Dual Channel Spectral Measurement

Measures the frequency response of the input signals and the coherence based on the current and previous input signals. This Express VI returns results such as Magnitude, Phase, Coherence, Real, and Imaginary.


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Dialog Box Options

Option Description
Input Comparison Specifies how to handle multiple signals in each input.
  • Ordered pairs—

    Calculates the frequency response of the first channel in Input Signal A against the first channel in Input Signal B, then the second channel in Input Signal A against the second channel in Input Signal B, and so on.

    • If there is one channel on Input Signal A and one channel on Input Signal B, the result is one output.
    • If there are multiple channels on Input Signal A and one channel on Input Signal B, the analysis result is the first channel in Input Signal A against the single channel in Input Signal B. The rest of the channels in Input Signal A are ignored and the VI returns a warning.
    • If there is one channel on Input Signal A and multiple channels on Input Signal B, the analysis result is the single channel in Input Signal A against the first channel in Input Signal B. The rest of the channels in Input Signal B are ignored and the VI returns a warning.
    • If there are multiple channels on both Input Signal A and Input Signal B, the analysis result is the first channel in Input Signal A against the first channel in Input Signal B, the second channel in Input Signal A against the second channel in Input Signal B, and so on. If there is a mismatched number of channels, the VI ignores unmatched channels and returns a warning.
    • If either Input Signal is empty, the result is empty and the VI returns an error.
  • All cross pairs—

    Calculates the frequency response of the first channel in Input Signal A against each channel in Input Signal B, then the second channel in Input Signal A against each channel in Input Signal B, and so on.

    • If there is one channel on Input Signal A and one channel on Input Signal B, the result is one output.
    • If there are multiple channels on Input Signal A and one channel on Input Signal B, the analysis result is the first channel in Input Signal A against the single channel in Input Signal B, then the second channel in Input Signal A against the single channel in Input Signal B, and so on. The output contains the same number of signals as Input Signal A.
    • If there is one channel on Input Signal A and multiple channels on Input Signal B, the analysis result is the single channel in Input Signal A against the first channel in Input Signal B, then the single channel in Input Signal A against the second channel in Input Signal B, and so on. The output contains the same number of signals as Input Signal B.
    • If there are M channels on Input Signal A and N channels on Input Signal B, the analysis result is the matrix set of Input Signal A versus Input Signal B. The signals are returned in the order 1-1, ... 1-N, 2-1, ... M-N.
    • If either Input Signal is empty, the result is empty and the VI returns an error.
Frequency Response Function Contains the following options:
  • Magnitude—

    Select to include magnitude results in the output.

    • dB—

      Select to return the magnitude results in decibels. Remove the checkmark from this checkbox to return the magnitude results in the original units.

  • Phase—

    Select to include phase results in the output. Select Unwrap phase to return the phase results in radians. Select Convert to degree to return the phase results in degrees.

    • Unwrap phase—

      Select to return the phase results in radians.

    • Convert to degree—

      Select to return the phase results in degrees.

  • Real—

    Select to include real results in the output.

  • Imaginary—

    Select to include imaginary results in the output.

  • Coherence—

    Select to include coherence results in the output.
Window

Specifies the window to apply to the signal.

  • None does not apply a window to Signals.
  • Hanning applies a Hanning window to Signals.
  • Hamming applies a Hamming window to Signals.
  • Blackman-Harris applies a Blackman-Harris window to Signals.
  • Exact Blackman applies an exact Blackman window to Signals.
  • Blackman applies a Blackman window to Signals.
  • Flat Top applies a Flat Top window to Signals.
  • 4 Term B-Harris applies a Four Term Blackman-Harris window to Signals.
  • 7 Term B-Harris applies a Seven Term Blackman-Harris window to Signals.
  • Low Sidelobe applies a Low Sidelobe window to Signals.
Refer to the Scaled Time Domain Window VI for information about coefficients and window parameters for each window type.
Averaging

Specifies whether the Express VI performs averaging.
Mode Contains the following options:
  • Vector—

    Computes the average of complex quantities directly.

  • RMS—

    Averages the energy, or power, of the signal.
Weighting Contains the following options:
  • Linear—

    Specifies linear averaging, which averages over the number of packets you specify in Number of Averages in a non-weighted manner.

  • Exponential—

    Specifies exponential averaging, which averages over the number of packets you specify in Number of Averages in a weighted manner. Exponential averaging gives the most recent packets more weighting in the average than older packets.
Number of Averages

Specifies the number of packets to average. The default is 10.
Produce Spectrum Contains the following options:
  • Every iteration—

    Returns the spectrum after every iteration of the Express VI.

  • Only when averaging complete—

    Returns the spectrum only after the Express VI gathers the number of packets you specify in Number of Averages.
Windowed Input Signal A

Displays the first channel of Input Signal A. This graph displays the first incoming signal with windowing applied.

If you wire data to the Express VI and run it, Windowed Input Signal A displays real data. If you close and reopen the Express VI, Windowed Input Signal A displays sample data until you run the VI again.
Windowed Input Signal B

Displays the first channel of Input Signal B. This graph displays the second incoming signal with windowing applied.

If you wire data to the Express VI and run it, Windowed Input Signal B displays real data. If you close and reopen the Express VI, Windowed Input Signal B displays sample data until you run the VI again.
Results

If you wire data to the Express VI and run it, Results displays real data. If you close and reopen the Express VI, Results displays sample data until you run the VI again.

  • Magnitude—

    Select to include magnitude results in the output.

    This page appears only if you place a checkmark in the Magnitude checkbox.

  • Phase—

    Select to include phase results in the output. Select Unwrap phase to return the phase results in radians. Select Convert to degree to return the phase results in degrees.

    This page appears only if you place a checkmark in the Phase checkbox.

  • Real—

    Select to include real results in the output.

    This page appears only if you place a checkmark in the Real checkbox.

  • Imaginary—

    Select to include imaginary results in the output.

    This page appears only if you place a checkmark in the Imaginary checkbox.

  • Coherence—

    Select to include coherence results in the output.

    This page appears only if you place a checkmark in the Coherence checkbox.

Inputs/Outputs

  • cexpdynwdt.png Input Signal A —

    Contains the first input signal or signals. This is assumed to be the excitation. The input signals must have the same number of data points, t0, and dt. If they do not, an error is returned.

  • cerrcodeclst.png error in (no error) —

    Describes error conditions that occur before this node runs.

  • cbool.png Restart Averaging (F) —

    Specifies whether to restart the selected averaging process. The default is FALSE. When you call this Express VI for the first time, the averaging process starts automatically.

    This input appears only if you place a checkmark in the Averaging checkbox.

  • cexpdynwdt.png Input Signal B —

    Contains the second input signal or signals. This is assumed to be the response. The input signals must have the same number of data points, t0, and dt. If they do not, an error is returned.

  • iexpdynwdt.png Magnitude —

    The magnitude from the frequency response calculations.

    This output appears only if you place a checkmark in the Magnitude checkbox.

  • iexpdynwdt.png Imaginary —

    The imaginary part from the frequency response calculations.

    This output appears only if you place a checkmark in the Imaginary checkbox.

  • iexpdynwdt.png Real —

    The real part from the frequency response calculations.

    This output appears only if you place a checkmark in the Real checkbox.

  • ibool.png Averaging Done —

    Returns TRUE when the number of averages completed equals or exceeds Number of Averages.

    This output appears only if you place a checkmark in the Averaging checkbox.

  • iexpdynwdt.png Coherence —

    The coherence from the frequency response calculations.

    This output appears only if you place a checkmark in the Coherence checkbox.

  • ierrcodeclst.png error out —

    Contains error information. This output provides standard error out functionality.

  • iexpdynwdt.png Phase —

    The phase from the frequency response calculations.

    This output appears only if you place a checkmark in the Phase checkbox.

    • Examples

    Refer to the following example files included with LabVIEW.

    • labview\examples\Express VIs\Express VI - Dual Channel Spectral Measurement.vi