Radiation Thermometry Research Articles

Scattering model for rough oxidized metal surfaces applicable to radiation thermometry of reformer furnaces

Experimental measurements of polarized light scattered from a rough oxidized metal surface are presented. The metal is a heavily oxidized nickel alloy taken from tubes in a large steam reformer furnace. Many of the existing models for reflections off rough surfaces are tested on the data. A semiempirical model based on the approach of Torrance and Sparrow is developed and gives a good fit to the data. The model is computationally inexpensive and permits modeling of the reflection corrections in the radiation thermometry of reformer furnaces.

A Scanning Radiation Thermometry Technique for Determining Temperature Distribution in Gas Turbines

A scanning radiation thermometry technique for determining temperature distributions in gas turbines is presented. The system, an enhancement of an earlier work, can be used by operators even without special training, since the temperature distribution is measured and corrected in terms of the error due to the reflected radiation only on the basis of the turbine’s known geometry and the physical properties of the materials. In the proposed model, the surface-exitent radiances are directly acquired via 360-deg scans. Experimental testing was performed on a static turbine-blading model. Since the angle factors emerged as a notable influence on the accuracy of the model, two angle factor calculation methods, selected for suitability from a literature survey, are exhaustively investigated, and their selection criteria defined.

Temperature measurement by UV thermal radiation

Summary Accurate measurement of temperature is of considerable importance in materials processing, such as welding, thermal cutting, and heat treatment of metals. Radiation thermometry has a distinct advantage over other temperature detection methods, since it requires no physical contact with the work. The reliability of thermometry, however, is limited if the emissivity of the work to be measured is not accurately known. Planck's law of radiation shows that the effect of temperature on the spectral radiance is greater at shorter wavelengths. The present paper experimentally describes the characteristics of UV (ultraviolet) thermometry. A temperature measurement test by the UV spot sensor (spectral range: 0.25 μm) shows that the melting point of Ni can be measured with an accuracy of ± 1 % regardless of any emissivity fluctuation. The CCD camera with UV filter used in this investigation makes it possible to detect the temperature image on the work in welding virtually independently of the emissivity of t...

A theory of reflections for traceable radiation thermometry

This paper develops a model that provides the means to calculate the errors and uncertainties in radiation thermometry measurements affected by reflections. This addresses the serious and frequently encountered problem of ensuring traceability when measuring the temperature of non-black objects. Measurement strategies are outlined for the three situations where there exists an extraneous source of radiation at a much lower, similar, and much higher temperature than that of the object of interest. In the first strategy shorter-wavelength thermometers have smaller reflection errors and experimental uncertainties than longer-wavelength thermometers. In the second strategy there is an optimum operating wavelength that makes a compromise between the reflection error and the uncertainty. In the third strategy, which corrects for the reflection error, there is also an optimum wavelength for which the uncertainty attains a minimum value. By considering all of the practical factors involved, this approach reveals limitations in previous error analyses which concluded that the longest-wavelength thermometers should be used to minimize reflection errors. Recommendations are given for the use of the three strategies in minimizing reflection errors and uncertainties.

Temperature error in radiation thermometry caused by emissivity and reflectance measurement error

A general expression for the temperature error caused by emissivity uncertainty is developed, and it is concluded that lower-wavelength systems provide significantly less temperature error. A technique to measure the normal emissivity is proposed that uses a normally incident light beam and an aperture to collect a portion of the energy reflected from the surface and to measure essentially both the specular component and the biangular reflectance at the edge of the aperture. The theoretical results show that the aperture size need not be substantial to provide reasonably low temperature errors for a broad class of materials and surface reflectance conditions.

High speed, two-wavelength radiation thermometry of single micro particles during CO 2 laser heating

A high speed, two-wavelength radiation thermometer that is capable of monitoring surface temperatures of 50–150 μm diameter particles in the 600–2000 K range and at heating rates of up to 10 6 K/s, characteristic of pulverized coal combustion, was designed and constructed. To meet the above characteristics, special attention was paid to detector wavelength range and speed, detection electronics and optical system alignment. The thermometer was calibrated using an in-house constructed, black cavity radiation source. Spherocarb model particles, which have more uniform size, physical properties and emissivity than coal particles, were used to demonstrate the level of short term reproducibility attainable. Consistent, reproducible temperature—time profiles obtained for particles from different coals indicate that non-grey body effects do not dominate these measurements.

紫外線放射計測による温度場の測定

The accurate measurement of temperature is of great importance in the materials processing such as welding, thermal cutting and heat treatment of metals. The radiation thermometry has a distinct advantage over other temperature detecting method, where it requires no physical contact with the work. The reliability of the thermometry is, however, limited if the emissivity of the work to be measured is not accurately known.According to Planck's law of radiation, it is evident that the effect of temperature on spectral radiance is greater at the shorter wavelengths. In the present paper, the characteristics of UV (ultra-violet) thermometry has been discussed experimentally. The temperature measurement test by UV spot-sensor (spectral range : 0.25μm) shows that the melting point of Ni can be measured with an accuracy of ±1% for any change of the emissivity. The CCD camera with UV-filter, used in this work, made it possible to detect the temperature image on the plate in welding, nearly independent of the emissivity of object.

Thermal metrology after the introduction of the ITS-90

The adoption of the international temperature scale of 1990 (ITS-90) is producing significant innovation in thermal metrology. The temperature range of the ITS is wider than that of the previous editions. Also the scale precision and the accuracy of the thermodynamic temperature values forming its base have been improved. A short presentation of the ITS-90 will introduce its most important features, describing briefly the types of interpolating instruments and fixed points. To realize the ITS-90, many national laboratories will have to develop within their premises relatively new techniques of measurement such as gas thermometry to interpolate between fixed points from 3 K and 24.6 K and high-temperature platinum resistance thermometry. The highest precision is acheived in the temperature range −40°C to 30° C, where the ITS-90 combines the most reproducible fixed points with the interpolating instrument exhibiting the highest accuracy and the lowest nonuniqueness. Since a reproducibility better than 0.2 mK can be achieved everywhere in that range, except in the proximity of the triple point of water where it is lower than 0.1 mK (all estimates being at the 1σ level), the size of the kelvin is reporoduced to within 7·10−6 in the worst case, and to within 2·10−7 at the triple point of water. Some practical problems may result from the dissemination of the iTS-90 to users of temperature measurements in the temperature range 420–1085°C. They are related to the construction and use of high-temperature platinum resistance thermometers (HTPRTs), to the practical exploitation of radiation thermometry, and to the availabiality of suitable transfer standards in this temperature range. Several practical realizations of the ITS-90 that are underway in various national laboratories will enable one to better estimate its precision. Such an operation will essentially be carried out through intercomparisons, which will be successful if highly-reproducible transfer standards like the sealed cells for fixed points will be made available. The basic level of the scale precision, i.e., its irreducible component, is given by the scale nonuniqueness. Some results are already available and some experiments have recently been proposed in order to provide further data in critical areas. Another important aspect is the scale smoothness and its effect on the measured thermal properties. With the introduction of the ITS-90 the projects for the determination of thermodynamic properties have not completely stopped. Radiometric determinations and noise thermometry are mainly carried out at temperatures between 660°C and 1085°C. Other experiments involving gas thermomery may lead to better determinations below 3 K. Thermal noise measurements are presently considered for the redetermination of the Boltzmann constant, kB. Their uncertainty should be within ± 10ppm, still too high to propose such a method for the definition of the kelvin in terms of kB and of the SI unit of energy. As regards the determination of thermophysical properties of matter, special importance is now attributed to the temperature dependence of the vapor pressure of sodium. Such an interest in connection with the use of pressure-controlled sodium heat pipes for temperature reference. In addition, some information is provided on methods for the determination of pulsed-energy excitation. There, advantage is taken from improvements in radiation thermometry.

Application of dual-wavelength radiation thermometry to the aluminum industry

The objectives of this paper are to introduce the basic principles of dual-wavelength radiation thermometry, to show their utility in inferring temperature, and to investigate the influences of time-at-temperature and temperature on the emissivity behavior of selected aluminum alloys in their processing conditions. Thirteen algorithms are mentioned in this paper, and the results from six of them are reported. Experimental procedures and apparatus are described. The emissivity behavior as a function of time correlated fairly well with the results of Cochran and Sleppy. The ISS algorithm is capable of inferring temperature to within ± 1.6 K . Thus, it is recommended that the ISS algorithm be used for measuring the temperature of 5052 aluminum alloy extruded samples.

Temperature measurements during the galvanneal process

During the galvanneal process, zinc-coated steel sheet is rapidly heat-treated in order to develop desirable characteristics in the material. The surface changes rapidly from a layer of highly specular liquid zinc with a spectral emissivity of approximately 0.1 to a highly diffuse intermetallic layer with an emissivity as high as 0.8. The variability of the emissivity makes application of traditional non-contact temperature measurement unreliable. This study explored the use of a linear relationship between two spectral emissivities together with Planck's equation to simultaneously determine temperature and spectral emissivities. A laboratory simulation of the galvanneal process was performed in order to obtain spectral radiance and temperature data, from which emissivities were calculated. Results obtained indicate that this dual-wavelength radiation thermometry method can infer temperature to within +/− 50 K. Hence, a simple linear relationship between the emissivities is not adequate for accurate temperature measurement. The results suggest that development of a nonlinear equation relating the emissivity values, or an equation including temperature as a parameter, would reduce the temperature errors.

International Workshop on Radiation Thermometry Noordwijkerhout, the Netherlands, 24–25 June 1993

Radiation thermometry is applied in the measurement of temperature where direct contact with the object is impossible, such as in the case of very high temperatures or moving bodies. Important industrial applications are metal, glass, ceramics and plastics and, latterly, semiconductor technology.Recent developments, such as multi-wavelength pyrometry, have motivated the Nederlands Meetinstituut and two Russian institutes, Energotechnica and Symco Association, to organize this workshop. Specialists from Russia, the USA, the UK, Germany and the Netherlands will present state-of-the-art practical applications in radiation thermometry.The workshop will be held on 24 and 25 June 1993 in the "Leeuwenhorst" Congress Centre, Noordwijkerhout, the Netherlands. Information on the technical contents of the programme can be obtained from Dr P Bloembergen, Tel. +31(15) 691 660.RegistrationFor further details please contact: The Training and Consultancy Department, Nederlands Meetinstituut, PO Box 654, 2600 AR Delft, the Netherlands Tel. +31 (15) 691 567.

新型放射測温システムの開発とCAPL,CGLプロセスへの適用

新型放射測温システムの開発とCAPL,CGLプロセスへの適用

Radiation thermometry for low temperatures using an infrared hollow waveguide

Various optical fibers were compared theoretically for application to remote radiation thermometry. The highest optical transmission efficiency is attained with a fluoride glass fiber for the temperature range of > 700°C, with a halide crystalline fiber for 120 to 700°C, and with a dielectric-coated metal hollow waveguide for < 120°C. To realize remote sensing of lower temperatures, i.e., from room temperature to ~300°C, a radiometric experiment was carried out using a Ge-coated Ag hollow waveguide. When ambient temperature changed from 22 to 50°C, a serious error arose in the measured temperature, which is attributed to the increase of thermal radiation from the heated waveguide. Since the effect of such noise radiation is inevitable in thermometry using infrared fibers, we propose a measurement method to compensate for the noise level. With the compensation, the effect of ambient temperature was reduced successfully and reliable thermometry was established.

A bulk similarity approach in the atmospheric boundary layer using radiometric skin temperature to determine regional surface fluxes

Profiles of wind velocity and temperature in the outer region of the atmospheric boundary layer (ABL) were used together with surface temperature measurements, to determine regional shear stress and sensible heat flux by means of transfer parameterizations on the basis of bulk similarity. The profiles were measured by means of radiosondes and the surface temperatures by infrared radiation thermometry over hilly prairie terrain in northeastern Kansas during the First ISLSCP Field Experiment (FIFE). In the analysis, the needed similarity functions were determined and tested; the main scaling variables used for the ABL were hi, the height of the convectively mixed layer, and Va and θa, the wind speed and potential temperature averaged over the mixed layer. Good agreement (r = 0.80) was obtained between values of friction velocity u* determined by this ABL bulk similarity approach and those obtained by Monin-Obukhov similarity in the surface sublayer. Similarly, values of surface flux of sensible heat H determined by this method compared well (r = 0.90) with the regional means measured at six ground stations. The corresponding regional evaporation values, determined with the energy budget equation, also compared favorably (r = 0.94).

Radiation thermometry of silicon wafers in a diffusion furnace for fabrication of LSI

A radiation thermometry technique suitable for measuring the temperature of silicon wafers in a diffusion furnace has been developed. A principal feature of this technique is that it measures the temperature of wafers that are not in the line of sight of a conventional pyrometer. An optical guide, consisting of two quartz prisms, gives optical access to interior wafers in the load. A measuring wavelength of 0.9 mu m is selected since a silicon wafer is opaque and its emissivity does not depend on temperature at this wavelength. The accuracy of the thermometry is examined by comparing the measured value of the pyrometer with that of a thermocouple. The two measured values agree within +or-2 degrees C in a steady state. When wafers are being inserted into or drawn out from the furnace, however, an error is caused by the veiling glare at the optical guide and the wafer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

RADIATION THERMOMETRY OF SILICON WAFERS IN A DIFFUSION FURNACE WITH ROD-TYPE AND PRISM-TYPE OPTICAL GUIDES

This article examines the accuracy of radiation thermometry in measuring the temperature of silicon wafers in a diffusion furnace. This technique uses optical guides to bring thermal radiation from the wafers to the outside of the furnace. The error due to veiling glare of a rod-type optical guide is 40°C and that of a prism-type is 0.5°C at steady state.

A thin-film bolometer for radiation thermometry at ambient temperature

Abstract A thin-film bolometer which has the advantages of batch processing and silicon technology is presented. The bolometer is designed for infrared radiation thermometry in the room temperature range. Special care was taken to allow precise compensation for the influence of the ambient temperature. A set of sensors with different geometries was fabricated. Their measurement characteristics can be understood with the help of a thermodynamic model. A sensitivity of E = 25 V/W was obtained together with a time constant of 12ms. The noise equivalent power was NEP ≤ 0.5 nV/√Hz.

Dual-wavelength radiation thermometry: Emissivity compensation algorithms

The traditional contact methods of temperature measurement for metal processing applications provide accuracies of ±10 K. Noncontact methods based upon emissivity compensation techniques have the potential for improved accuracy with greater ease of use but require prior knowledge of the target emissivity behavior. The features of the basie spectral and ratio methods and five dualwavelength methods are reviewed. Experiments were conducted on a series of aluminum alloys with different surface treatments characterized by x-ray photoelectron spectroscopy in the temperature range 600 to 750 K. Compensation algorithms that account for surface characteristics are required to achieve improved accuracy.

Problems with Porometry: Measuring Net Photosynthesis by Leaf Chamber Techniques

AbstractPrior experiments with cotton (Gossypium hirsutum L.) and water hyacinth [Eichhornia crassipes (Mart.) Solms] demonstrated that porometer chamber conditions may significantly perturb the measurement of leaf stomatal conductance. Thus, this study was conducted to determine if net photosynthesis rate measurements of water hyacinth and cotton leaves were similarly perturbed by leaf chamber conditions and, if so, to devise a method to correct for the instrument‐induced error. Several net photosynthesis rate and concurrent canopy environmental data sets for these two plant species were analyzed at Phoenix, AZ within the context of the non‐water‐stressed baseline paradigm, which relates foliage‐to‐air temperature difference to air vapor pressure deficit. It was found that leaf chamber measurements of net photosynthesis rate were subject to the same type of measurement error as that associated with porometer measurements of leaf stomatal conductance. For plants transpiring at potential rates, photosynthesis rates can be corrected by using ancillary data obtained by the leaf chamber system. However, the proper adjustment of net photosynthesis rates of water‐stressed plants measured with leaf chambers required free‐air foliage and air temperatures, as well as the free‐air humidity. It was demonstrated that concurrent infrared radiation thermometry, as well as simultaneous measurements of air wet‐ and dry‐bulb temperatures, are required to correctly evaluate, by leaf chamber techniques, the net photosynthesis rates of plants that are experiencing any degree of stomatal closure due to some aspect of their normal environment.

Measurement of the Silver Point with a Simple, High-Precision Pyrometer

A pyrometer is described which is simple and easy to construct, yet fulfils the requirements of a standards laboratory which wishes to perform radiation thermometry to very high accuracy. A test of its performance is described in which it was used to measure the ratio of the spectral radiances at 650 nm of black bodies at the melting points of silver and gold. Taking the gold-point temperature to be 1064.43 °C, this measurement gave a result of (961.961 ± 0.017) °C (99% confidence level) as the value of the silver-point temperature.