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  • Burns Engineering Measuring Temperature in Small Diameter Lines

    Measuring Process Temperature in Small Diameter Lines

    If you are experiencing audio problems please call the teleconference number below

    1-408-600-3600Access code 666 378 461

    Bill Bergquist, Sr. Applications EngineerJeff Wigen, National Account Manager

    Bill Jeff

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Accurate temperature measurement of fluids in 0.25 to 4.0 inch diameter lines can be difficult to achieve . . . Without proper selection and installation, even the most accurate sensing devices can have measurement errors of several degrees.

    Introduction

    Installationerrorsarethemostsignificanterrorsourcewhenmeasuringtemperatureinsmalldiameterlines.Therearemethodstoovercometheseerrorsandachieveanaccuratemeasurement.BurnsEngineeringwroteapaperonthistopicwhichthispresentationroughlyfollows.Youmaydownloadacopyathttp://www.burnsengineering.com/techpapers/

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Why?

    5.0 and larger diameter lines can typically be effectively measured with a traditional installation

    In most cases this utilizes 4.5 of immersion to achieve a sufficiently accurate measurement

    Obviously smaller diameter lines dont allow for this depth of immersion

    Therefore special installations are required to get accurate temperature measurements

    http://www.burnsengineering.com/tech-papers/

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    By choosing the proper piping design, selecting the correct sensor, and installing it correctly you can achieve the following in your small diameter line application: Higher measurement accuracy More consistent, higher quality product Fewer start-up and validation issues More efficient use of energy

    Introduction

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    What well cover today Technologies Terms and basic physical principles Key factors in selection and installation Application and installation details

    Agenda

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    RTDs/PRTsFeatures

    Accuracy Traceability Stability Repeatability

    ThermocouplesFeatures

    Durability Tip sensitive Time response

    Technologies

    TheRTDwill,inmostcases,providethebestcombinationofaccuracy,repeatability,andlongtermstability.Thermocouplesworkwellforhightemperatureapplicationsorwhereextremedurabilityisrequiredduetovibrationorshockpresentintheprocess.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Accuracy is the degree of conformity of a measured or calculated quantity to its actual (true) value.

    Includes error sources such as interchangeability, hysteresis, drift, self heating, and others.

    Terms and Physical Principles

    Aquickreviewofafewtermsusedthroughoutthispresentationisnecessary.Accuracy,interchangeability,timeresponse,andrepeatabilityarethemostimportant.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Interchangeability (largest component of accuracy)Refers to the closeness of agreement in the resistance vs. temperature (R vs. T) relationship of a PRT to a pre-defined nominal R vs. T relationship.

    Terms and Physical Principles

    Becausenothingisperfect,manufacturersrequireatolerancebandtoproduceRTDs.ASTMandIEChavecreatedspecificationsthatdefinesomeperformancecharacteristics.InterchangeabilityisthelargestcomponentofaccuracyandisthetargetmanufacturersshootforwhenadjustingtheicepointresistanceofanRTDsensingelement.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    ThisisthegraphicalformofthetolerancebandsforthetwoRTDstandards.TheASTMhasslightlytightertolerancesthantheIECstandard.WhenspecifyinganRTDchoosetheClassAorGradeAinterchangeabilityforthebestoutofboxaccuracy.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    RepeatabilityThe ability to give the same measurement under repeated, matched conditions.

    Repeatability in Temperature MeasurementsUsually quantified as a percent change of the resistance at 0C after many cycles through the temperature range.

    Terms and Physical Principles

    NexttointerchangeabilitythisisthemostimportantRTDperformancecharacteristic.Combinedwithlongtermstabilitythesearethemostdesirablecharacteristicsforanaccuratemeasurement.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Accuracy and Repeatability

    Lucky Accurate

    Repeatable Accurate and Repeatable

    Ananalogyforaccuracyandrepeatabilityisillustratedwitharrowsshotatatarget.Hittingthebull'seyetimeaftertimerepresentsgoodaccuracyandrepeatability.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Time ResponseGetting the sensor to follow as close to the process as possibleTime constant time required for the sensor to respond to 63.2% of a step change in temperature while in water moving at 3 fpsThe less thermal resistance between the sensor and the process, the better.

    Thinner sheaths Direct immersion sensors

    Terms and Physical Principles

    Timeresponsecanbealargesourceoferrorinanytemperaturemeasurement.Errorsofseveraldegreesarepossibleifthesensorresponsedoesnotkeepuptotheprocesstemperature.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Technologies and ScopeTerms and Basic Physical PrincipalsKey Factors in Selection and InstallationApplication and Installation Details

    Agenda

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    SensorInterchangeabilityStabilityRepeatability

    MaintenanceRemovable Sensor

    Calibration Replacement

    Thermowell

    Key Factors in Selection and Installation

    InstallationTime responseStem conductionAmbient conditions

    CostGoal is to achieve lowest life cycle cost

    Installation Calibration Replacement

    Wellfocusonthesensorandinstallationfactors.Theyrepresentthemajorityofthefactorsaffectingmeasurementaccuracy.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    CalibrationMatching to RTDSystem

    InstrumentationTransmitterController/PLC

    Key Factors in Selection and Installation

    Calibrationcanbeusedtodecreasesomeoftheinterchangeabilityerror.Includingthemeasurementsysteminthecalibrationloopcanimproveaccuracybyupto85%.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    A good installation will ensure:Accurate and repeatable measurementsHigh quality productEase at start-up

    A poor installation will result in:Uncertain product qualityWasted energyAdded uncertainties to the measurement point

    Key Factors in Selection and Installation

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Technologies and ScopeTerms and Basic Physical PrincipalsKey Factors in SelectionApplication and Installation Details

    Agenda

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Traditional InstallationMinimum recommended insertion

    Surface Mount SensorsNon-intrusive, or prepackaged options

    Direct Immersion SensorsDifferent installation considerations

    Thermowell InstallationsAlso referred to as indirect immersion

    Types of Installations

    Nextwelllookatthevarioustypesofinstallationsanddiscusssomeofthefeaturesandbenefitsofeach.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Traditional Installation

    85F

    10 x Assembly Diameterplus sensitive lengthAvoid stem conduction errors

    Aruleofthumbforminimumimmersionlengthtoavoidstemconductionerroris10timestheprobediameterplusthesensitivelengthoftheprobe.MostRTDshaveasensitivelengthof1.0.SoforadiameterRTDtheminimumrecommendedimmersionis3.5.Thermowellsrequireabout4.5asaminimumforbestaccuracy.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Direct Immersion

    Fluid

    SENSOR INSTALLEDPERPENDICULAR TO FLOW

    SENSOR INSTALLEDPARALLEL TO FLOW

    SENSOR INSTALLEDPARALLEL TO FLOW

    Good

    Better

    Best

    Insmalldiameterlinesthereistypicallynotenoughroomtogettheproperimmersionlengthtoavoidstemconduction.Thisillustratesthreemethodsofmodifyingthepipingtoprovideextraroom.Theoneontherightisthebestmethodbecauseitprovidesfortheflowcomingdirectlyatthetipofthesensorforlessstressontheprobeanditalsowashesoutthedeadlagportionofthetee.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Direct Immersion

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Elbow Style T-Wells

    Forthoseapplicationsthatrequireathermowell,theelbowstyleworkswellifsizedcorrectly.Animmersionlengthofatleast4isnecessarytoprovideanaccuratemeasurement.Shorterimmersionlengthswillworkokayforsomeprocessfluidsandflowrates.

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Elbow Style T-Wells

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Surface Mount Installation

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    Burns Engineering Measuring Temperature in Small Diameter Lines

    Surface Mount Installation

    Sensor should be covered withinsulation for best accuracy

    Surfacemountsensorsareeasytoinstallandarelowcost.Soundstoogoodtobetrue,anditis.Theygenerallydonotprovideaveryaccuratemeasurementofthefluidinsidethevessel.Improvementscanbemadewiththeadditionofinsulationandtheuseofaheattransferpasteatthemountinglocation.

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    Burns