I have an application in which I have a loop of flexible cable (braided steel, designed for physical strength, not for any particular electrical properties, though it could have wire added to it for that purpose). The cable forms a closed loop, about 8 inches in diameter. I need to be able to detect whether a metal tube is passing through the loop.
For the metal tube, think of the steel post designed for a chainlink fence as the primary example, though there's a fair amount of variability in material and diameter.
It would be good enough for now to be able to detect steel, though in a future redesign, detecting an aluminum tube might become important.
I'm not an expert on electromagnetic sensors, but my basic understanding is that if I go that route, my options are an inductive sensor (but this may limit applicability to aluminum in the future) or a capacitive sensor (but this may have challenges related to the presence of nearby things outside the loop.
Can anybody comment on what makes sense here and how to approach it?