Distortion

LabVIEW SignalExpress

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Distortion

Performs harmonic distortion analysis and/or SINAD measurement on the input signal.

This step returns the fundamental frequency, the percentage of total harmonic distortion, the total harmonic distortion plus noise value, and the SINAD value in decibels.

This step also returns a time-domain waveform and frequency-domain power spectrum for the different components of the signal, such as fundamental signal, residual signal, or harmonics.

ParameterDescription
Exported SignalDisplays the time signal you selected with Export signals in the Measurement Setup section on the Configuration page.
  • Displayed signal—Specifies the signal(s) to display in the preview graph(s). This option appears only when you select a group of signals for the input.
    Note  If the input signals include scalar values that depend on the values of input waveform signals, you cannot specify to display all signals in the preview graph(s).
Exported Power SpectrumDisplays the power spectrum of the signal the Exported Signal graph displays.
Autoscale magnitudeScales the magnitude of the exported power spectrum. The default is to autoscale the magnitude.
Input/OutputContains the following options:
  • Input signal—Specifies the input signal to be measured.
  • Export time signal—Exports the signal to the Project View as Export Signals (THD) or Export Signals (SINAD) specifies.
  • Export power spectrum—Exports the power spectrum to the Project View as Export Signals (THD) or Export Signals (SINAD) specifies.
ConfigurationContains the following options:
  • Measurement Setup—Contains the following options:
    • Distortion types—Specifies Harmonic Only, SINAD Only, or Harmonic and SINAD distortion.
    • Highest harm.—Specifies the highest harmonic to include in the calculation of the harmonic distortion. The default is 19, so the THD result is based on harmonics 2 to 19 (both included) assuming that the Exclude aliased harmonics checkbox does not include a checkmark. If you place a checkmark in the Exclude aliased harmonics checkbox, Highest harm. includes only the harmonics below the Nyquist frequency. The Nyquist frequency is half the sample rate of the input signal.
    • Export signals (THD)—Specifies which signals to display on the two graphs and to export to the Project View. Options include Input Signal, Fundamental Tone, Residual Signal, Harmonics Only, Noise and Spurs or None (no signal). The default is Input Signal.
    • Export signals (SINAD)—Specifies which signals to display on the two graphs and to export to the Project View. Options include Input Signal, Fundamental Tone, Residual Signal, or None (no signal). The default is Input Signal.
  • Measurement Results—Contains the following options:
    • Fund. Frequency—Returns the detected fundamental frequency of the input signal.
    • THD (%)—Returns the measured percentage of total harmonic distortion up to and including the highest harmonic or limited by the Nyquist frequency.
    • SINAD (dB)—Returns the measured sine in noise and distortion value in decibels.
    • THD + Noise (%)—Returns the measured total harmonic distortion plus noise. Notice that this result always includes all harmonics and is therefore independent of the value you specify for Highest harm.
AdvancedContains the following options:
  • Approx. fund. freq. (Hz)—Returns the center frequency to use in the frequency-domain search for the fundamental tone. A negative value specifies to search for the tone with the highest amplitude. The default is–1.
  • Exclude aliased harmonics—Exclude aliased harmonics should be set to TRUE (default) to include only frequencies less than the Nyquist frequency, or half the sampling rate, in the harmonic search. When set to FALSE, this step continues searching the frequency domain beyond Nyquist by assuming that higher frequency components have aliased according to the following equation.

    Aliased f = Fs – (f modulo Fs)

    where

    Fs = 1/dt = sampling rate.
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