A New Measure of Process Interaction in Time Domain Dynamics

Abstract

The process with multiple-input, multiple-output (MIMO) is quite common in process industries. Due to the presence of interactions in such systems, their analysis needs very different approach in comparison to the conventional single-input, single-output (SISO) systems. The relative gain array (RGA), as proposed by Bristol in 1966 [1] was the first formal tool in the analysis of MIMO processes with loop interaction. The RGA was originally defined, assuming a linearized, time-invariant, multivariable process. Thus it seeks minimal information about the process in particular the steady state gains. The analysis of closed loop interaction and pairing of manipulated inputs to the appropriate controlled outputs, considering only the steady state gains may lead to the selection of inferior control configuration. The open loop step response of the process transfer functions was then adopted to incorporate the effect of process dynamics on the selection of control configuration [2, 3]. Both the methods depends only on the open loop step responses and does not give a clear depiction about the closed loop interaction.