Watlow Series 920 Microprocessor-Based Ramping Control Manual de usuario descargar pdf (Pagina 34)

Tuning

For optimum control performance, tune the 920 to a 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 and dia-

grams and definitions on Pages

41,45

47 for prompt location and description.

NOTE:

When tuning in the Heat

mode, use

PID

prompts followed by H. Set the set

point above ambient.

When tuning in the Cool mode, use

PID

prompts followed by C. Set the set

point below ambient.

Apply power to the Series 920 and enter a set point in the SYSTEM

menu. Next, go into the SETUP mode, and enter ACCESS (1), the

PID

parameter Using the MODE, UP/DOWN, and ENTER keys, set the

Operat-

ing 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, (Rate band) RBH

(C)

2. Under ACCESS (0) enter CAL

Allow actual process temperature to stabilize at or near Set Point (SP). The

ACTUAL display will indicate when the load is stabilized near set point.

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. When tuning in the heat mode, the ACTUAL temperature will

stabilize below the desired set point. When tuning in the cooling mode, the

ACTUAL temperature stabilizes above set point. (When PB

RS,

RT,

and CT are inoperative, and the 920 functions as a simple ON/OFF control

with a 3°F or 1.7°C switching

differential.)

Reset Adjustment: Gradually increase

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 1.00 min. Then raise SP by

20°

WATLOW

Series 920 User’s

Manual

HowToTune The Series 92O,Chapter5

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Watlow Series 920 Microprocessor-Based Ramping Control Manual de usuario Pagina 34

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