1、Theory of Transmission Gauging forThickness Measurementof Metals穿透式测厚仪测量原理穿透式测厚仪测量原理Generating X-rays using an X-ray TubeX射线管产生的射线管产生的X射线射线Glass tubes 玻璃管玻璃管Metal ceramic tubes 金属陶瓷管金属陶瓷管Advantages 优点Economical 经济 AdvantagesSmall constructionRobust Longer lifeScreening of the radiation by means of t
2、he x-ray tube housing(Radiation protection)DisadvantagesLarge constructionGlass tube can easily be brokenDisadvantagesBasic Principles 基本原理基本原理Trans-missionDetectorSource射线源射线源 Metal-Thickness,t （物体物体-厚度厚度t)Measurement of Thickness厚度测量厚度测量Metal BlocksGamma/X-rays物体物体 伽玛伽玛/X射线射线Detector探头探头Source射线源射
3、线源Steel-Thickness,t（钢钢-厚度，厚度，t）I0=Full IntensityI0=总强度I=IntensityI=强度MeasurementOf Thickness厚度测量值Mean free path,主自由通道q=f(keV,chemistry)化学成份Three Ways to use Radiation for Measurement射线在测量领域应用的三种主要方式射线在测量领域应用的三种主要方式w Three modes of measurement may be used according to the application 按应用方式可分为三种方式 Tra
4、nsmission mode,used for direct measurement of strip thickness 穿透式，用于穿透板带测量物体厚度 Fluorescence mode,used to measure thickness of metallic coatings 莹光反射式，用于测量金属涂层厚度 Backscatter mode,used to measure thickness of paint coatings 反向散射式，用于测量漆层厚度Generation of X-rays&Gamma-raysX射线和伽玛射线的产生射线和伽玛射线的产生w Natural De
5、cay of Isotope:Am241&Cs137 are most commonly used 同位素核裂变：常用的同位素源是镅241和铯137源Single Fixed Energy (Mono-chromatic)单一固定能量 单色Reliable 可靠的Lower Cost 低成本Low Power 低功耗Cannot be turned off 射线不能被关闭w X-ray Tube:High voltage accelerates electrons to a target X射线管：高压加速电子轰击靶Energy Spectrum 能谱Selectable Energy 可变能
6、量Safer-Turn off HV to stop radiation output 安全-可通过关闭高压停止产生射线Greater photon intensity 光子强度大 Lower Noise 低噪声Higher Cost 成本较高Radiation Sources for Measuring Steel适用于测量钢铁厚度的射线适用于测量钢铁厚度的射线w Thickness Ranges Steel 测厚范围-钢 Sr90(Beta ray)0.05-1.00 mm 锶90 贝它射线 Am241(Gamma Ray)0.15-6.25 mm 镅241 伽玛射线 Cs137(Gamm
7、a Ray)6.0-125 mm 铯137 伽玛射线 100kV(X-ray)0.1-10.0 mm 100kV X射线 160kV(X-ray)0.2-25.0 mm 160kV X射线 240kV(X-ray)1.0-60.0 mm 240kV X射线Half-Lives of Radiation Sources射线源的半衰期射线源的半衰期Isotopes have“Half Lives”-the time for activity to decay to half of the original value 同位素有”半衰期“活度衰减到初期一半所用的裂变时间 Am241（镅241）433
8、 years（年）Cs137（铯137）3 0 years（年）Cm244（锔244）17.8 years（年）Sr90 （锶90）29.6 years（年）Kr85 （氪85）10.7 years（年）Pm137（钷137）2.6 years（年）Effect of Pass Angle 板带角度对测量的影响板带角度对测量的影响Detector探头探头Source射源射源Stripthickness,t 带钢厚度带钢厚度,tVDStrip angle error,a a板带角度板带角度,a aActual thickness,t =Apparent thickness,ta,multipli
9、ed by cos a a实际厚度实际厚度,t=初测厚度初测厚度ta乘以乘以cos a aStrip thickness appears thicker(ta)than actual value,t.板带初测量厚度板带初测量厚度ta会比实际厚度更厚会比实际厚度更厚 Advantages Isotope&X-ray 同位素、同位素、X射线的各自优缺点射线的各自优缺点w Isotope 同位素 Lower cost 低成本低成本 Higher reliability 高可靠性高可靠性 Lower maintenance 易维护易维护 Easy alloy correction 合金易较准合金易较准
10、 Slower mills&lines 低速轧制线低速轧制线 Measurement only applications 仅应用于测量仅应用于测量wX-ray X射线 High radiation output 射线强度高射线强度高 Faster response 响应快响应快 Best signal/noise ratio 低噪声低噪声 No“optimum”thickness 没有不适合的测量厚度没有不适合的测量厚度 Larger air gaps 高的气隙开口高的气隙开口Disadvantages Isotope&X-ray同位素和同位素和X射线的缺点射线的缺点w Isotope 同位素
11、 Fixed optimum thickness 仅适合一定的厚度范围仅适合一定的厚度范围 Slower 响应慢响应慢 Poor signal/noise ratio 噪声较高噪声较高 Small air gaps 气隙小气隙小 Limited control applications 应用受限制应用受限制 Special licensing 要特殊许可证要特殊许可证w X-ray X射线 Higher cost 费用高费用高 More maintenance 维护要求高维护要求高 Complex alloy correction(SuperCompPlus)合金补偿复杂合金补偿复杂 More maintenance 维护要求高维护要求高 Beam Hardening 射线管存在硬化现象
