BAC 3985C - Fan Control; Variable Frequency Drive Operation

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Fan Control
Resonant Speed
Identification Procedure
•
Asstatedpreviously,whenadjustingtheVFDspeed,proceedslowlywhilemonitoring
thevibrationlevels.Ifthevibrationvalueapproaches0.35ips(0-peak),slowly“zero
in”onthespeedwherethevalueequals0.35ips,andrecordthespeedatwhichthis
occursasthelowerendofthelockoutrange.Alsorecordthevibrationlevelatthis
speed.
• Continuetoslowlyincreasethespeedwhilemonitoringthevibrationlevel.Ifthisisa
resonance,thenthevalueshouldpeakandeventuallydecreasetoalevelthatisbelow
0.35ipsasthespeedisincreased.Afterthevibrationlevelhaspeakedandcontinues
tofall,recordthespeedwherethevalueequals0.35ipsastheupperendofthe
lockoutrange.
• Usingthisdata,abaselineforvibrationhistorycanbedeveloped.Thevibrationlevels
canbemonitoredyearlyandthetrendusedtoindicatepotentialwearortheneedto
replacecomponentsinthedrivesystem.
• Aftertheentirespeedrangehasbeencheckedandanyresonancesidentied,ensure
theVFDthatcontrolsthefanmotoristhenturnedoff,andthepowertothemotor
circuitislockedout.
• Entertheunit,andcarefullyremovetheaccelerometer,alongwithanyassociated
wiringfromtheunit.
• WorkwiththeVFDcontractortoenterthelockoutspeedrangesintotheVFD,sothe
unitwillnotoperateataresonantspeed.
• Onceithasbeenveriedthatthedrivesystemisallclear,returntheunittoitsnormal
operatingcondition.
• Keeparecordofanylockoutspeedrangesforfuturereference.