Total Measurement Uncertainty Research Articles

Development and evaluation of a petal thickness measuring device based on the dual laser triangulation method

The growth and health status of plants can be evaluated by their petal or leaf thickness. However, the thickness of these sections is difficult to measure because of the irregular curvature of petal and leaf surfaces and their soft nature. The petal surface is easily damaged when traditional contact mechanical apparatus is used to measure it. In this research, we developed a novel noncontact measuring device that uses dual laser triangulation based on the Scheimpflug principle to measure petal thickness. A cubic spline method is employed to curve fit the multipoints of the petal surface after dual laser triangulation module measurement. The actual petal thickness can be calculated precisely from the normal equations of curvatures of the petal surface. The measuring range and the resolution of the petal thickness measuring device are ±2mm and 2μm/pixel, respectively. The total measurement uncertainty (comprising measurement repeatability, different surface slopes, and colors) of the dual laser triangulation system is less than 16μm. Using Phalaenopsis as a sample case, we make various compensations according to the different surface curvatures of its petal.

Determining complex permittivity from propagation constant measurements with planar transmission lines

A new two-standard calibration procedure is outlined for determining the complex permittivity of materials from the propagation constant measured with planar transmission lines. Once calibrated, a closed-form expression for the material permittivity is obtained. The effects of radiation and conductor losses are accounted for in the calibration. The multiline technique, combined with a recently proposed planar transmission-line configuration, is used to determine the line propagation constant. An uncertainty analysis is presented for the proposed calibration procedure that includes the uncertainties associated with the multiline technique. This allows line dimensions and calibration standards to be selected that minimize the total measurement uncertainty. The use of air and distilled water as calibration standards gives relatively small measurement uncertainty. Permittivity measurement results for five liquids, covering a wide permittivity range, agree very closely with expected values from 0.5–5 GHz.

Measurement uncertainty of adaptive Chirp-z transform

In this paper analysis of measurement uncertainty of Adaptive Chirp-z transform (ACT) algorithm for power frequency measurement is presented. ACT is a new algorithm developed for real time monitoring of power frequency. Every element (hardware and software) of measurement chain is contributing to the total measurement uncertainty. The analysis of passive voltage dividers, analog-to-digital converters, numeric algorithms and processors (word length and type of arithmetic) are also presented. Estimated values of each contributing part of measurement chain are calculated to the final expression of measurement uncertainty.

Measurement of low-ppm mixing ratios of water vapor in the upper troposphere and lower stratosphere using chemical ionization mass spectrometry

Abstract. A chemical ionization mass spectrometer (CIMS) instrument has been developed for the fast, precise, and accurate measurement of water vapor (H2O) at low mixing ratios in the upper troposphere and lower stratosphere (UT/LS). A low-pressure flow of sample air passes through an ionization volume containing an α-particle radiation source, resulting in a cascade of ion-molecule reactions that produce hydronium ions (H3O+) from ambient H2O. The production of H3O+ ions from ambient H2O depends on pressure and flow through the ion source, which were tightly controlled in order to maintain the measurement sensitivity independent of changes in the airborne sampling environment. The instrument was calibrated every 45 min in flight by introducing a series of H2O mixing ratios between 0.5 and 153 parts per million (ppm, 10−6 mol mol−1) generated by Pt-catalyzed oxidation of H2 standards while overflowing the inlet with dry synthetic air. The CIMS H2O instrument was deployed in an unpressurized payload area aboard the NASA WB-57F high-altitude research aircraft during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) mission in March and April 2011. The instrument performed successfully during seven flights, measuring H2O mixing ratios below 5 ppm in the lower stratosphere at altitudes up to 17.7 km, and as low as 3.5 ppm near the tropopause. Data were acquired at 10 Hz and reported as 1 s averages. In-flight calibrations demonstrated a typical sensitivity of 2000 Hz ppm−1 at 3 ppm with a signal to noise ratio (2 σ, 1 s) greater than 32. The total measurement uncertainty was 9 to 11%, derived from the uncertainty in the in situ calibrations.

Automated High-Ohmic Resistance Bridge With Voltage and Current Null Detection

A high-ohmic bridge for automated resistance measurements in the range between 1 MΩ and up to and above 100 TΩ is described. Whereas similar setups reported so far use only current null detection, the present system developed at VSL can use either voltage or current null detection. We compare the two null detection methods and find no significant difference between the methods over the resistance range between 10 MΩ and 100 GΩ. Voltage null detection is more accurate for resistance values below 10 GΩ at 10 V measurement voltage, whereas for resistance measurements above 100 GΩ current null detection should be used. Careful automation and refinement of the measurement procedure lead to excellent results and uncertainties. For example, the measurement of the 1:100 ratio of the series and parallel connection of a 10 × 100 MΩ Hamon device agrees within (0.5 ± 0.4)μΩ/Ω with the nominal Hamon ratio. The total measurement uncertainty at 1 GΩ equals 1.7 μΩ/Ω ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> = 1), which has been confirmed in a recent international comparison.

Uncertainty evaluation in the measurement of power frequency electric and magnetic fields from AC overhead power lines

Measurements of power frequency electric and magnetic fields from alternating current power lines are carried out in order to evaluate the exposure levels of the human body on the general public. For any electromagnetic field measurement, it is necessary to define the sources of measurement uncertainty and determine the total measurement uncertainty. This paper is concerned with the problems of measurement uncertainty estimation, as the measurement uncertainty budget calculation techniques recommended in standardising documents and research studies are barely described. In this work the total uncertainty of power frequency field measurements near power lines in various measurement sites is assessed by considering not only all available equipment data, but also contributions that depend on the measurement procedures, environmental conditions and characteristics of the field source, which are considered to increase the error of measurement. A detailed application example for power frequency field measurements is presented here by accredited laboratory.

Determination of Plutonium Isotopic Content by Microcalorimeter Gamma-Ray Spectroscopy

Microcalorimeter detectors provide unprecedented energy resolution for gamma-ray spectroscopy. One application is measuring the isotopic composition of plutonium-bearing samples by non-destructive gamma-ray spectroscopy to support nuclear safeguards and nonproliferation efforts. When measured with conventional high-purity germanium (HPGe) detectors, data from these samples contain significant peak overlaps requiring spectral deconvolution for analysis. The improved energy resolution of the microcalorimeter detector reduces peak overlaps leading to improvement in the statistical error component of the total measurement uncertainty. In this paper, we describe analysis code that was developed for spectral peak fitting and isotopic content determination from microcalorimeter and HPGe data. We apply the code to data collected from several plutonium standards to quantify the improvement of the statistical error derived from the improved energy resolution.

Theoretical Considerations on Combined Optical Distance Measurements Using a Femtosecond Pulse Laser

We introduce a combined technique and the mathematical description for distance measurements using a femtosecond pulse laser in a long range and a fine resolution. For distance measurements, the maximum measurable range can be extended by combining measurement results from several different methods while requiring relationships between the different measurement uncertainties and unambiguity ranges. This paper briefly explains why the uncertainty of a rough measurement technique (RMT) should be, at least, smaller than the half unambiguity range of a fine measurement technique (FMT) in order to combine a FMT with a RMT. Further discussions about the total measurement range, resolution, and uncertainty for various optical measurement techniques are also discussed.

Estimation of measurement uncertainty arising from manual sampling of fuels

Sampling is an important part of any measurement process and is therefore recognized as an important contributor to the measurement uncertainty. A reliable estimation of the uncertainty arising from sampling of fuels leads to a better control of risks associated with decisions concerning whether product specifications are met or not. The present work describes and compares the results of three empirical statistical methodologies (classical ANOVA, robust ANOVA and range statistics) using data from a balanced experimental design, which includes duplicate samples analyzed in duplicate from 104 sampling targets (petroleum retail stations). These methodologies are used for the estimation of the uncertainty arising from the manual sampling of fuel (automotive diesel) and the subsequent sulfur mass content determination. The results of the three methodologies statistically differ, with the expanded uncertainty of sampling being in the range of 0.34–0.40mgkg−1, while the relative expanded uncertainty lying in the range of 4.8–5.1%, depending on the methodology used. The estimation of robust ANOVA (sampling expanded uncertainty of 0.34mgkg−1 or 4.8% in relative terms) is considered more reliable, because of the presence of outliers within the 104 datasets used for the calculations. Robust ANOVA, in contrast to classical ANOVA and range statistics, accommodates outlying values, lessening their effects on the produced estimates. The results of this work also show that, in the case of manual sampling of fuels, the main contributor to the whole measurement uncertainty is the analytical measurement uncertainty, with the sampling uncertainty accounting only for the 29% of the total measurement uncertainty.

Experimental investigation of three-dimensional interconnect processing wafers

The use and enhancement of a semi-automated wafer characterization tool, a dual channel capacitive sensor module, is demonstrated by implementing a new measurement algorithm for metallization process control. This tool is capable of measuring the deposited metal film thickness induced bow and warpage in a full wafer surface scan. The nondestructive solution can measure Cu metal film thickness with a total measurement uncertainty of 0.18 μm (1σ). The stress conversion map can be obtained based on the modified Stoney's formula and the capacitance-displacement technique. A wafer thinning process was also performed to characterize the warpage/bow of 8-in. wafers, which continues to increase as wafer thicknesses are reduced from 725 to 300 μm. There was a linear relationship between the wafer warpage and bow and the square of the inverse of the thickness. Metrology results from actual 3-D interconnect processing wafers are presented.

Initial-state radiation measurement of thee+e−→π+π−π+π−cross section

We study the process e+e- -> pi+pi-pi+pi-gamma, with a photon emitted from the initial-state electron or positron, using 454.3 fb^-1 of data collected with the BABAR detector at SLAC, corresponding to approximately 260,000 signal events. We use these data to extract the non-radiative sigma(e+e- ->pi+pi-pi+pi-) cross section in the energy range from 0.6 to 4.5 Gev. The total uncertainty of the cross section measurement in the peak region is less than 3%, higher in precision than the corresponding results obtained from energy scan data.

How the choice of data reduction can strongly influence uncertainty assessment: A re-analysis of Mn-bath experiments

Abstract The Mn-bath technique is widely used, especially by standardization laboratories, for the absolute determination of neutron emission rates. Understanding the limitations of the technique, and in particular the total measurement uncertainty, is crucial if quality results, fit for purpose, are to be reported. In this work, we show that the way in which the acquired data is analyzed can strongly influence the uncertainty assessment. We take a carefully performed set of Mn-bath measurements from the literature as our example and show that the same data when reanalyzed can be used to justify an uncertainty smaller by about an order of magnitude than was originally reported. This finding should caution all those involved in radiation measurements to critically assess their approach to data analysis and to perform a careful uncertainty analysis taking into account possible alternatives.

The contribution of sampling uncertainty to total measurement uncertainty in the enumeration of microorganisms in foods

Random samples of each of several food products were obtained from defined lots during processing or from retail outlets. The foods included raw milk (sampled on farm and from a bulk-milk tanker), sprouted seeds, raw minced meat, frozen de-shelled raw prawns, neck-flaps from raw chicken carcasses and ready-to-eat sandwiches. Duplicate sub-samples, generally of 100 g, were examined for aerobic colony counts; some were examined also for counts of presumptive Enterobacteriaceae and campylobacters. After log10-transformation, all sets of colony count data were evaluated for conformity with the normal distribution (ND) and analysed by standard ANOVA and a robust ANOVA to determine the relative contributions of the variance between and within samples to the overall variance. Sampling variance accounted for >50% of the reproducibility variance for the majority of foods examined; in many cases it exceeded 85%. We also used an iterative procedure of re-sampling without replacement to determine the effects of sample size (i.e. the number of samples) on the precision of the estimate of variance for one of the larger data sets. The variance of the repeatability and reproducibility variances depended on the number of replicate samples tested (n) in a manner that was characteristic of the underlying distribution. The results are discussed in relation to the use of measurement uncertainty in assessing compliance of results with microbiological criteria for foods.

A steady-state measurement system for total hemispherical emissivity

A steady-state calorimetric technique was developed for measuring the total hemispherical emissivity of a conductive material. The system uses a thin strip of the conductive sample electrically heated by alternating current to high temperatures in a vacuum chamber. The emissivity was measured in a central region of the sample with an approximately uniform temperature distribution. Considering the influences of the gray body assumption, wire heat losses, effects of residual gas and conductive heat loss from the region to the rest of the strip, the emissivity was accurately determined by solving the inverse one-dimension steady-state heat transfer problem. The emissivities of various metal samples (nickel and 45# steel) were measured to verify the system accuracy. And the results were then analyzed to estimate the relative errors of emissivity arising from the gray body assumption, wire heat losses, effects of residual gas, non-uniform temperature distribution and the measurement uncertainty of emissivity. In the temperature range from 700 to 1300 K, the accuracy is acceptable for practical applications within the total measurement uncertainties of 1.1%. To increase the system applicability, some issues related to sample specifications, heating power control and temperature uniformity of sample test section were discussed. Thus, this system can provide accurate measurements of the total hemispherical emissivity of conductive samples at high temperatures.

Enabling Scatterometry as an In-Line Measurement Technique for 32 nm BEOL Application

Conventional metrology tools are unable to precisely monitor some interconnect attributes such as trench sidewall angle either due to limited capability or excessive cycle time. But these attributes have great impact on interconnect performance for 32 nm technology node and beyond. Scatterometry, a non-destructive metrology technique, is proposed to address the shortcomings of current metrology tools while also potentially providing additional measurement capabilities that enable more comprehensive characterization of interconnect attributes. Enabling scatterometry for back-end-of-line metrology at 32 nm technology node is challenged by the inherent complexity of a multilayer film structure. The research reported describes the implementation of scatterometry measurements to explore the advantages of this technique for the 32 nm technology node. The results obtained demonstrate the superiority of scatterometry techniques over conventional semiconductor metrology tools such as throughput, process control capability, precision, and accuracy. The total measurement uncertainty of scatterometry results with tunneling electron microscope and cross-sectional scanning electron microscope results for line height shows 1.92 and 6.46 nm, respectively, which compare favorably to the reference metrology tools. Scatterometry techniques also exhibited impressive potential to estimate end-of-the-line electrical parametric data. Finally, physical dimensions obtained from scatterometry measurements are shown to be comparable to TEM results from product wafers.

Assessment of total uncertainty in cocaine and benzoylecgonine wastewater load measurements

To check the effectiveness of campaigns preventing drug abuse or indicating local effects of efforts against drug trafficking, it is beneficial to know consumed amounts of substances in a high spatial and temporal resolution. The analysis of drugs of abuse in wastewater (WW) has the potential to provide this information. In this study, the reliability of WW drug consumption estimates is assessed and a novel method presented to calculate the total uncertainty in observed WW cocaine (COC) and benzoylecgonine (BE) loads. Specifically, uncertainties resulting from discharge measurements, chemical analysis and the applied sampling scheme were addressed and three approaches presented. These consist of (i) a generic model-based procedure to investigate the influence of the sampling scheme on the uncertainty of observed or expected drug loads, (ii) a comparative analysis of two analytical methods (high performance liquid chromatography–tandem mass spectrometry and gas chromatography–mass spectrometry), including an extended cross-validation by influent profiling over several days, and (iii) monitoring COC and BE concentrations in WW of the largest Swiss sewage treatment plants. In addition, the COC and BE loads observed in the sewage treatment plant of the city of Berne were used to back-calculate the COC consumption. The estimated mean daily consumed amount was 107 ± 21 g of pure COC, corresponding to 321 g of street-grade COC.

Practical estimation of the uncertainty of analytical measurement standards

Nowadays, a lot of time and resources are used to determine the quality of goods and services. As a consequence, the quality of measurements themselves, e.g., the metrological traceability of the measured quantity values is essential to allow a proper evaluation of the results with regard to specifications and regulatory limits. This requires knowledge of the measurement uncertainties of all quantity values involved in the measurement procedure, including measurement standards. This study shows how the uncertainties due to the preparation, as well as the chemical and compositional stability of a chemical measurement standard, or calibrator, can be estimated. The results show that the relative standard uncertainty of the concentration value of a typical analytical measurement standard runs up to 2.8% after 1 year. Of this, 1.9% originates from the preparation of the measurement standard, while 2.0 and 0.53% originate from the chemical and compositional stability during storage at −20 °C. The monthly preparation of working calibrators stored at 4 °C and used on a weekly basis, results in an additional standard uncertainty of the analyte concentration value of 0.35% per month due to compositional stability. While the preparation procedure is the major contributor to the total measurement uncertainty, the uncertainties introduced by the stability measurements are another important contributor, and therefore, the measurement procedure to evaluate stability is important to minimize the total measurement uncertainty.

Sampling variability and uncertainty in total diet studies

Here, the uncertainty budget for a total diet study (TDS) was clarified by separating the total measurement uncertainty into the uncertainty arising from the compositional heterogeneity of food items between cities (referred to as inter-city variance), the heterogeneity of food items within cities (intra-city variance), and the chemical analysis of the food samples (analytical variance) at one study design. TDS samples were collected from 14 cities in Japan. Duplicate samples collected in each city were prepared from food items purchased from different shops, and the cadmium concentrations were measured individually to obtain the intra-city variance. These results were used to show the importance of sampling design in TDSs, by evaluating a sampling method known as a multi-stage design, in which multiple samples are collected from several cities. Such schemes have been applied to TDSs, but the uncertainty involved has not been assessed. An intra-city correlation was observed between the cadmium concentrations in samples from the same city, demonstrating that the effective sample size was not simply the number of cities and shops sampled. The TDS results showed a high intra-city variance, which was greater than the inter-city variance for all of the food groups studied, and particularly for the bean and potato groups. By combining the sampling and analytical uncertainties obtained, the sampling uncertainty across different primary sampling unit sizes and secondary sampling unit sizes was obtained. As suggested by the analysis of potatoes and beans, grouping food samples from different shops in the same city can improve the representativeness of the results.

Thermal Conductivity of Ionic Liquids: Measurement and Prediction

This study reports thermal-conductivity data for a series of [EMIM] (1-ethyl-3-methylimidazolium)-based ionic liquids (ILs) having the anions [NTf2] (bis(trifluoromethylsulfonyl)imide), [OAc] (acetate), [N(CN)2] (dicyanimide), [C(CN)3] (tricyanomethide), [MeOHPO2] (methylphosphonate), [EtSO4] (ethylsulfate), or [OcSO4] (octylsulfate), and in addition for ILs with the [NTf2]-anion having the cations [HMIM] (1-hexyl-3-methylimidazolium), [OMA] (methyltrioctylammonium), or [BBIM] (1,3-dibutylimidazolium). Measurements were performed in the temperature range between (273.15 and 333.15) K by a stationary guarded parallel-plate instrument with a total measurement uncertainty of 3 % (k = 2). For all ILs, the temperature dependence of the thermal conductivity can well be represented by a linear equation. While for the [NTf2]-based ILs, a slight increase of the thermal conductivity with increasing molar mass of the cation is found at a given temperature, the [EMIM]-based ILs show a pronounced, approximately linear decrease with increasing molar mass of the different probed anions. Based on the experimental data obtained in this study, a simple relationship between the thermal conductivity, molar mass, and density is proposed for the prediction of the thermal-conductivity data of ILs. For this, also densities were measured for [EMIM][OAc], [EMIM][C(CN)3], and [HMIM][NTf2]. The mean absolute percentage deviation of all thermal-conductivity data for ILs found in the literature from the proposed prediction is about 7 %. This result represents a convenient simplification in the acquisition of thermal conductivity information for the enormous amount of structurally different IL cation/anion combinations available.

The effect of calibration equations on the uncertainty of UV–Vis spectrophotometric measurements

The effect of adequateness of the calibration equations on measurement uncertainty was not mentioned by EURACHEM. In this work, we investigate the sources of uncertainty when measuring glucose concentration with a UV–Vis spectrophotometer. The effect of two calibration equations on the uncertainty was compared. The sources of the glucose concentration measurement uncertainty include purity, volume of flasks, mass and the calibration equations. The effects of two calibration equations, linear and polynomial equation, on the uncertainty source were evaluated using the inverse calibration equation. The results indicated that the uncertainty components from purity were the smallest. The volumes of the volumetric flasks had only modest effect on the uncertainty, while the mass was an important source of the uncertainty. The contribution of the calibration equation to the total relative measurement uncertainty was 59.39% for the linear equation and 30.34% for the polynomial equation. With the selection of the adequate equation, the uncertainty source of the calibration equation could be reduced significantly.