Physical Motion
Movement of a suspended internal element relative to its housing provides the mechanical signal for measuring acceleration or rotation. This proof mass displacement is the fundamental principle behind many inertial sensors. The distance the mass travels is proportional to the external force applied to the device.
Detection Method
Capacitive or optical sensors detect the change in position of the internal mass. During operation, proof mass displacement is usually kept small to maintain the linearity of the sensor. Feedback loops often apply an opposing force to keep the mass centered.
Error Source
Mechanical shocks or intense vibrations can cause the mass to hit its physical travel limits. Such excessive proof mass displacement leads to signal clipping or permanent damage to the suspension springs. Parasitic forces, such as electrostatic attraction or magnetic fields, may also induce unwanted motion.
Calibration must account for the stiffness of the springs and the damping of the surrounding gas. If the springs are not perfectly linear, the sensor output will exhibit distortion. Engineers design the suspension to be as symmetrical as possible to reject cross-axis sensitivity.
Performance Limit
The resolution of the sensor is limited by the smallest proof mass displacement that the electronics can resolve. Thermal noise eventually sets the floor for this measurement in miniaturized silicon sensors.
