value and empirical probability value associated with each measurement value; second function generator means for generating a correction function capable of providing a correction value for said measurement value, said correction value being related to a probability difference between said empirical probability value of said measurement value derived from said empirical probability density function and the true probability value of said measurement value derived from an equal probability density function; and output means for providing a corrected measurement value, said corrected measurement value being the sum of said measurement value and said correction value corresponding to said measurement value.