Tuning and Operating, Chapter 5
WATLOW Series 945 User's Manual 21
Tuning
In order for the 945 to successfully complete auto-tune, the process must cross set
point four times within 80 minutes after auto-tune has started. If this does not
happen within the 80 minute time limit, the Pb remains at 0 and the control
functions in an ON/OFF mode.
Auto-tuning
Auto-tuning applies to Output 1, heating only.
The auto-tuning procedure operates on a thermal response value — slow, medium,
or fast. Use the slow thermal response when your process does not reach set
point too rapidly, or if it usually does not exceed set point a lot. A fast thermal
response produces a rapid temperature change over a short period of time.
Once the auto-tune sequence has begun, the Output 1 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 tuning duration. Once the control learns the
thermal system response, it returns to a standard PID control using the PID values
automatically set as a result of auto-tuning. Output 2 cool PID values are
unaffected by auto-tuning, and remain at their factory default settings. See Manual
tuning on the next page to set cool PID parameters. Any change of the set point,
while in auto-tune, re-initiates the auto-tune procedure.
The Series 945 will not Auto-tune while in remote set point. Transferring from local
to remote set point takes the 945 out of auto-tune.
Chapter 5
How to Tune and Operate
Figure 33 -
Auto-tuning at a Set
Point of 200°F.
200
°Temp
Set Point
100
Process
180
Auto-tune
Begins
Auto-tune
Complete
90% of
Set Point
°Time
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