Watlow Electric Micro-Based Autotuning Control SERIES 980/985 - Manual (Page 30)

Tuning - Manual
For optimum control performance, tune the Series 985 to the thermal system
The tuning settings here are meant for a broad spectrum of applications; your
system may have somewhat different requirements.
1.
2.
3.
4.
5.
6.
Apply power to the Series 965 and enter a set point. Begin with these
Operation Parameters: Pbl = 1, rE1 = 0.00, rA1 = 0.00, Ct1 = 5, CAL = 0,
AUt= 0.
ProportionaI 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. PB1 = 0; rE1 and rA1 are inoperative, and
the 985 functions as a simple ON/OFF control with a 3°F or 1.7°C switching
differential.)
Reset Adjustment: Gradually increase rE1 until the upper display tem-
perature begins to oscillate or “hunt”. Then slowly decrease rE1 until the
Upper display stabilizes again near set point. NOTE: This is a slow proce-
dure, taking from minutes to hours to obtain optimum value.
Cycle Time Adjustment: Set Ct1 as required. Optimum system control is
sometimes 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: lncrease rA1 to 1.00 min. 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, increase rA1 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 rA1 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 between that temperature, perhaps at another point
in the system, and the process value showing in the Upper display. Then
enter the amount of CAL offset you want. Calibration offset adds or sub-
tracts degrees from the value of the input signal.
Manual and Automatic Operation
To change from manual to auto operation, press the AUTO/MAN key twice.
Manual operation provides direct (time proportioned % power) control of the
outputs from -100% to 100%. A negative output value is allowed only with a Cl
(Cool) selection on either Otl or 0t2. Automatic operation provides closed loop
ON/OFF or PID control. When the operation transfers from a closed loop to an
open loop, the 985 retains the power level from the closed loop control. When
returning to the closed loop control, the previous set point temperature is
restored.
30 WATLOW series 98O/985 User’s Manual
Tuning and Operating, Chapter