PMA KS 98, Manual

Page: 165 / 246

3
Hard manual (
sm/hm
)
Safety output value
Yhm
. The controller output goes to the preset value immediately, when hard manual is active (the
controller is switched to manual mode directly). Keys I / D are without effect. Switch-over to automatic mode is
bumpless.
ü
Cascade control
Particularly suitable for temperature control in e.g. steam boilers. A continuous master controller (load controller) pro-
vides its output signal as an external set-point to a slave controller, which varies the output value.
3
Override control (OVC)
r
page 201
Limiting of the min. (OVC-) or max. (OVC+) output value to the value of an analog input. Limitation by override control
can be used e.g. with control continued by a different controller dependent of different conditions when reaching de-
fined process statuses. The transitions from unlimited
r
limited output value and vice versa are bumpless.
ü
Program control
The effective set-point follows the profile of a programmer (APROG with APROGD) connected to input
Wext
; the con-
troller must be set to
we
(di9=0).
3
Process at rest
For a clear optimization attempt during self-tuning , the control variable must be in a stable position. Various rest condi-
tions can be selected:
Process behaviour with constant output
value Recommended
setting
Stability
PIR_H
is reached, if
A constant process value is reached in
relatively short time (standard process).
grad=0
the process value is constant during 1 minute.
After a relatively long time, a constant
process value is reached (slow process).
grad<0/>0
the process value decreases constantly during 1
minute (controller inverse) or increases
constantly during 1 minute (controller direct).
The process is affected from outside.
grad<>0
the process change is constant during 1 minute.
The output action is unimportant.
3
Ramp function
Set-point changes in ramps rather than in steps. See gradient control.
3
Control parameters
For controller optimization, the controller must be matched to the process characteristics
(
r
5 Optimizing help,
r
6 Self-tuning). The effective parameters are
Xp1
,
Tn
,
Tv
and
Y0
.
Dependent of controller operating principle, the following additional parameters are possible:
Tp1
(with 2-point / 3-point controllers ),
Xp2
and
Tp2
(with 3-point controllers ),
Xsh and Tpuls and Tm (with 3-point stepping controllers ).
3
Control behaviour
Generally, fast line-out to the set-point without overshoot is required. Dependent of process, various control behaviours
are desirable for this process:
w
easily controllable processes (k < 10%) can be controlled with PD controllers,
w
processes with medium controllability (k 10...22%) using PID controllers and
w
badly controllable processes (k > 22%) with PI controllers.
ü
Controller OFF (
off
)
With input
off
=1, there are no pulses at the switching output and the continuous outputs are 0%.
3
Self-tuning
For optimum process control, the controller must be matched to the process requirements. The time required for this purpose can
be reduced considerably by self-tuning (
r
6 Self-tuning). During self-tuning, the controller makes one adaptation attempt during
which the control parameters are determined automatically from the process characteristics for fast line-out to the set-point with-
out overshoot.
9499 040 50611
Controller
165 Small controller ABC