Emerson Vilter Vission 20/20 Operation And Service Manual page 235

Appendix B • Vission 20/20 Application Procedures
to the "Compressor Control" menu of the Master
Compressor.
Fast Load Offset
• Defines the offset from the control setpoint to moni-
tor compressor load. If suction pressure / process
temperature surpasses this setpoint's value then se-
quencing decisions are made according to the Fast
Load Timer.
Fast Unload Offset
• Defines the offset from the control setpoint to moni-
tor compressor unload. If suction pressure / process
temperature goes below this setpoint's value then
sequencing decisions are made according to Fast
Unload Timer.
Users below security level 2 (Supervisor) are not allowed
to edit the sequencing settings.
Example:
Pressure control setpoints for setpoint 20 psig,
Start Offset = 2 psig
Fast Load Pressure Offset = 4 psig
Suction Pressure setpoint = 20 psig
Fast Unload Pressure Offset = 4 psig
Slow Load Timer = 30 sec
Fast Load Timer = 15 sec
Slow Unload Timer = 30 sec
Fast Unload Timer = 15 sec
Assumptions:
• Master compressor is at 100% capacity
Suction pressure currently = 21 psig, so it falls within
start offset defined above. The sequencing will not start
and load highest priority slave when the suction pres-
sure is below start offset setpoint.
Now assume suction pressure currently = 23 psig, it is
above start offset, but less than fast load offset, so pro-
gram will start slave compressor and monitor suction
pressure every 30 sec (as per slow load timer).
Now assume suction pressure currently = 25 psig, it is
above fast load offset, so program will monitor suction
pressure every 15 sec (as per fast load timer).
Suction pressure currently = 17 psig, it is less than suc-
tion control setpoint, but greater than fast unload off-
set, so program will monitor suction pressure every 30
sec (as per slow unload timer).
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
Suction pressure currently = 15 psig, it is less than fast
unload offset, so program will monitor suction pressure
every 15 sec (as per fast unload timer).
COMPRESSOR SEQUENCING EQUIPMENT LIST
The first page of the Compressor Sequencing menu al-
lows the operator to view and adjust settings that are
used for sequencing the slave compressors, see Figure
B-7.
Min Trigger:
• Defines the Master's capacity value in percentage
which is used as a trigger to the step-wise decrease of
the slave compressor's capacity. Slave compressor's
capacity is decreased only if the Master is running
with capacity lower than set Min Trigger's value.
Max Trigger:
• Defines the Master's capacity value in percentage
which is used as a trigger to the step-wise increase of
the slave's compressor capacity. Slave compressor's
capacity is increased only if the Master is running
with capacity higher than set Max Trigger's value.
Equipment
• The options of this combo box are updated depend-
ing on devices shown in the Devices List Page. This con-
tains names of all the compressors in the network com-
municating with the Master compressor. Equipment
names can be selected from drop-down list. The same
Equipment name should not be configured more than
once in the sequencing table.
Examples of acceptable unique names:
• Master, slave no.1, slave no.2, comp no.1, comp no.2,
etc.
Control
• [ON/OFF] Inclusion/exclusion of a compressor par-
taking in the sequencing is decided on basis of this
toggle button. Operator can include / exclude com-
pressor by toggling the ON /OFF button.
Example:
The operator can configure all settings for a particular
slave compressor and set the control as OFF, so that it
won't be a part of sequencing steps. If the operator de-
cides to enable this compressor by selecting ON, then it
will be considered for the next load / unload cycle.
B - 17