Controls Lab OnLine


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Assignment 2

Assignment #2 -- Developing the
Steady State Operating Curve

Review: Last assignment you got the response of a system output when the input was constant. It would be good if you noticed that after a certain amount of time, the transient response disappeared and the output was constant (with possibly statistical noise variations). This latter, "constant," value is the "steady-state" output value for that input value.

Results pic is here


Here for example is the same results graph shown in Assignment 1.
The Input Function is a constant at a y-value of 30. The units of the Input Function are %. This is shown in the graph on the left.
The Output Function has some transient response for about the first 1.5 seconds and then levels off to about a y-value of 1.05.
This is shown on the graph on the right.
This experiment was for the Pressure system. The output pressure units are cm of water.

1. This assignment has you make several experiments. For each one, choose a different input value.
For each one, download the data to Excel and find the average and standard deviation of the output variable OVER THE RANGE OF TIME WHEN THE OUTPUT IS AT STEADY STATE. (In the example above, this would be from 1.5 to 5.0 seconds.)That is, DO NOT include the transient or "start-up" response in calculating these statistics.

Do this for about 10 different values of the input values, ranging from 0 to 100%.

Since each time you click on "RUN EXPERIMENT" a new browser window is spawned, you can go back for each experiment to the data-input window easily and change only the value of the Input Function.

2. To do the experiments now, click on " Constant Input Value Experiments "

Choose your system, then choose Constant Input Function

As in Assignment 1, fill in your name, location & e-mail name and then select a "length of experiment" and value of the "Manipulated variable"

3. In Excel, make a new table that summarizes your results. Column A for "Input values" and column B for "Average output values" and column C for "Standard deviation."

4. Make a graph of these results. This graph of Output vs. Input we call the Steady-State Operating Curve (SSOC). Include the error bars for each data point. The error bars should be twice the standard deviation in order to indicate 95% confidence limits.

Save this Excel sheet and chart.

5. Send an e-mail (report) within the next few days. (Click on "report" to get instructions.)

Here are graphs of the results for three experiments run at 20%, 40% and 60% as the value of the Constant input.

Several Results pic is here

Notice how the output value starts off near zero at time=0, increases for a few seconds and then levels off, more-or-less, to a steady value, even though it has fluctuations.

Here is a graph of the SSOC.

Sample SSOC pic is here

Notice how the output value increases as the input increases. These three points do not fall in a straight line, so we can observe that over this operating range (20% to 60%) the system is not linear.

**** 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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