Digital Tuning Flashcards
What tuning parameters would you use for flow of liquid and gas?
- P
- PI
- PID
- Adaptive
- Feedforward
Liquid> PI
Gas> PI
What tuning parameters would you use for pressure control of liquids, gases, and vapour?
- P
- PI
- PID
- Adaptive
- Feedforward
Gas> P
Liquids> P or PI
Vapour> PID or Feed Forward Control
What tuning parameters would you use for level control of liquid in Surge and Tight Control
- P
- PI
- PID
- Adaptive
- Feedforward
Tight control 5% to 10%> P or PI
Surge> P or PI
What tuning parameters would you use for Temperature
- P
- PI
- PID
- Adaptive
- Feedforward
Temp> PID or Feedforward Control
What tuning parameter would you use for Composition Control
- P
- PI
- PID
- Feedforward
- Adaptive
PID, Adaptive, Feedforward
When calculating tuning settings for a PID controller what happens if Td is less then .1 min?
Redo calculations as a PI controller, b/c controller is fast enough already
How does the interactive PID algorithm work?
Proportional effects Derivative, and both effect Integral
How does Standard PID algorithm work?
Most tuning rules are based on this algorithm
Proportional effects both Derivative and Integral, but Derivative and Integral don’t effect each other.
How does Parallel algorithm work?
Parallel removes any interaction between all three actions.
If load disturbances significantly affects the Non-Linear control loop what are three possible solutions and how do they work?
- Detune loop: tune loop for steepest slope, where its loop gain is highest. At all other points control will be slow
- Multipoint characterizer: find actual results versus entered and compensate.
- Adaptive control: cut graph in half, find loop gain for them and enter them in for desired regions.
True or False: Equal % valve linearizes control loop for load disturbances and SP changes
False.
Linearizes load changes, non-linear for SP changes
List 3 components that cause non-linearity in a control loop.
Hint: 3 components of a control loop
- TX
- Process
- FCE
How does Parallel algorithm work?
Parallel removes any interaction between all three actions.
If load disturbances significantly affects the Non-Linear control loop what are three possible solutions and how do they work?
- Detune loop: tune loop for steepest slope, where its loop gain is highest. At all other points control will be slow
- Multipoint characterizer: find actual results versus entered and compensate.
- Adaptive control: cut graph in half, find loop gain for them and enter them in for desired regions.
True or False: Equal % valve linearizes control loop for load disturbances and SP changes
False.
Linearizes load changes, non-linear for SP changes
List 3 components that cause non-linearity in a control loop.
Hint: 3 components of a control loop
- TX
- Process
- FCE
A Controller is tuned for 1/4 Amp decay, SP change causes the to CO kick to its limits. What actions are reacting to error?
PID action on error, making the PV overshoot the SP making the CO kick.
Overshoot
A Controller is tuned for 1/4 Amp decay, SP change causes a Proportional kick, what actions are reacting to error?
PI action on error, D action on how fast the PV changes. This way there is no Derivative action or kick to SP.
Undershoot/Underdamped
A Controller is tuned for 1/4 Amp decay, SP change causes PV to slowly raise to SP with zero overshoot. What action reacts to error?
I action reacts to error, P and D reacts to PV changes.
Critically under damped.
Proportional, Integral, and Derivative can all give unwanted responses in a closed loop response. What are they?
- Proportional and Derivative give CO response kicks. Can be softened with filter set point changes (first order) and set point ramping. (Proportional ramp)
- Integral gives reset wind-up, can be mitigated by using output limits to limit the wind up able to be used.
3 types of disturbances.
- Transient: temporary change in a parameter that effects controlled variable. Accidental decrease in supply pressure.
- Load: deliberate change in throughput of system. Increase in flow creates load disturbances deviating from SP
- Setpoint: SP change creates SP disturbance.
Specified Decay Ratio defines how quickly the amplitude of oscillations decrease. What is the equation?
DR= Little Peak/Big Peak
What controlled variable responses are Underdamped and critically damped?
Zero overshoot: first order critically damped
Specified decay ratio: Underdamped.
What does robustness mean in a loop?
The more robust a loop is the more stable the loop is to load disturbances. The controller proportional gain is set so the dynamic gain of the loop is below 1 (prevents oscillations). More robust the slower response
What is gain and phase margin?
Phase margin: how many degrees until phase shift equals 180. Apparent dead time in loop. Higher the phase margin, more robust
Gain margin: measurement of how much the control loop gain can change before loop is unstable. Higher gain margin, more robust.
What response does Lambda tuning give you?
Over-damped (First Order)
What does adding Integral Action do?
- eliminates offset
- loop becomes less Robust
- Changes loops Frequency
- Frequency of loop decreases, giving it longer period
- Kcu goes down
What does adding Derivative action do?
- Changes loop Frequency, makes period shorter.
- Changes loop Dynamic gain
- Increases Kcu
- Tends to make loop more stable since PV is brought back to SP faster
List three things needed to be configured to achieve Bump,Es Transfer?
- SP tracks PV in Manual
- PID Algorithm tracks CO in manual
- Controller manual tracks CO in auto
What is Derivative Gain or Derivative Filter is and what it is used for
Provides a First Order response to the Derivative action and is used to mitigate noise and soften responses.
