A Critical Performance Evaluation of Four Single Loop Self Tuning Control Products

This paper presents a critical evaluation of four low cost single loop self-tuning controls. They are manufactured by Bailey, Foxboro, Turnbull, and L&N under the trade names of "LOOP COMMAND", "EXACT", "AUTOTUNER", and "ELECTROMAX V+" respectively. The products are examined for: (i) set point change which occurs in a cascade loop, (ii) disturbance rejection which is quite common in process control loops, (iii) measurement noise which may be confused with measured process value. The process used was of high order and different time delays with a ratio of time delay/dominant time constant to be between .1 and 5. Each unit is examined per the performance expectations stated in product literature. The main purpose of the work is to inform and guide the potential users. The performance of each product is described and evaluated for its expected use in various applications. The performance results are selectively presented in graphical form.