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FFT Power Spectrum and PSD (Power Spectral Density » Continuous) (G Dataflow)

Last Modified: January 12, 2018

Computes the averaged power spectral density of a time-domain signal.

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window parameter

A value that affects the output coefficients when window type is Kaiser, Gaussian, or Dolph-Chebyshev.

If window type is any other type of window, this node ignores this input.

This input represents the following information for each type of window:

  • Kaiser—Beta parameter
  • Gaussian—Standard deviation
  • Dolph-Chebyshev—The ratio of the main lobe to the side lobe, s, expressed in decibels

Default: NaN—Causes this node to set beta to 0 for a Kaiser window, the standard deviation to 0.2 for a Gaussian window, and s to 60 dB for a Dolph-Chebyshev window

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window type

Time-domain window to apply to the signal.

Name Value Description
Rectangle 0 Applies a rectangle window.
Hanning 1 Applies a Hanning window.
Hamming 2 Applies a Hamming window.
Blackman-Harris 3 Applies a Blackman-Harris window.
Exact Blackman 4 Applies an Exact Blackman window.
Blackman 5 Applies a Blackman window.
Flat Top 6 Applies a Flat Top window.
4 Term B-Harris 7 Applies a 4 Term B-Harris window.
7 Term B-Harris 8 Applies a 7 Term B-Harris window.
Low Sidelobe 9 Applies a Low Sidelobe window.
Blackman Nutall 11 Applies a Blackman Nutall window.
Triangle 30 Applies a Triangle window.
Bartlett-Hanning 31 Applies a Bartlett-Hanning window.
Bohman 32 Applies a Bohman window.
Parzen 33 Applies a Parzen window.
Welch 34 Applies a Welch window.
Kaiser 60 Applies a Kaiser window.
Dolph-Chebyshev 61 Applies a Dolph-Chebyshev window.
Gaussian 62 Applies a Gaussian window.
Force 64 Applies a Force window.
Exponential 65 Applies an Exponential window.

Default: Hanning

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restart averaging

A Boolean that specifies whether the node restarts the selected averaging process.

True Restarts the averaging process.
False Does not restart the averaging process.

When you call this node for the first time, the averaging process restarts automatically. A typical case when you restart averaging is when a major input change occurs in the middle of the averaging process.

Default: False

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signal

Input signal.

This input accepts the following data types:

  • Waveform
  • Waveform in complex double-precision, floating-point numbers
  • 1D array of waveforms
  • 1D array of waveforms in complex double-precision, floating-point numbers
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dB on

A Boolean that specifies whether this node returns the results in decibels.

True Returns the results in decibels.
False Returns the results in the original units.

Default: False

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averaging parameters

Settings that define how this node computes the averaging.

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averaging mode

The mode this node uses to compute the averaging.

Name Description
No averaging Does not use averaging.
Vector averaging Uses vector averaging.
RMS averaging Uses RMS averaging.
Peak hold Uses peak hold averaging.

Default: No averaging

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weighting mode

Weighting mode for RMS and vector averaging.

Name Description
Linear Uses linear weighting.
Exponential Uses exponential weighting.

Default: Exponential

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number of averages

Number of averages to use 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 node computes the specified number of averages.

Default: 10

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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power spectral density

Averaged power spectral density of the input signals.

This output can return a cluster or a 1D array of clusters.

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f0

Start frequency, in Hz, of the spectrum.

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df

Frequency resolution, in Hz, of the spectrum.

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magnitude

Magnitude of the averaged power spectral density.

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averaging done

A Boolean that indicates whether the number of averages this node completed is greater than or equal to the specified number of averages.

True The number of averages this node completed is greater than or equal to the specified number of averages.
False The number of averages this node completed is less than the specified number of averages.

averaging done is True if averaging mode is No averaging.

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averages completed

Number of averages this node completed.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Algorithm for Computing the Power Spectral Density

This node completes the following steps to compute the power spectral density:

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

Where This Node Can Run:

Desktop OS: Windows

FPGA: This product does not support FPGA devices

Web Server: Not supported in VIs that run in a web application


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