Watlow Series 988LF - Manual (Page 49)

Tuning, Manual Operation, Alarms, and Error Codes, Chapter 7 WATLOW Series 988LF Users Manual 7.3
Manual and Automatic Operation
To change from auto to manual operation, press the Auto/Man key å
twice.
Manual operation provides open-loop control of the outputs from a range of
-100% to 100% output. The Series 988LF allows a negative output value
only when [`Ot1] or [`Ot2] (Output Menu) is set to [``CL] (cool). Auto-
matic operation provides closed-loop on/off or PID control. When the
operator transfers from a closed loop to an open loop, the Series 988LF
retains the power level from the closed loop control. When the Series 988LF
returns to closed-loop control, it restores the previous set-point value.
The Auto/Man LED (located on the Auto/Man key å) indicates whether
the controller is in automatic or manual operation. When the LED is lit, 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 controller switches from automatic to manual
operation.
• If the process has stabilized at a power level less than 75% ( ± 5%) for a
two-minute period prior to the sensor break, then the Series 988LF
switches to manual operation at the last automatic power level. If these
conditions are not met, the output goes to 0% power (output disabled).
When transferring from automatic to manual operation, the control output,
or outputs, remain stable — a bumpless, or smooth, transition. When
transferring from automatic to manual operation, the output value appears
in the lower display. In automatic operation, the set point appears.
Raise the set point by 20° to 30°F, or 11° to 17°C and watch the ap
proach to the new set point. If you increase [``rA] or [``dE] too
much, the approach to set point will be very sluggish. Repeat as
necessary until the system rises to the new set point without over
shooting or approaching the set point too slowly.
6. Calibration Offset Adjustment: You may want your system to control to
a process value other than the value coming from the input sensor. If
so, measure the difference between that process value (perhaps at
another point in the system) and the process value showing in the
upper display. Then enter the [`CAL] offset value you want. Calibra
tion offset adds or subtracts degrees from the value of the input signal.
Tuning