Application of the Multiharmonic Fourier Filter to Nonlinear System Fault Location

The Fourier Response Analyser (FRA) has become a widely used and accepted instrument with clearly defined noise and harmonic rejection characteristics. In a nonlinear system, however, the higher harmonics contain useful information on the system under test which this paper shows can be used by the test designer to assess system quality and pinpoint nonlinear fault locations if the system is classified as "sick." Backlash, saturation, and deadzone conditions are thereby detected in an analogue simulation model previously matched to a hardware servomechanism. The higher harmonic components are estimated by a special version of the FRA incorporating the Multiharmonic Fourier Filter (MFF) which is based on the same correlation principle as is used to detect the fundamental response.