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

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Sound and Vibration Measurement Suite 6.0 Help
December 2007

NI Part Number:
372416A-01

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Computes a subset of the FFT spectrum of scaled signal [EU]. The subset is defined by frequency range. FFT results are returned as real part [EU rms] and imaginary part [EU rms]. Each block of data corresponds to a single FFT block and has to be passed individually to the this VI. You can use this polymorphic VI to analyze signals from a single channel or from N channels. The data type you wire to the scaled signal [EU] input determines the polymorphic instance to use.

Use the pull-down menu to select an instance of this VI.

SVFA FFT Spectrum Subset (Real-Im) (1 Ch)

scaled signal [EU] specifies the scaled signal expressed in the selected engineering units. To obtain a properly scaled signal, you can use the SVL Scale Voltage to EU VI or define a virtual channel in National Instruments Measurement & Automation Explorer (MAX).

window specifies the time-domain window used.

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
10	Blackman Nuttall
11	Triangle
12	Bartlett-Hanning
13	Bohman
14	Parzen
15	Welch
16	Kaiser
17	Dolph-Chebyshev
18	Gaussian

frequency range defines 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.
	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.

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 VI computes the averaging.

Note When you set averaging mode 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	Vector averaging
2	RMS averaging
3	Peak hold

weighting mode specifies the weighting mode.

Note RMS and vector 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. 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.

real part [EU rms] returns the real part of the FFT spectrum.

	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 FFT spectrum.

imaginary part [EU rms] returns the imaginary part of the FFT spectrum.

	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 FFT 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 FFT Spectrum Subset (Real-Im) (N Ch)

scaled signals [EU] specifies the scaled signals expressed in the selected engineering units. To obtain a properly scaled signal, you can use the SVL Scale Voltage to EU VI or define a virtual channel in National Instruments Measurement & Automation Explorer (MAX).