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

The paper presents a relay method for the identification of completely unknown processes for autotune purposes. It is an extension of a previous technique (ATV; Li, W.; et al. Ind. Eng. Chem. Res. 1991, 30, 1530), which assumed the delay of the process to be known. By means of a maximum of three relay tests, with additional delay, models with up to five parameters can be built. The proposed procedure does not present any convergence problem and is 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 identification presents good accuracy in the high-frequency region, while some discrepancies of different nature may be present in the low frequency. When a suitable tuning method, which exploits this characteristic, is adopted, reasonably good closed-loop performance can be achieved for proportional-integral control in all cases. The low sensitivity to experimental errors and the simple implementation make the method interesting for application in industrial autotuners.