PILFERAGE CONTROL SYSTEM

• US 3,624,631 A
• Filed: 04/27/1970
• Issued: 11/30/1971
• Est. Priority Date: 04/27/1970
• Status: Expired due to Term

• Current Assignee: Donald E. Ellison, Marc Chomet, Robert F. Watterson
• Original Assignee: Donald E. Ellison, Marc Chomet, Robert F. Watterson
• Inventors: Chomet, Marc, Ellison, Donald E., Watterson, Robert F.
• Primary Examiner(s): Yusko, Donald J.
• Assistant Examiner(s): Slobasky, Michael
• Application Number:
  US05/031,902
• Time in Patent Office: 582 Days
• Field of Search: 340/258R,280 343/6.5SS,6.8R
• US Class Current: 340/568.1
• CPC Class Codes: G08B 13/2414 using inductive tags
• CPC Class Codes: G08B 13/2431 Tag circuit details

Abstract

An antipilferage system comprising a cooperating radio frequency transmitter and receiver pair. The transmitter directs swept radio frequency energy to the cooperating receiver circuit wherein balanced oscillating conditions are maintained in a normally steady state. Passive tuned circuits, preferably in the form of printed circuit elements are placed on the merchandise in a store and if an attempt is made to remove unpurchased merchandise from the store without first destroying a fusible link in the passive tuned circuit an unbalance is caused in the receiver oscillator circuits which operates to actuate a suitable alarm. A fully automatic deactivation circuit is also included as part of the invention.

Claims

1. A pilferage control system for detecting the unauthorized removal of goods from an area comprising a passive tank circuit affixed to said goods, tuned such as to have predetermined radiofrequency absorption characteristics in the presence of a radiation fiEld, and having fusible link disposed in series therein, means for transmitting a field of swept radiofrequency radiation of a preselected first level into a volume of space including an exit from said area, means disposed remotely with respect to said transmitting means for detecting said swept radiofrequency radiation and responsive to a selected change in said radiation level to produce an electrical output signal indicative thereof, tuned circuit deactivation means for selectively applying swept radiofrequency radiation of a preselected second level higher than said first level to said passive tank circuit said second level being sufficiently high to destroy said fusible link, and indicating means coupled to said detecting means and responsive to said electrical output signal therefrom to indicate the presence of a passive tuned tank circuit having a complete fusible link therein within said radiation field.

2. Apparatus as recited in claim 1 wherein said transmitting means comprises a variable radiofrequency oscillator, means coupled to said oscillator for varying the frequency thereof as a preselected function of time, a planar radiofrequency transmitting antenna, and means for driving said antenna coupled between said oscillator and said antenna.

3. Apparatus as recited in claim 1 wherein said detecting means comprises a planar radiofrequency receiving antenna, a radiofrequency passband receiver coupled to said receiving antenna, and means coupled to said receiver for rejecting detected changes in said radiation level which correspond to other than absorption produced by a passive tank circuit in said radiation field.

4. Apparatus as recited in claim 3 wherein said rejecting means includes a dual time constant detector means operative to produce an electrical output signal only in response to detected changes in said radiation level which correspond to the presence of a passive tuned tank circuit having a complete fusible link in said radiation field, and to reject detected changes both above and below a preselected frequency bandwidth.

5. Apparatus as recited in claim 4 wherein said rejecting means includes correlation means coupled to said dual time constant detector means comprising means for establishing a plurality of frequency bands within the frequency range of said transmitting means, means for determining in which one of said plurality of frequency bands a change in said radiation level corresponding to the presence of a passive tuned tank circuit is produced, means for detecting only changes in said radiation level which occur in said one frequency band for a predetermined number of sequential sweeps through said frequency range of said transmitting means, and means for producing an electrical output signal only in response to said predetermined number of sequential detections in said one frequency band.

6. Apparatus as recited in claim 1 further including means coupled between said detecting means and said indicating means for sensing the presence of a person in said radiation field and producing an electrical signal indicative thereof and wherein said indicating means is responsive only to the combined electrical signals from said detecting means and said sensing means.

7. Apparatus as recited in claim 1 wherein said passive tuned tank circuit comprises in series an inductance element, first and second capacitive elements, and a fusible link disposed in said circuit and susceptible to destruction by the application of radiofrequency energy above a preselected level.

8. Apparatus as recited in claim 1 wherein said tuned circuit deactivation means comprises means for transmitting swept radio frequency radiation at selectable first and second levels into a preselected volume of space, means colocated with said transmitting means for detecting said swept radiofrequency radiation and responsive to a selected change in said radiation level To produce an electrical output signal indicative of the presence of said tuned circuit, and means coupled to said detecting means and to transmitting means for selecting the higher of said first and second transmitting means output radiation levels for a preselected period of time said higher level being sufficiently high to burnout said fusible link in said tuned circuit.

9. Apparatus as recited in claim 8 further including means for indicating complete destruction of said fusible link.

10. A tuned passive tank circuit for use with a radiofrequency pilferage control system comprising in series an inductance element, first and second capacitive elements, and a fusible link disposed in said circuit and susceptible to destruction by the application of radiofrequency radiation above a preselected level.

11. Apparatus as recited in claim 10 wherein said fusible link is formed of an electrically conductive material wherein an electrical overload adequate to destroy said link is induced by a radiofrequency radiation level of one hundred milliwatts.

12. Apparatus as recited in claim 10 wherein:

said radio frequency pilferage control system employs swept radio frequency radiation, and said tuned passive tank circuit is tuned such as to absorb radiation over a frequency range less than and within the range of radiofrequencies over which said pilferage control system is swept.