Abstract: A method and device for distinguishing between partial discharge and electrical noise in high voltage conductors such as in motor and generator stators, power cables, gas insulated switchgear and other equipment where high voltage insulation is subject to deterioration. A series of comparators sets a trigger threshold and a voltage range, set by a computer, whereby pulses falling within the voltage range are sampled at four short intervals and then four longer intervals to produce a general pulse width profile. The voltage range is varied by the computer so that a number of voltage ranges are sampled during each selected portion of an ac cycle. The pulse width of pulses falling within each voltage range is recorded by the computer, and displayed graphically. In a preferred embodiment the device is provided with two channels, for receiving a signal from each end of a partial discharge detector described in U.S. Pat. No. 4,949,001.