紅外測溫的原則(一)

外文翻譯
紅外測溫的原則
 紅外線測溫對(duì)于確定一個(gè)精確的監(jiān)控系統(tǒng)是一個(gè)重要前。不幸的是，許多用戶不愿意花時(shí)間去了解基本的指南，因而否認(rèn)非接觸測溫能夠?qū)崿F(xiàn)精確測溫。
理論和本質(zhì)
 溫度測量可以分為兩累：接觸測溫和非接觸測溫。熱電耦和溫度計(jì)經(jīng)常應(yīng)用于溫度檢測。他們?cè)跍y量溫度的時(shí)候必須選擇一個(gè)相對(duì)較低的溫度作為參考溫度，他們的價(jià)格很低。非接觸傳感器靠測量目標(biāo)發(fā)出的紅外線的能量來確定被冊(cè)物體的溫度，它的響應(yīng)速度快，經(jīng)常用來測量運(yùn)動(dòng)的，不連續(xù)的，真空條件下的物體的溫度，并能夠在比較惡劣的條件下測溫。但是相對(duì)接觸測溫儀來說，它的價(jià)格較高。
 1666年艾薩克・牛頓先生發(fā)現(xiàn)了紅外輻射，他從穿過棱鏡能產(chǎn)生七彩光的陽光中提取出了電磁能。1800年，牛頓開始研究其它顏色的光的能量。但是他沒有發(fā)現(xiàn)非可見光的能量。20是世紀(jì)前期Planck, Stefan, Boltzmann, Wien和Kirchhoff進(jìn)一步研究，終于發(fā)現(xiàn)了紅外線的輻射能。通過這次研究，人們可以通過黑體單位面積的功率曲線來定義紅外線的能量。黑體單位面積的功率的概念是紅外測溫的基礎(chǔ)。有期限的放射性使物理定律出現(xiàn)了一定的變化。放射形是在同一溫度非黑體射線與黑體射線的比率。 由能量守衡定律可知，射線的傳輸系數(shù)，反射系數(shù)以及放射系數(shù)之和等于1。即tl+ rl+al=1。發(fā)射性等于吸收性。設(shè)El=al 則 El=1-tl-rl。這個(gè)發(fā)射性系數(shù)與Planck提出的作為可變物相對(duì)波長表面的特征描述的等式相符。多數(shù)被測物體是不透明的，放射性系數(shù)可以簡化為：El=1-rl。也有一些例外的材料，如：玻璃，硅以及塑料，但是通過一定的過濾，也能在他們的不透明紅外區(qū)對(duì)他們進(jìn)行測量。這種測量方法有很多要注意的地方，主要有以下幾點(diǎn)：紅外傳感器實(shí)質(zhì)上是色盲；如果目標(biāo)是視覺上反射性的，要注意，實(shí)際測量的是放射能和反射能的和；如果被測物體是透明的，要注意紅外線的過濾。90％的溫度測量，是不需要測量物體的絕對(duì)溫度的。反復(fù)和無漂移操作多用于閉環(huán)溫度控制。如果被測物體表面是發(fā)光的，就需要做放射性調(diào)整，可以自動(dòng)或者手動(dòng)調(diào)整放射形錯(cuò)誤。放射性調(diào)整應(yīng)用非常廣泛。如果存在放射性變化，在處理過程中，可以通過考慮雙波長或者多波長輻射去抵消放射性問題的影響。
設(shè)計(jì)元素
 紅外線溫度使光，電，外形以及風(fēng)裝物等附屬參數(shù)產(chǎn)生了很大的變化。相同的是，它們都以紅外輻射作為輸入，以電信號(hào)作為輸出。這個(gè)基本的鏈條由收集光學(xué)，透鏡，纖維光學(xué)和過濾組成。動(dòng)態(tài)處理有許多形式，可以被總結(jié)作為放大作用，熱量穩(wěn)定，　線性化和信號(hào)適應(yīng)。正常玻璃窗是能用波長介于中等長度范圍的短波的石英和8-14 μm范圍的鍺或鋅硫化物的。纖維光學(xué)在0.5-5.0 μm區(qū)域內(nèi)是可利用的。從應(yīng)用立場，光學(xué)的主要特征是視野(FOV)，即，什么是目標(biāo)大小在規(guī)定的遠(yuǎn)處？一個(gè)非常共同的組合系統(tǒng)，例如，是1寸在距離目標(biāo)15寸大小的工作距離。使用相對(duì)正方形定律，對(duì)目標(biāo)區(qū)域加倍。目標(biāo)大小(被測量的區(qū)域的)實(shí)際定義是根據(jù)供應(yīng)商和它的價(jià)格變化。其他光學(xué)配置從小斑點(diǎn)特寫鏡頭針尖測量到對(duì)遙遠(yuǎn)的光學(xué)遙遠(yuǎn)瞄準(zhǔn)變化。注意到是重要的，工作距離不應(yīng)該影響準(zhǔn)確性，如果FOV由targe 填裝。在測量FOV的一個(gè)技術(shù)，可變物是信號(hào)損失。一個(gè)嚴(yán)密的規(guī)則是1%能量減少，雖然一些數(shù)據(jù)被提出在半功率，或者63.2%。對(duì)準(zhǔn)線(瞄準(zhǔn))是另一個(gè)光學(xué)因素。許多傳感器缺乏那能力; 透鏡用于表面的排列和測量表面溫度。這與相當(dāng)大的目標(biāo)，例如，紙幅一起使用，精確度是不需要的。為使用小斑點(diǎn)光學(xué)的小目標(biāo)，并且為遙遠(yuǎn)的光學(xué)在遠(yuǎn)距離監(jiān)控，使用了視覺瞄準(zhǔn)，激光。有選擇性過濾對(duì)高溫廣泛地使用短波過濾器。這明顯地適合黑體分布曲線，并且有一些技術(shù)優(yōu)點(diǎn)。例如，高溫或短波用一個(gè)非常熱量地穩(wěn)定的硅探測器，短波設(shè)計(jì)由于發(fā)射性變異使溫度錯(cuò)誤減到最小。其他選擇性過濾的有塑料膠膜(3.43 μm和7.9 μm)，玻璃(5.1 μm)和火焰不敏感的 (3.8 μm)。各種各樣的探測器被用于最大化傳感器的敏感性。多數(shù)探測器是光電壓的，當(dāng)加強(qiáng)時(shí)，投入電壓，或者當(dāng)激發(fā)時(shí)改變的抵抗。這些快速的反應(yīng)，高敏感探測器有許多可以克服的交易熱量漂泊的方法，包括溫度補(bǔ)償(熱敏電阻)電路、溫度調(diào)節(jié)，自動(dòng)空電路和等溫保護(hù)。無漂泊操作在不同程度是可利用的，并且是好處很多。在紅外線測溫儀的電子包裹中，探測器非線性輸出信號(hào)在大約100-1000μV范圍內(nèi)可被處理。信號(hào)是被放大的1000 倍，經(jīng)調(diào)控和線性化，最后產(chǎn)品得到一線性mV或mA信號(hào)。趨向往使環(huán)境電子噪聲干擾減小的4-20 mA的產(chǎn)品方向發(fā)展。這個(gè)信號(hào)可能也被移置到RS 232或到PID控制器、遙遠(yuǎn)的顯示或者記錄器。額外的信號(hào)波形加工介入開關(guān)警報(bào)，為斷斷續(xù)續(xù)的目標(biāo)建立的可調(diào)整的高峰，可調(diào)整的反應(yīng)時(shí)間和樣本及保存電路。一般情況下，紅外線溫度計(jì)有300ms的反應(yīng)時(shí)間，雖然１0ms的輸出信號(hào)可以通過硅探測器得到。在現(xiàn)實(shí)世界，許多儀器有阻止阻尼輸入信號(hào)可調(diào)整的反應(yīng)能力，并能進(jìn)行靈敏度調(diào)整�？焖俚捻憫�(yīng)能里不是必須的。在加熱等典型的應(yīng)用情況下，響應(yīng)時(shí)間需要在１０-５０ms范圍內(nèi)，這可以通過紅外測溫儀器得以實(shí)現(xiàn)。
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
附錄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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