Uncertainty In Measured Values Research Articles

MEASUREMENT UNCERTAINTY EVALUATION OF BRINELL HARDNESS TEST: GUM AND MONTE CARLO METHOD

The Brinell hardness test is one of the most used mechanical tests in the industry to assure the quality of metallurgical processes. Based on the measured values, it is necessary to describe the measurement uncertainty values associated with the mathematical method used. Thus, measurement uncertainty values describe the reliability of the experimental results. The calculation of measurement uncertainty can be performed in several ways, and the method described by ISO/GUM is the most used by ISO/IEC 17025 accredited laboratories. The main objective of this work is to compare measurement uncertainty values based on different sources of uncertainty used in the measurement uncertainty evaluation for two Brazilian laboratories accredited by Cgcre/INMETRO. In addition, uncertainty values obtained by the GUM method and by the Monte Carlo method were compared. The results show that there is no great variation in the measurement uncertainty values as a function of the mathematical method used.

Challenges of HPLC determination of quinoline derivatives used in the treatment of malaria

ABSTRACTFully effective antimalarial drugs are yet to be isolated or synthesized, hence the search them continues. The study was aimed at establishing the most suitable conditions for the separation and determination of six biologically active alkaloids, quinoline derivatives, using high performance liquid chromatography with UV/Vis detection. The experiments involved the following derivatives: quinine, quinidine, cinchonine, cinchonidine, acetylcinchonine and acetylquinidine. Of the six stationary phases used, only the naphthylpropyl column enabled the separation of all alkaloids. The octadecyl column, considered by many analysts as a reference, did not provide successful separation. The naphthylpropyl column had also very good validation parameters, including a wide range of linearity, high values of correlation coefficients (0.9990‒0.9998) and low standard measurement uncertainty (1.8‒2.3 µg L‒1). The newly developed method was employed to evaluate the content of quinine in tonic-like beverages. The naphthylpropyl stationary phase provided ≤5% repeatability of quinine determination.

The influence of instrumental factors at uncertainty evaluation of scintillators technical light output measurements

This article complements the cycle of previous works that were devoted to the evaluation of uncertainty of measurement results of cylindrical scintillators on the base of NaI(Tl), CsI(Tl), CWO, BGO, p-terphenyl, anthracene, stilbene and long length strips based on polystyrene (PS strip) technical light output in photons/MeV (ph/MeV). The comparison method with the working sample was used. The investigated scintillators were manufactured at the Institute for Scintillation Materials of the National Academy of Sciences of Ukraine (ISMA NASU). Technical light output of the scintillators was in the range from 38 ph/MeV for strips to 55000 ph/MeV for CsI(Tl).In this work, we compared the estimates of instrumental uncertainty of type B of the measurement results of the technical light output of scintillators using pulse and current measurement modes. Factors influencing the magnitude of instrumental measurement uncertainty are determined. The contributions of these factors to the instrumental uncertainty for specified measurement modes are evaluated. It is established that the value of instrumental measurement uncertainty is related to the limited sensitivity of the scale of analyzing instrument and depends on the number of divisions of the used scale and the location of the measured parameter on this scale. The calculated values of contributions’ estimates to the uncertainty of the measurement results of the technical light output of scintillators are in the range from 0.05 to 0.18 % for CsI(Tl) and from 0.95 to 2.45 % for strip No. 1.Based on the results of the instrumental uncertainty estimates received in this work and taking into account the results of previous studies, the measurement uncertainty budgets for the technical light output of scintillators based on CsI(Tl) (pulse mode) and strip No. 3 (current mode) are compiled.

Evaluation of measurement uncertainties of digital volume correlation applied to laminography data

The effect of different data acquisition parameters on the displacement and strain uncertainties of kinematic fields is assessed via digital volume correlation applied to three-dimensional data sets imaged by synchrotron laminography. The measurement uncertainty is estimated for (1) different materials and associated varying contrast; (2) repeated scans, that is, uncertainty due to the imaging system and three-dimensional reconstruction; (3) rigid body motions between two subsequent scans; (4) rescaling of the gray level histogram during 32-bit floating point to 8-bit integer data conversion; (5) changes in the beam properties, that is, use of a monochromator or an undulator; and (6) changes in camera/detector characteristics. It is found that the amount of image contrast is not the only parameter that controls uncertainties for different materials. Furthermore, the rigid body motion procedure should be preferred over repeated scans as it provides more conservative measurement uncertainty values. The applied 32- to 8-bit conversion procedure, beam tuning and detector characteristics hardly affect the measurement uncertainty.

Measurement uncertainty of blood ethanol concentration in drink-driving cases in an emergency laboratory.

IntroductionThe quality of blood ethanol concentration (BEC) determination is important because of its legal ramifications. Measurement uncertainty provides quantitative information about the quality and reliability of test results. In this study, we aim to calculate the measurement uncertainty for the ethanol test in our laboratory measured with a Synchron Systems Ethanol assay kit by employing an enzymatic rate method on the Beckman-Coulter Olympus AU400 auto analyzer (Beckman Coulter Inc, Melville, USA).Materials and methodsThe measurement uncertainty values were calculated in accordance to the Nordtest guidelines. All vehicle drivers involved in a traffic accident were retrospectively inspected for the BEC test conducted during July to December 2016 in our emergency laboratory.ResultsA 1034 vehicle drivers had their BEC tested. The results for 181 drivers were > 0.50 g/L and reported as positive. The serum ethanol concentration in those showing a positive result was 2.04 ± 1.01 g/L, over four times the legal limit. The median BEC in those showing a negative result was 0.03 (IQR: 0.03) g/L. The expanded uncertainty obtained was 19.74%. When measurement uncertainty values were added to the results of the 1034 drivers who were retrospectively screened, eight vehicle drivers had results with 95% confidence intervals that exceeded the legal limit 0.50 g/L.ConclusionsThe BEC test results for vehicle drivers with values close to legal limits should be reported as the obtained ethanol concentration with corresponding measurement uncertainty.

Evaluation of Measurement Uncertainty for Torque Standard Machine Using Air Rotary Bearing

Calibration for torque measurement devices has become a great demand in many industrial areas. The most important in a calibration process is decreasing its uncertainty. This paper presents in building formula to evaluate the measurement uncertainty for torque standard machine using air rotary bearing which is experimented at the Hanoi University of Science and Technology. The uncertainty of the device is composed of the uncertainty of the component elements such as arm length, load, friction torque, axial tilt, vibration load...etc. Based on them the formula is built to estimate the measurement uncertainty of torque standard machine, find out factors that affect most to the measurement uncertainty value, therefore it can benefit the further researches to improve the accuracy of the torque standard machine.

Support of metrological traceability of capacitance measurements in Ukraine

The comparative analysis of the results of the RMO international key and supplementary comparisons of national standards of units of electrical capacitance is conducted with the aim of evaluation of convergence. For the comparisons, the reference values with the expanded uncertainties are calculated and the degrees of equivalence of standards of participants and expanded uncertainties for the nominal values of measures of 10 pF and 100 pF on frequencies of 1 kHz and 1.592 kHz are determined. Metrological traceability of the national standard of every participant of comparisons to the units of the International system of units SI is determined.For verification of consistency of the results of comparisons, the values of the χ2 criterion for the results of comparisons of standards of participants taking into account the measurement uncertainty are calculated. The obtained values of the criterion of consistency for the participants can be considered consistent, which is the objective confirmation of the measurement uncertainties declared by the participants.The evaluation of calibration and measurement capabilities of Ukraine for the unit of electrical capacitance is realized. The methodology of evaluation of measurement uncertainty in the wide range of capacitance values (from 10 pF to 10 nF) is proposed. The results the calculations of the values of measurement uncertainties according to the proposed methodology revealed that the results correspond to the data published in the international key comparison database for Ukraine in the range of capacitance values from 10 pF to 10 nF on frequencies of 1 kHz and 1.592 kHz.

Biological Variation of Chloride and Sodium in Sweat Obtained by Pilocarpine Iontophoresis in Adults: How Sure are You About Sweat Test Results?

The measurement of chloride and sodium concentrations in sweat is an important test for the diagnosis of cystic fibrosis (CF). The aim of this study was to assess the analytical variation (CVA) and within-subject (CVI) and between-subject (CVG) biological variation of chloride and sodium concentrations in sweat, collected by pilocarpine iontophoresis and to determine their effect on the clinical interpretation of sweat test results. Twelve Caucasian adults (six male and six female) without symptoms suggestive for CF and with a mean age of 41years (range 28-59) were included in the study. At least eight samples of sweat were collected from each individual by pilocarpine iontophoresis. Chloride and sodium concentrations were measured in duplicate for each sample using ion selective electrodes. After the removal of outliers, the CVA, CVI, and CVG of chloride and sodium were determined, and their impact on measurement uncertainty and reference change value were calculated. The CVA, CVI, and CVG of chloride in sweat samples were 6.5, 17.7, and 47.2%, respectively. The CVA, CVI, and CVG of sodium sweat samples were 6.0, 17.5, and 42.6%, respectively. Our study indicates that sweat chloride and sodium concentration results must be interpreted with great care. Different components of variation, particularly the biological variations, have a considerable impact on the interpretation of these results. If no pre-analytical, analytical, or post-analytical errors are suspected, repeated sweat testing to confirm first-measurement results might not be desirable.

Uncertainty Analysis in Humidity Measurements by the Psychrometer Method.

The most common and cheap indirect technique to measure relative humidity is by using psychrometer based on a dry and a wet temperature sensor. In this study, the measurement uncertainty of relative humidity was evaluated by this indirect method with some empirical equations for calculating relative humidity. Among the six equations tested, the Penman equation had the best predictive ability for the dry bulb temperature range of 15–50 °C. At a fixed dry bulb temperature, an increase in the wet bulb depression increased the error. A new equation for the psychrometer constant was established by regression analysis. This equation can be computed by using a calculator. The average predictive error of relative humidity was <0.1% by this new equation. The measurement uncertainty of the relative humidity affected by the accuracy of dry and wet bulb temperature and the numeric values of measurement uncertainty were evaluated for various conditions. The uncertainty of wet bulb temperature was the main factor on the RH measurement uncertainty.

An approach for estimating measurement uncertainty in medical laboratories using data from long-term quality control and external quality assessment schemes.

The present study was prompted by the ISO 15189 requirements that medical laboratories should estimate measurement uncertainty (MU). The method used to estimate MU included the: a) identification of quantitative tests, b) classification of tests in relation to their clinical purpose, and c) identification of criteria to estimate the different MU components. Imprecision was estimated using long-term internal quality control (IQC) results of the year 2016, while external quality assessment schemes (EQAs) results obtained in the period 2015-2016 were used to estimate bias and bias uncertainty. A total of 263 measurement procedures (MPs) were analyzed. On the basis of test purpose, in 51 MPs imprecision only was used to estimate MU; in the remaining MPs, the bias component was not estimable for 22 MPs because EQAs results did not provide reliable statistics. For a total of 28 MPs, two or more MU values were calculated on the basis of analyte concentration levels. Overall, results showed that uncertainty of bias is a minor factor contributing to MU, the bias component being the most relevant contributor to all the studied sample matrices. The model chosen for MU estimation allowed us to derive a standardized approach for bias calculation, with respect to the fitness-for-purpose of test results. Measurement uncertainty estimation could readily be implemented in medical laboratories as a useful tool in monitoring the analytical quality of test results since they are calculated using a combination of both the long-term imprecision IQC results and bias, on the basis of EQAs results.

The role of measurement uncertainty in the conformity assessment of the chemical composition of feeds

Official feed inspection has been directly related to the dispersion of the measures achieved by control laboratories, which can be due to several analytical techniques, calculation models and estimation approaches. The present study aims to demonstrate the importance of calculating the measurement uncertainty (MU) in the analysis of the chemical composition of several feedingstuffs, in order to avoid making wrong decisions due to incomplete measures. Samples of feedingstuffs (n=690), collected from 321 establishments, were analyzed. Complete measurements were compared to the labeling information declared by the processor. Animal feeds and mineral mixtures were the most frequent non-compliant samples and, among them, crude protein (n=94), calcium (n=50) and phosphorus (n=40) were the most frequent violations. Method performance was assessed in terms of in-house precision and recovery and by international proficiency testing. MU was calculated by using a bottom-up approach, combined with random effects inherited from the performance evaluation. A top-down approach based on the interlaboratory deviation was also carried out. The MU values calculated by the combined bottom-up approach were mostly lower than those calculated by interlaboratory experimental data. This latter approach overestimated the MU in most results, becoming inadequate. Titrimetric and spectrometric methods presented the higher and the lower MU among all techniques, respectively. A detailed study of the MU plays a key role in the conformity assessment of feedingstuffs, because the use of complete measures avoided 314 wrong decisions taking and prevented the disposal of approximately 1,000,007tons of animal feed.

Comparison of uncertainty in fatigue tests obtained by the Monte Carlo method in two softwares

The Supplement 1 to the “Guide to the expression of uncertainty in measurement” indicates the Monte Carlo method for calculating the expanded measurement uncertainty. The objective of this work is to compare the measurement uncertainty values obtained via Monte Carlo method through two commercial softwares (Matlab® and Crystal Ball®) for the parameter ‘adjusted strain’, obtained from fatigue tests. Simulations were carried out using different number of iterations and different levels of confidence. The results showed that there are short differences between the measurement uncertainty values generated by different software.

Rapid measurement of phytosterols in fortified food using gas chromatography with flame ionization detection

A novel method for the measurement of total phytosterols in fortified food was developed and tested using gas chromatography with flame ionization detection. Unlike existing methods, this technique is capable of simultaneously extracting sterols during saponification thus significantly reducing extraction time and cost. The rapid method is suitable for sterol determination in a range of complex fortified foods including milk, cheese, fat spreads, oils and meat. The main enhancements of this new method include accuracy and precision, robustness, cost effectiveness and labour/time efficiencies. To achieve these advantages, quantification and the critical aspects of saponification were investigated and optimised. The final method demonstrated spiked recoveries in multiple matrices at 85–110% with a relative standard deviation of 1.9% and measurement uncertainty value of 10%.

Shutter-less calibration of uncooled infrared cameras

Abstract. Infrared (IR) cameras based on microbolometer focal plane arrays (FPAs) are the most widely used cameras in thermography. New fields of applications like handheld devices and small distributed sensors benefit from the latest sensor improvements in terms of cost and size reduction. In order to compensate for disturbing influences derived from changing ambient conditions, radiometric cameras use an optical shutter for online recalibration purposes, partially also together with sensor temperature stabilization. For these new applications, IR cameras should consist only of infrared optics, a sensor array, and digital signal processing (DSP). For acceptable measurement uncertainty values without using an optical shutter (shutter-less), the disturbing influences of changing thermal conditions have to be treated based on temperature measurements of the camera interior. We propose a compensation approach based on calibration measurements under controlled ambient conditions. All correction parameters are determined during the calibration process. Without sensor temperature stabilization (TEC-less), the pixel responsivity is also affected by the camera temperature changes and has to be considered separately. This paper presents the details of the compensation procedure and discusses relevant aspects to gain low temperature measurement uncertainty. The residual measurement uncertainty values are compared to the shutter-based compensation approach.

Dimensional Validation of a 3D Digitization System

A three-dimensional measurement system has been set up. The digital models have been obtained using a webcam and structured light. After this, a software for measuring the digital geometries has been applied. In order to validate the digital models, the workpiece has been measured in a Laboratory of Metrology by means of a Coordinate Measuring Machine. While digital models can be obtained from multiple scan system configurations, not all of them get the same degree of accuracy. After analyzing the results, it can be determined the best condition for obtaining the digital model so that discrepancies between measurements and corresponding digital model of the workpiece are minimized. Also, it has been estimated a value of measurement uncertainty for each of the models studied.

In-house method validation, estimating measurement uncertainty and the occurrence of fumonisin B1 in samples of Brazilian commercial rice

Fumonisin B1 was investigated in samples of rice intended for human consumption, including polished parboiled rice, whole grain rice and whole grain parboiled rice. Until the present, no studies on the occurrence of fumonisin B1 have been performed on these types of rice that are commercially available in the south-eastern region of Brazil. A careful intralaboratory validation was carried out to demonstrate the fitness-of-purpose of the applied method for determining fumonisin B1 in the three studied rice types. The performance criteria – selectivity, reliable limits of detection (50 μg kg−1) and quantification (100 μg kg−1), linearity (range 100–2500 μg kg−1), precision (RSD values ≤ 17.0%) and recovery (71.7–112.0 %) were evaluated, and the expanded measurement uncertainty was estimated by using the data obtained from precision and recovery experiments. Matrix-matched calibration standards were employed to quantify the mycotoxin levels in the rice samples, in which the residual normality, homoscedasticity and independence were confirmed. In addition, the measurement uncertainty values are consistent with the maximum acceptable uncertainty established by European Union regulation for analytical methods for controlling mycotoxins in foodstuffs. Among the thirty-one commercial samples of rice analysed in the present study, five samples presented detectable levels of the mycotoxin, and these levels ranged from 64.8 to 163.0 μg kg−1.

Development and Validation of Method with Evaluation of Measurement Uncertainty for the Speciation Analysis of Chromium by Ion Chromatography

In the present study a simple, sensitive and accurate method has been developed for the speciation analysis of chromium(III) and chromium(VI) in aqueous solution using ion chromatography separation followed by detection through a UV detector. Chromium(III) was detected as its pyridine-2,6-dicarboxylic acid (PDCA) complex at 365 nm by pre-derivatizing it with eluent containing PDCA. Chromium(VI) was detected by post column derivatization with diphenylcarbazide at 540 nm. This paper discusses in details about the method validation and established each parameter according to the IUPAC and EURACHEM approaches. Method is validated for linearity, accuracy, precision, limit of detection and limit of quantification as per the guide lines. The evaluation of expanded uncertainty in measurement of Cr(III) and Cr(VI) was done at 95 % confidence level (k = 2) according to EURACHEM GUM guide. The method can be applied to determine Cr(III) and Cr(VI) up to 2 mg/kg and 40 µg/kg respectively with associated measurement uncertainty value of about 5 %. The major contribution of uncertainty is due to recovery. The method described in the present study is sensitive, selective and capable of quantifying trace level of Cr(VI) and Cr(III).

Derivation of uncertainty functions from validation studies in biological fluids: Application to the analysis of caffeine and its major metabolites in human plasma samples

Procedures for estimating the measurement uncertainty (MU) of the concentration of a given analyte in a sample are of major concern for analytical chemists. Unfortunately, it is still unclear how and why MU should be assessed. While several possibilities exist, an appropriate approach consists in using method validation data for the evaluation of MU. This was demonstrated by a validation study achieved in the framework of a clinical study related to caffeine in sports medicine, where the results were used for the evaluation of MU. After validation of the method developed using ultra-high pressure liquid chromatography–mass spectrometry for caffeine and its three main metabolites, accuracy profiles were built for each analyte. The first important conclusion is that the developed method was valid for all compounds and met the given specifications for the application (fit for purpose). Relevant estimates of combined standard uncertainty were computed to obtain uncertainty functions, which allow obtaining values of MU as a function of the concentration of the analyte. The great advantage of both uncertainty function and uncertainty profile is the development of a continuous model that enables easy calculation of the standard, expanded and relative expanded uncertainty at any concentration within the validation domain. In fact, the expanded uncertainty interval is assumed to contain 95% of all possible measurements, regardless of the concentration. Finally, the uncertainty function enables the determination of the lowest limit of quantification by selecting adequate acceptance limits, with the limit of quantification being defined as the point where the relative uncertainty equals the acceptance limit threshold. It has to be noted that further discussions remain mandatory to establish which criteria should be applied to define an adequate decision threshold, and the proposal afforded in this work may open new avenues in this direction.

The relationship between measurement uncertainty and reporting interval.

Measurement uncertainty (MU) estimates can be used by clinicians in result interpretation for diagnosis and monitoring and by laboratories in assessing assay fitness for use and analytical troubleshooting. However, MU is not routinely used to assess the appropriateness of the analyte reporting interval. We describe the relationship between MU and the analyte reporting interval. The reporting interval R is the smallest unit of measurement chosen for clinical reporting. When choosing the appropriate value for R, it is necessary that the reference change values and expanded MU values can be meaningfully calculated. Expanded MU provides the tighter criterion for defining an upper limit for R. This limit can be determined as R ≤ k·SDa/1.9, where SDa is the analytical standard deviation and k is the coverage factor (usually 2). Using MU estimates to determine the reporting interval for quantitative laboratory results ensures that reporting practices match local analytical performance and recognizes the inherent error of the measurement process.

Airfoil profile reconstruction under the uncertainty of inspection data points

A manufactured aero-engine blade is commonly inspected in sections, and its geometric errors are evaluated from the sectional inspection data points. To maintain consistency in evaluating the geometric errors, in particular, the position and twist errors of the stacked blade sections, reconstruction of valid sectional airfoil profiles from the measurement points is preferred. Considering that inspection data points are subject to measurement uncertainty, profile reconstruction via approximation-based curve fitting, rather than interpolation-based curve reconstruction, is adopted in this work. The fitting error of the approximated airfoil profile is deemed equivalent to the measurement uncertainty in the inspection data points. Thus, according to a given measurement uncertainty value, a progressive curve fitting scheme is proposed to generate the airfoil profile that meets the measurement uncertainty constraint. A closed nonperiodic B-spline curve is utilized to model the reconstructed airfoil profile due to its versatility in closed curve approximation. Typical computational tests have been carried out to demonstrate the effectiveness of the proposed airfoil profile reconstruction method, which is in fact generic and can be equally applied to approximating other closed sectional profiles.