Oxford Instruments has acquired California-based Asylum Research, a maker of scanning probe and atomic force microscopes. OI bought the 13-year-old company from its management for $32 million. It may pay shareholders another $48 million over the next three years if certain sales milestones are reached. In 2011, Asylum had sales of about $20 million. A producer of instruments and devices used in research and industry, OI was spun off from Oxford University more than 50 years ago.