测厚仪原理(中英对照)

• 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
Thickness Ranges – Steel 测厚范围-钢
– Sr90 (Beta ray) 锶90 贝它射线 – Am241 (Gamma Ray) 镅241 伽玛射线 – Cs137 (Gamma Ray) 铯137 伽玛射线 – 100kV (X-ray) 100kV X射线 – 160kV (X-ray) 160kV X射线 – 240kV (X-ray) 240kV X射线 0.05 - 1.00 mm ickness, t 带钢厚度, t
Source
射源
Advantages Isotope & X-ray 同位素、X射线的各自优缺点
Isotope 同位素
– Lower cost 低成本 – Higher reliability 高可靠性 – Lower maintenance 易维护 – Easy alloy correction 合金易较准 – Slower mills & lines 低速轧制线 – Measurement only applications 仅应用于测量
（3）管电压和管电流都必须稳定，才能确保检测的准确性。
X-ray control unit
X-ray DRIVER CHASSIS
X-ray SOURCE
X-RAY TUBE
Glass tubes 玻璃管 Metal ceramic tubes 金属陶瓷管
Advantages 优点 Economical 经济
Basic Structure of an X-Ray Tube
•The anode must be cooled. The efficiency of an x-ray tube is around 1-2%. 阳极必须具备冷却，只有大约1-2%转化成X射线。
（1）X射线的穿透力（能量）取决于管电压。 （2）在管电压一定时，X射线的强度取决于管电流，管电流通过灯 丝电流调节。
Generation of X-rays & Gamma-rays X射线和伽玛射线的产生
Natural Decay 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
X-ray
X射线
– High radiation output 射线强度高 – Faster response 响应快 – Best signal/noise ratio 低噪声 – No “optimum” thickness 没有不适合的测量厚度 – Larger air gaps 高的气隙开口
X-ray X射线
– Higher cost
费用高
– More maintenance
维护要求高
– Complex alloy correction (SuperCompPlus)
合金补偿复杂
– More maintenance
维护要求高
– Beam Hardening 射线管存在硬化现象
Disadvantages Isotope & X-ray 同位素和X射线的缺点
Isotope 同位素
– Fixed optimum thickness 仅适合一定的厚度范围 – Slower 响应慢 – Poor signal/noise ratio 噪声较高 – Small air gaps 气隙小 – Limited control applications 应用受限制 – Special licensing 要特殊许可证
• Due to the electrical field, electrons are emitted from the cathode and accelerated towards the anode. In order to assist in the emission of electrons, a filament in the cathode is heated.
化学成份
Measurement Of Thickness 厚度测量值
Three Ways to use Radiation for Measurement
射线在测量领域应用的三种主要方式
Three modes of measurement may be used according to the application 按应用方式可分为三种方式 – Transmission 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
Metal Blocks Gamma/X-rays
物体 伽玛/X射线
Detector 探头
I=Intensity I=强度
Mean free path,
Steel - Thickness, t （钢-厚度，t） I0 = Full Intensity I0 =总强度 Source 射线源
主自由通道
q=f(keV, chemistry)
6.0 - 125 mm
0.1 - 10.0 mm 0.2 - 25.0 mm 1.0 - 60.0 mm
Half-Lives of Radiation Sources
射线源的半衰期
Isotopes have ―Half Lives‖ --- the time for activity to decay to half of the original value
N
Incident Photon
Fluorescence Radiation
Basic Structure of an X-Ray Tube
Generating X-rays using an X-ray Tube
X射线管产生的X射线
• The x-ray tube consists of two parts: The anode and the cathode X射线管由两部分组成：阳极和阴极
Advantages Small construction Robust Longer life Screening of the radiation by means of the x-ray tube housing (Radiation protection)
Disadvantages Large construction Glass tube can easily be broken
Effect of Pass Angle
板带角度对测量的影响
VD Detector
Strip thickness appears thicker ( ta ) than actual value, t . 板带初测量厚度ta会比实际厚度更厚
Actual thickness, t = Apparent thickness, ta, Strip angle multiplied by cos a error, a 实际厚度, t=初测厚度ta乘以cos a 板带角度, a
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
Disadvantages
X-ray tube
Basic Principles
基本原理
Trans- 穿透射线探头 mission Detector
Metal - Thickness, t （物体-厚度t )
Source
射线源
Measurement of Thickness 厚度测量
I=I0e-t/q
Theory of Transmission Gauging for Thickness Measurement of Metals
穿透式测厚仪测量原理
X-ray Fluorescens Generation
X-ray Emission
Excited Electron Leaving Atom
Vacancy is filled by an outer orbital electron with emission of characteristic X-rays
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） Cs137 （铯137） Cm244（锔244） Sr90 （锶90） Kr85 （氪85） Pm137（钷137）
433 years （年） 3 0 years （年） 17.8 years （年） 29.6 years （年） 10.7 years （年） 2.6 years （年）
灯丝被通电加热，产生大量的电子，在极间的高压作用下，释放出来的电子高速从阴 极运动到阳极。 • The electrons hit the anode at great speed. 该电子高速撞击阳极。 • When the electrons collide with the anode material, x-rays are produced. 当电子碰撞阳极靶材，产生X射线。 • Example: 100kV, 3mA => Tube power 300W, 6W radiation power and 294W thermal losses. 6W辐射功率和294W以热量形式丧失。