Watlow Series 92 - Manual (Page 9)

WATLOW Series 92 User's Manual
9
Tuning
(cont.)
Tuning Procedure for PI Controls
92X 2 - XXXX - X0XX
Initial Settings:
•
Proportional band: 5 to 50
°
F/2.8 to 27.8
°
C
Maximum proportional band is clockwise (CW),
minimum (CCW). Located on the front of the
control labeled "Band."
• Cycle time, fixed. Typically 6 seconds.
• Automatic reset, fixed. Typically 0.25 repeats/
minute
Energize the system and allow the process tempera-
ture to stabilize. When the system is stable, the load
will cycle at a constant rate.
After an adjustment is made, the system may become
unstable. Allow sufficient time for the system to
stabilize before making another adjustment.
Proportional
Band
Figure 13 - PI Adjustment Graph
Proportional Band Adjustment:
Rotate the proportional band pot CCW 1/4 turn and
observe system stability. Repeat until the process
temperature begins to hunt (becomes unstable). When
hunting is observed, rotate the pot CW, in small
increments, until the system becomes stable. Some
systems may be stable enough to allow minimum
proportional band (maximum CCW).
Temperature
Figure 14 - Variable Time Base Example
NOTE:
The variable time base option is only
available with the PI control type.
Variable Time Base
92X 2 - X V XX - X0XX
When the time base varies upon load demand, this is
considered variable time base. The ON and OFF time
is proportional to the command signal, but the time
base changes according to the demand. At 50% it's
three AC cycles ON and three AC cycles OFF.
Zero cross SSR's must be used. If you are using
random fired SSR's, the Series 92 will not provide zero
cross output.
Time
Set point
Reduced Overshoot
Droop