Efficient Calibration Procedure Research Articles

Validation of an efficiency calibration procedure for a coaxial n-type and a well-type HPGe detector used for the measurement of environmental radioactivity

To obtain reliable measurements of the environmental radionuclide activity using HPGe (High Purity Germanium) detectors, the knowledge of the absolute peak efficiency is required. This work presents a practical procedure for efficiency calibration of a coaxial n-type and a well-type HPGe detector using experimental and Monte Carlo simulations methods. The method was performed in an energy range from 40 to 1460keV and it can be used for both, solid and liquid environmental samples. The calibration was initially verified measuring several reference materials provided by the IAEA (International Atomic Energy Agency). Finally, through the participation in two Proficiency Tests organized by IAEA for the members of the ALMERA network (Analytical Laboratories for the Measurement of Environmental Radioactivity) the validity of the developed procedure was confirmed. The validation also showed that measurement of 226Ra should be conducted using coaxial n-type HPGe detector in order to minimize the true coincidence summing effect.

An accurate prediction method of cutting forces in 5-axis flank milling of sculptured surface

The instantaneous uncut chip thickness and entry/exit angle of cutter/workpiece engagement continuously vary with tool path and workpiece geometry in 5-axis flank milling of sculptured surface, which results in the obvious time-varying characteristic for consecutive cutting forces. An accurate prediction method for cutting force in 5-axis flank milling of sculptured surface is proposed in this paper. Comprehensively considering curved tool path and actual tool motion process with cutter runout (offset and inclination) effects, an accurate representation model for instantaneous uncut chip thickness during cutter/workpiece engaging in 5-axis flank milling is presented firstly, which can reach a higher accuracy and efficiency with the aid of linear iteration process than the methods published. Then, based on the thin plate milling experiments, an efficient calibration procedure for cutter runout parameters and specific cutting force coefficients is given and further verified in practice. Finally, a series of validation experiments are conducted under different cutting conditions, and the results reveal that there is a very good agreement between the experimental and simulation data both in shape and magnitude and prove the effectiveness and accuracy of the proposed method.

CALIBRATION OF STOCHASTIC VOLATILITY MODELS VIA SECOND-ORDER APPROXIMATION: THE HESTON CASE

In this paper, we present a new, simple and efficient calibration procedure that uses both the short and long-term behavior of the Heston model in a coherent fashion. Using a suitable Hull and White-type formula, we develop a methodology to obtain an approximation to the implied volatility. Using this approximation, we calibrate the full set of parameters of the Heston model. One of the reasons that makes our calibration for short times to maturity so accurate is that we take into account the term structure for large times to maturity: We may thus say that calibration is not "memoryless," in the sense that the option's behavior far away from maturity does influence calibration when the option gets close to expiration. Our results provide a way to perform a quick calibration of a closed-form approximation to vanilla option prices, which may then be used to price exotic derivatives. The methodology is simple, accurate, fast and it requires a minimal computational effort.

Calibration of multiple fish‐eye cameras using a wand

Fish‐eye cameras are becoming increasingly popular in computer vision, but their use for three‐dimensional measurement is limited partly because of the lack of an accurate, efficient and user‐friendly calibration procedure. For such a purpose, the authors propose a method to calibrate the intrinsic and extrinsic parameters (including radial distortion parameters) of two/multiple fish‐eye cameras simultaneously by using a wand under general motions. Thanks to the generic camera model used, the proposed calibration method is also suitable for two/multiple conventional cameras and mixed cameras (e.g. two conventional cameras and a fish‐eye camera). Simulation and real experiments demonstrate the effectiveness of the proposed method. Moreover, the authors develop the camera calibration toolbox, which is available online.

An efficient calibration procedure for correction of drift in EMI survey data

Frequency domain electromagnetic induction (EMI) sensors with a small coil separation are used for near-surface surveys in a variety of domains. Regardless of the application, the instrument response(s) may suffer from a drift, meaning that a response at one given location may vary over time, despite no appreciable changes above or underneath the surface. Drift is unwanted as it may introduce global trends or abrupt changes in EMI data not related to the underground. In this paper, the effects of drift on the quadrature and in-phase responses of a ground-based system are researched by evaluating several multi-receiver EMI datasets. First, a stationary recording illustrates the need for a versatile drift compensation. For area surveys we propose an efficient drift correction procedure. To start, a calibration line that crosses the entire survey area within a short time frame is recorded. An approach to account for spatial offset between sensor midpoint and global navigation satellite system antenna is also detailed given the bearing it has on accurate localization. The residuals of coincident calibration and survey data can then be used to model and subtract the drift from the sensor data. This is performed by applying outlier detection and removal, followed by curve fitting of the comparison data. The developed procedure allows a near continuous evaluation of drift, without the need for ancillary data and is time efficient. The approach is shown to be suitable for various survey setups and drift effects.

Automatic Calibration System for Precision Angle Measurement Devices

A proposed optomechatronic module is intended for the automatic and efficient calibration procedure of compact autocollimators utilized for high precision angle measurement. Conventional autocollimators have the disadvantages, e.g. the large volume and high cost, hence novel compact autocollimators have been developed in the past decade. To satisfy the practical applications, the measuring performance of a compact autocollimator must be determined and it has become important to offer a proper and efficient calibration module for the compact autocollimator.

Calibration of an air monitor prototype for a radiation surveillance network based on gamma spectrometry

The objective of this work is to present the improvements that have been made in quasi-real-time air radioactivity concentration monitors which were initially based on overall activity determinations, by incorporating gamma spectrometry into the current prototype. To this end it was necessary to develop a careful efficiency calibration procedure for both the particulate and the gaseous fractions of the air being sampled. The work also reports the values of the minimum detectable activity calculated for different isotopes and acquisition times.

The performance of semi-distributed modelling in urban drainage: the trade-off between hydrological measurements and geographical data

Nowadays, high resolution geographical data are widely available for research and operational purposes. The inclusion of these data into hydrological models may suggest a direct and clear improvement of their performances. Different configurations and model structures, including an increasing quantity of geographical information, are tested using the widely used Stormwater Management Model 5 on a 2.5 km2 pilot catchment (located in Sucy en Brie, close to Paris, France). The Nash-Sutcliffe criterion is used to estimate the goodness of fit between model simulations and available measurements. If including some basic spatial information on landuse clearly improves the performance of the uncalibrated model, the increase in performance is less obvious if the user continues to refine geographical information on the catchment. Moreover, model predictions are comparable between a model calibrated with an efficient calibration procedure and a more physical approach including a fine spatial description and no calibration. Finally, the quality of data used for calibration and validation seems to be a key parameter to obtain a good fit between measurements and model predictions.

Development of a stochastic detection efficiency calibration procedure for studying collimation effects on a broad energy germanium detector

ISPRA, the Italian nuclear safety regulatory body, has started a measurement campaign for validating the performances of in situ gamma-ray spectrometry based on BEGe detectors and ISOCS software. The goal of the validation program is to verify if the mathematical algorithms used by Canberra to account for collimation effects of HpGe detectors continue to work well also for BEGe detectors. This has required the development of a calibration methodology, based on MCNPX code, which, by avoiding any mathematical algorithm utilization, is purely stochastic.Experimental results obtained by such a new procedure, were generally found to be 5% of the reference values. While, in the case of gamma-ray energies greater than 400keV and small angles collimation, results given by ISOCS software produced larger deviations, around 20%. This work presents a detailed description of the simulation procedure and of the first experimental results.

Low Cost Scanning Device Application for Footwear Industry

Notwithstanding laser scanning technology is a mature technology used in widening application fields, a variety of barriers hinds its integration in robotized production lines. To face well know problems, as high-costs and not customizable solutions among others, the authors have developed a new family of laser scanning devices based on off the shelves and low cost hardware components and on a modular design that allow the customization of the device according to the specific application requirements. High accuracy is guaranteed through a computationally efficient non-parametric calibration procedure. Keeping limited the overall cost of the solution provided while increasing in general the sensing capabilities of an Industrial Robot (IR) and in particular the autonomous recognition of position, orientation and furthermore shape and geometrical features of objects within the robotic workspace, can boost the penetration of IRs in typical traditional industrial sectors where SMEs productive scenario is mainly characterized by manual fabrication processes, high product variability, small batches and little capital investments. High added value footwear industry is a paradigmatic example where hard automation is limited from one side by high variability of products and huge request of autonomous adaptation to cope with different loosely structured fabrication processes and from the other side by a low propensity towards high capital investment that make difficult the penetration of industrial robots. Within the framework of the European Project ROBOFOOT (EU-FP7-SMP), authors have conceived and developed a new family of low cost modular and reconfigurable laser scanners and successfully applied in the footwear fabrication scenario. Various operations should be improved by actual measure of the shoe being manufactured, and among the others, the identification of the relative positioning between the last (the plastic element on top of which is built the shoe) and the gripping device is extremely critical because it is still performed manually. Positioning errors in this phase are critical since all robot part-programs depend on the correct alignment of the last with the robot end-effector. To face this problem, a procedure, based on the Iterative Closest Points (ICP) optimization method, has been developed and integrated on board of the laser scanning device that directly communicates with the robot controller to adapt and autonomously correct the part-program to align the tool nominal path with the actual shoe being manufactured. Efficacy of the proposed methods has been proved by measuring the interaction forces between the tool and the last handled by a robot during different technological operations (roughing, polishing etc) typical of the shoe fabrication cycle.

Study of laser megajoule calorimeter's thermal behaviour for energy measurement uncertainty optimisation

For laser megajoule (LMJ) facility, an accurate procedure for laser pulse energy measurement is a crucial requirement. In this study, the influence of measurement procedure on LMJ calorimeter uncertainty is experimentally and numerically investigated. To this end, a 3D thermal model is developed and two experimental techniques are implemented. The metrological characteristics of both techniques are presented. As a first step, the model is validated by comparing numerical and experimental results. Then, the influence of a large number of parameters considered as likely uncertainty sources on calorimeter response is investigated: wavelength, pulse duration, ambient temperature, laser beam diameter.... The post processing technique procedure is also examined. The paper provides some of the parameters required to allow a robust and efficient calibration procedure to be produced.

Human segmentation by geometrically fusing visible-light and thermal imageries

From depth sensors to thermal cameras, the increased availability of camera sensors beyond the visible spectrum has created many exciting applications. Most of these applications require combining information from these hyperspectral cameras with a regular RGB camera. Information fusion from multiple heterogeneous cameras can be a very complex problem. They can be fused at different levels from pixel to voxel or even semantic objects, with large variations in accuracy, communication, and computation costs. In this paper, we propose a system for robust segmentation of human figures in video sequences by fusing visible-light and thermal imageries. Our system focuses on the geometric transformation between visual blobs corresponding to human figures observed at both cameras. This approach provides the most reliable fusion at the expense of high computation and communication costs. To reduce the computational complexity of the geometric fusion, an efficient calibration procedure is first applied to rectify the two camera views without the complex procedure of estimating the intrinsic parameters of the cameras. To geometrically register different blobs at the pixel level, a blob-to-blob homography in the rectified domain is then computed in real-time by estimating the disparity for each blob-pair. Precise segmentation is finally achieved using a two-tier tracking algorithm and a unified background model. Our experimental results show that our proposed system provides significant improvements over existing schemes under various conditions.

An experimental approach to efficiency calibration for gamma-ray spectrometric analysis of large air particulate filters

A full-energy-peak efficiency (FEPE) calibration procedure for gamma-ray spectrometric analysis of air particulate samples collected on large filters is described herein. The experimental results are obtained for an unconventional measurement geometry, termed a “packet-sample”. The sample is obtained from a large cellulose filter (45cm×45cm) used to collect air particulate samples that is resized to dimensions suitable for spectrometric measurements (6cm×6cm×0.7cm). To determine the FEPEs, many standards were created, i.e., some filters containing a small amount of ThO2 and others containing a known amount of KCl.Efficiency curves obtained through best fits to experimental data for three high-purity germanium (HPGe) detectors, one of them for X-ray measurement, cover the energy range from 40keV to 2600keV. To validate the efficiency calibration procedure two experimental tests with the use of calibrated sources were conducted and, as application example, airborne concentrations of 131I (particulate matter), 134Cs and 137Cs at Palermo (Italy) in the days following the Fukushima accident in Japan were evaluated.

Thermal analysis of Laser MegaJoule calorimeters

For LMJ applications, an accurate procedure for laser pulse energy measurement is a crucial requirement. In this study, the influence of measurement procedure on LMJ calorimeter uncertainty is experimentally and numerically investigated. To this end, a 3D thermal model is developed and two experimental devices are implemented. The metrological characteristics of both devices are presented. As a first step, the model is validated by crossing numerical and experimental results. Then, the influence of a large number of parameters considered as likely uncertainty sources on calorimeter response is investigated: wavelength, pulse duration, ambient temperature, laser beam shape... The final goal is to define a robust and efficient calibration procedure in order to strongly reduce the uncertainty on LMJ laser pulse measurement.

Determining HPGe total detection efficiency using γ–γ coincidence

Both the peak and total detection efficiencies are generally needed in order to calculate sample activity from a gamma spectroscopic measurement, except in the case of isotope specific calibration. This is particularly true when the sample is in close proximity to the detector and corrections for cascade summing effects are required to avoid significant inaccuracy in the result. These corrections use the total detection efficiency to correct for summing-in and summing-out events, and the extent of the correction depends on both the geometry and the gamma cascade for the isotope in question. Experimentally determining the total efficiency is a labor intensive endeavor requiring multiple measurements with a set of single-gamma-emitting standards. Modeling the total efficiency vs. energy may be less time consuming, but is also likely to produce less confidence in the final result. Pacific Northwest National Laboratory’s Radiation Detection and Nuclear Sciences group has constructed a low background 14-crystal HPGe array for sample measurement; in all measurements, samples will be in close proximity to the germanium crystals. This close geometry and the sheer number of efficiency calibrations required for the system have led us to investigate methods to simplify the efficiency calibration procedure. One method we are developing uses the γ–γ coincidence plane to isolate Compton scattering event populations, allowing experimental determination of total detection efficiency values from the measurement of a single mixed isotope standard. A description of the analysis and experimental results of this method are presented.

Development of the LED measurement system of chromaticity coordinates correction

In this paper, we propose a procedure to adjust the chromaticity coordinates by using a few samples of the color measurement coordinate to do the error correction and choose the correction method of minimum color error difference average to be the procedure of measuring instruments, and to construct an efficient and predictable calibration procedure. This research adopts some engineering statistics methods, such as median and average methods, and corrects the experiments to obtain the chromaticity coordinates. The four calibration methods that we designed lower the average value of the color errors as 0.034. Moreover, the minimum average value of errors in the X-axis could be revised to 6.3% while the minimum average value of errors in the Y-axis 8.8%. The accuracy of best calibrated chromaticity coordinates could achieve to the percentage 71.1%.

Fast AT: A simple procedure for quasi direct orientation

Over the past two decades, the development of Global Navigation Satellite System (GNSS) technology, inertial navigation technology and Inertial Navigation Systems (INS) and their application to sensor orientation in photogrammetry and remote sensing has led to more precise, accurate, reliable and cost efficient orientation and calibration methods and procedures. Today, most airborne photogrammetric and remote sensing systems are equipped with GNSS receivers and inertial sensors. To a large extent and more or less independently from the imaging geometry and sensor type, orientation is performed with the “direct” and “integrated” methods. In this paper we introduce a new orientation method that we call “Fast AT” for frame images. The new method combines image measurements, ground control and aerial control observations in novel quantitative and qualitative ways. Depending on project specifications, Fast AT can be a robust alternative to direct orientation and, at the very least, a fast quality control tool for any orientation task. We analyze the performance of Fast AT with analogue and digital frame imagery and draw conclusions on its general properties.

Calibration of a model for selective catalytic reduction with ammonia, including NO oxidation, and simulation of NOx reduction over an Fe–zeolite catalyst under highly transient conditions

NOx reduction over an Fe–zeolite catalyst is simulated for highly transient conditions representative of automotive diesel engine operation. A transient 1D convection + 1D diffusion (1D + 1D) model for a single channel of a catalytic converter is developed, including a set of the most recently proposed kinetics for Fe–zeolite catalysts. The parameters specifying the characteristics of the selective catalytic reduction system are introduced, and an efficient calibration procedure is proposed that exploits the specific structure of the experimental dataset, consisting of a total of 90 operating conditions with varying space velocities, temperatures and inlet concentrations. Parameterization of the system is carried out by studying the system response to single step feeds in the inlet ammonia up to steady state (slow transient). Experimental data for highly dynamic ammonia dosing is subsequently employed to assess the model performance at highly transient conditions typical of diesel engine operation. Excellent agreement is reported for a total of 90 operating conditions; differences between the predictions and the experimental data in cumulative converted NOx after 20,000 s of operation are less than 2%.

Calibration of a microprobe array

Conventional coordinate measurement machines are not well adapted to the specific needs for the measurement of mechanical microstructures that are made in a highly parallel production process. In particular, the increase of the measurement speed is addressed by using an array of microprobes to measure a number of objects in parallel. It consists of multiple microprobes that are etched into the same silicon substrate. The styli are glued onto a boss structure in the middle of a silicon membrane. To facilitate the alignment of an array and the underlying wafer, the array is mounted on three stacked rotational stages. Due to the production tolerances, the positions of the touching balls of the probes relative to their pivot have to be calibrated. The probe sensitivity is another field of calibration. This paper describes an efficient calibration procedure of the probe array which is usable for arrays with a large number of probes and different array layouts. The validation method of this procedure is explained and calibration results are discussed

The gamma efficiency of the GAINS spectrometer

The GAINS (Germanium Array for Inelastic Neutron Scattering) setup was recently installed at the GELINA (Geel Linear Accelerator) neutron source of EC-JRC-IRMM. In order to produce reliable neutron inelastic cross-section data the setup requires a precise efficiency calibration for each sample under investigation. These samples represent extended sources in non-standard orientations and with significant self-attenuation of gamma rays. We present in detail the efficiency calibration procedure performed with two Monte Carlo simulations using MCNP and GEANT4. A good agreement is found between the two independent approaches. The general features of the simulations are discussed together with an in-depth description of the various factors influencing the efficiency.