Power Spectrum Express VI

LabView Acquire Signals Express VIs

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Power Spectrum Express VI

Owning Palette: Frequency-Domain Measurements Express VIs

Installed With: LabVIEW SignalExpress

Computes the averaged magnitude spectrum, power spectrum, or power spectral density for a single or multiple channels. This step can return the spectra in root-mean-square, peak, and peak-to-peak units.

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs
 Place on the block diagram  Find on the Functions palette

Dialog Box Options

ParameterDescription
GraphSpectra—Displays the spectra for all channels. Use the Zoom button to zoom in and out of the display.

Signals—Displays the time-domain signals for all channels. Use the Zoom button to zoom in and out of the display.
ViewSpecifies if the graph displays time domain signals or the computed power spectra.
AutoscaleAutomatically adjusts the scales of the graph to display the data.
InputContains the following option:
  • Input signal—Specifies the analog waveform for the step.
ConfigurationContains the following options:
  • Window—Specifies the window to apply to the input signal. Choose from one of the following window options:
    • None
    • Hanning
    • Hamming
    • Blackman-Harris
    • Exact Blackman
    • Blackman
    • Flat Top
    • 4 Term B-Harris (Four Term Blackman-Harris)
    • 7 Term B-Harris (Seven Term Blackman-Harris)
    • Low Sidelobe
    • Gaussian
  • Scaling—Specifies the scaling parameter for the step.
    • Spectrum type—Specifies if the spectrum is in units of Magnitude or Power, where power equals magnitude squared. The default is Power.
    • Magnitude scale—Specifies if zoom power is in linear units or in decibels. The default is decibels.
    • Peak conversion—Specifies the peak scaling of the converted spectrum. You can select RMS (default), Peak, or Peak to Peak.
    • Spectral density—Specifies if the spectrum is returned as power spectral density (PSD). The default is Off.
AveragingSpecifies the averaging parameters.
  • Averaging mode—Specifies the averaging mode from the following options:
    • No Averaging (Default)
    • Vector Averaging
    • RMS Averaging
    • Peak Hold
  • Weighting mode—Specifies either Exponential or Linear weighting. Exponential averaging applies more weight to the most recent data, and linear averaging applies equal weighting to all the data.
  • Number of averages—Specifies the number of averages used by the selected Weighting mode.
  • Auto-restart—Specifies if the averaging process automatically restarts once the step reaches the Number of averages value. When you set Weighting mode to linear, use Auto-restart to configure averaging to automatically restart when Averages completed equals the Number of averages.
  • Averages completed—Displays the number of averages completed.
  • Averaging done—Indicates when the number of Averages completed equals or exceeds the Number of averages. Averaging done is always TRUE if the selected Averaging mode is No averaging.

Block Diagram Inputs

ParameterDescription
input signalsSpecifies the scaled input signal.
error in (no error)Describes error conditions that occur before this VI or function runs.
restart averagingSpecifies whether to restart the selected averaging process. The default is FALSE. When you call this Express VI for the first time, the averaging process restarts automatically.

Block Diagram Outputs

ParameterDescription
spectrumReturns the power spectrum computed by the Express VI.
spectrum infoReturns spectrum information. This information is needed by the Peak Search Express VI and the Power in Band Express VI.
unit labelsReturns the unit labels.
averages completedReturns the number of averages completed by the Express VI.
averaging doneReturns TRUE when the number of averages completed equals or exceeds the number of averages specified in averaging parameters. Otherwise, averaging done returns FALSE. averaging done is always TRUE if the selected averaging mode is No averaging.
error outContains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator and select Explain Error from the shortcut menu for more information about the error.
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