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.
110 | C4 Manual Rev 7.5.2 |