Step Response
The time response the system gives when the command is stepped abruptly from one value to another. It is summarized with three numbers: rise time, overshoot percentage and settling time. This is the measurement that shows fastest whether the controller settings are right.
For the measurement the command is changed abruptly and the result is recorded. Three things are looked for on the graph:
- Rise time: the time to reach the greater part of the target. Being short indicates agility.
- Overshoot: the amount of going above the target. Overshoot above ten percent is generally considered excessive in hydraulic position control.
- Settling time: the moment of staying permanently within a narrow band. If there is oscillation this time lengthens.
Overshoot and oscillation are the classic sign that the controller gain is set too high; reducing the gain or increasing the derivative term improves damping. If the response is too slow the opposite applies. In hydraulics the compressibility of the oil and the inertia of the load also set a natural limit, and you cannot go below that limit with electronics. Long hoses and air in the oil noticeably distort the measured response; make sure the hydraulic side is sound before tuning the controller.
Where this term is used: What Does the HCT402 Achieve, How, and How Much? A Technical Review