Mõõtemääramatuse allikad ja analüüsimeetodid SI õhuniiskuse ühikute realiseerimisel Eestis

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Õhuniiskus on oluline füüsikaline suurus, mis mõjutab kliimat, inimeste soojusmugavust ja materjalide omadusi. Õhuniiskuse sisaldust peab mõõtma ja kontrollima näiteks muuseumides, raamatukogudes, pooljuhtmaterjalide tootmisel ja mujal. Õhuniiskuse mõõturite näite on vaja perioodiliselt võrrelda etaloni näitudega, et saada teada kui hea on näitude kooskõla nn „tõeliste“ väärtustega. Kuna iga mõõtmisega kaasneb mõõtemääramatus, siis pole tõelised väärtused rangelt võttes määratavad. Seetõttu kasutatakse tõeliste väärtuste hinnangutena nn tugiväärtusi, mis realiseeritakse tugietalonide abil. Käesolevas doktoritöös on edasi arendatud Eesti õhuniiskuse tugietaloni. Tugietaloni näitude mõõtemääramatust on hinnatud kolmel erineval meetodil, mille tulemused langevad hästi kokku. Õhuniiskuse tugietaloni kohapeal kontrollimiseks on konstrueeritud lihtsustatud niiskus-generaator, mis tekitab soovitud niiskusega õhku kitsas õhuniiskuse väärtuste vahemikus. Doktoritöös leiti, et erinevate ioonide loomulikul viisil sattumine niiskus-generaatorisse põhjustab niiskuse tekitamise vea, mida võib lugeda tühiseks. Samuti leiti nii mõõtmise teel kui ka arvutuslikult, et mõõdukas ülerõhk niiskusgeneratorist väljuvas torus, milles voolab väga kuiv õhk, praktiliselt peatab niiskuse sattumise torusse läbi selle seinas olevate väikeste avade. Niiskuse sattumine torusse läbi pisut vabastatud toruliitmike leiti olevat võimalik ka siis, kui torus oli mõõdukas ülerõhk. Käesoleva doktoritöö tulemused on arvesse võetud Eesti õhuniiskuse tugietaloni usaldusväärsuse tõstmisel ja võimaldavad tulevikus etaloni edasi arendada.Air humidity is a physical quantity that affects climate, human thermal comfort and properties of materials. Air humidity should be measured and controlled in museums, libraries, for manufacturing semiconductor materials, etc. It is necessary to periodically compare the readings of air humidity measuring devices to the readings of standard (etalon) in order to get to know how well the readings agree with the so-called “true” values of air humidity. No physical measurement is entirely accurate. Each measurement is accompanied by some uncertainty. Therefore true values are experimentally inaccessible and reference values of measurement standards are used instead. This dissertation is dedicated to developing Estonian air humidity reference measurement standard further. The measurement uncertainty of the reference values of the reference standard has been assessed using three different methods. The results agree well to each other. In order to check the readings of the reference standard on site, a simplified humidity generator has been constructed. It generates air with wished humidity in a narrow range of air humidity values. It was found that the natural presence of different ions in the humidity generator causes humidity generation error that can be considered insignificant. It was also found experimentally and theoretically that moderate overpressure in the tubing of a humidity generator practically stops escaping of humid air into the tubing through small holes inside the wall of the tubing even if very dry air is flowing in it. However, the escaping of humid air into the tubing through slightly loosened connectors is possible if there is moderate overpressure in the tubing. The results of the current dissertation have been taken into account for enhancing the reliability of Estonian air humidity reference standard and enable to develop the standard further in future

Quantitative GC–MS Analysis of Artificially Aged Paints with Variable Pigment and Linseed Oil Ratios

In this study, quantitative gas chromatography–mass spectrometry (GC–MS) analysis was used to evaluate the influence of pigment concentration on the drying of oil paints. Seven sets of artificially aged self-made paints with different pigments (yellow ochre, red ochre, natural cinnabar, zinc white, Prussian blue, chrome oxide green, hematite + kaolinite) and linseed oil mixtures were analysed. In the pigment + linseed oil mixtures, linseed oil concentration varied in the range of 10 to 95 g/100 g. The results demonstrate that the commonly used palmitic acid to stearic acid ratio (P/S) to distinguish between drying oils varied in a vast range (from especially low 0.6 to a common 1.6) even though the paints contained the same linseed oil. Therefore, the P/S ratio is an unreliable parameter, and other criteria should be included for confirmation. The pigment concentration had a substantial effect on the values used to characterise the degree of drying (azelaic acid to palmitic acid ratio (A/P) and the relative content of dicarboxylic acids (∑D)). The absolute quantification showed that almost all oil paint mock-ups were influenced by pigment concentration. Therefore, pigment concentration needs to be considered as another factor when characterising oil-based paint samples based on the lipid profile

Performance evaluation of Monte Carlo simulation: Case study of Monte Carlo approximation vs. analytical solution for a chi-squared distribution

The guide to the expression of uncertainty in measurement (GUM) describes the law of propagation of uncertainty for linear models based on the first-order Taylor series approximation of Y = f(X1, X2, …, XN). However, for non-linear models this framework leads to unreliable results while estimating the combined standard uncertainty of the model output [u(y)]. In such instances, it is possible to implement the method(s) described in Supplement 1 to GUM – Propagation of distributions using a Monte Carlo Method. As such, a numerical solution is essential to overcome the complexity of the analytical approach to derive the probability density functions of the output. In this paper, Monte Carlo simulations are performed with the aim of providing an insight into the analytical transformation of the probability density function (PDF) for Y = X2 where X is normally distributed and a detailed comparison of analytical and Monte Carlo approach results are provided. This paper displays how the used approach enables to find PDF of Y = X2 without the use of special functions. In addition, the singularity of the PDF and the nonsymmetric coverage interval are also discussed

Comparison of Air Temperature Calibrations

European national metrology institutes use calibration systems of various types for calibrating thermometers in air. These were compared to each other for the first time in a project organized by the European Association of National Metrology Institutes (EURAMET). This EURAMET P1061 comparison project had two main objectives: (1) to study the equivalence of calibrations performed by different laboratories and (2) to investigate correlations between calibration methods and achievable uncertainties. The comparison was realized using a pair of 100 platinum resistance thermometer probes connected to a digital thermometer bridge as the transfer standard. The probes had different dimensions and surface properties. The measurements covered the temperature range between −40 ◦C and +150 ◦C, but each laboratory chose a subrange most relevant to its scope and performed measurements at five nominal temperature points covering the subrange. To enable comparison between the laboratories, comparison reference functions were determined using weighted least-squares fitting. Various effects related to variations in heat transfer conditions were demonstrated but clear correlations to specific characteristics of calibration systemwere not identified. Calibrations in air and liquid agreed typically within±0.05 ◦C at +10 ◦C and +80 ◦C. Expanded uncertainties determined by the participants ranged from 0.02 ◦C to 0.4 ◦C and they were shown to be realistic in most cases