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Generating of very low (and well-known) gas flows meets a wide variety of needs in industry and research (especially in vacuum science and technology), but also among consumers and society (e.g: calibrations of vacuum gauges and leak detectors, leak testing to verify the tightness of many industrial products, assurance of product reliability and performance, environmental and other safety issues, and so on). So far, many methods and devices have been developed for generating very- and ultra-low flows, generally with the goal of setting flow standards for metrology. However, most of them are very complex, so that in case of certain particular research applications, new or adapted methods and devices appear to be more suitable. Such particular case is the calibration of the measurements of hydrogen isotopes permeation fluxes, when very low flows of hydrogen and/or deuterium are injected directly into the permeation cell which is operated in very different modes. This paper presents the concept of a new method proposed to accomplish this purpose, its corresponding mathematical model of flow, as well as the experiments performed to test the feasibility of the method. Briefly, the concept is based on two leaks of constant conductance through which a so-called reference flow is generated, with two stages of pressure reduction, as well as on a variable leak valve through which well-controlled flows (and over a wide range) are generated to be injected into the permeation cell.

A NEW METHOD TO GENERATE VERY LOW GAS FLOWS FOR CALIBRATION OF HYDROGEN PERMEATION MEASUREMENT. PART 1: CONCEPT AND FEASIBILITY TESTING