Isolating the source of whole-plant oscillations through bi-amplitude ratio analysis

Derived from bi-spectral analysis, a new diagnostic index, the bi-amplitude ratio, is proposed as an aid to the isolation of the source of non-linearity-induced oscillations that can propagate through a process plant. This ratio relates the power pertaining to the fundamental, to the power pertaining to its third harmonic, and hence it can quantify harmonic attenuation or amplification as the oscillation propagates. An oscillatory source can then be isolated provided that low-pass filtering is inherent. The method is demonstrated on both simulated data and real industrial data.