Emerson Vilter MicroVission - Page 234

C - 4
MicroVission Controller • Operation and Service Manual • Emerson • 35391MV 1.3
Appendix C • Remote Control and Monitoring
NOTE
Offset is used at Load Step % and is 5%.
NOTE
Once Compressor is Loading or Unloading a step,
next step would be allowed to Load or Unload
respectively only after 5 seconds.
Cap Hold Operation with VFD:
Using a VFD with a compressor requires considering the
VFD capacity as part of the entire capacity of the com-
pressor.WhenCapacityHold%valueisvariedfrom0%
to 50% compressor capacity is varied based on unloader
steps and when Capacity Hold % value is varied from 50%
to 100%, compressor capacity is varied based on the VFD
speed.Hencetheunloaderstepsareconsideredtherst
½ of the total capacity and VFD is considered as the oth-
er½ofthetotalcapacity.WhenaVFDisemployed,the
normalcontrolmethodistorstmovethestepsfrom
0% - 100% (i.e. rst½ofthetotal capacity)andwhen
additional capacity is still required, then the VFD speed
is ramped up from 0% - 100% (i.e. other ½ of the total
capacity)Whencapacityneedstoberemovedfromthe
system,rstVFDspeedisrampeddowntill0%andthen
unloader steps are removed.
Forexample,IfthenumberofUnloadersconguredin
conguration screenis4(25%,50%,75%,100%),then
Load Steps would be 0%, 25%, 50% & 75%. Progress
bar on Main Screen should display the total capacity at
which the compressor is currently operating. The rules
of capacity hold algorithm with VFD are:
1. If Capacity Hold % value is greater than or equal to
((Next Load Step % - Offset) / 2), step will be added.
WhenCapacityHold%valueisabove10%((25–5)
/ 2), then unloader steps would be loaded at 25%
and progress bar should be loaded at 12% (25 / 2),
referFigureC-5.WhenCapacityHold%valueisabove
22.5% ((50 – 5) / 2), then unloader steps would be
loaded at 50% and progress bar should be loaded at
25%(50/ 2). WhenCapacityHold % valueis above
35% ((75 – 5) / 2), then unloader steps would be load-
ed at 75% and progress bar should be loaded at 37%
(75/2).WhenCapacityHold%valueisabove47.5%
((100 – 5) / 2), then unloader steps would be loaded
at 100 % and progress bar should be loaded at 50%
(100 / 2) i.e. ½ of the total capacity. Once unloader
steps are loaded to 100%, it constitutes ½ of the to-
tal capacity (i.e. 50%), then if Capacity Hold % value
goes above 50%, VFD speed will start ramping up and
progress bar should be loaded at Capacity Hold % val-
ue. For example, when Capacity Hold % is set to 75%,
then unloader steps would be loaded at 100% & VFD
Speed would be set at 50% (VFD Output at 12 mA)
and progress bar should be loaded at 75% ((100 + 50)
/ 2). VFD Speed would be at maximum (VFD Output
at 20 mA) when Capacity Hold % value is set at 100%.
2. If Capacity Hold % value is varied from 100% to 50%,
VFD speed would be ramped down from 100% till
0%. VFD Speed would be at minimum (VFD Output
at 4 mA) when Capacity Hold % value is set at 50%.
If Capacity Hold % value goes below 50%, then un-
loader steps will start getting removed. If Capacity
Hold % value is less than or equal to ((Previous Load
Step % + Offset) / 2), step will be removed. When
Capacity Hold % value is below 40% ((75 + 5) / 2),
then unloader steps would be loaded at 75% and
progressbarshouldbeloadedat37%(75/2).When
Capacity Hold % value is below 27.5% ((50 + 5) / 2),
then unloader steps would be loaded at 50% and
progressbarshouldbeloadedto25%(50/2).When
Capacity Hold % value is below 15% ((25 + 5) / 2), then
unloader steps would be loaded at 25% and progress
barshouldbeloadedat12%(25/2).WhenCapacity
Hold % value is below 2.5% ((0 + 5) / 2), then unloader
steps would be loaded at 0% and progress bar should
be loaded at 0%.
3. If Capacity Hold % value varies within the range of
((Previous Load Step % + Offset) / 2) and ((Next Load
Step % - Offset) / 2), then unloader step would not
varyandwouldstayatcurrentstep.WhenCapacity
Hold % value is greater than 15% ((25 + 5) / 2) and
lesser than 22.5% ((50 - 5) / 2), then unloader steps
would be loaded at 50% and progress bar should be
loaded at 25% (50 / 2). This is only applicable when
Capacity Hold % value is varying from 0% to 50%.
Modbus Register 40177 - Active Setpoint
This register is used in conjunction with Register 40172
= 0, Auto Control mode.
• 1 = Setpoint #1 Active
• 2 = Setpoint #2 Active (note: you must enable two
setpointsfromcongurationscreenrst).
Sometimes compressors are switched from Suction
Pressure control mode to Process Temp control mode or
vice versa. This can be done via communications using
the following register.
Modbus Register 40173 - Auto Capacity Control Type
• 0=SuctionPressure(ifenabledfromConguration
screen)
• 1 = Process Temp (if enabled from Conguration
screen)
• 2=DischargePressure(ifenabledfromConguration
screen)