Watlow Series 988LF - Manual (Page 48)

7.2 WATLOW Series 988LF Users Manual Tuning, Manual Operation, Alarms, and Error Codes, Chapter 7
4. When tuning is complete, the displays return to their previous state
and [`AUt] reverts to [`OFF]. The Series 988LF 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 988LF 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.
NOTE:
Tune heating outputs at a set point above the ambient process value.
Tune cooling outputs at a set point below the ambient process value.
1. Apply power to the Series 988LF and enter a set point. Begin with
[``Pb] set to [```1]; [``rE] or [``It] set to [`0)0]; [``rA] or
[``dE] set to [`0)0]; [``Ct] set to [``%0]; [`CAL] set to [```0]; and
[`AUt] set to [`OFF].
2. Proportional Band Adjustment: Gradually increase [``Pb] until the
upper display process value stabilizes at a constant value. The
process value will not be right on set point because the initial reset
value is 0.00 repeats per minute. (If [``Pb] is set to [```0] then
[``rE], [``It], [``rA] and [``dE] are inoperative, and the Series 988
functions as a simple on/off control.) The [`HYS] prompt determines
the switching differential value.
3. Reset/Integral Adjustment: Gradually increase [``rE] or [``It] until
the upper display process value begins to oscillate or “hunt.” Then
slowly decrease [``rE] or [``It] until the upper display stabilizes
again near set point.
4. Cycle Time Adjustment: Set [``Ct] 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 may be desirable to minimize wear on the mechanical compo
nents. Experiment until the cycle time is consistent with the quality of
control you want. [``Ct] will not appear on units with a process
output (98__-__F_-____ or 98__-___F-____).
5. Rate/Derivative Adjustment: Increase [``rA] or [``dE] to 0.10
minute. Then raise set point by 20° to 30°F, or 11° to 17°C. Observe
the system’s approach to the set point. If the load process value over
shoots the set point, increase [``rA] or [``dE] to 0.50 minutes.
Tuning