《传感器与检测基础》电磁流量计.pptx

传感器与检测基础FundamentalsofSensorsandDetection

FlowMeasurement流量测量05

ElectromagneticflowmetersEMF电磁流量计1.IntroductionElectromagneticflowmeters,alsoknownas‘Magflows’or‘Magmeters’,havenowbeeninwidespreadusethroughoutindustryformorethan40yearsandwerethefirstofmodernmeterstoexhibitnomovingpartsandzeropressuredrop.1.概述 2.法拉第电磁感应定律3.Construction 4.励磁方式 5.非满管报警6.安装使用 7.优缺点分析

ElectromagneticflowmetersEMF电磁流量计2.BasicPrincipal—ElectromagneticInduction—Whenanelectricalconductormovesperpendiculartoamagneticfield,avoltageisinducedinthatconductorperpendiculartoboththemagneticfluxlinesandthedirectionofmotion.

IllustrationofFaraday’sLawofelectromagneticinduction.iftheconductoroflength(l)ismovedthroughthemagneticfieldhavingamagneticfluxdensity(B)atavelocity(v),thenavoltagewillbeinducedwhere:E=BlvE-inducedvoltage(V);B-magneticfluxdensity（Tesla)(Wb/m2);l-lengthofconductor(m);v-velocityofconductor(m/s).ElectromagneticflowmetersEMF电磁流量计2.BasicPrincipal—ElectromagneticInduction

2.BasicPrincipal—ElectromagneticInductionEx—感应电势；B—磁感应强度；D—管道内径；v—垂直于磁力线方向的流速；C—比例系数，即单位换算系数。k—仪表常数，取决磁感应强度、管径ElectromagneticflowmetersEMF电磁流量计感应电动势的方向？弗来明右手定则

（1）只能测量导电介质电导率限制条件δ≥1～5μS/cm（水20μS/cm）(低电导率0.05μS/cm使用专用仪表）只要阈值后，与电导率无关。不能测非导电介质,如气体,油类，如介质含大量气体，测量严重波动（2）必须存在磁场励磁电流流经测量管上下励磁线圈产生磁场。励磁线圈断路，流量计不工作，励磁电流稳定性直接影响仪表测量测量管必须为非导磁材料（采用不锈钢材质），保证磁场穿过导管（3）实际测量值为流体流速速度式流量计测量介质的体积流量熟练流速换算Q(流量）=π/4DN2V2.BasicPrincipal—ElectromagneticInductionElectromagneticflowmetersEMF电磁流量计uS/cm1.00110K50-500Kerosene煤油MethylAlcohol甲醇OrangeJuice果汁TapWater自来水Beer啤酒1250D.I.Water除盐水30%H2SO430%硫酸21MSeaWater海水80K90%H2SO490%硫酸

ConductivitiesofsometypicalfluidsElectromagneticflowmetersEMF电磁流量计LiquidConductivity(μS/cm)Carbontetrachloride四氯化碳at18℃Toluene甲苯

Kerosene煤油Analineat25??℃Soyabeanoil

Distilledwater

Acetone丙酮at25??℃Phosphoro