Measurement of the pressure differences in a large chamber where the pressure is generated dynamically

Abstract

The need to know the pressure in relatively large vacuum chambers arises at different measurements (calibration of the vacuum gauges, out-gassing measurements, TDS, etc.). Although the uniformity of the gas pressure over some areas in the chamber is crucial for the accuracy of the measurement, it is checked mainly by means of theoretical computations. The experimental determination of the pressure differences between various gauge positions at a chamber of cylindrical shape is described in the paper. The pressure in the chamber was generated dynamically by adjustable gas flow introduced into the chamber, simultaneously pumped by a constant pumping speed. The measurements were performed in the pressure range 1×10 −3–1×10 −6 mbar by means of a spinning rotor gauge and two ionisation gauges; they were connected to various positions and during measurements, mutually changed in order to exclude the influence of the difference between them. The differences between positions at different levels along the axis (i.e. along the gas flow direction) as well as the differences between positions in the same level were followed. The method of data evaluation enabling to recognise the influence of the non-linearities of the gauge was developed. The differences in the order of some per cent between positions in the same level were observed.