Use of a calibrated leak to calibrate vacuum gauges

A calibrated leak method is reported for calibrating a spinning rotor gauge (SRG) ora capacitance diaphragm gauge (CDG) of 133 Pa full scale range. The leak element and the gauge under test are connected to a vacuum chamber and the rise of pressure with time is monitored for a known volume. From the known leak rate and vessel volume, the gas pressure after a given time is calculated, and this is compared with the indicated pressure to find the correction factor. For the SRG, extrapolation over the pressure range of 10(-2)-1 Pa allowed calculation of the gauge coefficient. The calibrations obtained were also compared with those from a static expansion method, giving an agreement of +/-1.0%. The results of the study of the behaviour of a commercial SRG over the pressure range of 1-140 Pa with three gases Ar, He and N-2, using the method are discussed together with the limitations. (C) 1997 Elsevier Science Ltd. All rights reserved.