National Instruments 320571-01 用户手册

Generates the set of filter
coefficients to implement an
IIR filter as specified by the
Butterworth filter model.
You can then pass these
coefficients to the DSP IIR
Filter VI to filter a sequence
of data.

filter type specifies the passband of the filter.  It has four options:

0:  lowpass.
1:  highpass.
2:  bandpass.
3:  bandstop.

filter type defaults to lowpass.

sampling freq : fs is the sampling frequency and must be greater than 0.  If it is less than or equal to
zero, the VI returns an error.  sampling freq : fs defaults to 1.0.

high cutoff freq: fh is the high cutoff frequency.  The VI ignores this parameter when filter type is
lowpass.  high cutoff freq: fh defaults to 0.45.

low cutoff freq: fl is the low cutoff frequency.  The VI ignores this parameter when filter type is
highpass.  low cutoff freq: fl defaults to 0.125.

Note: fh and fl must observe the Nyquist criterion:    0 

≤

 fl 

≤

 fh 

≤

 fs /2.

Forward Coefficients in is a DSP Handle Cluster that indicates the memory buffer on the DSP board
that will contain the forward coefficients.

Feedback Coefficients in is a DSP Handle Cluster that indicates the memory buffer on the DSP board
that will contain the feedback coefficients.

Forward Coefficients out is a DSP Handle Cluster that is identical to the Forward Coefficients in, but
with the forward coefficients already stored in the memory buffer on the DSP board.

Feedback coefficients out is aDSP Handle Cluster that is identical to the Feedback Coefficients in, but
with the feedback coefficients already stored in the memory buffer on the DSP board.

order must be greater than zero.  If order is less than or equal to zero, the VI returns an error.  order
defaults to 2.

error in (no error) contains the error information from a previous VI.  If an error occurs, it is passed out
error out and no other calls are made.

error out contains the error information for this call.