Emerson Vission 20/20 Operation And Service Manual page 170

Appendix B • Vission 20/20 Application Procedures
Unload Rate 2 Offset (Outer)
• Defi nes the outer pressure setpoint offset to moni-
tor compressor unload. If Suction pressure / proc
temp goes surpasses the Control Setpoint minus
unload rate 1 offset and then goes beyond Control
Setpoint minus unload rate 2 offset then sequencing
decisions are made according to unload rate 2 timer.
Users below security level 2 (Supervisor) are not allowed
to edit the sequencing settings.
Example:
Pressure control setpoints for setpoint 20 psig,
Load Rate 2 Offset (Outer) = 4 psig
Load Rate 1 Offset (Inner) = 2 psig
Suction Pressure setpoint = 20 psig
Unload Rate 1 Offset (Inner) = 2 psig
Unload Rate 2 Offset (Outer) = 4 psig
Timers:
Load Rate 1 (Inner) = 30 sec
Load Rate 2 (Outer) = 20 sec
Unload Rate 1 (Inner) = 25 sec
Unload Rate 2 (Outer) = 20 sec
Assumptions:
• Master compressor is at 100% capacity
• Slave compressor has started and loaded to its mini-
mum capacity setpoint
Suction pressure currently = 21 psig, so it falls within
deadband region defi ned above. The sequencing will
stop loading / unloading when the suction pressure is
within deadband.
Now assume suction pressure currently = 23 psig, it is
beyond load rate 1 offset, but less than load rate 2 off-
set, so program will monitor suction pressure every 30
sec (as per load rate 1 timer).
Suction pressure currently = 17 psig, it is less than un-
load rate 1 offset, but greater than unload rate 2 offset,
so program will monitor suction pressure every 25 sec
(as per unload rate 1 timer).
COMPRESSOR SEQUENCING EQUIPMENT LIST
The last 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.
Equipment
• Options of this combo box are updated
B - 14
automatically. This contains names of all the com-
pressors in the network communicating with the
Master compressor. Operator can select Equipment
name from drop down list. Operator should make
sure that same equipment name is not repeated in
the table. If it is, rename the offending slave(s).
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
partaking in the sequencing is decided on basis of
this toggle button. Operator can include / exclude
compressor by toggling the ON /OFF button. Note:
The master compressor is always "ON" and cannot
be deselected.
Example:
The operator can confi gure 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.
Switching a slave compressor control to OFF
while it is running in auto sequencing mode puts
the respective slave compressor into local auto
mode. This feature is used to add / remove slave
compressors to sequence table when running in
auto sequence mode. The slave compressor can
be put back into remote mode for sequencing by
pressing Auto Start->Remote again on the slave
CFM
• CFM column is a read only fi eld ( it is not settable ).
These values are updated automatically when a slave
compressor is selected from the Equipment combo
box. The value shown is the compressor's capacity
in CFM. The CFM is used to determine when there
is enough "system" compressor capacity available
so that the master can shut a slave compressor off
without causing slave compressor cycling.
PRIORITY
• This defi nes priorities of compressors on the net-
work. This priority will decide the sequence order in
which compressors will be turned on and off during
sequence cycle. The lower the priority number, the
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0
NOTE
compressor.