Constrained linear motion inertial balance

Abstract

A suspension system for an inertial balance constrains the weighing platform when oscillated to undergo uniform linear motion, thereby ensuring high measurement accuracy. The suspension system includes a supporting framework and a first plurality of elongate elastic support members for suspending the weighing platform from the supporting framework. The elongate support members are disposed in a common plane when the weighing platform is at rest and their inner ends intersect at a first common point to which the weighing platform is firmly linked. A second plurality of such elongate support members is similarly disposed in a second common plane parallel to but spaced from the first common plane. A stiff connecting rod joins the intersection points of the two pluralities and also serves to support the weighing platform and, in conjunction with a feedback system, serves to induce and maintain the weighing platform in oscillation at a resonant frequency dependent upon mass loading. The elongate support members preferably operate in a bending mode, are hollow, and are constructed of a material having a temperature independent Young's modulus over the operating temperature range of the inertial balance. The elongate support members may also be tapered and/or have an elongated, e.g. elliptical or rectangular cross-sectional configuration. Provision is also made to allow fluid flow from the weighing platform to an outlet on the supporting framework, and to effectively fix the center of mass of the moving portion of the balance to thereby minimize damping losses to the outside.