温度测量仪表资料

1、Fundamental TrainingLevel 1温度测量仪表(ybio)基础1共五十三页Topics:Slide No:为什么要测量温度? 3 - 5温度的定义(dngy) 6 - 8温度测量技术 14 - 40传感器的附件 41 - 52温度变送器 53 - 64内容提要(ni rn t yo)2共五十三页因为温度影响(yngxing)许多物质的属性: 同时,温度(wnd)是影响以下工艺过程的关键因素:物理及化学反应的速率粘度物质的状态材料的强度食品的质量及品味工业过程的安全纸浆与造纸乳品工业的巴氏灭菌消毒真空包装化学反应为什么要测量温度?3共五十三页安全效率例如空分工业产品的质量及产

2、出率温度(wnd)偏离优化值会导致;产出率极低产生废物精确的控温将带来高的出率:炼厂常压分馏催化裂化为什么要测量温度?4 个常见(chn jin)的原因4共五十三页贸易交接(jioji)买卖双方的交易量确定气体的标态体积时,温度测量极为重要给定体积气体中的物质含量将随温度升高而减少将随温度降低而增加温度测量误差将导致:用户的支出将有很大的误差为什么要测量温度(wnd)?4 个常见的原因5共五十三页SteamColdWaterHotWaterLoad Disturbance TTTICI/P温度控制回路(hul)温度控制回路通常的问题是: 液体对加热输入的反应有很大的滞后 因此需要某些先进(xi

3、njn)控制策略例如前馈控制6共五十三页373 100 672 212 273 0 492 32 0 -273 0 -460 C = 5/9 (F - 32 ) F = 9/5 (C) + 32 K = 273 +C R = 460 + FKelvin & Rankine are absolute scalesBOILING POINT OF WATERICE POINTABSOLUTE ZEROkELVINCELSIUSRANKINEFAHRENHEIT温度(wnd)测量的刻度单位7共五十三页Differential TemperatureC = 5/9 FF = 9/5 C K = CR

4、= FExample: 2 points in a process differ in temperature by 100 C. These 2 points differ by 180 Fi.e. 180 = 9/5(100)Whereas, they also differ by 100KExample #120C= 20 + 273= 293K20C= 9/5*(20) +32= 68F温度(wnd)测量的刻度单位8共五十三页温度(wnd)测量技术之一/双金属温度计使用(shyng)不同温度膨胀系数的双金属片及连杆齿轮系统组成的温度指示仪表.9共五十三页例如:蒸汽温度计基本原理是利用可

5、挥发性液体受热后产生汽化,汽化压力经毛细管传导至指示机构(jgu).其压力与温度成正比!温度测量技术之二/膨胀液体(yt)压力温度计利用液体的汽化膨胀特性制成的温度计测温探头导压毛细管压力指示10共五十三页Example:石英(shyng)晶体温度计外形类似于RDT热电阻的封装,可以实现高精度的直接数字测温,但价格昂贵!温度测量技术(jsh)之三/石英晶体传感器利用晶体的谐振频率与温度之间的关系制成的温度仪表.11共五十三页例如(lr): 光电式红外线辐射温度计/非接触式测温仪.温度(wnd)测量技术之四/非接触式辐射温度传感器原理基于任何物体均有温度的热辐射,例如红外线辐射.12共五十三页E

6、xample:半导体温度(wnd)敏感元件RTD 金属热电阻温度(wnd)测量技术之五/热敏电阻/RTD温度传感器基本原理:利用导体的温度与电阻的相关关系进行温度测量. 分为负温度系数NTC及正温度系数PTC两种半导体热敏电阻Thermistor13共五十三页热电阻温度传感器RTDs什么(shn me)是 RTD ?Resistance Temperature Detector Platinum resistance changes with temperatureRosemounts Series 78, 88Rosemounts Series 68, 58Series 65两种常见的制造工

7、艺:线绕式或薄膜式Wire-wound sensing elementThin-film sensing element铂电阻 (Platinum usually): 元件的温度(wnd)常数/PT100Typical Tc=9s50%FS!14共五十三页热电阻温度传感器RTDs RTD的工作原理?重复性精度(jn d)好 IEC 751/PT100铂电阻的特性曲线(Ro=100 Ohms)Resistance (Ohms)Temperature (oC)oCOhms0100.0010103.9020107.7930111.67International Resistance vs. Temp

8、erature Chart:IEC 751IEC751IEC 751 Constants are :- A = 0.0039083, B = - 5.775 x 10 -7, If t=0, C=0, If t=0C, then b = 0)IEC 751 CurveTemperature (oC)Resistance (W)Class B ToleranceThe transmitter does not use the IEC 751 standard curve.Instead, the Callendar-Van Dusen constants can be used in the e

9、quation below to create the true sensor curve. Or, the actual IEC 751 constants A,B, and C can be used in the IEC 751 equation if known. Sensor Matching - Mapping the Real RTD Curve4th Order Callendar-VanDusen Equation26共五十三页ProcessTemperatureHot junction两种异型金属形成的结点.Cold junction+-MV只要引自该结点的导线的另一端的温

10、度与结点温度有所不同,该温度差将会在这一点的导线间产生与温度成正比的MV电势!温度高的一端称之为热端,反之为冷端.DT该MV数可以由标准化的标度表格查到!作为实用性测温技术,冷端的温度必须知道!什么(shn me)是热电偶?热电偶测温27共五十三页 +-MVHeatHot junctionCold junctionoC Millivolts00.000100.591201.192301.801Thermoelectric Voltagevs. Temperature Chart:TYPE E THERMOCOUPLEDTVoltage (mV)Temperature (oC)IEC584Mea

11、surement JunctionT2Reference JunctionT1热电偶测温IEC 584-热电偶的温度/MV转换(zhunhun)标准参考(cnko)温度28共五十三页Groundedimproved thermal conductivityquickest response timessusceptible to electrical noiseUngroundedslightly slower response timenot susceptible to electrical noiseSingle GroundedDual GroundedSingle Ungrounde

12、d热电偶测温元件(yunjin)热端的结构-1Hot-Junction Configurations29共五十三页Unisolatedjunctions at the same temperatureboth junctions will typically fail at the same timeIsolatedjunctions may/may not be at the same temperatureincreased reliability for each junctionfailure of one junction does not affect the other热电偶测温

13、元件热端的(dund)结构-2Hot-Junction ConfigurationsDual Ungrounded, Un-isolatedDual Ungrounded, Isolated30共五十三页ICEBATHT1 = 10CWhy is Cold Junction Compensation needed?参考端,通常为冷端温度(wnd)要保持恒定.MeasureReferenceIronConstantan+_VoltMeterT2 = 100 + 10C5.812 mV 2 种方法(fngf): 将冷端置于冰浴桶中 NOT Practical ! C-100-0+0100 MILL

14、IVOLTS 0-4.6320.0000.0005.268 2-4.550-0.9951.0195.376 6-4.876-0.3010.3035.594 10-5.036-0.5010.5075.812 14-5.194-0.6990.7116.031 T = 110C冷端补偿的方法-1,保持冷端恒温?热电偶分度表31共五十三页MeasureReferenceJunctionIronConstantan+_TransmitterT2 = 110C4.186 mV另一种方法(fngf):冷端补偿. Electronic Circuitry passing current through a T

15、hermistor 通常(tngchng)的做法! T = 80CConnection HeadExtension WiresExample: Ambient Temp = 30C C-100-0+0100 MILLIVOLTS 0-4.6320.0000.0005.268 10-5.036-0.5010.5075.812 30-5.801-1.4811.5366.907 60-6.821-2.8923.1158.560 80-7.402-3.7854.1869.667+1.536 mV= 5.722 mV1100 CSpecial Thermocouple R, S or B热电偶与热电阻的

16、对比/温度(wnd)范围39共五十三页为什么要延长段? 降低由过程(guchng)传导的温度延伸探头的插入深度将探头拆除时教方便两种类型:螺母及对丝/Coupling and nipple. 联结器及对丝/Union and nipple.01020304050603456789815C Oven Temp.540C Oven Temp.250C Oven Temp.Extension Length, InchesHousing Temp.Rise Above Ambient CTransmitter Housing Temperature Rise vs.Extension Length f

17、or a test Installation传感器的附件/延长(ynchng)段的选择40共五十三页Example #1 4 inch extension01020304050603456789815C Oven Temp.Extension Length, InchesHousing Temp.Rise Above Ambient CExample of ApplicationTransmitter Housing Temperature Rise vs.Extension Length for a test InstallationLets say:Temp Limit of Transm

18、itter is 70CAmb. Temp is 32C 62C Ceiling32C+ 30CExample #2 6 inch extension 52C Ceiling32C+ 20C传感器的附件/延长段的选择及降温(jing wn)效果41共五十三页什么是热套管 ?对传感器进行保护方便超出(choch)传感很大的时间常数 (一般为传感器的5倍)不同的材质 ?考虑(kol)到腐蚀温压等级传感器的附件/热套管42共五十三页ProcessPressureTimeResponseWake FrequencyPriceDragForceRating: 1= BestThermowell Desi

19、gn Styles - Comparison Table311 or 21211311231 or 212TaperedSteppedStraight三种外形(wi xn)的热套管比较43共五十三页三种(sn zhn)外形的热套管比较螺纹连接最常见的安装容易拆卸焊接式永久性安装高流速高温高压用于无泄漏场合法兰安装防腐要求(yoqi)高流速高温44共五十三页损坏原因(yunyn)-1冯-卡尔曼效应及尾流振动.热套管的自然谐振频率.热套管(to un)的尾流振动及共震频率45共五十三页流体的牵拽作用(zuyng)引起套管的折断!FLOWSTRESS热套管(to un)的尾流振动及共震频率46共五十

20、三页 过高的静压引起(ynq)套管的变形.热套管(to un)的静压损坏47共五十三页外形材质尺寸流速及流量(liling)过程压力温度密度和粘度管道尺寸T 型套的计算: 1.尾流频率 2.自然谐振频率 3.牵拽力 4. 静压力Look on the back of your Sensor PDS!热套管(to un)的选型考虑48共五十三页影响温度(wnd)测量的时间常数Sensor 7 to 10 sec Sensor in Thermowell 60 to 120 secTransmitter.5 to .9 secProcessSeconds to Hours49共五十三页Exerci

21、se A 4-20 mA transmitter is spanned 50 to 150C. Express the span in the following units:1. to F2. to K3.What is the temperature reading if the above transmitter outputs 10 mA?C4.An old differential temperature indicator witha scale of 0 - 100F is reading 60F. What is that reading in C?C5.An Pt 100 R

22、TD has the following C.V.D constantsR0 =100.00W, = 0.003842, d =1.415, b = 0.11. If the temperature being measured is 30C,What will be the resistance value? 50共五十三页Exercise Identify the characteristics for RTD & Thermocouple & indicate them by entering a “R” or a “T” respectively.6.High accuracy.7.Can handle wider temperature range.8.CJC isnot required.9.Can be matched to transmitter.10.Faster response time.Id