Watlow Series 942 - Manual (Page 41)

Tuning and Operating, Chapter 6
41
WATLOW Series 942 User's Manual
Tuning
Tuning - Manual
For optimum control performance, tune the Series 942 to the 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 proce-
dure, taking from minutes to hours to obtain optimum value.
1. Apply power to the Series 942 and enter a set point. Begin with these
Operation Parameters: Pb1 = 1, rE1/It1 = 0.00, Ct1 = 5, rA1/dE1 = 0.00,
CAL = 0, AUt= 0.
2. Proportional Band Adjustment (Output 1): Gradually increase Pb1 until
the Upper display temperature stabilizes to a constant value. The process
temperature will not be right on set point because the initial reset value is
0.00 repeats per minute. (When Pb1 = 0; rE1 and rA1 are inoperative, and
the 942 functions as a simple ON/OFF control.) The HYSX parameter
determines the switching differential value.
3. Reset/Integral Adjustment: Gradually increase rE1/It1 until the upper
display temperature begins to oscillate or "hunt." Then slowly decrease
rE1/It1 until the Upper display stabilizes again near set point.
4. Cycle Time Adjustment: Set Ct1 as required. Faster cycle times some-
times 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 components. Experiment
until the cycle time is consistent with the quality of control you want.
5. Rate/Derivative Adjustment: Increase rA1/dE1 to 1.00 minute. Then
raise set point by 20
°
to 30
°
F, or 11
°
to 17
°
C. Observe the system's
approach to set point. If the load temperature overshoots set point, in-
crease rA1/dE1 to 2.00 minutes.
Then raise set point by 20 to 30
°
F, or 11 to 17
°
C and watch the approach to
the new set point. If you increase rA1/dE1 too much, 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, such as
when the sensor cannot directly measure the process. 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 CAL offset value you want. Calibration offset adds or subtracts degrees
from the value of the input signal.
NOTE:
An X applies to
either Hysteresis
1 or 2.
NOTE:
The cycle time (Ct1)
parameter will not
appear if Output 1
(Ot1) is a process
output.