As part of my job, I regularly present oil analysis training seminars. One of the tests we discuss is ferrous density. I find that this test is seldom well understood, and, probably as a result, is seldom used. Explanation of the Test Ferrous density is the density of ferrous, or more correctly, of ferromagnetic particles distributed in the oil. The other ferromagnetic elements that one might encounter in lubricated components are nickel and cobalt, but in practice, these elements are likely to be present only in comparatively small quantities. Therefore, we are effectively measuring the concentration of magnetic steel alloys. There is no single way to conduct a ferrous density analysis. There are many ways of performing this rather essential test. Perhaps the two most common are the direct-reading ferrography, a technique which uses light blockage analysis of material deposited on a glass slide; and electromagnetic induction, which measures the voltage induced in a current-carrying ...
