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Owning Palette: Frequency-Domain Measurements Express VIs

Installed With: Sound and Vibration Measurement Suite

Computes the averaged zoom magnitude spectrum or zoom power spectrum. This measurement can return the spectrum in root-mean-square, peak, and peak-to-peak units. Data accumulates each time you pass new data. However, zoom analysis returns a new spectrum only when sufficient data accumulates.

Dialog Box Options

Block Diagram Inputs

Block Diagram Outputs

Dialog Box Options

Parameter	Description
View	Specifies the display that appears in the Signals graph.
Spectrum	Displays the baseband power spectrum and the zoom power spectrum if enough data has accumulated. Use the Zoom button to zoom in and out of the display. If you select Frequency spectra from the View pull-down menu, you can use the Cursor button to move the cursors. You can use these two cursors on the Frequency spectra graph to set the Start frequency and the Stop frequency.
Autoscale	Automatically adjusts the scales of the graph to display the data.
Input	Specifies whether to operate on a single channel or on N channels. This option is available only with the NI Sound and Vibration Assistant. Input signal—Configures the measurement for a single channel or N channels. Changing this selection changes the data types of the input signals and computed measurements.
Configuration	Specifies the configuration parameters. 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 parameters. Spectrum type—Specifies if the zoom power 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 zoom power spectrum. You can select RMS (Default), Peak, or Peak to Peak.
Zoom Settings	Specifies the zoom setting parameters. Frequency Resolution Settings—Specifies the frequency resolution settings for the zoom power spectrum. You also can use the green, vertical cursors in the Spectra graph to set frequency range. Start frequency (Hz)—Specifies the lowest frequency of the zoom power spectrum, in hertz. You also can use the green, vertical cursors in the Spectra graph to set Start frequency (Hz) and Stop frequency (Hz). The default is 1k. Stop frequency (Hz)—Specifies the highest frequency of the zoom power spectrum, in hertz. You also can use the green, vertical cursors in the Spectra graph to set Start frequency (Hz) and Stop frequency (Hz). The default is 2k. Number of lines—Specifies the number of spectral lines to compute between start frequency and stop frequency. The default is 400. % Overlap—Specifies the percentage of data reused by consecutive FFT computations. You can use % Overlap to make the zoom more responsive when the values of Frequency range and Number of lines require a longer measurement time. The default is 0. Frequency Resolution—Returns the frequency resolution parameters. Baseband resolution—Returns the frequency resolution of the baseband spectrum, in hertz. Zoom resolution—Returns the frequency resolution of the zoom spectrum, in hertz. Acquisition Time—Returns the acquisition time required to compute the first spectrum and subsequent spectra. First spectrum—Returns the time, in seconds, required to acquire data to compute the first zoom spectrum. The value depends on Start frequency, Stop frequency, and Number of lines. For the data acquisition time required for subsequent spectra, refer to New spectrum. New spectrum—Returns the time required, in seconds, to acquire data in order to get any spectrum after the first one. This value depends on Start frequency, Stop frequency, Number of lines, and % Overlap. Available—Returns TRUE every time a new zoom power spectrum computes.
Averaging	Contains the following options: Averaging Settings—Specifies the averaging parameters. Averaging mode—Specifies the averaging mode from the following options: No Averaging (Default) 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 when Averaging mode is RMS averaging. 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. Status—Returns status information about the averaging process. Averages completed—Displays the number of averages completed. Averaging done—Indicates when the number of Averages completed equals or exceeds the Number of averages.

Block Diagram Inputs

Parameter	Description
input signal	Specifies the input signals.
error in	Describes error conditions that occur before this Express VI runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node.
frequency range	Specifies the frequency range of the zoom power spectrum. start frequency—Specifies the lowest frequency of the zoom power spectrum, in hertz. The default is 1000. stop frequency—Specifies the highest frequency of the zoom power spectrum, in hertz. The default is 2000.
number of averages	Specifies the number of averages used by the selected Weighting mode when Averaging mode is RMS averaging.
number of lines	Specifies the number of spectral lines to compute between start frequency and stop frequency. The default is 400.
restart averaging	Specifies 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

Parameter	Description
zoom spectrum	Returns the zoom power spectrum.
spectrum info	Returns spectrum information. This information is needed by the Peak Search Express VI and the Power in Band Express VI.
unit label	Returns the unit label for the input signal.
averages completed	Returns the number of averages completed by the Express VI.
averaging done	Returns TRUE when the number of averages completed equals or exceeds the number of averages specified in averaging parameters. Otherwise, averaging done returns FALSE.
error out	Contains error information. This output provides standard error out functionality.
new spectrum	If TRUE, new spectrum indicates that zoom spectrum contains a new measurement and is not empty. When you wire the output value to the selector terminal of a Case structure, you can perform subsequent measurements or display the results in the TRUE case of the Case structure.