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.


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Inputs/Outputs

  • cu16.png filter structure option —

    filter structure option specifies the order of the IIR cascade filter in IIR Filter Cluster.

    0IIR 2nd Order—Returns IIR second-order filter stages.
    1IIR 4th Order—Returns IIR fourth-order filter stages.
    2Auto 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.
  • cenum.png filter type —

    filter type specifies the passband of the filter.

    0
    Lowpass
    1
    Highpass
    2
    Bandpass
    3
    Bandstop
  • cdbl.png sampling freq: fs —

    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.

  • cdbl.png high cutoff freq: fh —

    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.

  • cdbl.png low cutoff freq: fl —

    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.

  • ci32.png order —

    order is the order of the IIR filter and must be greater than zero.

  • icclst.png IIR Filter Cluster —

    IIR Filter Cluster contains the cascaded form of IIR filter coefficients.

  • ienum.png filter structure —

    filter structure indicates either IIR second-order or IIR fourth-order filter stages.

  • i1ddbl.png Reverse Coefficients —

    Reverse Coefficients is the reverse coefficients of the IIR cascade filter.

  • i1ddbl.png Forward Coefficients —

    Forward Coefficients is the forward coefficients of the IIR cascade filter.

  • ii32.png error —

    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.

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

    0 < f1 < f2 < 0.5fs

    where f1 is low cutoff freq: fl, f2 is high cutoff freq: fh, and fs 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.

    Examples

    Refer to the following example files included with LabVIEW.

    • labview\examples\Signal Processing\Filters\Online Filtering.vi