A trial-and-error method that is a variation of Ziegler-Nichols tuning
has been employed in the past for field tuning of PID controllers. Th
is method is now extended for tuning of multiloop PI controllers. The
Nyquist array method is refined to determine ultimate gains for multil
oop tuning. The proposed method is simple to use and simulation result
s show that it avoids sluggish responses and unbalanced responses betw
een loops that occur with other tuning methods such as BLT and sequent
ial autotuning. (C) 1998 Elsevier Science Ltd. All rights reserved.