Static Accelerometer Orientation Tumble Calibration Procedures
Static tumble calibration calculates accelerometer bias, scale factor, and cross-axis matrices by optimizing spatial vector residuals against local gravity.
Gravitational Acceleration
Reference Force
Natural physical constants acting on a known mass provide the fundamental reference standard for calibrating acceleration transducers. The local value of gravitational acceleration acts as the primary acceleration vector during static sensor calibration. This reference is used to establish the sensitivity of the sensor by rotating it through a full circle in the gravity field.
The accuracy of this method depends on the precision of the positioning stage and the local gravity model.
Geographical Variation
Values of gravity change depending on the latitude and elevation of the test laboratory. When utilizing gravitational acceleration for high-precision sensor calibration, engineers must calculate the local acceleration using a gravimeter or a detailed geographic model. The difference between the standard value and the actual local gravity can introduce a measurable systematic error.
This variation is compensated for by adjusting the calibration software parameters.
Calibration Datum
Inscribing the sensor with a precise sensitivity factor requires a traceable link to the international standard value. For an accelerometer calibrated against local gravitational acceleration, the uncertainty budget includes the local gravity calculation and the alignment of the calibration axis. The tolerance of the tilt stage must be verified to ensure the sensor axis is aligned with the gravitational vector.
If the alignment is off, the measured acceleration is reduced by the cosine of the misalignment angle.
Buoyancy Disturbance
Atmospheric pressure changes affect the force on the proof mass inside the sensor during testing. While the influence on gravitational acceleration itself is non-existent, air density variations must be monitored. The calibration is carried out in a sealed chamber to avoid these issues.