DT = 2 minutes
Process Variable
62.0
60.0
58.0
56.0
54.0
52.0
50.0
48.0
Time, minutes
T1 = 22, T2 = 0
T1 = 20, T2 = 2
–10
0
10
20
30
40
50
60
70
80
90 100 110 120
Figure 10.2 Open-loop process response to step change from 50% to
60% controller output.
108 ◾  Distillation Control, Optimization, and Tuning
dead time and the maximum rate of change in the process variable, that is, the maximum process response rate.
Two data points were taken from each response curve in
Figure 10.2: when the process variable had reached 10% and
20% of the steady-state response. The results are listed in
Table 10.1. These data can be used to calculate the maximum
process response rate and apparent dead time for each case.
Table 10.1 Data Points from
Figure 10.2 for Z-N Calculations
with Controller Output Step from
50% to 60%
DT T 1 T 2
Time
(min)
Process Variable
(%)
2
22 0
4.1
51
2
22 0
6.7
52
2
20 2
5.5
51
2
20 2
8.1
52