v 1.0 — February 2020 Altanium Matrix5
82 Possible Causes of Oscillation
7.8.2 Possible Causes of Oscillation
It is possible to set the control terms incorrectly, which could cause an oscillation. Table 7-19
gives the most common causes.
Table 7-19 Possible Causes of Oscillation
Cause Description
“P” too large Power change is too great with the degrees of temperature change.
“I” too large Power changes 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 an increase in temperature
in excess of 33 °C (60 °F) under severe conditions. Thus, if large
temperature variations occur during molding, it is worth plotting this
variation against the molding cycle time. As the controller cannot start
additional cooling, it is only possible to minimize this effect with correct PID
term selections.
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