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FFT Power Spectrum and PSD VI

LabVIEW 2013 Help

Edition Date: June 2013

Part Number: 371361K-01

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Owning Palette: Waveform Measurements VIs

Requires: Full Development System

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

Details  

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

FFT Power Spectrum and PSD for 1 Chan

export mode selects the output to export to Power Spectrum / PSD.

0Power Spectrum–exports the power spectrum of the input signal.
1Power Spectral Density–exports the power spectral density of the input signal.
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.

0Rectangle
1Hanning (default)
2Hamming
3Blackman-Harris
4Exact Blackman
5Blackman
6Flat Top
74 Term B-Harris
87 Term B-Harris
9Low Sidelobe
11Blackman Nutall
30Triangle
31Bartlett-Hanning
32Bohman
33Parzen
34Welch
60Kaiser
61Dolph-Chebyshev
62Gaussian
dB On specifies whether the results are expressed in decibels. The default is FALSE.
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.

0No averaging (default)
1Vector averaging
2RMS averaging
3Peak hold
weighting mode specifies the weighting mode for RMS and vector averaging.

0Linear
1Exponential (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.
Power Spectrum / PSD returns the averaged power spectrum or power spectral density and the frequency scale, according to export mode.
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 spectrum or power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared (Vrms2) for power spectrum and volts-rms squared per hertz (Vrms2/Hz) for power spectral density. If the input signal is not in volts, magnitude has units of the input signal unit-rms squared for power spectrum, and input signal unit-rms squared per hertz for power spectral density.
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.
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 Spectrum and PSD for N Chan

export mode selects the output to export to Power Spectrum / PSD.

0Power Spectrum–exports the power spectrum of the input signal.
1Power Spectral Density–exports the power spectral density of the input signal.
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.

0Rectangle
1Hanning (default)
2Hamming
3Blackman-Harris
4Exact Blackman
5Blackman
6Flat Top
74 Term B-Harris
87 Term B-Harris
9Low Sidelobe
11Blackman Nutall
30Triangle
31Bartlett-Hanning
32Bohman
33Parzen
34Welch
60Kaiser
61Dolph-Chebyshev
62Gaussian
dB On specifies whether the results are expressed in decibels. The default is FALSE.
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.

0No averaging (default)
1Vector averaging
2RMS averaging
3Peak hold
weighting mode specifies the weighting mode for RMS and vector averaging.

0Linear
1Exponential (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.
Power Spectrum / PSD returns the averaged power spectrum or power spectral density and the frequency scale, according to export mode.
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 spectrum or power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared (Vrms2) for power spectrum and volts-rms squared per hertz (Vrms2/Hz) for power spectral density. If the input signal is not in volts, magnitude has units of the input signal unit-rms squared for power spectrum, and input signal unit-rms squared per hertz for power spectral density.
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.
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 Spectrum and PSD for 1 Chan (CDB)

export mode selects the output to export to Power Spectrum / PSD.

0Power Spectrum–exports the power spectrum of the input signal.
1Power Spectral Density–exports the power spectral density of the input signal.
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.

0Rectangle
1Hanning (default)
2Hamming
3Blackman-Harris
4Exact Blackman
5Blackman
6Flat Top
74 Term B-Harris
87 Term B-Harris
9Low Sidelobe
11Blackman Nutall
30Triangle
31Bartlett-Hanning
32Bohman
33Parzen
34Welch
60Kaiser
61Dolph-Chebyshev
62Gaussian
dB On specifies whether the results are expressed in decibels. The default is FALSE.
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.

0No averaging (default)
1Vector averaging
2RMS averaging
3Peak hold
weighting mode specifies the weighting mode for RMS and vector averaging.

0Linear
1Exponential (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.
Power Spectrum / PSD returns the averaged power spectrum or power spectral density and the frequency scale, according to export mode.
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 spectrum or power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared (Vrms2) for power spectrum and volts-rms squared per hertz (Vrms2/Hz) for power spectral density. If the input signal is not in volts, magnitude has units of the input signal unit-rms squared for power spectrum, and input signal unit-rms squared per hertz for power spectral density.
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.
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 Spectrum and PSD for N Chan (CDB)

export mode selects the output to export to Power Spectrum / PSD.

0Power Spectrum–exports the power spectrum of the input signal.
1Power Spectral Density–exports the power spectral density of the input signal.
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.

0Rectangle
1Hanning (default)
2Hamming
3Blackman-Harris
4Exact Blackman
5Blackman
6Flat Top
74 Term B-Harris
87 Term B-Harris
9Low Sidelobe
11Blackman Nutall
30Triangle
31Bartlett-Hanning
32Bohman
33Parzen
34Welch
60Kaiser
61Dolph-Chebyshev
62Gaussian
dB On specifies whether the results are expressed in decibels. The default is FALSE.
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.

0No averaging (default)
1Vector averaging
2RMS averaging
3Peak hold
weighting mode specifies the weighting mode for RMS and vector averaging.

0Linear
1Exponential (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.
Power Spectrum / PSD returns the averaged power spectrum or power spectral density and the frequency scale, according to export mode.
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 spectrum or power spectral density. If the input signal is in volts (V), magnitude has units of volts-rms squared (Vrms2) for power spectrum and volts-rms squared per hertz (Vrms2/Hz) for power spectral density. If the input signal is not in volts, magnitude has units of the input signal unit-rms squared for power spectrum, and input signal unit-rms squared per hertz for power spectral density.
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.
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 Spectrum and PSD Details

The FFT Power Spectrum VI completes the following steps to compute power spectrum or power spectral density:

  1. Computes the FFT of time signal.
  2. Forms the power spectrum or power spectral density of time signal.
  3. Averages the current power spectrum/power spectral density with the power spectra/power spectral densities computed in previous calls to the VI since the last time the averaging process was restarted.
  4. Returns the averaged power spectrum or power spectral densities in Power Spectrum/PSD.

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.

 

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