(Calib.) Artículos

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Acceso Abierto
Measurement, Validation and Uncertainty of an Experimental Procedure to Characterize the Size-of-Source Effect of Radiation Thermometers, in the Framework of an Industrial Calibration Laboratory
(Multidisciplinary Digital Publishing Institute (MDPI), 2022-10-28) De Lucas Veguillas, Javier; Instituto Nacional de Técnica Aeroespacial (INTA)
An experimental procedure for characterizing the size-of-source effect (SSE) is proposed. Such an effect is the cause of one of the main influence variables generating uncertainty in the measurement, both in calibration and use, of direct reading radiation thermometers (RT). The procedure and uncertainty calculation described in the paper are aligned in terms of metrological traceability, with the requirements generally imposed to ensure the accuracy of measurements in industry and science. Results of application and validation of this particular procedure with equipment, including black body (BB) sources normally used in radiation thermometry calibration laboratories in the industrial field, are shown.
Restringido
Geometrical and thermal optimization of cylinder-conical blackbody cavities to uniform radiance temperature profiles in the infrared
(Elsevier, 2023-04-07) De Lucas Veguillas, Javier; Segovia, José Juan; Instituto Nacional de Técnica Aeroespacial (INTA)
Large-area blackbody cylinder conical cavities are generally used as primary radiation sources for calibrating and characterizing radiation thermometers and quantitative thermal imagers in the infrared, both in metrology laboratories or for industrial applications. The radiation temperature of the emitted radiation depends on effective emissivity and surface (contact) temperature. The instrument’s field of view generally only covers the cavity bottom since this is where contact temperature is best measured. A non-uniform effective emissivity profile at the bottom poses a problem if instruments with a different field of view have to be calibrated with the same blackbody. Spatial uniformity depends principally on the cone angle and temperature gradient along the cavity. In this paper, we analyse blackbody optimization in terms of uniform radiance temperature profiles as a function on geometric parameters and temperature. For the isothermal case, we conclude that angles between 160° and 170° are the optimum, depending on intrinsic emissivity and length-to-diameter ratio of the cavity. For non-isothermal cavities, the effect of the temperature gradient on uniformity is relatively small, with only the temperature near the bottom proving significant. The use of multi-zone maintenance furnaces would allow temperature gradients to be designed that can improve uniformity in addition to geometric optimization.
Restringido
Aperturas efectivas en calibración y comparación de termómetros de radiación
(Federación de Asociaciones de Ingenieros Industriales de España, 2020-09-15) De Lucas Veguillas, Javier; Instituto Nacional de Técnica Aeroespacial (INTA)
Los termómetros de radiación (TR) se calibran con cuerpos negros (CN) cuya apertura debe cubrir suficientemente el blanco nominal del termómetro. Debido a posibles imperfecciones en su sistema óptico, radiación proveniente de regiones exteriores al blanco puede llegar al detector. Es el efecto del tamaño de la fuente (ETF) y constituye una limitación importante en el uso de TR en aplicaciones especialmente en un entorno industrial y fuente entre otras de incertidumbre de medida.
Restringido
Measurement and analysis of the temperature gradient of blackbody cavities, for use in radiation thermometry
(Springer Link, 2018-03-24) De Lucas Veguillas, Javier; Segovia, José Juan; Instituto Nacional de Técnica Aeroespacial (INTA)
Blackbody cavities are the standard radiation sources widely used in the fields of radiometry and radiation thermometry. Its effective emissivity and uncertainty depend to a large extent on the temperature gradient. An experimental procedure based on the radiometric method for measuring the gradient is followed. Results are applied to particular blackbody configurations where gradients can be thermometrically estimated by contact thermometers and where the relationship between both basic methods can be established. The proposed procedure may be applied to commercial blackbodies if they are modified allowing secondary contact temperature measurement. In addition, the established systematic may be incorporated as part of the actions for quality assurance in routine calibrations of radiation thermometers, by using the secondary contact temperature measurement for detecting departures from the real radiometrically obtained gradient and the effect on the uncertainty. On the other hand, a theoretical model is proposed to evaluate the effect of temperature variations on effective emissivity and associated uncertainty. This model is based on a gradient sample chosen following plausible criteria. The model is consistent with the Monte Carlo method for calculating the uncertainty of effective emissivity and complements others published in the literature where uncertainty is calculated taking into account only geometrical variables and intrinsic emissivity. The mathematical model and experimental procedure are applied and validated using a commercial type three-zone furnace, with a blackbody cavity modified to enable a secondary contact temperature measurement, in the range between 400 °C and 1000 °C.
Restringido
A simple geometrical model for calculation of the effective emissivity in blackbody cylindrical cavities
(Springer Link, 2015-10-15) De Lucas Veguillas, Javier; Instituto Nacional de Técnica Aeroespacial (INTA)
A simple geometrical model for calculating the effective emissivity in blackbody cylindrical cavities has been developed. The back ray tracing technique and the Monte Carlo method have been employed, making use of a suitable set of coordinates and auxiliary planes. In these planes, the trajectories of individual photons in the successive reflections between the cavity points are followed in detail. The theoretical model is implemented by using simple numerical tools, programmed in Microsoft Visual Basic for Application and Excel. The algorithm is applied to isothermal and non-isothermal diffuse cylindrical cavities with a lid; however, the basic geometrical structure can be generalized to a cylindro-conical shape and specular reflection. Additionally, the numerical algorithm and the program source code can be used, with minor changes, for determining the distribution of the cavity points, where photon absorption takes place. This distribution could be applied to the study of the influence of thermal gradients on the effective emissivity profiles, for example. Validation is performed by analyzing the convergence of the Monte Carlo method as a function of the number of trials and by comparison with published results of different authors.
Restringido
Validation of a geometrical model for the calculation of the integrated effective emissivity of conical cavities with a lid
(IOP Science Publishing, 2015-08-03) De Lucas Veguillas, Javier; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN)
In this paper, a geometrical model for the numerical calculation of the integrated effective emissivity of conical isothermal cavities with a lid, is described in detail. We make use of the Montecarlo method and the 'back ray tracing' technique, assuming diffuse reflection and a detector situated at an arbitrary distance from the cavity aperture. First, the geometry of the problem is discussed and the local hemispherical emissivity profiles along the cone generatrix are calculated for different configurations. Then we proceed to the validation of the model, by calculating the distribution of the reflected photons in the interior of the cavity, such as it is provided by the numerical algorithm. The calculated distribution is compared with theoretical values, obtained from the expressions of the view factors for the conical geometry. The calculated values for the local and integrated effective emissivity are compared with results published by other authors, highlighting the differences between them, and the internal consistency of our model is demonstrated. Special attention to the calculation of the view factors in conical cavities affected by vignetting due to the obstruction produced by the lid, is paid. The view factors of points at the penumbral region are numerically calculated, applying the Montecarlo method, including a complete analysis of the uncertainty.
Restringido
Uncertainty calculation of the effective emissivity of cylinder-conical blackbody cavities
(IOP Science Publishing, 2015-12-30) De Lucas Veguillas, Javier; Segovia, José Juan; Instituto Nacional de Técnica Aeroespacial (INTA)
A numerical and geometrical model for calculating the local effective emissivity of isothermal blackbody cylinder-conical cavities with lid, assuming diffuse reflection, is described. This has been developed by generalizing previous models based on conical and cylindrical geometries. The model has been validated by determining the diffusely reflected photon trajectories and the corresponding experimental view factors between given pairs of surface elements. Differences compared to theoretical values, were subsequently analyzed in terms of the model's intrinsic uncertainty. A well-defined numerical function that calculates the effective emissivity as a function of its natural variables, intrinsic emissivity and geometrical parameters, is established. In order to calculate the probability distribution of the output quantity, we use the Monte Carlo method for the propagation of the probability distributions that characterize our knowledge concerning the values of the influence variables. The model is applied to heat-pipe black bodies installed at our laboratory, previously characterized at the PTB. A comparison with published uncertainty results, obtained by applying classical uncertainty propagation techniques, is also made.
Restringido
A subcell FDTD Scheme implementation for thin slot modeling
(Institute of Electrical and Electronics Engineers, 2022-07-08) Cabello, M. R.; Martín Valverde, A. J.; Plaza Gallardo, B.; Frövel, M.; Poyatos Martínez, D.; Rubio Bretones, A.; González García, S.; Instituto Nacional de Técnica Aeroespacial (INTA); Ministerio de Ciencia e Innovación (MICINN); Agencia Estatal de Investigación (AEI); Junta de Andalucía
The finite-difference time-domain (FDTD) method is not able to efficiently model thin features without a drastic reductions of the spatial mesh size, potentially yielding an unfeasible use of memory and CPU requirements. In this work we propose two stable and efficient techniques for dealing with thin apertures in FDTD, one based on conformal and one based on subgridding. These are compared, in two different scenarios, with the classical dispersive magnetic material approximation [DMMA] based on Gilbert-Holland's models.
Acceso Abierto
Uncertainty in the Calibration Transfer of Solar Irradiance Scale: From Absolute Cavity Radiometers to Standard Pyrheliometers
(Multidisciplinary Digital Publishing Institute (MDPI), 2022-04-02) Balenzategui, José Lorenzo; Molero, María; Silva, José Pedro; Fabero, Fernando; Cuenca, José; Mejuto, Eduardo; De Lucas Veguillas, Javier
In this work, the method for calculation of uncertainty of pyrheliometers’ responsivity during their outdoor calibration process in the laboratory is exposed. It is applied first for calibration of standard pyrheliometers by comparison to cavity radiometers, and after for calibration of an end-user pyrheliometer against that standard pyrheliometer. The dissemination of the WRR irradiance scale is illustrated in practice and the increasing uncertainty in the traceability chain is quantified. The way of getting traceability to both WRR scale and to SI units in the current situation, where the shift between these radiometric scales is pending to be solved, is also explained. However, the impact of this gap between scales seems to be more important for calibrations of reference Class A pyrheliometers than in the final determination of DNI irradiance, because in this case, the cumulative uncertainty is large enough as to not significantly be affected for the difference. The way to take into account different correction terms in the measurement model function, and how to compute the corresponding uncertainty, is explained too. The influence of temperature of some pyrheliometers during calibration process and the potential impact on the DNI irradiance calculated with these instruments is exemplified.
Restringido
Characterization of absolute cavity radiometers for traceability to SI of solar irradiance
(IOP Science Publishing, 2022-08-12) Balenzategui, José; De Lucas Veguillas, Javier; Cuenca Alba, José; González Leiton, Ana María; Molero García, María; Fabero, Fernando; Silva, J. P.; Mejuto, E.; Muñoz, R.; Arce, A.; Instituto Nacional de Técnica Aeroespacial (INTA)
Solar-type cavity radiometers are instruments of the highest metrological level for measuring solar direct normal irradiance. To ensure their traceability and performance, they are periodically compared to the World Group of Standards, which realizes the World Radiometric Reference (WRR), in the International Pyrheliometer Comparisons (IPCs). Additionally, they can be characterized in an absolute way, with direct traceability to SI units and with their measurement uncertainty calculated. This paper describes the different techniques and procedures applied for the characterization and calibration of solar cavity radiometers, with the main results obtained to date in the case of an Automatic Hickey–Frieden (AHF) radiometer. Voltmeters, resistors, temperature sensors and the area of the precision apertures have been calibrated, while the effective absorptance, temperature coefficients, optical scattering and non-equivalence factor have been evaluated. The temperature dependence of the electrical current in the cavity heater has also been analysed. The resulting corrections obtained for the AHF by characterization are compatible with the WRR factors obtained by this instrument in the past IPCs. An uncertainty of 0.42% (k = 1) has been obtained, and this paper discusses further improvements that may be able to reduce this figure to the desired expanded uncertainty of U = 0.1% (k = 2).
Acceso Abierto
Investigación del efecto del tamaño de la fuente en equipos de termografía infrarroja y termómetros de radiación
(Gobierno de España: Ministerio de Defensa, 2018-10-03) De Lucas Veguillas, Javier; Alonso, S.; Bernal, M.; Ángeles Sierra, M.; Macías, R.
Las cámaras y los sistemas de termografía infrarroja son utilizados en múltiples aplicaciones en sectores de seguridad y defensa: optrónica, sensores, contrame didas, estudio termográfico del estrés del combatiente, etc. Su evolución ha sido espectacular, especialmente desde la introducción del microbolómetro como detector elemental. En el pasado se utilizaban básicamente para medidas cualitativas, interesando únicamente el contraste térmico, la búsqueda de puntos calientes o fugas de calor, etc. Hoy son más las aplicaciones cuantitativas, combinando la imagen térmica con medidas absolutas de temperatura. La necesidad de garanti zar la trazabilidad al SI de los valores de temperatura proporcionados exige a los laboratorios de calibración investigar los factores de influencia que afectan a los resultados de las medidas realizadas. La incertidumbre en la medida depende de multitud de factores (por ejemplo, la emisividad) y uno de los más significativos es el efecto del tamaño de la fuente (ETF), por el cual, debido a imperfecciones en el sistema óptico (difracción, reflexiones internas, etc.), radiación proveniente de zonas fuera del blanco correspondiente a un píxel pueden llegar a este. En termografía se habla del efecto sobre la temperatura indicada por el píxel y de valores leídos por detectores vecinos. Es equivalente a considerar que el tamaño de la fuente incide en el valor de temperatura que proporciona un termómetro de radiación. El laboratorio de Temperatura y Humedad del INTA (Instituto Nacional de Técnica Aeroespacial) tiene acreditación ENAC (Entidad Nacional de Acreditación) para la calibración de termómetros de radiación y la indicación de temperatura de cámaras termográficas, y actúa en este ámbito como laboratorio metrológico del Ministerio de Defensa. En este trabajo se presentan resultados de la investigación realizada sobre el ETF y se analiza su influencia en la incertidumbre y sobre los valores de temperatura proporcionados por estos instrumentos.
Acceso Abierto
Radon transport events associated with the impact of a NORM repository in the SW of Europe
(Elsevier, 2021-08-13) Gutiérrez Álvarez, I.; Guerrero, J. L.; Martín, J. E.; Adame, J. A.; Vargas, A.; Bolívar, J. P.; Ministerio de Economía y Competitividad (MINECO)
Two radon measurement stations located to the north and south of a NORM (Naturally Occurring Radioactive Materials) repository of phosphogypsum (southwest of Europe) were used to monitor radon behavior during 2018. The stations are located at opposing sides of the repository, one in Huelva City to the north and other one in a rural area to the south. This setup aimed to identify the influence of the NORM repository on each station and use radon levels as a marker of atmospheric transport in the local area. To achieve this, a comparison was carried out with other coastal stations in the south of Spain, finding higher average concentrations in Huelva City, ~3.3 Bq m−3. Hierarchical clustering was applied to identify days with different radon patterns at each Huelva station, detecting possible local radon transport events from the repository. Three events were investigated with WRF (Weather Research and Forecasting) and FLEXPART-WRF (FLEXible PARTicle dispersion model). It was found that both sampling sites required atmospheric stagnant conditions to reach high radon concentration. However, under these conditions the urban station showed high radon regardless of wind direction while the rural station also required radon transport from the repository, either directly or indirectly.
Restringido
The Calibration of Data Loggers for the Characterization of Sterilization Autoclaves
(Springer Link, 2011-10-16) De Lucas Veguillas, Javier; Elvira, Gregorio; Fuentes, H.; Benyon Puig, Robert
An experimental setup established for the calibration of temperature and pressure data loggers for use in the characterization of autoclaves and steam sterilizers is described. The results obtained on two devices in the range of 25 °C to 125 °C at absolute pressures from 100 kPa to 375 kPa are presented and discussed in the context of the manufacturer’s specifications and their suitability for on-site characterization of the temperature and pressure conditions during the normal operational cycles. The recommendations on the calibration of these devices and the estimation of the contributions to the expanded uncertainty of measurement for the characterization of autoclaves are addressed.
Restringido
Evaluation of a Portable Apparatus for the Realization of the Triple Point of Argon
(Springer Link, 2014-06-21) De Lucas Veguillas, Javier; Benyon Puig, Robert
In this paper, the evaluation of the performance of a portable triple-point-of-argon apparatus, via the analysis of the calibration history of selected working (fused silica) standard platinum resistance thermometers (SPRTs), is presented. These have an extensive calibration history, both internally (using different apparatus) and externally at two National Measurement Institutes. A special procedure had to be developed, for the calibration of metal-sheathed SPRTs, in order to ensure adequate thermal contact between the SPRT and the well and to minimize the influence of stem conduction, inherent in the compact design of the maintenance system. The results show good agreement between the measurements performed with this system and those with the previously used apparatus, to a level of uncertainty consistent with the INTA calibration and measurement capability (CMC) of 3.0 mK (k = 2). This CMC is given by the Spanish accreditation body (ENAC), under accreditation No. 16/10.007, for the routine calibration of SPRTs at the triple point of argon. It is concluded that the portable apparatus is suitable for use as a transfer standard for the comparison of local realizations of the triple point of argon. This avoids the need to shipping fragile SPRTs, with a valuable long calibration history, and eliminates the contributions due the long-term stability of the thermometers subjected to transportation. The long-term stability of the portable apparatus reported in this work has only been determined in laboratory conditions.
Restringido
Practical Calibration of Platinum Resistance Thermometers in the Range −190 °C to 0 °C
(Springer Link, 2011-10-22) De Lucas Veguillas, Javier; Benyon Puig, Robert
The results obtained in the characterization of a low-temperature comparator and its performance in relation to the calibration of metal and borosilicate sheathed standard platinum resistance thermometers (SPRTs) calibrated at the International Temperature Scale of 1990 (ITS-90) fixed points, are presented and discussed. The principal influence quantities are addressed and the estimation of measurement uncertainty supporting the calibration and measurement capability (CMC) accredited by Entidad Nacional de Acreditación (ENAC), the Spanish Accreditation Body, are presented and discussed.
Restringido
Numerical optimization of the radial dependence of effective emissivity in blackbody cylindrical cavities
(IOP Science Publishing, 2014-06-25) De Lucas Veguillas, Javier
The effective emissivity of a blackbody with cylindrical geometry has a definite radial dependence, at the bottom cavity, which is a function of the surface intrinsic emissivity, cavity geometry (L/D) and the temperature gradient along the cylinder walls. The optimal use of large aperture blackbody cavities, particularly in thermal imager calibration applications or for the characterization of size-of-source effect of radiation thermometers for example, requires quite precise control of the thermal gradient, in order to achieve sources as uniform as possible in effective emissivity, over the complete aperture. In this paper, we present a numerical model in which the radial profile of effective emissivity is optimized, by means of the theoretical modification of the temperature gradients in a cylindrical diffuse cavity. The distribution functions of secondary absorption impacts are defined and the criteria for a suitable choice of experimentally realizable temperature gradients are presented, including the uncertainty analysis.

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