SI Estimate Frequency Response VI

SI Estimate Frequency Response (Waveform)

	freq in log? specifies whether to use logarithmic mapping for the frequency points. The default is TRUE.
	magnitude in dB? specifies whether to return the amplitude response in decibels. The default is TRUE.
	stimulus signal specifies the input waveform of the stimulus signal.
	response signal specifies the input waveform of the response signal.
	window length specifies the length of the window to use in frequency computation. The value of window length must be less than the length of stimulus signal and greater than 0.
	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.
	num of freq bins specifies the number of frequency bins for which this VI computes the frequency response. The value of num of freq bins must be greater than or equal to 2.
	magnitude response returns the amplitude response of an unknown system at a given frequency. freq point (mag) returns the frequency points at which this VI estimates the magnitude response. magnitude returns the estimated amplitude response at each freq point (mag).
	phase response returns the phase response of an unknown system at a given frequency. freq point (phase) returns the frequency points at which this VI estimates the phase response. phase returns the estimated phase response at each freq point (phase).
	std deviations returns the standard deviation for each estimated amplitude and phase response. magnitude std dev returns the standard deviation for each estimated amplitude response. phase std dev returns the standard deviation for each estimated phase response.
	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.

SI Estimate Frequency Response (Array)

	freq in log? specifies whether to use logarithmic mapping for the frequency points. The default is TRUE.
	magnitude in dB? specifies whether to return the amplitude response in decibels. The default is TRUE.
	stimulus signal specifies the input array of the stimulus signal.
	response signal specifies the input array of the response signal.
	window length specifies the length of the window to use in frequency computation. The value of window length must be less than the length of stimulus signal and greater than 0.
	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.
	sampling rate specifies the sampling frequency in hertz. The value of sampling rate must be greater than 0. The default is 1.
	num of freq bins specifies the number of frequency bins for which this VI computes the frequency response. The value of num of freq bins must be greater than or equal to 2.
	magnitude response returns the amplitude response of an unknown system at a given frequency. freq point (mag) returns the frequency points at which this VI estimates the magnitude response. magnitude returns the estimated amplitude response at each freq point (mag).
	phase response returns the phase response of an unknown system at a given frequency. freq point (phase) returns the frequency points at which this VI estimates the phase response. phase returns the estimated phase response at each freq point (phase).
	std deviations returns the standard deviation for each estimated amplitude and phase response. magnitude std dev returns the standard deviation for each estimated amplitude response. phase std dev returns the standard deviation for each estimated phase response.
	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.

SI Estimate Frequency Response Details

The following equation defines a frequency response estimated using the spectral analysis method:

where	G(ejw) is the frequency response of the system.
	uy(ejw) is the cross-spectral density between the stimulus signal and the response signal. This VI computes uy(ejw) by applying a Fourier transform on the cross correlation between the stimulus signal and the response signal.
	uu(ejw) is the auto-spectral density of the stimulus signal. This VI computes uu(ejw) by applying a Fourier transform on the autocorrelation of the stimulus signal.

In order to reduce leakage and improve resolution, this VI applies a Hanning window on the cross correlation and autocorrelation before applying the Fourier transform. The larger the window length, the larger the variance, but the smaller the bias of the estimated frequency response.

Examples

Refer to the following VIs for examples of using the SI Estimate Frequency Response VI:

• Estimate Frequency Response VI: labview\examples\System Identification\Getting Started\Nonparametric Estimation.llb

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• Steel Subframe Flexible Structure VI: labview\examples\System Identification\Industry Applications\Mechanical Systems.llb

   Open example  Browse related examples