Micromod MOD: Modcell 2050R Users Guide - Manual (Page 159)

IB-23C650
TUNING
TUNING
MANUAL TUNING
The controller response parameters: Gain (P), Integral (I), and Derivative (D)
are adjustable over a wide range of values to accommodate many different
process characteristics. After the controller is installed in a specific control
application, these response parameters must be tuned to the characteristics of
the process so that overall system performance is at its best.
Optimum settings provide a compromise between the maximum deviation
from set-point and the time away from set-point during recovery after a
disturbance. Recovery after a disturbance should take approximately two and
one-half cycles.
These settings are an approximation. Other factors may require more
conservative or less conservative settings. For example, if there are frequent
disturbances, the responses may be set for greater stability with less gain, so
as to reduce the demand on the manipulated variable or minimize wear on the
valve.
The settings on many controllers are made by someone who has previous
experience with the same or a similar application, and the settings found to be
successful are used as a starter. Readjustments are made only when
necessary.
The procedures outlined here start with very stable settings and work toward
less stability primarily because this is less disturbing to the process. Some
processes can tolerate much disturbance. This is frequently true with flow
control loops, which may be fast acting and quick to recover. It is not
uncommon to start OFF with a cycling system, and adjust the gain for the
smallest sustained cycle.
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