Open-Loop Testing of Process Response ◾  117
After the recommended controller tuning constants have
been calculated, they need to be put into the controller and
then tested in closed loop for a final evaluation. Closed-loop
performance results, that is, with the controller in automatic
output mode, can be evaluated by the pattern recognition
methods presented in Chapter 9.
Exercises
10.1 A controller was put in manual mode, and the controller output was changed from 50% to 60%. Two points
on the response rate were 51% at 4.1 min and 52% at
6.7 min. What proportional gain and integral time constant would be recommended from the Ziegler–Nichols
open-loop response curve method for a PI controller?
Would these tuning constants be expected to give a
more aggressive controller response than K c = 4.08 and
T i = 13 min or a more sluggish response?
10.2 Using the data from Table 10.3 for DT = 2, T 1 = 22, and
T 2 = 0, what proportional gain and integral time constant would be recommended for a PI controller using
the quarter decay ratio tuning rules?
10.3 Using the data from Table 10.3 for DT = 2, T 1 = 22, and
T 2 = 0, what proportional gain and integral time constant would be recommended for a PI controller using
the aggressive SIMC tuning rules? Would the tuning
constants from the SIMC tuning rules be expected to
give a more aggressive response than K c = 4.08 and T i =
13 min or a more sluggish response?
References
1. Ziegler, J. G., and Nichols, N. B., Optimum settings for automatic controllers, Trans. ASME, 64, 759, November 1942.