(131c) Troubleshooting of Oscillatory Control Loops

The presence of oscillations in control loop increases the variability of the process variables thus causing inferior products, larger rejection rates, increased energy consumption and reduced average throughput. Existing methodologies for oscillation diagnosis in control loops are suffered by many draw-backs such as; indecisive or wrong diagnostic regions in the spectrum of process dynamics, failure in case of multiple faults occurring simultaneously, incapability to extend to multi-variable control system diagnosis and, absence of quantification of root-cause. In this work, a novel methodology has been devised to bridge all these gaps in oscillation diagnostics. Power spectral density (PSD) based oscillation detection method followed by a model based approach for identifying and quantifying the root cause of the oscillations is proposed. Proposed technique is validated on first order with time delay (FOPTD) system and integrating system with variety of dynamics under various cases of stiction, poor controller tuning and external disturbances.