CHE 185 – PROCESS CONTROL AND DYNAMICS

1. CHE 185 – PROCESS CONTROL AND DYNAMICS WORKSHOP 1

2. Motivation and Terminology of Automatic Process Control • All material from Control Station Knowledge Base http://www.controlstation.com/page/86-knowledge-base • House heating example

3. Motivation and Terminology of Automatic Process Control • Primary Definitions • process variable (PV) • set point value (SP) • disturbances (D). • final control element (FCE) • controller output (CO) • e(t) = SP - PV (error = set point - measured process variable)

4. Components of a Control Loop • Primary components are • Sensor • Controller • Final control element • Loop Configurations • open loop = manual mode • closed loop = automatic mode

5. Control Loop Block Diagram • General

6. Control Loop Block Diagram • Specific for House Heating

7. Dynamic Modeling • First order plus dead time (FOPDT) model • Simulate the system • Test the response of the simulation • Use the test results to calculate FOPDT parameters

8. FOPDT Model • Kp, process gain, amplification • Tp, process time constant , response rate • Өp, process dead time (tells how much delay before PV first begins to respond) • PV(t) = measured process variable as a function of time • CO(t - Өp) = controller output signal as a function of time and shifted by Өp • t = time

9. Controller Tuning • Controller is configured to use alternate control algorithms • Proportional control, P-only • CO signal is instantly adjusted on multiple of error • Proportional plus Integral control, PI • Integral considers history of signal (sums error) and eliminates offset • CO signal has two imputs

10. Controller Tuning • Proportional plus Integral plus derivative, PID • Derivative considers the rate of change or the error over time • PID control has 3 terms to set the CO • Other variations are available

11. Controller Action • Direct acting – PV increases with CO increase • Reverse acting – PV decreases withCO increase • Is typically a function of the control element

12. Gravity Drained Tanks Experiment • Objective is to set control parameters to : • Maintain lower tank level at a specified value • Over the normal range of variation

13. Gravity Drained Tanks Experiment • Collect data in open loop mode to define process characteristics

14. Gravity Drained Tanks Experiment • Manually change the CO output and record the system responses. Bump (step) Tests.

15. Gravity Drained Tanks Experiment • Use test data to calculate Kp, Τp and θp.

16. Gravity Drained Tanks Experiment • Τp calculation:

17. Gravity Drained Tanks Experiment • θp calculation:

18. Gravity Drained Tanks Experiment • Insert Kp, Τp and θpdata in to FOPDT equation and check for fit with experimental data. • Switch system to automatic control and insert calculated values • Select type of control, P, PI or PID and test how system responds to deviations. • (PV) is liquid level in the lower tank. • (CO) adjusts the valve to maintain the PV at set point (SP).

19. Gravity Drained Tanks Experiment System on automatic control

20. Workshop 1: Dynamics of the Gravity Drained Tanks Worksheet

21. Workshop 1: Dynamics of the Gravity Drained Tanks Worksheet

22. Workshop 1: Dynamics of the Gravity Drained Tanks Worksheet

23. TYPICAL RESULTS • CO step from 70%  80% CO step from 50%  60%

24. TYPICAL RESULTS • CO step from 70%  80% CO step from 50%  60%

25. TYPICAL RESULTS • CO step from 70%  80% CO step from 50%  60%

26. TYPICAL RESULTS • Is the gravity drained tanks a linear or nonlinear process?