Apparatus utilizing a test surface with a magnetic flux gap for detecting dimensional disconformities of manufactured elements

Apparatus for determining if at least one dimension of each of a series of ferromagnetic elements differs from a predetermined desired value, comprising:

• an electromagnetic sensing device having a ferromagnetic core forming a magnetic flux path, said core having an exteriorly exposed test surface against which successive ones of said elements may be disposed in a predetermined position relative thereto, said core having a gap in said flux path at said test surface with said gap being located in said test surface to be spanned by disconforming ones of said elements which differ along said dimension from other conforming ones of said elements that conform to said desired value, said gap being further located in said test surface to remain unspanned by said conforming ones of said elements thereby causing said core to exhibit a substantially lower reluctance when a disconforming one of said elements is positioned against said test surface as compared with when a conforming one is positioned thereagainst, said sensing device further having an electrical winding magnetically coupled to said core to establish said magnetic flux therein,
• a power supply for electrically energizing said winding,
• circuit means for detecting a predetermind degree of change of the self-inductance value of said winding whereby said disconforming ones of said elements may be distinguished from said conforming ones thereof, and
• guide means for receiving each of said elements in sequence and for defining said predetermined position of said elements at said test surface of said sensing device.