ABSTRACT

This chapter describes how to characterize the response of a process variable with a controller in manual output mode, that is, with no feedback from changes in the process variable. The most common model of a self-regulating process response is a first-order plus dead time (FOPDT) response. Many different tuning rules have been published for estimating the controller tuning parameters to use for a FOPDT process response. An integrating process response, for example, the level in a reflux drum or distillation column base, will eventually overflow or run empty in an open-loop step test without further manual intervention. The values of apparent dead time, first-order time constant, and process gain were used to characterize an open-loop self-regulating process response. The values of apparent dead time and percentage change in accumulator level per minute were used to characterize the open-loop integrating process response.