| Abstract | Pouzdanost i sljedivost mjerenja niskih i kriogenih temperatura uvjet je o kojem ovise mnoge
grane industrije i znanosti, no zbog specifičnosti mjerenja niskih temperatura, mjeriteljska
infrastruktura najviše razine u tom području u Republici Hrvatskoj još nije razvijena. U sklopu
ovog doktorskog istraživanja razvijen je etalonski sustav za primarnu realizaciju temperaturne
ljestvice ITS-90 u području od trojne točke argona (- 189,3442 °C) do trojne točke vode
(0,01 °C), čime je napravljen značajan iskorak u smjeru proširenja i ojačanja mjeriteljskih
kapaciteta najviše razine. U radu je detaljno opisana važeća Međunarodna temperaturna
ljestvica ITS-90, s pregledom postojećih sustava i praktičnih smjernica za njenu realizaciju te
je zaključno opisan neizostavan postupak procjene mjerne nesigurnosti. Eksperimentalni dio
istraživanja proveden je u Laboratoriju za procesna mjerenja na Fakultetu strojarstva i
brodogradnje Sveučilišta u Zagrebu (FSB-LPM), krovnoj instituciji u području mjeriteljstva
temperature, vlažnosti i tlaka. Fokus eksperimentalnog dijela rada bio je na razvoju sustava za
realizaciju trojne točke argona s novim automatskim regulatorom tlaka dušika u kriostatu. U
radu je prikazan razvoj novog automatskog regulatora tlaka s pripadnim softverom za
upravljanje i prikupljanje mjernih podataka. Uz to, razvijen je i novi sustav za punjenje uložnog
otvora za termometar unutar fiksne točke argona helijem te novi sustav za praćenje temperature
i razine tekućeg dušika u kriostatu. Rad prikazuje rezultate probnih realizacija trojne točke
argona s novim regulatorom, temeljem kojih je provedena optimizacija i usklađivanje svih
komponenti etalonskog sustava. Definirana je eksperimentalna metoda za realizaciju trojne
točke argona kojom se postiže dulji plato s manjim nagibom u usporedbi sa sustavom s ručnom
regulacijom tlaka, a što je posljedica preciznije i stabilnije regulacije tlaka. U sklopu
istraživanja opisan je i matematički model realizacije temperaturne ljestvice te je procijenjena
ukupna mjerna nesigurnost realizacije. Bilateralnom usporedbom s Laboratorijem za
metrologiju in kakovost na Fakultetu za elektrotehniku Sveučilišta u Ljubljani (MIRS/ULFE/
LMK) u području od trojne točke argona (-189,3442 °C) do trojne točke vode (0,01 °C),
potvrđena je funkcionalnost i mjerne sposobnosti etalonskog mjernog sustava razvijenog u
sklopu ovog doktorskog istraživanja. |
| Abstract (english) | Reliability and traceability of low and cryogenic temperature measurements are crucial factors
for many branches of industry and science, which are in need for support through a significant
strengthening of the metrology infrastructure for calibration of thermometers at temperatures
below -40 °C. Due to the specifics and complexity of low-temperature measurements, the
highest metrology infrastructure in this part of the temperature range has not been developed
so far in the Republic of Croatia. As part of this doctoral research, a standard measurement
system for the primary realization of the ITS-90 temperature scale in the range from the triple
point of argon (-189.3442 °C) to the triple point of water (0.01 °C) was developed, which is a
significant step forward in the direction of expanding and strengthening of metrology capacities
at the highest level.
The doctoral dissertation is structured as follows.
In the theoretical part of the research, the historical development of the temperature scales is
described together with the recent redefinition of the kelvin and its impact on the temperature
metrology. Although the temperature is currently defined through the fundamental Boltzmann
constant, the ITS-90 temperature scale still remains the best approximation of the
thermodynamic temperature. Therefore, the theoretical part focuses on the International
Temperature Scale from 1990, providing a detailed description of practical guidelines for its
implementation. The theory of measurement uncertainty analysis, essential to all
measurements, is also presented.
The experimental part of the research was carried out in the Laboratory for Process
Measurements at the Faculty of Mechanical Engineering and Naval Architecture, University
of Zagreb (FSB-LPM), which acts as a Croatian national calibration laboratory for temperature,
humidity, and pressure. The focus of the experimental part of the work was on the development
of a system for realizing the argon triple point with a new automatic pressure control system
for a liquid nitrogen cryostat. The work presents the development of a new automatic pressure
controller with associated software for control and acquisition of measurement data. In
addition, a new system for filling the thermometer well, inside the argon fixed point, with
helium was developed, as well as a new system for monitoring the temperature and level of
liquid nitrogen in the cryostat.
Following this, the research focuses on an extensive mathematical model for realization of the
ITS-90 temperature scale. The measurement uncertainty analysis of the realisation has been
conducted. All of the influencing parameters have been investigated, and the uncertainty
contributions have been estimated. The expanded measurement uncertainty of the realization
has been calculated. The coefficients of the deviation function for the temperature probe used
for interpolation between the fixed points in the range from - 189,3442 °C to 0,01 °C have been
determined, together with the associated uncertainty of interpolation.
Lastly, the final chapter presents the results of this doctoral thesis and follows with a discussion
and conclusion. Through a trial realization of the triple point of argon with the manual pressure
regulator, the needed improvements were identified. The presented results of trial realizations
of the argon triple point with a new controller, served as a basis for optimization and
coordination of all components of the measurement system. An extensive investigation of the
characteristics of the new controller has been performed and the characteristics of the manual
and automatic pressure regulation were compared. An experimental method for realizing the
argon triple point was defined, utilizing automatic pressure regulation of higher precision and
stability, which ensures a longer temperature plateau with a smaller slope compared to a system
with manual pressure regulation. A bilateral comparison with the Laboratory for Metrology
and Quality at the Faculty of Electrical Engineering, University of Ljubljana
(MIRS/UL- FE/LMK) in the temperature range from the triple point of argon (-189.3442 °C)
to the triple point of water (0.01 °C) confirmed the functionality and measurement capabilities
of the primary calibration system developed in the scope of this doctoral research.
To conclude, the scientific contributions achieved through this research are as follows:
A new pressure control system was developed for automatic adjustment of the nitrogen
pressure in the argon triple point cryostat. This system is more flexible, stable, and accurate
than the manual regulator, which makes it possible to achieve an argon triple point plateau with
a longer duration and smaller slope.
An experimental procedure was developed for the realization of the triple point of argon with
automatic control of the nitrogen pressure in the cryostat, which made it possible to realize up
to three triple point plateaus of satisfactory duration and slope, with only one filling of the
cryostat with liquid nitrogen.
The new measurement system was developed for independent primary temperature realization
from the temperature of triple point of argon (-189.3442 °C) to the temperature of triple point
of water (0.01 °C) with measurement uncertainties of the realization of 1.85 mK in the triple
point of argon and 1.54 mK at the triple point of mercury, expressed at the 95% confidence
level (k=2). The stated realization uncertainties were confirmed through successful
participation in a bilateral comparison with an equivalent standard system whose measurement
capabilities in the subject area are internationally recognized.
Through the scientific contributions made, it is evident that by using the results of experimental
measurements, along with the characterization and optimization of individual components, a
unique measurement system has been developed for the primary realization of the ITS-90
temperature scale in the temperature range from the triple point of argon to the triple point of
water, with realization uncertainties of less than 5 mK (k=2). This confirms the hypothesis of
the doctoral research. |
