34
Watlow Series 935B User’s Manual
Auto-tuning
Manual Tuning
For optimum performance, tune the Series 935B 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 935B 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]
=
[``50]
,
[`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 dis-
play 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 some-
times achieve the best system control. However, if a mechanical contactor
or solenoid is switching power to the load, a longer cycle time will mini-
mize 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.
Auto-tuning the Series 935B
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-tuning. Display reverts to normal after auto-tuning.
4.
[`Aut]
=
[``no]
stops auto-tuning.
NOTE:
[`Aut]
is
not visible at
factory default.
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CAUTION:
Successful Series
935B 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.
Figure 7 - Auto-tuning the Series 935B
Temperature
Time
90%
Set Point
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
Auto-tuning occurs at 90%
of set point in less than or
equal to 85 minutes
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