Auto-Tune Operation; Figure 2.6 Auto Tuning Process - ILX Lightwave LDT-5900 Series User Manual

Auto-Tune Operation

The auto tune algorithm in the LDT-5900 series of temperature controllers will
calculate a thermal system's PID coefficients through an iterative PID temperature
control process. Figure 2.6 describes the tuning process pictorially.
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The auto tune algorithm starts controlling temperature (Point 2 on Figure 2.6) with
an arbitrary coefficient for the loop gain (P term), and slowly increases it until the
temperature begins to oscillate. Once the temperature begins to oscillate, the P
term is reduced by 40% and the D term is calculated (Point 3). The derivative
term (D term) is calculated from the period of the oscillations that occurred during
the tuning of the P term. The control loop is allowed to settle after the P and D
terms are calculated and set. If the defined tuning set point is above the ambient
temperature, the decrease in the P term will cause a decrease in the control
temperature (Point 4).
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3) P & D Values Tuned
(P Term is Lowered)
4) P Term being Decreased
Causes Temperature Decrease
2) Auto-Tune Start (Only Proportional Term Used)
1) Ambient Temperature
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Figure 2.6 Auto Tuning Process

O P E R A T I O N S
Front Pa nel Opera t ion
5) Integral Term Added to Control
10 15
Time (Minutes)
C H A P T E R
6) Tuning Set Point
7) I Value Tuned
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LDT-5980/ 5948
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