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Basic process control

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- 1. Basic Process Control
- 2. Basic Control Principles Level (Controlled Variable) Overflow Pump Inflow Supply l ll l ll
- 3. Open vs Closed Loop ! Closed loop ! Automatic control ! Open Loop ! Manual control ! Person takes the place of the controller
- 4. Feedback Control Comparator Amplifier Process (Tank) Error (SP - M) Manipulated Output (Controlled Variable - Level) Disturbances Variable Process Sensor Signal Measurement Set Point Controller
- 5. Feedback vs. Feedforward ! Feedback ! Control action after an error exists ! Feedforward ! Reacting to the disturbance before the error occurs
- 6. Typical ON/OFF Control System P1 L1 L2 V Qin SP Qout 1 P1 closes @ L1 P1 opens @ L2 Power Supply Solenoid Solenoid valve Electrically Operated Inflow l ll l ll
- 7. Typical ON/OFF Response L2 Periodic Time L1 SP time
- 8. Proportional Control
- 9. Level Control of Open Tank Qout LT SP Qin V1 20 - 100 kPa A/C l ll l ll
- 10. Simple Proportional System Pivot Outflow Float Valve Inflow lll ll l
- 11. Open Tank Control Qin Qout SP LT 20 - 100 kPa A/O LIC
- 12. Controller Action Qin Qout SP LT 20 - 100 kPa A/C LICl ll l ll Qin Qout SP LT 20 - 100 kPa A/O LICl ll l ll Direct Reverse
- 13. Proportional Control + - k•e Setpoint Measurement Error Bias + + Output m= k(SP-M) + bias
- 14. Proportional Band and Gain Proportional Band– the input change required to change the output 100% PB gain %100 = input output gain ∆ ∆ =
- 15. Narrow, Wide, High & Low Wide PB – Low Gain Narrow PB – High Gain OutIn
- 16. Proportional Control Response Curve Offset Outflow Loss in Volume New mass balance occurs here New level below setpoint timet 1 1t0t 0t time at setpoint Level originally Input/Output Level t Inflow
- 17. Proportional Response with Narrower PB Level originally Offset tt 0 time 1Level at setpoint below setpoint New level New mass balance occurs hereLoss in Volume Inflow Input/Output 0 t 1 t t Outflow time
- 18. Response Versus PB, Proportional Control Only time Step Disturbance LoadChange Offset Offset time SystemResponse SP SP SP "Wide" PB "Moderate" PB "Narrow" PB
- 19. ¼ Decay Response Curve A A/4 A/16 SystemResponse time
- 20. For You To Do ! Read pp. 89-105 ! Answer Questions pp. 121-122, #1-19
- 21. Reset or Integral
- 22. Response Curve: Proportional Control Only SystemResponse SP Step Disturbance time Offset
- 23. Additional Control Signal Restores Process to Setpoint Setpoint Initial mass balance Inflow Outflow Final mass balance Reset Action time Offset Removed
- 24. Integral Action biasedt TR kem + += ∫ 1 + - k•e Setpoint Measurement Error Bias + + Output ∫edt TR 1
- 25. Units ! Minutes per repeat ! MPR ! The length of time that it will take the integrator to add an amount equal to the proportional response ! Repeats per minute ! RPM ! The number of times the proportional response is repeated in one minute
- 26. Proportional Plus Reset, Open Loop Response time e Fast Reset Normal Reset Slow Reset error ke Proportional Response} ControlSignal
- 27. A problem Output initially 50%, Gain = 2, reset = 2 minutes per repeat A direct acting controller control is subjected to a sustained error of 5% What is the output after 4 minutes? Proportional Response = ke = 2x5=10% Integral Action- in 4 minutes the control will go through 2 repeats. Integral action = 2 x 10 = 20% Total output change is proportional + integral = 30%
- 28. A Couple More Things ! Reset Windup ! Instability because of lag
- 29. For You to Do ! Read over text pp. 89 –110 ! Answer questions pp. 121-122, 1-24
- 30. Rate or Derivative
- 31. Proportional and Derivative – Open Loop Pressure time InputOutput Derivative Derivative ceases as error stops changingProportional Action
- 32. Derivative Control + - k•e Setpoint Measurement Error Bias + + Output ∫edt TR 1 dt de TD + + + bias dt de kTedt T kem D R ++ += ∫ 1
- 33. Simple Flow Control System lll FT FC A/C √ _
- 34. The open Loop Response of Proportional Plus Derivative (PD) Action to Rapidly Changing Error Signals 0 t 1 t 2 t 0 t 1 t 2 t time time A B C Rate action due to cessation of increase in e Rate action B -C Rate action A - B Proportional action A - B Proportional action B - C Rate action due to cessation of increase in e Control signal at end of excursion Control Signal % Process
- 35. Large System Under Proportional and Proportional Plus Derivative Control time Control Signal Setpoint Level Load Disturbance Applied Prop. + Derivative Prop. Only
- 36. Multiple Control Modes ! Virtually all controls have a proportional response ! Integral and derivative are added to improve performance ! Majority have proportional and integral ! Some, typically heat exchangers have derivative added
- 37. Open Tank Level Control With Valve In Inflow Qi A/O l ll l llQo SP LIC LT
- 38. Typical Flow Control Loop ll FT FIC A/O √ _ SP
- 39. Pressure Control – Constant Bleed PIC PT A/C Feed SP Pressure Vessel Pressure Bleed
- 40. Split Ranged Feed and Bleed Pressure Control PIC PT A/C Feed SP Pressure Vessel Bleed A/O
- 41. Representative Hot Bleed/Cold Service Water Heat Exchanger TT TC A/C SP Cooled Bleed Hot Bleed Cold
- 42. For You To Do ! Read pp. 106-120 ! Answer Questions pp. 122-123, #20-38

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