Conceptual study of an absolute falling-ball viscometer

The restrictions inherent in the use of the conventional reference in capillary viscometry, the viscosity of water at 20 °C, have led to increased interest in absolute viscometers. The viscosity laboratory of the Bureau National de Métrologie, Laboratoire National d"Essais (BNM-LNE) has begun the study of an absolute falling-ball viscometer. The principal difficulties with this system are the measurement of the velocity of the ball and the corrections to compensate for the effects exercised on the ball. Results from a preliminary experiment indicate that uncertainties better than those of capillary viscometers can be obtained. The use of a velocity measurement video system should further reduce the uncertainties.