Rotating magnet dispersion tester

The device described provides an in-line measurement of the concentration of magnetic particles dispersed in a flowing fluid. For a given magnetic material and particle size distribution, the output signal is linearly proportional to the particle concentration. It employs a rotating NdFeB cylindrical permanent magnet to generate a several hundred Oe, elliptically rotating, magnetic field. This field is applied to a matched pair of parallel coils: a measuring coil that contains the fluid line, and an empty bucking coil. The magnetic particles in the fluid rotate with the applied field, and the net signal from the two coils is proportional to the magnetic flux from the dispersed particles. The device has sufficient sensitivity to measure the very low concentration dispersions typical of those used for preparation of thin transparent coatings for magnetic recording on photographic film