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Bumpless switchover 270, Bumpless auto/manual switch-over – West Control Solutions KS98-1 User Manual

Page 270

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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