Anti-theft alarm systems for stores

• US 4,724,426 A
• Filed: 03/05/1986
• Issued: 02/09/1988
• Est. Priority Date: 03/08/1985
• Status: Expired due to Fees

• Current Assignee: Luxor AB
• Original Assignee: Luxor AB
• Inventors: Lundberg, Leif B.
• Primary Examiner(s): Swann III, Glen R.
• Application Number:
  US06/836,473
• Time in Patent Office: 706 Days
• Field of Search: 340/551, 340/533, 340/524, 340/572, 340/552, 340/554
• US Class Current: 340/551
• CPC Class Codes: G08B 13/2474 Antenna or antenna activator geometry, arrangement or layout loop antennae H01Q1/22
• CPC Class Codes: G08B 13/2488 Timing issues, e.g. synchronising measures to avoid signal collision, with multiple emitters or a single emitter and receiver

Abstract

In self-service stores, pay desks are usually arranged in a row side by side. Anti-theft detectors are often arranged in conjuction with the pay desks, and comprise coil loops generating magnetic fields. The coils are usually fed with a common alternating current. The result of this is that an alarm-generating object at one pay desk can give an alarm at the detectors of an adjacent pay desk. The invention is based on feeding the coil loops in alternate systems with one alternating frequency and the ones in between with a deviating frequency, whereby detection isolation between the systems with the same frequency is achieved.

Claims

1. Arrangement for reducing interference noise between adjacent magnetic field generating detection systems, particularly in conjunction with store anti-theft installations, comprising:

a first set of opposed coil loops for detecting anti-theft tags, said coil loops generating the magnetic field in one system and being of a first frequency; and

a second set of opposed coil loops for detecting anti-theft tags, said second set of coil loops generating the magnetic field in another system adjacent a first side of the one system at a second frequency, different from said first frequency.

2. The arrangement as claimed in claim 1 comprising:

a third set of coil loops for detecting anti-theft tags, generating a magnetic field in a third system adjacent a second side of the one system, opposite the first side, at said second frequency.

3. An anti-theft alarm system for stores comprising:

a plurality of side-by-side passage gates, each passage gate including a pay desk and a means for detecting anti-theft tags and avoiding false detection, including a respective pair of opposed coil loops having an alternating current, one of said passage gates operating said coil loops at a first frequency, and another passage gate on a first side of said one passage gate operating said coil loops at a second frequency, different from said first frequency.

4. The alarm system of claim 3, further including:

a further passage gate on a second side of said one passage gate, opposite said first side, operating said coil loops at said second frequency.