A review of low pressure measurement from an industrial viewpoint

Recent advances in the measurement of total pressures and their equivalent both by direct and indirect methods over the whole vacuum range are reviewed from an industrial viewpoint. Mechanical manometers, together with suitable transducers, measure total gas pressure in a more fundamental way than other vacuum gauges and hence the development of micromanometers has been given some attention. The review includes brief discussions on viscosity gauges, especially of the resonance types, recent work on thermal conductivity gauges, the possible application of radiometer and Knudsen type gauges, and improvements in cold-cathode ionization gauges using radioactive materials. Cold-cathode ionization gauges operating in a magnetic field are used widely in industrial vacuum systems and have been subject to a number of investigations. The consolidation of the Bayard-Alpert type ionization gauges has led to many investigations into the physical and chemical interactions between gauges and the gases in vacuum systems leading to developments in gauge construction which are discussed. Finally, some consideration is given to developments of thermionic ionization gauges to extend their range to lower pressures.