Operational Modal Analysis
When the excitation forces causing a structure to vibrate are not measured, then FRFs cannot be calculated, and modal parameters can only be extracted for output-only or operational measurements. Nevertheless, a key advantage of OMA is that data can be acquired under real-world operating conditions. This option contains all of the features of the Multi-Reference Modal Analysis option, plus special tools for curve fitting measurements obtained from output-only or operating data. A common OMA measurement is a Cross spectrum, which is calculated between a roving accelerometer and a reference (fixed) accelerometer. After a set of Cross spectra has been specially windowed, they can be curve fit using FRF-based curve fitting methods to obtain operating mode shapes.