射频导纳仪表基本原理和操作.ppt

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1、RFAdmittanceBasicsTheoryofOperation射频导纳仪表基本原理和操作WhatisPointLevel?什么是点位控制?PointlevelorOn/Offmeasurementindicatestheabsenceorpresenceofmaterialatacertainpointinthevessel,pit,pipe,etc…点位控制或开关量测量指示的是在容器或深井或管道里某一点被测介质的有无Pointlevelmeasurementsareusedfor点位控制主要应用于Hi

2、ghLevel高液位测量SpillPrevention溢出保护StopFill停止溢出LowLevel低液位测量StopEmpty防止空罐RefillIndication填充指示PumpProtection泵保护A=4.4sqIn2.1”2.1”D=1”pFTypicalValues介电常数值MaterialBetweenPlatesKCapacitanceinpFVacuum1.00001.000Air1.00061.0006Polyeth.Chips1.31.3SoapPowder1.551.55Keros

3、ene1.81.8Sand4.84.8Alcohol3333D.I.Water7878DielectricConstant(K)介电常数(K)TheTankandProbeformaCapacitor罐壁和探头形成一个电容C=kAdC=CapacitanceinpF电容pFk=DielectricConstantofmaterial介电常数A=Areaoftheplates探头测量区域d=Distancebetweenplates探头与罐壁距离Akair=1dCkoil=2TheTankandProbeform

4、aCapacitor罐壁和探头形成一个电容C=kAdC=CapacitanceinpF电容pFk=DielectricConstantofmaterial介电常数A=Areaoftheplates探头测量区域d=Distancebetweenplates探头与罐壁距离kkair=1AdCkoil=2AffectsofDielectricandConductivity介电常数和电导率对电容值的影响VerticalInsulatedProbes垂直的绝缘探头InchesofLevel液位高度Cp(pF)010203

5、0绝缘探头InsulatedProbe油Oil水WaterAffectsofDielectricandConductivity介电常数和电导率对电容值的影响VerticalBareProbes垂直的非绝缘探头InchesofLevel液位高度Cp(pF)0102030油Oil水WaterBareProbe探头PropertiesofMaterial物质的特性AMaterial’sphysicalpropertydoesnotaffectRFAdmittancemeasurements.物质的物理特性不会影响RF

6、Admittance测量.RFAdmittanceusestheproduct’selectricalpropertiestomakethemeasurement.RFAdmittance利用的是物质的导电特性来进行测量的.Physical物理特性Density密度Viscosity黏度Electrical导电特性Dielectric介电常数Conductivity导电率DielectricConstant(k)Scale介电常数范围1.00061.32.5918.333.63756.680+Air空气Poly

7、Chips聚乙烯MostHydrocarbons多数碳氢化合物Phenol苯酚IsopropylAlcohol异丙醇Methanol甲醇EthyleneGlycol乙烯TapWaterandMostAcids自来水和大部酸Sand沙子4.8D.I.Water除盐水1.6Propane丙烷1Vacuum真空MethylAlcohol甲醇Conductivity(g)Scale导电率uS1.00110K50-500Kerosene煤油MethylAlcohol甲醇OrangeJuice果汁TapWater自来水Be

8、er啤酒1250D.I.Water除盐水30%H2SO430%硫酸21MSeaWater海水80K90%H2SO490%硫酸2TheCapacitanceDisadvantage:电容式测量的缺点:AffectedbyConductiveCoatings挂料会影响测量Capacitance电容Nocurrentflow没有电流Currentflow电流FalseAlarm!错误报警Th