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FFT Spectrum (Magnitude-Phase » Continuous) (G Dataflow)

Version:
Last Modified: August 28, 2017

Computes the averaged FFT spectrum of a time-domain signal and returns the FFT results as magnitude and phase.

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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
  • 1D array of double-precision, floating-point numbers
  • 1D array of complex double-precision, floating-point numbers
  • 2D array of double-precision, floating-point numbers
  • 2D array of complex double-precision, floating-point numbers
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view

Settings that define how this node returns results.

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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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unwrap phase

A Boolean specifying whether to unwrap the phase.

True Unwraps the phase.
False Does not unwrap the phase.

Unwrapping eliminates discontinuities that have an absolute value greater than pi.

Default: False

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convert to degree

A Boolean specifying whether this node converts the phase results from radians to degrees.

True Returns the phase results in degrees.
False Returns the phase results in radians.

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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dt

Sample period of the time-domain signal in seconds.

Set this input to 1/fs, where fs is the sampling frequency of the time-domain signal.

This input is available only if you wire one of the following data types to signal:

  • 1D array of double-precision, floating-point numbers
  • 1D array of complex double-precision, floating-point numbers
  • 2D array of double-precision, floating-point numbers
  • 2D array of complex double-precision, floating-point numbers

Default: 1

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magnitude

Magnitude of the averaged FFT spectrum of the input signal.

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 FFT spectrum.

If the input signal is in volts (V), this output has units of volts-rms (Vrms). If the input signal is not in volts, this output has units of the input signal unit-rms. If the results are in decibels and the input signal is in volts, this output has units of dBV.

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phase

Phase of the averaged FFT spectrum of the input signal.

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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phase

Phase, in radians, of the averaged FFT spectrum.

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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 Magnitude and Phase

This node completes the following steps to compute magnitude and phase:

  1. Computes the FFT of signal.
  2. Averages the current FFT spectrum of signal with the FFT spectra computed by the node since the last time the averaging process was reset.
  3. Returns the magnitude and phase of the averaged spectrum.

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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