Position Feedback
Position feedback is measuring with a sensor the position the actuator is actually at and comparing it with the commanded position. The actuator is driven until the difference is zero. In this way the system verifies not that the motor has turned but that the target has really been reached.
Without feedback an actuator only carries out the command "drive this much in this direction"; if there is an obstacle on the way, if mechanical strain occurs or if the supply fluctuates, the actual position deviates from the command and the system cannot know it.
- Seeing the deviation: if the difference between command and measurement grows and does not close, there is a mechanical binding or cable slippage. This is a direct clue in fault diagnosis.
- Repeatability: the same command gives the same physical position every time; the effect of friction hysteresis is reduced.
On the GS740-3P this measurement is made with the AS5600 magnetic encoder and the closed-loop P controller works on this difference. Its limit must be stated clearly too: the quantity measured is the actuator's angle, not the engine's speed. If the cable comes off the throttle lever the encoder still reads the correct angle and the system thinks it has reached the target; for that reason the soundness of the mechanical connection must be checked periodically.
Context in which this term is used: Electronic speed and throttle control on a diesel engine