Adams Basic Package > Adams View > Adams View > Dialog box - F1 help > A - D > Create/Modify Filter Function

Create/Modify Filter Function

(Adams PostProcessor)

Plot → Filter → Create/Modify

Shortcut: Curve Edit toolbar → Filter Curve Tool → Right-click Filter Name text box → filter_function → Create

Creates or modifies a curve filter to eliminate noise on time signals or to emphasize a specific frequency content of a time signal. Adams PostProcessor supports two different types of filters:

■Butterworth filter - butter() in MATLAB™ developed by The MathWorks, Inc.

■Transfer function - A filter you define by directly specifying the coefficients of a transfer function.

Once you create a filter, you can apply it to any curve.

Learn about Filtering Curve Data.

For the option:	Do the following:
Filter Name	If creating a filter function, enter a name for the filter.
Defined by	Select to create either a Butterworth filter or a transfer function.
If you selected Butterworth, Adams PostProcessor displays the following options:
Analog/Digital	Select to create either an analog or digital Butterworth filter. Learn About Filtering Methods.
Filter Type	Select the type of filter: ■Low Pass - Removes frequencies above the cutoff frequency. ■High Pass - Removes frequencies below the cutoff frequency. ■Band Pass - Removes frequencies outside the two cutoff frequencies. ■Band Stop - Removes frequencies between the two cutoff frequencies.
Order	Set how much the filter will have damped the signal at the cutoff frequency, often referred to as how sharp the filter is. ■First-order filter damps 3dB at the cutoff frequency. ■Second-order damps 6dB. ■Third-order damps 9dB.
Cutoff Frequency (Scaled) - Digital filters Cutoff Frequency (Hz) - Analog filters	Set the frequency of cutoff. ■For a digital filter - Determines the cutoff frequency as a ratio of the Nyquist frequency (half the sample frequency). Therefore, for a signal sampled (simulated) with 100 Hz, the Nyquist frequency is 100/2=50Hz. A scaled cutoff frequency=0.3 then has a cutoff frequency=0.3*50=15 Hz. Note that if the same filter is applied to a signal sampled at 200 Hz, the filter cutoff is at 30 Hz. If you selected Band Pass or Band Stop for Filter Type, you must provide two cutoff frequencies. ■For an analog filter - Enter the cutoff frequency in the current units (rad/s or Hz). If you selected Band Pass or Band Stop for Filter Type, you must provide two cutoff frequencies.
If you selected Transfer Function, Adams PostProcessor displays the following options:
Analog/Digital	Select to create either an analog or digital Butterworth filter.
Create from Butterworth Filter	Select to display the Create Butterworth Filter dialog box to define the transfer function coefficients based on a Butterworth filter.
Numerator/Denominator Coefficients	Specify the coefficients for the transfer function that define the filter. ■For an analog filter, the transfer function is defined by the continuous Laplace s polynomial. ■For a digital filter, the transfer function is defined in the z-plane. The coefficients should be given according to MATLAB convention, which is descending powers of s (or z): This differs from how a transfer function is defined for Adams Solver, where the coefficients are given in increasing order:
Check Format and Display Plot	Select to display a plot of the transfer function's gain (magnitude) or phase. Always check the filter before using it. Note: ■If you have not defined the filter correctly, an error message appears. ■If you’ve defined the filter correctly, a plot appears in which you can switch between the filter’s gain and phase plots and change scales.