Feedback Mechanism
Closed-loop control architectures counter physical displacement of a sensing element by applying an opposing electromagnetic or electrostatic restoring force. In high-precision inertial sensors and force-balance accelerometers, a rebalance loop maintains the proof mass at a fixed null position relative to the housing. The magnitude of the electrical current required to hold the mass stationary provides a direct measurement of the input acceleration or force.
This active compensation mechanism ceases to operate when input forces exceed the maximum restoring force capacity of the driver actuator.
Restoring Force
Electromagnetic actuators generate counter-forces proportional to feedback current. Inside force-balance instruments, a rebalance loop drives current through a coil positioned within a magnetic field. Electrostatic feedback configurations apply variable voltage across capacitive plates instead of current through coils.
Dynamic Response
Control loop bandwidth determines the tracking capability and high-frequency noise attenuation of the sensor system. Phase margin and gain margin parameters prevent self-oscillation while ensuring rapid response to transient inputs. When high-frequency vibration excites mechanical resonances in the proof mass, improper loop tuning introduces measurement distortion or instability.
Digital rebalance loop implementations digitize the pickoff signal and compute feedback commands using digital signal processors. Quantization noise and loop processing delay require careful compensation to maintain scale factor linearity across dynamic operating ranges.
Circuit Topology
Analog feedback circuits utilize high-gain operational amplifiers to drive restoring actuators. Precision current-sensing resistors convert feedback current into calibrated output voltage signals for acquisition systems. Temperature drift in reference voltages alters the scale factor calibration over time.
Sensor characterization tests quantify thermal scale factor coefficients to enable downstream software compensation.
