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Owning Palette: Correlation and Spectral Analysis VIs

Installed With: Advanced Signal Processing Toolkit

Computes the single-sided power spectral density (PSD) of an input univariate time series using the Welch method, which is a variation of the periodogram method. This VI estimates the PSD by averaging periodograms of overlapping, windowed subsequences of the time series. Wire data to the Xt input to determine the polymorphic instance to use or manually select the instance.

Details  Example

Use the pull-down menu to select an instance of this VI.

Select an instance TSA Welch (waveform)TSA Welch (array)

TSA Welch (waveform)

	frequency bins specifies the number of frequency bins for which this VI computes the single-sided power spectral density PSD. The length of the single-sided PSD is (frequency bins/2+1). The default is 1024.
	Xt specifies the input univariate time series.
	window info specifies the information of the sliding window that divides the time series into subsequences. window specifies the time-domain window applied to the time series. Options include None (default), Hanning, Hamming, Blackman-Harris, Exact Blackman, Blackman, Flat Top, 4 Term B-Harris, 7 Term B-Harris, and Low Sidelobe. length specifies the length of the window. A large window generates a power spectral density (PSD) with small bias but results in a coarse PSD plot. A small window generates a smooth PSD plot but leads to large bias. The default is –1, which indicates that the window length equals the length of the input time series. overlap specifies the overlap, in percentage, of the moving window that this VI applies to the time series. This parameter determines how much data this VI reuses for the signal space matrix. A large overlap reduces the variance of the resulting power spectrum but increases computation time. The default is 50, which specifies that the overlap is half of the window length.
	error in describes error conditions that occur before this VI or function runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. This VI or function runs normally only if no error occurred before this VI or function runs. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node. status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE. code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code. source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.
	dB on? specifies whether this VI returns the PSD in decibels or in a linear scale. If dB on? is TRUE, this VI returns the PSD in decibels. If dB on? is FALSE, this VI returns the PSD in a linear scale. The default is TRUE.
	PSD returns information about the single-sided power spectral density (PSD). f0 returns the lower boundary, in hertz, of the frequency range. df returns the frequency increment, in hertz. S(f) returns the magnitude of the PSD at each frequency. The value of dB on? determines the unit of measurement for this parameter.
	unit returns the engineering unit of the PSD. You can specify an engineering unit for a time series by using the TSA Scale to EU VI.
	error out contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator and select Explain Error from the shortcut menu for more information about the error. status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code. source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

TSA Welch (array)

	sampling rate specifies the sampling rate, in hertz, of the input univariate time series Xt. The default is 1.
	frequency bins specifies the number of frequency bins for which this VI computes the single-sided power spectral density PSD. The length of the single-sided PSD is (frequency bins/2+1). The default is 1024.
	Xt specifies the input univariate time series.
	window info specifies the information of the sliding window that divides the time series into subsequences. window specifies the time-domain window applied to the time series. Options include None (default), Hanning, Hamming, Blackman-Harris, Exact Blackman, Blackman, Flat Top, 4 Term B-Harris, 7 Term B-Harris, and Low Sidelobe. length specifies the length of the window. A large window generates a power spectral density (PSD) with small bias but results in a coarse PSD plot. A small window generates a smooth PSD plot but leads to large bias. The default is –1, which indicates that the window length equals the length of the input time series. overlap specifies the overlap, in percentage, of the moving window that this VI applies to the time series. This parameter determines how much data this VI reuses for the signal space matrix. A large overlap reduces the variance of the resulting power spectrum but increases computation time. The default is 50, which specifies that the overlap is half of the window length.
	error in describes error conditions that occur before this VI or function runs. The default is no error. If an error occurred before this VI or function runs, the VI or function passes the error in value to error out. This VI or function runs normally only if no error occurred before this VI or function runs. If an error occurs while this VI or function runs, it runs normally and sets its own error status in error out. Use the Simple Error Handler or General Error Handler VIs to display the description of the error code. Use error in and error out to check errors and to specify execution order by wiring error out from one node to error in of the next node. status is TRUE (X) if an error occurred before this VI or function ran or FALSE (checkmark) to indicate a warning or that no error occurred before this VI or function ran. The default is FALSE. code is the error or warning code. The default is 0. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code. source specifies the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning. The default is an empty string.
	dB on? specifies whether this VI returns the PSD in decibels or in a linear scale. If dB on? is TRUE, this VI returns the PSD in decibels. If dB on? is FALSE, this VI returns the PSD in a linear scale. The default is TRUE.
	PSD returns information about the single-sided power spectral density (PSD). f0 returns the lower boundary, in hertz, of the frequency range. df returns the frequency increment, in hertz. S(f) returns the magnitude of the PSD at each frequency. The value of dB on? determines the unit of measurement for this parameter.
	error out contains error information. If error in indicates that an error occurred before this VI or function ran, error out contains the same error information. Otherwise, it describes the error status that this VI or function produces. Right-click the error out front panel indicator and select Explain Error from the shortcut menu for more information about the error. status is TRUE (X) if an error occurred or FALSE (checkmark) to indicate a warning or that no error occurred. code is the error or warning code. If status is TRUE, code is a nonzero error code. If status is FALSE, code is 0 or a warning code. source describes the origin of the error or warning and is, in most cases, the name of the VI or function that produced the error or warning.

TSA Welch Details

This VI estimates the PSD of a time series with the Welch method according to the following steps:

1. Divides the time series into subsequences. The size of each subsequence equals the value of the length parameter.
2. Applies a window to each subsequence and computes the PSD of each subsequence with the periodogram method.
3. Averages the PSDs of the subsequences to form the resulting PSD s(f).

The PSD generated with the Welch method has smaller variance and is smoother than the PSD generated with the periodogram method.

Example

Refer to the Power Spectral Density Estimation VI in the labview\examples\Time Series Analysis\TSAGettingStarted.llb for an example of using the TSA Welch VI.