Cargo monitor apparatus and method

• US 3,961,323 A
• Filed: 12/18/1972
• Issued: 06/01/1976
• Est. Priority Date: 02/22/1971
• Status: Expired due to Term

• Current Assignee: American Multi-Lert Corporation
• Original Assignee: American Multi-Lert Corporation
• Inventors: Hartkorn, Albert W.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/315,852
• Time in Patent Office: 1,261 Days
• Field of Search: 340/280, 340/224, 340/409, 340/63, 340/64, 340/65, 343/712, 325/1, 325/4, 325/7, 325/102, 325/117, 325/139
• US Class Current: 340/539.1
• CPC Class Codes: G08B 13/22 Electrical actuation
• CPC Class Codes: G08B 13/2491 Intrusion detection systems, i.e. where the body of an intruder causes the interference with the electromagnetic field
• CPC Class Codes: H04K 2203/22 for communication related to vehicles
• CPC Class Codes: H04K 3/22 including jamming detection and monitoring
• CPC Class Codes: H04K 3/88 related to allowing or preventing alarm transmission

Abstract

A container monitoring system has a small transmitter unit adapted for easy attachment to and removal from a container such as a truck, trailer or railroad car when not in motion and a receiver which alerts a guard as to a theft-related movement either of the container itself or motion into or out of the container, or to a condition within the container such as temperature. The apparatus has provision for transmitting a low power, radio frequency carrier signal, preferably 27 MHz with a wire loop which is mounted to utilize the metallic body of the container as part of the antenna radiation system. The carrier is modulated with a mid-frequency signal that is interrupted at a precisely controlled low frequency rate and has a signal duration of a predetermined different inerval as measured from the theft-related movement. The coding, including the analysis of the signal at the receiver, minimizes false alarms from non-system transmissions on the same carrier frequency and with the same mid-frequency modulation, and permits detection of intentional jamming of the receiver as well as other forms of sabotage to the surveillance system.

Claims

1. Cargo container monitoring system comprising:

a plurality of transmitter units each adapted for separate attachment to different cargo containers and each comprising;

a radio frequency oscillator and antenna;

means for generating a mid-frequency signal and for modulating the signal from said radio frequency oscillator;

circuit means operating at a low frequency up to about 1000 Hz connected to continuously interrupt said mid-frequency signal and including a device for controlling frequency of said interruptions with sufficient precision to enable a transmitter unit to be distinguished from other transmitter units in the system; and

a sensing element connected to cause initiation of a transmitter signal;

and

a receiver station having an antenna adapted to receive signals from a transmitter antenna and comprising;

a radio frequency section connected to said antenna;

circuit means including a bandpass filter for passing said mid-frequency signal connected to receive an output signal from said radio frequency station;

a circuit including a frequency selective unit connected to receive an output signal from said bandpass filter responsive only to the interruption rate at said low frequency of said mid-frequency signal for selectively producing a signal; and

an alarm circuit connected to be actuated in response to the signal from said frequency selective unit.

2. The monitoring system according to claim 1 wherein the receiver station includes a plurality of circuits connected to receive the output signal from said band-pass filter with each circuit having a separate frquency selective unit to produce an output signal in response to a different low frequency interruption rate, and a separate alarm circuit connected to be actuated by the output signal from a respective frequency selective unit.

3. The monitoring system according to claim 2 comprising a plurality of cargoes located in groups with each group defining a different zone and wherein all of the frequency interruption control devices associated with the transmitters attached to the cargoes in each zone operate at the same interruption rate and one of each of said separate alarm circuits corresponds to one of each of said zones.

4. The monitoring system according to claim 1 wherein the receiver station antenna is connected to the radio frequency section by a coaxial cable including a central conductor and outer grounded sheath and wherein said receiver station further comprises means for detecting a break in said cable comprising a source of voltage, an electrical current indicator, and means for connecting said indicator to said voltage source through a circuit including the central conductor and the outer sheath of said cable and the cable connection to said antenna.

5. The monitoring system according to claim 1 wherein each of said transmitter units has an output signal power less than about one watt at a predetermined radio frequency and the receiver station includes means for detecting jamming of the system comprising a jamming alarm connected to a signal level detector actuated in response to the detection of said predetermined radio frequency at a signal level in excess of that produced by a nearby one watt transmitted signal over an interval of time greater than about 3 seconds.

6. The monitoring system according to claim 1 wherein the alarm circuit further includes an alarm element and a timing circuit connected to receive the signal from said frequency selective unit, said timing circuit requiring the continuous presence of the signal from said frequency selective unit for a period of at least 3 seconds before producing a signal for actuating said alarm element.

7. The monitoring system according to claim 1 wherein each transmitter unit is in a separate housing containing a power battery, said radio frequency oscillator, said mid-frequency signal generating means, said low frequency circuit means and said sensing element, and wherein the sensing element includes a switch contact that is normally open but which is closed momentarily when subjected to an acceleration force, and the transmitter unit further comprises in said housing a timing circuit connected to be initiated in response to opening of said switch contact to limit the period of a transmitted signal to a predetermined time interval to have a duration between about 12 and 30 seconds.

8. The monitoring system according to claim 7 wherein each of said transmitter units has an output signal power less than about 1 watt at a frequency of approximately 27 MHz and a radiation system having a plurality of elements of conductive material mounted in spaced planes substantially parallel to a metal surface of said cargo container, said metal surface having a height and width of approximately 9 ft. and one of said radiation system elements comprises a loop of wire free of any direct electrical connection to the metal surface of the cargo container and having a size greater than 14 gauge;

and the receiver station antenna is connected to the radio frequency section by a coaxial cable including a central conductor and outer grounded sheath with the receiver station further comprising means for detecting a break in said coaxial cable comprising a source of voltage, an electrical current meter, and means for connecting said meter to said voltage source through a circuit including the central conductor and the outer sheath of said coaxial cable and the cable connection to the antenna; and

wherein said radio frequency section includes means for detecting jamming of the system comprising a jamming alarm connected to a signal level detector actuated in response to detection of the transmitted signal at a signal level in excess of that produced by a nearby 1 watt transmitted signal over an interval of time greater than about 3 seconds.

9. Cargo container monitoring system comprising:

a plurality of transmitter units each adapted for separate attachment to different cargo containers which have a door having a metal surface through which cargo is adapted to be loaded and unloaded and each comprising;

a radio frequency oscillator and antenna radiation system having a plurality of elements of conductive material in spaced planes substantially parallel to each other and to the metal surface of said door, and the transmitted radio frequency signal has a wavelength which is approximately four times the width or height of the metal surfaces of a container wall having said door;

means for generating a mid-frequency signal and for modulating the signal from said radio frequency oscillator;

circuit means operating at a low frequency up to about 1000 Hz connected to momentarily interrupt said mid-frequency generator signals and including a plug-in device for controlling frequency of said interruptions with sufficient precision as to enable a transmitter unit to be distinguished from other transmitter units in the system;

a sensing element connected to cause initiation of a transmitter signal;

and

a receiver station having an antenna adapted to receive signals from a transmitter antenna and comprising;

a radio frequency section connected to said antenna;

circuit means including a bandpass filter for passing said mid-frequency signal connected to receive an output signal from said radio frequency station;

a circuit including a frequency selective plug-in unit connected to receive an output signal from said bandpass filter responsive to the interruption rate of said mid-frequency signal for selectively producing a signal; and

an alarm circuit connected to be actuated in response to the signal from said frequency selective unit.

10. The monitoring system of claim 9 wherein one of the transmitter radiation system elements comprises a loop of wire free of any direct electrical connection to the metal surface of the cargo container and having a size greater than 14 gauge, the height and width of the metal surface container wall are both approximately nine feet, and the transmitted frequency is approximately 27 MHz.

11. A cargo container monitoring system characterized by having separate transmitter units attached to different cargo containers with each of said transmitter units having an output signal power less than about one watt at about 27 MHz, said transmitter units being normally de-energized, a motion responsive unit for each transmitter unit for energizing the transmitter unit, means for limiting the duration of each transmitted signal from said transmitter unit to a period of between about 12 and 30 seconds after cessation of a motion which caused energization of said transmitter unit, and a central station located in the vicinity of but remotely from said containers has a receiver with an incoming radio frequency signal level detector responsive to signals at about 27 MHz, and means for detecting jamming of the system including a jamming alarm connected to a signal level detector actuated in response to the detection of radiation energy at about 27 MHz having a signal level in excess of that produced by a nearby one watt transmitted signal over an interval of time greater than about 3 seconds.

12. A cargo container monitoring system characterized by having separate transmitter units attached to different cargo containers with each cargo container having a door with a metal surface through which cargo is adapted to be loaded and unloaded, and each of said transmitter units having a radiation system including a plurality of elements of conductive material mounted in spaced planes substantially parallel to the metal surface of said door, and an output signal power less than about one watt at about 27 MHz to have a wavelength approximately four times the width or height of the metal surface of a container wall having said door, said transmitter units being normally de-energized, a motion responsive unit for each transmitter unit for energizing the transmitter unit, means for limiting the duration of each transmitted signal from said transmitter unit to a period of between about 12 and 30 seconds after cessation of a motion which caused energization of said transmitter unit, and a central station located in the vicinity of but remotely from said containers having a receiver with an incoming radio frequency signal level detector responsive to signal at said about 27 MHz, and means for detecting jamming of the system including a jamming alarm connected to a signal level detector actuated in response to the detection of radiation energy at said about 27 MHz having a signal level in excess of that produced by a nearby one watt transmitted signal over an interval of time greater than about 3 seconds.

13. The monitoring system of claim 12 wherein one of the transmitter radiation system elements comprises a loop of wire free of any direct electrical connection to the metal surface of the cargo container and having a size larger than 14 gauge, and the height and width of the metal surface of said container wall are approximately nine feet.

14. An alarm system for monitoring a plurality of movable objects each of which has a wall with a substantially flat metal surface, the system comprising a plurality of transmitter units each including means for mounting the transmitter unit on one of the objects, means for transmitting a coded radio frequency signal from each respective transmitter unit upon movement of the object to a predetermined extent, said flat metal surface on said object having a dimension that is approximately one fourth of the wavelength of said radio frequency signal and the transmitter unit being mounted adjacent said metal surface at the approximate midpoint of said dimension, said radio frequency signal including an intermediate frequency modulation signal that is precisely controlled by a low frequency, narrow band modulation signal unique to each of said plurality of transmitter units, and a receiver including means for detecting the unique signals from the plurality of transmitter units and an alarm means responding only to the presence of the low frequency modulation signal.

15. An alarm system for monitoring a plurality of movable objects, comprising a plurality of transmitter units each including means for mounting the transmitter unit on one of the objects, means for transmitting a coded radio frequency signal from each respective transmitter unit upon movement of the object to a predetermined extent, said radio frequency signal including an intermediate frequency signal that is further modulated by a narrow band modulation signal having a frequency less than 1000 Hz that is generated by a crystal controlled tuning fork and unique to each of said plurality of transmitter units, and a receiver including means for detecting the unique signals from the plurality of transmitter units comprising a band pass filter for passing said intermediate frequency signal and a plurality of detector circuits each containing a separate crystal controlled tuning fork operative at different frequencies corresponding to different frequencies generated by the crystal controlled tuning forks in said transmitter units, an an alarm means responding only to the presence of a tuning for, frequency signal.

16. An alarm system according to claim 15, wherein the low frequency modulation signal is precisely controlled to within ±

3 cycles.

17. A method of maintaining mobile cargo containers under surveillance while stored in a transportation terminal having a central station including a console with a plurality of alarm devices by use of a wireless radio system comprising:

removably attaching a battery powered transmitter unit to the door of the cargo container while the cargo container is located in the transportation terminal;

positioning a transmitter antenna element along a central portion of the container metal side wall having a dimension of approximately nine feet;

providing a transmitter circuit in said transmitter unit having a maximum power output of less than about 1 watt;

operating said transmitter circuit to generate a radio frequency signal having a wavelength approximately four times greater than said dimension of said container sidewall to thereby utilize the cargo container as a radio frequency radiating element for the transmitter unit; and

removing said transmitter unit from the cargo container when the cargo container is to be no longer under surveillance.

18. A method of maintaining mobile cargo containers under surveillance when stored in a transportation terminal by use of a wireless radio system comprising:

removably attaching a battery powered transmitter unit to a cargo container under surveillance while the cargo container is located in the transportation terminal adjacent a central monitoring station;

energizing the transmitter circuit in response to a variation of a condition being monitored for a brief period of at least 10 seconds and otherwise maintaining the transmitter circuits in a non-operating condition;

modulating a carrier signal which for all the transmitters in the system is at the same radio frequency with a mid-frequency signal that is also substantially the same for all transmitted signals for the transmitters in the system;

interrupting the mid-frequency signal at a predetermined low frequency less than about 1000 Hz generated by a first circuit means controlling said low frequency to be within about ±

3Hz of a predetermined value;

detecting at the receiver station the interruption at the predetermined low frequency rate of the mid-frequency signal by a second circuit means substantially identical to said first circuit means;

generating an alarm at the central station only in response to the detection of the interruption at the predetermined low frequency rate of the mid-frequency signal for a preselected minimum time interval to thereby prevent false alarm signals from other carrier waves containing said mid-frequency signal; and

removing said transmitter unit from the cargo container when the cargo container is to be no longer under surveillance.

19. A method of maintaining mobile cargo containers having a metal sidewall with a predetermined dimension under surveillance when stored in a transportation terminal by use of a wireless radio system comprising:

removably attaching a battery powered transmitter unit near a center portion of the metal side wall of a cargo container under surveillance while the cargo container is located in the transportation terminal adjacent a central monitoring station;

utilizing the cargo conainer as a radiating element for the transmitter carrier wave;

energizing the transmitter circuit to generate a carrier wave frequency having a wavelength that is approximately four times greater than said container sidewall dimension in response to a variation of a condition being monitored for a brief period of at least 10 seconds and otherwise maintaining the transmitter circuits in a non-operating condition;

modulting a carrier signal which for all of the transmitters in the system is at the same radio frequency with a mid-frequency signal that is also substantially the same for all transmitted signals for the transmitters in the system;

interrupting the mid-frequency signal at a predetermined low frequency rate;

detecting at the receiver station and generating an alarm at the central station in response to the detection of the interruption at the predetermined low frequency rate of the mid-frequency signal for a preselected minimum time interval to thereby prevent false alarm signals from other carrier waves containing said mid-frequency signal; and

removing said transmitter unit from the cargo container when the cargo container is to be no longer under surveillance.

20. The method according to claim 19 wherein the carrier frequency of all the transmitter units in the system is approximately 27 MHz, the mid-frequency signal has a frequency in the range of from 3 to 20 KHz, and the frequency of the interrupting signal is in the range of 200 to 800 Hz.