Magnetic bridge proximity sensor

Claim 1

A proximity sensor for indicating the spatial proximity of a ferrous object comprising: a magnetic reluctance bridge including a dc magnetic field generating means including first and second magnetic poles with an axis of symmetry therebetween; a first high magnetic permeability ferrous section having first and second ends disposed in a non-touching manner across said first and second magnetic poles and balanced relative to said axis of symmetry; a first low magnetic permeabilty gap with a reluctance R 1 disposed between said first magnetic pole and said first end of said first ferrous section; a second low magnetic permeability gap with a reluctance R 2 disposed between said second magnetic pole and said second end of said first ferrous section; wherein said first and second magnetic poles, said first low magnetic permeability gap, said first ferrous section, and said second low magnetic permeability gap form a first magnetic flux circuit; a second high magnetic permeability ferrous section with third and fourth ends disposed in parallel with said first ferrous section a predetermined distance therefrom away from said first and second magnetic poles and balanced relative to said axis of symmetry; a third low magnetic permeability gap with a reluctance R 3 disposed between said first magnetic pole and said third end of said second ferrous section; a fourth low magnetic permeability gap with a reluctance R 4 between said magnetic pole and said fourth end of said second ferrous section; wherein said first and second magnetic poles, said third low magnetic permeability gap, said second ferrous section, and said fourth low magnetic permeability gap form a second magnetic flux circuit; wherein said reluctances R 1 , R 2 , R 3 , R 4 are related by the equation R 1 /R 2 =R 3 /R 4 ; magnetic flux sensing element disposed approximately along said axis of symmetry between said first and second ferrous elements to form the center reluctance path for said magnetic reluctance bridge in order to sense flux when the magnetic reluctance bridge is unbalanced in reluctance; wherein said first and third low magnetic permeability gaps overlap and are disposed on one side of said magnetic flux sensing element, and said second and fourth low magnetic permeability gaps over lap and are disposed on the opposite side of said magnetic flux sensing element from said first and third low magnetic permeability gaps; wherein a ferrous object disposed adjacent either said third low magnetic permeability gap or said fourth low magnetic permeability gap will unbalance said magnetic reluctance bridge and cause flux to be detected by said sensing element; and means for generating a triggering signal in response to flux detected by said flux sensing element.