Over the past few weeks I have been working to try to find the optimal method for eliminating the null bias without using sensor fusion methods (e.g. other sensors and a Kalman filter). The elimination of null bias is of particular importance in our application since the rate is integrated over time to find the total angular deflection; a bias leads to an erroneous deflection that is linear in time. The method that was most reported in the literature, including one found on the Analog Devices webpage, was to take stationary measurements for a period of time, average the data, and subtract from future measurements; this method did not provide adequate results. As seen in the attached plot, the stationary gyro reports a wide range of apparent deflections most showing some degree of linear dependence, indicating that the bias was not entirely eliminated to a reasonable degree.
The null bias determination process took 200 samples over a 30 second time interval and then subtracted the calculated value from all subsequent readings. A moving filter (averaging window of 32) was also applied to eliminate noise.
An Allan Variance curve was determined and future steps will include null bias determination over a period that captures bias instability (approximately 200 seconds) to see if it improves bias resolution.
My questions are as follows:
- - Are their any other recommended methods for null bias elimination you could suggest?
- - Since the sensor is already temperature compensated is there any need to further calibrate?
- - Do you believe the a null bias that captures the bias instability would greatly improve performance?