| AVS 55th International Symposium & Exhibition | |
| Vacuum Technology | Monday Sessions |
| Session VT-MoA |
| Session: | Vacuum Cleanliness, Outgassing, Contamination, and Gas Dynamics |
| Presenter: | J.A. Fedchak, National Institute of Standards and Technology |
| Authors: | J.A. Fedchak, National Institute of Standards and Technology R.F. Berg, National Institute of Standards and Technology D.R. Defibaugh, National Institute of Standards and Technology |
| Correspondent: | Click to Email |
The Pressure and Vacuum Group at NIST utilizes two constant pressure flowmeters as primary standards to calibrate helium leak artifacts, spinning rotor gauges, and ion gauges, using an orifice flow technique. A molar flow rate is produced by allowing gas to leak out of a small volume through a leak valve. By driving a piston into the volume such that the pressure within the volume remains constant, the gas flow rate through the leak valve is determined from the pressure measurement times the volume displacement of the piston per unit time (L/s). In the absence of other sources or sinks of gas, the conductance of the leak is identical to the volume rate of change of the piston. Therefore, the NIST flowmeters can be directly used to measure the conductance of leaks in the range of 10-6 to 10-5 L/s. Similar measurements have been done by other labs with primary flow standards (see Jousten et al.,1 for example), but with limited success due to the inability to accurately model the conductance of leaks with complicated geometries. We directly use the flowmeter to measure the conductance of small leaks with simple geometries, such as thin orifices (OD~10 µm) and capillaries. Small leaks with a known, precisely measured conductance may be used as check standards and in a variety of other applications. The conductance measurements and the applications will be presented.
1 K. Jousten, H. Menzer, and R. Niepraschk, Metrologia, 39, 519 (2002).