Emerson Vilter Vission 20/20, Operation And Service Manual

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B - 21
Appendix B • Vission 20/20 Application Procedures
Vission 20/20 • Operation and Service Manual • Emerson • 35391SC 2.7
setpoint for the time period of the unload timer, then a
calculation of the operating CFM of the slave compres-
sor is made. This value is compared against the available
CFM of the other running compressors. If enough CFM is
available, then the machine stop timer is started. When
it times out, and provided there is still enough CFM avail-
able from the remaining running compressors, the slave
compressor is stopped.
In the example below, during the unloading cycle when
suction pressure falls below a value less than the suc-
tion control setpoint value (20 psig) for the time period
of the unload 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 configured till it reaches its Min Cap setpoint.
Once slave 3 is unloaded to its Min Cap setpoint and suc-
tion pressure is still below suction control setpoint, then
the program picks the second lowest priority compres-
sors (in this case slave 2 - eligible active compressor)
from all running compressors list and starts unloading
it. The program unloads slave 2 (eligible active compres-
sor) to a point where it can handle the load of active
compressor (running at min cap).
After the 2nd interval, it can be seen that slave 2 can
handle the load of slave 3 so slave 3 can be stopped.
The program then starts machine stop timer (120 sec)
for the active compressor (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 the 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 identified 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 opera-
tional failure, then it 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 1 min-
ute to occur and the “Remote Comm Timeout” message
will be logged into the Event List on the slaves.
3. Future Program Release
Advanced Sequence Configuration
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 effi -
ciently. Rather than have one compressor operate at
70% and another operate at 30%, the balancing algo-
rithm will determine a more efficient position for all
compressors online.
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 the status symbols of all compressors on the
sequencing table.
3. Check errors / info log on the compressor sequenc-
ing event log screen.