Patent ID: 7667597

Claim:
An apparatus comprising a seal device that includes: a locking member having a portion made of a magnetically permeable material; a magnetic field generator for generating a magnetic field; a magnetic field detector; and structure that can receive said locking member, said structure supporting said magnetic field generator and said magnetic field detector at locations spaced from each other and from a region that is respectively free of and occupied by said portion of said locking member respectively before and after said locking member is received by said structure, said structure defining a main flux path for said magnetic field, said flux path being a loop and having a first portion, a second portion and a remainder that are mutually exclusive, said remainder being the entirety of said flux path other than said first and second portions thereof, said structure including magnetically permeable material, said first portion of said flux path being within said magnetic field generator, said second portion of said flux path being within said region, and most of said remainder of said flux path extending through magnetically permeable material of said structure, said detector being disposed at a selected location where said magnetic field has different characteristics when said portion of said locking member is respectively present in and absent from said region.