Fault location in a noisy multiple-nonlinearity servosystem

In certain applications it is desirable to isolate faults in a nonlinear system using dynamic measurements at a limited number of access points. This can be achieved by stimulating the system with a serial mode sinusoidal signal and using the fundamental and higher harmonic responses at the access points to form the system "signature." The fault signature is then compared with a restricted number of stored signatures of known faults via the nearest neighbor rule.