The ICMmonitor is a compact instrument for evaluating the condition of medium and high voltage insulation. It comprises a spectrum analyzer, an acoustic detector, and a conventional PD monitor in one instrument. This combination enables PD measurements even with high levels of background noise, e .g. on power transformers within substations or power plants. A built-in multiplexer offers scanning of three-phase systems or multiple sensors. The instrument is used principally for permanent, continuous on-line monitoring of rotating machines, cable systems, power transformers, and gas-insulated switch gear (GIS).