Absolute falling ball viscometer, adapted to the low viscosities of liquids

摘要

The Joint Metrology Laboratory LNE-CNAM had an absolute falling ball viscometer, which was operating only at laboratory temperature. Its development ceased in 2005 but resumed in 2010, the aim being to make it operational, by regulating, at first, its temperature between 15?°C and 50?°C, and adapting it to low liquid viscosities up to a value of 15?mPa?s. This study aims to approach the viscosity of fuels or biofuels. Their low viscosity requires the use of a small-diameter ball. A silicon ball with 0.48?mm diameter was selected. The small diameter of this ball mandated the design and the construction of a gripper. This gripper uses the following microsystem-specific technique: the adhesion by van der Waals forces. The operation of this gripper is described in this article. It was designed to perform the following dual function: freeing the ball into the liquid at the top, then recovering it at the bottom of the viscometer, in order to reposition and prepare it for another release.