The new UME primary standard for pressure generation in the range from 9 × 10 ⁴ Pa to 10³ Pa

Abstract

A new primary standard for generation of vacuum pressures between 9 × 10 −4 Pa and 10 3 Pa has been completed at the Ulusal Metroloji Enstitüsü (UME). It is based on the static expansion method, whereby the range is extended to lower pressures by multiple expansions. The apparatus consists of six vessels that provide a pressure reduction by a factor of about 10 −6 in the main calibration vessel after a three-step expansion. Seventeen platinum resistance thermometers are mounted on the vessels to determine the correction due to temperature effects. The whole apparatus is built using the UHV technique and can be baked up to 400 ˚C. The expanded (k = 2) relative uncertainties of pressures, generated by this new standard, range from 2.1 × 10 −3 at 9 × 10 −4 Pa to 9.5 × 10 −4 at 10 3 Pa.

Analysis of the mathematical modelling of a static expansion system

“…Regarding the modelling of the process, some institutions have chosen to use the ideal gas model [13], [24], [25], while others have proposed the use of the virial equation as a real gas model for the expansion process [5], [7], [8], [23]. One aspect that is quite generalised is the assumption that the initial pressure in the calibration tank is zero, although the question remains whether this assumption is valid as the final pressure is smaller (that is, as the vacuum increases).…”

“…One aspect that is quite generalised is the assumption that the initial pressure in the calibration tank is zero, although the question remains whether this assumption is valid as the final pressure is smaller (that is, as the vacuum increases). Equation (1) presents the calculation of the pressure after a static expansion process, modelling the substance as an ideal gas and neglecting the initial pressure in the large tank [10], [13], [24], [25].…”

The KRISS Primary Vacuum Gauge Calibration Standards: A Review

“…In the medium pressure range 0.1 Pa to 1000 Pa, mercury manometers are not suitable and the characteristics of continuous expansion systems become poorly deˆned, as they depend on pressure, so primary standards are based on static expansion of a gas 25) . That is why, the static expansion systems (also called volume or series expansions systems) are used as primary standards for the calibration of vacuum gauges 26,27) .…”

“…Static expansion systems have been used routinely for more than 35 years as a primary deˆnition of low pressure 29) . This is the most suitable method above 10 -1 Pa 30) , however, newly developed systems (UME of Turkey) have extended this limit from 9×10 -4 Pa to 10 3 Pa 26) . In such systems, known pressures are generated by expanding a known gas amount enclosed in a small volume V 1 into a much larger evacuated volume V 2 by opening a valve in between the two volumes.…”

Improvement of INRiM static expansion system as vacuum primary standard between 10-4 Pa and 1000 Pa.

“…Vacuum packaging of food, semiconductor devices fabrication, metallurgical and chemical processes, optical and electrical thin-film coating are only few examples of such applications. In this range, the pressure is measured by standards such as capacitance diaphragm gauges (CDGs) and spinning rotor gauges (SRGs), which must be calibrated using primary standards, including static expansion systems, where the standard pressure is obtained through a static expansion of a pure gas, applying the law of the perfect gases [1][2][3][4][5]. The INRiM static expansion system has been developed in the past [6,7], but it has been recently modified in order to improve its performance and extend the working range down to 5•10 -4 Pa.…”