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7.4 WATLOW Series 988 User’s Manual
Tuning, Manual Operation, Alarms and Error Codes, Chapter 7
Auto/Man
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 988 allows a negative output value
only when [`Ot1] or [`Ot2] (Output Menu) is set to [``CL] (cool).
Automatic operation provides closed-loop on/off or PID control. When the
operator transfers from a closed loop to an open loop, the Series 988 sets
the power level to the setting of the [FAIL] parameter. If [FAIL] is set to
[BPLS] the controller retains the power level from the closed-loop control.
When the Series 988 returns to closed-loop control, it restores the previ-
ous set-point process 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.
• If [FAIL] is set to [BPLS] and 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 988 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 out-
put, or outputs, remain stable — a bumpless, or smooth, transition. The
lower display changes from the set point to the % output value.
• If [FAIL] is set from [`=00] to [`100], the Series 988 switches to man-
ual operation at that percent power.
˜
NOTE:
When a sensor
opens, the con-
troller switches
from automatic to
manual operation.
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