Bessel Coefficients VI

Owning Palette: Advanced IIR Filtering VIs

Requires: Full Development System

Generates the set of filter coefficients to implement an IIR filter as specified by the Bessel filter model.

You then can pass these coefficients to the IIR Cascade Filter VI.

Details  Example

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	filter structure option specifies the order of the IIR cascade filter in IIR Filter Cluster. 0 IIR 2nd Order—Returns IIR second-order filter stages. 1 IIR 4th Order—Returns IIR fourth-order filter stages. 2 Auto Select (default)—Returns either IIR second-order or IIR fourth-order filter stages according to the filter type. If filter type is Lowpass or Highpass, this VI returns IIR second-order filter stages. If filter type is Bandpass or Bandstop, this VI returns IIR fourth-order filter stages.
	filter type specifies the passband of the filter. 0 Lowpass 1 Highpass 2 Bandpass 3 Bandstop
	sampling freq: fs is the sampling frequency in Hz and must be greater than zero. The default is 1.0 Hz. If sampling freq: fs is less than or equal to zero, the VI sets Reverse Coefficients and Forward Coefficients to empty arrays and returns an error.
	high cutoff freq: fh is the high cutoff frequency in Hz. The default is 0.45 Hz. The VI ignores this parameter when filter type is 0 (Lowpass) or 1 (Highpass). When filter type is 2 (Bandpass) or 3 (Bandstop), high cutoff freq: fh must be greater than low cutoff freq: fl and observe the Nyquist criterion.
	low cutoff freq: fl is the low cutoff frequency in Hz and must observe the Nyquist criterion. The default is 0.125 Hz. When filter type is 2 (Bandpass) or 3 (Bandstop), low cutoff freq: fl must be less than high cutoff freq: fh.
	order is the order of the IIR filter and must be greater than zero.
	IIR Filter Cluster contains the cascaded form of IIR filter coefficients. filter structure indicates either IIR second-order or IIR fourth-order filter stages. Reverse Coefficients is the reverse coefficients of the IIR cascade filter. Forward Coefficients is the forward coefficients of the IIR cascade filter.
	error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.

Bessel Coefficients Details

The values for low cutoff freq: fl and high cutoff freq: fh must observe the following relationship.

0 < f₁ < f₂ < 0.5f_s

where f₁ is low cutoff freq: fl, f₂ is high cutoff freq: fh, and f_s is sampling freq: fs. If you violate any of these conditions, this VI sets Reverse Coefficients and Forward Coefficients to empty arrays and returns an error.

The Bessel Coefficients VI is a subVI of the Bessel Filter VI.

Example

Refer to the Online Filtering VI in the labview\examples\Signal Processing\Filters directory for an example of using the Bessel Coefficients VI.

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