红外测温的原则(一)

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红外测温的原则(一)

外文翻译
红外测温的原则
红外线测温对于确定一个精确的监控系统是一个重要前。不幸的是，许多用户不愿意花时间去了解基本的指南，因而否认非接触测温能够实现精确测温。
理论和本质
温度测量可以分为两累：接触测温和非接触测温。热电耦和温度计经常应用于温度检测。他们在测量温度的时候必须选择一个相对较低的温度作为参考温度，他们的价格很低。非接触传感器靠测量目标发出的红外线的能量来确定被册物体的温度，它的响应速度快，经常用来测量运动的，不连续的，真空条件下的物体的温度，并能够在比较恶劣的条件下测温。但是相对接触测温仪来说，它的价格较高。
1666年艾萨克・牛顿先生发现了红外辐射，他从穿过棱镜能产生七彩光的阳光中提取出了电磁能。1800年，牛顿开始研究其它颜色的光的能量。但是他没有发现非可见光的能量。20是世纪前期Planck, Stefan, Boltzmann, Wien和Kirchhoff进一步研究，终于发现了红外线的辐射能。通过这次研究，人们可以通过黑体单位面积的功率曲线来定义红外线的能量。黑体单位面积的功率的概念是红外测温的基础。有期限的放射性使物理定律出现了一定的变化。放射形是在同一温度非黑体射线与黑体射线的比率。由能量守衡定律可知，射线的传输系数，反射系数以及放射系数之和等于1。即tl+ rl+al=1。发射性等于吸收性。设El=al 则 El=1-tl-rl。这个发射性系数与Planck提出的作为可变物相对波长表面的特征描述的等式相符。多数被测物体是不透明的，放射性系数可以简化为：El=1-rl。也有一些例外的材料，如：玻璃，硅以及塑料，但是通过一定的过滤，也能在他们的不透明红外区对他们进行测量。这种测量方法有很多要注意的地方，主要有以下几点：红外传感器实质上是色盲；如果目标是视觉上反射性的，要注意，实际测量的是放射能和反射能的和；如果被测物体是透明的，要注意红外线的过滤。90％的温度测量，是不需要测量物体的绝对温度的。反复和无漂移操作多用于闭环温度控制。如果被测物体表面是发光的，就需要做放射性调整，可以自动或者手动调整放射形错误。放射性调整应用非常广泛。如果存在放射性变化，在处理过程中，可以通过考虑双波长或者多波长辐射去抵消放射性问题的影响。
设计元素
红外线温度使光，电，外形以及风装物等附属参数产生了很大的变化。相同的是，它们都以红外辐射作为输入，以电信号作为输出。这个基本的链条由收集光学，透镜，纤维光学和过滤组成。动态处理有许多形式，可以被总结作为放大作用，热量稳定，　线性化和信号适应。正常玻璃窗是能用波长介于中等长度范围的短波的石英和8-14 μm范围的锗或锌硫化物的。纤维光学在0.5-5.0 μm区域内是可利用的。从应用立场，光学的主要特征是视野(FOV)，即，什么是目标大小在规定的远处？一个非常共同的组合系统，例如，是1寸在距离目标15寸大小的工作距离。使用相对正方形定律，对目标区域加倍。目标大小(被测量的区域的)实际定义是根据供应商和它的价格变化。其他光学配置从小斑点特写镜头针尖测量到对遥远的光学遥远瞄准变化。注意到是重要的，工作距离不应该影响准确性，如果FOV由targe 填装。在测量FOV的一个技术，可变物是信号损失。一个严密的规则是1%能量减少，虽然一些数据被提出在半功率，或者63.2%。对准线(瞄准)是另一个光学因素。许多传感器缺乏那能力; 透镜用于表面的排列和测量表面温度。这与相当大的目标，例如，纸幅一起使用，精确度是不需要的。为使用小斑点光学的小目标，并且为遥远的光学在远距离监控，使用了视觉瞄准，激光。有选择性过滤对高温广泛地使用短波过滤器。这明显地适合黑体分布曲线，并且有一些技术优点。例如，高温或短波用一个非常热量地稳定的硅探测器，短波设计由于发射性变异使温度错误减到最小。其他选择性过滤的有塑料胶膜(3.43 μm和7.9 μm)，玻璃(5.1 μm)和火焰不敏感的 (3.8 μm)。各种各样的探测器被用于最大化传感器的敏感性。多数探测器是光电压的，当加强时，投入电压，或者当激发时改变的抵抗。这些快速的反应，高敏感探测器有许多可以克服的交易热量漂泊的方法，包括温度补偿(热敏电阻)电路、温度调节，自动空电路和等温保护。无漂泊操作在不同程度是可利用的，并且是好处很多。在红外线测温仪的电子包裹中，探测器非线性输出信号在大约100-1000μV范围内可被处理。信号是被放大的1000 倍，经调控和线性化，最后产品得到一线性mV或mA信号。趋向往使环境电子噪声干扰减小的4-20 mA的产品方向发展。这个信号可能也被移置到RS 232或到PID控制器、遥远的显示或者记录器。额外的信号波形加工介入开关警报，为断断续续的目标建立的可调整的高峰，可调整的反应时间和样本及保存电路。一般情况下，红外线温度计有300ms的反应时间，虽然１0ms的输出信号可以通过硅探测器得到。在现实世界，许多仪器有阻止阻尼输入信号可调整的反应能力，并能进行灵敏度调整。快速的响应能里不是必须的。在加热等典型的应用情况下，响应时间需要在１０-５０ms范围内，这可以通过红外测温仪器得以实现。

附录3
外文原文
Principles of Infrared
Thermometry
The fundamentals of IR thermometry are an important prerequisite for specifying an accurate monitoring system. Unfortunately,many users do not take the time to understand the basic guidelines, and consequently reject the concept of noncontact temperature measurement as inaccurate.
Theory and fundamentals
Temperature measurement can be divided into two categories:contact and noncontact.Contact thermocouples, RTDs, and thermometers are the most prevalent in temperature measurement applications. They must contact the target as they measure their own temperature and they are relatively slow responding, but they are inexpensive. Noncontact temperature sensors measure IR energy emitted by the target, hcs is the field of view (FOV), i.e., what is the target size at a prescribed distance? A very common lens system, for example, would be a 1 in. dia. target size at a 15 in. working distance. Using the inverse square law, by doubling the distance (30 in.) the target area theoretically doubles (2 in. dia.). The actual definition of target size (area measured) will vary
depending upon the supplier, and it is price dependent. Other optical
configurations vary from small spot for close-up pinpoint measurement, to distant optics for distant aiming. It is important
to note that working distance should not affect the accuracy if the FOV is filled by the target. In one technique for measuring FOV, the variable is signal loss vs. diameter. A strict rule is a 1% energy reduction, although some data are presented at half power, or 63.2% Alignment (aiming) is another optical factor. Many sensors lack that capability; the lens is aligned to the surface and measures surface temperature. This works with sizable targets, e.g., paper web, where pinpoint accuracy is not required. For small targets that use small-spot optics,and for distant optics used in remot monitoring, there are options of visual aiming, aim lights, and laser alignment. Selective spectral filtering typically uses short-wavelength filters for hightemperature applications. This obviously fits the blackbody distribution curves, and there are some technological advantages. For example, high temperature/short wavelength uses a very thermally stable silicon detector, and the short-wavelength design minimizes temperature error due to emissivity variations. Other selective filtering is used for plastic films (3.43 μm and 7.9 μm), glass (5.1 μm), and flame insensitivity (3.8 μm). A variety of detectors are used to maximize the sensitivity of the sensor. Most detectors are either photovoltaic, putting out a voltage when energized, or photoconductive, changing resistance when excited. These fast-responding, high sensitive detectors have a tradeoff thermal drift that can be overcome in many ways, including temperature compensation (thermistors) circuitry, temperature regulation, auto null circuitry, chopping (AC vs. DC output),and isothermal protection. Drift-free operation is available in varying degrees and is price dependent. In the IR thermometer’s electronics package, the detector’s nonlinear output signal, on the order of 100-1000 μV, is processed. The signal is amplified 1000 x, regulated, and linearized, and the ultimate output is a linear mV or mA signal. The trend is toward 4-20 mA output to minimize environmental electrical noise interference. This signal can also be transposed to RS 232 or fed to a PID controller, remote display, or recorder. Additional signal conditioning options involve on/off alarms, adjustable peak hold for intermittent targets, adjustable response time, and/or sample-and-hold circuitry. On the average, IR thermometers have a response time on the order of 300 ms, although signal outputs on the order of 10 ms can be obtained with silicon detectors. In the real world, many instruments have an adjustable response capability that permits damping of noisy incoming signals and field adjustment on sensitivity. It is not always necessary to have the fastest response available. There are cases involving induction heating and other types of applications, however, where response times on the order of 10-50 ms are required, and they are attainable through IR thermometry.
ave fast response, and are commonly used to measure moving and intermittent targets, targets in a vacuum, and targets that are inaccessible due to hostile environments, geometry limitations, or safety hazards. The cost is relatively high, although in some cases is comparable to contact devices.
Infrared radiation was discovered in 1666 by Sir Isaac Newton, when he separated the electromagnetic energy from sunlight by passing white light through a glass prism that broke up the beam into colors of the rainbow. In 1800, Sir William Herschel took the next step by measuring the relative energy of each color. He also discovered energy beyond the visible. In the early 1900s,Planck, Stefan, Boltzmann, Wien, and Kirchhoff further defined the activity of the electromagnetic spectrum and developed quantitative data and equations to identify IR energy. This research makes it possible to define IR energy using the basic blackbody emittance curves 。The concept of blackbody emittance is the foundation for IR thermometry. There is, however, the term “emissivity” that adds a variable to the basic laws of physics. Emissivity is a measure of the ratio of thermal radiation emitted by a graybody (non-blackbody) to that of a blackbody at the same temperature. The law of conservation of energy states that the coefficient of transmission, reflection, and emission (absorption) of radiation must add up to 1: tl+rl+al= 1 and the emissivity equals absorptivity: El=al Therefore: El=1-tl-rl This emissivity coefficient fits into Planck’s equation as a variable describing the object surface characteristics relative to wavelength. The majority of targets measured are opaque and the emissivity coefficient can be simplified to: El=1-rl Exceptions are materials like glass, plastics, and silicon, but through proper selective spectral filtering it is possible to measure these objects in their opaque IR region. There is typically a lot of confusion regarding emissivity error, but the user need remember only four things: IR sensors are inherently colorblind.If the target is visually reflective, beware-you will measure not only the emitted radiation, as desired, but also reflected radiation. If you can see through it, you need to select IR filtering Nine out of ten pplications do not require absolute temperature measurement. Repeatability and drift-free operation yield close temperature control. If the surface is shiny, there is an emissivity adjustment that can be made either manually or automatically to correct for emissivity error. It is a simple fix for most applications. In cases where emissivity varies and creates processing problems, consider dual- or multiwavelength radiometry to eliminate the emissivity problem.
Design elements
IR thermometers come in a wide variety of configurations pertaining to optics, electronics, technology, size, and protective enclosures. All, however, have a common chain of IR energy in and an electronic signal out. This basic chain consists of collecting optics, lenses, and/or fiber optics, spectral filtering, and a detector as the front end. Dynamic processing comes in many forms, but can be summarized as amplification, thermal stability, linearization, and signal conditioning. Normal window glass is usable at the short wavelength, quartz for the midrange, and germanium
or zinc sulfide for the 8-14 μm range. Fiber optics are available to cover the 0.5-5.0 μm region. From an applications standpoint, the
primary characteristic of the opti

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