Company Events Academic NI Developer Zone Support Solutions Products & Services Contact NI MyNI

SVFA Cross Spectrum (Real-Im) (Sound and Vibration Measurement Suite)

Sound and Vibration Measurement Suite 6.0 Help
December 2007

NI Part Number:
372416A-01

»View Product Info

Computes the cross power spectrum of scaled signal X [EUx] and scaled signal Y [EUy]. Results are returned in real part [EUx EUy rms] and imaginary part [EUx EUy rms].

Details  

force/exp settings contains the parameters for the force and exponential windows.
force window [%] specifies the length of the force window that is used if window is set to Force-Exponential. 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. exp window [%] specifies the remaining level of the applied exponential window at the end of the signal as a percentage.
scaled signal X [EUx] contains the scaled signal expressed in the selected engineering units. scaled signal X [EUx] is generally the stimulus or excitation signal in dual-channel measurements.
scaled signal Y [EUy] contains the scaled signal expressed in the selected engineering units. scaled signal Y [EUy] is generally the response signal in dual-channel measurements.
window specifies the time-domain window to use.
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 describes error conditions that occur before this VI or function 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. This VI or function runs normally only if no error occurred before this VI or function runs. 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. Refer to Controlling Error Notification to treat what is normally an error as no error or to treat a warning as an error. 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.
status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE.
code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code.
source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.
averaging parameters defines how the averaging is computed.
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
weighting mode specifies the weighting mode.
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. 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.
real part [EUx EUy rms] returns the real part 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.
real part is the real part of the cross power spectrum.
imaginary part [EUx EUy rms] returns the imaginary part 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.
imaginary part is the imaginary part of the cross power spectrum.
unit label returns the selected engineering units.
spectrum info returns information about the spectrum needed by the Spectrum Extended Measurements VIs, the Waterfall Display VIs, the Distortion VIs, and the Single Tone Measurements VIs. Do not modify the spectrum info values.
error out contains 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.
status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred.
code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code.
source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.
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 Cross Spectrum (Real-Im) Details

Each block of data corresponds to a single FFT block and has to be passed individually to the SVT Cross Spectrum (Real-Im) VI.


Resources


 

Your Feedback! poor Poor  |  Excellent excellent   Yes No
 Document Quality? 
 Answered Your Question? 
Add Comments 1 2 3 4 5 submit