The difference between inductive proximity, displacement, and eddy-current sensors

April 05, 2016 // By Patrick Mannion
It seems like engineering 101, but do you actually remember the specific differences between inductive proximity, inductive displacement, and eddy-current sensors? I asked a few friends and everyone had a pretty good idea, to varying degrees, but if you aren’t immersed in the topic the nomenclature can throw you off, as they’re all reliant on eddy currents.

Eddy currents, also called Foucault current, are loops of electrical current induced within a conductor by a time-varying magnetic field in that conductor (Figure 1). This phenomenon of induction was first observed by Michael Faraday way back in 1831, and he summed up his experiments in Faraday’s Law. This of course states that the induced electrical current (electromotive force, or EMF) in a closed circuit is equal to the negative of the rate of change of the magnetic flux, or:



where ε is the EMF and ΦB is the magnetic flux.