West Control Solutions KS98-1 - Manual (Page 270)

Which one of the two controllers influences the process is decided in the slave controller logic. The first “close” pulse
coming from the limiting controller switches over to override control. The limited controller automatically retrieves the
positioning authority, when it first tries to close the actuator further.
Bumpless auto/manual switch-over
Sudden process interventions by control mode switch-over are usually not desired. Excepted is purposeful switch-over
y r Y2.
A r M switch-over is always bumpless; the last correcting value is frozen and can be changed manually. M r A
switch-over is different. Correcting value differences are compensated as follows: when switching over, the controller
integral action is set to correcting value Y
M
output last plus correcting variable portions of the controller P and D action
running in the background (Y
I
= Y
M
+ Y
PD
).
Now, only the integrator, which adapts the correcting variable slowly to the stationary value according to the actual
control deviation, is active.
9499-040-82711
III-270 Process value calculation
A M r
Zeit
correcting variable y
M A r
max. limiting correcting variable y+
min. limiting correcting variable y-
Manual Automatic Automatic
Y
I
Ypid
Y
M
Ypid
Y = Y
I M
Automati-
correcting variable Y
PD
Fig.:97