INSTRUMENTATION TOOLSPressureGauge Instrumentation
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How to Select a Pressure GaugeInstrumentationDesign
January31,2016
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SevenStepstoSelectaPressureGauge
1.ACCURACY
Foramechanicalpressuregauge,accuracyisdefinedasapercentageof the
fullscale range.While requirements differ fromone industry
toanother,thefollowingaregeneralguidelines:
Test Gauges and Standards: 0.25% through 0.10% full
scaleaccuracies.
CriticalProcesses:0.5%fullscaleaccuracy.
GeneralIndustrialProcesses:1.0%accuracy.LessCriticalCommercialUses:2.0%accuracy.
RefertoASMEB40.100formoreinformationonaccuracy.
2.DIALSIZE
Pressure gauge dial sizes range from less than 1 to 16
diameters.Generally, readability require ments, space limitations
and requiredgauge accuracy determine dial size. Accuracies of 0.25%
or
0.5%generallyhavedialsizesof412orlargersincemoredialgraduationsarerequired.
3.CASESTYLE/MATERIAL
Environmental considerations include ambient temperature,
airborne
particulate,condensation,humidity,waterandchemicals,allofwhichcanaffectgaugeperformance.
Ambient temperature may affect the accuracy and integrity of
thegauge.Gaugesareavailableeither
temperaturecompensatedornontemperature compensated. Ambient
conditions may require that thegauge be isolated from temperature
extremes. When required,
thegaugeshouldbeisolatedfromtemperatureextremeswithaflexiblelineassembly.
Whenambientconditionsarecorrosive,containa
largenumberofparticulateor if thegaugewill be exposed to awet or
humidenvironment like humidity,washdownsor rain, specify
agaugethatisweatherproof/hermeticallysealedorliquidfilled.
4.MEDIA/WETTEDPARTS
Thewettedpartsof thepressuregauge,
theBourdontubeandsocketmustbecompatiblewith theprocessmedia.
Ifnotcompatiblewith thewetted parts of the gauge, corrosion will
occur. Corrosion of gaugewetted parts will eventually cause gauge
failure and possibly safetyissues. When the gauge wetted parts are
not compatible with
theprocessmedia,adiaphragmshouldbeconsidered.
5.CONNECTIONSIZE
Gaugesareavailablewithavarietyofconnections includingNPT,DIN,
JIS, BSP & SAE. Process pressure gauges with 41 2
dialsizesorlargeraremostoftensuppliedwitha12NPTconnectionto best
support the gauge. Factors to consider when selecting
apressuregaugeconnection
includeprocesspressures,gaugesizeandweight,spacelimitations,leakintegrity,andpastexperience.
6.CONNECTIONLOCATION
Consider the following mounting options when selecting a
pressuregauge:
Stemmountlowerconnect
Wall/surfacemountlowerconnect
Panelmountbackconnect
Uclampflushmountbackconnect,forpanelmounting
Frontflangeflushmountbackconnect,forpanelmounting
7.PRESSURERANGES
ASME B40.100 recommends that normal operating pressure
beconfinedto25%75%ofthescale.Ifpulsationispresentintheprocess,maximumoperatinggaugepressureshouldnotexceed50%ofthefullscalerange.
CONCLUSION
To properly select a pressure gauge, consider the gauge process,
range,
environment,accuracy,dialsize,connectionandmountingrequirements.
AlsoRead:WorkingPrincipleofPressureGauge
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