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Owning Palette: Waveform Measurements VIs

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Computes the averaged power spectral density of time signal. Wire data to the time signal input to determine the polymorphic instance to use or manually select the instance.

Details  Example

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

Select an instance FFT Power Spectral Density for 1 ChanFFT Power Spectral Density for N ChanFFT Power Spectral Density for 1 Chan (CDB)FFT Power Spectral Density for N Chan (CDB)

FFT Power Spectral Density 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 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 Four Term Blackman-Harris 8 Seven Term Blackman-Harris 9 Low Sidelobe 11 Blackman Nutall 30 Triangle 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	dB On specifies whether the results are expressed in decibels. The default is FALSE.
	error in (no error) 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.
	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.
	power spectral density returns the averaged power spectral density and the frequency scale. 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 averaged power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared per hertz (Vrms2/Hz). If the input signal is not in volts, magnitude has units of the input signal unit-rms squared per hertz.
	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 Power Spectral Density 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 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 Four Term Blackman-Harris 8 Seven Term Blackman-Harris 9 Low Sidelobe 11 Blackman Nutall 30 Triangle 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	dB On specifies whether the results are expressed in decibels. The default is FALSE.
	error in (no error) 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.
	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.
	power spectral densities returns an array of averaged power spectral densities, one per input waveform. 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 averaged power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared per hertz (Vrms2/Hz). If the input signal is not in volts, magnitude has units of the input signal unit-rms squared per hertz.
	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 Power Spectral Density 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 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 Four Term Blackman-Harris 8 Seven Term Blackman-Harris 9 Low Sidelobe 11 Blackman Nutall 30 Triangle 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	dB On specifies whether the results are expressed in decibels. The default is FALSE.
	error in (no error) 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.
	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.
	power spectral density returns the averaged power spectral density and the frequency scale. 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 averaged power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared per hertz (Vrms2/Hz). If the input signal is not in volts, magnitude has units of the input signal unit-rms squared per hertz.
	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 Power Spectral Density 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 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 Four Term Blackman-Harris 8 Seven Term Blackman-Harris 9 Low Sidelobe 11 Blackman Nutall 30 Triangle 60 Kaiser 61 Dolph-Chebyshev 62 Gaussian
	dB On specifies whether the results are expressed in decibels. The default is FALSE.
	error in (no error) 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.
	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.
	power spectral densities returns an array of averaged power spectral densities, one per input waveform. 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 averaged power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared per hertz (Vrms2/Hz). If the input signal is not in volts, magnitude has units of the input signal unit-rms squared per hertz.
	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 Power Spectral Density Details

The FFT Power Spectral Density VI completes the following steps to compute power spectral density:

1. Computes the FFT of time signal.
2. Forms the power spectral density of time signal.
3. Averages the current power spectral density with the power spectral densities computed by the VI since the last time the averaging process was restarted.
4. Returns the averaged power spectral density in power spectral density

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 VIs for examples of using a multichannel version of a VI like the FFT Power Spectral Density VI in a loop: labview\examples\measure\maxmpl.llb labview\examples\analysis\measxmpl.llb

Example

Refer to the Noise Waveforms and PS Density VI in the labview\examples\measure\maxmpl.llb for an example of using the FFT Power Spectral Density VI.