Manual

8of16 MN301035 RevB
GETTINGSTARTED(continued) StepSix
HowdoesSpecificGravityaffectpressuretransmitters?
The Specific Gravity (SG) of a liquid will not change the pressure  of the transmitter, but will affect how the
transmitterreadstheliquidheight.Remember,liquids withaSQ<1.0arelighterthanwaterandliquidswith
aSG>1.0areheavierthanwater.
 WaterhasaSG=1.0.
 ASG<1.0requiresmoreliquid(atallerwatercolumn)toequalthesamepressureaswithwater.
 ASG>1.0requireslessliquid(shorterwatercolumn)toequalthesamepressureaswithwater.

SG=0.9

SG=1.0

SG=1.2
TocalculatetheMaximumLiquidHeightofasensor,usethefollowingformula:
MaximumLiquidHeight(feet)=(PressureRangex2.31)/SG
MaximumLiquidHeight(meters)=(PressureRangex0.704)/SG
Example:15psitransmitterinstalledinaliquidwithaSG=0.9willhavea
MaximumLiquidHeight=38.5feet(11.73m)or[(15psix2.31’/psi)/0.9=38.5’].
Note:TheaboveformulawillalwaysprovidetheMaximumLiquidHeightforanypressuretransmitter.
Example:ComparetheMaximumLiquidHeightofaliquidwitha
SG=0.9toonewithaSG=1.0.
 SG=0.9:a15psitransmitterwillhaveaMaximumLiquidHeight=38.5’(11.73m)
 SG=1.0:a15psitransmitterwillhaveaMaximumLiquidHeight=34.65’(10.56m)
AchangeinSGof0.1willincreasetheMaximumLiquidHeightofatransmitterby3.83’(1.2m).Thus,when
theSpecificGravityislessthan1.0,theMaximumLiquidHeightofthetransmitterwillincrease.
ThereverseistruebyincreasingtheSpecificGravity.Witha SG=1.2,theMaximum Liquid Height
=  28.88’
(8.80m)witha15psitransmitter
MaximumLiquidHeight(28.88’)=(PressureRange(15psi)x2.31)/SG(1.2)
Compare to a liquid with a SG = 1.0, the Maximum Liquid Height will decrease by 5.77’ (1.8 m).When the
SpecificGravityisgreaterthan1.0,
theMaximumLiquidHeightofthetransmitterwilldecrease.
Note:Identifyingthecorrectspecificgravityforthefluidiscriticalinunderstandingtheoperationalrangeof
thepressuretransmitter.
