PMA KS 98, Manual

Page: 164 / 246

24.5 Small controller ABC
Some operating principles, which are realized in the controller (
d
) or which are possible by means of an additional en-
gineering are explained in the following section ( ü ). Cross references are shown in italics.
3
Anti-reset-wind-up
Measure which prevents the controller integrator from saturation.
3
Working point (
Y0
)
The working point of a P or a PD controller indicates the value output to the process with process value = set-point. Al-
though this value is only important for P and PD controller, it can also be of interest for controllers with integrator (au-
tomatic working point).
3
Automatic operation
Normal controller operation. The controller controls the process by means of the adjusted control parameters. Auto-
matic operation is effective with
a/m
(di7) set to 0 (automatic) AND automatic selected via front-panel key
H
AND
sm/hm
(di16) set to 0 (soft manual). Contrary: manual operation.
3
Cutback
Reset of the integral action shortly before reaching the end setpoint with setpoint ramps.
3
Cycle time
The duration of a switching cycle (pulse and pause) at 50 % power control of a 2-point controller.
3
Line-out to the target
By early setpoint switch-over to the ramp end setpoint, the controller
is given a new target orientation for smooth line-out to the target.
ü
Bandwidth control
With program control or gradient control, there may be a considerable control deviation if the process is slow. This can
be prevented by monitoring the control deviation for an adjusted tolerance band by means of additional function blocks.
With out-of-tolerance, the set-point change is stopped (
w stop
with controller or
stop
with program controller).
3
Three-element control
Particularly suitable for processes in which load changes would be detected too late (e.g. level control for steam boil-
ers). In this case, a disturbance variable is used at which the mass balance (steam removal, feed water) is evaluated,
subtracted and added to the control variable (after differentiation, if necessary).
ü
Feed-forward control
Especially suitable for processes with long delay time, e.g. pH-control. A disturbance variable is used, at which the
evaluated, differentiated or delayed value of an analog input (
YAdd
) is added directly to the controller output for
avoiding the controller time behaviour.
3
Gradient control
Particularly suitable for processes in which energy shocks or quick set-point changes must be avoided. Set-point
changes are bumpless in both directions, since the effective set-point always runs towards the changed set-point (des-
tination set-point) by means of gradients Grw+ or Grw-. For the second set-point w2, gradient Grw2 acts in both direc-
tions, also with w
r
w2 switch-over.
3
Manual operation
When switching over to manual operation, the automatic sequence in the control loop is interrupted. Modes soft man-
ual and hard manual are available. Switch-over automatic
r
manual and vice versa are bumpless. Manual operation is
effective with
a/m
(di7) set to 1 (manual) OR manual selected via front-panel key
H
OR
sm/hm
(di16) set to 1 (hard
manual). Contrary: automatic .
g
If
automatic
remains selected via key
H
, the controller changes to
automatic
after omission of the di7
signal. With
manual
selected additionally via key
H
, the controller remains in manual mode after
omission of the di7 signal.
Controller
9499 040 50611
Small controller ABC 164