| 摘要 |
<p>A counterflow helium mass spectrometer leak detector in which a helium sample passes in a reverse direction through a diffusion pump (26) to a mass spectrometer (36) for measurement. The diffusion pump (26) includes a conventional foreline (24) and a second foreline (32) provided with an ejector stage (79). A test sample (8) is coupled from a test port (10) through a bypass valve (22) to the conventional foreline (24) in a high sensitivity mode and is coupled to the second foreline (32) in a low sensitivity mode. In the low sensitivity mode, the bypass valve (22) is closed. An apertured control plate (84) in the diffusion pump (26) controls the relative reverse rates of diffusion from each foreline (24, 32) to the diffusion pump inlet (38) by controlling the rates of vapor flow to annular pumping stages (75, 77) and to the ejector stage (79). The ejector stage (79) includes a nozzle (80) for directing a stream of vapor into the second foreline (32) so as to inhibit flow of helium into the diffusion pump (26) and establish a lower reverse diffusion rate at the second foreline (32). The disclosed configuration permits measurement of a large range of leak rates.</p> |
