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SVFA Spectrum Peak Search VI

NI Sound and Vibration Measurement Suite 2009 Help

Edition Date: June 2009

Part Number: 372416C-01

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Owning Palette: Spectrum Extended Measurements VIs

Requires: Sound and Vibration Measurement Suite

Performs a peak search on a spectrum or spectra. The spectrum or spectra can be in either the frequency domain or the order domain. Detects single or multiple peaks in Power, PSD, and COP spectra. Wire data to the spectrum input to determine the polymorphic instance to use or manually select the instance.

The time-domain window previously applied to the signal is used to accurately estimate the frequency and amplitude of the peak.

Details  Example

Use the pull-down menu to select an instance of this VI.

SVFA Spectrum Peak Search (1 Spectrum)

spectrum specifies the abscissa scaling and the magnitude of the spectrum.
x0 specifies the start frequency or order of the spectrum. The default is 0.00.
dx specifies the frequency or order resolution of the spectrum. The default is 0.00.
magnitude specifies the magnitude of the spectrum.
peak search settings specifies the criteria for the peak search.
single/multiple specifies whether the VI returns a single max peak or multiple peaks (default).
0Multiple Peaks (default)
1Single Max Peak
threshold specifies the level a peak must exceed to be considered a valid peak. The default is Inf. Set threshold to the same units as spectrum.
spectrum info specifies properties of the computed spectrum.
Note  You must wire spectrum info when performing extended measurements. Do not modify the spectrum info values. If you want to view the information, you can right-click the spectrum info wire and select Custom Probe»Spectrum Info from the shortcut menu.
error in (no error) describes error conditions that occur before this node runs. This input provides standard error in functionality.
peaks returns the frequency or order and value for each peak that meets the search criteria.
freq. or order returns the frequency or order of the peak.
value returns the peak value of the peak in the same units as the spectrum input.
number of peaks indicates the number of peaks that satisfied the search criteria.
unit label returns the selected engineering units.
error out contains error information. This output provides standard error out functionality.

SVFA Spectrum Peak Search (N Spectra)

spectra specifies the abscissa scaling and the magnitude for each spectrum.
x0 specifies the start frequency or order of the spectrum. The default is 0.00.
dx specifies the frequency or order resolution of the spectrum. The default is 0.00.
magnitude specifies the magnitude of the spectrum.
peak search settings specifies the criteria for the peak search.
single/multiple specifies whether the VI returns a single max peak or multiple peaks (default).
0Multiple Peaks (default)
1Single Max Peak
threshold specifies the level a peak must exceed to be considered a valid peak. The default is Inf. Set threshold to the same units as spectrum.
spectrum info specifies properties of the computed spectrum.
Note  You must wire spectrum info when performing extended measurements. Do not modify the spectrum info values. If you want to view the information, you can create a custom probe.
error in (no error) describes error conditions that occur before this node runs. This input provides standard error in functionality.
peaks returns the frequency or order and value for each peak that meets the search criteria.
freq. or order returns the frequency or order of the peak.
value returns the peak value of the peak in the same units as the spectrum input.
number of peaks indicates the number of peaks that satisfied the search criteria for each spectrum.
unit labels returns the selected engineering units for each channel.
error out contains error information. This output provides standard error out functionality.

SVFA Spectrum Peak Search Details

The SVFA Spectrum Peak Search VI finds all the peaks within the spectrum and performs amplitude/frequency or amplitude/order estimation on each individual peak. The VI operates on magnitude and power spectra.

Usually, the spectrum is computed based on a windowed input signal. The closed form of any cosine window, such as Hanning, Hamming, Blackman-Harris, and so on, is known. The presence of three dominant bins indicates a local maximum on the power spectrum. Therefore, when the SVFA Spectrum Peak Search VI locates three dominant bins, a curve fitting algorithm maps the window shape onto the three bins and estimates the true frequency and amplitude of that particular tone. The following illustration diagrams the concept of the algorithm.

Example

Refer to the SVXMPL_Peak Search (Simulated) VI in the labview\examples\Sound and Vibration\Frequency Analysis\Extended Measurements directory for an example of using the SVFA Spectrum Peak Search VI.

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