Learn more about System Identification Toolbox

Preparing Data for System Identification

On this page…
Loading Data into the MATLAB Workspace Opening the System Identification Tool GUI Importing Data Objects into the System Identification Tool Plotting and Processing Data

Loading Data into the MATLAB Workspace

Load the data in proc_data.mat by typing the following command in the MATLAB Command Window:

load proc_data

This command loads the data into the MATLAB workspace as the data object z. For more information about iddata objects, see the corresponding reference page.

Back to Top

Opening the System Identification Tool GUI

To open the System Identification Tool GUI, type the following command MATLAB Command Window:

ident

The default session name, Untitled, appears in the title bar.

Back to Top

Importing Data Objects into the System Identification Tool

You can import data object into the GUI from the MATLAB workspace.

You must have already loaded the sample data into MATLAB, as described in Loading Data into the MATLAB Workspace, and opened the GUI, as described in Opening the System Identification Tool GUI.

If you have not performed these steps, click here to complete them.

To import a data object into the System Identification Tool GUI:

1. In the System Identification Tool GUI, select Import data > Data object.

   This action opens the Import Data dialog box.

   

2. Specify the following options:

   • Object — Enter z as the name of the MATLAB variable that is the time-domain data object. Press Enter.

   • Data name — Use the default name z, which is the same as the name of the data object you are importing. This name labels the data in the System Identification Tool GUI after the import operation is completed.

   • Starting time — Enter 0 as the starting time. This value designates the starting value of the time axis on time plots.

   • Sampling interval — Enter 1 as the time between successive samples in seconds. This value represents the actual sampling interval in the experiment.

   The Import Data dialog box now resembles the following figure.

   

3. Click Import to add the icon named z to the System Identification Tool GUI.

   

4. Click Close to close the Import Data dialog box.

Back to Top

Plotting and Processing Data

In this portion of the tutorial, you evaluate the data and process it for system identification. You learn how to:

• Plot the data.

• Subtract the mean values of the input and the output to remove offsets.

• Split the data into two parts. You use one part of the data for model estimation, and the other part of the data for model validation.

The reason you subtract the mean values from each signal is because, typically, you build linear models that describe the responses for deviations from a physical equilibrium. With steady-state data, it is reasonable to assume that the mean levels of the signals correspond to such an equilibrium. Thus, you can seek models around zero without modeling the absolute equilibrium levels in physical units.

You must have already imported data into the System Identification Tool, as described in Importing Data Objects into the System Identification Tool.

If you have not performed this step, click here to complete it.

To plot and process the data:

1. In the System Identification Tool GUI, select the Time plot check box to open the Time Plot window.

   

   The bottom axes show the input data—a random binary sequence, and the top axes show the output data.

   The next two steps demonstrate how to modify the axis limits in the plot.

2. To modify the vertical-axis limits for the input data, select Options > Set axes limits.

3. In the Limits for Time Plot dialog box, set the new vertical axis limit of the input data channel u1 to [-1.5 1.5]. Click Apply and Close.

   

   Note   The other two fields in the Limits for Time Plot dialog box, Time and y1, let you set the axis limits for the time axis and the output channel axis, respectively. You can also specify each axis to be logarithmic or linear by selecting the corresponding option.

   The following figure shows the updated time plot.

   

4. In the System Identification Tool GUI, select <--Preprocess > Quick start to perform the following four actions:

   • Subtract the mean value from each channel.

   • Split the data into two parts.

   • Specify the first part of the data as estimation data (or Working Data).

   • Specify the second part of the data as Validation Data.

Learn More

For information about supported data processing operations, such as resampling and filtering the data, see the System Identification Toolbox User's Guide.

Back to Top

What Is a Continuous-Time Process Model?

Estimating a Second-Order Transfer Function (Process Model) with Complex Poles

© 1984-2009- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS