Electronic monitoring system and responder device

• US 4,095,214 A
• Filed: 06/17/1976
• Issued: 06/13/1978
• Est. Priority Date: 06/17/1976
• Status: Expired due to Term

• Current Assignee: Knogo North America, Inc. (Sentry Technology Corp.)
• Original Assignee: Knogo Corp (Johnson Controls International plc)
• Inventors: Minasy, Arthur J.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): Groody, James J.
• Application Number:
  US05/697,128
• Time in Patent Office: 726 Days
• Field of Search: 340/258 B, 340/258 C, 340/258 R, 340/279, 340/280, 325/118, 343/6.8 R, 343/5 PD, 336/92, 63/3, 324/41, 324/34 PS
• US Class Current: 340/552
• CPC Class Codes: G01V 3/101 by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil measuring impedance or characteristics derived therefrom G01R27/00, e.g. quality factor G01R27/26
• CPC Class Codes: G01V 3/15 specially adapted for use during transport, e.g. by a person, vehicle or boat
• CPC Class Codes: G07C 9/10 Movable barriers with registering means
• CPC Class Codes: G07C 9/28 the pass enabling tracking or indicating presence
• CPC Class Codes: G08B 13/2434 Tag housing and attachment details
• CPC Class Codes: G08B 13/2437 Tag layered structure, processes for making layered tags
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22

Abstract

An electronic monitoring system for monitoring the passage of objects, such as persons, past a monitoring station. An antenna is provided flat on the floor of the station to generate electromagnetic fields in the vicinity of the station and to generate electrical alarm signals whenever the electromagnetic fields are disturbed by the passage of an object carrying a special responder device. The responder device comprises an elongated bar of ferromagnetic material about which is wound the coil of a resonant electrical circuit. A mounting strap is provided to mount a responder device the leg of each object to be monitored such that the elongated bar is held perpendicular to the floor whereby maximum electrical interaction is provided between the antenna and the resonant electrical circuit.

Claims

1. An electronic monitoring system for detecting the passage of objects past a given monitoring station, said system comprising an essentially flat loop antenna means which lies in a single plane, said antenna means being disposed at the surface of the floor adjacent a passageway through said given monitoring station so that said plane of said antenna is substantially parallel to the plane of the floor, electromagnetic monitoring means connected to said antenna means, said monitoring means being operable to energize said antenna means in a predetermined frequency range and to detect predetermined electromagnetic responses produced upon said antenna means when a resonant circuit is present in the vicinity of said antenna means, and a responder device comprising an elongated bar of ferromagnetic material, an insulated electrically conductive wire coiled about said bar, a capacitor connected to the ends of said wire to form a resonant circuit and means mounting said bar, wire and capacitor on the leg of an object whose movement is to be monitored, said mounting means comprising a casing which holds said bar, said coil and said capacitor and a fastening element for holding said casing to the leg of said object, said fastening element being oriented with respect to said casing such that the longitudinal axis of said bar is maintained substantially perpendicular to said plane of said loop antenna means, whereby said predetermined electromagnetic responses cause a signal change in said antenna which change is detected by said monitoring means.

2. An electronic monitoring system according to claim 1 wherein said antenna means comprises at least one essentially rectangular loop extending across said passageway.

3. An electronic responder device for use in monitoring the movement of personnel past a monitoring station, said responder device comprising an elongated bar of ferromagnetic material, an electrically conductive, insulated wire coiled about said bar, a capacitor mounted adjacent said bar and connected to opposite ends of said wire to form therewith a resonant circuit, an ankle strap configured to fit around the ankle of a person, a mounting member comprising a hollow casing attached to said ankle strap, said casing holding said bar, said insulated wire coiled about said bar and said capacitor, said mounting member being formed with upper and lower lugs extending inwardly of said casing to contact opposite end regions of said bar for mounting said bar with its longitudinal axis extending perpendicular to the plane of said ankle strap.