Watlow Electric 93 - Manual (Page 29)

W a t l o w S e r i e s 9 3 T u n i n g a n d O p e r a t i n g ■ 5 . 3
Tuning and Operating
Manual and Automatic Operation
To change from auto to manual operation, press the ˆInfinity key twice.
Manual operation provides open loop control of the outputs from a range of -100%
(full cooling) to 100% (full heating) power. The Series 93 allows a negative output
value only when [`Ot2] is set to [`Con]. Automatic operation provides closed-
loop on-off or PID control. When the operator transfers from a closed-loop to an
open loop, the Series 93 retains the power level from the closed-loop control,
referred to as bumpless transfer. When the Series 93 returns to closed-loop con-
trol, it restores the previous set point temperature.
The percent indicator light indicates auto or manual operation. When the percent
indicator light is on, the control is in manual operation and displays the percent
power value in the lower display. When the percent indicator light is off, it is in
automatic operation. Press the ˆInfinity key to flash the percent indicator light.
Press the ˆInfinity key again to complete the manual/automatic change.
When a sensor opens, the Series 93 switches from automatic to manual operation
if [`LOC] is set to 0, 1 or 2.
•If [`LOC] is set to 0, 1 or 2 and the bumpless transfer conditions are met, the
Series 93 switches to manual operation at the last automatic power level. The
bumpless transfer conditions are: the process has stabilized within a ± 5%
power level for at least two minutes prior to sensor break provided the power
level is less than 75%.
•If [`LOC] is set to 3 or 4, the Series 93 switches into manual operation at 0%
power (outputs disabled).
When transferring from auto to manual operation, the controller output(s)
remains stable ("bumpless," smooth transition). When transferring from manual
to automatic operation, the controller output(s) may change significantly. In
manual operation, the output value appears in the lower display; in automatic
operation, the set point appears.
NOTE:
A process input does
not have sensor break
protection or bump-
less transfer. Outputs
selected as [``ht]
(reverse acting) will
be full on if a sensor
break occurs.