Filter Express VI

LabVIEW 2018 Help


Edition Date: March 2018
Part Number: 371361R-01
View Product Info

DOWNLOAD (Windows Only)


LabVIEW 2016 Help
LabVIEW 2017 Help
LabVIEW 2018 Help
LabVIEW 2019 Help
LabVIEW 2020 Help

Owning Palette: Signal Analysis Express VIs

Requires: Full Development System

Processes signals through filters and windows.

Details  

Dialog Box Options
Block Diagram Inputs
Block Diagram Outputs

Dialog Box Options

ParameterDescription
Filtering TypeSpecifies the following types of filters to use: lowpass, highpass, bandpass, bandstop, or smoothing. The default is Lowpass.
Filter SpecificationsContains the following options:
  • Cutoff Frequency (Hz)—Specifies the cutoff frequency of the filter. This option is available only when you select Lowpass or Highpass from the Filtering Type pull-down menu. The default is 100.
  • Low cutoff frequency (Hz)—Specifies the low cutoff frequency of the filter. Low cutoff frequency (Hz) must be less than High cutoff frequency (Hz) and observe the Nyquist criterion. The default is 100. This option is available only when you select Bandpass or Bandstop from the Filtering Type pull-down menu.
  • High cutoff frequency (Hz)—Specifies the high cutoff frequency of the filter. High cutoff frequency (Hz) must be greater than Low cutoff frequency (Hz) and observe the Nyquist criterion. The default is 400. This option is available only when you select Bandpass or Bandstop from the Filtering Type pull-down menu.
  • Finite impulse response (FIR) filter—Creates an FIR filter, which depends only on the current and past inputs. Because the filter does not depend on past outputs, the impulse response decays to zero in a finite amount of time. Because FIR filters return a linear phase response, use FIR filters for applications that require linear phase responses.
  • Taps—Specifies the total number of FIR coefficients, which must be greater than zero. The default is 29. This option is available only when you select the Finite impulse response (FIR) filter option. Increasing the value of Taps causes the transition between the passband and the stopband to become steeper. However, as the value of Taps increases, the processing speed becomes slower.
  • Infinite impulse response (IIR) filter—Creates an IIR filter that is a digital filter with impulse responses that can theoretically be infinite in length or duration.
  • Topology—Determines the design type of the filter. You can create either a Butterworth, Chebyshev, Inverse Chebyshev, Elliptic, or Bessel filter design. This option is available only when you select the Infinite impulse response (IIR) filter option. The default is Butterworth.
  • Order—Order of the IIR filter, which must be greater than zero. This option is available only when you select the Infinite impulse response (IIR) filter option. The default is 3. Increasing the value of Order causes the transition between the passband and the stopband to become steeper. However, as the value of Order increases, the processing speed becomes slower, and the number of distorted points at the start of the signal increases.
  • Moving average—Yields forward-only (FIR) coefficients. This option is available only when you select Smoothing from the Filtering Type pull-down menu.
  • Rectangular—Specifies that all samples in the moving-average window are weighted equally in computing each smoothed output sample. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Moving average option.
  • Triangular—Specifies that the moving weighting window applied to the samples is triangular with the peak centered in the middle of the window, ramping down symmetrically on both sides of the center sample. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Moving average option.
  • Half-width of moving average—Specifies the half-width of the moving-average window in samples. The default is 1. For a half-width of moving average of M, the full width of the moving-average window is N = 1 + 2M samples. Therefore, the full width N is always an odd number of samples. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Moving average option.
  • Exponential—Yields first-order IIR coefficients. This option is available only when you select Smoothing from the Filtering Type pull-down menu.
  • Time constant of exponential average—Specifies the time constant of the exponential-weighting filter in seconds. The default is 0.001. This option is available only when you select Smoothing from the Filtering Type pull-down menu and the Exponential option.
Input SignalDisplays the input signal. If you wire data to the Express VI and run it, Input Signal displays real data. If you close and reopen the Express VI, Input Signal displays sample data until you run the Express VI again.
Result PreviewDisplays a preview of the measurement. The Result Preview plot indicates the value of the selected measurement with a dotted line. If you wire data to the Express VI and run the VI, Result Preview displays real data. If you close and reopen the Express VI, Result Preview displays sample data until you run the VI again. If the cutoff frequency values are invalid, Result Preview does not display valid data.
View ModeContains the following options:
Note  Changing the options in the View Mode section does not impact the behavior of the Filter Express VI. Use the View Mode options to visualize what the filter does to the signal. LabVIEW does not save these options when you close the configuration dialog box.
  • Signals—Displays the filter response as real signals.
  • Show as spectrum—Specifies whether to display the real signals of the filter response as a frequency spectrum or to leave the display as a time-based display. The frequency display is useful for viewing how the filter affects the various frequency components of the signal. The default is to display the filter response as a time-based display. This option is available only when you select the Signals option.
  • Transfer function—Displays the filter response as a transfer function.
Scale ModeContains the following options:
  • Magnitude in dB—Presents the magnitude response of the filter in decibels.
  • Frequency in log—Presents the frequency response of the filter on a logarithmic scale.
Magnitude ResponseDisplays the magnitude response of the filter. This display is available only when you set View Mode to Transfer function.
Phase ResponseDisplays the phase response of the filter. This display is available only when you set View Mode to Transfer function.

Block Diagram Inputs

ParameterDescription
SignalSpecifies the input signal. The signal can be a waveform, a real array, or a complex array.
Lower Cut-OffSpecifies the low cutoff frequency of the filter. Lower Cut-Off must be less than Upper Cut-Off and observe the Nyquist criterion. The default is 100.
Upper Cut-OffSpecifies the high cutoff frequency of the filter. Upper Cut-Off must be greater than Lower Cut-Off and observe the Nyquist criterion. The default is 400.
error inDescribes error conditions that occur before this node runs.

Block Diagram Outputs

ParameterDescription
Filtered SignalReturns the filtered signal.
error outContains error information. This output provides standard error out functionality.

Filter Details

Note  Use the Filters PtByPt VIs to implement continuous, point-by-point filtering.

This Express VI operates similarly to the following VIs and functions:

Digital IIR Filter
Digital FIR Filter

WAS THIS ARTICLE HELPFUL?

Not Helpful