Tuning
-
Manual
For optimum control
performance,
tune the
Series
985 to the
thermal
system
The tuning
settings
here
are meant for a broad
spectrum
of applications; your
system may have somewhat
different
requirements.
1.
2.
3.
4.
5.
6.
Apply power to the
Series
965 and enter a
set
point.
Begin
with these
Operation Parameters: Pbl
=
1,
rE1
=
0.00,
rA1
=
0.00, Ct1
=
5, CAL
=
0,
AUt= 0.
ProportionaI
Band Adjustment (Output 1): Gradually increase Pb1 until
the
Upper display
temperature
stabilizes to a constant
value.
The
process
temperature will
not
be right on Set point because the initial
reset
value
is
0.00
repeats
per
minute.
PB1 =
0;
rE1
and
rA1
are
inoperative,
and
the 985 functions as a simple ON/OFF control with a
3°F
or
1.7°C
switching
differential.)
Reset
Adjustment: Gradually
increase
rE1
until the upper display
tem-
perature
begins to oscillate or “hunt”.
Then
slowly decrease
rE1
until the
Upper display
stabilizes
again
near
set point. NOTE: This is a slow
proce-
dure,
taking from minutes to hours to obtain optimum value.
Cycle
Time
Adjustment:
Set
Ct1 as required. Optimum
system
control is
sometimes achieved with faster cycle times.
However,
if a mechanical
contactor or solenoid is switching power to the load, a longer cycle time may
be
desirable
to
minimize
wear on the mechanical components. Experiment
until
the cycle time is consistent with the quality of control you want.
Rate Adjustment: lncrease
rA1
to 1.00 min. Then
raise
set point by
20°
to
30°F,
or 11° to
17°C
Observe
the
system’s approach to set point. If the
load temperature overshoots set point, increase
rA1
to 2.00 minutes.
Then raise set point by 20 to
30°F,
or 11 to
17°C
and watch the approach to
the new set point. If
rA1
is
advanced
too far, approach to
the
set point will
be very sluggish. Repeat as necessary until the system
rises
to the
new
set
point without
overshooting
or approaching the set point too slowly.
Calibration Offset Adjustment: You may want your system to control to a
temperature other than the
value
coming from the input
sensor.
If
so,
measure the
difference
between that temperature, perhaps at
another
point
in the system, and the process value showing in the Upper display. Then
enter the amount of CAL offset you want. Calibration offset adds or sub-
tracts
degrees
from the value of the input signal.
Manual and Automatic Operation
To
change
from manual to auto operation, press the AUTO/MAN key twice.
Manual
operation
provides direct (time proportioned
%
power)
control of the
outputs from -100% to 100%. A negative output
value
is allowed only with a Cl
(Cool) selection on either Otl or 0t2. Automatic operation provides closed loop
ON/OFF or
PID
control. When the
operation
transfers from a closed loop to an
open loop, the 985 retains the power
level
from the closed loop control. When
returning to the closed loop control,
the
previous set point temperature is
restored.

30

WATLOW series
98O/985
User’s
Manual
Tuning and Operating, Chapter
5