Bias Instability Figures That Decide Whether Dead Reckoning Holds
Inertial dead reckoning holds only while gyroscope bias instability bounds cubic tilt divergence within allowable spatial position tolerance thresholds.
Gravity Vector Coupling
Axis Interaction
Interaction between the local gravitational field and the sensing axes of an accelerometer or inclinometer that results in cross axis interference. Misalignment between the internal sensing element and the external package housing leads to gravity vector coupling when the device is not perfectly level. It establishes the baseline error for static tilt measurements in industrial leveling and structural monitoring applications.
Geometric Alignment
Orthogonality errors between the three primary axes of a sensor chip cause a portion of the vertical gravity force to appear on the horizontal outputs. In a system prone to gravity vector coupling, a tilt in one plane will register as a change in an unrelated axis. Precision machining of the mounting surface is required to minimize this mechanical offset during installation.
Measurement Bias
Calibration procedures identify the transformation matrix needed to rotate the raw sensor data into the true coordinate frame. This correction for gravity vector coupling involves a multi-position tumble test where the sensor is held stationary at various orientations. The difference between the expected gravity value and the measured value defines the coupling coefficients.
Interference from local magnetic fields or vibrations can obscure these readings if the test environment is not isolated.
Tolerance Verification
Manufacturers specify the maximum cross axis sensitivity as a percentage of the full scale output. This limit for gravity vector coupling is verified at the factory using precision dividing heads. End users must periodically re-calibrate the system to account for any mechanical shifts caused by thermal cycling or aging.