West Control Solutions N8840 - Manual (Page 23)

3.5.7 Examples for self-tuning attempts
(controller inverse, heating or heating/cooling)
Start: heating power switched on
Heating power Y is switched off (1).
When the change of process value X
was constant during one minute (2),
the power is switched on (3).
At the reversal point, the self-tuning
attempt is finished and the new
parameter are used for controlling to
set-point W.
Start: heating power switched off
The controller waits 1,5 minutes (1).
Heating power Y is switched on (2).
At the reversal point, the self-tuning
attempt is finished and control to the
set-point is using the new parameters.
Self-tuning at the set-point a
The process is controlled to the
set-point. With the control deviation
constant during a defined time (1)
(i.e. constant separation of process value
and set-point), the controller outputs a
reduced correcting variable pulse (max.
20%) (2). After determination of the
control parameters using the process
characteristic (3), control is started
using the new parameters (4).
Three-point controller a
The parameter for heating and cooling are
determined in two attempts. The heating
power is switched on (1). Heating
parameters Pb1, ti1, td1 and t1 are
determined at the reversal point. Control to
the set-point occurs(2). With constant
control deviation, the controller provides a
cooling correcting variable pulse (3).
After determining its cooling parameters
Pb2, ti2, td2 and t2 (4) from the
process characteristics , control operation is started using the new parameters (5).
a
During phase 3, heating and cooling are done simultaneously!
Operation
8840 profiler 23 Self-tuning
t
2
100%
Y
0%
X
W
Start r 1 3 t reversal point
blinks
t
100%
Y
0%
X
W
start r 1 2 t reversal point
blinks
t
2
100%
Y
0%
X
W
1 3
blinks
4
r t
Start r
t
+100%
Y 0%
-100%
X
W
t reversal
point
Start r 1 2
3
4 5
r t