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SVFA Frequency Response (Real-Im) VI

NI Sound and Vibration Measurement Suite 2009 Help

Edition Date: June 2009

Part Number: 372416C-01

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Owning Palette: Baseband FFT VIs

Requires: Sound and Vibration Measurement Suite

Computes the frequency response and the coherence based on stimulus signal X [EUx] and response signal Y [EUy]. Results are returned as coherence, real part [EUy/EUx rms], and imaginary part [EUy/EUx rms].

Details  Example

force/exp settings specifies the parameters for the force and exponential windows. These windows are specified in percentages and are used to analyze transients.
force window [%] specifies the length of the force window that is used if window is set to Force-Exponential. The default is 50.00%. force window [%] specifies the duration of the force window as a percentage of the total duration of the signal. Setting force window % at 100 has the effect of not applying any window on the stimulus signal.
exp window [%] specifies the decay rate of the exponential window that is used if window is set to Force-Exponential. The default is 10.00%. exp window [%] specifies the remaining level of the applied exponential window at the end of the signal as a percentage.
FRF mode specifies how to compute the frequency response function (FRF). FRF mode determines whether H1, H2, or H3 is computed when performing frequency response measurements. The default is H1.
Note  FRF mode only applies to RMS or vector averaging. FRF mode changes the result in RMS averaging but not in vector averaging. In vector averaging, H1 = H2 = H3.
0H1 (default)
1H2
2H3
stimulus signal X [EUx] specifies the scaled signal acquired from the stimulus channel expressed in the selected engineering units.
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.
response signal Y [EUy] specifies the scaled response signal expressed in the selected engineering units.
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.
window specifies the time-domain window to use. The default is Hanning.
Note  When you use a Force-Exponential window, wire force/exp settings.
0None
1Hanning (default)
2Hamming
3Blackman-Harris
4Exact Blackman
5Blackman
6Flat Top
74 Term B-Harris
87 Term B-Harris
9Low Sidelobe
10Force-Exponential
11Blackman Nuttall
12Triangle
13Bartlett-Hanning
14Bohman
15Parzen
16Welch
17Kaiser
18Dolph-Chebyshev
19Gaussian
error in (no error) describes error conditions that occur before this node runs. This input provides standard error in functionality.
averaging parameters specifies how the averaging 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.

0No averaging (default)
1Vector averaging
2RMS averaging
3Peak hold
weighting mode specifies the weighting mode. The default is exponential.
Note  RMS and vector averaging support linear weighting and exponential weighting.


0Linear
1Exponential (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.

0One shot—(default) Specifies that the averaging process stops once the value of number of averages is reached.
1Auto 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.
coherence returns information about the coherence.
f0 returns the start frequency of the coherence expressed in hertz.
df returns the frequency resolution of the coherence expressed in hertz.
coherence returns the coherence.
real part [EUy/EUx rms] returns the real part of the frequency response.
f0 returns the start frequency, in hertz, of the spectrum.
df returns the frequency resolution, in hertz, of the spectrum.
real part returns the real part of the frequency response.
imaginary part [EUy/EUx rms] returns the imaginary part of the frequency response.
f0 returns the start frequency, in hertz, of the spectrum.
df returns the frequency resolution, in hertz, of the spectrum.
imaginary part returns the imaginary part of the frequency response.
unit label returns the selected engineering units.
spectrum info returns information about the spectrum needed by the Spectrum Extended Measurements VIs, the Display VIs, the Distortion VIs, and the Single Tone Measurements 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 averages completed is greater than or equal to 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.

SVFA Frequency Response (Real-Im) Details

Frequency response is typically an averaged measurement. Each block of data corresponds to a single FFT block and must be passed individually to the SVFA Frequency Response (Real-Im) VI.

Example

Refer to the SVXMPL_Baseband FRF (Simulated) VI in the labview\examples\Sound and Vibration\Frequency Analysis\Dual Channel Analysis directory for an example of using the SVFA Frequency Response (Real-Im) VI.


 

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