Pyrometric Measurements Research Articles

Investigating the dependence of the temperature of high-intensity discharge (HID) lamp electrodes on the operating frequency by pyrometric measurements

Phase-resolved temperature distributions are determined along a rod-shaped tungsten electrode, by which an ac arc is operated within a model lamp filled with argon. Switched dc and sinusoidal currents are applied with amplitudes of several amperes and operating frequencies being varied between 10 Hz and 10 kHz. The temperature is deduced from the grey body radiation of the electrode being recorded with a spectroscopic measuring system. Phase-resolved values of the electrode tip temperature Ttip and of the power input Pin are determined comparing the measured temperature distributions with the integral of the one-dimensional heat balance with these parameters as integration constants. They are supplemented by phase-resolved measurements of the sum of cathode and anode fall called the electrode sheath voltage. If a switched dc current is applied it is found that both quantities are within the cathodic phase only marginally higher than for a cathode being operated with a dc current. Ttip and Pin start to decrease for low currents and to increase for high currents at the beginning of the anodic phase. But with increasing operating frequency the deviations from the cathodic phase are reduced until they cannot be resolved for frequencies of several kHz. A more pronounced modulation, but the same tendencies, is observed with a sinusoidal current waveform. For 10 kHz a diffuse arc attachment with an almost phase-independent electrode tip temperature, which deviates only marginally from that of a dc cathode, and an electrode sheath voltage proportional to the arc current is established with both current waveforms.

Sensor Fusion Algorithm for Filtering Pyrometer Measurement Noise in the Czochralski Crystallization Process

The Czochralski (CZ) crystallization process is used to produce monocrystalline silicon for solar cell wafers and electronics. Tight temperature control of the molten silicon is most important for achieving high crystal quality. SINTEF Materials and Chemistry operates a CZ process. During one CZ batch, two pyrometers were used for temperature measurement. The silicon pyrometer measures the temperature of the molten silicon. This pyrometer is assumed to be accurate, but has much high-frequency measurement noise. The graphite pyrometer measures the temperature of a graphite material. This pyrometer has little measurement noise. There is quite a good correlation between the two pyrometer measurements. This paper presents a sensor fusion algorithm that merges the two pyrometer signals for producing a temperature estimate with little measurement noise, while having signicantly less phase lag than traditional lowpass

10.2478/s11814-009-0252-1

A combined run-to-run (R2R) and LQG control method has been proposed for rapid thermal processing (RTP) equipment for run-wise improvement and real-time multivariable control of the temperature uniformity over the wafer surface. The standard LQG objective was modified to include a quadratic penalty term for input deviation from bias values which are updated by an R2R control law. The proposed method has been applied to commercial 12-inch rotating RTP equipment with four pyrometers and ten circular groups of tungsten-halogen lamps for measurements and manipulation of wafer temperatures. The performance of LQG control was evaluated under wafer rotation and found to show quite accurate tracking. For evaluation of the combined control technique, a wafer with seven thermocouples (TC’s) attached along the radial direction has been employed for the TC measurements to be used for R2R control, whereas the pyrometer measurements are fed back for real-time LQG control. It was observed that the temperature uniformity is improved as the run number increases.

Thermophysical properties of 22 pure metals in the solid and liquid state – The pulse-heating data collection

The workgroup of subsecond thermophysics in Graz has a long tradition in performing fast pulse- heating experiments on metals and alloys. Thereby, wire-shaped specimens are rapidly heated (10 8 K/s) by a large current-pulse (10 4 A). This method provides thermophysical properties like volume-expansion, enthalpy and electrical resistivity up to the end of the liquid phase. Today, no more experiments on pure metals are to be expected, because almost all elements, which are suitable for pulse-heating so far, have been investigated. The requirements for pulse-heating are: a melting point which is high enough to enable pyrometric temperature measurements and the availability of wire-shaped specimens. These elements are: Co, Cu, Au, Hf, In, Ir, Fe, Pb, Mo, Ni, Nb, Pd, Pt, Re, Rh, Ag, Ta, Ti, W, V, Zn, and Zr. Hence, it is the correct time to present the results in a collected form. We provide data for the above mentioned quantities together with basic information on each material. The uniqueness of this compilation is the high temperature range covered and the homogeneity of the measurement conditions (the same method, the same laboratory, etc.). The latter makes it a good starting point for comparative analyses (e.g. a comparison of all 22 enthalpy traces is in first approximation conform with the rule of Dulong-Petit which states heat capacity - the slope of enthalpy traces - as a function of the number of atoms). The data is useful for input parameters in numerical simulations and it is a major purpose of our ongoing research to provide data for simulations of casting processes for the metal working industry. This work demonstrates some examples of how a data compilation like this can be utilized. Additionally, the latest completive measurement results on Ag, Ni, Ti, and Zr are described.

Pyrometric temperature measurement of ceramic thermal shock samples

The determination of critical failure parameters during thermal shock requires a time and space resolved temperature measurement of the sample. High frequency pyrometry is a suitable technique for such a measurement task, which usually requires the knowledge of the optical properties of the investigated material. Another challenge is the infrared transparency of materials to be checked in the wavelength range of the pyrometer. The thermal shock disks are very thin, due to the need of homogeneous temperature distribution and to maintain a two-dimensional problem. To allow a pyrometric temperature measurement a universal calibration method for high frequency infrared cameras has been developed. Pyrometry in various media was demanded, as well as the estimation of optical properties (reflection, transmittance and emission) for the selected ceramics to be tested.

Testing a solar-blind pyrometer

Surface temperatures are key parameters in many concentrated solar radiation applications. Pyrometric temperature measurement of solar irradiated material surfaces is the alternative to contact measurement techniques, which are inadequate for measuring the temperatures of such surfaces. However, reflected solar radiation is an important uncertainty variable in this non-contact methodology. A promising method for eliminating this solar perturbation is by using centred passband filters on the atmospheric solar absorption bands, creating solar-blind pyrometric systems. A commercial pyrometer has been tested in the wavelength band at around 1.4 µm in the solar furnace at Plataforma Solar de Almería, showing its advantages and limitations. An estimation of temperature measurement uncertainty for a real case is presented with theory and experiment in agreement: the higher the temperature, the lower the uncertainty. Another experiment has shown that the pyrometer measures temperature properly even through quartz windows in this spectral range.

Temperature Measurement Deviation during Annealing of Multiphase Steels

A pyrometric analysis of the temperature of continuous annealed strip material is an essential component of industrial production. However, despite calibration, the development of composition-dependent oxides during annealing prevents an accurate pyrometric measurement of actual strip temperature. An Al-based and a Si-based transformation induced plasticity (TRIP)-assisted steel were pyrometrically analyzed during annealing under a reducing atmosphere (5 pct H2 and 95 pct Ar). Oxide development on both steels led to a deviation between pyrometer readings and simultaneous thermocouple measurements. The developing oxides influenced the pyrometer readings to different extents because of unique emissivities and different growth kinetics.

Pyrometric Temperature Measurement in Concentrated Sunlight With Emissivity Determination

Abstract Pyrometers are commonly used for high temperature measurement, but their accuracy is often limited by uncertainty in the surface emissivity. Radiation heating introduces additional errors due to the extra light reflected off the measured surface. While many types of specialized equipment have been developed for these measurements, this work presents a method for measuring high temperatures using single color pyrometers when the surface emissivity is unknown. It is particularly useful for correcting errors due to reflected light in solar heating applications. The method requires two pyrometers and is most helpful for improving measurement accuracy of low cost commercial instruments. The temperature measurements of two pyrometers operating at different wavelengths are analyzed across a range of sample temperatures to find the surface emissivity values at each wavelength that minimize the difference in temperature measurements between pyrometers. These are taken as the surface emissivity values, and the initial temperature measurements are corrected using the calculated emissivity values to obtain improved estimates of the surface temperature. When applied to temperature data from a solar furnace, the method significantly decreased the difference in the temperature measurements of two single color pyrometers. Simulated temperature data with both random noise and systematic errors are used to demonstrate that the method successfully converges to surface emissivity values and reduces temperature measurement errors even when subjected to significant errors in the model inputs. This method provides a potential low cost solution for pyrometric temperature measurement of solar-heated objects. It is also useful for temperature measurement of objects with unknown emissivity.

Combined run-to-run and LQG control of a 12-inch RTP equipment

A combined run-to-run (R2R) and LQG control method has been proposed for rapid thermal processing (RTP) equipment for run-wise improvement and real-time multivariable control of the temperature uniformity over the wafer surface. The standard LQG objective was modified to include a quadratic penalty term for input deviation from bias values which are updated by an R2R control law. The proposed method has been applied to commercial 12-inch rotating RTP equipment with four pyrometers and ten circular groups of tungsten-halogen lamps for measurements and manipulation of wafer temperatures. The performance of LQG control was evaluated under wafer rotation and found to show quite accurate tracking. For evaluation of the combined control technique, a wafer with seven thermocouples (TC’s) attached along the radial direction has been employed for the TC measurements to be used for R2R control, whereas the pyrometer measurements are fed back for real-time LQG control. It was observed that the temperature uniformity is improved as the run number increases.

Dental Treatment with Laser Beam -Monitoring Enabling Safe Hard-Tooth-Tissue Removal-

With laser-based dental treatment coming into increasing use, we introduce in-process monitoring using a two-color pyrometer and spectroscopic measurement ensuring safe treatment. Sound level monitoring is proposed for detecting hard-dental-tissue removal based on the relationship between tissue removal and sound.

Four-channel sensor-array for the non-contact temperature measurement of liquids in hermetically closed systems

Non-contact thermometers would ideally be suited for temperature control in food industry because they bear no risk of contamination. This paper presents a new method for temperature measurement inside hermetically closed vessels that allows measuring the liquid temperature independent of the superposed thermal radiation of the wall. It solves the problem that conventional pyrometric measurements require a free surface. It extends the range of application of radiation thermometers in food industry extraordinarily. A model of the spectral distribution of the radiant power is given. It includes the temperature distribution and the optical properties of liquid and vessel and proves that the shares of thermal radiation from liquid or container depend on the wavelength. This fact is exploited by a sensor-array. It disposes of four channels with different optical bandwidths that evaluate the thermal radiation emitted by the entire system. The achieved precision is considerably better than the mere determination of the liquid temperature by the outer wall temperature. For polytetrafluorethylen (PTFE), well suited for applications in chemical industry but with weak transparency in mid infrared, the first prototype has an accuracy of 4 K for the worst case with temperature differences between liquid and outer surface of the wall up to 40 K, a 90% improvement to the already existing conventional pyrometers.

Visualization of the Gas-Phase Emitter Effect of Dysprosium in Ceramic Metal Halide Lamps

The gas-phase emitter effect of dysprosium is demonstrated by high-speed photography, spectroscopic, and pyrometric measurements at a high-pressure mercury lamp doped with Nal/Tll/Dyl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , which is operated in a transparent yttrium-aluminia-garnet tube with an f = 100 Hz switched dc current.

Pyroreflectometry to Determine the True Temperature and Optical Properties of Surfaces

In this paper, we present a theoretical analysis and experimental results of a pyrometric temperature measurement method based on a two-color pyroreflectometer (working wavelengths of 1.3μm and 1.55μm) equipped with an optical fiber probe. By measuring simultaneously the radiance temperature and the normal reflectivity, the true temperature of the measurement target can be determined without the previous knowledge of the optical properties of the sample. The method is based on the introduction and the definition of the diffusivity factor ηd and the assumption that it is equal for the two wavelengths. Besides the experimental results, the sources of errors and their impact on the method accuracy and the performance of the setup are discussed. The quality of the measurement results demonstrates the utility of the pyroreflectometry in a domain where fundamental parameters, such as the temperature and radiative properties, present the major measurement difficulties. The diffusivity factor appears not only a step to determine the true temperature but also as a parameter very useful to evaluate the diffusing behavior of opaque materials.

Determination of Scattering and Absorption Coefficients for Plasma‐Sprayed Yttria‐Stabilized Zirconia Thermal Barrier Coatings

Prediction of radiative transport through translucent thermal barrier coatings (TBCs) can only be performed if the scattering and absorption coefficients and index of refraction of the TBC are known. To date, very limited information on these coefficients, which depend on both the coating composition and the microstructure, has been available for the very commonly utilized plasma‐sprayed 8 wt% yttria‐stabilized zirconia (8YSZ) TBCs. In this work, the scattering and absorption coefficients of freestanding plasma‐sprayed 8YSZ coatings were determined from room‐temperature normal‐incidence directional‐hemispherical reflectance and transmittance spectra over the wavelength range from 0.8 to 7.5 μm. Spectra were collected over a wide range of coating thickness from 60 to almost 900 μm. From the reflectance and transmittance spectra, the scattering and absorption coefficients as a function of wavelength were obtained by fitting the reflectance and transmittance values predicted by a four flux model to the experimentally measured values at all measured 8YSZ thicknesses. While the combined effects of absorption and scattering were shown in general to exhibit a nonexponential dependence of transmittance on specimen thickness, it was shown that for sufficiently high absorption and optical thickness, an exponential dependence becomes a good approximation. In addition, the implications of the wavelength dependence of the plasma‐sprayed 8YSZ scattering and absorption coefficients on (1) obtaining accurate surface‐temperature pyrometer measurements and on (2) applying mid‐infrared reflectance to monitor TBC delamination are discussed.

Determination of the hot gas concentration from the difference between contact and remote measurements of the temperature

A method of determining small concentration of hot gases from the difference between indications of sensors whose operation principles are based on contact and remote methods of measuring the temperature of a gas volume is suggested in the paper. It is assumed that the contact measurements allow the true kinetic gas temperature to be determined, and the remote pyrometric measurements yield the radiant temperature. The temperature difference depends unambiguously on the gas concentration, and for the proper chosen working spectral ranges corresponding to concrete requirements, the numerical value of the concentration can be found.

Pyrometric measurement of the temperature of shocked molybdenum

Measurements of the temperature of Mo shocked to $\ensuremath{\sim}60\text{ }\text{GPa}$ and then released to $\ensuremath{\sim}28\text{ }\text{GPa}$ were previously attempted by using high explosive driven flyer plates and pyrometry. The analysis of the radiance traces at different wavelengths indicates that the temporal evolution of the radiance can be explained by a contribution from the LiF window to the measured thermal radiation. By fitting the radiance traces with a simple model, which is supported by continuum dynamics studies, which were able to relate structures in the radiance history to hydrodynamic events in the experiment, the contribution of the window, and hence the temperature of the Mo sample, was obtained. The shock and release temperature obtained in the Mo was $762\ifmmode\pm\else\textpm\fi{}40\text{ }\text{K}$, which is consistent with calculations taking the contribution of plastic work to the heating into account. The radiance obtained for the LiF window shows a nonthermal distribution that can be described by a bulk temperature of $624\ifmmode\pm\else\textpm\fi{}112\text{ }\text{K}$ and hot spots (less than 0.5% in total volume) within the window at a temperature of about 2000 K.

Investigation of the Microwave Iron-Production Process with Multipoint Pyrometric and Spectroscopic Measurements

Carbothermic reduction of magnetite in a 2.45-GHz microwave multimode furnace was investigated with multipoint pyrometric and spectroscopic measurements. Both experimental results emphasize the importance of surface heating of the specimen by microwave-generated plasma for reducing iron oxide. The pyrometric observation shows a shift of the heating mode from the direct volumetric heating by microwave to the surface heating by microwave-generated plasma, when the temperature of the material suddenly rises from ∼800 to ∼1000 °C accompanied by light emission from plasma. The emission spectrum in the near-UV range (240-310 nm) changes drastically from a continuous spectrum to a line emission spectrum of iron, representing progress of carbothermic reduction of iron oxide. The multipoint spectroscopic observation indicates extensive carbothermic reduction occurring on the entire upper surface of the specimen.

全息记录过程中表面温度的实时测量

Photo-induced processes in organic materials mostly occur on molecular levels. Excited molecules may split to form radicals, starting a polymerization process with diffusing monomers. The azo-dyes perform an optically induced cis-trans isomerization. During pattern formation like a holographic grating, the local temperature increase, especially in thin films, is up to date a subject of estimation from absorption and dissipation data. However, the exact knowledge of the surface temperature would help a lot in understanding the resulting refractive index and thickness patterns during holographic exposure. In this paper, in-situ pyrometer measurements are presented. As examples, different photosensitive materials, varying from a photopolymer to polycrystalline azo dyes, are used in order to outline the magnitude of this effect and demonstrate the feasibility of this technique.

The Effect of Dielectric Properties of Sintering Additives on Microwave Sintered Silicon Nitride Ceramics

Silicon nitride requires the use of susceptive additives for microwave liquid phase sintering due to the material’s low dielectric loss. In this article, we report the effect of complex dielectric properties of two compositions of sintering aids on 2.45 GHz microwave sintered Si3N4 with respect to power absorption, temperature distribution and densification behavior. The temperature dependent dielectric properties were measured from 25°C to 1400°C using a conventional cavity perturbation technique. Finite Difference Time Domain (FDTD) electromagnetic simulations coupled with a thermal solver was used to predict the microwave power absorption and the corresponding temperature evolution inside the samples.The additive with higher dielectric loss (4 wt% MgO, 6 wt% Y2O3 and 2.5 wt% ZrO2) produces a greater sintered density than the lower loss additive (4 wt% MgO and 6 wt% Y2O3) or pure Si3N4. Although microwave loss at temperatures below 600°C is insignificant with or without the additives, the loss begins to increase at higher temperatures when the additives are present and has a strong upward trend above 1000°C. Above 1200°C the sample containing ZrO2 exhibited the greatest loss. Numerical simulations at the peak sintering temperature show greater microwave power absorption and higher temperature in the sample with the highest loss additive. The simulation results correlate to the difference in densification behavior observed. The simulation was also useful because the material temperature was not accurately provided by optical pyrometer measurements of the crucible sample holder.

Evaluation of sapphire substrate heating behaviour using GaN band-gap thermometry

The recent development of a commercial band-gap thermometry system for wide band-gap materials such as GaN (the k-Space Associates’ “ BandiT TM ”) has allowed a systematic study of the relationship between pyrometric or thermocouple temperature-monitoring methods and the directly determined layer temperature. The wide band gap of GaN gives a weak and sample-dependent coupling to radiant heat sources, and it is common in molecular beam epitaxy (MBE) to use a sputtered Mo coating on the rear of the sapphire substrate to improve the efficiency and consistency of heat transfer. We have investigated the role of this backing layer and the use of a PBN diffuser in an MBE chamber, but similar results are expected to be obtained from band-gap thermometry in a metal-organic vapour phase epitaxy (MOVPE) system. The wide range spectrometer used for the band-edge determination can also be employed in a pyrometric mode, at wavelengths both within the band gap of GaN and above it. The latter is insensitive to thickness oscillations, and is less affected by the presence or absence of a Mo backing layer. Results are presented comparing all these measurement techniques, and analysed to show that the Mo backing does not significantly increase the power coupling into the epitaxial layer, although it does improve the accuracy of pyrometric measurements.