Method and apparatus for active tamper indicating device using optical time-domain reflectometry

• US 6,002,501 A
• Filed: 06/30/1997
• Issued: 12/14/1999
• Est. Priority Date: 06/30/1997
• Status: Expired due to Fees

• Current Assignee: Lockheed Martin Energy Research Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Energy Research Corporation (Martin Marietta Corporation)
• Inventors: Pickett, Chris A., Earl, D. Duncan, Smith, D. Barton, Muhs, Jeffrey D.
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): SEDIGHIAN, REZA
• Application Number:
  US08/885,972
• Time in Patent Office: 897 Days
• Field of Search: 356/73.1, 359/154, 359/110, 359/173
• US Class Current: 398/9
• CPC Class Codes: G01M 3/28 for pipes, cables or tubes; for pipe joints or seals; for valves ; for welds

Abstract

An optical time-domain reflectometer (OTDR) launches pulses of light into a link or a system of multiplexed links and records the waveform of pulses reflected by the seals in the link(s). If a seal is opened, the link of cables will become a discontinuous transmitter of the light pulses and the OTDR can immediately detect that a seal has been opened. By analyzing the waveform, the OTDR can also quickly determine which seal(s) were opened. In this way the invention functions as a system of active seals. The invention is intended for applications that require long-term surveillance of a large number of closures. It provides immediate tamper detection, allows for periodic access to secured closures, and can be configured for many different distributions of closures. It can monitor closures in indoor and outdoor locations and it can monitor containers or groups of containers located many kilometers apart.

Claims

1. A tamper indicating device, comprising:

a plurality of fiber optic loops, each loop optically connecting a plurality of connector assemblies within the loop;

a control computer functionally connected to the loops and, for each loop, operative to detect a breach in the loop by comparing representations of optical signals injected into the loop to representations of return signals received from the loop;

an optical time-domain reflectometer operative to generate optical breach-identification signals and to receive corresponding return breach-identification signals;

a matrix router optically connected to the reflectometer and operative to selectively connect the reflectometer to each of the fiber optic loops, the matrix router functionally connected to the control computer, which is operative to cause the matrix router to switch the reflectometer into optical connection with a selected one of the fiber optic loops in response to detection of a breach in the selected loop; and

the reflectometer is operative to interrogate the selected loop to identify a particular one of the connector assemblies associated with the breach by comparing breach-identification signals injected into the selected loop to corresponding return breach-identification signals.

2. The tamper indicating device of claim 1, wherein:

each loop defines first and second ends;

the matrix router selectively connects the reflectometer to each loop at its first and second ends; and

the reflectometer is further operative to inject optical signals into both ends of the selected fiber optic loop to monitor the integrity of non-breached connector assemblies while the breach subsists in the selected fiber optic loop.

3. The tamper indicating device of claim 1, wherein:

each loop comprises an optical transmitter for injecting breach-detection signals into a first end of the loop, and a receiver for detecting corresponding return breach-detection signals at a second end of the loop;

for each fiber optic loop, the control computer is operative to generate trigger signals for causing the transmitter to inject the breach-detection signals into the first end of the loop, to receive indicator signals from the receiver in response to the breach-detection signals, and to detect a breach in the loop by comparing the trigger signals to the indicator signals; and

the control computer is functionally connected to the transmitter and the receiver of each loop.

4. The tamper indicating device of claim 3, wherein:

each transmitter comprises a light-emitting diode; and

each receiver comprises a photodiode.

5. The tamper indicating device of claim 4, wherein the control computer is operative to randomly pulse the breach-detection signals.

6. The tamper indicating device of claim 4, wherein the control computer is operative to frequency modulate the breach-detection signals.

7. The tamper indicating device of claim 4, wherein the reflectometer identifies a particular one of the connector assemblies associated with the breach by detecting Fresnel reflection in the return breach-identification signals and determining a temporal relationship between the Fresnel reflection and the corresponding breach-identification signals.

8. The tamper indicating device of claim 4, wherein, for each connector assembly:

the connector assembly is integrated into a bolt assembly;

the bolt assembly secures a lid ring on a storage drum; and

rotation of the bolt assembly to remove the lid ring causes a breach in the connector assembly.

9. The tamper indicating device of claim 8, further comprising an acetate film within the connector assembly that falls apart upon rotation of the bolt assembly causing the breach in the connector assembly.

10. A tamper indicating device, comprising:

a plurality of fiber optic loops, each loop defining first and second ends, optically connecting a plurality of connector assemblies between the first and second ends, and comprising an optical transmitter for injecting breach-detection signals into the first end of the loop and a receiver for detecting corresponding return breach-detection signals at the second end of the loop;

a control computer functionally connected to the transmitter and the receiver of each loop and, for each loop, the control computer is operative to generate trigger signals for causing the transmitter to inject the breach-detection signals into the first end of the loop, to receive indicator signals from the receiver in response to the breach-detection signals, and to detect a breach in the loop by comparing the trigger signals to the indicator signals;

an optical time-domain reflectometer operative to generate optical breach-identification signals and to receive corresponding return breach-identification signals;

a matrix router optically connected to the reflectometer and operative to selectively connect the reflectometer to each of the fiber optic loops, the matrix router functionally connected to the control computer, which is operative to cause the matrix router to switch the reflectometer into optical connection with a selected one of the fiber optic loops in response to detection of a breach in the selected loop; and

the reflectometer is operative to interrogate the selected loop to identify a particular one of the connector assemblies associated with the breach by comparing breach-identification signals injected into the selected loop to corresponding return breach-identification signals.

11. The tamper indicating device of claim 10, wherein, for each connector assembly:

the matrix router selectively connects the reflectometer to the first and second ends of each loop;

the reflectometer is further operative to inject optical signals into both ends of the selected fiber optic loop to monitor the integrity of non-breached connector assemblies while the breach subsists in the selected fiber optic loop;

each transmitter comprises a light-emitting diode; and

each receiver comprises a photodiode.

12. The tamper indicating device of claim 11, wherein the control computer is operative to randomly pulse the breach-detection signals or frequency modulate the breach-detection signals.

13. The tamper indicating device of claim 12, wherein the reflectometer identifies a particular one of the connector assemblies associated with the breach by detecting Fresnel reflection in the return breach-identification signals and determining a temporal relationship between the Fresnel reflection and the corresponding breach-identification signals.

14. The tamper indicating device of claim 13, wherein, for each connector assembly:

the connector assembly is integrated into a bolt assembly;

the bolt assembly secures a lid ring on a storage drum; and

rotation of the bolt assembly to remove the lid ring causes a breach in the connector assembly.

15. A method for optically detecting tampering, comprising the steps of:

providing a plurality of fiber optic loops, each loop optically connecting a plurality of connector assemblies within the loop;

for each loop, detecting a breach in the loop by comparing representations of optical signals injected into the loop to representations of return signals received from the loop;

in response to detecting a breach in a selected loop, injecting optical breach-identification signals to interrogate the selected loop to identify a particular one of the connector assemblies associated with the breach by injecting breach-identification signals into the selected loop and comparing the breach-identification signals to corresponding return breach-identification signals; and

injecting optical signals into both ends of the selected fiber optic loop to monitor the integrity of non-breached connector assemblies while the breach subsists in the selected fiber optic loop.

16. The method of claim 15, further comprising the step of randomly pulsing the breach-detection signals.

17. The method of claim 15, further comprising the step of frequency modulate the breach-detection signals.

18. The method of claim 15, wherein the step of comparing the breach-identification signals to corresponding return breach-identification signals comprises the step of detecting Fresnel reflection in the return breach-identification signals and determining a temporal relationship between the Fresnel reflection and the corresponding breach-identification signals.

19. The method of claim 18, further comprising the steps of, for each connector assembly:

integrating the connector assembly into a bolt assembly in which rotation of the bolt assembly causes a breach in an optical path through the connector assembly;

securing a lid ring on a storage drum with bolt assembly; and

monitoring the connector assembly for a breach.

20. The method of claim 19, further comprising the step of multiplexing the breach-detection signals among the loops.