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Abstract

An interference filter for the removal of power line interference from amplifying systems, such as electrocardiographs, which includes a band-rejection filter tuned to reject the power line frequency interference, a differential amplifier to which the signal being amplified and the output of the notch filter are applied to produce an output consisting of only the interference signal. The interference signal is fed to and stored in a memory which is constantly updated and the output of the memory is then summed with the original signal. Since the phase of the output of the memory is reversed from the interference in the original signal, only the original signal will result. An electronic switch is connected between the output of the differential amplifier and the memory and is operated by a velocity detector connected with the output of the band-rejection filter. If at any time the velocity detector senses a rate of rise of the incoming signal exceeding a selected value, it functions to open the switch for a predetermined period and thereafter closes the switch. This procedure in the case of electrocardiographs, prevents distortion of electrocardiographic signals.

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First Claim