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Temperature measurement is regarded to be straightforward by means of standard electronic sensors, however, it becomes considerably more challenging if the sensor is exposed to strong electromagnetic interference or harsh environmental conditions such as e.g. chemical agents. In some cases, the problem may be solved by remote sensors, as pyrometers, but their application is conditioned by the possibility of the direct object observation, which is often excluded. In this contribution a solution is presented which allows for the temperature tracking in the fiber optic system which facilitates temperature measurements of distant, subjected to the harsh environment objects by transferring their temperatures to the Peltier module. The idea of the system is to adjust the temperature of the reference FBG (at the measurement stage) to the temperature of the sensor FBG with the use of the Peltier module and thus recover its temperature to have it measured with an arbitrary method. As all electronic part of the system can be installed far from the harsh environment and the system consists of low-cost optical and electronic components, the idea may be found competitive with other methods of the temperature measurements in onerous applications.

3D mathematical model of non-stationary processes of heat and mass transfer was developed for additive manufacturing of materials by direct laser metal deposition. The model takes into account self-consistent dynamics of free surface, temperature fields, and melt flow speeds. Evolution of free surface is modelled using combined Volume of Fluid and Level-Set method. Article presents experimental results of the measurement of temperature distribution in the area of bead formation by direct laser metal deposition, using multi-channel pyrometer, that is based on two-color sensors line. A comparison of experimental data with the results of numerical modeling was carried out. Features of thermal dynamics on the surface of melt pool have been detected, which were caused by thermo-capillary convection.

Time-resolved surface temperature of single crystal silicon was measured by an infrared radiation pyrometer. The silicon sample was irradiated by two pulsed Nd:YAG lasers with pulse duration of 1ms superposed by 7ns pulses, referred to as combined pulse laser (CPL). The change of the damage radius with the millisecond (ms) laser energy density was studied, and then compared with that of single ms laser irradiation. An axisymmetric numerical model was established for calculation of the temperature field distribution while silicon was irradiated by single ms laser and CPL, respectively. Compared with experimental results, the CPL-silicon damage mechanism was discussed.

Spectral emissivity is one of the most critical thermophysical properties of a material for heat design and analysis. Especially in the traditional radiation thermometry, normal spectral emissivity is very important. We developed a prototype instrument based upon an integral blackbody method to measure material’s spectral emissivity at elevated temperatures. An optimized commercial variable-high-temperature blackbody, a high speed linear actuator, a linear pyrometer, and an in-house designed synchronization circuit was used to implemented the system. A sample was placed in a crucible at the bottom of the blackbody furnace, by which the sample and the tube formed a simulated reference blackbody which had an effective total emissivity greater than 0.985. During the measurement, a pneumatic cylinder pushed a graphite rode and then the sample crucible to the cold opening within hundreds of microseconds. The linear pyrometer was used to monitor the brightness temperature of the sample surface, and the corresponding opto-converted voltage was fed and recorded by a digital multimeter. To evaluate the temperature drop of the sample along the pushing process, a physical model was proposed. The tube was discretized into several isothermal cylindrical rings, and the temperature of each ring was measurement. View factors between sample and rings were utilized. Then, the actual surface temperature of the sample at the end opening was obtained. Taking advantages of the above measured voltage signal and the calculated actual temperature, normal spectral emissivity under the that temperature point was obtained. Graphite sample at 1300°C was measured to prove the validity of the method.

Spectral emissivity is a critical material’s thermos-physical property for heat design and radiation thermometry. A prototype instrument based upon an integral blackbody method was developed to measure material’s spectral emissivity above 1000 ℃. The system was implemented with an optimized commercial variable-high-temperature blackbody, a high speed linear actuator, a linear pyrometer, and an in-house designed synchronization circuit. A sample was placed in a crucible at the bottom of the blackbody furnace, by which the sample and the tube formed a simulated blackbody which had an effective total emissivity greater than 0.985. During the measurement, the sample was pushed to the end opening of the tube by a graphite rod which was actuated through a pneumatic cylinder. A linear pyrometer was used to monitor the brightness temperature of the sample surface through the measurement. The corresponding opto-converted voltage signal was fed and recorded by a digital multi-meter. A physical model was proposed to numerically evaluate the temperature drop along the process. Tube was discretized as several isothermal cylindrical rings, and the temperature profile of the tube was measurement. View factors between sample and rings were calculated and updated along the whole pushing process. The actual surface temperature of the sample at the end opening was obtained. Taking advantages of the above measured voltage profile and the calculated true temperature, spectral emissivity under this temperature point was calculated.

The First European South African Experiment (FESTER) was conducted over about a 10 month period at the Institute of Maritime Technology (IMT) in False Bay, South Africa. One of the principal goals was recording of static and dynamic thermal infrared signatures under different environmental conditions for both validations of existing thermal equilibrium signature prediction codes, but also to aid development of dynamic thermal signature models. A small scientific work boat (called Sea Lab) was used as the principal target and sensor platform. Painted metal plates of different thicknesses were also used as infrared targets on-board Sea Lab to study static/dynamic thermal signatures and were also fitted with pyrgeometers, pyrometers and iButton temperature sensors/loggers. First results focused on the variable of thermal signatures as function of environmental conditions and the accuracy of calculated source temperatures (from measured radiometric temperatures) compared to the physical temperature measurements of the plates.

The theoretical concept of a perfect thermal radiator, the blackbody, was first introduced by the German physicist Gustav Robert Kirchhoff in 1860. By the latter half of the nineteenth century it had become the object of intense theoretical and experimental investigation. While an attempt at trying to theoretically understand the behavior of radiation emitted from a blackbody was undertaken by many eminent physicists of the day, its solution was not found until 1900 when Max Planck put forward his now famous law for thermal radiation. Today, of course, understanding blackbody behavior is vitally important to many fields including infrared systems, illumination, pyrometry, spectroscopy, astronomy, thermal engineering, cryogenics, and meteorology. Mathematically, the form Planck’s law takes is rather cumbersome meaning calculations made with it before the advent of modern computers were rather tedious, dramatically slowing the process of computation. Fortunately, during those early days of the twentieth century researchers quickly realized Planck’s equation, and the various functions closely related to it, readily lend themselves to being given a graphical, mechanical, or numerically tabulated form for their evaluation. The first of these computational aids to appear were tables. These arose shortly after Planck introduced his equation, were produced in the greatest number, and remained unsurpassed in their level of accuracy compared to all other aids made. It was also not long before nomograms designed to aid thermal radiation calculations appeared. Essentially a printed chart and requiring nothing more than a straightedge to use, nomograms were cheap and extremely easy to use. Facilitating instant answers to a range of quantities relating to thermal radiation, a number were produced and the inventiveness displayed in some was quite remarkable. In this paper we consider the historical development of many of the nomograms and tables developed and used by generations of scientists and engineers before their sudden and irrevocable decline shortly after the arrival of affordable digital computers and hand-held electronic calculators during the mid-1970s. This work represents a continuation of our earlier work on a number of radiation slide rules developed and used for thermal radiation calculations, with all three of these computational aids being the subject of a forthcoming book.

The influence of the distance between the fiber end and the machined surface on temperature measurements in a two-color fiber-optic pyrometer is analyzed. The propose fiber-optic pyrometer is capable of measuring highly localized temperatures, while avoiding the use of lenses or fiber bundles, by using a standard graded index glass fiber OM1 with 62.5/125 core and cladding diameters. The fiber is placed very close to the target and below the tool insert. The output optical power at both wavelength bands is theoretically and experimentally analyzed for a temperature of 650°C at different fiber positions in a range of 2mm. The results show that there is no influence of the fiber position on the measured optical power and therefore, on the measured temperature.

A 4-color imaging pyrometer was developed to investigate the thermal behavior of laser-based metal processes, specifically laser welding and laser additive manufacturing of stainless steel. The new instrument, coined a 2x pyrometer, consists of four, high-sensitivity silicon CMOS cameras configured as two independent 2-color pyrometers combined in a common hardware assembly. This coupling of pyrometers permitted low and high temperature regions to be targeted within the silicon response curve, thereby broadening the useable temperature range of the instrument. Also, by utilizing the high dynamic range features of the CMOS cameras, the response gap between the two wavelength bands can be bridged. Together these hardware and software enhancements are predicted to expand the real-time (60 fps) temperature response of the 2x pyrometer from 600 °C to 3500 °C. Initial results from a calibrated tungsten lamp confirm this increased response, thus making it attractive for measuring absolute temperatures of steel forming processes.

Process observation in 3D printing of metals currently is one of the central challenges. Many companies strive to employ this additive manufacturing process in their production chains in order to gain competitive advantages through added flexibility in product design and embedded features. The new degrees of freedom are accompanied with the challenge to manufacture every detail of the product to the predefined specifications. Products with filigree internal structures for example require a perfect build to deliver the performance that was designed into these structures. Melting conditions determine properties such as grain structure and density of the finished part before it is sent to post processing steps. Monitoring of such melting conditions is still a challenge where the use of photodiodes, pyrometry and camera systems contribute to an overall picture that might identify errors or deviations during the build process. Additional considerations must be made to decide if these sensors are applied coaxially or from a lateral perspective. Furthermore, setting parameters of focal plane array (FPA) sensors are discussed and events that are seen in the machine vision image are compared against the pyrometry data. The resume of the experiments suggests the application of multiple sensors to the selective laser melting process (SLM) as they jointly contribute to an identification of events. These events need to be understood in order to establish cause effect relationships in the future.

Development and manufacturing of LED structures is still driven by production cost reduction and performance improvements. Therefore, in-situ monitoring during the epitaxial process plays a key role in view of further yield improvement and process optimization. With the continuing trend towards larger wafers, stronger bow and increased aspherical curvature are additional challenges the growers have to face, leading to non-uniform LED-emission. Compared to traditional in-situ metrology like curvature measurement and near UV pyrometry, in-situ photoluminescence measurements can provide a more direct access to the quantum well emission already during growth. In this paper we show how in-situ photoluminescence measurements can be used in a production type multi-wafer MOCVD system to characterize the quantum well emission already during growth. We also demonstrate how deviations from the desired wavelength can be detected and corrected in the same growth run. Since the method is providing spatially resolved line-scans across the wafer, also the uniformity of the emission wavelength can be characterized already during growth. Comparison of in-situ and ex-situ photoluminescence data show excellent agreement with respect to wavelength uniformity on 4 inch wafers.

Quasi-simultaneous laser transmission welding is a well-known joining technique for thermoplastics and mainly used in the automotive as well as in the medical industry. For process control usually the so called set-path monitoring is used, where the weld is specified as "good" if the irradiation time is inside a defined confidence interval. However, the detection of small-sized gaps or thermal damaged zones is not possible with this technique. The analyzation of the weld seam temperature during welding offers the possibility to overcome this problem. In this approach a 3D-scanner is used instead of a scanner with flat-field optic. By using a pyrometer in combination with a 3D-scanner no color-corrected optic is needed in order to provide that laser- and detection-spot are concentric. Experimental studies on polyethylene T-joints have shown that the quality of the signal is adequate, despite the use of an optical setup with a long working distance and a small optical aperture. The effects on temperature are studied for defects like a gap in the joining zone. Therefore a notch was milled into the absorbent polymer. In case of producing housings for electronic parts the effect of an electrical wire between the joining partners is also investigated. Both defects can be identified by a local temperature deviation even at a feed rate of four meters per second. Furthermore a strategy for signal-processing is demonstrated. By this, remaining defects can be identified. Consequently an online detection of local defects is possible, which makes a dynamic process control feasible.

The Velocity Interferometer System for Any Reflector (VISAR) is a critical diagnostic in Inertial Confinement Fusion and High Energy Density research as it has the ability to track shock fronts or interfaces moving 0.1-100 km/s with great accuracy. At the National Ignition Facility (NIF), the VISAR has recently been used successfully for implosion tuning and equation of state measurements. However, the initial design of the companion Streaked Optical Pyrometer (SOP) to measure spectral radiance - hence shock temperature - suffers from large background levels and poor spatial resolution. We report on an upgrade to improve the spatial resolution in the 560-640nm band by using custom lenses and replacing the Dove prism with a K-mirror and implementing a gating-circuit for the streak camera to reduce background signal. We envision that upgraded SOP will provide high quality data collection matching NIF VISAR's standards.

Temperature is an important feature of infrared targets. However, due to the attenuation and distortion parameters in radiation transmission process are unknown, precise temperature measurement is a difficult task. In this paper, a modified Dual-Band Ratio (DBR) temperature measurement method for remote target is proposed. The method is based on a new presented variation derived from the temperature change process named Dual-Band Differential Ratio (DBDR). Firstly, the temperature of the target is estimated by the traditional DBR method, and then a correction using DBDR information is carried out to improve the measurement accuracy. Experiment results showed that the proposed method can improve the temperature measurement accuracy and it could also be carried out without any prior information about the target.

In order to solve the problem of the existing single waveband thermal imaging system can’t get precise temperature of object with emissivity unknown, an optical system of beam splitting lens and filter were used to established a colorimetric temperature measurement system based on infrared thermal imaging system. Completed the compensation for non-effective pixel, enhancement of contrast, calibration of nonhomogeneity and coherence for infrared thermal imaging system according to the application requirement, then acquired the calibration data with blackbody as radiation source at 200°~500° and fit it. A temperature measurement test performed at last, compared with the result acquired by thermocouple and single waveband thermal imaging system, it was shown that the colorimetric pyrometry system achieve the attractive precision after calibration and applied to measure the temperature of the object with emissivity unknown.

Applications involving space based instrumentation and aerodynamically heated surfaces often require knowledge of the bi-directional reflectance distribution function (BRDF) of an exposed surface at high temperature. Addressing this need, the Johns Hopkins University Applied Physics Laboratory (JHU/APL) developed a BRDF facility that features a multiple–port vacuum chamber, multiple laser sources covering the spectral range from the longwave infrared to the ultraviolet, imaging pyrometry and laser heated samples. Laser heating eliminates stray light that would otherwise be seen from a furnace and requires minimal sample support structure, allowing low thermal conduction loss to be obtained, which is especially important at high temperatures. The goal is to measure the BRDF of ceramic-coated surfaces at temperatures in excess of 1000°C in a low background environment. Most ceramic samples are near blackbody in the longwave infrared, thus pyrometry using a LWIR camera can be very effective and accurate.

To achieve the highest possible turbine inlet temperature requires to accurately measuring the turbine blade temperature. If the temperature of blade frequent beyond the design limits, it will seriously reduce the service life. The problem for the accuracy of the temperature measurement includes the value of the target surface emissivity is unknown and the emissivity model is variability and the thermal radiation of the high temperature environment. In this paper, the multi-spectral pyrometer is designed provided mainly for range 500-1000℃, and present a model corrected in terms of the error due to the reflected radiation only base on the turbine geometry and the physical properties of the material. Under different working conditions, the method can reduce the measurement error from the reflect radiation of vanes, make measurement closer to the actual temperature of the blade and calculating the corresponding model through genetic algorithm. The experiment shows that this method has higher accuracy measurements.

In order to determine true radiometric quantities in intense fires a three dimensional (3D) understanding of the fire radiometric properties is desirable, e.g., for estimating peak fire temperatures. Imaging pyrometry with a single infrared camera view can provide only two dimensional path-averaged radiometric information. Multiple camera views, however, can form the basis for determining 3D radiometric information such as radiance, emissivity, and temperature. Analytically the fire can be divided into sub-volumes in which radiometric properties are assumed roughly constant. Using geometric and thermal equilibrium relationships between the fire sub-volumes, together with LWIR camera imagery acquired at multiple carefully defined camera views, radiometric properties of each sub-volume can be estimated. In this work, initial proof-of-principle results were obtained by applying this analysis to sets of LWIR camera imagery acquired during intense (2500 – 3000 K) fires. We present 3D radiance and temperature maps of the fires obtained using this novel approach.

An innovative optical train for a selective laser melting based manufacturing system (SLM) has been designed under the objective to track the course of the SLM process. In this, the thermal emission from the melt pool and the geometric properties of the interaction zone are addressed by applying a pyrometer and a camera system respectively. The optical system is designed such that all three radiations from processing laser, thermal emission and camera image are coupled coaxially and that they propagate on the same optical axis. As standard f-theta lenses for high power applications inevitably lead to aberrations and divergent optical axes for increasing deflection angles in combination with multiple wavelengths, a pre-focus system is used to implement a focusing unit which shapes the beam prior to passing the scanner. The sensor system records synchronously the current position of the laser beam, the current emission from the melt pool and an image of the interaction zone. Acquired data of the thermal emission is being visualized after processing which allows an instant evaluation of the course of the process at any position of each layer. As such, it provides a fully detailed history of the product This basic work realizes a first step towards self-optimization of the manufacturing process by providing information about quality relevant events during manufacture. The deviation from the planned course of the manufacturing process to the actual course of the manufacturing process can be used to adapt the manufacturing strategy from one layer to the next. In the current state, the system can be used to facilitate the setup of the manufacturing system as it allows identification of false machine settings without having to analyze the work piece.

The production of complex titanium components for various industries using laser welding processes has received growing attention in recent years. It is important to know whether the result of the cohesive joint meets the quality requirements of standardization and ultimately the customer requirements. Erroneous weld seams can have fatal consequences especially in the field of car manufacturing and medicine technology. To meet these requirements, a real-time process control system has been developed which determines the welding quality through a locally resolved temperature profile. By analyzing the resulting weld plasma received data is used to verify the stability of the laser welding process. The determination of the temperature profile is done by the detection of the emitted electromagnetic radiation from the material in a range of 500 nm to 1100 nm. As detectors, special high dynamic range CMOS cameras are used. As the emissivity of titanium depends on the wavelength, the surface and the angle of radiation, measuring the temperature is a problem. To solve these a special pyrometer setting with two cameras is used. That enables the compensation of these effects by calculating the difference between the respective pixels on simultaneously recorded images. Two spectral regions with the same emissivity are detected. Therefore the degree of emission and surface effects are compensated and canceled out of the calculation. Using the spatially resolved temperature distribution the weld geometry can be determined and the laser process can be controlled. The active readjustment of parameters such as laser power, feed rate and inert gas injection increases the quality of the welding process and decreases the number of defective goods.

Under full temperature monitoring investigation of the melting of overhang layers has been conducted. Mechanisms of the melt penetration into loose powder bed have been determined. Also temperature regimes of the selective laser melting process of the 3D object from steel 316L powder were investigated.

Thermography methods have found their applications in different fields of human activity. The non-destructive feature of these methods along with the additional advantage by automated remote control and tests of nuclear installations without personnel attendance in the contaminated zone are of particular interest. Laser active pyrometry and laser lock-in thermography for in situ non-destructive characterization of micrometric layers on graphite substrates from European tokamaks were under extensive experimental and theoretical studies in CEA (France). The studies were aimed to obtain layer characterization with cross-checking the layer thermal contact coefficients determined by active laser pyrometry and lock-in thermography. The experimental installation comprised a Nd-YAG pulsed repetition rate laser (1 Hz - 10 kHz repetition rate frequency, homogeneous spot) and a home-made pyrometer system based on two pyrometers for the temperature measurements in 500 - 2600 K range. For both methods, the layer characterization was provided by the best fit of the experimental results and simulations. The layer thermal contact coefficients determined by both methods were quite comparable. Though there was no gain in the measurements accuracy, lock-in measurements have proved their advantage as being much more rapid. The obtained experimental and theoretical results are presented. Some practical applications and possible improvements of the methods are discussed.

When measuring rapid temperature change as well as measuring high temperatures (

This work describes a temperature and emissivity measurement methodology that applies the multi-wavelength pyrometry principle to IR thermography using two IR cameras in a stereo arrangement with detectors working in different wavelength bands. The two radiation distributions measured by the IR cameras are rebuilt on the object surface mesh by means of the pinhole camera model and are used to write a system of equations in which emissivities and temperatures are unknown quantities. By solving the system, the temperature and directional emissivity of the material under test can be measured for each wavelength band.

The measurement data of temporal temperature fluctuation on the cut front while laser cutting of sheet metal (3 mm, 6 mm and 10 mm thickness) are obtained using two-color multi-channel pyrometer. Measurements were carried out for several values of cutting speed and pressure of assisted gas (oxygen), using a 1500W CO2 laser radiation and 1800W Ytterbium fiber laser. The relationship between the temperature fluctuations and the deformation of the melt flow surface on the cutting front in the frequency range above 3 kHz was proven. It is shown that in the case of CO2 laser cutting the temperature fluctuations RMS is greater than 10 K in the range of sub-millimeter capillary waves, but in the case of Fiber Laser cutting the temperature fluctuations RMS is less than 3 K. The spectrum of capillary waves in case of Fiber- Laser cutting is formed under the effect of forced surface deformation at lower frequencies, in particular related to the assisted gas jet. It is shown, that thermo-capillary effect with capillary-wave turbulence generation can be observed in the locations, where exposition intensity of melt surface to CO2 laser radiation exceeds 1 MW/cm2. Thus, an additional mechanism of the anomalous absorption on the front of cutting can compensate the low absorption of the metal in case of 10.6 im laser in comparison with the absorption of the metal in the near infrared range.

Temperature measurement in an extremely harsh environment, such as in a coal gasifier and gas turbine, presents significant challenges to any conventional temperature sensing technology, including thermocouples, IR camera, pyrometer, and blackbody radiation measuring methods. The commonly used fiber Bragg grating (FBG)-based temperature sensors have many advantages, making them very successful in structural health monitoring application. However, conventional FBGs have poor thermal stability and survivability when environmental temperature is beyond 500oC. A band-gap engineering method has been used to transform amorphous fiber material into tetrahedral dominated microstructures, and the mass density modulated grating structure has shown the same fundamental characteristics as conventional FBG but the tetrahedral dominated fiber material enables such grating structure more tolerable to extremely temperature without losing structure integrity. The developed tetrahedral fiber Bragg grating (TFBG) have been prototyped for coal gasification radial and axial distributed temperature measurements. The field validations have demonstrated these TFBG sensors can provide reliable temperature measurement under 1200oC harsh conditions.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

At present, Multi-spectral pyrometer (MSP) used in high-temperature measurement has already had high resolution and high signal to noise ratio. However, the non-source temperature (higher than 3000°C) calibration falls far behind the development of MSP and has already seriously hindered the precision and application range of the pyrometer. In order to break through the limitation of calibration of non-source temperature, a new calibration method has been put forward in this paper. The temperature-voltage (T-U) model is formed based on power function where output voltage U of the MSP is derived from its corresponding known temperature point. Based on the model, Derivative least square method is used to obtain the parameters of the model to realize the non-source temperature calibration. Both theoretical and experimental data have proved the efficiency and precision of the calibration method. In addition, within the spectral range of high-temperature measurement pyrometer (0.4um~1.1um), the theoretical aberration within 1800°C extrapolation range is less than 13.54°C.

Spectral irradiance scale of 250nm-400nm has been realized with the temperature of blackbody traced back to the eutectic fixed-points blackbody. Since the ITS-90 can only be extended to 2473 K and spectral irradiance of 250 nm-400nm requests that the blackbody be operated around 3000 K. The temperature determination of blackbody is calculated using the ratio of spectra radiance at working temperature and a temperature no more than 2473 K. In the experiment, a pyrometer is calibrated by the Pt-C and Re-C eutectic fixed-points blackbody. Accordingly, the measuring scope of the pyrometer can be extends to 2747 K, which is more close to the working temperature. On the other hand, high temperature blackbody BB3500M is first used as the primary standard of spectral irradiance at the National Institute of Metrology (NIM).

The temperature profile of the reaction zone inside the substrate tube of a modified chemical vapour deposition (MCVD) optical fibre perform lathe has been characterised using thermal chirp compensated ultra-high temperature stable regenerated optical fibre Bragg gratings (FBGs). Results indicate significant differences in measured internal temperatures than those predicted theoretically or measured externally.

This work presents a pyrometer for measurement of temperature of a substrate surface during the MBE growth of semiconductor heterostructures. The pyrometer sensor is based on a high-sensitivity low-noise photodiode sensor representing a microassemblage of a Si p-i-n photodiode with an electronic signal processing scheme using time-pulse modulation. The basic advantage of the proposed pyrometer is its high sensitivity, accuracy (not worse than 1.5 o C ) and reproducibility within the temperature interval 450-1200 o C for the operation speed 0.001-1 s under the condition of changing transmission of a vacuum chamber observation (pyrometric) window by up to 10 times. High accuracy and reproducibility of results has been achieved due to implementing the calibration principle against characteristic temperature points inherent in an object and received in situ on indirect measurements.

Mid-infrared immersion lens photodiodes developed at the Ioffe Institute have high spectral selectivity (λmax/uλ≈0.1...0.15) at different wavelengths -2.9, 3.3, 4.2 and 4.7 microns, the response time (up to 10 -9 s) and detectivity (D* ≈ 10 9 -10 11 , (cm√Hz)/W) being significantly higher than those of currently known detectors of thermal radiation[1].The analysis of the transfer function of the temperature sensors based on A3B5 photodiodes has shown that they permit implementing the methods of color and two-color pyrometry providing a significant decrease of the methodical error in optical temperature measurements associated with unknown values of object surface emissivity and uncontrollable changes in the environment transmission.

Temperature monitoring in the laser impact zone is carried out by an originally developed bi-colour pyrometer which is integrated with the optical scanning system of the PHENIX PM-100 machine. Experiments are performed with variation of basic process parameters such as powder layer thickness (0-120μm), hatch distance (60μm-1000μm), and fabrication strategy (the so-called "one-zone" and "two-zone").

According to the energy ratio value of multi-band radiating from the measured surface, the 'true' temperature can be calculated by multi-band pyrometer. Multi-band pyrometer has many advantages: it can hardly be affected by the emission of measured surface and the environment radiation, and it has higher Signal-to-Noise Ratio and higher temperature measurement accuracy. This paper introduces the principle of a multi-band pyrometer and the uncertainty of measurement result is evaluated by using Monte-Carlo Method (MCM). The result shows that the accuracy of effective wavelength is the largest source of uncertainty and the other main source is reference temperature. When using ordinary blackbody furnace with continuous temperature, which can provide reference temperature and calibrate effective wavelength, the uncertainty component is 2.17K and 2.48K respectively. The combined standard uncertainty is 3.30K. A new calibration method is introduced. The effective wavelength is calibrated by monochromator, and the reference temperature is provided by fixed point black body furnace. The uncertainty component is decreased to 0.73K and 0.12K respectively. The measurement uncertainty is decreased to 0.74K. The temperature measurement accuracy is enhanced.

Laser metal deposition (LMD) with high power lasers consists of manufacturing precise layers of materials by fusing metal powder with a laser beam over a substrate. Typical dilution of 5% allows metallurgical adhesion of the coating. This technique provides a unique combination of high accuracy and low heat affecting zone which is attractive for processing high added value components such aeroengines. Nickel (Ni) base superalloys are widely used in aeroengines because of their high mechanical properties when working at high temperatures (creep). A repairing or manufacturing chain of these components by LMD requires a good understanding of many parameters; therefore process control plays an important role. This work is focused on the study of the LMD processing of a Ni base superalloy using two colour pyrometry for the process monitoring. Presented results show how temperature and cooling rates of the LMD tracks affect the shape, microstructure and corrosion of the LMD coatings.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Pyrometer calibration is a common task in most radiometry labs. When measurements are made in a wide range of temperatures, it is necessary to use different blackbody radiators to cover the whole interval. A problem that arises with this is the lack of concordance in the signals measured by the pyrometer when taken from different radiators. In a recent publication, Fourier theory is applied to measure the temperature of inhomogeneous objects, particularly periodic objects 1 . Those results are used to measure the temperature of the coil filament of a reference lamp (in a range from 300 K to 3300 K, approximately), considering the filament as a periodic object, which is modeled with a simple functions arrangement. Measurement verification is also presented by comparing our calculations to the experimental data of the lamp's temperature.

The optical systems for temperature monitoring of SLS/SLM process are developed and integrated with industrial SLS/SLM machines. The system provides the possibility to spatial distribution of brightness temperature at two wavelengths and selected temperature profiles, calculation of colour temperature and express analysis of possible deviations of the maximum temperature from its optimal value. Optimal regimes of SLS process for the sintering of the high porosity powder body was determined.

The surface temperature distribution of a GaAs wafer, heated under vacuum, has been measured using a digital camera. A method is proposed to remove parasitic signals from the image. The accuracy of the thermal image is validated by comparing the results with a separate measurement from absorption band-edge spectroscopy (ABES). The thermal imaging data are observed to be within the experimental error from the ABES technique for the entire surface of the wafer. We observe a radial temperature profile with a center-to-edge difference that varies as a function of the central temperature. A difference of 25 °C is observed for a central temperature of 565 °C. This difference increases with the wafer temperature, confirming that it is due to a net heat flux escaping the wafer by its edge, which is in contact with a graphite holder. Based on these results, a solution is proposed in which the graphite wafer holder is replaced by a ceramic version.

This paper proposes a set of mathematical equations for modelling the REMS GTS, a pyrometer dedicated to measure the brightness temperature of the Martian surface. The equations complete a new simplified analytical thermal model based on an energy balance theory, which considers the inte rnal thermopile structure and operation, and the exchanged heat fluxes between detector transducer and the rest of the elements. The main advantage of this model, versus previous ones, is that it includes a direct relation between the sensor physical properties and the parameters of the model. Therefore, it is simple to establish a methodology to calibrate the system after a change or de gradation in any part of the sensor. In remote or hostile applications this property is very important and ne cessary. The model permits to establish a practical method to identify the model constants, and a differential in-flight calibration algorithm to determine and compensate the degradation of the sensor due to the depositi on of dust over the thermopile window. The main objective of this paper is to show, by using experimental data, the performance of the proposed model, analyzing its capability to measure the temperature of a target surface. It is also included a practical demons tration of the correct behaviour of the in-flight calibration algorithm. Keywords: IR temperature sensor; Sensor thermal model; Sensor calibration; Spacecraft instrumentation; Soil emissivity; Ground temperature; In-flight calibration; Dust deposition.

This paper addresses the development of a laser metal deposition process which consists of a 2 kW Fibre Laser, a CNC table, a wire feeder and a temperature monitoring system. During its development, six infrared pyrometers were tried to compare their performance. The system utilizes two pyrometers to measure both the melt-pool and workpiece (upper layer) temperatures. Experiments have been performed to study the metal deposition parameters with stainless steel 308L wire deposited on stainless steel 304, and good quality metal deposition has been achieved. The results of the parameters study and the development of the temperature monitoring system are presented.

Uncertainty of a target emissivity and environment transmittance and possible reflected radiation are major origins of pyrometer inaccuracy. Measurement without knowledge of emissivity requires gaining at least two independent signals relating to the target. The patented method takes advantage of two same infrared detectors but maintained on different temperatures. A simplified approach implies a radiation enclosure that consists of 2 bodies (target vs. detector), thus a formula for temperature obtained from a set of 2 equations appears simple. Infrared detectors that can work at considerable high temperature are unavailable so temperature range of this method is limited. In an experimental facility, the first thermopile detector is heated by a transistor, the second one is cooled by a Peltier cooler. The swivel radiant heater of cube shape exhibits single of 4 surfaces with different emissivity towards the detectors. The radiation is both concentrated and switched to single detector by a pivoted toric mirror. Close mutual arrangement without optics is optional. All sensors and actuators are connected to a Data Acquisition Switch Unit. The experiment including control loops is fully managed by a PC program. Various side effects of realization like probably an influence of housing radiation at ambient temperature and reflection cause that simple formula is not adequate so that multivariable regression had to be involved. Experimental results are shown in graphs.

The fast growing market for micro technical products requires parts with increasing complexity. While sheet metal forming enables low cost mass production with short cycle times, it is limited by the maximum degree of deformation and the quality of the cut edge. The technology of warm forming partially eliminates these deficiencies. This operation takes place at elevated temperatures before structural transformation is initiated. It combines characteristic advantages of traditional cold and hot forming processes. Lasers as heat sources provide a high, selective and controllable energy input. The general difficulty of a uniform temperature distribution during the heating process can be reached by using an Axicon which generates an annulus on the sheet metal surface. The temperature of the workpiece, measured by a pyrometer, is tuned by a PI-Controller. A tool incorporating a multistage operation die is used for the manufacturing of up to three parts at the same time. The tool is integrated into a hydraulical press. A gearwheel made of the magnesium alloy AZ31 is chosen as metal demonstrator. The quality of these punched parts could be significantly improved at elevated temperatures

Pulse-heating experiments were performed on the strip specimen, taking the specimen from room temperature to melting point based on rapid resistive self-heating of the specimen. The normal spectral emissivity of the specimen was measured by integrating sphere reflectometry developed at HIT. At the same time, the radiance temperature is measured by high-speed pyrometer from 1100K to melting point. Details of the measurement technique, measurement apparatus and the calibration technique are described. Results of normal spectral emissivity of niobium at 905nm from room temperature to its melting point are presented and discussed.

Based on the Kirchhoff's Law, a practical dual-wavelength fiber-optic colorimeter, with the optimal work wavelength centered at 2.1 μm and 2.3 μm is presented. The effect of the emissivity on the precision of the measured temperature has been explored under various circumstances (i.e. temperature, wavelength) and for different materials. In addition, by fitting several typical material emissivity-temperature dependencies curves, the influence of the irradiation (radiant flux originating from the surroundings) and the surface reflected radiation on the temperature accuracy is studied. The results show that the calibration of the measured temperature for reflected radiant energy is necessary especially in low target temperature or low target emissivity, and the temperature accuracy is suitable for requirements in the range of 400-1200K.

By the recent development in electronics, including new solid-state image sensors such as area CCD and C-MOS sensors and the progress of image processing techniques, new imaging radiometers have been developed which two-dimensionally acquire image data of objects moving at a high speed and under high temperature, and (graphically) present the temperature distribution over the object immediately. We successfully measured the temperature distribution and the term KL distribution, which is the absorption strength of combustion in diesel engine cylinders or other luminous flames taking place at a high speed, using single-sensor color high-speed cameras and applying two-color pyrometry introduced by H. C. Hottel and F. P. Btoughton. The measurement accuracy depends on the accuracy of color reproducibility of the high-speed camera being used which is considered a brightness pyrometer, because two-color pyrometry for measuring luminous flames is based on the brightness temperature at two wavelength bands such as red and green. In this paper, we present a method of maintaining the accuracy of measurement using a high-speed camera as a brightness pyrometer and of two-color pyrometry that was developed based on it.

In this paper, a novel technique is presented to measure temperature and axial displacement of turbine blades simultaneously with a single sensor probe, by using non-contact measurement method. The heat radiation property of high temperature objects and the principle of optical fiber transducers in pyrometry are described. Based on the basic principle of colorimetric measurement, a fiber-optic temperature sensor is selected, in view of its high measurement accuracy and practicability, which is suitable for hostile environments. For dynamic external surface measurement, a new reflective intensity-modulated displacement sensor with a simple and reliable structure is proposed .In this project, the main elements for the sensor, circuit system and single chip ADuC848 are discussed. Especially, a concentric multi-circle fiber bundle is used in the sensor probe, which is designed on the basis of the required temperature measurement range and displacement measurement range.

Thermopile pyrometer modules are the state of the art for contactless temperature measurements in automotive applications. In such an application, the thermopile has to operate precisely in a challenging thermal environment. While the compensation of the steady state ambient temperature is a well known technique when using thermopiles for temperature measurments, transient thermal effects are still an issue. The change of the ambient temperature as well as temperature flow through the sensor can lead to substantial errors due to unwanted thermal gradients within the device. In the thermopile chip they lead to an error signal since the measurement principle is based on quantifying thermal gradients of the chip that result from the detected IR-radiation. Thermal gradients in the cap and between the cap and the thermopile chip will lead to an exchange of heat radiation between the thermopile chip and the cap, which also leads to measurement errors. Different methods were developed that separately or in combination allow for a significant improvement of the accuracy and signal stability. The methods are based on the reduction of thermal gradients within the thermopile chip and the entire sensor device (isothermal, high thermal mass cap), reduction of radiation exchange between the sensor chip and the housing (low emissive inner cap surface) and prediction and software compensation of the error signal.

It is very critical to develop sensor that can operate in high temperature and chemically harsh environments. Sapphire (Al 2 O 3 ) material, which possesses a melting point of 2050 °C and a wide transmission wavelength region as high as ∼3.5 μm, has been demonstrated to be an ideal candidate for high temperature fiber-based environmental sensing applications. Under harsh environment, the performance of conventional blackbody radiation based sapphire fiber high temperature sensor could be easily affected due to the lack of cladding. In this paper, a fiber-optic temperature sensor with a single-crystal sapphire fiber as the light guide and a high temperature ceramic coating as the sensing element as well as the protection layer was presented. The radiance emitted from the ceramic coating is used to measure the temperature, and it is transmitted to optical receiver through the sapphire fiber. This ceramic coating greatly improved the stability and dynamical range of pyrometer. Preliminary experimental results demonstrated that the sensor is very promising for measuring ultra-high temperature up to 1900 °C in the harsh environment.

Thermal imaging is an important, though challenging, diagnostic for shockwave experiments. Shock-compressed materials undergo transient temperature changes that cannot be recorded with standard (greater than ms response time) infrared detectors. A further complication arises when optical elements near the experiment are destroyed. We have designed a thermal-imaging system for studying shock temperatures produced inside a gas gun at Sandia National Laboratories. Inexpensive, diamond-turned, parabolic mirrors relay an image of the shocked target to the exterior of the gas gun chamber through a sapphire vacuum port. The 3000-5000-nm portion of this image is directed to an infrared camera which acquires a snapshot of the target with a minimum exposure time of 150 ns. A special mask is inserted at the last intermediate image plane, to provide dynamic thermal background recording during the event. Other wavelength bands of this image are split into high-speed detectors operating at 900-1700 nm and at 1700-3000 nm, for time-resolved pyrometry measurements. This system incorporates 90-degree, off-axis parabolic mirrors, which can collect low f/# light over a broad spectral range, for high-speed imaging. Matched mirror pairs must be used so that aberrations cancel. To eliminate image plane tilt, proper tip-to-tip orientation of the parabolic mirrors is required. If one parabolic mirror is rotated 180 degrees about the optical axis connecting the pair of parabolic mirrors, the resulting image is tilted by 60 degrees. Different focal-length mirrors cannot be used to magnify the image without substantially sacrificing image quality. This paper analyzes performance and aberrations of this imaging diagnostic.

Alexandrite crystal is commonly used for making alexandrite laser, and it also has a less-known phenomenon called the alexandrite effect that refers to the color change between different light sources. A novel spectropyrometer for temperature measurement of a radiating body utilizing the alexandrite effect is introduced. The alexandrite effect method for temperature measurement is based on the relationship between the temperature of blackbody and the hue-angle in the CIELAB color space. The alexandrite effect spectropyrometer consists of an optical probe, a spectrometer, a computer, and an alexandrite filter. It measures the spectral power distribution of a radiating body through the alexandrite filter, calculates the hue-angle, and determines the temperature. The spectropyrometer is suitable for temperature measurement of any radiating body with or without spectral lines in its spectral power distribution from 1000 K to 100000 K. The spectropyrometer is particularly useful for high to ultrahigh temperature measurement of any radiating bodies with spectral line emissions, such as electric arcs and discharges, plasmas, and high temperature flames.

The paper describes the newest layouts and the basic properties of pyroelectric single-element detectors and linear arrays with up to 512 responsive elements which are built on the basis of lithium tantalate. The research aimed to develop detectors with a signal-to-noise ratio that is as high as possible thereby ensuring optimum adjustment of the detectors to their planned application. Typical applications can be found in pyrometry, gas analysis, spectrometry and security technique. It is shown that special technologies (e. g., ion beam etching, absorption layers) are used to manufacture responsive elements for detectors with very high signal-to-noise ratios. For example, a specific detectivity D* (500 K; 10Hz; 1 Hz; τW=1) ≥ 1.5 x 109 cmHz1/2W-1 has been obtained for single-element detectors with a responsive area of [2x2] mm2. The measured peak value of the NEP for a linear array with 256 responsive elements was smaller than 0.5 nW (128 Hz). Moreover, the acceleration responsivity (disturbance variable) of the examined detectors was fundamentally reduced (factor 5) thanks to the application of new chip and detector layouts.