Abstract: The invention relates to an adaptive filtering system for cancelling one or more sinusoidal interference signal contained with a desired signal in an incoming signal. A phase-locked loop is used to track a sinusoidal interference frequency and to synthesize various synchronous in-phase/in-quadrature square wave signals. Each of these signals is weighted in accordance with variations in the amplitude and the phase of the sinusoidal interference signal and the weighted square wave signals are combined together with the incoming signal so as to deliver the desired signal substantially free from any sinusoidal interference signal. In the case of multiple correlated signals, the instant filtering system gives a steady state performance substantially better than that of the well known Widrow-Hoff adaptive notch filter.

Abstract: A method and an apparatus for automatically measuring the thickness and the roughness of elongated articles, such as wooden boards. The device comprises a housing having an opening therethrough to receive at least a portion of a board to be measured. At least one contact probe is provided in the housing and is biased against at least one surface of the board to sense irregularities in the flatness of the surface along a measured length thereof. A measuring circuit is connected to the contact probe to provide a measurement signal representative of the sensed irregularities and variations in thickness. A distance measuring device is also provided in the housing to measure the distance of displacement of the board past the contact probe. An output display means indicates selected ones of the measurements obtained. A computing means accumulates measured values of the means, minimum and maximum thickness, for a group of boards and permits the extraction of such statistical information.