Lab 2 Process Control Computer-based Control Systems Flow Control

Transcription

1 Lab 2 Process Control Computer-based Control Systems Flow Control 1. Aims To operate PC-based instrumentation and control systems To get familiar with open-loop control, ON-OFF, and PID control systems To explain P, PI, PD, and PID control actions To transfer MAN mode to AUTO smoothly. 2. Apparatus Process/Plant: Flow Control Bench consists I/P Converter, Pneumatic Control Valve, Orifice and D/P Cell Transmitters, Pipes and Pump, and Rotameter Computer, LabVIEW 8.6, NI DAQ 6036E Card, Current-to-Voltage converter (4mA-20mA to 1 to 5V) and Voltage-to-Current converter (-10V/+10V to 4mA-20mA). Multimeter, mameter 3 Connection Diagram The connection diagram for control systems is shown in Fig. 1. Pneumatic supply Water supply I/P kpa Valve MI Process (Plant) PV Sensor/s Actuator CS 4-20mA V/I V V I/V MV 4-20mA PC, DAQ PCI 6036E and LabVIEW PC-based controller Figure 1 Connection diagram Schematic diagram for flow control system is shown in Fig. 2 (a & b). 4. Further Information Refer to Chapters 7, 8, 9 (Pressure, Flow and Level), Chapter 12 Actuators and Chapter 13 Basic Control Theory (Direct Acting On-Off Control, PID Control) 1

2 Globe valve ma 4-20mA COMPUTER LABView DAQ 6036E I/V & V/I ma Pneumatic supply kpa Rotameter Q (lpm) Output current I/P Converter Actuator Control valve DC 24V D/P Cell Valve (Open) Gauge 1 Gauge 2 Orifice plate Valve (Closed) Valve (Closed) Pump Water tank Figure 2a Schematic diagram of Flow Control System (Flow Control Bench) Flow Bench D/P Cell kpa Pneumatic supply DC 24V Current 4-20mA (0-30kPa) Orifice plate I/P converter 250R Current 4-20mA kpa (designed) Flow AI channel V Control signal 10V to +10V Control signal 4-20mA COMPUTER DAQ 6036E and LabVIEW V-to-I Figure 2b Connection diagram of the Flow Control System 2

3 Methods 1. Connection and turning on the power Connect the computer, I/V converters, and V/I converter to the process (sensor/s and actuators) by referring to the above scheme/connection diagrams Supply control air (or confirm if the pneumatic supply is done) Turn on the power Log on to the computer 2. Identification of Components and Variables Identify all components and their variable of the process control system (that you have selected) and complete Table 1. Table 1 Components and variables Process system: Component / Model Code No (where applicable) Example: Controller (PC) Input (variable, unit) Process variable: flow [mm, ma, V] Set point [mm, ma, V] Output (variable, unit) Control signal [V, ma] 3. Hands-on Exercises 3.1 Hands-On Exercise 1: Getting Started with Open-Loop Flow Control System Purpose: The purpose of this hands-on exercise is to get familiar with a control system and its components, variables and signals. In the Open Loop Control System there is no comparison of feedback signal to the Set Point. In almost controllers MAN mode is an Open Loop mode. Learning Objectives: Operate the open loop control system Understand components of the control system and their signals 3

4 Explain the principles and functions of the components including process, measurement devices (flow transmitters, pressure gauges), actuators, valves and valve positioners. Procedure Run the LabVIEW On-Off controller program Flow: C:\Documents and Settings\All Users\LabVIEW Data\JEE326_2009\Lab 2\OnOffFlowControlSys\ OnOffFlowControlSys.exe The On-Off controller program looks like... (from D/P cell) SP, PV and CS in ma Manual Controller P and PV in litre/min Diagram Figure 3 On-Off controller program (for flow control) The program is running. If not, click to run the On-Off Controller Program. Make sure that the Auto/Man mode switch is in Man position) Make sure that the Write to File is at Write position and change the path for data files if necessary Enter a minimum value of voltage (Manual Controller), i.e. -10V, write down in Table 2 and Table 3. Change the value of voltage with a step of 2.5 volts and complete Table 2 and Table 3. 4

5 Table 2 Data collection for components and variables of open loop system No Component and/or variable [unit] Examples: Controller (PC), control signal: V: ma Symbol u c u c Volt-to-Curr Converter, control signal [ma] u c I/P converter Output (pressure) kpa P c Control valve Upstream kpa Downstream kpa P 1 P 2 Control valve Output (flowrate) [l/m] D/P Cell Measured flowrate [ma] In PC: Meas flowrate [V] Meas flowrate [ma] Meas flowrate [l/m] Table 3 Ranges of variables No Component / Instrument Open-loop (MAN) Controller 0 Example: Rotameter Input (range, unit) Output (range, unit) Min Max Min Max -10V 10V 4 ma 20mA Flowrate Reading of flowrate on scale 20 l/min 220 l/min 20 l/min 220 l/min 5

6 Label the components, variables and their ranges in the following block diagram. V/I S7 converter Indicators (Virtual Instruments) PC + Controller Air supply Disturbances S1 S2 S3 S4 S5 S6 C1 C2 C3 C4 Figure 4 Block diagram of the open-loop control system (for flow control) 6

7 QUESTION 1 What type is the pneumatic control valve? QUESTION 2 When the Controller Output changes from 0% (4mA) to 50% (12mA) (of span) How much (%) does the Valve Opening change?... How much (%) does the Process Variable change?... Return the Controller Output to the minimum value. Stop the Open-Loop Control System by clicking button. Important: Don t forget to copy data files to your USB flash memory stick! Notes for Hands-on Exercise 1 (Open Loop Control System) 7

8 3.2 Hands-on Exercise 2: Operation of On-Off Flow Control System Purpose The purpose of this hands-on exercise is to get familiar with an On-Off Flow Control System. Learning Objectives To operate the On-Off Flow Control System To perform settings of ON and OFF values to optimize the system response. Introduction The On-Off flow control system is based on the following principle: Error (E) = PV SP SP Error If E > 0 then OFF (large) CLOSE If E < 0 then ON (small) OPEN Controller Output PV Figure 5 On-Off control algorithm for the flow control system The CLOSE and OPEN values of the valve can be set at different values: Fully close: +10 V (in PC) or 20 ma Fully open: -10 V (in PC) or 4 ma SP, PV and CS in ma Manual Controller P and PV in litre/min Diagram Figure 6 On-Off flow control program (Front Panel) 8

9 Procedure (It is supposed that this exercise is started after Exercise 3.1, the On-Off Flow Controller Program is still open). Run the On-Off Flow Controller Program In MAN mode, confirm SP at 220 litre/min (fully open) and the valve is fully opened. Confirm the OPEN value at -10V, and the CLOSE value (fully open) at +10V (fully close). Switch to AUTO mode. The controller is working in the On-Off control mode. Observe the change in PV. Change the SP to 50% of the span, i.e. 120 lit/min (or 12mA), observe the change in PV. Change the OPEN value to -8V and the CLOSE value to +8V, and observe the change in PV. QUESTION 1 How is the system response changing? Select an OPEN value and a CLOSE value so that the system response hunts the set-point with the least oscillation. You may execute several trials to select appropriate valves. QUESTION 2 What are the best values? To stop the On-Off Controller Program click Close the On-Off Controller Program. button. Notes: Don t forget to copy data files to your USB flash memory stick! Notes for Hands-on Exercise 3.2 9

10 3.3 Hands-On Exercise 3: Operation of PID Control System Introduction The PID control system is based on the following principle: Error (E) = SP PV or PV SP SP Error de u PID = K e P + K edt K I + D dt Controller Output PV The PID controller program has the MAN mode similar to that of the On-Off controller program. In AUTO (closed-loop) mode, the PID controller can work in the following control actions: P only control by setting K i = 0 and K d = 0 I only control by setting K p = 0 and K d = 0 (rarely used for this flow system because I control action makes the system unstable) PI control by setting K d = 0 PD control by setting K i = 0 Control gains (Kp, Ki and Kd) are adjusted by on the following formula of the PID Control Algorithm: de VPID = K Pe + K I edt + K D dt Proportional Band is Integral Time: Derivative Time: P I D K T I = K 100% PB = K P P I K T D = K D P. The control signal is computed based 10

11 Figure 7 PID flow control program (Front Panel) Purpose The purpose of this hands-on exercise is to get familiar with the PID Flow Control System. Learning Objectives Operate the PID flow control system with different control actions: o P control o PI control o PD control o PID control Explain the effects of P, I, D, PI, PD and PID on the system response. Switch between the AUTO and MAN modes smoothly. Procedures (It is suggested that you have closed the On-Off Controller Program.) Run the PID Controller Program Confirm the PID Controller Program in MAN mode. Observe the SP, PV, Controller Output and confirm the following values (if not adjust accordingly): Setpoint: 220 lit/min K p = 2, K i = 0, K d = 0 (Proportional Only Control) Controller Output: -10V (4 ma) PV: 20 ma (220 lit/min) 11

12 Switch to the AUTO mode. The controller is working with Proportional Only Control. Proportional Only Control and Effects of Proportional Gains on System Response and Offset Wait until the system response is stable, fill in Table 1 Execute the Trials 1-10 and fill in Table 1. Table 1 Proportional Band Effect on OFFSET TRIAL K P PB SETPOINT MEAS. (PV) + OR - ERROR OUTPUT (Control Signal) QUESTION 1 How does the system response change when the Proportional Gain changes? Proportional and Integral Control Switch to the MAN and confirm the following value: Setpoint: 220 lit/min K p = 2, K i = 0, K d = 0 (Proportional Only Control) Controller Output: 2V (4 ma) PV: 20 ma (220 lit/min) Change the SP to 180 lit/min What is the error? (ma, lit/min) 12

13 What is the P action? (ma) Change K i to What is the I action? (ma) How is the PI action changing? (You can draw a diagram for I action) Stop the PID Controller Program. Start the PID Controller Program. What is the P action? (ma) How is the I action changing? (You can draw a diagram for I action) Change SP to 220 lit/min and K i = 0 (confirm K p = 2.0). Switch to the AUTO mode. Confirm the system is stable at SP of 220 l/min. Change SP to 180 lit/min. Wait until the system is stable. What is offset value? (ma, lit/min) Change K i to Observe the system response (PV). How does the PV change? Is the offset compensated? Change SP to 160 lit/min. Observe the system response (PV). How does the PV change? Change SP to 180 lit/min. Observe the system response (PV). How does the PV change? Change K i to 0.5. Observe the system response (PV). Change SP to 160 lit/min. Observe the system response (PV). How does the PV change? Change the following value: SP to 220 lit/min 13

14 K i to 0.0 K p to 2.0 Switch to the MAN mode. Stop the PID Control Program. Proportional and Derivative Control Run the PID Control Program in MAN mode. Confirm the following: K p = 2 K i = 0.0 K d = 0.0 SP = 220 lit/min Change K d to 2 and SP to 180 lit/min. Change SP to 160 lit/min How does the D action change? (You may change the Sampling Interval to 1 to observe the D action). Draw a diagram showing the D action. Change K d to 2 and SP to 220 lit/min. Wait until the system response is stable. Switch to AUTO Mode PD control Change the SP to 180 l/min, wait until the system response is stable. Change the SP to 160 l/min, wait until the system response is stable. Is the OFFSET compensated by PD control action? Stop the PID Control Program. Proportional plus Integral plus Derivative Control and AUTO/MAN Transfer From previous trial, change the following values: SP = 220 lit/min K p = 2 K i = K d = 2 AUTO/MAN = MAN Run the PID Control Program. Wait until the system is stable. Switch to the AUTO Mode PID Control Action. At this point, you have experienced with the effects of P, I, PI, PD actions. In this section, please do several trials in order to find some values of K p, K i and K d such that the system response has less oscillation and reaches the SP quickly. Change SP to 160 lit/min. How does the PV change? You can do several trials with different sets of K p, K i and K d. 14

15 You can also do several trials with transfer between AUTO/MAN modes when: o SP = PV o SP is different from PV Describe your observations: Conclusion At this point the following LOs have been met: Operate the PID flow control system with different control actions: o P control o PI control o PD control o PID control Explain the effects of P, I, D, PI, PD and PID on the system response. Switch between the AUTO and MAN modes smoothly. Notes: Don t forget to copy data files to your USB flash memory stick! 4. Calculation and Report In your report, do the following tasks (but not restricted to): Introduction Relevant theory on On-Off control Relevant theory on PID control Relevant theories related to level or flow transmitters/sensors and actuators Using AS Standard Drawing Symbols, draw a flow diagram for the above control system you have selected. Draw a block diagram for the closed-loop control system you have selected. Find transfer functions/sensitivities for all components of the systems. Hints: For the level control system the ODE for the tank is Ah & + k vh = q or in A h& + k v h = q in For the flow control system the ODE for the piping system (flow dynamics) is Qout K e Td s = Q Ts + 1 in Find the total feedback transfer function (refer to Chapter 15) Plot sketches and graphs (from data files) Discussions, evaluations and conclusions 15

16 Appendix 1 Flow Control Bench Global Valve Control Valve Rotameter D/P Cell I/O Converter Appendix 2 Block Diagram for On-Off Controller Program (flow control) 16

17 Appendix 3 Block Diagram of the PID Controller Program (flow control) 17

18 Lab 2 Process Control Computer-based Control Systems Level Control 1. Aims To operate PC-based instrumentation and control systems To get familiar with open-loop control, ON-OFF, and PID control systems To explain P, PI, PD, and PID control actions To transfer MAN mode to AUTO smoothly. 2. Apparatus Process/Plant: Process Control Trainer Cart with Level Control Mode of I/P Converter consists of a tank, a pneumatic control valve (with a pneumatic positioned), a D/P level transmitter, an orifice plate and D/P flow transmitter, pipes and pump, and a D/P pressure transmitter (not used in this experiment). Computer, LabVIEW 8.6, NI DAQ 6036E Card, Signal Conditioning SC-2345 (for level control) including a current-to-voltage converter (4mA-20mA to 1 to 5V, with two channels) and a voltage-to-current converter (0V-+10V to 0mA-20mA). A multimeter. 3 Connection Diagram The connection diagram for control systems is shown in Fig. 1 and Fig. 2b. Pneumatic supply Water supply I/P kpa Valve MI Process (Plant) PV Sensor/s Actuator CS 4-20mA V/I V V I/V MV 4-20mA PC, DAQ PCI 6036E and LabVIEW PC-based controller Figure 1 Connection diagram Scheme diagram for level control system is shown in Fig. 2 (also see Appendix 1). 4. Further Information Refer to Chapters 7, 8, 9 (Pressure, Flow and Level), Chapter 12 Actuators and Chapter 13 Basic Control Theory (Direct Acting On-Off Control, PID Control) 1

19 Air supply I/P converter 0-20mA kpa 0-10V AO-0 1-5V AI V Supply liquid 4-20mA Flow transmitter 4-20mA Orifice plate Level transmitter Pneumatic control valve Positioner q in (0-85% square root) Level m DAQ PCI 6036E, PC and LabVIEW AI-10 SC-2345 Isolation valve Valve 1 q out1 Valve 2 q out2 Figure 2a Schematic diagram for level control system I/P converter Air supply 0-20mA kpa (desired) Controller 0-10V AO-0 1-5V AI V FT Supply liquid 4-20mA DC 24V 4-20mA Pneumatic control valve LT Positioner q in (0-85% square root) Level m PC, DAQ PCI 6036E, and LabVIEW AI-10 SC-2345 DC 24V Isolation valve Figure 2b Connection diagram for level control system Valve 1 q out1 Valve 2 q out2 2

20 Methods 1. Connection and turning on the power Connect the computer, I/V converters, and V/I converter to the process (sensor/s and actuators) by referring to the above scheme/connection diagrams Supply control air (or confirm if the pneumatic supply is done) Turn on the power Log on to the computer 2. Identification of Components and Variables Identify all components and their variable of the process control system (that you have selected) and complete the following table. Table 1 Components and variables Process system: No 1 Component / Model Code (where applicable) Example: PC-based controller (Manual Controller) Input (variable, unit) Setpoint level [ma, V, mm] Measured level [ma, V, mm] Output (variable, unit) Control signal: [V] 2 V/I converter (SC-2345) Control signal: [V] Control signal: [ma] Hands-on Exercises 3.1 Hands-On Exercise 1: Getting Started with Open-Loop Level Control System Purpose: The purpose of this hands-on exercise is to get familiar with a control system and its components, variables and signals. In the Open Loop Control System there is no comparison of feedback signal to the Set Point. In almost controllers MAN mode is an Open Loop mode. Learning Objectives: Operate the open loop control system Understand components of the control system and their signals 3

21 Explain the principles and functions of the components including process, measurement devices (flow transmitters, level transmitter, pressure gauges), actuators, valves and valve positioner. Procedure Run the LabVIEW On-Off controller program C:\Documents and Settings\All Users\LabVIEW Data\JEE326_2009\Lab 2\OnOffLevelControl\ OnOffLevelControl01.exe The controller program is running. If not, click MAN (open-loop) mode. The controller program looks like... to run the On-Off Controller Program in Process variable: level Manual controller Flow rate Diagram Drain valves Figure 3 On-Off controller program in the Manual mode (for level control) Make sure that the Auto/Man mode switch is in Man position. Make sure that the Write to File is at Write position and change the path for data files if necessary Enter a minimum value of voltage, i.e. 0V, write down in Table 2 and Table 3. Change the value of voltage to 2V and then with a step of 1 volt and complete Table 2 and Table 3. 4

22 Table 2 Data collection for components and variables of open loop system No 0 1 Component and/or variable [unit] Examples: Controller (PC), control signal: V: ma Sym u c u c 0 0 Volt-to-Curr Converter, control signal [ma] u c I/P converter Air supply pressure kpa Output (pressure) kpa P 1 Positioner Instrument pressure Air supply pressure Output pressure Control valve Flow transmitter Tank P 2 P 3 P c 0 Table 3 Ranges of variables No Component / Instrument Open-loop (MAN) Controller 0 Example: I/P converter Input (range, unit) Output (range, unit) Min Max Min Max 0V 10V 0 ma 20mA Control signal Control pressure 0 20 ma 0 bar 1.2 bar 5

23 Label the components, variables and their ranges in the following block diagram. V/I S7 converter Indicators (Virtual Instruments) PC + Controller Air supply Disturbances S1 S2 S3 S4 S5 S6 C1 C2 C3 C4 Figure 4 Block diagram of the open-loop control system (for level control) 6

24 QUESTION 1 What type is the pneumatic control valve? QUESTION 2 When the Controller Output changes from 0% (4mA) to 50% (12mA) (of span) How much (%) does the Valve Opening change?... How much (%) does the Process Variable change?... Return the Controller Output to the minimum value. Stop the Open-Loop Control System by clicking button. Important: Don t forget to copy data files to your USB flash memory stick! Notes for Hands-on Exercise 1 (Open Loop Control System) 7

25 3.2 Hands-on Exercise 2: Operation of On-Off Level Control System Purpose The purpose of this hands-on exercise is to get familiar with an On-Off Control System. Learning Objectives To operate the On-Off Control System To perform settings of ON and OFF values to optimize the system response. Introduction The On-Off level control system is based on the following principle: Error (E) = SP PV SP Error If E > 0 then ON (large) OPEN If E < 0 then OFF (small) CLOSE Controller Output PV Figure 5 On-Off control algorithm for level control system Confirm ON (OPEN) and OFF (CLOSE) values of the control valve for your control system: ON (OPEN) Fully open: 10 V or 20 ma OFF (CLOSE) Fully close: 0 V or 0 ma Figure 6 Level controller program (Front Panel) 8

26 Procedure (It is supposed that this exercise is started after Exercise 3.1, the On-Off Level Controller Program is still open). Run the On-Off Level Controller Program In MAN mode, confirm SP at 400 mm and the valve is fully opened. If not, adjust the Manual Control to 10 V to fill water in the tank up to 400 mm. (Notes: There are two drain valves. One is fully closed, the other is half opened. If the tank is empty you may need to closed the half-opened valve, and then return it back to the half opening position when the water reaches 400 mm.) Confirm the OFF (CLOSE) value (fully close) at 0V, and the ON (OPEN) value (fully open) at 10V. Switch to AUTO mode. The controller is working in the On-Off control mode. Observe the change in PV. Change the SP to 50% of the span, i.e. 200 mm (or 12 ma), observe the change in PV. Change the OFF value to 2V (4 ma) and the ON value to 6V (12 ma), and observe the change in PV. QUESTION 1 How is the system response changing? Select an OPEN value and a CLOSE value so that the system response hunts the set-point with the least oscillation. You may execute several trials to select appropriate valves. QUESTION 2 What are the best values? To stop the On-Off Controller Program click Close the On-Off Controller Program. button. Important: Dot not forget to copy data files to your USB flash memory stick! Conclusion At this point, the learning objectives have been met. You are able to To operate the On-Off Control System To perform settings of ON and OFF values to optimize the system response. Notes for Hands-on Exercise 2 9

27 3.3 Hands-On Exercise 3: Operation of PID Control System Introduction The PID control system is based on the following principle: Error (E) = SP PV SP Error de u PID = K e P + K edt K I + D dt Controller Output PV Figure 7 PID control algorithm for the level control system The PID controller program has the MAN mode similar to that of the On-Off controller program. In AUTO (closed-loop) mode, the PID controller can work in the following control actions: P only control by setting K i = 0 and K d = 0 I only control by setting K p = 0 and K d = 0 (rarely used for this level system because I control action makes the system unstable) PI control by setting K d = 0 PD control by setting K i = 0 Control gains (K p, K i and K d ) are adjusted by on the following formula of the PID Control Algorithm: de VPID = K Pe + K I edt + K D dt Proportional Band is Integral Time: Derivative Time: P I D K T I = K 100% PB = K P P I K T D = K D P. The control signal is computed based Purpose The purpose of this hands-on exercise is to get familiar with the PID Control System. Learning Objectives Operate the PID level control system with different control actions: o P control o PI control o PD control o PID control Explain the effects of P, I, D, PI, PD and PID on the system response. Switch between the AUTO and MAN modes smoothly. 10

28 Figure 8 PID controller program (Front Panel) Procedures (It is suggested that you have closed the On-Off Controller Program.) Run the PID Controller Program Confirm the PID Controller Program in MAN mode. Observe the SP, PV, Controller Output and confirm the following values (if not, adjust accordingly): Setpoint: 200 mm K p = 2, K i = 0, K d = 0 (Proportional Only Control) Controller Output: 0V (0 ma) PV: 12 ma (200 mm) Switch to the AUTO mode. The controller is working with Proportional Only Control. Proportional Only Control and Effects of Proportional Gains on System Response and Offset Wait until the system response is stable, fill in Table 4. Execute the Trials 1-10 and fill in Table 4. 11

29 Table 4 Proportional Band Effect on OFFSET TRIAL K P PB SETPOINT MEAS. (PV) + OR - ERROR OUTPUT (Control Signal) QUESTION 1 How does the system response change when the Proportional Gain changes? Proportional and Integral Control Switch to the MAN and confirm the following value: Set-point: 200 mm K p = 2, K i = 0, K d = 0 (Proportional Only Control) PV: 12 ma (200 mm) (if not, adjust the Manual Control to 10V to fill water up to 200 mm. Switch to the Auto Mode. Wait until the level is stable. What is the error? (V, ma, mm) What is the P action? (V, ma) Change the SP to 180 mm What is the error? (V, ma, mm) What is the P action? (V, ma) Change K i to What is the P action? (ma) How is the PI action changing? (You can draw a diagram for I action) 12

30 Stop the PID Controller Program. Start the PID Controller Program. What is the P action? (ma) How is the I action changing? (You can draw a diagram for I action) Change SP to 200 mm and K i = 0 (confirm K p = 2.0). Switch to the AUTO mode. Wait until the system is stable. Change SP to 180 mm. Wait until the system is stable. What is offset value? (ma, mm) Change K i to Observe the system response (PV). How does the PV change? Is the offset compensated? Change SP to 160 mm. Observe the system response (PV). How does the PV change? Change SP to 180 mm. Observe the system response (PV). How does the PV change? Change K i to 0.5. Observe the system response (PV). Change SP to 160 mm. Observe the system response (PV). How does the PV change? Change the following value: SP to 200 mm K i to 0.0 K p to 2.0 Switch to the MAN mode. Stop the PID Control Program. 13

31 Proportional and Derivative Control Run the PID Control Program in MAN mode. Confirm the following: K p = 2 K i = 0.0 K d = 0.0 SP = 200 mm Change K d to 2 and SP to 180 mm. Change SP to 160 mm How does the D action change? (You may change the Sampling Interval to 1 to observe the D action). Draw a diagram showing the D action. Change K d to 2 and SP to 200 mm. Wait until the system response is stable. Switch to AUTO Mode PD control Change the SP to 180 mm, wait until the system response is stable. Change the SP to 160 mm, wait until the system response is stable. Is the OFFSET compensated by PD control action? Stop the PID Control Program. Proportional plus Integral plus Derivative Control and AUTO/MAN Transfer From previous trial, change the following values: SP = 200 mm K p = 2 K i = K d = 2 AUTO/MAN = MAN Run the PID Control Program. Wait until the system is stable. Switch to the AUTO Mode PID Control Action. At this point, you have experienced with the effects of P, I, PI, PD actions. In this section, please do several trials in order to find some values of K p, K i and K d such that the system response has less oscillation and reaches the SP quickly. Change SP to 160 mm. How does the PV change? You can do several trials with different sets of K p, K i and K d. You can also do several trials with transfer between AUTO/MAN modes when: o SP = PV o SP is different from PV 14

32 Describe your observations: Conclusion Operate the PID level control system with different control actions: o P control o PI control o PD control o PID control Explain the effects of P, I, D, PI, PD and PID on the system response. Switch between the AUTO and MAN modes smoothly. Notes: Don t forget to copy data files to your USB flash memory stick! 4. Calculation and Report In your report, do the following tasks (but not restricted to): Introduction Relevant theory on On-Off control Relevant theory on PID control Relevant theories related to level or level transmitters/sensors and actuators Using AS Standard Drawing Symbols, draw a level diagram for the above control system you have selected. Draw a block diagram for the closed-loop control system you have selected. Find transfer functions/sensitivities for all components of the systems. Hints: For the level control system the ODE for the tank is Ah& + k vh = qin For the flow control system the ODE for the piping system (flow dynamics) is Qout K e Td s = Q Ts + 1 in Find the total feedback transfer function (refer to Chapter 15) Plot sketches and graphs (from data files) Discussions, evaluations and conclusions 15

33 Appendix 1 Process Control Trainer Cart Tank Control valve Microprocessor-based controllers and chart recorders Valve positioner Pressure transmitter Level transmitter Flow transmitter I/P converter Process Control Trainer Cart Appendix 2 Block Diagram for On-Off Controller Program (level control) 16

34 Appendix 3 Block Diagram of the PID Controller Program (level control) 17