FFT Spectrum (Real-Im) VI

Owning Palette: Waveform Measurements VIs

Requires: Full Development System

Computes the averaged FFT spectrum of time signal. This VI returns the FFT results as real and imaginary parts. Wire data to the time signal input to determine the polymorphic instance to use or manually select the instance.

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Select an instance FFT Spectrum (Real-Im) for 1 ChanFFT Spectrum (Real-Im) for N ChanFFT Spectrum (Real-Im) for 1 Chan (CDB)FFT Spectrum (Real-Im) for N Chan (CDB)

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FFT Spectrum (Real-Im) for 1 Chan

	restart averaging specifies whether the VI restarts the selected averaging process. If restart averaging is TRUE, the VI restarts the selected averaging process. If restart averaging is FALSE, the VI does not restart the selected averaging process. The default is FALSE. When you call this VI for the first time, the averaging process restarts automatically. A typical case when you should restart averaging is when a major input change occurs in the middle of the averaging process.
	time signal is the input time-domain waveform.
	window (Hanning) is the time-domain window to apply to the time signal. The default window is Hanning. 0 Rectangle 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 11 Blackman Nutall 30 Triangle 31 Bartlett-Hanning 32 Bohman 33 Parzen 34 Welch 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	averaging parameters is a cluster that defines how this VI computes the averaging. The specifications of the parameters include the type of averaging, the type of weighting, and the number of averages. 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 for RMS and vector averaging. 0 Linear 1 Exponential (default) number of averages specifies the number of averages used for RMS and vector averaging. If weighting mode is exponential, the averaging process is continuous. If weighting mode is linear, the averaging process stops after this VI computes the selected number of averages.
	window parameter specifies the beta parameter for a Kaiser window, the standard deviation for a Gaussian window, and the ratio, s, of the main lobe to the side lobe for a Dolph-Chebyshev window. If window is any other window, this VI ignores this input. The default value of window parameter is NaN, which sets beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 for a Dolph-Chebyshev window.
	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.
	real part returns the real part of the averaged FFT spectrum and the frequency scale. 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 averaged FFT spectrum. If the input signal is in volts (V), real part has units of volts-rms (Vrms). If the input signal is not in volts, real part has units of the input signal unit-rms.
	imaginary part returns the imaginary part of the averaged FFT spectrum and the frequency scale. 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 averaged FFT spectrum.
	averages completed returns the number of averages completed by the VI at that time.
	error out contains error information. This output provides standard error out functionality.

FFT Spectrum (Real-Im) for N Chan

This VI applies the same averaging parameters settings to each waveform in time signals.

	restart averaging specifies whether the VI restarts the selected averaging process. If restart averaging is TRUE, the VI restarts the selected averaging process. If restart averaging is FALSE, the VI does not restart the selected averaging process. The default is FALSE. When you call this VI for the first time, the averaging process restarts automatically. A typical case when you should restart averaging is when a major input change occurs in the middle of the averaging process.
	time signals is the input array of time-domain waveforms.
	window (Hanning) is the time-domain window to apply to the time signal. The default window is Hanning. 0 Rectangle 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 11 Blackman Nutall 30 Triangle 31 Bartlett-Hanning 32 Bohman 33 Parzen 34 Welch 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	averaging parameters is a cluster that defines how this VI computes the averaging. The specifications of the parameters include the type of averaging, the type of weighting, and the number of averages. 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 for RMS and vector averaging. 0 Linear 1 Exponential (default) number of averages specifies the number of averages used for RMS and vector averaging. If weighting mode is exponential, the averaging process is continuous. If weighting mode is linear, the averaging process stops after this VI computes the selected number of averages.
	window parameter specifies the beta parameter for a Kaiser window, the standard deviation for a Gaussian window, and the ratio, s, of the main lobe to the side lobe for a Dolph-Chebyshev window. If window is any other window, this VI ignores this input. The default value of window parameter is NaN, which sets beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 for a Dolph-Chebyshev window.
	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.
	real parts returns an array of the real part of the averaged FFT spectra, one per input waveform. 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 averaged FFT spectrum. If the input signal is in volts (V), real part has units of volts-rms (Vrms). If the input signal is not in volts, real part has units of the input signal unit-rms.
	imaginary parts returns the imaginary part of the averaged FFT spectra and the frequency scale. 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 averaged FFT spectrum.
	averages completed returns the number of averages completed by the VI at that time.
	error out contains error information. This output provides standard error out functionality.

FFT Spectrum (Real-Im) for 1 Chan (CDB)

	restart averaging specifies whether the VI restarts the selected averaging process. If restart averaging is TRUE, the VI restarts the selected averaging process. If restart averaging is FALSE, the VI does not restart the selected averaging process. The default is FALSE. When you call this VI for the first time, the averaging process restarts automatically. A typical case when you should restart averaging is when a major input change occurs in the middle of the averaging process.
	time signal is the input time-domain waveform.
	window (Hanning) is the time-domain window to apply to the time signal. The default window is Hanning. 0 Rectangle 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 11 Blackman Nutall 30 Triangle 31 Bartlett-Hanning 32 Bohman 33 Parzen 34 Welch 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	averaging parameters is a cluster that defines how this VI computes the averaging. The specifications of the parameters include the type of averaging, the type of weighting, and the number of averages. 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 for RMS and vector averaging. 0 Linear 1 Exponential (default) number of averages specifies the number of averages used for RMS and vector averaging. If weighting mode is exponential, the averaging process is continuous. If weighting mode is linear, the averaging process stops after this VI computes the selected number of averages.
	window parameter specifies the beta parameter for a Kaiser window, the standard deviation for a Gaussian window, and the ratio, s, of the main lobe to the side lobe for a Dolph-Chebyshev window. If window is any other window, this VI ignores this input. The default value of window parameter is NaN, which sets beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 for a Dolph-Chebyshev window.
	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.
	real part returns the real part of the averaged FFT spectrum and the frequency scale. 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 averaged FFT spectrum. If the input signal is in volts (V), real part has units of volts-rms (Vrms). If the input signal is not in volts, real part has units of the input signal unit-rms.
	imaginary part returns the imaginary part of the averaged FFT spectrum and the frequency scale. 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 averaged FFT spectrum.
	averages completed returns the number of averages completed by the VI at that time.
	error out contains error information. This output provides standard error out functionality.

FFT Spectrum (Real-Im) for N Chan (CDB)

	restart averaging specifies whether the VI restarts the selected averaging process. If restart averaging is TRUE, the VI restarts the selected averaging process. If restart averaging is FALSE, the VI does not restart the selected averaging process. The default is FALSE. When you call this VI for the first time, the averaging process restarts automatically. A typical case when you should restart averaging is when a major input change occurs in the middle of the averaging process.
	time signals is the input array of time-domain waveforms.
	window (Hanning) is the time-domain window to apply to the time signal. The default window is Hanning. 0 Rectangle 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 11 Blackman Nutall 30 Triangle 31 Bartlett-Hanning 32 Bohman 33 Parzen 34 Welch 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
	averaging parameters is a cluster that defines how this VI computes the averaging. The specifications of the parameters include the type of averaging, the type of weighting, and the number of averages. 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 for RMS and vector averaging. 0 Linear 1 Exponential (default) number of averages specifies the number of averages used for RMS and vector averaging. If weighting mode is exponential, the averaging process is continuous. If weighting mode is linear, the averaging process stops after this VI computes the selected number of averages.
	window parameter specifies the beta parameter for a Kaiser window, the standard deviation for a Gaussian window, and the ratio, s, of the main lobe to the side lobe for a Dolph-Chebyshev window. If window is any other window, this VI ignores this input. The default value of window parameter is NaN, which sets beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 for a Dolph-Chebyshev window.
	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.
	real parts returns an array of the real part of the averaged FFT spectra, one per input waveform. 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 averaged FFT spectrum. If the input signal is in volts (V), real part has units of volts-rms (Vrms). If the input signal is not in volts, real part has units of the input signal unit-rms.
	imaginary parts returns the imaginary part of the averaged FFT spectra and the frequency scale. 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 averaged FFT spectrum.
	averages completed returns the number of averages completed by the VI at that time.
	error out contains error information. This output provides standard error out functionality.

FFT Spectrum (Real-Im) Details

The FFT Spectrum (Real-IM) VI completes the following steps to compute real part and imaginary part:

1. Computes the FFT of time signal.
2. Averages the current FFT spectrum of time signal with the FFT spectra computed by the VI since the last time the averaging process was reset.
3. Returns the real and imaginary parts of the averaged spectrum.

The single-channel version of this VI can perform single-channel measurements in both one-shot mode, meaning a single call, and continuous mode, meaning multiple calls with history. The single-channel version can perform multichannel measurements only in one-shot mode. If you want to make multichannel measurements in continuous mode, use the multichannel version of this VI.

The single-channel version of this VI maintains internal state information for a single channel only. Calling the single-channel version to process another channel without using the restart averaging control to clear the history results in an unexpected behavior of this VI. The unexpected behavior results from the VI passing the internal state information from one channel to another.

Note  The single-channel version of this VI is intended primarily for continuous processing of a single channel. Do not generalize this behavior to the multichannel case and use the single-channel version in a For Loop to continuously process multiple channels by indexing an array of waveforms. Refer to the following LabVIEW project for examples of using a multichannel version of a VI like the FFT Spectrum (Real-IM) VI in a loop: labview\examples\Signal Processing\Waveform Measurements\Waveform Measurements.lvproj  Open examples

Related Information

Output Units for FFT-Based VIs