Emerson Vission 20/20 Operation And Service Manual page 171

Appendix B • Vission 20/20 Application Procedures
greater the priority of the compressor. Operator
should choose the priorities of the compressors.
Example:
"1" is highest priority.
Compressor with priority "2" has higher priority than
compressor with priority "4".
STEP
• This parameter defi nes the size of the capacity
step, for a slave compressor, that will occur when a
change in capacity is needed. The step is defi ned as
a percentage of the compressor capacity. In the case
when last step makes total capacity greater than
maximum capacity (Max Cap) setpoint, the total
capacity will get reduced to maximum capacity set-
ting. Same is applicable when last step makes total
capacity lower then minimum capacity (Min Cap)
setpoint. The Min Cap setting will take priority.
Example:
Confi gured step = 20 %
Confi gured min cap = 10 %
Confi gured max cap = 80 %
Program starts loading slave compressor in steps of
20 %, so every interval values will be,
Interval 1 – 10 % (min cap)
Interval 2 – 10% + 20% = 30 %
Interval 3 – 30% + 20% = 50 %
Interval 4 – 50% + 20% = 70 %
Interval 5 – 70% + 20% = 90 % (which is more than
max cap, so last step will be 80%)
MIN CAP / MAX CAP (slave compressors)
• Defi nes the lowest and highest capacity in percent-
age with which a slave compressor is allowed to run.
Minimum capacity value takes preference on fi rst
step value. Maximum capacity value takes prefer-
ence over last step value.
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0
Example:
Confi gured step = 5 %
Confi gured min cap = 10 %
Confi gured max cap = 80 %
Program starts loading compressor in steps of 5 %,
so every interval values will be,
Interval 1 – 10 % (min cap)
Interval 2 – 10% + 5% = 15 %
Interval 3 – 15% + 5% = 20 %
Interval 4 – 20% + 5% = 25 %
.
.
Last Interval – 75% + 5 % = 80 % = ( max cap)
MIN CAP / MAX CAP (master compressor)
• Defi nes the "trigger" points at which the master
will begin to make decisions to either start or stop
another compressor. Unlike the slave compressor(s)
Min and Max Cap values, which actually "limit"
capacity, the master compressor can and will load
and unload past its Min and Max Cap value setpoints
– which act as sequencing "trigger" points.
MAX CAP (master)
• When master compressor reaches the "Max Cap"
setpoint and the suction pressure is more than a
value of load rate 1 offset, then the master starts the
machine start timer to start the next priority slave
compressor available.
Max Cap (master) Example:
Confi gured max cap of master compressor = 80 %
Load Rate 1 Offset (Inner) = 2 psig
Suction Pressure Setpoint = 20 psig
Suction Pressure Currently at 23 psig
Master Compressor Capacity at 85 %.
At this point, the Master compressor will start the ma-
chine start timer to start the next priority slave compres-
sor available.
MIN CAP (master)
• When master compressor reaches its "Min Cap"
setpoint and the suction pressure is less than a
value of unload rate 1 offset for the time period of
the unload rate 1 timer, then the master will adjust
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