3. Estimating Residues

After modal frequencies & damping have been estimated, modal residues (mode shape components) are estimated during a second curve fitting step.

Residues Dialog Box.

Estimates of residue magnitude & phase for all 10 modes and each FRF Trace are added to the Modal Parameters spreadsheet.

Residue Curve Fit of 10 Modes and 99 FRFs.

Fit Function

After the modal frequency, damping, & residue have been estimated, a red Fit Function is also overlaid on each Trace, as shown above.

Using the Band Cursor

If the Band Cursor is displayed, curve fitting is done using data from within the cursor band  It is often more convenient to curve fit using several cursor bands to avoid noise or non-resonance peaks in the FRFs.

Notice that the red Fit Function is only displayed over the cursor band because only that data was used for curve fitting.  The residue estimates will also be slightly different when residue curve fitting is done in cursor bands instead of using all of the FRF data.

Residue Curve Fitting in a Cursor Band.