8. FUNCTIONS
IMS01J02-E2
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8.2.7 Output change rate limiter
The output change rate limiter limits the variation of manipulated output (MV) for a time unit. You
can set an output variation, and control the output, when your object requires to avoid sudden variation.
The output variation limiter is particularly effective when a sudden variation may cause the controller
to crash, or when it may cause a large current. Also, it is very effective when you are dealing with
current output or voltage output.
The output change rate limiter is effective in the following cases
•
If the output starts from 100 % when putting power on (if a sudden change of 100 % causes a
problem with variation of flow, etc.)
•
If the output changes suddenly when changing the set value.
As it is described in the figure above, the output does not make a sudden change, but it changes based
on the set inclination, when giving power (outside of the proportional band), or changing the set value
(large change).
The figure above is an example of upward output variation. For the downward variation, downward
variation (inclination) has to be set.
Response to the control becomes slow, and the effect of differentiation is lost, when the
output change rate limiter is set too small (small inclination).
The output change rate limiter is disabled, when it is set at 0.0.
When the output change rate limiter is used, you may not be able to obtain appropriate PID
constants during autotuning.
Output limiter (high)
100 %
Output limiter (low)
0 %
Manipulated output (MV)
Manipulated output (MV)
Sudden
variation of
output
When the output change rate limiter is disabled
MV
MV
0.0 to
100.0 %
of span
1 second
Set the amount of increase given to
the operation output in the
percentage of span for each second.
Sudden change in the output when power on, set value
change or disturbance
