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20
WATLOW Series 733/734 Service Manual
Tuning, Chapter 4
Tuning
Figure 24 -
Auto-tuning at a Set
Point of 200°F.
˜
NOTE:
An X applies to
either Zone 1 or
Zone 2.
˜
NOTE:
In dual zone applica-
tions, allow Zone 1
to complete before
tuning Zone 2.
Chapter 4
Tuning
Auto-tuning
Auto-tuning applies to Zone 1 or 2.
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 Zone 1 or 2 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
display alternates between At _ and the current parameter.
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.
Any change of the set point, while in auto-tune, re-initiates the auto-tune
procedure.
In order for the 733/734 to successfully complete auto-tune, the process must
cross the 90% value of 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.
200
°Temp
Set Point
100
Process
180
Auto-tune
Begins
Auto-tune
Complete
90% of
Set Point
°Time
To start auto-tuning:
1. Enter the Service mode by pressing the key sequence .
[AUt1] appears in the display.
To auto-tune Zone 2, press the Time key and [AUt2] appears.