Transfer leak studies and comparisons of primary leak standards at the National Bureau of Standards and Sandia National Laboratories

Primary leak standards are being developed at the National Bureau of Standards (NBS), and a cooperative NBS--Sandia National Laboratories (SNL) program is underway to compare their different primary standards and investigate the properties of transfer leaks. Initial results of comparisons of the primary standards at the two laboratories, accomplished via sintered metal transfer leaks in the range 5 x 10-12 to 5 x 10-9 mol/s, show that the calibration methods used in the two laboratories agree to within a few percent for nitrogen, argon, and helium. Significant instabilities with time have been observed for one of the two leaks used in the comparison. Temperature coefficient data for helium diffusion leaks are presented which illustrate the possibility of significant errors when a linear temperature dependence is assumed over too wide a temperature range