A Density and Viscosity Sensor Utilizing a Levitated Permanent Magnet

We present a measurement system for the viscosity and density of a fluid featuring a permanent magnet as measurement body, which is levitated in an actively controlled magnetic field. The behavior of the system is illustrated using different measurement body shapes. The basic concepts and the modeling of the electromechanical system are discussed. Utilizing special measurement modes, the sensor system allows for measuring viscosity and density independently. When put into operation, the magnet is controlled to stay at a constant levitation position. Due to a special actuation scheme, the magnet also rotates around its vertical axis. Using this setup and immersing the magnet in a fluid, it is possible to analyze viscosity and density of all kinds of fluids, except ferrofluids (which would distort the magnetic fields). The magnetic levitation system avoids any electrical or mechanical connections penetrating the walls of the measurement chamber; only the levitated permanent magnetic measurement body is in contact with the sample fluid.