This paper presents a practical procedure for the determination and precision calibration of the volume ratio and absolute value of the volume of vacuum chamber by using static expansion method. Such systems for calculations of volume ratio consist from two vessels connected via a valve called the expansion valve. For determination of absolute value of the volume we added another volume with simple shape (determined by dimensional measurements). In such systems, under the isothermal conditions, the gas pressure is reduced by the ratio of the small volume to the sum of the first volume (small volume) and second volume. The uncertainty of measurement of the volume ratio and absolute volume is calculated as well. Relative volume calibration is performed with uncertainties below 0.75 %.
This paper presents a gas-sorption method, based on an in situ calibrated throughput, for characterizing nonevaporable getters (NEGs) of Ti- and Zr-based alloys. The main characteristics of the method are the adjustment of a constant injected gas flow, the prompt calibration of a throughput, and the measurement of an increasing sorption pressure. It is essential that inert vacuum gauges be selected for measurements of total pressure to prevent contamination of a test gas and poisoning of an NEG under test. A capacitance diaphragm gauge is used for preparation of the injected gas flow by filling the gas reservoir with a test gas and adjusting the conductance of a variable leak valve. A spinning rotor gauge (SRG) is used for in situ calibration of the throughput by means of an integrated gas-flow calibration facility and the rate-of-pressure-rise method, and by continuous measurement of the sorption pressure in a test chamber. A getter pumping speed and a sorbed quantity are calculated while considering the throughput, the sorption pressure, and the sorption time. The throughput must be selected in accordance with both the sorption characteristics of a particular NEG type and the measurement capabilities of the SRG. At room temperature, porous thick-film NEGs and structured thin-film NEGs exhibit an initial getter pumping speed on the order of 1 and 0.1 l s−1 cm−2, respectively. The corresponding sorption capacity of a few times 10−4 mbar l cm−2 is comparable for all chemically active gases except for H2, which amounts to a few times 100 × 10−3 mbar l cm−2 in the case of porous NEGs and ∼1 × 10−3 mbar l cm−2 in the case of structured NEGs. Detailed analysis of uncertainties of SRG pressure measurements below 1 × 10−3 mbar gives an expanded uncertainty of the getter pumping speed and the sorbed quantity of 1.9% and 3.5%, respectively. While temporally interrupting the throughput, the setup enables discrete measurements of the background pressure, which increases because of the accumulation of nongetterable gases. After completion of the gas-sorption test, a qualitative determination of the accumulated inert gas composition is performed by the gas-burst method using a quadrupole mass spectrometer (QMS) mounted on a vacuum system. The quantitative analysis is enabled by the use of a QMS calibrated in situ by known amounts of a certain gas such as H2, CH4, CO, Ar and Kr.
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