You are here: NI Home > Support > Product Reference > Manuals > LabVIEW 8.5 Help

Filters x using the IIR filter specified by Reverse Coefficients and Forward Coefficients.

This VI is similar to the IIR Filter with I.C. VI.

Details  

	initialize, when TRUE, initializes the internal state of the VI.
	x is the input signal to filter.
	Reverse Coefficients is the reverse coefficients of the filter design. If the set of reverse coefficients is empty, the forward coefficients should be empty too. Otherwise, the VI returns an error. If both sets of coefficient inputs are empty, Filtered x is set equal to x.
	Forward Coefficients is the forward coefficients of the filter design.
	Initial X Conditions contains the most recent inputs. The most recent prior input should be the last element in the array. The number of elements in this array should be one less than the number of elements in the Forward Coefficients array.
	Initial Y Conditions contains the most recent outputs. The most recent output should be the last element in the array. The number of elements in this array should be one less than the number of elements in the Reverse Coefficients array.
	Filtered x contains the result of filtering the input sequence x by convolution.
	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.
	Final X Conditions contains the most recent inputs. You can use Final X Conditions as Initial X Conditions on the next call to this VI.
	Final Y Conditions contains the most recent outputs. You can use Final Y Conditions as Initial Y Conditions on the next call to this VI.

IIR Filter with I.C. PtByPt Details

The IIR Filter with I.C. PtByPt VI obtains the elements of Filtered X using the following equation.

where y is Filtered X, N_b is the number of Forward Coefficients, b_j is Forward Coefficients, N_a is the number of Reverse Coefficients, and a_k is Reverse Coefficients.

The filter initialization uses the following equations.

y[i] = y_ic[N_a + i – 1]  for i < 0

x[i] = x_ic[N_b + i – 1]  for i < 0

where y_ic is the array of Initial Y Conditions and x_ic is the array of Initial X Conditions.

Note  You can use the IIR Filter PtByPt VI to perform FIR filtering by passing an empty array into Reverse Coefficients or by leaving Reverse Coefficients unwired.