Sartorius YDK04 Betriebsanleitung Seite 10

Air Buoyancy
Dependingonthetemperature,humidity
andairpressure,a1cm
haveaweightofaround1�2mg�When
weighinginair,theobjectexperiences
acorrespondingbuoyancypercm
volume�Theerrorthatresultsiftheair
buoyancyisnotallowedforshowsupin
thethirddecimalplaceandshould
thereforebecorrected�
Thebuoyancyforceistakenintoaccount
inthefollowingformula:
 W(a)∙[ρ (fl)–ρ(a)]
ρ=
 W(a)–W(fl)
Whereρ(a)=0�0012g/cm
airundernormalconditions(temperature
20°C,pressure101�325kPa)�
10 10
3
volumeofairwill
3
ofits
+ρ (a)�
3
=densityof
Immersion Depth
Thesampleholdertocollectand/or
immersethesampleduringtheweighingin
liquidisfastenedrigidlytotwowiresand
plungesabout30mmdeepintotheliquid�
Sincethebalanceistaredpriortoeach
measurement,theadditionalbuoyancy
fromthesubmergedpartofthe
measurementsetupisnotfactored
intothedeterminationofthedensity�
Whenweighinginliquid,avolumeof
liquidcorrespondingtothevolumeofthe
samplebodygetsdisplaced�
Thiscausesthefasteningwiresonthepan
toplungedeeperandgenerateadditional
buoyancy,creatinganerrorinthedensity
determination�
Thefollowingformulawillcorrectthe
error:
 W(a)∙[ρ(fl)–ρ(a)]
ρ=
 Corr[W(a)–W(fl)]
+ρ(a)