AIMANT A POLE EXTERIEUR DEFERRISANT LES POUDRES Deux puissants aimants capteurs sont installés à l’extérieur de l’enveloppe en acier inoxydable...

The external pole magnet has two powerful plate magnets mounted onto the outside of the stainless steel (304) casing and, depending on the design, separate coarse and very fine iron particles from various material flows. One advantage of this external core mounting arrangement is that bridge formation and blockages can not occur internally. The external core magnet can be installed in free-fall pipes or pneumatic transport pipes and is suitable for the plastics, recycling and animal feed industries, as well as for the pharmaceutical and food industries.
http://www.goudsmit-magnetics.nl/fr/systems/ontijzering/pr_b...

Tra l'altro, visto che esistono i magneti a polo centrale, tradurrei semplicemente con magnete a polo esterno.