A Small Gas Inlet System for Orbital Mass-Spectrometer Calibrations

摘要

A gas inlet system is described for generating precise gas pressures that are to be used as calibration references for the mass spectrometers aboard the dual air density (DAD) Explorer satellites. This gas inlet system was developed as an in-flight calibration technique in which a known amount of onboard gas is released in the satellite cavity and is detected by the mass spectrometer. Although several flight mass-spectrometer experiments have been proposed, none make use of the in-flight calibration technique described in this report. Laboratory measurements and calibration of the metering leak technique for the gas inlet systems are discussed. The systems tested have metering leak rates between 2 and 4 μl/sec at 298 K for argon-40, and they produce molecular flow up to 100 torr, which is the highest test pressure in this experiment. One set of equations is presented that can be used to predict the satellite calibration pressures as a function of time during the metered gas flow. Another set of equations is also presented to predict the satellite pressure during the time the metered gas flow is terminated. These equations are useful for designing similar systems for future applications and for extending data comparisons beyond the limits tested in this program. Test data show that metering leak rates are reproducible within 1 percent of established means for helium-3, helium-4, and argon—40.