TRACEABILITY TO INTERNATIONAL SYSTEM OF UNITS (SI) OF LIQUID AND GAS FLOW MEASUREMENTS – EMPHASIS TO SPECIFIC AND UNSOLVED PROBLEMS

DŽEMIĆ, ZIJAD (avtor), Drnovšek, Janko (mentor), Širok, Branko (komentor)

This doctoral dissertation addresses traceability to the International System of Units (SI) for flow measurements, with the emphasis on specific and unsolved problems. It is divided into parts, according to the affinity of the problem to provide complete and traceable measurement results and calibration certificates of gas flow meters, which reflect specific installation conditions. The features of the measurement traceability are that it has a well-known history of calibrations, up to the definition of the Measurement Units, that the measurement uncertainty in the next chain becomes larger, and that the measurement uncertainty cannot be decreased by calibration with reference to the higher level standard. The main idea is to obtain complete and accurate measurement results of flow meters operating in real conditions. Therefore, the results from the calibration laboratory must additionally contain corrections and uncertainty contributions due to the specific installation situation, if necessary. When uncertainty sources are well understood and controlled, they might even be considered as corrections, therefore decreasing the overall uncertainty of the flow measuring device. The extensive research was done to allow more reliable decisions on how to deal in particular situations with the measurement uncertainty as the subject of a flow meter’s calibration, as the quantitative parameter obtained in the calibration in the laboratory, and with the qualitative statement about the accuracy of the meter operating in the field. Critical consideration about the possibilities and capabilities of calibration installations and capabilities of meters, on the one hand, and metrological requirements, on the other, are explored. New contributions, conclusions and recommendations are provided. Regarding this, the identification and characterization of the traceability issues in real-life gas measurements, conducted in complex distribution systems in terms of “installation-specific” error sources, is one of the objectives of this research. It is necessary to continually explore the sources of measurement uncertainty, which will give a better insight into the number of factors affecting the measurement process, which leads to an increased and more realistic measurement-uncertainty value. The concept of the uncertainty of a measurement result, based on a theoretical definition, in some cases, is insufficient. Because of this, measurements in real conditions will not be able to achieve the measurement uncertainty defined by written standards and will be much higher in reality. It is imperative that the estimation for all contributions that influence the measurement results are made correctly. These contributions are sometimes neglected or misinterpreted, which leads to a wrong interpretation of the measurement results, especially in real measurement conditions, resulting eventually in the wrong decisions. The unnecessary overstatement of the measurement uncertainty can increase the costs of the overall system of measurement and the control of delivery and supply, as the level of reports about the faults increases. The unnecessary understatement of the measurement uncertainty might cause too much trust to be placed in the values reported, having sometimes devastating consequences. Therefore, the overestimation of the measurement uncertainty due to the lack of knowledge is equally problematic as an underestimation. If these concerns and certain flow measurements are analyzed, the number of unsolved traceability problems of flow measurements under real conditions will decrease. A number of international normative documents and standards define measuring procedures, routes for establishing measurement traceability, the analysis and evaluation of measurement uncertainty, and the on-site calibration of gas-flow meters. However, additional considerable research is still necessary in order to improve the relevance of these documents in real-life applications from the perspective of scientific, industrial and legal metrology aspects. In order to keep as many uncertainty sources under control, the experiments conducted as part of this dissertation were made in a high-performance laboratory that has a very high quality and complexity and thus quite expensive installations. It is important to keep in mind that other sources of uncertainty coming from poor installation and by using different meter types have to be considered for each individual case. The subject of the dissertation and research is how to make the correct judgment regarding the measurement results performed by gas-flow meters using different calibration methods, legal aspects, technologies, instruments, fluids, and flow conditions, with regards to dynamic range and response. Specific unsolved flow measurement problems regarding the traceability to SI, according to the identified origin, are organized here in three chapters.

• Jezik: Angleški jezik
• Ključne besede: measurement unit, measurement, calibration, verification, result of a measurement, traceability, uncertainty of measurement, metrology, measurement method, measurement procedure, measurement result, measurement accuracy, measurement trueness, measurement precision, measurement error
• Vrsta gradiva: Doktorsko delo/naloga
• Organizacija: FE - Fakulteta za elektrotehniko
• Leto izida: 2019
• PID: 20.500.12556/RUL-107825
• Datum objave v RUL: 28.05.2019

Sekundarni jezik

• Jezik: Slovenski jezik
• Naslov: SLEDLJIVOST DO MEDNARODNEGA SISTEMA ENOT (SI) PRI MERJENJIH PRETOKOV TEKOČIN IN PLINOV – POUDAREK NA KONKRETNIH IN NEREŠENIH PROBLEMIH

Izvleček

Doktorska disertacija obravnava raziskave meroslovne sledljivosti meritev pretoka plinov do mednarodnega sistema enot (SI), s poudarkom na nerešenih problemih v praksi. Razdeljena je v podpodročja glede na specifiko problemov pri realnih namestitvah merilnikov pretoka plina v merilni sistem, s ciljem zagotoviti popolnost in sledljivost merilnih rezultatov in kalibracijskih certifikatov. Značilnost merilne sledljivosti je, da ima dobro znano zgodovino kalibracij z nepretrgano verigo na višje hierarhične nivoje vse do definicije osnovnih enot merskega sistema SI. Pri posamezni kalibraciji merilna negotovost ne more biti manjša od merilne negotovosti referenčnega merila, torej se s prenosam na nižje nivoje merilna negotovost povečuje. Poglavitni cilj je zagotoviti popolne in točne merilne rezultate, ko merilniki pretoka plinov delujejo v realnih pogojih. Zaradi razlik med instalacijo merila pri kalibraciji ter pri nadaljni rabi, je običajno potrebno k rezultatom iz kalibracijskega certifikata dodati nadaljne korekcije in dodatne prispevke k merilni negotovosti. Kadar so viri negotovosti dobro poznani, razumljivi in nadzorovani, se lahko obravnavajo kot popravki, s čimer se zmanjša skupna merilna negotovost naprave za merjenje pretoka. Opravljene so bile obsežne raziskave, ki omogočajo zanesljivejšo odločitev o tem, kako v posameznih primerih obravnavati merilno negotovost, ki je bila določena kot kvantitativni parameter v času kalibracije merilnika pretoka v kalibracijskem laboratoriju, da jo je možno razširiti v ustrezno kvalitativno izjavo o merilni negotovosti, ko merilnik deluje v realnem okolju. Podana je kritična obravnava različnih možnostih kalibracijskih sistemov in njihovih zmogljivosti kot tudi zmogljivosti merilnikov na eni strani, ter meroslovnih zahtevah na drugi strani, nato pa so podani novi prispevki, sklepi in priporočila. V zvezi s tem je bil cilj raziskav opredelitev in ovrednotenje vprašanj sledljivosti v realnih pogojih pri meritvah pretoka plina, ki se izvajajo v kompleksnih distribucijskih sistemih, z vidika specifičnih dodatnih virov merilne negotovosti zaradi same instalacije merila. Kontinuirane raziskave vseh pomembnih virov merilne negotovosti so potrebne, da se omogoči boljši vpogled v številne dejavnike, ki vplivajo na merilni proces, kar vodi do povečane in bolj realistične ocene merilne negotovosti. Koncept negotovosti merilnega rezultata, ki temelji samo na teoretični obravnavi, v nekaterih primerih ni zadosten. Zaradi tega meritve v realnih razmerah ne morejo doseči merilne negotovosti, ki so opredeljene s pisnimi standardi, in so v resnici veliko višje. Nujno je, da se ocena vseh prispevkov, ki vplivajo na rezultate meritev, pravilno izvede. Ti prispevki so včasih zanemarjeni ali napačno interpretirani, kar vodi do napačne interpretacije rezultatov meritev, zlasti v realnih merilnih pogojih. To posledično vodi do napačnih odločitev. Nepotrebna precenitev merilne negotovosti lahko znatno poveča stroške nakupa celotnega merilnega sistema in kontrole ob dobavi, saj se možnost za identifikacijo neustreznosti povečuje. Na drugi strani lahko podcenjevanje merilne negotovosti povzroči neupravičeno zaupanje v dobljene rezultate, kar ima v izjemnih primerih lahko tudi uničujoče posledice. Zato je precenjevanje merilne negotovosti zaradi pomanjkanja znanja prav tako problematično kot podcenjevanje merilne negotovosti. Z ustrezno analizo zahtev po merilni negotovosti ter samega merilnega procesa je možno zmanjšati število nerešenih problemov glede sledljivosti merilnih rezultatov pretoka plina v realnih razmerah. Številni mednarodni normativni dokumenti in standardi že določajo merilne postopke in podajajo vodila za določanje sledljivosti meritev, analizo in vrednotenje merilne negotovosti ter kalibracijo meril pretoka plinov na mestu uporabe. Klub temu so še vedno možne znatne izboljšave teh vodil, za to pa so potrebne obširne dodatne raziskave delovanja meril v realnih aplikacijah, tako z vidika znanstvenega in industrijskega meroslovja, kot tudi zakonskih meroslovnih vidikov. Da bi prepoznali in obvladali čim več virov negotovosti, so bili eksperimenti v okviru te disertacije izvedeni v visoko zmogljivem laboratoriju. To pomeni zelo visoko kakovost merilnih rezultatov ter kompleksnost izvedbe in s tem precej drage inštalacije. Pomembno je vedeti, da je treba pri vsakem posameznem primeru upoštevati dodatne vire negotovosti, ki izhajajo iz slabe namestitve in uporabe različnih tipov merilnikov. Predmet disertacije in raziskav je, kako pravilno ovrednotiti merilne rezultate, izvedene z merilniki pretoka plina, glede na kalibracije z različnimi metodami, zakonske zahteve, tehnologijo, instrumente, vrste plina in pogoje pretoka, kot tudi z vidika dinamičnega obsega in odziva. Specifični nerešeni problemi merjenja pretoka v zvezi s sledljivostjo do SI sistema so, glede na ugotovljeno poreklo, predstavljeni v treh poglavjih.

• Ključne besede: merska enota, meritev, kalibracija, validacija, merilni rezultat, sledljivost, merilna negotovost, meroslovje, merilna metoda, merilni postopek, merilni rezultat, točnost merjenja, merilna točnost, pravilnost merjenja, natančnost merjenja, merilna napaka