Emerson Vission 20/20 Operation And Service Manual page 174

Appendix B • Vission 20/20 Application Procedures
In this example, during unloading cycle when suction
pressure falls below a value less than confi gured unload
rate 1 value (20 – 2 = 18 psig) for the time period of the
unload rate 1 timer , then the program picks the lowest
priority compressor (slave 3) from the list and starts un-
loading the compressor. The program unloads slave 3 as
per steps confi gured till it reaches its Min Cap setpoint.
Once slave 3 is unloaded to its Min Cap setpoint and
suction pressure is still not within deadband, then pro-
gram picks second lowest priority compressors (in this
case slave 2 - eligible active compressor) from all run-
ning compressors list and starts unloading it. Program
unloads slave 2 (eligible active compressor) to a point
where it can handle load of active compressor (running
at min cap).
After 2nd interval it can be seen that slave 2 can handle
load of slave 3 so slave 3 can be stopped. Program then
starts machine stop timer (150 sec ) for active compres-
sor (slave 3) and stops the same when timer is lapsed.
This process is continued till either setpoint is achieved
or all compressors are stopped.
During loading / unloading phase if the communica-
tion with any of the active / running / idle compressor
is lost then master compressor logs event for the same.
Compressor with errors / trip can be identifi ed with its
respective status symbol. The Master compressor acts
as trim compressor.
SLAVE EXPERIENCING A FAILURE
When a slave compressor experiences an operational
failure, then that slave will be is temporarily skipped dur-
ing the sequencing decisions. The slave will be placed
into a "Local" mode. The fault needs to be reset and
cleared before the compressor can be placed back into
the sequencing routine. The slave compressor can be
put back into remote mode for sequencing by pressing
Auto Start->Remote again on the slave compressor. It
will resume its "set" priority order and any future com-
mand to increase capacity of a slave compressor will re-
sult in the compressor being restarted.
1. Master experiencing a Failure
When the master compressor experiences an operation-
al failure, then the master will continue to sequence the
slave compressors based on the setpoints that are set in
the sequencing menu of the master compressor.
2. Power to master compressor turned off
If the power to the master compressor is turned off,
then the slave compressors that are currently being se-
quenced will experience a "Remote Comm Timeout"
– an indication that the slave has lost communication
to the master compressor. This takes approximately
B - 18
4 minutes to occur and the "Remote Comm Timeout"
message will be logged into the Event List on the slaves.
3. Future Program Release
Advanced Sequence Confi guration
Equalized Load Enable
• This selection on the master compressor will provide
the ability to equalize (or balance) the load between
compressors, allowing them to operate more ef-
fi ciently. Rather than have one compressor operate
at 70% and another operate at 30%, the balancing
algorithm with determine a more effi cient position
for all compressors online.
Sync
• This selection on the master compressor will provide
a means to broadcast all the master sequencing
parameters found on the master sequencing screen
(such as CFM, priority, step etc) to all slave com-
pressors on the network. This will provide an easier
way to setup a different compressor so that it can
Assumptions master status when operator enables it
as the new master.
Troubleshooting
1. If a slave compressor's status shows this
symbol, then the operator should check if the slave
compressor is in Remote Idle mode.
2. Check status symbols of all compressors on se-
quencing table.
3. Check errors / info log on event screen.
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0