射频导纳仪表基本原理和操作

1、RF Admittance BasicsTheory of Operation射频导纳仪表基本原理和操作射频导纳仪表基本原理和操作2What is Point Level?什么是点位控制什么是点位控制?Point level or On/Off measurement indicates the absence or presence of material at a certain point in the vessel, 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点被测介质的有无Poi

2、nt level measurements are used for点位控制主要应用于点位控制主要应用于 High Level高液位测量 Spill Prevention溢出保护 Stop Fill 停止溢出 Low Level 低液位测量 Stop Empty防止空罐 Refill Indication填充指示 Pump Protection泵保护3A=4.4 sq In2.1”2.1”D=1”pFTypical Values介电常数值介电常数值MaterialBetween PlatesKCapacitanceinpFVacuum1.00001.000Air1.00061.0006Poly

3、eth. Chips1.31.3Soap Powder1.551.55Kerosene1.81.8Sand4.84.8Alcohol3333D.I. Water7878Dielectric Constant (K)介电常数介电常数 (K)4The Tank and Probe form a Capacitor罐壁和探头形成一个电容罐壁和探头形成一个电容C =k AdC= Capacitance in pF 电容电容 pFk= Dielectric Constant of material介电常数介电常数 A= Area of the plates探头测量区域探头测量区域d= Distance

4、between plates探头与罐壁距离探头与罐壁距离Ak air = 1dCk oil = 25The Tank and Probe form a Capacitor罐壁和探头形成一个电容罐壁和探头形成一个电容C =k A dC= Capacitance in pF 电容电容 pFk= Dielectric Constant of material介电常数介电常数 A= Area of the plates 探头测量区域探头测量区域d= Distance between plates 探头与罐壁距离探头与罐壁距离kk air = 1AdCk oil = 26Affects of Diele

5、ctric and Conductivity介电常数和电介电常数和电导率对电容值的影响导率对电容值的影响Vertical Insulated Probes垂直的绝缘探头垂直的绝缘探头Inches of Level液位高度C p (pF)0102030绝缘探头Insulated Probe油Oil 水Water7Affects of Dielectric and Conductivity介电常数和电导率对电容值的影响介电常数和电导率对电容值的影响Vertical Bare Probes垂直的非绝缘探头垂直的非绝缘探头Inches of Level液位高度C p (pF)0102030油Oil水W

6、aterBare Probe探头8Properties of Material物质的特性物质的特性A Materials physical property does not affect RF Admittance measurements. 物质的物理特性 不会影响RF Admittance 测量.RF Admittance uses the products electrical properties to make the measurement. RF Admittance 利用的是物质的导电特性来进行测量的.Physical物理特性物理特性Density密度Viscosity黏度E

7、lectrical导电特性导电特性Dielectric介电常数Conductivity导电率9Dielectric Constant (k) Scale介电常数范围介电常数范围1.00061.32.5918.333.63756.680+Air空气Poly Chips聚乙烯Most Hydrocarbons多数碳氢化合物Phenol苯酚Isopropyl Alcohol异丙醇Methanol甲醇Ethylene Glycol乙烯Tap Water and Most Acids自来水和大部酸Sand沙子4.8D.I. Water除盐水1.6Propane丙烷1Vacuum 真空Methyl Alc

8、ohol甲醇10Conductivity (g) Scale导电率导电率uS1.00110K50 - 500Kerosene 煤油Methyl Alcohol甲醇Orange Juice 果汁Tap Water自来水Beer 啤酒1250D.I. Water 除盐 水30% H2SO430% 硫酸21MSea Water 海水80K90% H2SO490% 硫酸211The Capacitance Disadvantage:电容式测量的缺点电容式测量的缺点:Affected by Conductive Coatings挂料会影响测量挂料会影响测量Capacitance电容电容No curren

9、t flow没有电流Current flow电流False Alarm!错误报警错误报警12The RF Advantage:射频导纳的优势射频导纳的优势:Not Affected by Conductive Coatings 抗挂料抗挂料RF Admittance射频导纳射频导纳Current flow is not measured电流未被测量No current flow没有电流Cote-ShieldNormalNormal正常正常13Cote-Shield Mounting Consideration Cote-Shield安装用于抗挂料安装用于抗挂料Cote-shield must

10、extend at least 50mm (2”) through the mounting and past any build up Cote-shield 最少最少 50mm (2”) 这样安装才能起到抗挂料作用这样安装才能起到抗挂料作用NozzleNoYesYesNoCote-Shield14Cote Shield Demonstration Cote Shield 演示演示15Point Level Tuning Fork点位测量点位测量 音叉音叉16Tuning Fork Operation音叉的操作原理音叉的操作原理Tuning fork uses piezoelectric c

11、rystals to drive the fork and make it vibrate at approximately 1200 Hz.音叉是利用压电晶体产生振动频率音叉是利用压电晶体产生振动频率(1200赫兹赫兹)来进来进行工作的行工作的 When the tuning fork is covered in the product the frequency changes当音叉被物体覆盖时振动频率发生改变当音叉被物体覆盖时振动频率发生改变. The frequency change is detected by the internal oscillator and converte

12、d to a switching command频率的改变会被内部的震荡器检测出来并把它转换成开关输频率的改变会被内部的震荡器检测出来并把它转换成开关输出出17Tuning Fork音叉音叉The TF-100 series tuning fork is to be used on clean liquids only TF-100 系列音叉系列音叉 仅仅是用于纯净液体的测量的仅仅是用于纯净液体的测量的Liquid applications that contain air are not aproblem for the tuning fork.液体中含有气泡对音叉无影响液体中含有气泡对音叉

13、无影响. Tuning forks should not be used on liquids that coat or crystallize.音叉不能被用于产生黏附和结晶的液体测量音叉不能被用于产生黏附和结晶的液体测量18Tuning Fork音叉音叉Independent of electrical characteristics不受被测介质介电常数的影响不受被测介质介电常数的影响 Trip point repeatability 2mm 重复精度 2mm Short Insertion Lengths 可以截断插入深度Measure total level in non-dedicat

14、ed vessels可以测量液体液位可以测量液体液位 Clean liquids 纯净的液体Will measure liquid level under foam可以测量泡沫以下的液位可以测量泡沫以下的液位 Ignores Foam 忽略泡沫影响19Point Level Ultrasonic点位测量点位测量 超声波超声波20Theory of “Gap Switch” Operation超声波测量开关的原理超声波测量开关的原理 Piezoelectric crystal on one side of the gap transmits acoustic energy Piezoelectr

15、ic crystal on the other side of the gap acts as a receiver for this energy 超声波测量开关有两个极板一个极板的压电晶体产生能量并且传送能量,另一个极板接收能量。 With air or gas in the gap the energy is not sufficient to cross the gap to the receive crystal 在空气或气体中能量不足以在两个极板间传送21Theory of “Gap Switch” Operation超声波测量开关的原理超声波测量开关的原理 Liquids tra

16、nsmit acoustic energy more effectively than air or any other gas 液体的声波能量传导性好于气体液体的声波能量传导性好于气体 When liquid fills the gap, the acoustic signal signal travels though the liquid to the receive crystal causing the output to go to the alarm condition (high level 当液体充满在两个极板间的时候当液体充满在两个极板间的时候,声波传导能量增大因声波传导能

17、量增大因此产生报警此产生报警22Gap Switch超声波测量开关超声波测量开关Gap switches are for clean liquids超声波液位开关用于纯净的液体测量超声波液位开关用于纯净的液体测量Gap switches should not be used on超声波液位开关不能应用以下测量超声波液位开关不能应用以下测量: Liquids with entrained air 内部含有气泡的液体 Liquids with suspended solids 含有悬浮物的液体 Coating liquids 有黏附性的液体23Gap Switch超声波测量开关超声波测量开关Ind

18、ependent of electrical characteristics不受被测介质的介电常数的影响不受被测介质的介电常数的影响 Trip point repeatability 1/16” 重复精度 1/16” Short Insertion Lengths 可以截断插入长度Measure total level in non-dedicated vessels可以测量液体液位可以测量液体液位 Clean liquids 纯净的液体Will measure liquid level under foam可以测量泡沫以下的液位可以测量泡沫以下的液位 Ignores Foam 忽略泡沫影响2

19、4Common Point Level Terminology点位测量技术的共同点点位测量技术的共同点25Integral vs. Remote 整体整体 与分体与分体Integral整体整体Remote分体分体Cost成本成本Typically Less通常会少一些Typically more常会多一些Installation安装安装Sensor & electronics mounted on vessel 传感器和变送器整体安装在罐上Sensor mounted on vesselCoax cable is run to the remote mounting of the el

20、ectronics传感器安装在罐上而变送器通过同轴电缆与传感器相连Location地点地点At the measuring point在测量点位上In safe area在安全区域Personnel调试人员调试人员On the vessel在罐上调试Away from heat, vibration toxins, and danger远离高温震动有害气体和危险26Fail Safe安全保护安全保护High Level Fail - Safe高液位安全报警高液位安全报警 Relays de-energize when materials touches sensing element 当介质接

21、触到探头时,继电器会翻转Low Level Fail-Safe低液为安全报警低液为安全报警 Relays de-energize when material leaves the sensing element 当介质离开探头时,继电器会翻转27Installation Orientation 安装方向安装方向Vertical Application垂直安装垂直安装Horizontal Application水平安装水平安装C = KA D28Time Delay 时间延迟时间延迟HLFSGoes into alarm immedaiatelyon contact with Material接

22、触到物质后立刻报警Goes into alarm a specified time afteruninturrupted contact with Material接触的物质后在一个定义的时间后报警LLFSGoes into alarm immedaiatelyon drop-off of Material当介质脱离测量探头时报警Goes into alarm a specified time after mostrecent contact with Material当介质脱离测量探头时在一个定义时间后报警Agitator 搅拌器搅拌器29Differential区别区别Relay ener

23、gizes and de-energizes at different points along the sensor.继电器动作与不动作在一个传感继电器动作与不动作在一个传感器的不同点上器的不同点上Pump on 泵开Pump off 泵关30Linepower vs. 2-Wire供电模式供电模式 与与. 2-线制比较线制比较Function功能功能Local Control using relay使用继电器进行控制Centralized Control and Alarming集中控制和报警Diagnositcs诊断诊断Fail Safe故障模式Fail Safe and Loop Di

24、agnostics故障模式和自检Instrument Cost仪表成本仪表成本enerally higher than two-wire butdoes not require receiver通常造价高于两线制但是不需要接收器Less than line powered, but may requirereceiver.Greatly reduced overall cost (two-wire,vs. 4-wire).造价会低于供电模式但是需要接收器并且比四线制降低成本LSafety安全安全Many units FM or CSA X-proof多数FM or CSA 隔爆认证Intrin

25、sically Safe - work on hot unit本安认证312-Wire Current Output两线制电流输出两线制电流输出Intellipoint and ThePoint AlarmNormal5mA+/- 18mA+/- 116mA+/-1FaltAlarmNormal5mA+/- 18mA+/- 116mA+/-1FaltNormal8mA+/- 116mA+/-122mA+/- 1FaultAlarmNormal8mA+/- 116mA+/-1+/- 1FaultOr Field Changeable too32What is Verify?校验是什么校验是什么?

26、A test which mimics a high level conditionwithout actually raising the level in the tank模拟高物位状态进行仪表测试模拟高物位状态进行仪表测试.Available on 主要用于主要用于: High Level Only 高液位报警测试 RF Intellipoint (Two Wire or Line Power) 射频导纳RF Intellipoint两线或线路供电产品 Ultrasonic line powered and two wire VeriGAP 超声波线路供电和两线 VeriGAP产品Ideal for Overfill and Spill Prevention用于溢出保护是很理想的用于溢出保护是很理想的33How RF Verify works射频导纳是如何完成校验工作的射频导纳是如何完成校验工作的 Intellipoint The Intellipoint product runs an Auto-Verify check 3 times a second Intellipoint 产品运行自动检测功能每秒三次 The test compares the current capacitance to the a