초록 ▼

A device for detecting the passage of a ferromagnetic object through a predetermined space has a substantially circular base which circumscribes the space. An inner detector coil and an outer detector coil are concentrically mounted in coplanarity on the base. Voltages are induced on the coils in re

A device for detecting the passage of a ferromagnetic object through a predetermined space has a substantially circular base which circumscribes the space. An inner detector coil and an outer detector coil are concentrically mounted in coplanarity on the base. Voltages are induced on the coils in response to the passage of a nearby magnetic field, such as the small permanent magnetic field associated with a ferromagnetic object. A signal processing circuit compares the induced voltages on the coils to indicate passage of a metal object through the circumscribed space when the inner coil voltage exceeds the outer coil voltage.

대표청구항 ▼

A ferromagnetic object detector which comprises: a base; a first detecting coil defining a passageway and mounted on said base for generating a first electrical signal when a magnetic object is passed near said first detector; a second detecting coil surrounding said first detecting coil and mounted

A ferromagnetic object detector which comprises: a base; a first detecting coil defining a passageway and mounted on said base for generating a first electrical signal when a magnetic object is passed near said first detector; a second detecting coil surrounding said first detecting coil and mounted on said base for generating a second electrical signal when a magnetic object is passed near said second detecting coil; means electrically connected to said coils for comparing said first and second signals to indicate the passage of said object through said passageway; and timing means electrically connected to said comparing means for electrically isolating said comparing means from said coils for a predetermined period of time to permit said first and second signals to increase to a respective maximum value before the maximum value of said first signal is compared with the maximum value of said second signal by said comparing means.