Owning Palette: Zoom FFT VIs

Requires: Sound and Vibration Toolkit

Computes the zoom cross power spectrum of scaled signal X [EUx] , scaled signal Y [EUy] , and zoom settings . Results are returned in magnitude and phase. Data accumulates each time the VI is called. However, it returns a new spectrum only when sufficient data accumulates. Indicators and subsequent processing should only be called when new spectrum available is TRUE.

scaled signal X [EUx] specifies the scaled signal expressed in the selected engineering units. scaled signal X [EUx] is generally the stimulus or excitation signal in dual-channel measurements.
t0 specifies the start time of the waveform.
dt specifies the time interval in seconds between data points in the waveform.
Y specifies the data values of the waveform.
scaled signal Y [EUy] specifies the scaled signal expressed in the selected engineering units. scaled signal Y [EUy] is generally the response signal in dual-channel measurements.
t0 specifies the start time of the waveform.
dt specifies the time interval in seconds between data points in the waveform.
Y specifies the data values of the waveform.
zoom settings specifies the properties of the zoom analysis.
frequency range specifies the frequency band of analysis. The valid range for the start frequency and for the stop frequency is between 0 and the Nyquist frequency.
start frequency specifies the lowest frequency of interest for the analysis band in hertz. The valid range is between 0 and the Nyquist frequency. The default is 1,000.00 Hz.
stop frequency specifies the highest frequency of interest for the analysis band in hertz. The valid range is between 0 and the Nyquist frequency. Specify a value of –1 to select the highest frequency as the maximum frequency of interest. The default is 5,000.00 Hz.
window specifies the time-domain window used. The default is Hanning.
Note The Zoom FFT VIs do not apply the window to each incoming block of data. Instead, the Zoom FFT VIs apply the window to the decimated set of data used by the Discrete Zak Transform (DZT).
0 None
1 Hanning (default)
2 Hamming
3 Blackman-Harris
4 Exact Blackman
5 Blackman
6 Flat Top
7 4 Term B-Harris
8 7 Term B-Harris
9 Low Sidelobe
number of lines specifies the number of spectral lines to compute between start frequency and stop frequency . The default is 400. number of lines determines the size of the FFT that is computed.
% overlap specifies the percentage of data reused by consecutive FFT computations. The valid range is between 0 and 100. The default is 0.00. 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 Zoom FFT VIs typically do not return a spectrum each time the VI is called. You can use % overlap to increase the rate at which a new spectrum is computed by reusing acquired data. For example, setting % overlap to 50 causes the VI to compute a new zoom spectrum twice as often as a setting of 0 because half the data is reused with each computation.
view specifies how the different results from this VI are returned. view allows you to choose whether magnitude results are displayed in dB, phase results are unwrapped, and phase results are converted from radians to degrees.
dB On specifies if results are expressed in decibels. The default is FALSE.
unwrap phase specifies whether to unwrap the phase. Unwrapping eliminates discontinuities that have an absolute value greater than pi. The default is FALSE, meaning the phase is not unwrapped. When unwrap phase is TRUE, the phase is unwrapped.
convert to degree specifies whether the phase results are converted from radians to degrees. The default is TRUE, which means that results are expressed in degrees.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
averaging parameters specifies how the selected averaging type is computed. The specifications of the parameters include the type of averaging, the type of weighting, and the number of averages.
Note When averaging mode is set to No averaging, the VI ignores the weighting mode , number of averages , and linear mode settings.
averaging mode specifies the averaging mode.
0 No averaging (default)
1 Vectoring averaging
2 RMS averaging
3 Peak hold
weighting mode specifies the weighting mode. The default is exponential.
Note RMS and linear averaging support linear weighting and exponential weighting.
0 Linear
1 Exponential (default)
number of averages specifies the number of averages used by the selected weighting mode . The default is 10. If weighting mode is set to Linear , the measurement stops or automatically restarts after the value of number of averages has been reached. Whether the measurement stops or automatically restarts depends on the linear mode setting.
linear mode specifies the behavior of the averaging if you set the value of the weighting mode parameter to Linear . If you set weighting mode to Exponential , linear mode is ignored.
0 One shot (default)€”Specifies that the averaging process stops once the value of number of averages is reached.
1 Auto restart €”Specifies that the averaging process automatically restarts after the value of number of averages is reached.
restart averaging specifies if the selected averaging process has to be restarted. The default is FALSE. When you call this VI for the first time, the averaging process restarts automatically.
new spectrum available , when TRUE, indicates that the output data is valid, or not empty. Use the output value as the switch to a Case structure. You can perform subsequent measurements or display the results in the TRUE case of the Case structure.
magnitude [dB EUx EUy] returns the magnitude of the cross power spectrum.
f0 returns the start frequency, in hertz, of the spectrum.
df returns the frequency resolution, in hertz, of the spectrum.
magnitude is the magnitude of the cross power spectrum.
magnitude unit label returns the unit label for the selected magnitude units.
phase [degrees] returns the phase of the cross power spectrum.
f0 returns the start frequency, in hertz, of the spectrum.
df returns the frequency resolution, in hertz, of the spectrum.
phase returns the phase of the cross power spectrum.
phase unit label returns the unit label for the selected phase units.
spectrum info returns information about the spectrum needed by the Spectrum Extended Measurements VIs, the Display VIs, and the Tone and Distortion VIs.
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 out contains error information. This output provides standard error out functionality.
averages completed returns the number of averages completed by the VI at that time.
averaging done returns TRUE when the number of averages completed equals or exceeds the number of averages specified in averaging parameters and new spectrum available is TRUE. Otherwise, averaging done returns FALSE. averaging done is always TRUE if averaging mode is No averaging .