(a) Settling Time:
Settling time refers to the time it takes for the output of a control system to reach and stay within a specified percentage (usually 2% or 5%) of its final value after a step change in the input or a disturbance. It reflects the system’s responsiveness and ability to stabilize around the desired operating point. A shorter settling time indicates faster response and better disturbance rejection.
(b) Repeatability:
Repeatability refers to the consistency of a control system’s output for repeated applications of the same input under identical conditions. A highly repeatable system produces essentially the same output every time it encounters the same input, demonstrating consistent and reliable behavior.
(c) Dead Zone:
Dead zone is a range of input values around the setpoint where the controller produces no output change. In other words, even if the input deviates slightly from the setpoint within the dead zone, the control system remains inactive. This can be intentional to avoid unnecessary actuator movements for minor fluctuations, but it can also lead to sluggish response and steady-state errors if the dead zone is too large.
(d) Hysteresis:
Hysteresis is a phenomenon where the output of a control system depends not only on the current input value but also on the history of the input. It creates a different response for increasing and decreasing input values around the setpoint, resulting in a “staircase” effect. This can be desirable in some applications for switching actions (e.g., thermostat), but it can also cause oscillations and limit control accuracy.
(e) Proportional Bandwidth (PB):
Proportional bandwidth (PB) is a measure of the range of input values that will produce the full output range of a proportional controller. It is expressed as a percentage of the setpoint and is inversely proportional to the controller gain. A higher PB means a smaller gain, resulting in less sensitive but more stable control. Conversely, a lower PB indicates higher gain, leading to more responsive but potentially less stable behavior.