PID Auto Center: Auto calculates center value based on Set Point. This adds stability at low Set Points, without sacrificing the ability to achieve high temperatures.
PID Smith Predictor: Builds on PID Auto Center and adds predictive logic to reduce overshoots.
NOTES:
It is recommended the PID Smith Predictor controller is run on a 15 second cycle with a Min Cycle Ratio of 0.05. The shorter cycle improves the predictive functionality of the controller, while the lower Min Cycle Ratio allows it to achieve lower temperatures. With the shorter cycle times and lower cycle ratio, no flameouts have been observed.
The Auto Center functionality can account for both F and C temperatures.
TUNING
To tune the PID Smith Predictor, the following methods were used.
THETA: The time from initial input to seeing a temperature change. (td in the Cohen-Coon Tuning image)
TAU: The time from seeing the initial temp change to reaching 63.2% of the final Set Point. (tau in the Cohen-Coon Tuning Image)
Overview
Two new PID Controllers:
NOTES:
TUNING
To tune the PID Smith Predictor, the following methods were used.
A good PID Tuning reference is this article on the Cohen-Coon Tuning Rules