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Section 5 • Compressor Control
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
Example Operation:
Assume the current Suction Pressure value is at 85 psig
and the setpoint we want to get to is 20 psig. The op-
erator wants to allow 48 hours of pulldown time. Pick a
reasonable step pressure of 5 psig for every step. This de-
nes a change of (80 – 20 = 60) psig.
1. Note: the rst step is applied immediately. So, rst
step starts at (85 – 5 = 80) psig
2. Number of steps = delta (60 psig change * 1 step/5
psig) = 12 steps.
3. Delay per Step = (48 hours / 12 steps) = 4 hours/
step.
4. So for the rst 4 hours, the compressor runs at 80
psig.
5. Next 4 hours @ 75 psig
6. Next 4 hours @ 70 psig
7. And so forth.
After the 12th step (running at 25 psig), 48 hours will
have elapsed, and the new pulldown setpoint becomes
20 psig, achieving the 20 psig setpoint after 48 hours.
After the pulldown setpoint is equal to Pulldown Stop
Pressure, the pulldown operation will complete after
three minutes.
When the Pulldown feature is enabled, the Pumpdown
checkbox is automatically grayed out. Similarly, when
the Pumpdown feature is enabled, the Pulldown check-
box is automatically grayed out and hence, the user will
not be able to operate the Pulldown feature. This is done
to keep the Pulldown and Pumpdown features mutually
exclusive.
NOTE
If the Run Mode is changed while Pulldown is
running, the Pulldown Operation will stop running.
NOTE
If the Pulldown Operation is running and the
compressor is stopped due to auto cycle, the
pulldown operation will continue to run, even
though the compressor run mode will not be Local
Auto / Direct I/O Auto.
NOTE
If the Pulldown feature is enabled but the
compressor is started in Manual or Remote mode
or in Process Control 2 or Suction Pressure 2 control
mode, then the Pulldown Operation will not run
until compressor is stopped and started again in
Local Auto / Direct I/O Auto run mode and Suction
Pressure 1 / Process Control 1 control mode.
NOTE
If the Pulldown feature is enabled after the
compressor is started in Local Auto / Direct I/O Auto
run mode with Suction Pressure 1 / Process Control
1 control mode, then the Pulldown Operation will
not run until compressor is stopped and started
again in Local Auto / Direct I/O Auto run mode and
Suction Pressure 1 / Process Control 1 control mode.
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