The Control of a Process Having Appreciable Transport Lag-A Laboratory Case Study

The control of a process characterized by major " pure time delay" or " transport lag" by means of a coentonal analog controller is difficult because of the finite time which must elapse before a change in the controller output produces any measurable change in the process output. Linear predictor control is a well-known theoretical scheme for compensating the dead time; this requires incorporation of dead time in the controller itself and hardware difficulties have limited the use of this scheme in practice. It is shown in this paper that using an approximate-analog model of dead time synthesized from relatively inexpensive electronic components, a controller using the linear predictor approach is quite practicable in a typical process conatrol situation. A design of a control scheme for a laboratory process implementing the linear predictor control principle is given and it is shown that the improvement obtained in the control of the process, using an approximate analog model of dead time, is considerable.