^4fExperience of the Czech metrology institute with utilization of non-rotating piston manometers in primary metrology of low pressures

摘要

^7fThe primary metrology of pressure based on the use of the classical piston manometers with rotating piston becomes inaccurate, when approaching to low pressures, both absolute and gauge. The solution can be found in the use of the non-rotating piston. But now the low flow of lubricating gas through the piston-cylinder gap must serve for the centering of the piston in the cylinder instead of its rotation. Additionally this design requires utilization of an electronic dynamometer instead of the loaded weights for compensation of the pressure force acting on the piston. Today commercially available systems based on this principle can be divided into those employing a laminar flow in a straight gap and those employing a transient flow in a conical gap. Czech Metrology Institute uses the first system in the gauge pressure measuring arrangement and the second one for both absolute and gauge pressure measurement. But for the field of primary metrology some adaptations were made. In the first case the internal measurement of the piston-cylinder temperature was added, the more suitable method of centering the piston in the cylinder was developed and stabilization of the generated pressure was increased due to the use of the mass flow controllers in the pressure supply and vent. The evaluation of the effective area was made not only by direct comparisons, but also by the measurement of the geometry of the piston. In the second case a turbo-molecular pump was added, the measurement of the reference vacuum was improved. In the middle of this paper the uncertainty evaluation of both instruments and their international comparisons will be listed and finally they will be compared with the classical technologies.