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This feature allows the warm-up characteristics to be tuned
separately from normal running conditions and is particularly useful
for applications where the sensor is some distance from the
heater. The setting determines where the derivative action starts
with respect to set point. The smaller the setting, the closer to
setpoint. Refer to Figure 5-8.
5.6 DERIVATIVE (RATE) TIME
5.7 DERIVATIVE APPROACH CONTROL
Setting too long
Ideal Setting Setting too short
Setting too small
Setting Ideal Setting too large
Derivative enables the controller to shift the proportional band up
or down in an amount proportional to the rate of temperature
change to help the system compensate for rapidly changing
temperature.
The derivative term is added to Proportional Control action to
speed up response to disturbances and to suppress overshoot.
Refer to Figure 5-7. In applications where these two requirements
would need different settings, the use of Derivative Approach
Control for adjusting warm-up characteristics allows the Derivative
setting to be biased in favor of disturuance behavior.
Figure 5-7. Derivative (Rate) Time
Figure 5-8. Derivative Approach Control
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