Security system using optical sensors

• US 5,912,619 A
• Filed: 12/31/1997
• Issued: 06/15/1999
• Est. Priority Date: 12/31/1997
• Status: Expired due to Term

• Current Assignee: Wells Fargo Alarm Services Inc (Johnson Controls International plc)
• Original Assignee: Wells Fargo Dealer Services Incorporated (Wells Fargo & Company)
• Inventors: Vogt, William R.
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): TRIEU, VAN THANH
• Application Number:
  US09/001,890
• Time in Patent Office: 531 Days
• Field of Search: 340/541, 340/542, 340/545, 340/547, 340/551, 340/552, 340/555, 340/556, 340/545.1, 340/545.3, 340/545.6, 340/545.7, 340/545.8
• US Class Current: 340/545.1
• CPC Class Codes: G08B 13/08 by opening, e.g. of door, of window, of drawer, of shutter, of curtain, of blind
• CPC Class Codes: G08B 13/1481 with optical detection

Abstract

A security system (40) monitoring displacement between a first, fixed unit (20) and a second, movable unit (21) normally in close proximity to each other. A code generator (51) in the first unit (20) generates a coded electrical signal (Sc) supplied to an optical transducer (24) that converts the signal into an optical signal transmitted at the second unit. A transducer (34) in the second unit receives the transmitted signal, converts it back into an electrical signal now supplied to a code generator (56) in the second unit This generator determines if the electrical signal corresponds to the coded signal. If so, this second code generator generates a second coded electrical signal which is supplied to a transducer (35) in the second unit that converts the signal into an optical signal transmitted back toward the first unit. A transducer (28) in the first unit receives this reply signal and converts it back into an electrical signal. The first code generator now determines if the reply signal supplied corresponds to the second coded signal. Failure of the first unit to either receive the return signals or of the fist code generator to determine the reply signal corresponds to the second coded signal indicates either the units are no longer in close proximity; or, someone is trying to compromise the security system. Either condition constitutes an alarm condition for which an alarm is produced.

Claims

1. A security system monitoring a relative displacement between a first unit and a second unit which are normally in close proximity to each other but which are movable relative to one another, comprising:

a first code, generator in the first unit for generating a first coded electrical signal corresponding to a first predetermined coded signal;

a first transducer in the first unit to which said first coded electrical signal is supplied by said first code generator, said first transducer being responsive to said first coded electrical signal to convert said first coded electrical signal into a signal transmitted toward said second unit;

a first transducer in the second unit receiving a signal transmitted from said first unit and for converting said received signal back into an electrical signal;

a second code generator in said second unit to, which said an electrical signal from the first trasducer in the second unit is supplied, said second code generator determining if the electrical signal supplied to it corresponds to said first predetermined coded signal and, if so, said second code generator generating a second coded electrical signal corresponding to a second predetermined coded signal;

a second transducer in the second unit to which said second coded electrical is supplied, said second transducer being responsive to said second coded electrical signal to convert said second coded electrical signal into a signal transmitted toward said first unit; and

,

a second transducer in the first unit receiving a signal transmitted from said second unit and converting said received signal back into an electrical signal, said first code generator determining if the electrical signal supplied to it corresponds to said second predetermined coded signal, failure of said first unit to receive said second predetermined coded signal from said second unit indicating either that said first and second units are no longer in close proximity with each other, or that someone is trying to compromise the security system, either condition being an alarm condition for which an appropriate alarm is produced by said security system.

2. The security system of claim 1 wherein said transducers in said first and second units are light transducers for appropriately converting said coded electrical signals from the respective code generators into light signals transmitted between the units and for converting received light signals into the electrical signals supplied to the respective code generators.

3. The security system of claim 1 wherein said first and second code generators are each microprocessors each of which monitors both the code content of the electrical signal supplied to it by the appropriate transducer and the amplitude of the electrical signal, the microprocessors being responsive to the code content of the electrical signal not corresponding to the coded content of the appropriate predetermined coded signal, or to the amplitude of the electrical not being within a predetermined range of amplitude values to cause the alarm to be produced by the system.

4. The security system of claim 1 wherein said first and second predetermined coded signals are different in content.

5. The security system of claim 3 wherein said microprocessors are each programmed to change said predetermined coded messages so the coded messages sent between units at one time differ from the coded messages sent at another time.

6. The security system of claim 1 wherein each unit includes its own source of power.

7. The security system of claim 1 having a common source of power for the two units.