Pulsafeeder MPC Vector - Manual (Page 67)

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21.3 PID Basic Summary, what happens when I…
When the proportional control is increased:
Initial rise time to setpoint gets faster
Overshoot once setpoint is reached tends to increase (gets worse)
Steady-state error can be reduced but will never be eliminated
Settling time (ability to hold setpoint) is not strongly affected
Proportional is used mainly to affect the initial startup of the system, how quickly it reaches the desired
setpoint. Too much proportional control will result in overshoot and oscillation, and inability to hold a
setpoint over time.
When the integral control is increased:
Initial rise time to setpoint gets faster
Overshoot once setpoint is reached tends to increase (gets worse)
Steady state error is eliminated with the proper setting
Settling time (ability to hold setpoint) is increased (gets worse)
Transient response ( for example to an upset condition) may get worse
Integral is used mainly to tune the system to reach a certain setpoint, to eliminate any offset the might be
present, for example the desired flow rate is 5.0 gph, but the system settles and runs at a consistent 5.2 gph. If
too much integral control is used, the system can overshoot, not settle, and not react smoothly to transient
(temporary) upset events.
When the derivative control is increased:
Stability of the system is increased
Rise time to setpoint is not significantly affected
Overshoot is controlled and decreased with the proper setting
Settling time is decreased and controlled with the proper setting
Steady state operation is not affected significantly
Derivative is used to tune out oscillation of the system around the desired setpoint. Too much derivative
control will result in a system that never reaches setpoint, reacts too slowly, or is unstable and will not hold
setpoint.
A properly tuned PID loop will:
Reach the desired setpoint in a reasonable amount of time
Maintain operation at or very close to the setpoint with minimal oscillation
React quickly to transient changes or upset conditions