ABB C300 Operating Manual page 24

...7 CONTROL LEVEL
...7.1 Introduction to Standard Control
Response
On/Off Hysteresis
Proportional Band
Integral
Derivative
22
Contributions
Helps to prevent
rapid switching of
output
Stable control with
the minimum offset
a n d m i n i m u m
period of oscillation
c o n s i s t e n t w i t h
stability.
Time for variable to
Eliminates offset
return to set point
between Process
increases
and Set Point.
Increases stability,
permitting smaller
proportional band
and larger integral
action times to be • Stability decreases
used.
• Process noise is
Reduces height of
first peak.
Reduces period of
oscillation.
Fig. 7.2 Effect of Control Responses on Processes
Effect Of Response Settings
Too High
Process swings
Output switches
too far above
too rapidly
and below set
point
• More stable
• Longer period
S t a b i l i t y
decreases
• Larger oofset
M a x i m u m
contribution not
amplified
realized
Too Low
Hysteresis too high
Hysteresis too Low
High Prop. Band
Low Prop. Band
Integral Action too
High
• Stability
Correct Integral
Action Time
decreases
• Period of
Integral Action Time
too Low
oscillation
increases
Derivative Action
Time too Low
Derivative Action
Time Correct
Derivative Action
Time too High
1
Decay
4