Watlow Series 998 - Manual (Page 104)

Tuning
Tuning, Alarms and Error Codes, Chapter 7 7.2 WATLOW Series 998 User’s Manual
Tuning ç
To start auto-tuning:
1. Press the Mode key µ until the [`AUt] prompt appears in the lower
display.
2. Use the Up-arrow or Down-arrow key > < to select [`PidA] or
[`Pidb] depending on which channel you want to tune. Only one PID
set can be auto-tuned at a time.
3. Press the Mode key. While the control is in the tuning mode, the lower
display alternately displays the normal information and the [tunE]
prompt. The time between alternations is one second.
4. When tuning is complete, the display return to their previous state and
[`AUt] reverts to [`OFF]. The 998 installs appropriate PID tuning para-
meters and saves them in non-volatile memory.
To abort auto-tuning either reset the [`AUt] prompt to [`OFF] or cycle
power off and on. In all cases, aborting auto-tune restores all values to
those previous to auto-tuning.
Manual Tuning ç
For optimum control performance, tune both channels of the Series 998
to your thermal system. The tuning settings here are for a broad spec-
trum of applications; your system may have somewhat different require-
ments. NOTE: This is a slow procedure, taking from minutes to hours to
obtain optimum values.
If you are not familiar with tuning a thermal system, we suggest you
obtain and become familiar with the reference below before attempting to
tune your system.
Tuning of Industrial Control Systems
by Armando B. Corripio
Published by the Instrument Society of America (ISA)
Member $48.00, list $60.00 (approx). phone: (919) 549-8411
Perform this procedure on both channels PID sets, they are functionally
identical. The parameters within the procedure apply to both output 1A,
2A, 1b and 2b and PID A and PID B.
1. Apply power to the Series 998 and enter a set point. Begin with
these PID parameters:
[``Pb] set to [```1];
[``rE] or [``It] set to [`)00];
[``rA] or [``dE] set to [`)00];
[``Ct] set to [``%0];
[`CAL] set to [```0];
[`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] or [``It]
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. Typical life of
a mechanical relay
is 100,000 cycles.
NOTE:
Tune heating out-
puts at a set point
above the ambient
process value.
Tune cooling out-
puts at a set point
below the ambient
process value.