West Control Solutions KS98-1 - Manual (Page 261)

External setpoint Wext
Switching between the internal setpoint ( wi) and the external setpoint (we) is possible only if the parameter
WFuncis adjusted to W/Casc.
The change-over can be triggered via interface or the digital control input
we/wi.
In order to make the internal setpoint effective, on we/wi must be attached a logic 1. If the external setpoint is to
be active, a logic 0 must be given on we/wi.
If the digital control input we/wi is not wired, the external setpoint is effective.
The internal setpoint W is evaluated with priority. If in a place (interface or the digital control input we/wi) is swit-
ched to internal setpoint it is not possible to switch over to the external setpoint Wext from another source.
Gradient control - setpoint changes with gradients
Normally, setpoint changes occur stepwisely. Unless this behaviour is required, a gradient can be set-up using parame -
ters
Grw+ and Grw- or Grw2.
If these parameters are set, the setpoint changes are made bumplessly. With digital input ‘ gr_off‘ not set, effec-
tive setpoint Weff runs linearly towards the changed setpoint (target value), whereby the slope is determined by
gradients Grw+ and Grw- adjustable at parameter setting level (r see Fig.: 78). For the second W2, an indepen-
dent gradient Grw2 was introduced, which is valid for both change directions and for w r W2 switchover.
The gradient function is switched off when setting Grw+ and Grw- or Grw2 to “----”
( engineering tool = off), or with digital input Gr off set to 1.
Switch-over with gradients (W
rW2, WrWext, controller"on")
The new setpoint is linear started outgoing from the momentary process-value. The slope of the ramp is determined re -
lated to the direction of
Grw+, Grw- and/or Grw2.
+ This principle applies, even if the process-value is outside the adjustable range W0/W100 at switch-over time (e.g.
when starting).
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Setpoint functions III-261
Setpoint 1
Setpoint 2
Adjustment of
1 2 Setpoint Setpoint r
upper setpoint limit W100
effective setpoint
x
w
Wext
W2
Time
Setpoint, process value
Grw-
Setpoint
Grw+
Adjustment of
Setpoint2 Setpoint 1 r
lower setpoint limit W0
Fig.78:
Setpoint
e.g. 1
W2
Setpoint
e.g. 2
Wext
Setpoint 3
e.g. w
upper setpoint limit W100
effective setpoint
x
w
Wext
W2
Time
Setpoint, process value
Process value
Grw2
Grw-
Grw+
lower setpoint limit W0
Switch over
Setpoint Setpoint 3 1 r
Switch over
Setpoint Setpoint 3 2 r
Controller "on"
Fig.79: