Total Uncertainty Of Measurements Research Articles

Radon Equilibrium Equivalent Concentration Uncertainty of Calibration System With Alpha Self-Absorption Consideration

Abstract The measurement of radon decay products level in dwellings or working places separately is not preferable. The estimation of radon equivalent equilibrium concentration (EECRn) is more simple and quick technique. In this work, the uncertainty of calibration system for EECRn measurements will present and the reduction will be suggesting. The calibration system for EECRn measurements was presented and described in previous work with gamma spectrometer as a reference measuring device. The influence of alpha particles absorption in filters materials and filter efficiency taken into account. The measurements of EECRn by gamma spectrometry and improved alpha radiometry are in good agreement and the systematic shift between average values is observed and resolved. The total standard uncertainty of EECRn measurements with gamma spectroscopy is 3.8%. About 71% of this total uncertainty value is related to the uncertainty of the count rate at full absorption peak with gamma spectroscopy. If the time between the end of sampling and gamma spectroscopy measurements reduced to 2000s not 4000 s, this value will reduce to 1.6% and the total standard uncertainty of EECRn will be 2.6%.

Metrology for low-cost CO<sub>2</sub> sensors applications: the case of a steady-state through-flow (SS-TF) chamber for CO<sub>2</sub> fluxes observations

Abstract. Soil CO2 emissions are one of the largest contributions to the global carbon cycle, and a full understanding of processes generating them and how climate change may modify them is needed and still uncertain. Thus, a dense spatial and temporal network of CO2 flux measurements from soil could help reduce uncertainty in the global carbon budgets. In the present study, the design, assembly, and calibration of low-cost air enquirer kits, including CO2 and environmental parameters sensors, is presented. Different types of calibrations for the CO2 sensors and their associated errors are calculated. In addition, for the first time, this type of sensor has been applied to design, develop, and test a new steady-state through-flow (SS-TF) chamber for simultaneous measurements of CO2 fluxes in soil and CO2 concentrations in air. The sensors' responses were corrected for temperature, relative humidity, and pressure conditions in order to reduce the uncertainty in the measured CO2 values and of the following calculated CO2 fluxes based on SS-TF. CO2 soil fluxes measured by the proposed SS-TF and by a standard closed non-steady-state non-through-flow (NSS-NTF) chamber were briefly compared to ensure the reliability of the results. The use of a multiparametric fitting reduced the total uncertainty of the CO2 concentration measurements by 62 %, compared with the uncertainty that occurred when a simple CO2 calibration was applied, and by 90 %, when compared to the uncertainty declared by the manufacturer. The new SS-TF system allows the continuous measurement of CO2 fluxes and CO2 ambient air with low cost (EUR ∼1200), low energy demand (<5 W), and low maintenance (twice per year due to sensor calibration requirements).

Development of Methodologies for the Chemical Quality Control of Zircon, A Precursor for Zirconium Production

AbstractMethodologies have been developed for the chemical quality control of zircon mineral by EDXRF and D.C.Arc carrier distillation technique. EDXRF technique was found to be preferred for major and minor constituents including non‐metal analytes, while D.C.Arc carrier distillation OES was found to be good for minor and trace metallic constituents including low Z elements. A comparative evaluation of the analytical performance (detection limit, sensitivity, precision, linear dynamic range) was performed. A multipoint standardization was carried out using the base material of 1 : 1 SiO2 : ZrO2 powder mixture to establish calibration curves for the analytes after identification of interference free and the best performed emission and X‐ray analytical lines. In zircon sample, Si, Zr and Y were found to be present as major constituent, with Ga, Ca, Ru, Rh, Fe, Mn, Mg, I, S as minor and Zn, Cr, Sn, Li as trace constituents. The total uncertainty of the EDXRF measurements was evaluated. The statistical t‐test analysis was carried out for 10 degrees of freedom with 95 % confidence interval. The experimentally obtained t‐values were found to be lower compared to the corresponding tcri value revealing the reliability of the measurements. Elemental distributions of the analytes were also investigated using five different zircon samples.

Stabilization of the Temperature of Resonator of an Acoustic Gas Thermometer

The application of an AK-10 thermocontroller developed at the All-Russia Research Institute of Physicotechnical and Radio Measurements in the temperature control system of an acoustic gas thermometer makes it possible to improve the characteristics of this system. We performed temperature measurements with the use of an MI6020T bridge and demonstrate the possibility of stabilization of temperature of the resonator at a level of 15 μK. The total standard relative uncertainty of temperature measurements in the transmission of the values of temperature from the resonator to a resistance thermometer is reduced down to 0.25 ppm.

Development of absolute acoustic gas thermometer for the state primary standard of the temperature unit – kelvin in the range 0.3-273.16 K in VNIIFTRI and the total standard uncertainty of the thermodynamic temperature measurements near the triple point of water

An absolute primary acoustic gas thermometer has been developed and successfully tested in VNIIFTRI. The acoustic gas thermometer is planned to be included in the Russian state primary standard of the temperature unit – kelvin in the range 0.3-273.16 K. The uncertainty of the thermodynamic temperature measurements with the acoustic gas thermometer near the triple point of water was experimentally researched.

Thermal Conductivity of Aqueous Solvents Used in CO2 Capture

The growing CO2 concentration in the atmosphere forces researchers to work on improving existing carbon dioxide capture technologies. This technology is energy-intensive and consumes significant amount of heat for solvent regeneration. Thermal conductivity is a key property for the estimation of the heat required for solvents regeneration. Accordingly, in the present work thermal conductivity is measured for six aqueous solvent used for this purpose; monoethanolamine (MEA), diethanolamine (DEA), 2-amino-2methyl-1-propanol (AMP), sodium hydroxide (NaOH), potassium carbonate (K2CO3), and potassium glycinate (PG) aqueous solutions for mole fraction range from 0.00 to 0.0825. The measurements were carried out at constant temperature (294.82K) and pressure (102.02kPa). The total experimental standard uncertainty of thermal conductivity, pressure, temperature, and mole fraction measurements were estimated to be ± 0.001 Wm-1K-1, ± 0.02kPa, ± 0.1K, and ± 0.0002, respectively. The measured values of thermal conductivity were compared with data and correlations reported in the literature. The average absolute deviation between measured and calculated values from available correlation equations for the thermal conductivity was lease than 0.5%.

Performance Evaluation of Material Decomposition With Rapid-Kilovoltage-Switching Dual-Energy CT and Implications for Assessing Bone Mineral Density.

The purpose of this article is to quantitatively investigate the accuracy and performance of dual-energy CT (DECT) material density images and to calculate the areal bone mineral density (aBMD) for comparison with dual-energy x-ray absorptiometry (DEXA). A rapid-kilovoltage-switching DECT scanner was used to create material density images of various two-material phantoms of known concentrations under different experimental conditions. They were subsequently also scanned by single-energy CT and DEXA. The total uncertainty and accuracy of the DECT concentration measurements was quantified by the root-mean-square (RMS) error, and linear regression was performed to evaluate measurement changes under varying scanning conditions. Alterations to accuracy with concentric (anthropomorphic) phantom geometry were explored. The sensitivity of DECT and DEXA to changes in material density was evaluated. Correlations between DEXA and DECT-derived aBMD values were assessed. The RMS error of DECT concentration measurements in air ranged from 9% to 244% depending on the materials. Concentration measurements made off-isocenter or with a different DECT protocol were slightly lower (≈ 5%), whereas measurement in scattering conditions resulted in a reduction of 8-27%. In concentric phantoms, higher-attenuating material in the outer chamber increased measured values of the inner material for all methods. DECT was more sensitive than DEXA to changes in BMD at 2 mg/mL K2HPO4. Measurements of aBMD using DECT and DEXA were highly correlated (R(2) = 0.98). DECT material density images were linear in response but prone to poor accuracy and biases. DECT-based aBMD could be used to monitor relative change in bone density.

Profiles of second- to fourth-order moments of turbulent temperature fluctuations in the convective boundary layer: first measurements with rotational Raman lidar

Abstract. The rotational Raman lidar (RRL) of the University of Hohenheim (UHOH) measures atmospheric temperature profiles with high resolution (10 s, 109 m). The data contain low-noise errors even in daytime due to the use of strong UV laser light (355 nm, 10 W, 50 Hz) and a very efficient interference-filter-based polychromator. In this paper, the first profiling of the second- to fourth-order moments of turbulent temperature fluctuations is presented. Furthermore, skewness profiles and kurtosis profiles in the convective planetary boundary layer (CBL) including the interfacial layer (IL) are discussed. The results demonstrate that the UHOH RRL resolves the vertical structure of these moments. The data set which is used for this case study was collected in western Germany (50°53'50.56'' N, 6°27'50.39'' E; 110 m a.s.l.) on 24 April 2013 during the Intensive Observations Period (IOP) 6 of the HD(CP)2 (High-Definition Clouds and Precipitation for advancing Climate Prediction) Observational Prototype Experiment (HOPE). We used the data between 11:00 and 12:00 UTC corresponding to 1 h around local noon (the highest position of the Sun was at 11:33 UTC). First, we investigated profiles of the total noise error of the temperature measurements and compared them with estimates of the temperature measurement uncertainty due to shot noise derived with Poisson statistics. The comparison confirms that the major contribution to the total statistical uncertainty of the temperature measurements originates from shot noise. The total statistical uncertainty of a 20 min temperature measurement is lower than 0.1 K up to 1050 m a.g.l. (above ground level) at noontime; even for single 10 s temperature profiles, it is smaller than 1 K up to 1020 m a.g.l. Autocovariance and spectral analyses of the atmospheric temperature fluctuations confirm that a temporal resolution of 10 s was sufficient to resolve the turbulence down to the inertial subrange. This is also indicated by the integral scale of the temperature fluctuations which had a mean value of about 80 s in the CBL with a tendency to decrease to smaller values towards the CBL top. Analyses of profiles of the second-, third-, and fourth-order moments show that all moments had peak values in the IL around the mean top of the CBL which was located at 1230 m a.g.l. The maximum of the variance profile in the IL was 0.39 K2 with 0.07 and 0.11 K2 for the sampling error and noise error, respectively. The third-order moment (TOM) was not significantly different from zero in the CBL but showed a negative peak in the IL with a minimum of −0.93 K3 and values of 0.05 and 0.16 K3 for the sampling and noise errors, respectively. The fourth-order moment (FOM) and kurtosis values throughout the CBL were not significantly different to those of a Gaussian distribution. Both showed also maxima in the IL but these were not statistically significant taking the measurement uncertainties into account. We conclude that these measurements permit the validation of large eddy simulation results and the direct investigation of turbulence parameterizations with respect to temperature.

Continuous measurements of atmospheric water vapour isotopes in western Siberia (Kourovka)

Abstract. The isotopic composition of atmospheric water vapour at the land surface has been continuously monitored at the Kourovka astronomical observatory in western Siberia (57.037° N, 59.547° E; 300 m a.s.l.) since April 2012. These measurements provide the first record of δD, δ18O and d-excess in this region. Air was sampled at 8 m height within a forest clearing. Measurements were made with a wavelength-scanned cavity ring-down spectroscopy analyzer (Picarro L2130-i). Specific improvements of the measurement system and calibration protocol have been made to ensure reliable measurements at low humidity during winter. The isotopic measurements conducted till August 2013 exhibit a clear seasonal cycle with maximum δD and δ18O values in summer and minimum values in winter. In addition, considerable synoptic timescale variability of isotopic composition was observed with typical variations of 50–100‰ for δD, 10–15‰ for δ18O and 2–8‰ for d-excess. The strong correlations between δD and local meteorological parameters (logarithm of humidity and temperature) are explored, with a lack of dependency in summer that points to the importance of continental recycling and local evapotranspiration. The overall correlation between δD and temperature is associated with a slope of 3‰ °C−1. Large d-excess diurnal variability was observed during summer with up to 30‰ decrease during the night and the minima manifested shortly after sunrise. Two dominant diurnal cycle patterns for d-excess differing by the magnitude of the d-excess decrease (21‰ and 7‰) and associated patterns for meteorological observations have been determined. The total uncertainty of the isotopic measurements was quantified as 1.4–11.2‰ for δD, 0.23–1.84‰ for δ18O and 2.3–18.5‰ for d-excess depending on the humidity.

Accuracy of force and center of pressure measures of the Wii Balance Board

The Nintendo Wii Balance Board (WBB) is increasingly used as an inexpensive force plate for assessment of postural control; however, no documentation of force and COP accuracy and reliability is publicly available. Therefore, we performed a standard measurement uncertainty analysis on 3 lightly and 6 heavily used WBBs to provide future users with information about the repeatability and accuracy of the WBB force and COP measurements. Across WBBs, we found the total uncertainty of force measurements to be within ±9.1N, and of COP location within ±4.1mm. However, repeatability of a single measurement within a board was better (4.5N, 1.5mm), suggesting that the WBB is best used for relative measures using the same device, rather than absolute measurement across devices. Internally stored calibration values were comparable to those determined experimentally. Further, heavy wear did not significantly degrade performance. In combination with prior evaluation of WBB performance and published standards for measuring human balance, our study provides necessary information to evaluate the use of the WBB for analysis of human balance control. We suggest the WBB may be useful for low-resolution measurements, but should not be considered as a replacement for laboratory-grade force plates.

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.

Total Uncertainty of Radiocarbon Measurements of Marine Dissolved Organic Carbon and Methodological Recommendations

We report results of duplicate measurements of dissolved organic carbon concentrations ([DOC] as μM) and Δ14C in seawater in order to assess the total uncertainty of reported [DOC] and Δ14C measurements via the UV oxidation method. In addition, pure International Atomic Energy Agency standards analyzed over a 4-yr period are evaluated. We find the total uncertainty of Δ14C measurements to be ±4.0. However, in samples that were thawed, subsampled, and refrozen prior to UV oxidation, the total uncertainty of Δ14C measurements is on the order of ±10. The [DOC] measurements of these samples were also higher by 1.8 ± 0.3 μM. The reason(s) for these documented increases in total [DOC] and Δ14C uncertainty are unclear. In order to minimize any effects on sample measurements, we recommend the following: 1) regular monitoring of duplicate samples, DOC standards, and diluent (Milli-Q™) water for Δ14C and [DOC] measurements; 2) thawing a sample immediately and only once prior to UV oxidation; 3) avoid the use of DOC-leachable plumbing (such as PVC pipe) in both water systems feeding and within Milli-Q systems; and 4) consider the use of DOC-free diluents (i.e. pre-UV oxidized Milli-Q or sample water).

Determination of stray light at the PTB goniophotometer facility

For improved luminous flux measurements, the Physikalisch-Technische Bundesanstalt (PTB) was equipped with a new robotic goniophotometer. In order to characterize this instrument, to reduce the combined measurement uncertainty, and to determine the respective uncertainty components, the influence of stray light on the measurement results was investigated. Considering the specific structure of the robotic goniophotometer, stray light was measured on-line by means of a purpose-built “back-looking” photometer. By this means, the influence of the luminous intensity distribution of each individual light source with regard to its stray light could be considered. Before the first experimental application, the invented procedure was tested by means of calculations using mathematical models. In this paper, the mathematical model for the calculation of stray light in the goniophotometer room is presented together with the calculation results and the results of the first measurements. The achieved results indicate that the recommended stray light measurements can decrease the total relative standard measurement uncertainty of luminous flux measurements down to 2 × 10−3.

Interlaboratory comparisons in EMF survey measurements

This article presents methods and results of interlaboratory comparison in the electromagnetic field (EMF) survey measurements performed by Electromagnetic Environment Protection Laboratory. Based on the results, the author analyzed factors affecting the precision of EMF measurements, in particular—difficult to estimate—the “human factor”. In practice, the human factor has never been taken into account in the EMF measurements accuracy estimations budget, and the author estimate the importance of this factor that may include even up to half of the total uncertainty of measurements. Taking into account all factors depredating the accuracy of measurements, the uncertainty of the survey EMF measurements was estimated at the level of 2–4 dB.

High temperature and high pressure volumetric properties of (methanol + [BMIM+][OcSO− 4]) mixtures

The (p, ρ, T) and some derived volumetric properties such as excess, partial and apparent molar volumes of [BMIM+][] in methanol at temperatures T = (298.15–398.15) K and pressures up to p = 40 MPa have been measured with a vibrating-tube densimeter. Measurements were made at seven concentrations of x = (0.0388, 0.1351, 0.2785, 0.4961, 0.7497, 0.9312 and 1.0) mole fraction of [BMIM+][]. The total uncertainty of density, temperature, pressure and concentration measurements were estimated to be less than 0.15 kg m−3, 15 mK, 5 kPa and 10−4 mole fraction, respectively. The uncertainties reported in this article are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The effect of temperature, pressure and concentration on the density and derived volumetric properties was studied. The measured densities were used to develop a Tait-type equation of state (EOS) for the mixture and the pure components. The derived values of apparent molar volumes were extrapolated to zero concentration using Pitzer's ion-interaction model to calculate the values of apparent molar volumes (or partial molar volumes) at infinite dilution. The method of correlation function integrals is used to study the structural and thermodynamic properties of dilute methanol + ILs mixtures. The structural properties, such as direct and total correlation function integrals and cluster size (coordination number), were calculated using the Krichevskii function concept and EOS for the mixture at infinite dilution.

High-pressure densities and derived volumetric properties (excess and partial molar volumes, vapor-pressures) of binary methanol + ethanol mixtures

The densities of five (0.08564, 0.19998, 0.41971, 0.68017, and 0.84236 mol fraction of methanol) binary methanol + ethanol mixtures have been measured with a vibrating-tube densimeter. Measurements were performed at temperatures from T = (298.15 to 423.15) K and at pressures up to 40 MPa. The total uncertainty of density, temperature, pressure, and concentration measurements were estimated to be less than 0.15 kg m −3, 15 mK, 5 kPa, and 10 −4, respectively. The uncertainties reported in this paper are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The effect of temperature, pressure, and concentration on the density and derived volumetric properties such as excess and partial molar volumes was studied. Using the analytical extrapolating technique the vapor-pressure and saturation liquid densities of the mixture were derived. The measured densities were used to develop polynomial type equation of state for the mixture. The structural properties such as direct and total correlation function integrals and clusters size (excess coordination number) were calculated using the Krichevskii function concept and equation of state for the mixture at infinite dilution.

Densities and Excess, Apparent, and Partial Molar Volumes of Binary Mixtures of BMIMBF4 + Ethanol as a Function of Temperature, Pressure, and Concentration

The densities of five BMIMBF4 (1-butyl-3-methylimidazolium tetrafluoroborate) + ethanol binary mixtures with compositions of (0.0701, 0.3147, 0.5384, 0.7452, and 0.9152) mole fraction BMIMBF4 and of pure BMIMBF4 have been measured with a vibrating-tube densimeter. Measurements were performed at temperatures from 298 K to 398 K and at pressures up to 40 MPa. The total uncertainty of density, temperature, pressure, and concentration measurements were estimated to be less than 0.1 kg · m−3, 15 mK, 5 kPa, and 10−4, respectively. The uncertainties reported in this article are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The measured densities were used to study derived volumetric properties such as excess, apparent, and partial molar volumes. It is shown that the values of excess molar volume for BMIMBF4 + ethanol mixtures are negative at all measured temperatures and pressures over the whole concentration range. The effect of water content on the measured values of density is discussed. The volumetric (excess, apparent, and partial molar volumes) and structural (direct and total correlation integrals, cluster size) properties of dilute BMIMBF4 + ethanol mixtures were studied in terms of the Krichevskii parameter. The measured densities were used to develop a Tait-type equation of state.

Experimental densities and derived thermodynamic properties of liquid propan-1-ol at temperatures from 298 to 423 K and at pressures up to 40 MPa

Densities of pure propan-1-ol have been measured in the liquid phase with a modified high pressure–high temperature Anton-Paar vibrating-tube densimeter (model DMA 5000). Measurements were made at six isotherms (298.15, 323.15, 348.15, 373.15, 398.15, and 423.15 K) as a function of pressure. The range of pressure was 0.1–40 MPa. The total uncertainty of density, temperature, and pressure measurements were estimated to be less than 0.15 kg m −3, 15 mK, and 5 kPa, respectively. The uncertainties reported in this paper are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. Values of saturated densities were determined by extrapolating experimental P– ρ data to the vapor pressure at fixed temperature. The measured values of density were used to calculate the derived properties such as isothermal compressibility ( K T ), thermal expansion coefficient ( α P ), isochoric ( C V ) and isobaric ( C P ) heat capacities, and sound velocity ( W). All measured and derived properties were compared in detail with the data reported in literature. Measured values of p, ρ, and T were used to develop Tait and polynomial type equations of state. The quality and predicting capability of the Tait type equation of state was examined by comparing with direct measured values of heat capacity at constant volume and constant pressure, speed of sound, isothermal compressibility, etc.

Framework for Estimating Uncertainty of ADCP Measurements from a Moving Boat by Standardized Uncertainty Analysis

In spite of the extensive use of acoustic-Doppler current profilers (ADCP) for measurement of velocity and discharge in open-channel and riverine environments, a rigorous methodology for estimating ADCP discharge measurement uncertainty that follows current engineering standards for uncertainty analysis is not yet available. In this paper, we apply the broadly accepted engineering standard for uncertainty analysis put forth by the American Institute of Aeronautics and Astronautics in 1995 (AIAA) to develop a framework for the estimation of uncertainty in ADCP measurements from a moving boat. First, we summarize the terminology and methodology of measurement uncertainty analysis and review the data reduction equations used by ADCPs to estimate the total discharge in measurements from a moving boat. Second, we discuss briefly the various elemental error sources that contribute to the uncertainties of the ADCP measured variables, which in turn contribute to the total uncertainty of ADCP discharge measurements. In discussing the elemental errors, we look into what determines their uncertainties and whether they can be evaluated using available information. We then apply the guidelines of the AIAA standard to develop an analytical framework for propagating the uncertainties from the elemental sources to obtain the total uncertainty of ADCP discharge measurements from a moving boat.

Measurements of the isochoric heat capacity, the critical point ( TC, ρC) and vapor–liquid coexistence curve ( TS, ρS) of high-purity toluene near the critical point

Isochoric heat capacities ( C V, V, T), phase boundary properties ( T S, ρ S) and the critical ( T C, ρ C) parameters for high-purity (0.9999+ mole fraction) toluene have been measured with a high temperature, high pressure, nearly constant volume adiabatic calorimeter and quasi-static thermogram technique. Measurements were made at three selected liquid and vapor isochores 777.8, 555.25, and 214.64 kg m −3 in the temperature range from 379 to 591 K. For five near-critical isochores 268.68, 281.68, 296.62, 301.52, and 318.28 kg m −3, the measurements were made in the immediate vicinity of the coexistence curve in order to accurately determine the phase transition temperatures ( T S, ρ S) (shape of the coexistence curve near the critical point) and the critical parameters ( T C, ρ C). The total combined uncertainty of heat capacity, density, and temperature measurements were estimated to be less than 2%, 0.06%, and 15 mK, respectively. The uncertainties reported in this paper are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The uncertainty of the phase transition and the critical temperature value was 0.02 K. The Krichevskii parameter for some toluene-containing binary mixtures was calculated. The derived values of the Krichevskii parameter were used to estimate the effect of dilute impurities on the critical parameters of toluene. The measured values of saturated density near the critical point were interpreted in terms of the “complete scaling” theory in order to study singularity behavior of the coexistence curve diameter. The measured isochoric heat capacities and saturated densities were compared with the data reported by other authors and values calculated from an equation of state and other correlations.