Calculation Of Measurement Uncertainty Research Articles

Bias in Clinical Chemistry

Clinical chemistry uses automated measurement techniques and medical knowledge in the interest of patients and healthy subjects. Automation has reduced repeatability and day-to-day variation considerably. Bias has been reduced to a lesser extent by reference measurement systems. It is vital to minimize clinically important bias, in particular bias within conglomerates of laboratories that measure samples from the same patients. Small and variable bias components will over time show random error properties and conventional random-error based methods for calculating measurement uncertainty can then be applied. The present overview of bias presents the general principles of error and uncertainty concepts, terminology and analysis, and suggests methods to minimize bias and measurement uncertainty in the interest of healthcare.

Optical measuring equipments. Part I: Calibration model and uncertainty estimation

This study aims to propose and describe a procedure for calibrating the “vision subsystem” of digital optical machines, based on the affine camera model, valid for telecentric optical equipment. From this procedure, it is possible to systematise the calculation of the uncertainty of the calibration parameters associated with the “vision subsystem” by using the Monte Carlo method. The identification and characterisation of the calibration parameters of the “vision subsystem” and its associated uncertainty, obtained through this study, make it possible to characterise the metrological properties of the indicated optical equipment and ensure the metrological traceability of the measurements that have been subsequently taken.This work is divided into two parts. Part I focuses on developing a mathematical model of the “vision subsystem” and calculating the uncertainties of its parameters. Part II develops an example of measuring and calculating measurement uncertainty, based on the theoretical development of Part I.

Uncertainty determination of in situ airborne sound insulation measurements

In building acoustics the measurement uncertainty of sound insulation measurements is traditionally either not reported or reported as stated in the corresponding standard ISO 12999–1:2014. Determination and application of measurement uncertainties in building acoustics—Part 1: Sound insulation (former ISO 140-2). An alternative procedure is presented in this paper, aiming at evaluating the need of performing individual uncertainty calculations and the effect of extending the frequency range used to calculate sound insulation single number quantities. A large set of in situ airborne sound insulation measurements is investigated following the ISO Guide to the Expression of Uncertainty in Measurement (GUM) both for DnT 1/3 octave bands values and for single number rating DnTA. Two alternative assessment frequency ranges (50/100–5000Hz) have been considered. The paper describes a methodology for uncertainty determination to emphasize that it is possible to determine such individual uncertainties following the ISO GUM approach to a certain extent and that each individual measurement needs a corresponding measurement uncertainty calculation. In addition, the results show that if the assessment frequency range is extended below 100Hz, the uncertainty of the single number quantity is increased.

Study on Linearity of Impulse Voltage Divider

The uncertainty contribution related to linearity shall be considered in the calculation of measurement uncertainty when using the impulse voltage measuring system. Under the condition that the national standard is not yet established at present, the paper proposed an experimental method to measure the linearity of 600kV damped capacitive impulse divider (HCR600). The paper used low voltage resistance divider R200S to measure the linearity of generator, and obtained the linearity curve. With the increase of charging voltage, the linearity of divider can be obtained by measuring the charging voltage of impulse voltage generator precisely and its ratio of indicating value of the sample divider HCR600 after corrected. The result shows that the linearity of HCR600 decreases from +0.4% to-0.8%; the maximum difference between positive polarity and negative polarity is 0.14% and the linearity of negative polarity is superior to that of positive polarity. Besides, the paper used a 500kV resistance divider (SMR 7.7/ref500) calibrated by PTB to compare with HCR600, and obtained the linearity curve. By comparison, two curves show a good agreement, the maximum difference between them is 0.15% at the same voltage. The result shows that the method proposed in the paper can be used to measure the linearity of divider accurately. It also can be used as experimental verification in the process of the national standard establishing and to calibrate the ultrahigh voltage impulse voltage measuring equipments when equipments satisfy some requirements.

Evaluation of True Position Using Coordinate Measuring Machine

The article makes a contribution to the ever-important topic of evaluating geometric deviations of tolerated forms related to the datum system using coordinate measuring machines with a touch probe system. The datum system consists of the coordinate system and the coordinates planes. An integral part of the article is the quantification of the true position tolerated form related to the datum system and experimental evaluation of the deviation with calculation of measurement uncertainty, according to STN EN ISO 15530-3.

GUM conformity of software products - a discussion from a software tester's perspective

<span style="font-family: " lang="EN-US"><span style="color: black;"><p class="Text" style="text-indent: 0cm; margin: 0cm 0cm 0pt;"><span style="font-family: ";Calibri";,";sans-serif";; font-size: 9pt; mso-ascii-theme-font: minor-latin; mso-hansi-theme-font: minor-latin; mso-ansi-language: EN-US; mso-fareast-language: KO;" lang="EN-US">This paper describes how to assess GUM conformity of software products which claim to offer a GUM-compliant calculation of measurement uncertainties. To bridge the gap between the GUM guideline and the required test specification, an analysis of the GUM from the perspective of software testing is presented. </span><span style="font-family: ";Calibri";,";sans-serif";; font-size: 9pt; mso-ascii-theme-font: minor-latin; mso-hansi-theme-font: minor-latin; mso-fareast-language: KO;" lang="EN-GB">Problems of testability and ambiguity of GUM statements are analysed in detail. </span><span style="font-family: ";Calibri";,";sans-serif";; font-size: 9pt; mso-ascii-theme-font: minor-latin; mso-hansi-theme-font: minor-latin; mso-ansi-language: EN-US; mso-fareast-language: KO;" lang="EN-US">The benefit and the limits of the developed validation procedure and test environment are outlined<span style="color: black;">.</span></span><span style="font-family: ";Calibri";,";sans-serif";; font-size: 9pt; mso-ascii-theme-font: minor-latin; mso-hansi-theme-font: minor-latin; mso-ansi-language: EN-US;" lang="EN-US"></span></p></span></span>

Gas flow calibrations performed at the National Metrology Institute of South Africa (NMISA)

The National Metrology Institute of South Africa (NMISA) Gas Flow Laboratory provides traceability to the South African Industry for gas flow measurements. A new primary standard for gas flow calibrations was purchased and commissioned. With three flow cells, a flow range of 0.5 mL/min to 50 000 mL/min is covered. The main features of this standard are accuracy, speed and convenience. This paper describes the activities of the NMISA Gas Flow Laboratory – a discussion of the primary standard, the validation thereof, calibration methods for client instrumentation, analysis of measurement results and the calculation of measurement uncertainties.

Microfluidic chip designs process optimization and dimensional quality control

The challenge of fabricating geometries with critical dimensions ranging from few microns down to 10 nm with high production rate is delaying the development of nanotechnology based products. Diverse research works have shown the capability of technologies such as UV lithography, nano imprint lithography and e-beam lithography to produce micro and nano features. However, their application for tooling purposes is relatively new and the potential to produce nanometer features with high volume and low cost is enormous. Considering possible implementation in a mass production environment the precision of measuring results and the accuracy of measurement relocation are very relevant. In this paper, the capability of producing with high volume Lab-on-chip devices through injection molding is evaluated. Preparation of master geometries was made in a Si wafer using e-beam lithography and reactive ion etching. Subsequent nickel electroplating was employed to replicate the obtained geometries on the tool, which was used to mold on transparent polymer substrates the functional structures. To assess the critical factors affecting the replication quality throughout the different steps of the proposed process chain, test geometries were designed and produced on the side of the functional features. The so-called "Finger Print" of the lithography and molding processes was qualitatively and quantitatively evaluated through scanning electron microscopy and atomic force microscopy respectively. The entire process chain is therefore characterized and the degree of replication among the different replication steps quantified with precise measurements using a high accuracy relocation technique on the produced key test geometries. Influence of injection molding process parameters, feature dimensions and orientation relative to the polymer flow direction have been assessed in respect of the replication fidelity of the produced micro/sub-μm channels. Finally the paper addresses product compliance with specifications, focusing on tolerances of vertical dimensions using a metrological approach: sub-μm features on silicon, nickel stampers and injection molded substrates are measured. Results of measurement uncertainty calculation, quantitative replication fidelity assessment, and dimensional tolerances at the nanometer scale verification are reported.

Models of distributions of probability density in calculating measurement uncertainty

Models of distributions of the probability density in conversion of the standard uncertainty of measurements into the expanded uncertainty along with models of distributions of the input quantities used in calculation of their standard uncertainty are discussed. Upper bounds are given for the coefficients used in both problems where information about the form of the distributions is lacking.

Quantification of 60Fe atoms by MC-ICP-MS for the redetermination of the half-life

In many scientific fields, the half-life of radionuclides plays an important role. The accurate knowledge of this parameter has direct impact on, e.g., age determination of archeological artifacts and of the elemental synthesis in the universe. In order to derive the half-life of a long-lived radionuclide, the activity and the absolute number of atoms have to be analyzed. Whereas conventional radiation measurement methods are typically applied for activity determinations, the latter can be determined with high accuracy by mass spectrometric techniques. Over the past years, the half-lives of several radionuclides have been specified by means of multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) complementary to the earlier reported values mainly derived by accelerator mass spectrometry. The present paper discusses all critical aspects (amount of material, radiochemical sample preparation, interference correction, isotope dilution mass spectrometry, calculation of measurement uncertainty) for a precise analysis of the number of atoms by MC-ICP-MS exemplified for the recently published half-life determination of 60Fe (Rugel et al, Phys Rev Lett 103:072502, 2009).

The uncertainty of purity of reference materials must be known

Quantitative chromatographic analyses do not belong to the class of primary methods, but the analyst needs to calibrate the obtained signals with well-known solutions made of high-purity reference materials. Every analyte, to be quantified by a non-primary method, needs the chemically identical compound as its reference. It is not necessary that the content of the reference is 100.0%, but it is crucial that its purity is known, together with the uncertainty of this value (e.g., 99.9±0.05%). Any high-quality analytical result should include information about the associated measurement uncertainty, and the purity uncertainty of the reference is a parameter which always appears in the overall measurement uncertainty calculation of the measurand (such as the concentration or content of an analyte).Our general postulation is that the purity and the uncertainty of all reference materials must be known. It concerns all types of reference materials although we focus our discussion on the analysis of drug products. Unfortunately, at present only a few pharmaceutical reference materials are commercially available from regulatory bodies with a certificate confirming their purity with the related uncertainty. In contrast, such well-characterized materials, traceable to the International System of Units (SI), are available from various commercial suppliers.

Computed Tomography as a Tool for Tolerance Verification of Industrial Parts

Computed tomography (CT) is becoming an important technology for industrial applications, enabling fast and accurate control of manufactured parts. In only a few minutes, a complete 3D model of a part may be obtained, allowing measurements of external and internal features. This paper presents results of tolerance verification of a plastic housing for an insulin pen manufactured by Novo Nordisk A/S. Calculation of measurement uncertainties was taken into account in decision making regarding the specified tolerance limits. Variables in terms of CT systems, data sets, and evaluation software are considered in this study.

Calculation of measurement uncertainty for plastic (ABS) material in flexural testing

In order to determine mechanical properties of materials various kind of tests can be applied by means of using their tensile strength, lower yield stress, proof stress, impact strength, Brinell, Rockwell and surface hardness, elongation after fracture properties. Among these tests, three point flexural testing method has some advantages such as easy preparation (production) of samples and no gripping problems comparing to tension test. Flexural tests results should be obtained accurately to provide expected testing performance. The measurement uncertainty of flexural tests should be calculated by conducting all effective uncertainty parameters during the test procedure. In this study, the measurement uncertainty of the flexural test of ABS (Acrylonitrile Butadiene Styrene) material was investigated, which is widely used as industrial plastic material in many applications.

Software support for the Nordtest method of measurement uncertainty evaluation

Software support for the Nordtest method of measurement uncertainty evaluation is described. According to the Nordtest approach, the combined measurement uncertainty is broken down into two main components—the within-laboratory reproducibility (intermediate precision) sRw and the uncertainty due to possible laboratory bias u(bias). Both of these can be conveniently estimated from validation and quality control data, thus significantly reducing the need for performing dedicated experiments for estimating detailed uncertainty contributions and thereby making uncertainty estimation easier for routine laboratories. An additional merit of this uncertainty estimation approach is that it reduces the danger of underestimating the uncertainty, which continues to be a problem at routine laboratories. The described software tool—MUkit (measurement uncertainty kit)—fully reflects the versatility of the Nordtest approach: it enables estimating the uncertainty components from different types of data, and the data can be imported using a variety of means such as different laboratory data systems and a dedicated web service as well as manual input. Prior to the development of the MUkit software, a laboratory survey was carried out to identify the needs of laboratories related to uncertainty estimation and other quality assurance procedures, as well as their needs for a practical tool for the calculation of measurement uncertainty.

Alternative calculation of measurement uncertainty with global approach in food microbiology

Calculation of measurement uncertainty is a requirement for all laboratories accredited to ISO/IEC 17025 including those carrying out microbiological analyses. Today, calculation of measurement uncertainty in microbiological analyses using precision data according to global approach principles is widely recognized by the microbiologists due to difficulties in quantification of individual uncertainty sources. In food microbiology, precision data obtained from different samples usually show over-dispersion, and the use of over-dispersed data may result in large variance. The current ISO standard on measurement uncertainty in food microbiology proposes the use of log-transformed precision data to overcome this problem. This paper proposes an alternative procedure to calculate the measurement uncertainty in food microbiology using non-logarithmic precision data. The calculations used in this procedure based on relative range of duplicate analyses can be applied to intra-laboratory reproducibility data obtained from microbiological analyses of which duplicate results show relatively low variation.

Development and validation of a ultra high performance liquid chromatography–tandem mass spectrometric method for the direct detection of formoterol in human urine

Formoterol is a long acting β(2)-agonist and has proven to be a very effective bronchodilating agent. Hence it is frequently applied therapeutically for the treatment of asthma. Because β(2)-agonists might be misused in sports for the stimulatory effects and for growth-promoting action their use is restricted. Since January 2012, formoterol is prohibited in urinary concentrations higher than 30 ng/mL. The objective of this study was to develop and validate a simple and robust ultra high performance liquid chromatographic-tandem mass spectrometric (UHPLC-MS/MS) method for the direct quantification of formoterol in urine. Sample preparation was limited to an enzymatic hydrolysis step after which 2 μL was injected in the chromatographic system. Chromatography was performed on a C(8)-column using gradient conditions. The mobile phase consisted of water/methanol (H(2)O/MeOH) both containing 0.1% acetic acid (HOAc) and 1mM ammonium acetate (NH(4)OAc). Calibration curve were constructed between 15 and 60 ng/mL. Validation data showed bias of 1.3% and imprecision of 5.4% at the threshold. Ion suppression/enhancement never exceeded 7%. Calculating measurement uncertainty showed proof of applicability of the method. Stability of formoterol was also investigated at 56 °C (accelerated stability test) at pH 1.0/5.2/7.0 and 9.5. At the physiological pH values of 5.2 and 7.0, formoterol showed good stability. At pH 1.0 and 9.5 significant degradation was observed.

Simulation of GNSS Signal with Noise and Distance, Speed Probability Distribution Calculation

Calibration or verification of measurement equipment needs standard measurement which must have sufficient precision and accuracy. GNSS usually has variable precision and accuracy with each measurement. In this article signal generation directly in frequency-delay representation is presented which can be used for decomposition or multipath interference correction. Demodulated signal maximal value distributions for frequency and delay are found from signal and known noise. These distributions allow to calculate measurement uncertainties for each satellite separately. Ill. 9, bibl. 5 (in English; abstracts in English and Lithuanian).DOI: http://dx.doi.org/10.5755/j01.eee.122.6.1839

Calculation of measurement uncertainty for cellulose based transformed board material in tensile testing

Today’s global economy obliges manufacturers to produce their products in high quality with cheaper cost. Thus, manufacturers must develop their products applying tests to get better performance and higher quality before distributing them to the competitive market. In order to produce long working life of transformer reactors without losing their performance, different tests including axial and flexural testing are applied on the cellulose based laminated board material used in production. During development of laminated board material, test results should be known very well and the measurement uncertainty of tensile tests should be calculated taking into account all parameters. In this study, effective parameters on the quality of tensile testing causing an increase on the measurement uncertainty are investigated. Tensile strength and elongation test of laminated board material were carried out according to IEC 60641-2 and the uncertainty contributions based on experimental results were calculated. The results and impact of the uncertainty parameters are presented in detail.

Improved water δ2H and δ18O calibration and calculation of measurement uncertainty using a simple software tool

The calibration of all δ(2)H and δ(18)O measurements on the VSMOW/SLAP scale should be performed consistently, based on similar principles, independent of the instrumentation used. The basic principles of a comprehensive calibration strategy are discussed taking water as example. The most common raw data corrections for memory and drift effects are described. Those corrections result in a considerable improvement in data consistency, especially in laboratories analyzing samples of quite variable isotopic composition (e.g. doubly labelled water). The need for a reliable uncertainty assessment for all measurements is discussed and an easy implementation method proposed. A versatile evaluation method based on Excel macros and spreadsheets is presented. It corrects measured raw data for memory and drift effects, performs the calibration and calculates the combined standard uncertainty for each measurement. It allows the easy implementation of the discussed principles in any user laboratory. Following these principles will improve the comparability of data among laboratories.

Calculation and Verification of Blood Ethanol Measurement Uncertainty for Headspace Gas Chromatography

An estimate was made of the measurement uncertainty for blood ethanol testing by headspace gas chromatography. While uncertainty often focuses on compliance to a single threshold level (0.08 g/100 mL), the existence of multiple thresholds, related to enhanced sentencing, subject age, or commercial vehicle licensure, necessitate the use of an estimate with validity across multiple specification levels. The uncertainty sources, in order of decreasing magnitude, were method reproducibility, linear calibration, recovery, calibrator preparation, reference material, and sample preparation. A large set of reproducibility data was evaluated (n = 15,433) in order to encompass measurement variability across multiple conditions, operators, instruments, concentrations and timeframes. The relative, combined standard uncertainty was calculated as ±2.7%, with an expanded uncertainty of ±8.2% (99.7% level of confidence, k = 3). Bias was separately evaluated through a recovery study using standard reference material from a national metrology institute. The uncertainty estimate was verified through the use of proficiency test (PT) results. Assigned values for PT results and their associated uncertainties were calculated as robust means (x*) and standard deviations (s*) of participant values. Performance scores demonstrated that the uncertainty estimate was appropriate across the full range of PT concentrations (0.010-0.370 g/100 mL). The use of PT data as an empirical estimate of uncertainty was not examined. Until providers of blood ethanol PT samples include details on how an assigned value is obtained along with its uncertainty and traceability, the use of PT data should be restricted to the role of verification of uncertainty estimates.