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7.2 WATLOW Series 988 User’s Manual
Tuning, Manual Operation, Alarms and Error Codes, Chapter 7
Tuning
When the control finishes “learning” the system, it resumes standard PID
control using the PID values established by the auto-tuning process.
Changing the set point during an auto-tune restarts the auto-tune proce-
dure.
During auto-tuning the process must cross the set point four times within
an 80-minute time span for the Series 988 to successfully complete the
auto-tune. If this does not happen within the 80-minute time limit, the
Series 988 chooses PID values based on the 80-minute tuning cycle per-
formed.
To start auto-tuning:
1. Press the Mode key µ to advance to the System Menu [`SyS].
Press the Mode key µ to advance through the menu until the [`AUt]
prompt appears in the lower display.
2. Use the Up-arrow > or Down-arrow < key to select [PidA] or [Pidb],
if your controller is equipped with enhanced software (
98_ B -_ _ _ _-_ _ _ _)
.
Only one PID set can be auto-tuned at a time.
3. Press the Display key ¥. While the control is in the tuning mode
the lower display alternates every second between the normal informa-
tion and the [tunE] prompt.
4. When tuning is complete, the displays return to their previous state
and [`AUt] reverts to [`OFF]. The Series 988 installs the PID tuning
parameters it has calculated and saves them in non-volatile memory.
To abort auto-tuning either reset the [`AUt] prompt to off, press the
Auto/Man key å twice, or cycle power off and on. In all cases, aborting
auto-tune restores all values to their state before auto-tuning began.
Manual Tuning
For optimum control performance, tune the Series 988 to your thermal
system. The tuning settings here are for a broad spectrum of applications;
your system may have somewhat different requirements. NOTE: This is a
slow procedure that may take hours to obtain optimum values.
Tune heating outputs at a set point above the ambient process value.
Tune cooling outputs at a set point below the ambient process value.
If your controller is equipped with enhanced software (
98_B-_ _ _ _-_ _
_ _)
, the [Pidb] parameters may need to be tuned also. Perform this
procedure on both PID sets, they are functionally identical. The para-
meters within the procedure apply to both output 1 and 2, and PID A
and B.
ç
CAUTION:
If a mechanical
relay or contactor is
switching power to
the load, a longer
cycle time may be
desirable to mini-
mize wear on the
mechanical compo-
nents. The typical
life of a mechanical
relay is 100,000
cycles. Verify that
the cycle time
selected is appro-
priate for the output
device type. Failure
to do so could
result in damage to
equipment and/or
property.
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