A particle counter and classification system comprising: an imaging subsystem configured to determine the size of particles above a predetermined size in a fluid in a sample cell; a first stage magnetometer sensor subsystem for the fluid tuned to detect and determine the size of ferrous and/or conducting particles in said fluid above said predetermined size; a second stage magnetometer sensor subsystem for said fluid tuned to detect the overall ferrous particle content of the fluid; and a processor subsystem, responsive to the imaging subsystem, the first stage magnetometer sensor subsystem, and the second stage magnetometer sensor subsystem, configured to calculate and report the number of particles in the fluid in a plurality of size ranges, the number of ferrous and/or conducting particles in said size ranges, and the overall ferrous content of the fluid, and further configured to classify individual particles detected by said imaging subsystem, and to reclassify said individual particles based on feedback information from said first stage magnetometer sensor subsystem, characterized in that the first stage magnetometer sensor subsystem includes a small diameter fluid conduit upstream or downstream of the sample cell with a small diameter sense coil and the second stage magnetometer sensor subsystem includes a larger diameter fluid conduit downstream of the sample cell with a larger diameter sense coil, wherein the diameters of the larger diameter fluid conduit and the larger diameter sense coil are larger than the diameters of the small diameter fluid conduit and the small diameter sense coil respectively. an imaging subsystem configured to determine the size of particles above a predetermined size in a fluid in a sample cell; a first stage magnetometer sensor subsystem for the fluid tuned to detect and determine the size of ferrous and/or conducting particles in said fluid above said predetermined size; a second stage magnetometer sensor subsystem for said fluid tuned to detect the overall ferrous particle content of the fluid; and a processor subsystem, responsive to the imaging subsystem, the first stage magnetometer sensor subsystem, and the second stage magnetometer sensor subsystem, configured to calculate and report the number of particles in the fluid in a plurality of size ranges, the number of ferrous and/or conducting particles in said size ranges, and the overall ferrous content of the fluid, and further configured to classify individual particles detected by said imaging subsystem, and to reclassify said individual particles based on feedback information from said first stage magnetometer sensor subsystem, characterized in that the first stage magnetometer sensor subsystem includes a small diameter fluid conduit upstream or downstream of the sample cell with a small diameter sense coil and the second stage magnetometer sensor subsystem includes a larger diameter fluid conduit downstream of the sample cell with a larger diameter sense coil, wherein the diameters of the larger diameter fluid conduit and the larger diameter sense coil are larger than the diameters of the small diameter fluid conduit and the small diameter sense coil respectively.