NBM 520 The Narda Broadband Field Meter NBM-520 is a very compact hand held device for measuring electric and magnetic fields. The simplest possible operation with just four Buttons. NBM-520 is part of the NBM-500 instrument family. It gives extremely accurate results for electromagnetic field strength measurements. The NBM-520, like its bigger counterpart NBM-550, handles applications from long wave up to high frequency microwave radiation using a selection of interchangeable probes for electric and magnetic fields. The field strengths are captured with flat frequency response probes or probes with shaped frequency response, allowing the measurement values to be assessed against an environmental or occupational safety standard. The calibration factors for each probe are stored in the probe itself and are read out and taken into account automatically by the measuring set.