Possible Causes of Oscillation 51
User Guide v 1.4 — September 2015 Making Adjustments
7.3.11.2 Possible Causes of Oscillation
It is possible to set the control terms incorrectly, inducing an oscillation. The following are the
most common causes:
Table 7-2 Possible Causes of Oscillation
Cause Description
“P” too large Power change too great per °C of temperature change.
“I” too large Power changing too quickly for the process to follow it.
“D” too large Stepped power change too large for the rate of change of temperature.
Shear An important issue often overlooked is the effect of shear in the material as
it passes through the gating area. This can cause rises in temperature in
excess of 33 °C (60 °F) under severe conditions. Therefore, if large
temperature variations occur during molding, it is worth plotting this
variation against the molding cycle time. As the controller cannot initiate
additional cooling, it is only possible to minimize this effect with properly
selected PID terms.
To Next Page
Loading...
