Implementation of an asymmetric relay autotuner in a sequential control language

Control applications contain both logic, sequencing, and control algorithms. A holistic view of this is seldom presented in teaching and papers. One reason is the separation of communities - automation groups typically come from the Programmable Logic Controller (PLC) world while control engineers primarily come from the Distributed Control System (DCS) world. Both logic, sequencing, and control algorithms are, however, well integrated in today´s control systems since DCS systems now contain logic and sequencing and PLCs now contain control algorithms. This paper shows that both logic, sequencing, and control algorithms can be integrated seamlessly in a sequential control language. The particular application considered is a PID controller with a relay autotuner. The presented autotuner implementation yields good controller parameters and is freely available.