Tuning PID loops for level control

摘要

One-in-four control loops are regulating level, but techniques for tuning PID controllers in these integrating processes are not widely understood. Since the first two PID controller tuning methods were published in 1942 by J. G. Ziegler and N. B. Nichols, more than 100 additional tuning rules have been developed for self-regulating control loops (such as flow, temperature, pressure). In contrast, fewer than 10 tuning methods have been developed for integrating (level) process types, though roughly one-in-four industrial proportional-integral-derivative (PID) loops controls liquid level. The original Ziegler-Nichols tuning methods' aimed for a super-fast response capability, which was achieved at the expense of control loop stability. However, a slight modification of these tuning rules improves loop stability while still maintaining a fast response to set-point changes and disturbances. As most process experts will agree, stability is generally more important than speed in the majority of industrial applications.