Experiments on the Effect of Torque Used in Mounting the Cylinder on the Effective Area of a Pressure Balance

Abstract

Variations in the effective area of a pressure balance due to the cylinder mounting were listed as one of the influence quantities in the EUROMET Project 220 on pressure balance uncertainties. As there were very few data on this subject, some experiments on two Desgranges & Huot (DH) type 5200 pressure balances were carried out in the Centre for Metrology and Accreditation in Finland. The nominal areas of the two DH piston-cylinder assemblies used in the tests were 98 mm2. One of them was taken as the standard and the other as the subject under test. The mounting torque of the standard was kept constant and that on the test assembly was varied from 0 Nm to 8 Nm. The effective area of the test assembly, determined by an ordinary cross-floating method, shows a small increase with increasing torque, the maximum increase in the area being approximately 2 parts per million at the torque value of 8 Nm. The result is, of course, valid for this particular case only, but it obviously shows the order of magnitude for the torque effect. The cylinder mounting, according to the instructions given in the DH type 5200 balance manual, typically results in a torque value between 0 Nm and 4 Nm.