Emerson Vilter MicroVission - Pulldown Control

5 – 16
Section 5 • Compressor Control
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
Pulldown Control
The Pulldown Control denes a method of slowly pulling
the suction pressure/process control down from a high
value. This is sometimes required on systems that have
liquid recirculation systems or on new building to prevent
structural damage by limiting the rate at which the build-
ing should be cooled.
This feature can be enabled or disabled from this page, see
Figure 5-14. If Pulldown is enabled, this feature will only
function when the compressor is running in Local Auto
/ Direct I/O Auto mode and when the Control mode is
Suction Pressure 1 / Process Control 1.
The Pulldown feature provides a method to slowly pull
the suction pressure / process control down to operating
conditions. The pulldown method used is to step the suc-
tion pressure / process control down over a dened time
interval.
If the Pulldown Operation is running, then;
• Compressor will load/unload as per the Pulldown
Setpoint. i.e. Pulldown Setpoint will act as Control
setpoint instead of Suction Pressure Control
Setpoint / Process Control Setpoint.
• For Suction Pressure, Pulldown Auto Cycle Start
Pressure and Pulldown Auto Cycle Stop Pressure
will be used to start and stop the compressor us-
ing auto cycle instead of Suction Pressure Auto
Cycle Start and Stop Pressure.
• For Process Temperature, Pulldown Auto Cycle
Start Temperature and Pulldown Auto Cycle
Stop Temperature will be used to start and stop
the compressor using auto cycle instead of
Process Temperature Auto Cycle Start and Stop
Temperature.
Pulldown operation can be aborted through –
• Switching Run Mode to Manual / Remote from
Auto run Modes.
• Switching the Active Control Mode from any
other.
• When Compressor is Stopped due to Trip or on
press of ‘Stop’ button.
If Suction Pressure is already below Pulldown Stop
Pressure Setpoint during Compressor Start, Pulldown
Operation will not start. Similarly, If Process Temperature
is already below Pulldown Stop Temperature Setpoint
during Compressor Start, Pulldown Operation will not
start.
Figure 5-14. Compressor Control Screen – Pulldown Control
(Active Control Mode – Suction Pressure SP1)