Despatch MIC1422 Controller - Manual (Page 64)

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New instruments supplied by the factory contain PID terms set at "DEFAULT" values
which have been found to give adequate and safe control over a wide range of
applications. In the "Pre-Tune" mode of operation, the "default" PID terms are loaded
and the controller demands 100% power until the process value has moved
approximately halfway to the setpoint. At that point, power is removed thereby
introducing a deviation oscillation. Once the oscillation peak has passed, the Pre-Tune
algorithm can calculate its first approximation to the optimum PID values. The power is
reapplied using new values. This technique limits possibility of setpoint overshoot when
the instrument is new or the application has been changed.
FIGURE 12-1
FIGURE 12-2