Patent ID: 6637265
Filing Date: 2003-10-28
Classification: G01G,G01N

Abstract:
An apparatus for determining density of a sample having a sample mass and a sample volume while the sample is immersed in a gaseous medium having variable density, and while the sample is exposed to an acceleration in a first direction and a net buoyancy force in a second direction opposite the first direction, where the net buoyancy force is a sum of buoyancy forces in the first and second directions exerted on the sample by the gaseous medium, the apparatus comprising:a chamber for containing the gaseous medium and the sample immersed in the gaseous medium; means for selectively varying the density of the gaseous medium in the chamber over a range of densities; means for producing at least one electrical signal related to the density of the gaseous medium in the chamber as the density of the gaseous medium is varied; a balance beam disposed within the chamber and having opposing first and second ends, the balance beam further comprising: a sample pan disposed adjacent the first end of the balance beam, the sample pan having a sample pan volume and a sample pan mass, and creating a sample pan moment adjacent the first end of the balance beam; a first counter-weight disposed adjacent the second end of the balance beam, the first counter-weight having a first counter-weight volume which is substantially equivalent to the sample pan volume, a first counter-weight mass which is substantially equivalent to the sample pan mass, and creating a first counter-weight moment adjacent the second end of the balance beam which is substantially equivalent to the sample pan moment; a coil assembly disposed adjacent the second end of the balance beam, the coil assembly having a coil assembly volume and a coil assembly mass, and creating a coil assembly moment adjacent the second end of the balance beam, the coil assembly electrically coupled to a controller; a second counter-weight disposed adjacent the first end of the balance beam, the second counter-weight having a second counter-weight volume which is substantially equivalent to the coil assembly volume, a second counter-weight mass which is substantially equivalent to the coil assembly mass, and creating a second counter-weight moment adjacent the first end of the balance beam which is substantially equivalent to the coil assembly moment; a magnet assembly disposed adjacent to and magnetically interacting with the coil assembly; the controller for providing a coil current to the coil assembly, thereby generating a magnetic field which interacts with the magnet assembly, the interaction between the magnetic field of the coil assembly and the magnet assembly causing a force to be applied to the second end of the beam to keep the beam balanced as the density of the gaseous medium in the chamber is varied over the range of densities, where the force applied to the second end of the beam is substantially equivalent to the difference between the net buoyancy force and the product of the sample mass times the acceleration while the sample is immersed in the gaseous medium as the density of the gaseous medium is varied over the range of densities; and a computing device for receiving the at least one electrical signal related to the density of the gaseous medium and at least one electrical signal related to the coil current, and for calculating the density of the sample based at least in part upon the at least one electrical signal related to the density of the gaseous medium and the at least one electrical signal related to the coil current.