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.
ç
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
ç
Auto-tuning occurs at 90% of set point
in less than or equal to 85 minutes.
