US 5,448,222 A · Coupled transmission line sensor cable and method

Abstract

A transducer cable includes an inner conductor, an outer conductor, and dielectric between the inner conductor and the outer conductor. A longitudinal passage and a sense wire loosely disposed therein extend through the dielectric. Movement, (e.g., intruder-caused vibration) of the transducer cable results in movement of the sense wire relative to the outer conductor, causing corresponding changes in characteristic impedance of the sense wire. A carrier signal transmitted down the inner conductor produces an electromagnetic field that couples energy to the sense wire. The change in characteristic impedance causes reflection of some of the coupled energy, which produces a corresponding signal that is sensed by a receiver circuitry. The receiver circuitry produces a signal indicating the occurrence of the intruder-caused vibration. The receiver circuitry includes a system that digitizes the received signals at successive times that correspond to successive sections of the cable, performs digital filtering to eliminate a cable profile or clutter response, and produces target response values for sections of the cable that undergo changes in characteristic impedance. Target responses in several adjoining sections are interpolated to precisely locate the intrusion activity causing the vibrations.

Claims39

Dependent claims

A transducer cable comprising in combination:

(a) a first conductor;
(b) a second conductor;
(c) solid non-magnetic dielectric material between the first conductor and the second conductor generally parallel to the first conductor,
(d) a longitudinal passage generally parallel to the first and second conductors extending through the non-magnetic dielectric material;
and
(e) a sense wire extending through the passage and having a cross section substantially smaller than that of said passage so that the sense wire fits loosely in said passage, so that physical movement of the transducer cable results in free movement of the sense wire relative to one of the first and second conductors, resulting in corresponding changes in the characteristic impedance of a first transmission line formed by the sense wire and the one of the first and second conductors.

3 more elements

A method of sensing physical movement of a portion of a transducer cable including a first conductor surrounding a dielectric, a second conductor surrounded by the dielectric, and a flexible sense wire, the method comprising the steps of:

(a) providing a passage through the dielectric extending the length of the transducer cable, and placing the sense wire to extend through the passage, the sense wire fitting loosely in the passage such that the physical movement and consequent relative transverse movement of the sense wire in the passage results in a change in characteristic impedance of a first transmission line formed by the first conductor and the sense wire at the location of the movement;
(b) transmitting a carrier signal from a first end of the transducer cable down a second transmission line formed by the first conductor and the second conductor;
(c) coupling energy from the carrier signal to the first transmission line, and reflecting a portion of the coupled energy at the location;
(d) measuring a first signal produced on the sense wire by the reflected energy;
and
(e) determining the location of the movement by measuring an amount of time required for the first signal to propagate from the location of the movement to the first end of the transducer cable.

3 more elements

An intrusion detection system, comprising in combination:

(a) a transducer cable including
i. an inner conductor,
ii. an outer conductor,
iii. dielectric material between the inner conductor and the outer conductor, the outer conductor being tubular, the dielectric material being inside the outer conductor,
iv. a longitudinal passage extending through the dielectric material, and
v. a sense wire extending through the passage and loosely fitting therein so that vibration or flexing of the transducer cable results in movement of the sense wire relative to the outer conductor, causing corresponding changes in the characteristic impedance of a first transmission line formed by the outer conductor and the sense wire;
(b) a transmitting circuit adapted to transmit a RF signal from a first end of the transducer cable down a second transmission line formed by the inner conductor and the outer conductor, an electromagnetic field being produced inside the outer conductor by the carrier signal and coupling energy to the first transmission line, an intrusion activity causing movement, such as vibration or flexing, of the transducer cable resulting in movement of the sense wire relative to the passage and changing an characteristic impedance of the first transmission line at the portion thereof undergoing the relative movement, the characteristic impedance change causing a reflection of a portion of the coupled energy back along the first transmission line toward the first end, the sense wire carrying a first signal resulting from the reflected energy;
(c) a receiver circuit connected to receive the first signal at the first end to amplify and filter high frequency components from the first signal to thereby produce a second signal;
(d) an analog-to-digital converter connected to receive the second signal;
(e) a control circuit connected to apply a conversion signal to the analog-to-digital converter, the conversion signal including a plurality of pulses timed to cause the digital-to-analog converter to digitize values of the second signal representing responses of a plurality of different portions of the transducer cable to the second signal, respectively;
and
(f) a processor adapted to receive the digitized values, perform a high pass digital filtering operation on the digitized values to isolate a disturbance component from a clutter response component thereof, perform an interpolating operation on the isolated disturbance component to determine a peak value and a corresponding location along the transducer cable, compare the peak value to a stored threshold value for the corresponding location, and generate an alarm signal if the peak value succeeds the threshold value.

9 more elements

A method of operating a transducer cable in an intrusion detection system, the transducer cable including a first conductor, a second conductor, and non-magnetic solid dielectric material between the first conductor and the second conductor generally parallel to the first conductor, the method comprising the steps of:

(a) providing a longitudinal passage extending through the dielectric material approximately parallel to the first and second conductors, and providing a sense wire extending through the passage, said sense wire having a cross section substantially smaller than that of said passage so that the sense wire fits loosely in said passage;
(b) physically moving the cable in response to an intrusion act;
and
(c) moving the sense wire within the passage, hence causing free movement of the sense wire relative to the first and second conductors, thereby causing a corresponding change in a characteristic impedance of a first transmission line formed by the sense wire and the second conductor.

1 more element

Dependencies are inferred from the claim text.

Coupled transmission line sensor cable and method

Life of this patent

Coupled transmission line sensor cable and method

Life of this patent

Abstract

Claims39