Electronic flow meter for determining low gas pressures

A special electronic flow meter is described which was designed to measure small particle number densities (about 10 to the 13th particles/cu cm) of a scattering target. The principle of operation is based on measuring the flow time of a precisely measurable portion of gas under conditions of steady free-molecular flow in a collision chamber. The relative error of measurement of gas flow rates in the range 0.01 to 0.0001 milliliters/sec at atmospheric pressure and corresponding pressures of the scattering target (1 to 0.0001 millitorr) does not exceed 1%.