Watlow Series 982 - Manual (Page 109)

WATLOW Series 982 User’s Manual
8.1 Tuning, Alarms and Error Codes, Chapter 8
Auto-tuning (Heat and/or Cool)
The Series 981/982 can automatically tune the PID parameters to fit the char-
acteristics of your particular thermal system.
Before beginning the auto-tune sequence, make sure the AtSP parameter
located in the Global menu is at the proper setting. This allows the user to
select the tuning set point as a percentage of the current control set point. See
Chapter 4 for more information on this parameter. The figure below uses the
90% default setting to define the auto-tuning process.
Once the auto-tune sequence has begun, the Output 1 and Output 2 propor-
tional band is set to 0 and the control goes into an ON/OFF mode of control at
the set point percentage determined by the AtSP parameter. The displayed set
point remains unchanged.
Once the control finishes “learning” the system, it returns to a standard PID
control with the PID values automatically set as a result of auto-tuning. Any
change in the set point while in auto-tune re-initiates the auto-tune proce-
dure.
Once auto-tune has begun, the process must cross the auto-tune set point
four times within an 80 minute time span for the 981/982 to successfully
complete auto-tune. If this does not happen within the 80 minute time limit,
the Series 981/982 chooses PID values based on the 80 minute tuning cycle
performed.
200
°Temp
Set Point
100
Process
180
Auto-tune
Begins
Auto-tune
Complete
90% of
Set Point
(AtSP Default Setting)
Auto-tuning at a Set Point of 200°F
Time
Figure 8.1 -
Auto-tuning
Example.
Chapter 8 Operation, Tuning, Alarms
and Error Codes