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Assignment 3
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Web-Lab Assignment #3 Step Response Experiments |
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BEFORE proceeding with this Assignment, get approval from the instructor. |
| 1. Next, we want to investigate the TRANSIENT response of our system. We want to do our experimentation in a "linear" range of the operating curve. So look at your SSOC from Assignment 2 and choose a value in the "linear" region and we'll call this the "baseline." The value of the Input (%) for this baseline we call the "Input baseline." For example, the Input baseline may be 50%. The corresponding value of the output variable we call the "Output baseline." |
| 2. We will have the Input function take a step from the input baseline to some other input value, still in the linear operating range. The difference between these two values of the input function is the Height of the step. For example if we want to step from 50% to 90%, the height of the step is 40%. By the way, the Height of the step CAN BE negative (!) if you want it to. |
Input Function and Output Function for a Step Input Function  This is an example of the Input Function stepping from 50 to 90 (%) at the time of 5 seconds. The Output Function undergoes some transients for about 4 seconds and then settles down before responding to the Input Function step which occurs at t=5. The Output Function takes a fraction of a second before any response happens then it responds to a new steady value after about 1.5 seconds. It is the details of this Step Response that you are to analyze in this Assignment. This response graph happens to be for the Flow system. The Output Function units are pounds per minute of water flowing. Your system's response may be similar to this or it may differ in speed or magnitudt. |
| 3. The experiment has to run long enough at the Input Function baseline in order for the Output Function to reach a steady value. So we don't want the step in the Input Function to occur before this steady Output Function baseline is reached. From our experiences before, we should have some idea of the time required for the Output Function steady state to be reached. In the example given in Assignment 1, we see that at least 5 or 6 seconds needs to pass before the system reaches steady output and can be ready to have the input change. So, we ought to have the "Time of the step" to be 6 seconds or more. |
| 4. Then AFTER the step occurs, we need to have the experiment run long enough for the system to again reach Output Function steady state. This length AFTER the step plus the length of time up to the step is the total length of the experiment. Looks like it ought to be at least 12 seconds. |
5. When you're ready, click on "Step Function Input Value Experiments" Go to your system, select Step Function Input. |
| 6. Fill in your name, location & email name and then select a "length of experiment" and values of the the other parameters & click the "RUN EXPERIMENT" button. |
| 7. Run experiments for a number of different values of Input Function baseline and Height of step. Include some negative step heights. We need to learn about the system Output Function transients (dynamics) for a slowing down system as well as a speeding up system. |
8. Look at and analyze the graphs in terms of FOPDT parameters. See Smith & Corripio, pages 310-317 (2nd edition) or pages 212-213 (1st edition). |
| 9. Report your results in a report which describes your experiments and results. Provide a table of results. The table includes Gain, dead time (to) and first-order time constant, tau. |
| 10. Send an e-mail (report) within the next few days. (Click on "report" to get instructions.) |
**** CONTINUOUS IMPROVEMENT ***
For suggestions and feedback,
contact Jim Henry - Lab-Master Send E-Mail to Jim Henry
Last revised 29 November 1997
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