Measurement of pressure differences between various positions in a vacuum chamber where pressure is generated dynamically

The pressure differences between the positions for gauge connection in a chamber for gauge comparison were measured and evaluated in two ways: (a) by the mutual interchange of two ionization gauges at the positions; and (b) by readings of one ionization gauge at various positions and of a spinning rotor gauge at a fixed position. The pressure in the chamber was set up by simultaneous admission and pumping of the gas. Differences of the order of a few percent were observed, probably caused by imperfect adjustment of the gas-introducing jet. Those differences are specific to the given apparatus, they depend on its adjustment, the geometry and some other parameters. The two methods are suitable for checking and adjusting the apparatus.