Identification of a two input two output distillation column using noninteracting multifrequency ternary and quaternary signals

This paper presents a new approach to the system identification of a two input multivariable system. In a similar manner to that used for the single-input/single-output system, the multi-input multi-output system response may be obtained directly from measured input output frequency responses. An investigation of compact multifrequency data measurement signals, which have been extensively catalogued by the authors, has provided compact multifrequency ternary and quaternary input signals that have uncorrelated spectra. They are powerful multisymbol, multilevel computer generated measurement signals whose signal power is concentrated in either two or three dominant harmonics. As the signals, which are given in this paper, have six, seven or eight symbols in their measurement codes, it is ensured that both the computation time for the frequency estimates and the experimental time are minimized. Two multifrequency quaternary signals with uncorrelated spectra are used to identify a simulated distillation column. It is shown that the cross coupling terms between the measurement channels may be removed by these digital measurement signals with the same number of symbols but different measurement codes.