Dwyer 8600 - Manual (Page 15)

December, 1998 Page 15 949-1277-3
OPERATION OF SELF TUNE® FUNCTION
Self Tune® allows automatic selection of the necessary parameters to
achieve best control operation from your 8600 Series control. If you are
using the control output as a simple on-off function (Out1 set for OnOF),
none of the following will apply.
Theory of Operation
The Self Tune function calculates the Pb1, rES, and rtE parameters under
the PID tunE selection, and the Fbnd and FrtE parameters, as shown in the
Secondary Menu . These values are determined by measuring the response
of the process connected to the control. When Self Tune is started, the
control temporarily acts as an on-off control. While in this mode the control
measures the overshoot and undershoot of the process, and the period of
the process (the time from peak value to the next peak value). These
measurements are collected over a period that lasts three periods of
overshoot and undershoot. The data collected over this time is then
compared and calculated into final PID and Fuzzy Logic values. The effect
of Fuzzy Logic on the process is still controlled by the Fint (fuzzy intensity)
setting. If Fint is 0, the Fbnd and FrtE will be calculated, but will have no
effect. The calculations for the PID values are the same as used in the
standard Ziegler - Nichols equations that have been recognized as standard
for decades.
The only modification to the application of the Ziegler - Nichols equations is
controlled by the dFAC menu item. This menu item controls the amount of
rate (derivative) that is applied. A dFAC setting of 3 (factory default) or less
allows for less damping. A dFAC setting of 4 allows for critical damping as
set forth in Ziegler - Nichols. A dFAC setting of 5 or more allows over
damping of the process.
Program Setup and Operation
In the secondary menu set tunE to SELF. Skip LErn and check to make
sure that dFAC is set to the desired value. Back up to LErn and set to YES.
The control will begin the Self Tune function. While the Self Tune function
is active, the right hand decimal point on the lower display will blink. When
Self Tune is complete, the blinking will stop.
After Self Tune is complete, the tunE setting automatically switches to PID.
This allows examination and / or modification of the values calculated. We
recommend that you do not change the calculated values unless you have
a firm understanding of the parameters involved and their function. For more
information on PID tuning, please contact your supplier.