AN IMPROVED AUTOTUNE IDENTIFICATION METHOD

The method proposed by Luyben (1987) for obtaining simple transfer function models from one autotune test requires that the steady-state gain be known. This limits its usefulness for identification when only plant data are available. This paper presents a modified procedure that does not require knowledge of the steady-state gain. The method uses two autotune tests. The first is a normal one; the second is run with an additional known dead time added so that the phase angle is shifted about 45-degrees and a smaller ultimate frequency is obtained. Then a least-square method is used to determine the unknown parameters: two time constants and the steady-state gain. The method was demonstrated on several simulated processes and successfully tested on an experimental heat-exchanger process. Autotune testing of both continuous and sampled-data systems were considered.