Pid Basic Summary, What Happens When I - Idex Pulsafeeder MPC Vector Installation, Operation & Maintenance Manual

22.3

PID Basic Summary, what happens when I...

When the proportional control is increased:
Initial rise time to set point gets faster
Overshoot once set point is reached tends to increase (gets worse)
Steady-state error can be reduced but will never be eliminated
Settling time (ability to hold set point) is not strongly affected
Proportional is used mainly to affect the initial startup of the system, how quickly it reaches the desired set point.
Too much proportional control will result in overshoot and oscillation, and inability to hold a set point over time.
When the integral control is increased:
Initial rise time to set point gets faster
Overshoot once set point is reached tends to increase (gets worse)
Steady state error is eliminated with the proper setting
Settling time (ability to hold set point) 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 set point, 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 set point 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 set point. Too much derivative control will
result in a system that never reaches set point, reacts too slowly, or is unstable and will not hold set point.
A properly tuned PID loop will:
Reach the desired set point in a reasonable amount of time
Maintain operation at or very close to the set point with minimal oscillation
React quickly to transient changes or upset conditions
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