Watlow Series 942 - Manual (Page 40)

Tuning and Operating, Chapter 6 40
WATLOW Series 942 User's Manual
Tuning
Chapter 6
How to Tune and Operate
Tuning - Automatic
Auto-tuning: The Series 942 can automatically tune the PID parameters to fit the
characteristics of your particular thermal system.
The auto-tuning procedure operates on a thermal response value — slow, medium,
or fast. Use the slow thermal response when your process does not need to reach
set point too rapidly, or if it usually does not exceed set point. A fast thermal
response produces a rapid temperature change over a short period of time.
Once the auto-tune sequence has begun, the heat proportional band is set to 0 and
the control goes into an ON/OFF mode of control at 90% of the established set
point. The displayed set point remains unchanged.
The cool output remains off for the duration of tuning. Once the control finishes
"learning" the system, it returns to a standard PID control with the heat PID values
automatically set as a result of auto-tuning. Tuning is complete within 80 minutes.
Any change of set point, while in auto-tune, re-initiates the auto-tune procedure.
To start auto-tuning:
1. Press the MODE key until the AUt parameter appears in the data display.
The AUt parameter will not appear under the Operation menu if the set point
value is OFF.
2. Select a thermal response value, 1 = slow, 2 = medium, and 3 = fast, using
the UP/DOWN keys. A thermal response value of 2 satisfactorily tunes most
thermal systems.
3. Press the MODE key. While the control is in the tuning mode, the lower
display alternately displays the normal information and the AUt parameter.
The time between alternations is 1 second.
4. When tuning is complete, the displays return to their previous state and AUt
reverts to 0. The 942 installed the appropriate PID tuning parameters and
saved them in the non-volatile memory.
To abort auto-tuning, reset the AUt parameter to 0, or cycle power off and on. In
all cases, aborting auto-tune restores all original values.