Watlow Series 920 Microprocessor-Based Ramping Control - Manual (Page 35)

30°F, or 11° to 17°C. Observe the system’s approach to SP. If the load
temperature overshoots SP, increase RT to 2.00 minutes.
Then raise SP by 20 to 30°F, or 11 to 17°C and watch the approach to
the new set point. If RT is advanced too far, approach to the set point will
be 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 (as much as ±90°F or ±50°C) between that tem-
perature, perhaps at another point in the system, and the process value
showing in the alphanumeric display. Then enter the amount of CAL offset
you want. Calibration offset adds or subtracts degrees from the value of
the input signal.
The LOPWR and HIPWR Parameters
The LOPWR and HIPWR parameters allow you to limit the duty cycle of the
beat output to minimum and maximum values. The LOPWR parameter is used
to generate a minimum duty cycle regardless of the duty cycle calculated by
the PID circuit.
LOPWR Example: LOPWR = 20%
The PID circuit calls for a duty cycle of 10%. The LOPWR parameter overrides
the PID circuit and outputs a duty cycle of 20%.
For the HIPWR parameter, a maximum duty cycle is generated regardless of
the duty cycle calculated by the PID circuit.
HIPWR Example: HIPWR = 80%
The PID circuit calls for a duty cycle of 100%. The HIPWR parameter over-
rides the PID circuit and outputs a duty cycle of 80%. These two parameters
help insure that an “idle” duty cycle is always applied, or that the heaters
cannot apply full power to the thermal system.
Where To Go From Here
Once you have tuned your Series 920, continue to Chapter 6 to learn how to
program your Series 920 for your system.
WATLOW Series 920 User’s Manual
35
How To Tune The Series 920, Chapter 5