The present invention provides an abnormality detector for a rolling bearing including an outer race, and an inner race. The abnormality detector includes a filter configured to prevent metal pieces contained in lubricating oil flowing through the bearing space between the outer and inner races from passing through the filter, while allowing the lubricating oil to pass through the filter so as to flow to the outside space of the bearing space; an electric circuit including a pair of permanent magnets mounted, as a pair of electrodes, to the filter so as to be spaced apart from each other, and lines extending from the respective electrodes to a power source; and an output detector configured to detect a change in electrical output from the electric circuit when metal pieces adhere between the pair of permanent magnets, thereby detecting the state of metal pieces contained in the lubricating oil.

An assembly providing a bearing, a lubricant and a contamination sensor for determining a level of contamination in the lubricant. The sensor includes an EM wave generator for generating an EM signal, and an EM sensing element arranged in contact with the lubricant. The EM sensing element receives the generated EM signal and transmits an output signal whose properties are responsive to real and imaginary parts of a complex relative permittivity of the lubricant. The output signal is received by an EM measuring device that measures first and second parameters of the output signal, which are respectively representative of the real and imaginary parts of the complex relative permittivity. The EM measuring device determines a level of water contamination in the lubricant, based on the measured first parameter alone and determines a level of metal particle contamination in the grease, based on the measured first and second parameters.