Dual Channel Spectral Measurement Express VI

Owning Palette: Signal Analysis Express VIs

Requires: Full Development System

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.

Example

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs
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Dialog Box Options

ParameterDescription
Input ComparisonSpecifies 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 FunctionContains the following options:
  • Magnitude—Select to include magnitude results in the output.
    • Magnitude—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.
    • 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.
WindowSpecifies 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.
AveragingSpecifies whether the Express VI performs averaging.
ModeContains the following options:
  • Vector—Computes the average of complex quantities directly.
  • RMS—Averages the energy, or power, of the signal.
WeightingContains 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 AveragesSpecifies the number of packets to average. The default is 10.
Produce SpectrumContains 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 ADisplays 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 BDisplays 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.
ResultsIf 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—Displays a preview of the magnitude measurement of the signals. This page appears only if you place a checkmark in the Magnitude checkbox.
  • Phase—Displays a preview of the phase measurement of the signals. This page appears only if you place a checkmark in the Phase checkbox.
  • Real—Displays a preview of the real measurement of the signals. This page appears only if you place a checkmark in the Real checkbox.
  • Imaginary—Displays a preview of the imaginary measurement of the signals. This page appears only if you place a checkmark in the Imaginary checkbox.
  • Coherence—Displays a preview of the coherence measurement of the signals. This page appears only if you place a checkmark in the Coherence checkbox.

Block Diagram Inputs

ParameterDescription
Input Signal AContains 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.
Input Signal BContains 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.
Restart AveragingSpecifies 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.
error inDescribes error conditions that occur before this node runs.

Block Diagram Outputs

ParameterDescription
MagnitudeThe magnitude from the frequency response calculations. This output appears only if you place a checkmark in the Magnitude checkbox.
PhaseThe phase from the frequency response calculations. This output appears only if you place a checkmark in the Phase checkbox.
RealThe real part from the frequency response calculations. This output appears only if you place a checkmark in the Real checkbox.
ImaginaryThe imaginary part from the frequency response calculations. This output appears only if you place a checkmark in the Imaginary checkbox.
CoherenceThe coherence from the frequency response calculations. This output appears only if you place a checkmark in the Coherence checkbox.
error outContains error information. This output provides standard error out functionality.
Averaging DoneReturns 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.

This Express VI operates similarly to the following VIs and functions:

Frequency Response Function (Mag-Phase)
Frequency Response Function (Real-Im)

Example

Refer to the Express VI - Dual Channel Spectral Measurement VI in the labview\examples\Express VIs directory for an example of using the Dual Channel Spectral Measurement Express VI.

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