How does a Metal detection machine work

Metal detection machines work according to an inductive measuring principle. A high-frequency, electro-magnetic alternating field is generated by a transmitter coil. If a metal part moves through the Metal detection machine, this field undergoes a change which corresponds to the magnetic and electrical properties of the metal part.

The change in field is registered by a matched pair of receiver coils and then processed and digitally evaluated in the electronics

This measuring principle reacts to electrical conductivity and magnetism and thus detects all types of metal, including non-ferrous metals (e.g. aluminum or brass) and stainless steel. However, magnetic metals can be detected slightly better than non-magnetic ones. The measuring field penetrates the tested food and detects metal particles even inside the product or in packaging.

The food itself is not affected or changed in any way by the measurement.

Technical limits

The maximum sensitivity is limited by the physical laws underlying the measuring principle. Food often has a more or less strong electrical conductivity due to salt, sugar, minerals and water. In practice, the attainable sensitivity mainly depends on how well the Metal detection machine can compensate for these product effects.

Classical metal detection systems

Metal detection conveyors: A Metal detection machine is integrated into a conveyor belt, which encloses the conveyor belt in a frame or is mounted as a surface underneath it. There are various methods available to separate detected metal particles (e.g. pusher).

Downpipe: Giant material falls in a pipeline through frame or ring-shaped Metal detection machines. Detected metal particles are separated by a separation flap.

Inline detector as a component of a pipe conveyor system: This inline system is used to detect metal particles in pasty or liquid products and is integrated into the conveyor line (e.g. with a milk pipe fitting). Product parts contaminated with metal are discharged via special valves.

Place of installation

Packaged as well as unpackaged products can be examined for metal. The inspection of already packed goods is usually preferable, because a new contamination with metal is almost impossible at this stage. Unpackaged goods, however, sometimes take up considerably less space – so a much smaller Metal detection machine can be used. Under certain circumstances, this can also detect significantly smaller metal parts.

Unpackaged goods or packed goods that cannot be monitored sensibly (e.g. because of metal-containing packaging or too large packaging dimensions) should be checked additionally. If a Metal detection machine is primarily used for machine protection, it should be installed as close as possible to the machine to be protected.