110 C4 Manual Rev 7.5.2
There will always be some oscillation, but a proper setting of the integral term
will keep these oscillations very minor and within the range of established control
accuracy. When the C4 is shipped from the factory, the integral term is set such
that it will work well for most applications. Small adjustments to the proportional
term rarely require adjustment of the integral term. Change this setting in small
amounts only after careful demonstration of the need.
The Differential Term
The Differential term (Setup field 11) is the least often changed term. It’s effects
on the other terms are subtle and illusive to most users. Don’t change this term
unless you are thoroughly convinced of the necessity for doing so. The differential
term supplies an anticipatory response that can be helpful with slow processes
(large loads). It helps to compensate for the effects of thermal inertia at it’s
extremes. If the term is too small, anticipation may be inadequate for slow
responding systems and the setpoint may be illusive. If the differential term is
too large, the system may over anticipate and begin excessive oscillation. The
differential term changes the period of any temperature oscillations. This can be
helpful in the rare event that a change in the proportional or integral term has set
up an oscillation that seems “hard to break”. If this term is excessive, the
oscillations that develop are typically more rapid than those associated with an
excessive integral term value. Note that this term has such profound effects on
the other two that there is a strong possibility that if you change this value, you
will have to adjust one or both of the other term values as well.