chgFreqUnit

Change frequency units of frequency-response data model

Syntax

sys_new = chgFreqUnit(sys,newfrequnits)

Description

sys_new = chgFreqUnit(sys,newfrequnits) changes units of the frequency points in sys to newfrequnits. Both Frequency and FrequencyUnit properties of sys adjust so that the frequency responses of sys and sys_new match.

Input Arguments

sys

Frequency-response data (frd, idfrd, or genfrd) model

newfrequnits

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

  • 'rad/TimeUnit'

  • 'cycles/TimeUnit'

  • 'rad/s'

  • 'Hz'

  • 'kHz'

  • 'MHz'

  • 'GHz'

  • 'rpm'

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

Default: 'rad/TimeUnit'

Output Arguments

sys_new

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

Examples

This example shows how to change units of the frequency points in a frequency-response data model.

  1. 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.

  2. Change the frequency units.

    sys1 = chgFreqUnit(sys,'rpm');

    The FrequencyUnit property of sys1 is rpm.

  3. Compare the Bode responses of sys and sys1.

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

    The magnitude and phase of sys and sys1 match.

  4. (Optional) 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');

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

More About

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Tips

  • Use chgFreqUnit to change the units of frequency points without modifying system behavior.

See Also

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Tutorials


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