Method for diagnosis of parts of nonlinear system

To analyze the fault in parts of nonlinear system, a model named Volterra nucleus fitting line was developed. We fit each order Volterra nucleus into a curve in some arithmetic, recognize the fitting line and separate each order based on the spring response. Then, the error can be identified according to its different effect on fitting line. It was imitated on a certain hydraulic amplifier used in aeroengine, the result is accurate and the calculation is simple. It is useful and may be applied for diagnosis of the fault or error in nonlinear system.