Emerson Vilter Vission 20/20 Operation And Service Manual page 103

Section 10 • Compressor Sequencing
Suction Pressure Control Setpoints
The Compressor sequencing screen defines settings that
are used by the master compressor for sequencing. For
Suction Pressure Control Setpoints see Figure 10-2.
PRESSURE SETPOINTS
Start Offset:
• Defines the offset from suction pressure control set-
point to start slave compressor. If suction pressure
surpasses start offset setpoint and master compres-
sor's capacity has reached max trigger setpoint, then
the sequencing algorithm allows the starting and
loading of slave compressors to cater for increasing
load requirements.
Setpoint:
• The target setpoint is a read-only value here. This
setpoint can be changed by logging on to the
"Compressor Control" Screen.
Fast Load Pressure Offset:
• Defines the offset from suction pressure control set-
point to monitor compressor load. If suction pressure
surpasses this setpoint's value then sequencing deci-
sions are made according to the Fast Load Timer.
Fast Unload Pressure Offset:
• Defines the offset from suction pressure control set-
point to monitor compressor load. If suction pressure
Figure 10-2. Compressor Sequencing Screen - Suction Pressure Control Setpoints (Page 2)
10 – 4
drops below this setpoint's value then sequencing
decisions are made according to Fast Unload Timer.
CAPACITY LOAD/UNLOAD TIMERS
One of the following Capacity Load/Unload timers is
used to make sequencing decisions periodically. Suction
Pressure setpoints are monitored to identify which one
of the following timers will be used.
Slow Load Timer:
• If suction pressure surpasses the suction pressure
control setpoint then this timer's value is used to
make periodic sequencing decisions.
Fast Load Timer:
• If suction pressure surpasses the fast load pressure
offset setpoint then this timer's value is used to make
periodic sequencing decisions.
Slow Unload Timer:
• If suction pressure drops below the suction pressure
control setpoint then this timer's value is used to
make periodic sequencing decisions.
Fast Unload Timer:
• If suction pressure drops below the fast unload pres-
sure offset setpoint then this timer's value is used to
make periodic sequencing decisions.
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7