APX50, the first fully automatic absolute pressure balance in the range 10kPa to 1 MPa

Desgranges et Huot, a French company specializing in pressure metrology, ha s been cooperating with the Bureau National de Metrologie-Laboratoire Natio nal d'Essais (BNM-LNE) for the past five years in the development of the fi rst fully automatic absolute pressure balance in the range 10 kPa to 1 MPa, designated APX50. The different steps of this project are explained and th e technical specifications and configuration of the APX50 are presented. A new measuring block has been developed, based on a rotating cylinder and re ceiving large effective area piston-cylinders. In addition, a very original mass-loading system has been created allowing the automatization of this o peration down to the fractional 1 g mass. The new design concept of this sy stem allows automatic absolute pressure measurements to be carried out with a relative uncertainty down to 5 x 10(-6). The complete metrological chara cteristics of the pressure balance are presented by the BNM-LNE elsewhere i n this issue. This system, which offers the reliability and specifications of high-accuracy pressure balances together with unique features simplifyin g its operation, could potentially replace the mercury columns used as refe rence standards in national metrology institutes worldwide.