Metal detectors monitor material flows and are used to protect valuable equipment such as crushers, grinders and con¬veyor systems. If a sufficiently large piece of metal passes through the detector zone of the plant it is spotted immediately. Any change in the constantly active alternating field is subsequently evaluated by the processor control system. The device can detect both ferrous and non-ferrous metals, as well as high-grade steel. The distance between the detector and the electronic controls can be up to 50m. This allows the metal detector to be monitored from the control center.