Practice
Integral action, and how it gets stuck
Before you start
Removing the offset without paying for it in overshoot.
Integral action accumulates error over time. However small the remaining gap is, the integrator keeps adding to the valve command until the gap is gone. That is what removes the offset proportional action leaves behind.
It buys that with time. The integrator only knows where the process has been, not where it is going, so it keeps pushing after the level is already on its way back. Too much integral action and the level sails past setpoint and has to be pulled back: overshoot.
There is a worse failure. If the valve reaches its limit and the error persists, the integrator keeps accumulating against a valve that cannot move any further. When the process finally turns around, that stored-up command has to be unwound before the valve responds at all: the controller is briefly deaf. That is integral windup.
This simulator limits the integrator to keep windup survivable, and holds it in place while the valve is saturated. Real controllers do the same thing, and for the same reason.
The order that works is Kp first, then Ki, then Kd if it earns its place. Tune Kp until the response is fast but calm, then add just enough integral to close the offset.
Your task
- You now have Kp and Ki. Derivative is still locked off.
- Start from the proportional tuning you found in the last lesson and add integral action gradually.
- Your target is a level that returns to setpoint with no standing offset and without a large overshoot.
Configure both controllers before starting. Gains are locked during the attempt.
SEP-101 horizontal separator with gas, oil, and water. True total level 0.0 percent; measured total level 0.0 percent. True interface 0.0 percent; measured interface 0.0 percent. Total inlet 0.0 cubic metres per hour; oil outlet 0.0 cubic metres per hour; water outlet 0.0 cubic metres per hour. Actual oil valve 0.0 percent; actual water valve 0.0 percent. Safety: Filling: low-level protection bypassed.
SEP-101 · engineering fallback
Separator process cutaway
Filling: low-level protection bypassed
- Total true
- 0.0%
- Total measured
- 0.0%
- Total SP
- 50.0%
- Interface true
- 0.0%
- Interface measured
- 0.0%
- Interface SP
- 20.0%
- Total inlet
- Stopped / 0.0 m³/h
- Oil outlet
- Stopped / 0.0 m³/h
- Water outlet
- Stopped / 0.0 m³/h
- Oil command
- 0.0%
- Oil actual
- 0.0%
- Water command
- 0.0%
- Water actual
- 0.0%
- Active safety
- Filling: low-level protection bypassed
2D engineering fallback · process values and safety logic remain fully active.
LIC-101
Ready to tuneTotal level / oil valve
More valve opening → more oil out → lower total level
- Total level process value
- 0.0%
- Total level measured value
- 0.0%
- Total level setpoint
- 50.0%
- Oil valve command
- 0.0%
- Oil valve actual position
- 0.0%
- P / I / D
- 0.0 / 0.0 / 0.0
Advanced settings
IIC-101
Ready to tuneInterface / water valve
More valve opening → more water out → lower interface
- Interface process value
- 0.0%
- Interface measured value
- 0.0%
- Interface setpoint
- 20.0%
- Water valve command
- 0.0%
- Water valve actual position
- 0.0%
- P / I / D
- 0.0 / 0.0 / 0.0
Advanced settings
Synchronized historian
Live control trends
Oil/water interface
Truth, LT-102, SP and protection limits · %Phase flows
Feed and phase flows · m³/h; water cut · %Valve response
Commands and actual positions · %Four synchronized trends compare both controlled levels, phase flows, water cut, and both valve responses.
Debrief
Run the exercise to see how you did.