Watlow Series 935A - Manual (Page 34)

Auto-tuning
Auto-tune automatically sets PID parameters for your system.
1. Press . and , for three seconds.
2. You'll see [`Aut] .
3. Press and hold ß , then select [`YES] with . or , . [tune] will flash to indicate auto-tun-
ing. Display reverts to normal after auto-tuning.
4. [`Aut] = [``no] stops auto-tuning.
Figure 7 - Auto-tuning the Series 935A
Manual Tuning
For optimum performance, tune the Series 935A to your thermal system. The settings here are for a
broad spectrum of applications; your system may have different requirements.
Tune heating outputs at a set point above ambient temperature.
Tune cooling outputs at a set point below ambient temp.
1. Apply power to the 935A and enter a set point.
In the Operations Menu,
[`Aut] must = [``no] .
Begin with these Configuration Menu settings:
[Pb`h = [```1] , [``1t] = [`000] , [``dE] = [`000] ,
[Ct`h] = [`%0]] , [`CAL] = [```0] .
2. Proportional Band Adjustment: Gradually increase [Pb`h] until the upper display temp. stabilizes
at a constant value.
3. Integral Adjustment: Gradually decrease [``It] from 30.00 until the display temperature begins to
oscillate or “hunt.” Then slowly increase [``It] until the upper display stabilizes again near set
point.
4. Cycle Time Adjustment: Set [Ct`h] as required. Faster cycle times sometimes achieve the best
system control. However, if a mechanical contactor or solenoid is switching power to the load, a
longer cycle time will minimize wear on relays.
5. Derivative Adjustment: Increase [``dE] to 0.10 minute. Then raise set point by 20° to 30°F, or 11°
to 17°C. Observe approach to set point. If load temperature overshoots, increase [``dE] by 0.50
minute. Raise set point by 20 to 30°F, or 11 to 17°C and watch approach again. Repeat until sys-
tem rises to new set point appropriately.
6. Calibration Offset Adjustment: Enter the [`CAL] offset value you want. Calibration offset adds or
subtracts degrees from the value of the input signal.
Temperature
Time
90%
Set Point
3 2 Watlow Series 935A User’s Manual
Auto-tuning
NOTE:
[`Aut] is
not visible at
factory default.
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CAUTION:
Successful Series
935A auto-tuning
requires 3
oscillations thru the
90% set point in 85
min. or less. If the
system cannot
perform the
oscillations in that
time, the control will
revert to the
previous PID values.
NOTE:
Manual tuning is a
slow procedure,
taking from minutes
to hours to obtain
optimum value.
Operations Menu
[`Aut]
✓
Auto-tune
[`ALO]
Alarm Range Low
[`Ah1]
Alarm Range High
[tMr]
Countdown Timer
[IdLE]
Idle
[`L-r]
Local / Remote
[`Pid]
PID
[CnFg]
Configuration
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Auto-tuning occurs at 90% of set point
in less than or equal to 85 minutes.