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Frequency Response Function (Real-Imaginary » All Cross Pairs) (G Dataflow)

Version:
    Last Modified: March 15, 2017

    Computes the frequency response and the coherence and returns the results as the real and imaginary parts of the averaged frequency response.

    This node calculates the frequency response of the channels in the stimulus signal against the channels in the response signal according to the following table:

    Stimulus Signal Response Signal Results
    One channel One channel One output.
    Multiple channels One channel The first channel in the stimulus signal against the single channel in the response signal, the second channel in the stimulus signal against the single channel in the response signal, and so on. The output contains the same number of channels as the stimulus signal.
    One channel Multiple channels The single channel in the stimulus signal against the first channel in the response signal, the single channel in the stimulus signal against the second channel in the response signal, and so on. The output contains the same number of channels as the response signal.
    N channels M channels The matrix set of the stimulus signal versus the response signal. The node returns the signals in the order 1 - 1, ..., 1 - M, 2 - 1, ..., 2 - M, ..., N - M.
    Empty Empty If either the stimulus signal or the response signal is empty, the result is empty and the node returns an error.
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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, s, of the main lobe to the side lobe

    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 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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    stimulus signal

    The input, time domain signal x.

    This input can be a waveform or an array of waveforms.

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    response signal

    The input, time domain signal y.

    This input can be a waveform or an array of waveforms.

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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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    FRF Mode

    The mode this node uses to compute the frequency response function (FRF).

    If you know that noise, which does not propagate through the system under test, infiltrates the input or output signals, you can select the method for computing the FRF to minimize the measurement error.

    Name Description
    H1 Minimizes errors in the result when extraneous noise contaminates the output signal.
    H2 Minimizes errors in the result when extraneous noise contaminates the input signal.
    H3 When noise contaminates both the input and output signals, H1 and H2 provide the lower and upper bounds of the true frequency response of the system. In this case, select H3, the average of H1 and H2.

    Default: H1

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    real

    Real part of the averaged frequency response of the input signals.

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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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    real

    Real part of the averaged frequency response.

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    imaginary

    Imaginary part of the averaged frequency response of the input signals.

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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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    imaginary

    Imaginary part of the averaged frequency response.

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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.
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    coherence

    Coherence of the averaged frequency response of the input signals.

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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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    coherence

    Coherence of the averaged frequency response.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: This product does not support FPGA devices


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