Abstract: An apparatus and method are provided in which direct ohmic connection is made to a comminution device (e.g., a wood chip or pulp refiner) to obtain transient voltages, existing on the refining elements, that are directly related to fiber impacts. These voltages are characterized by severity (S) (i.e., magnitude), rate (N), rise time (RT) and polarity (.+-.P). The characteristics of these voltages taken separately and/or in mathematical combinations predict the properties of refined wood chips and pulps, i.e., freeness, tensile strength, tear, burst, breaking length and fiber length. Signal characteristics further track refiner plate wear and detect the occurrence of "critical gap" as well as the onset of plate clash.