Isolating Micro-Machined Accelerometer Zero-G Bias Shifts under Static Thermal Cycles
Static thermal zero-g bias shifts in MEMS accelerometers are isolated by enforcing prolonged thermal dwell periods to decouple stress creep from thermal gradients.
Dual-Path Hysteresis Tracking
Error Correction
Compensating for direction-dependent sensor offsets requires modeling the distinct behaviors of the sensor output during loading and unloading cycles. This method, termed dual-path hysteresis tracking, uses separate mathematical paths or correction curves depending on the direction of change of the measured variable. The system determines the current direction of the input signal and applies the corresponding calibration curve to generate an accurate output.
This approach is widely used in piezoresistive pressure sensors and mechanical displacement gauges.
Tracking Mechanism
The system utilizes a direction-detection algorithm that monitors the sign of the first derivative of the input signal to decide which path to follow. To prevent rapid switching and noise at the transition points, a small deadband or threshold is implemented around the reversal point. This deadband ensures that the algorithm does not switch paths due to high-frequency noise when the signal is stable.
These distinct paths are merged smoothly at the limits of the measurement range to prevent any discontinuous jumps in the output value.
Calibration Verification
Verifying the performance of this tracking system requires cyclic testing that spans the entire operating range of the sensor at different rates of change. The test sequence must include partial cycles that do not reach the full scale, ensuring that the algorithm can handle minor reversals correctly. These partial cycles are particularly challenging because the tracking algorithm must transition smoothly between the upper and lower correction curves.
This testing ensures that the sensor maintains its specified linearity under realistic, non-monotonic operating conditions.
Application Threshold
High-speed signal variations can degrade the tracking accuracy if the direction-detection algorithm cannot keep pace with the changes. When the frequency of the input signal exceeds the sampling rate of the algorithm, the system may apply the incorrect correction path, resulting in large measurement errors.