You are here: NI Home > Support > Product Reference > Manuals > Sound and Vibration Measurement Suite 6.0 Help

You can use the Spectrum Extended Measurements VIs to perform the following measurements:

• Limit testing
• Frequency-domain weighting
• Frequency-domain integration
• Spectrum value
• Spectrum subset
• Power in band
• Spectrum peak search
• Units conversion

Get Spectrum Value

The SVFA Get Spectrum Value VI returns the value of a spectrum at a specified frequency. This VI operates on any real-valued spectrum. This VI facilitates measurements like operational deflection shapes.

Get Spectrum Subset

The SVFA Get Spectrum Subset VI returns a portion of a spectrum in a specified range. You can restrict viewing and processing to the desired subset with this VI.

Power in Band

The SVFA Power in Band VI measures the total power within a specified frequency range. The following table shows the equations for computing power in band based on the type of input spectrum.

Type of Input Spectrum	Equation for Power in Band
Power Spectrum (PS)
Power Spectral Density (PSD)
Magnitude Spectrum (MS)

where

ENBW is the equivalent noise bandwidth.

df is the frequency resolution of the measurement.

You also can use the Power in Band Express VI to interactively configure power in band computations.

Spectrum Peak Search

The SVFA Spectrum Peak Search VI operates on magnitude and power spectra. This VI estimates the frequency and amplitude of the tones that satisfy the search criteria specified in the peak search settings input parameter. For the SVFA Spectrum Peak Search VI to identify a tone, the spectrum must exceed the specified threshold. Specify the threshold in the same units as the input spectrum.

The SVFA Spectrum Peak Search VI uses an algorithm to estimate the actual frequency and amplitude of each tone that meets the search criteria. The algorithm also estimates the frequency and amplitude of tones that are not exactly periodic within the measurement window. The ability to identify nonperiodic tones that are not exactly on-bin enables you to use a smaller block size, therefore a smaller FFT, and still accurately identify tones present within the spectrum.

You also can use the Peak Search Express VI to interactively configure peak search computations.

Unit Conversion

The SVFA Unit Conversion VI operates on complex, magnitude, and power spectra. You can use this VI to convert the complex spectra produced by distortion and single-tone measurements to a magnitude or power spectrum more suitable for display on a waveform graph. You also can use the conversion utility to switch between magnitude and power spectra, switch between linear and logarithmic scaling, change the decibel reference for the spectrum, switch between peak units of RMS and peak-to-peak, and switch between spectrum and spectral density.

Note  You cannot use the SVFA Unit Conversion VI to scale the data to engineering units or change the spectrum physical units. Use Measurement & Automation Explorer, the DAQ Assistant, or the SVL Scale Voltage to EU VI to scale data to the proper engineering units.

You do not need to perform unit conversions on the decibel reference. The decibel reference always has the same units as the converted spectrum. For example, if you have a magnitude spectrum in V_rms, you can convert this spectrum to a power spectrum in decibels referenced to 10 V_pk by specifying the desired scaling parameters shown in the following table.

desired scaling
linear/decibels	dB
dB reference (0: no change)	10
power/magnitude	power
view	peak