West Control Solutions N8840 - Manual (Page 24)

3.6 Manual self-tuning
The optimization aid should be used with units on which the control parameters
shall be set without self-tuning.
For this, the response of process variable x after a step change of correcting
variable y can be used. Frequently, plotting the complete response curve (0 to
100%) is not possible, because the process must be kept within defined limits.
Values T
g
and x
max
(step change from 0 to 100 %) or ∆t and ∆x (partial step
response) can be used to determine the maximum rate of increase v
max
.
The control parameters can be determined from the values calculated for delay
time T
u
, maximum rate of increase v
max
, control range X
h
and characteristic K
according to the formulas given below. Increase Pb1, if line-out to the set-point
oscillates.
Operation
Manual self-tuning 24 8840 profiler
Tu
Tg
t
x
y
100%
0%
t
Yh
Xmax
{X
{t
y = correcting variable
Y
h
= control range
Tu = delay time (s)
Tg = recovery time (s)
X
max
= maximum process value
V
max
= Xmax
Tg
= ∆
∆
x
t
= max. rate of increase of process value