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Log and Plot Simulation Data

This example shows how you can log and plot simulation data instead of adding sensors to your model.

The model shown represents a permanent magnet DC motor.

This model is very similar to the Permanent Magnet DC Motor example, but, unlike the example model, it does not include the Ideal Rotational Motion Sensor and the Current Sensor blocks, along with the respective PS-Simulink Converter blocks and scopes. For a detailed description of the Permanent Magnet DC Motor example, see Evaluating Performance of a DC Motor.

  1. Build the model, as shown in the preceding illustration.

  2. To enable data logging, open the Configuration Parameters dialog box, in the left pane, select Simscape, then set the Log simulation data parameter to all and click OK.

  3. Simulate the model. This creates a workspace variable named simlog (as specified by the Workspace variable name parameter), which contains the simulation data.

  4. The simlog variable has the same hierarchy as the model. To see the whole variable structure, at the command prompt, type:

    simlog.print

    This command prints the whole data tree.

         dc_motor2
         +-Electrical_Reference2
         | +-V
         | | +-v
         | +-i
         +-Friction_Mr
         | +-C
         | | +-w
         | +-R
         | | +-w
         | +-t
         | +-w
         +-L
         | +-i
         | +-i_L
         | +-n
         | | +-v
         | +-p
         | | +-v
         | +-v
         +-Load_Torque
         | +-C
         | | +-w
         | +-R
         | | +-w
         | +-S
         | +-t
         | +-w
         +-Mechanical_Rotational_Reference
         | +-W
         | | +-w
         | +-t
         +-Mechanical_Rotational_Reference1
         | +-W
         | | +-w
         | +-t
         +-Motor_Inertia_J
         | +-I
         | | +-w
         | +-t
         +-Rotational_Electromechanical_Converter
         | +-C
         | | +-w
         | +-R
         | | +-w
         | +-i
         | +-n
         | | +-v
         | +-p
         | | +-v
         | +-t
         | +-v
         | +-w
         +-Rotor_Resistance_R
         | +-i
         | +-n
         | | +-v
         | +-p
         | | +-v
         | +-v
         +-Simulink_PS_Converter
         +-x1_5V
           +-i
           +-n
           | +-v
           +-p
           | +-v
           +-v
    
  5. Every node that represents an Across, Through, or internal block variable contains series data. To get to the series, you have to specify the complete path to it through the tree, starting with the top-level variable name. For example, to get a handle on the series representing the angular velocity of the motor, type:

    s1 = simlog.Rotational_Electromechanical_Converter.R.w.series;

    From here, you can access the values and time vectors for the series and analyze them.

  6. You do not have to isolate series data to plot its values against time, or against another series. For example, to see how the motor speed (in revolutions per minute) changes with time, type:

    plot(simlog.Rotational_Electromechanical_Converter.R.w, 'units', 'rpm')

  7. Compare this figure to the RPM scope display in the Permanent Magnet DC Motor example. The results are exactly the same.

  8. To plot the motor torque against its angular velocity, in rpm, and add descriptive axis names, type:

    plotxy(simlog.Rotational_Electromechanical_Converter.R.w, simlog.Motor_Inertia_J.t, ...
       'xunit', 'rpm', 'xname', 'Angular velocity', 'yname', 'Torque')
    

    For more information on plotting logged simulation data, see the simscape.logging.plot and simscape.logging.plotxy reference pages.

    Note   Plotting simulation data for a high-level node and its children can generate a large number of plots. By default, the plots are not docked in the desktop, which results in a multitude of separate figure windows. To avoid this inconvenience, you can issue a command to make figures automatically dock in the desktop. For more information, see Docking Figures Automatically in the MATLAB® documentation.

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