Effects of Magnetism of Materials on Fluid Density Measurement in a Magnetic Levitation Densimeter and the Correction Methods

Abstract

A magnetic levitation densimeter for accurate PVT-property measurement has been investigated. For the existing densimeter, the most serious factor of the measurement uncertainty is a density measurement error caused by magnetism of materials around magnetic coupling which is composed of a permanent magnet in a sample fluid and an electromagnet suspended from an electronic balance. The error was quantitatively analyzed by the Finite Element Method (FEM), and two methods for reducing the error were devised; one is to keep the permanent magnet at the same position in every measurement state by controlling the position of the electromagnet, while the other is to use a hybrid magnet which is composed of an electromagnet combined with a permanent magnet. In addition, the new preliminary densimeter was developed, which is able to correct the error by using two sinkers with different densities even if magnetism of the sample fluid is unknown.