Control Stability Reduction
Decrease in the safety buffer of a feedback loop leads to oscillations and unpredictable system behavior. When phase margin degradation occurs, the delay between the corrective action and the measured error increases toward a critical threshold. This loss of stability is often caused by adding slow sensors or heavy digital filtering to a high speed control circuit.
Loop Gain
Amplification of the error signal affects how the system reacts to changes. If the gain is too high at the frequency where the phase shift reaches 180 degrees, the system becomes unstable. Engineers use Bode plots to visualize the relationship between the gain and the phase across the frequency spectrum.
System Oscillation
Physical symptoms of a low margin include ringing or overshoot when the setpoint changes. In a motion control system, this might appear as a vibration in the motor shaft. In a temperature controller, the heater may cycle on and off too slowly to maintain a steady value.
Feedback Correction
Adjusting the controller parameters can restore the stability of the loop. Reducing the proportional gain or increasing the derivative time can compensate for the phase loss. Careful selection of sensor bandwidth and filter settings prevents the problem from occurring during the initial design phase.
