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.
Static Tumble Calibration
Orientation Sequence
Multi-position rotation sequences for accelerometers use the Earth’s gravity vector as a constant acceleration reference to determine sensor errors. During a static tumble calibration, the sensor is held in a series of predetermined orientations on a multi-axis indexing table. This procedure allows each axis to experience the full range of plus and minus one g.
The data gathered is used to calculate the sensor biases and scale factors.
Gravity Referencing
Utilizing a constant natural field eliminates the need for expensive dynamic acceleration standards like centrifuges during the baseline test. For a static tumble calibration, the indexing table must position the sensor with high angular accuracy to prevent tilt errors from skewing the results. The local gravity value must be known and stable during the test.
This referencing provides a highly traceable calibration path for the sensor.
Error Identification
Mathematical separation of the different sensor errors is achieved by analyzing the sensor outputs across the complete set of orientations. When executing a static tumble calibration, the software fits the collected data to a mathematical model of the sensor. The algorithm can separate the bias, scale factor and misalignment errors because each has a distinct signature across the tumble sequence.
If the sequence is incomplete, some of these parameters may become coupled, leading to calibration errors. This coupling is avoided by using a full twelve-position tumble sequence. The resulting parameters are saved to the device register.
Sourcing Assembly
Automated tumble stages are integrated into high-volume sensor testing cells to calibrate hundreds of modules simultaneously. For a static tumble calibration setup, the stage must be free from thermal expansion that could alter the alignment of the rotation axes. The mounting fixture is monitored with temperature sensors to detect and correct for thermal drift.