949-1239-3
12
Rev. 10/98
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 the initial Self Tune is complete, the instrument will look at the LErn
menu item to determine if you wish to have the process continually tuned.
Setting LErn to Cont will allow the control to periodically check the tuning
parameters. If you wish to have the tuning values locked in, set Lern to End.
If you wish at any time to view the PID values, change the tunE setting 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.
METHOD FOR SET UP OF A HEAT / COOL CONTROL WITH SELF
TUNE
Determine if the process is predominantly heating or cooling. An extruder,
for example, is predominantly cooling when running product. An environ-
mental chamber can be either heating or cooling.
If the process is predominantly cooling, set S1St to dir and S2St to rE. If the
process is predominantly heating, set S1St to rE and S2St to dir. Redirect
SP1 to output A or B as required by the hardware (see SP1o). Set S2t to
dE. Set SP2 for zero (no overlap of bands, no deadband). Set Pb2 to a
desired value (default is 12° F). Set tunE to SELF, Strt to YES, and LErn
to End.
Start the process and wait for it to come to stability. Occasionally check that
the Self Tune has completed the learning process by INDEXing to Strt in the
secondary menu. If the YES value has changed to no, then the process has
been learned. Once learning is complete, you may adjust SP2 to either
overlap the SP1 band (SP2 value less than zero), or add some separation
(or dead band) between them (SP2 greater than zero). Adjust SP2 as
required to optimize control.
