Watlow Electric 93 - Manual (Page 28)

5 . 2 ■ T u n i n g a n d O p e r a t i n g W a t l o w S e r i e s 9 3
Tuning and Operating
4. When tuning is complete, the displays return to their previous state and
[`AUt] reverts to 0. The Series 93 installs appropriate PID tuning parameters
and saves them in the non-volatile memory. If a mechanical relay or contac-
tor is switching power to the load, a longer cycle time may be desirable
to minimize wear on the mechanical components. Typical life of a me-
chanical relay is 100,000 cycles.
To abort autotuning either reset the [`AUt] parameter to 0, press the
ˆInfinity key twice, or cycle power off and on. In all cases, aborting autotune
restores all values to those previous to autotuning.
Manual Tuning
For optimum controller performance, tune the Series 93 to your thermal sys-
tem. The tuning settings here are for a broad spectrum of applications; your
system may have somewhat different requirements. NOTE: This is a slow
procedure, taking from minutes to hours to obtain optimum value.
1. Apply power to the Series 93 and enter a set point. Set Operation parame-
ters as follows: [``Pb] to [```1], [``rE] / [``It] to [`)00], [``rA] /
[``dE] to [`)00], [``Ct] to [``%0], [`CAL] to [```0], [`AUt] to [```0].
2. Proportional Band Adjustment: Gradually increase [``Pb] until the
upper display temperature stabilizes to a constant value. The process tem-
perature will not be right on set point because the initial reset value is 0.00
repeats per minute. (When [``Pb] is set to 0; [``rE] / [``It] and [``rA] /
[``dE] are inoperative, and the Series 93 functions as a simple on-off con-
troller.) The [`HSC] parameter determines the switching differential value.
3. Reset/Integral Adjustment: Gradually increase [``rE], or decrease
[``It] until the upper display temperature begins to oscillate or "hunt."
Then slowly decrease [``rE] or increase [``It] until the upper display sta-
bilizes again near the set point.
4. Cycle Time Adjustment: Set [``Ct] as required. Faster cycle times
sometimes achieve the best system control. However, if a mechanical contac-
tor or solenoid is switching power to the load, a longer cycle time may be de-
sirable to minimize wear on the mechanical components. Experiment until
the cycle time is consistent with the quality of control you want. [``Ct] will
not appear on units with a process output.
5. Rate/Derivative Adjustment: Increase [``rA] / [``dE] to 1.00 minute.
Then raise the set point by 11° to 17°C, or 20° to 30°F. Observe the system's
approach to the set point. If the load temperature overshoots the set point, in-
crease [``rA] / [``dE] to 2.00 minutes.
Raise the set point by 11 to 17°C, or 20 to 30°F and watch the approach to the
new set point. If you increase [``rA] / [``dE] too much, the approach to the
set point is very sluggish. Repeat as necessary until the system rises to the
new set point without overshooting or approaching the set point too slowly.
6. 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 calibration offset value you want. Calibration offset adds or sub-
tracts degrees from the value of the input signal.
NOTE:
Tune heating outputs at a
set point above ambient
temperature.
Tune cooling outputs at a
set point below ambient
temperature.