Metrological Point Of View Research Articles

Metrological Approach in the Study of Biodiesel Viscosity Variation with Temperature

Abstract In this article, we study the relation between viscosity and temperature of several biodiesel types (soybean, sunflower, corn, castor bean, and animal fat based) in a metrological point of view. All the biodiesel types were obtained by a transesterification reaction with methanol in the presence of an alkaline base as a catalyst. The biodiesels had their viscosities measured using capillary viscometers following Brazilian standards, in temperatures ranging from 20°C to 40°C. An extra study was performed with another beef tallow biodiesel (transesterified with ethanol) with temperatures up to 100°C. For all the measurements, the uncertainties were calculated. Even though there have been many studies on biodiesel on recent years, most of these do not have a metrological focus. This study shows the behavior of the biodiesel viscosity in a temperature range of 20°C to 40°C, and also how its composition influences the viscosity.

On the long-term stability of calibration standards in different matrices

In order to assure Quality Control in accordance with ISO/IEC 17025, it was important, from metrological point of view, to examine the long-term stability of calibration standards previously prepared. Comprehensive reconsideration on efficiency curves with respect to the ageing of calibration standards is presented in this paper. The calibration standards were re-used after a period of 5 years and analysis of the results showed discrepancies in efficiency values.

Mid-infrared quantitative spectroscopy by comb-referencing of a quantum-cascade-laser: Application to the CO2 spectrum at 4.3 μm

A robust phase-lock of a quantum-cascade-laser to a near-infrared frequency-comb allows absorption spectra of a CO2 gas sample to be acquired at different pressures with extreme repeatability and accuracy by tuning the repetition-rate of the comb, thus ensuring an absolute frequency scale on the acquired spectra. The method proves useful to retrieve traceable spectroscopic parameters such as line-center frequencies, line intensity factors, pressure shift, and pressure broadening coefficients, with unprecedented quality from the metrological point of view.

Metrological traceability of oceanographic salinity measurement results

Abstract. Consistency of observed oceanographic salinity data is discussed with respect to contemporary metrological concepts. The claimed small uncertainty of salinity measurement results traceable to the conductivity ratio of a certified IAPSO Standard Seawater reference is not metrologically justified if results are compared on climatic time scales. This applies in particular to Practical Salinity SP, Reference Salinity SR, and the latest estimates of Absolute Salinity using the TEOS-10 formalism. On climate time scales an additional contribution to the uncertainty that is related to unknown property changes of the reference material must be accounted for. Moreover, when any of these measured or calculated quantity values is used to estimate Absolute Salinity of a seawater sample under investigation, another uncertainty contribution is required to quantify the accuracy of the equations relating the actually measured quantity to the Absolute Salinity. Without accounting for these additional uncertainties, such results cannot be used to estimate Absolute Salinity with respect to the International System of Units (SI), i.e. to the unit chosen for the mass fraction of dissolved material in the sample, which is "g kg−1". From a metrological point of view, such deficiencies in the calculations involving other quantities will produce SI-incompatible results. We outline how these problems can be overcome by linking salinity to primary SI measurement standards.

3D part inspection path planning of a laser scanner with control on the uncertainty

This article concerns the measurement process of mechanical parts using laser scanners. From the point of view of industrial applications, the objective is to guarantee the measurement accuracy during the scanning with regard to the geometrical product specifications. The proposed method can be summarized as follows: the first step consists of analyzing the interval of tolerance for the different specifications and to attribute to every geometrical entity a maximal uncertainty of measurement. This uncertainty depends on the angle of incidence between the laser plane and the scanned surface. In the second step, an approach based on the concept of visibility is used from the CAD model of the inspected part to find correct sensor guidance in a metrological point of view. A few position-points from this set are used to define the scanning path. Finally, the measurement can be carried out and the specifications can be controlled after the segmentation of the point clouds. An example illustrates the approach.

Some metrological aspects of the comparison between two ordinal measuring systems

The usage of ordinal scales (sometimes called ‘semi-quantitative’ scales) for performing measurements in the area of applied chemical metrology and quality assurance is widespread. This paper presents a method for handling actions such as calibration, measuring systems’ capabilities comparison and reproducibility evaluation as a comparison between two measuring systems (MSs) referring to a known/unknown reference standard. The strength of the agreement between these MSs is evaluated through two known versions of Cohen’s kappa statistics (the traditional one and the modified one). The effectiveness of these statistics from the metrological point of view is examined, and the preferability of the modified kappa statistics is demonstrated via an example.

Characterization of Density of Biodiesel from Soybean, Sunflower, Canola, and Beef Tallow in Relation to Temperature, Using a Digital Density Meter with a Metrological Point of View

Abstract In this article we study the behavior of biodiesel density from soybean oil, sunflower oil, canola oil, and beef tallow, the last one transesterified with ethanol and the others with methanol in relation to temperature with a metrological point of view. These quantities were measured with a digital density meter, one of the Brazilian density standards, in a temperature range between 15 and 40°C. Measurement uncertainty was calculated. The behavior of density is analyzed considering the estimated uncertainty. The density from all the samples investigated shows a linear behavior with respect to temperature.

TDR moisture measurements in granular materials: From the siliceous sand test case to the applications for agro-food industrial monitoring

Different approaches are commonly available for the continuous monitoring of moisture and dielectric properties of various materials. In particular Time Domain Reflectometry (TDR) is the standard method for measuring soil water content. Nevertheless, the state of the art is rather lacking in assessing specific calibration procedures allowing the accurate moisture monitoring of granular materials. To fill this gap, the adoption of TDR for such purposes is investigated. Starting from measurements on siliceous sand, an in-depth analysis is extended to various feedstuff materials (such as corn, corn flour and bran). Furthermore, the adopted methodology is fully assessed from a metrological point of view, thus confirming its suitability for the considered applications.

Verification of equipment for measuring the diffusion capacity of the lung for carbon monoxide: Fig. 1—

To the Editors: In the paper by Jensen et al. 1 and the accompanying editorial by Farre and Navajas 2 the importance of quality assurance in the respiratory physiology laboratory is highlighted. The Jensen et al . 1 study represents a tremendous and successful effort on quality assurance and quality control as part of a large clinical study. The study or probably more likely the presentation of the study by Jensen et al . 1 has a few limitations seen from a metrological point of view to which I want to draw attention. Traceability is the key stone of quality control of measurements and must be addressed in all metrological studies. Metrological traceability is a property of a measurement result relating the result to a stated metrological reference through an …

A $t$-Norm-Based Fuzzy Approach to the Estimation of Measurement Uncertainty

From a metrological point of view, a measurement process rarely consists of a direct measurement but, rather, of digital signal processing (DSP) performed by one or more instruments. The measurement algorithm makes the numerical results available as functions of acquired samples from input signals. Moreover, when repeated direct measurements are performed, one may speak about interactions in subsequent results (and it may be dependent on the type of instrument being used). With mathematical formalism, the complex relations involved can be described, although again, an indirect measurement result would be obtained. Regardless, no matter what kind of process is being examined, the distribution of the uncertainty associated with the measurement needs to be known. To express a measurement result with its associated uncertainty, the recommendations of the ISO Guide need to be met. Many published papers have proposed the use of fuzzy intervals to describe both the systematic and statistical effects of repeated measurements on the distribution of their results. In this paper, we use a random-fuzzy model, the single measure is represented as a fuzzy set, and the propagation of the possibility distribution through the DSP stage (which simply consists of an average operation) is performed using the extension principle of Zadeh based on a particular triangular norm: the so-called Dombi's.

A Vector Approach for Image Quality Assessment and Some Metrological Considerations

The main purpose of this paper is to present a metrology-based view of the image quality assessment (IQA) field. Three main topics are developed. First, the state of the art in the field of IQA is presented, providing a classification of some of the most important objective and subjective IQA methods. Then, some aspects of the field are analyzed from a metrological point of view, also through a comparison with the software quality measurement area. In particular, a statistical approach to the evaluation of the uncertainty for IQA objective methods is presented, and the topic of measurement modeling for subjective IQA methods is analyzed. Finally, a vector approach for full-reference IQA is discussed, with applications to images corrupted by impulse and Gaussian noise. For these applications, the vector root mean squared error (VRMSE) and fuzzy VRMSE are introduced. These vector parameters provide a possible way to overcome the main limitations of the mean-squared-error-based IQA methods.

Quality Evaluation Techniques of Processing the ECG Signal

In this research, methods to detect and evaluate the main parameters of the ECG signal are presented in order to improve its clinical properties. Two techniques are addressed in this research, Piecewise method and the Analytical Approach. These techniques are used to determine such as: percent (rms) difference (PRD), signal-noise-ratio (SNR) and the compression ratio (CR) which are used to evaluate the quality of ECG signals. The evaluation and processing of the methodology quality and the metrological point of view of ECG signal problems are subsequently obtained from detection and filtration. This technique has been successfully implemented to determine the legal accuracy rang of ECG signal for detection, filtration and compression.

An Original Fuzzy Method for the Comparison of Measurement Results Represented as Random-Fuzzy Variables

Generally, the final result of a measurement process is used to make decisions according to the result of a comparison between the measurement result and a threshold, which could be a single numerical value or another measurement result. Of course, the latter case is the more general one since the single-value threshold is, from a metrological point of view, a measurement result with zero associated uncertainty or, more specifically, a measurement result whose associated uncertainty is much lower, or negligible, with respect to the uncertainty associated to the other measurement result. Moreover, in recent years, because of the great diffusion of instruments based on digital signal processing, decisions can be required not only at the end but also within the measurement process itself so that the comparison of measurement results becomes part of the measurement process itself. The comparison of measurement results or, in other words, decision making, is a very important task. This paper proposes a method based on the use of suitable fuzzy operators for comparing measurement results, which are expressed in terms of random-fuzzy variables, taking into account measurement uncertainty.

Conformity assessment and metrology: update on the state of affairs

A couple of years ago, ISO CASCO launched a major project of transforming all the existing ISO Guides on conformity assessment to a comprehensive series of ISO standards 17000 being now in various stages of development. As the concept of traceability underpinning all measurements has been a basic mission of metrology, a number of these standards have a direct bearing on metrology. The series is logically based on a definition standard, ISO 17000, giving, among others, a guidance which activities fall under conformity assessment. The fact that calibration does not, might have important consequences which must yet be assessed. A controversial discussion on some issues has been in progress concerning ISO 17011 on accreditation bodies which touches both on national metrology institutes (NMIs) with an accreditation function and on calibration labs at large. ISO 17040 on peer review could be used with an advantage to support mutual recognition arrangements among a limited number of bodies of a specialized expertise (e.g., CIPM MRA among NMIs under the Metre Convention). ISO 17025 has been the most important standard for the metrology community and has undergone a major overhaul taking on board the uncovered requirements from ISO 9001:2000. In general, the paper will give an update on the developments outlined above and discuss the consequences and further steps from the viewpoint of metrology.

Advances in Scanning Force Microscopy for Dimensional Metrology

This paper presents the state of the art in scanning force microscopy for dimensional metrology. A detailed description is given of the important factors affecting the major components of a scanning force microscope from the metrological point of view. Both instrument design and calibration are discussed together with an overview of industrial applications. Recent achievements by national metrology institutes and others to improve calibration procedures, traceability, reduce measurement uncertainty, ensure consistancy of measurement and broaden the range of applications are described.

Non-linear dynamic system modelling based on modified Volterra series approaches

The empirical “black-box” characterization of non-linear systems with memory is a complex problem which cannot be dealt with by means of a unique, general-purpose mathematical approach such as the Volterra series. In fact, from a metrological point of view, the feasibility and reliability of the measurement procedure must be the criterion on the basis of which any mathematical approach for modelling purposes must be evaluated. This paper describes different solutions for the behavioural identification of non-linear dynamic systems, all based on a modified Volterra series, which are characterized by a reduced number of operators with respect to the classical Volterra approach. The operator reduction, which does not affect the accuracy of the obtained models if a mild assumption on the system memory time duration is satisfied, allows a reliable extraction of the model parameters by means of conventional instrumentation, without the need for the generation of complicated input probing signals or additional approximations. A detailed discussion is provided in order to estimate when each of the proposed approaches can be practically used, by pointing out the hypotheses that must be taken into account in order to minimise the modified series truncation errors. Experimental examples, showing the validity of the proposed approaches, are given in the last section of the paper, as well as a comparison between the performances of the different solutions when applied to the important field of electron device characterization.

Comparability of thermodynamic data - a metrological point of view

In order to compare and to interpret chemical measurements, compliance with general rules of metrology is compulsory. Such rules are the more important the more the chemical measurements are applied under circumstances where material assets and goods or immaterial values like health may be affected. Metrology of chemical measurements attempts to define rules for achieving comparability and for guaranteeing quality of analytical data. Thermodynamic data are commonly derived from a set of analytical measurements. Comparability among thermodynamic data is an important issue especially for those data to be applied in politically sensitive issues of environmental prognosis, long-term safety assessment of nuclear waste repositories in deep geological formations and assessment of environmental impact of technical intervention in the geosphere. Taking the data evaluation step in the traceability chain of thermodynamic data as an example, the existing thermodynamic data is shown to be affected by deficiencies in comparability and quality that may severely limit its dependability in environmental prognosis. The need for a metrologically acceptable approach is demonstrated. Statistical concepts improving a reliable assignment of meaningful measurement uncertainty to a thermodynamic datum are presented. Unresolved issues, i.e. measurement uncertainty of a pH measurement, hampering the construction of a traceability chain are outlined.

A Fizeau interferometer for astrometry in space: the metrology point of view

In space astrometry one seeks to determine positions, parallaxes and proper motions of stars to within 50 prad. The proposed GAIA mission is based on a rotating instrument made up of two telescopes set at a large base angle to each other and scanning the same great circle in the sky. Since the intended performances impose very strict stability requirements, a sophisticated metrological system is needed, whose actual implementation requires an integrated design of telescopes and laser interferometers. This paper examines the response of the instrument to small perturbations, special emphasis being placed on the location of star images. In order to exploit laser interferometry as much as possible, the original design was reconsidered, the base-angle implementation was improved, the number of degrees of freedom was reduced and the critical parameters were factorized. Although the present paper considers only the original proposal, in which each telescope was designed as a Fizeau interferometer, the results can be readily extended to other configurations.

Effect of temperature errors on accuracy of deep traps parameters obtained from transient measurements

The procedure of determination of deep traps parameters by both deep level transient capacitance spectroscopy (DLTS) and photoinduced transient spectroscopy (PITS) is based on Arrhenius plot illustrating the dependence of thermal emission rates as a function of temperature. In this article the effect of temperature measurement inaccuracy on the values of activation energy and capture cross- section obtained from the Arrhenius plot is analyzed. The inaccurate values of temperature involve both a change of slope and shift of the Arrhenius plots along vertical axis. The practical application of the analysis is exemplified by estimation of the temperature errors responsible for the shift of Arrhenius plots related to the center A in irradiated silicon. This article addresses the issue of temperature errors in DLTS and PITS measurements from the metrological point of view.

Non-intrusive solids charge and mass flow measurements with an electrostatic flow probe

An electrostatic flow probe for measurement of the electric charge, mass flow rate, volume loading, or concentration of solid particles travelling along a pneumatic transport pipe is mounted on a dielectric pipe section. The particles contact the inner wall surface of the dielectric pipe and cause it to be charged. The charging of this wall can be a serious metrological problem because of its influence on any non-contact measuring system based upon the electrostatic (inductive) flow probe which is a non-contact, non-intrusive device. The objective of this paper is to prove mathematically that there does not exist a problem of the dielectric pipe wall tribocharging from the metrological point of view when certain conditions are fulfilled. For the sake of illustration a sample measurement result obtained in a series of experiments performed with different powdered and granulated materials is shown to retain the validity of the mathematical and physical models. Also there have been carried out computer simulation and numerical analyses of an equivalent circuit of the probe and preamplifier to show the time response of the system to the charging of the dielectric pipe inner wall and its influence on the readings.