Difference between revisions of "Single-Board-Heater-System/C2/Implementing-Proportional-Controller-on-SBHS-remotely/English"

1. Use Ziegler-Nichols tuning method to calculate proportional controller gain
2. Modify step test code to design a proportional controller
3. Implement this proportional controller on SBHS

Ensure that Scilab is installed on your computer.

Also, ensure that you have internet connectivity before you begin with this tutorial.

I am recording this tutorial on a Windows 7 32-bit OS

This tutorial is available on the Spoken Tutorial website.

It will teach you how to do a basic step test experiment on SBHS, remotely.

You also need to have basic knowledge of PID tuning.

You should also have the step test experiment data file with you.

If not, then it is recommended that you re-do the step test experiment and generate a new data file.

Point to the file.

Here is a folder with my username and here is my data file.

Open a web browser and go to the web site sbhs.os-hardware.in

Here it is.

The file downloaded will be in zip format.

A folder named Scilab codes analysis will be created.

Locate and open the folder Step Analysis.

The Step Analysis folder will have few more folders.

This will launch Scilab automatically and will also open the file in Scilab editor.

Choose the file firstorder and click on Open.

I will copy paste the filename to avoid spelling mistakes.

Keep the .txt extension.

If the data file is not corrupted and there are no errors, a plot window will open.

• the SBHS temperature plot which has noise
• and output of SBHS first order model which is a smooth curve.

This code basically does the job of fitting a first order transfer function using the data file.

The value of time constant tau and gain Kp is displayed on the top.

In this tutorial, we will not use the first order transfer function.

We will only use the plot of the SBHS output.

Locate the line plot2d of t comma y underscore prediction.

We don't want the prediction output to appear on the plot.

Comment out this line by putting two forward slashes at the beginning of the line.

Switch to the plot window.

Notice that the plot window now has only the SBHS temperature plot.

Then choose Export to option.

Give a name to the image file.

I will type sbhsplot.

Click on the drop down menu for Files of type and choose PNG.

Choose a directory where you want to save the file.

I will choose Desktop and click on Save.

Here it is.

• Reaction curve method and
• Instability method.

We will see the Reaction curve method.

• a step input is given to the system
• and its output is observed over a period of time.

Any practical system would respond exponentially to a step input.

A tangent is drawn at the point of inflection.

That is, when the curve changes from convex to concave.

The dead time and time constant is calculated from the time axis.

This is the tangent line drawn at the point of inflection .

• K is the gain of the system
• L is the dead time
• T is the time constant

Let me open this file.

• gain equal to 2.78
• dead time equal to 1 second
• and time constant equal to 50 seconds

Note that these are all approximate values.

The values depend on the accuracy with which you draw the tangent line at the inflection point.

• refer to the table given by Ziegler-Nichols
• to calculate the value of proportional gain.

For a proportional controller, we need to calculate only the value of proportional gain.

In my case the value of proportional gain comes out to be 18.

We would modify the step test code for this.

Here it is. Make a copy of this folder.

Rename this folder as proportional and open it.

Rename the steptest dot sci file to proportional.

Rename the steptest dot xcos file to proportional.

Double-click on the proportional dot sce file.

This should launch Scilab automatically and also open the file in Scilab editor.

>> Choose proportional.sce >> Open

Choose the file proportional dot sce and click on Open.

Save this file.

>> Choose proportional.sci >> Open>> Change steptest to proportional.

Select the file proportional.sci file and click on Open.

Change the function name from steptest to proportional.

In the next line, type global, leave a space and then type temp and press Enter.

Add semicolon at the end and press Enter.

Add semicolon at the end.

Here 18 is the value of the proportional gain for my SBHS.

You may change it according to what you would have calculated for your SBHS.

To do so, add a space after temp and type setpoint.

Type xcos and press Enter.

xcos window will open.

Close the palette window.

Browse to the proportional directory.

Select proportional.xcos and click on Open.

Xcos file will open.

Delete it and type setpoint.

Click once anywhere on the xcos window to save the label.

Change the initial value to 30 and final value to 40.

Keep step time as 300.

Click on Ok.

A window will appear. Click on OK.

Here there is an option to enter the function name to be called by this xcos block.

Change the function name from step test to proportional.

Click on Ok.

Keep clicking on Ok three times to finish configuring the function block.

Save the xcos diagram and close it.

Close the xcos untitled window as well.

On the left hand side, click on Virtual labs.

Login with your registered username and password.

Book a slot.

Double click on the file run.

Login with your username and password.

Make sure you are logging in at the booked slot time.

Expect the message Ready to execute Scilab code.

Type get d space dot dot slash common files

Press Enter

Execute the file proportional.sce

If the network is fine, then it will automatically open the xcos window with proportional controller xcos diagram.

Execute the xcos diagram and expect a plot window.

Setpoint will also be plotted in the temperature graph.

Observe that the proportional controller

• computes the value of heat
• in order to achieve the setpoint value of temperature.

You can observe that the proportional controller inherently has the property of offset.

A proportional controller will always have an offset between the setpoint value and the actual value.

1. Use Ziegler-Nichols tuning method to calculate proportional controller gain for SBHS
2. Modify step test code to design a proportional controller
3. Implement the designed proportional controller on SBHS

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