Development of a novel humidity standard: measurement and validation of a thermodynamic trace water generator.

The analysis of water vapor impurity is important in a number of cutting-edge technology, fields such as the semiconductor manufacturing process, display industry, and gas industry. The sensing of trace-moisture in gases, with an amount-of substance fraction less than 1 μmol.mol-1, has become increasingly important in the recent decade, because it has been recognized that even such a small amount of water vapor plays a critical role in the yield and product quality. International Vocabulary of Metrology (VIM) defined Metrological Traceability that is a property of a measurement result whereby the result can be related to a reference through a documented unbroken chain. When reporting the result of a measurement of a physical quantity, it is obligatory that some quantitative indication of the quality of the result be given to comparing the result, either among themselves or with reference values. It is therefore necessary that there be a readily implemented, easily understood, and generally accepted procedure for characterizing the quality of a result of a measurement, that is, for evaluating and expressing its uncertainty. There are many analytical methods for the determination of trace water vapor which all require regular, traceable calibration. Humidity can be fully described with a single parameter if the gas pressure and temperature are known. So, many national humidity laboratories have chosen the dew-point temperature as the primary humidity parameter As the realization of a dew-point temperature scale, a dew-point generator provides a simple source of traceability in a wide range at a good uncertainty level. INRIM03 is a novel humidity standard, an ultra-low frost-point generator which developed to extend the Italian humidity calibration measurement capabilities down to few parts per billion of water. The system object of this thesis can generate a humid gas flow with an amount of water down to tens of parts per billion. This generator is among the few ones in the world able to work at frost point temperatures down to -95 °C and at sub-atmospheric pressures (200 hPa) independent of the gas flow rate, the inlet gas flow rate ∅ which is varying from 1.5 l 〖min〗^(-1) to 7 l 〖min〗^(-1). The result of the thesis will be published as uncertainty budget for frost point temperature T_fp and water vapor mole fraction, x_w, generated by the generator The design was tested in order to guarantee the stability of temperature and pressure. By varying flow rate and inlet dry gas, the generator efficiency is examined. Also, after changing step-by-step the pressure and temperature the performance of the system is monitored. The uncertainty analysis for all the temperature and pressure was done. The final combined for the uncertainty severe condition (Tfp = -95℃ at atmospheric pressure ) is u_c (T_fp) = 0.314℃ and u_c (x_w) = 2.11 ×〖10〗^(-9) .