Closed-Loop Control
In closed-loop control the controlled quantity is measured, compared with the reference, and an output is produced in the direction that reduces the error between them. The loop repeats continuously. This structure compensates by itself for disturbances, wear and supply variation; that is what open loop cannot compensate for.
A closed loop has four elements: reference, sensor, comparator and actuator. What determines its quality is the accuracy of the sensor and how often the loop runs. As the gain rises the error closes faster but the stability margin shrinks; in every closed loop a balance is struck between speed and stability.
- Whatever quantity is measured is the one that is guaranteed. If you measure position you guarantee position, if you measure speed you guarantee speed.
- When the sensor reads wrongly the system does not know about the error; a closed loop is only as good as the accuracy of its sensor.
On the GS740-3P the loop closes like this: the 0-3.3 V potentiometer signal is the reference, the AS5600 measures the actuator angle, the P controller computes the difference and drives the actuator with a soft ramp. In this way the commanded position is reached repeatably despite vibration and cable friction. Engine speed is outside this loop.
Context in which this term is used: Electronic speed and throttle control on a diesel engine