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Load Control via P.I.D

Load Control via P.I.D. By: Katie Willenborg CEE 398KUC March 5, 2004. Role of a Load Controller. Eliminates need for vigilant operators Examples Speed Cruise Thermostat Controls anything that is a function of load Displacement Velocity Acceleration Load. What is P.I.D?.

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Load Control via P.I.D

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  1. Load Control via P.I.D By: Katie Willenborg CEE 398KUC March 5, 2004

  2. Role of a Load Controller • Eliminates need for vigilant operators • Examples • Speed Cruise • Thermostat • Controls anything that is a function of load • Displacement • Velocity • Acceleration • Load

  3. What is P.I.D? • Proportional, Integral, Derivative • Provides many algorithms to control output • All algorithms include P, I, and D effect • Operates on closed loop • Other schemes a load controller may use: • One or two of P, I, or D • Open loop scheme

  4. Proportional Gain • Controller ouptut = Kp*error • Output is proportional to error • May become unstable if offset grows too large • Reduces rise time and steady-state error • Most effective at moderate frequencies

  5. Integral Gain • Controller output = Ki ∫ error d(t) • Output is proportional to time the error is present • Eliminates offset and steady-state error • May make the transient response worse • Most effective at low frequencies

  6. Derivative Gain • Control Output = Kd*derror/dt • Output is proportional to rate of change of error • Used to avoid overshoot • Increases the stability of the system • Improves transient response • Most effective at high frequencies

  7. CAUTION • There are many algorithms: • Out = Kp*[e(t) + 1/Ki*∫e(t)d(t) + Kd*de(t)/dt] • Each controller manufacturer uses a different algorithm • Some algorithms may not be appropriate for certain systems • Much disagreement on optimal way to tune a loop

  8. PID Software • LabVIEW PID Control Kit for Windows • National Instruments • Adds control algorithms to instrumentation software • ~$1000

  9. Load Controllers • Instron FastTrack • 8800 Series • Continuous update of PID control terms • Optimizes control parameters throughout test to suit changing stiffness characteristics of specimen • Automatic identification and calibration of all compatible transducers for accuracy and reliability

  10. Questions or Comments

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