Estimation of SOPDT transfer function models using an auto-tuning test

The second-order plus dead-time (SOPDT) model is useful for design of controllers and for assessment of closed-loop systems. A new method that uses data from a relay feedback (RF) loop to derive a SOPDT transfer function model is proposed. It is found that through one simple run of the proposed relay feedback testing, all parameters in a SOPDT model can be estimated with adequate accuracy. The resulting SOPDT model emphasizes on having very close step response behavior to that of the process. This proposed method could also work well when constant unknown disturbances exist.