chgFreqUnit

Change frequency units of frequency-response data model

collapse all in page

    Syntax

    sys_new = chgFreqUnit(sys,newfrequnits)

    Description

    sys_new = chgFreqUnit(sys,newfrequnits) changes units of the frequency points in sys to newfrequnits without modifying system behavior. Both Frequency and FrequencyUnit properties of sys adjust so that the frequency responses of sys and sys_new match.

    example

    Examples

    collapse all

    This example uses:

    Open Live Script

    Create a frequency-response data model.

    load('AnalyzerData');
sys = frd(resp,freq);

    The data file AnalyzerData has column vectors freq and resp. These vectors contain 256 test frequencies and corresponding complex-valued frequency response points, respectively. The default frequency units of sys is rad/TimeUnit, where TimeUnit is the system time units.

    Change the frequency units.

    sys1 = chgFreqUnit(sys,'rpm');

    The FrequencyUnit property of sys1 is rpm.

    Compare the Bode responses of sys and sys1.

    bodeplot(sys,'r',sys1,'y--');
legend('sys','sys1')

    MATLAB figure

    The magnitude and phase of sys and sys1 match because chgFreqUnit command changes the units of frequency points in sys without modifying system behavior.

    Change the FrequencyUnit property of sys to compare the Bode response with the original system.

    sys2 = sys;
sys2.FrequencyUnit = 'rpm';
bodeplot(sys,'r',sys2,'gx'); 
legend('sys','sys2');

    MATLAB figure

    Changing the FrequencyUnit property changes the system behavior. Therefore, the Bode responses of sys and sys2 do not match. For example, the original corner frequency at about 2 rad/s changes to approximately 2 rpm (or 0.2 rad/s).

    Input Arguments

    collapse all

    Frequency response data model, specified as an idfrd model.

    New units of frequency points, specified as one of the following values:

    • 'rad/TimeUnit'

    • 'cycles/TimeUnit'

    • 'rad/s'

    • 'Hz'

    • 'kHz'

    • 'MHz'

    • 'GHz'

    • 'rpm'

    The rad/TimeUnit and cycles/TimeUnit values express frequency units relative to the system time units specified in the TimeUnit property.

    Output Arguments

    collapse all

    Frequency-response data model of the same type as sys with new units of frequency points. The frequency response of sys_new is the same as sys.

    Version History

    Introduced in R2012a

    See Also

    | (Control System Toolbox) |

    Topics