10 – 5
Section 10
•
Compressor Sequencing
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
Process Control Setpoints - Temperature
The compressor sequencing screen defines settings that
are used by the master compressor for sequencing, de-
pending on the Process Control Mode.
When the Process Control Mode selected is Temperature,
sequencing uses temperature setpoints, see Figure 10-3.
TEMPERATURE SETPOINTS
Start Offset:
•
Defines the offset from the process temperature con
-
trol setpoint to start the slave compressor. If the pro-
cess temperature surpasses the start offset setpoint
and the master compressor’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 set-
point can be changed by logging on to “Compressor
Control” Screen.
Fast Load Temp Offset:
•
Defines the offset from the process temperature con
-
trol setpoint to monitor compressor load. If process
temperature surpasses this setpoint’s value then the
Figure 10-3. Compressor Sequencing Screen - Process Control Setpoints for Temperature
sequencing decisions are made according to Fast
Load Timer.
Fast Unload Pressure Offset:
•
Defines the offset from the process temperature
control setpoint to monitor compressor load. If pro-
cess temperature drops below this setpoint’s value
then the 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. Process
Temperature setpoints are monitored to identify which
one of the following timers to be used.
Slow Load Timer:
• If process temperature surpasses the process tem-
perature control setpoint then this timer’s value is
used to make periodic sequencing decisions.
Fast Load Timer:
• If process temperature surpasses the fast load temp
offset setpoint then this timer’s value is used to
make periodic sequencing decisions.
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