Determine the proper proportional band, reset rate, and derivative time on a three-mode controller using the Ziegler-Nichols continuous cycling method, the process identification waveform in Figure 12-1a, and the Table 12-1b.Figure 12-1a
Controller ModeProportional Gain Kc
Proportional Band PB
Reset Time Ti (Minutes per Repeat)
Reset Rate Tr (Repeats per Minute)
Derivative Time Td
P
0.5 Gu
2 PBu
N/A
N/A
N/A
PI
0.45 Gu
2.2 PBu
Pu/1.2
1.2/Pu
N/A
PID
0.6 Gu
1.7 PBu
0.5 Pu
2/Pu
Pu/8
Table 12-1b

What will be an ideal response?


Proportion Setting 28.34
PB = 1.7PBu = 1.7 ยด 16.67 = 28.34
Integral Setting 2 Repeats/min
Tr = 2/Pu = 2/4 = .5
Derivative Setting 0.5 minutes
Td = Pu/8 = 4/8 = 0.5

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