The Senis Magnetic Field Mappers, or Field Scanners, were initially developed for high position resolution mapping of the three field components Bx, By, Bz in a 3D volume around a permanent magnet assembly. The Mapper hardware, signal processing and display software can also be applied for ac field measurement. Maps of the AC magnetic field in and around a power supply can show the fringe magnetic field from the transformer and inductor magnetic components as a function of position. Changes in the field amplitude and harmonic content can be used to estimate inductive coupling into nearby sensitive circuits and evaluate different component ratings or shielding strategies. Three-component Field Probes with field ranges to +/-3T and as thin as 0.25 mm can be used in the stator-rotor gap of an operating motor to make field maps at selected axial and polar positions as a function of speed and torque loading to compare with the motor design model. The harmonic content can help determine and reduce vibration and acoustic noise sources.