West Control Solutions KS 45 - Manual (Page 46)

7.4 Manual 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, plot-
ting 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
Dt and Dx (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
, and characteristic K according to the formulas given below. Increase Pb1, if line-out to the setpoint oscillates.
Controlling
Manual tuning 46 KS 45
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
Parameter adjustment effects
Parameter Control Line-out of disturbances Start-up behaviour
Pb1 higher increased damping slower line-out slower reduction of duty cycle
lower reduced damping faster line-out faster reduction of duty cycle
td1 higher reduced damping faster response to disturbances faster reduction of duty cycle
lower increased damping slower response to disturbances slower reduction of duty cycle
ti1 higher increased damping slower line-out slower reduction of duty cycle
lower reduced damping faster line-out faster reduction of duty cycle
Formulas
K = Vmax w Tu controller behavior Pb1 [phy.units] td1 [s] ti1 [s]
With 2-point and 3-point con-
trollers, the cycle time must be
adjusted to
t1 / t2 £ 0,25 * Tu
PID 1,7 w K 2 w Tu 2 w Tu
PD 0,5 w K Tu OFF
PI 2,6 w K OFF 6 w Tu
P K OFF OFF
3-point-stepping 1,7 w K Tu 2 w Tu