Tuning – Watlow Series 922 User Manual

Page 37

How To Tune and Run the Series 922, Chapter 5

WATLOW Series 922 User's Manual

Tuning

Tuning

For optimum control performance, tune the 922 to the thermal system. The
tuning settings here are meant for a broad spectrum of applications; your
system may have somewhat different requirements. Refer to the key flow
charts, diagrams and definitions on Pages 42 - 61 for prompt location and
description. Repeat this tuning procedure for both Channel 1 and 2.

NOTE:
When tuning in the Heat mode, use PID prompts followed by H.
When tuning in the Cool mode, use PID prompts followed by C.

Apply power to the Series 922 and enter a set point in the SYSTEM,
menu. Next, go into the SETUP mode, and enter ACCESS (1), the
SPCLFUNC (Special Function) parameter. Using the MODE, UP/DOWN,
and ENTER keys, set the Operating Parameters initially: (Proportional
Band) PB_H (C) = 0, (Reset) RS_H (C) = 0.00, (Rate) RT_H (C) = 0.00,
(Cycle Time) CT_H (C) = 5. Under ACCESS (0) enter CAL_ = 0.

Allow actual process temperature to stabilize at or near Set Point (SP). The
ACTUAL display will indicate when the load is stabilized near setpoint.

Proportional Band Adjustment: Gradually increase PB until the ACTUAL
display temperature stabilizes to a constant value. The temperature will
not be right on set point because the initial reset value is 0.00 repeats per
minute. The ACTUAL temperature will stabilize below the desired setpoint.
(When PB = 0, RS, RT, and CT are inoperative, and the 922 functions as a
simple ON/OFF control with a 3

F or 1.7

C switching differential.)

Reset Adjustment: Gradually increase RS until the ACTUAL display
temperature begins to oscillate or "hunt". Then slowly decrease RS until
the ACTUAL display stabilizes again near set point NOTE: This is a slow
procedure, taking from minutes to hours to obtain optimum value.

Cycle Time Adjustment: Set CT as required. Optimum system control is
always achieved with faster cycle times. 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.

Rate Adjustment: Increase RT to 0.10 min. Then raise SP by 20

F, or 11

to 17

C. Observe the system's approach to SP. If the load

temperature overshoots SP, increase RT to 0.20 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.

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

F or

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.

After you have tuned your Series 922, continue to Chapter 6 to learn how to
Program your Series 922 for your system.