Overshoot
Overshoot is the speed or actuator position going past the target after a command change. An overshoot of a few percent of the target is acceptable in most applications; overshoot beyond ten percent indicates that the gain is too high or that inertia is building up in the mechanics.
Overshoot arises from the combination of the system's inertia and the controller's aggressiveness. The controller sees a large error and drives the actuator hard; when the error approaches zero the kinetic energy is still there and the target is passed. A correction in the opposite direction follows, and the system settles after a few oscillations.
- Lowering the gain reduces overshoot but lengthens the settling time.
- Applying a ramp cuts overshoot at the source: the command is given as a controlled slope, not as a step.
On an engine, the practical cost of overshoot is not just comfort. If the throttle opens abruptly, a diesel gets momentarily too much fuel, producing black smoke and an unnecessary speed spike; on a pump, a sudden flow increase creates a shock in the line. On the GS740-3P the position command is applied with a soft ramp, which limits overshoot on the actuator side. Steadily growing overshoot is the first sign that the stability limit is being approached.
Context in which this term is used: Electronic speed and throttle control on a diesel engine