Test 1 - Open Loop Level Step Response Test

1)Objective: To get familiar with the process vessel and to measure the time constant.

Procedure 1

1) Start the CE2000 software and load ?le ‘exp4-1.ict'. You will see the software user interface as shown in Figure 1.

2) Close the loop bypass valve, fully open the process vessel drain valve and the air vent.

3) Connect the CE117 Mimic Panel as shown in Figure 2. Set Pump 2 switch to External. Analogue signals will pass from the ADA section to Pump 2, the proportional valve S and from level transmitter LT. Such connections will build up a system which is schematically shown in Figure 3.

4) On the software (as shown in Figure 1), set Pump 2 voltage to 4 V and the Valve to 10 V (fully open). Run the software and use it to record the level.

5) Carefully adjust the pump voltage until the level stabilizes just above the top of the heat exchanger. When you have done this, wait for at least 10 minutes to ensure that the level remains stable. Make a note of the height of the water in the process vessel and the how rate. This is Level A.

Increase the pump voltage by 0.5 V. Monitor the level until it becomes stable, this should take less than 15 minutes. Make a note of the height of the water in the process vessel and the ?ow rate. This is Level B.

7) Stop the CE2000 software running. Use its graph features to plot the level and pump input against time (time response curve).

8) Switch o? the apparatus.

9) Draw a block diagram of the system.

10) From your plot, estimate the time constant (approximately 62.3% of the time to reach Level B) for the process vessel. You may use the time constant function of the CE2000 graph software to do this for you.

Test 2 - Level Control by Pump Speed

2) Objective 2 To control the level in the process vessel using PID control.

2.3 Procedure 2

1. Start the CE2000 software and load ?le ‘exp4-2.ict'.

2. Close the loop bypass valve, fully open the process vessel drain valve and the air vent.

3. Connect the CE117 Mimic Panel as shown in Figure 4. Set Pump 2 switch to External. Analogue signals will pass from the ADA section to Pump 2, the proportional valve (S) and from level transmitter (LT).

4. On the software, the block titled PID is a three term controller that controls the pump voltage. You may adjust the controllers values of  Proportional gain, Integral and Derivative. Set the PID controller to: Proportional gain= 10, Integral gain= 0.5, Derivative gain= 0.

5. Run the software. Adjust the setpoint to 6 V and the valve voltage to 10 V (fully open) and wait for the level to stabilize.

6. Increase the setpoint by 0.5 V and use the software to monitor the level until it becomes stable. Compare the response with the open loop test of Procedure 1.

7. Reduce the setpoint back to 6 V and let the system stabilize. Repeat the procedure with PID values:

A (Gain Only) B (Integral Only) Proportional gain - 20 Proportional gain - 5 Integral - 0 Integral - 0.5 Derivative - 0 (zero) Derivative - 0 (zero)

8. Record the results for the experiments using the plot function of ‘CE2000'. Note how well the system responds.

9. Draw a block diagram of the system.

Your report should contain the following sections.

- A brief Introduction stating the aims and objectives of the exercise, as well as a brief overview of the organisation of rest of the report.

- A section containing a description of the systems considered in the experiment.

Do not copy the materials in the Lab notes, but to use your own language based on your understanding of the materials and the experiment you worked on. - You need to present all the data, plots, block diagrams and analysis that you are asked to do in the two Procedures. However, do not present your answers to different items separately, but try to present your material in a smooth and logic way.

- A Conclusion section is needed to discuss your own opinions on the experiment and the general usefulness of PID control in water level control problem.