Ground Alignment Error Bounds for Inertial Navigation Initialization
Ground alignment error bounds depend on accelerometer turn-on bias for leveling and East gyro bias stability divided by cosine latitude for heading accuracy.
Multi-Position Indexing
Calibration Method
Calibration method that involves rotating a sensor into several precisely known orientations to isolate and calculate individual error terms. This multi-position indexing allows for the simultaneous determination of bias and scale factor for each axis of an inertial instrument. The process uses the gravity of the earth or the rotation of the planet as a constant and reliable reference stimulus.
Procedure Sequence
A sensor is mounted on a high-precision rate table or dividing head that can move it through specific angles. During multi-position indexing, the device is typically held stationary at each point to collect a large sample of data. Comparing the measured values at these different positions provides the mathematical basis for solving the error equations of the sensor.
Mathematical Model
Equations describe how the sensor output changes as its sensitive axis is aligned with or against the reference vector. Through multi-position indexing, engineers can separate the constant bias from the portion of the signal that varies with the orientation. This process generates a correction matrix that is programmed into the navigation computer to improve the accuracy of the device.
The resulting coefficients account for the physical mounting errors that are unique to each individual unit.
Efficiency Gain
Modern automated test stands perform these rotations rapidly to minimize the total time required for calibration.