Active magnetic field cancellation systems reduce low-frequency magnetic fields caused by vehicles, elevators, trains, electrical installations or other sources of interference in real time. Using a sensitive sensor, the interference fields are measured and actively compensated by counter fields.

A prerequisite for effective compensation is that the interference field is homogeneous and has a low gradient. This is usually the case for distant field sources such as high-voltage power lines, trams and railway installations. If the sources are close by, such as power rails or electric cables, the compensation effect is reduced.

To reduce inhomogeneous fields or to guarantee the best possible performance in a room, active cancellation systems are often combined with passive room shielding (see Systron LabShield^®).