Watlow Series 965 - Manual (Page 23)

Tuning and Operating, Chapter 5 WATLOW Series 965 User's Manual
23
Tuning/Operation
to minimize wear on the mechanical components. Experiment until the
cycle time is consistent with the quality of control you want. Ct will not
appear on units with a process output.
5. Rate/Derivative Adjustment: Increase rA/dE 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, increase rA/dE to
2.00 minutes.
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 rA/dE1 too much, approach to set point is
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 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.
Manual and Automatic Operation
To change from auto to manual operation, press the A/M key twice.
Manual operation provides open loop control of the outputs from a range of
-100% (full cooling) to 100% (full heating) power. The 965 allows a negative
output value only with a Cl (Cool) selection on either Ot1 or Ot2 = Con. Auto-
matic operation provides closed loop on/off or PID control. When the operator
transfers from a closed loop to an open loop, the 965 retains the power level
from the closed loop control, referred to as bumpless transfer. When the 965
returns to closed loop control, it restores the previous set point temperature.
The MN LED indicates auto or manual operation. When the LED is on, the
control is in manual operation. When the LED is off, it is in automatic operation.
When the LED flashes, press the key again within five seconds to complete the
change in operation.
When a sensor opens, the 965 switches from automatic to manual operation if
LOC = 0, 1 or 2.
• If LOC = 0, 1 or 2 and the bumpless transfer conditions are met, process has
stabilized at a
±
5% power level for a 2 minute period prior to sensor break
provided the power level is less than 75%. The 965 switches to manual
operation at the last automatic power level.
• If LOC = 3 or 4, the 965 switches into manual operation at 0% power (outputs
disabled).
When transferring from auto to manual operation, the control output(s) remains
stable ("bumpless," smooth transition). When transferring from manual to
automatic operation, the control output(s) may change significantly. In manual
operation, the output value appears in the lower display; in automatic operation,
the set point appears.
NOTE:
Process input does
not have sensor
break protection or
bumpless transfer.
Outputs selected as
Ht (reverse acting)
will be full on if
sensor break
occurs.