United States Patent m
Schwarz et al.
 ELECTRO-MAGNETIC DESENSITIZER
 Inventors: Werner Schwarz; Josef Graessle, both of Nuess, Fed. Rep. of Germany
 Assignee: Minnesota Mining and
Manufacturing Company, St. Paul,
 Appl. No.: 697,644
 Filed: May 8,1991
 Foreign Application Priority Data
May 16, 1990 [DE] Fed. Rep. of Germany 4015779
 Int. CI.' G08B 13/24
 U.S. CI 340/551; 340/572
 Field of Search 340/551, 572, 515, 538,
340/310 R, 310 A, 693; 335/284; 324/228
 References Cited
U.S. PATENT DOCUMENTS
3,820,104 6/1974 Fearon 340/572
4,484,184 11/1984 Gregor et al 340/572
4,906,974 3/1990 Render 340/551
5,027,106 6/1991 Lizzi et al 340/572
FOREIGN PATENT DOCUMENTS
3014667 10/1981 Fed. Rep. of Germany .
3015811 10/1981 Fed. Rep. of Germany 340/572
3045703 7/1982 Fed. Rep. of Germany 340/572
[ii] Patent Number: 5,210,524  Date of Patent: May 11,1993
Primary Examiner—Thomas J. Mullen, Jr.
Attorney, Agent, or Firm—Gary L. Griswold; Walter N.
Kirn; William B. Barte
The invention is related to a process of deactivating a magnetic security marker of an article surveillance system, wherein the security marker is detected by simulating conditions normally present in such a system, e.g., by creating between a transmitter and a receiver a sinewave electromagnetic field and the deactivating the security marker by means of the electronically switchable magnetizing apparatus in response to the detection of the magnetic field which corresponds to the magnetization of the security marker in the surveillance zone. It is the object of the invention to enable the magnetic security marker to be deactivated using any alternating power line. To this end, the magnetic system is automatically connected to a power line without circuit change when the security marker is detected. The magnetizing apparatus gradually builds up a magnetic field by rectifying the flow current, monitoring it by a current sensor and increasing it at each change of phase until the current reaches a level to which the sensor is set as effecting deactivation. Thereafter, the magnetizing apparatus is electronically disconnected from the power line.
11 Claims, 4 Drawing Sheets