Relay with additional delay for identification and autotuning of completely unknown processes

The paper presents a relay method for the identification of completely unkn own processes for autotune purposes. It is an extension of a previous techn ique (ATV; Li, W.; et al. Ind. Eng. Chem. Res. 1991, 30, 1530), which assum ed the delay of the process to be known. By means of a maximum of three rel ay tests, with additional delay, models with up to five parameters can be b uilt. The proposed procedure does not present any convergence problem and i s equivalent to the original one in terms of relative accuracy and duration of tests. The application of the identification procedure to a much wider set than in the original paper shows that the model obtained from the ident ification presents good accuracy in the high-frequency region, while some d iscrepancies of different nature may be present in the low frequency. When a suitable tuning method, which exploits this characteristic, is adopted, r easonably good closed-loop performance can be achieved for proportional-int egral control in all cases. The low sensitivity to experimental errors and the simple implementation make the method interesting for application in in dustrial autotuners.