Metrological Foundation
Mechanical compliance rests upon the proof mass suspension to constrain inertial displacement within designated spatial limits while maintaining a defined scale factor. Metrological traceability demands that the mechanical linkage preserves linearity across the operating range without introducing parasitic stiffness that distorts the output signal. Laboratory calibration establishes the nominal transfer function under reference gravitational conditions, yet deployment realities frequently introduce thermal gradients that alter material elasticity.
Thermal expansion coefficients mismatch between the proof mass and the surrounding chassis, shifting the zero-bias point unless compensated by internal algorithms. Calibration protocols verify the scale factor against known rotational velocity inputs, separating true inertial response from mechanical hysteresis induced by hinge friction.
Electrical Coupling
Capacitive pickoff electrodes monitor proof mass suspension displacement by measuring changes in electrical capacitance between fixed plates and the moving element. Excitation voltages applied to the plates generate electrostatic forces that can null the motion, operating the sensor in a closed loop configuration to enhance linearity. Parasitic capacitance within the routing traces adds a fixed offset to the raw reading, requiring baseline subtraction during initial factory tuning.
Signal demodulation circuits extract the displacement magnitude from the carrier frequency, converting analog motion into a digitized measurement stream. Voltage stability directly influences scale factor accuracy, because fluctuations in the supply rail translate immediately into perceived acceleration errors.
Damping Mechanics
Squeeze film damping governs the dynamic response of the proof mass suspension as gas molecules between the moving structure and the substrate compress during travel. Viscous drag forces suppress high frequency resonance peaks, preventing signal saturation during sudden shock events or high vibration episodes. Sealed enclosures maintain a regulated internal pressure of dry nitrogen, stabilizing the damping coefficient against ambient barometric changes encountered in the field.
Molecular rarefaction effects occur if the internal pressure drops below a specific threshold, altering the damping regime from continuous fluid mechanics to free molecular flow. Temperature variations modify the dynamic viscosity of the enclosed gas, shifting the frequency response profile away from the nominal damping ratio specified by the manufacturer.
Failure Boundaries
Overload conditions exceed the elastic limit of the proof mass suspension flexures, inducing permanent plastic deformation that invalidates the calibration history. Shock impacts generate lateral forces outside the primary sensing axis, causing stiction between the moving proof mass and the fixed stop structures. Material fatigue accumulates through continuous micro-oscillations, eventually degrading the spring constant and precipitating sudden mechanical fracture without prior indication.
Electrostatic discharge events can weld the capacitive sensing plates together, fusing the suspension in a permanently deflected state that halts all signal generation. Permanent zero-bias shifts exceeding the electronic reset range signal the end of operational viability for the entire sensor assembly.
