US 5,206,640 A · Surveillance system

Abstract

A system for detecting and positioning objects, the electric conductivity of which differs from the surrounding medium thereof by measuring variations in an electric field generated into the medium. More precisely, the invention concerns a method and assembly for detecting objects or objectives, for example vessels, in electrically conductive medium, for example sea, by measuring changes, disturbances, signs, indications or the like caused by the object or objective, especially for surveying water fairways and/or extent. According to the invention, electric current is supplied in the extent to be surveyed via electrodes, magnitude of the current or magnitude of an electric field caused by the current is continuously or uncontinuously measured at selective points by a measuring device for observing when any object or objective to be detected is undetectable in the surveillance extent and when an object or objective to be detected is detectable is in the surveillance extent, and that measurement results originating from an undetectable object or objective and detectable object or objective are compared and differences observed are utilized for detection and/or positioning of the object or objective.

Claims33

Dependent claims

A method of detecting an anomaly, the anomaly being located in an electrically conductive medium, the method comprising the steps of:

arranging a plurality of current feeding electrodes and detecting devices in a predetermined manner, said predetermined manner including at least a pair of said detecting devices arranged generally in an equipotential surface;
generating at least two electric fields by means of at least two pairs of said current feeding electrodes, said at least two electric fields having different orientations;
measuring an electric field parameter between a said pair of said current feeding electrodes;
and
comparing said measured electric field parameter to an electric field reference parameter, said electric field reference parameter representing absence of the anomaly.

2 more elements

An apparatus for detecting an anomaly located in an electrically conductive medium, said apparatus comprising:

(a) means for supplying an electric field in said electrically conductive medium, said means comprising at least two pairs of current feeding electrodes located in such positions, that the electric fields generated have different orientations;
(b) a plurality of detection devices, said devices connected in pairs and placed in an area of said electrically conductive medium to be surveyed;
(c) an electronic assembly for providing an indication of a state of detection of the anomaly, the input of said assembly connected to said pairs of detection devices, said electronic assembly comprising an amplifier, a filter tuned at least to one of the frequencies used in the feeding current, and a display unit, said electronic assembly comprising:
(i) means for measuring an electric field parameter between said pair of detection devices;
(ii) means for comparing said electric field parameter to an electric field reference parameter, said electric field reference parameter representing absence of the anomaly;
and
(iii) a display system for displaying results obtained by said means for comparing;
and
(d) a switching system for connecting said current feeding electrodes to respective current sources and for connecting said detecting devices to respective electronic assemblies.

6 more elements

An arrangement for impairing detection of an object in an electrically conductive medium to be detected by means of an apparatus comprising:

(a) means for supplying an electric field in said electrically conductive medium, said means comprising at least two pairs of current feeding electrodes located in such positions, that the electric fields generated have different orientation;
(b) a plurality of detection devices, said devices connected in pairs and placed in an area of said electrically conductive medium to be surveyed;
(c) an electronic assembly for providing an indication of a state of detection of the anomaly, the input of said assembly connected to said pairs of detection devices, said electronic assembly comprising an amplifier, a filter tuned at least to one of the frequencies used in the feeding current, and a display unit, said electronic assembly comprising:
(i) means for measuring an electric field parameter between said pair detection devices;
(ii) means for comparing said electric field parameter to an electric field reference parameter, said electric field reference parameter representing absence of the anomaly;
and
(iii) display system for displaying results of said step of comparing;
and
(d) a switching system for connecting said current feeding electrodes to respective current source and for connecting detection devices to respective electronic assemblies, wherein:
said arrangement for impairing detection of said object comprises:
at least one electrode to be mounted on each of at least two sides of the object;
a measuring device for measuring said electric field parameter between at least two of said electrodes;
and
means for connecting a load between at least between two of said electrodes, whereas the impedance of said load is adjusted to a value, which makes the object look as the conductive medium round the object.

11 more elements

An arrangement for impairing detection of an object to be detected by means of an apparatus comprising:

(a) means for supplying an electric field in said electrically conductive medium, said means comprising at least two pairs of current feeding electrodes located in such positions, that the electric fields generated have different orientations;
(b) a plurality of detection devices, said devices connected in pairs and placed in an area of said electrically conductive medium to be surveyed;
(c) an electronic assembly for providing an indication of a state of detection of the anomaly, the input of said assembly connected to said pairs of detection devices, said electronic assembly comprising an amplifier, a filter tuned at least to one of the frequencies used in the feeding current, and display unit, said electronic assembly comprising:
(i) means for measuring an electric field parameter between said pairs detection devices;
(ii) means for comparing said electric field parameter to an electric field reference parameter, said electric field reference parameter representing absence of the anomaly;
and
(iii) display system for displaying results of said step of comparing;
and
(d) a switching system for connecting said current feeding electrodes to respective current source and for connecting detection devices to respective electronic assemblies, said arrangement for impairing detection comprising:
a tree-layer covering for at least one surface of the object to be detected, said tree-layer covering comprising:
(i) an inner-most layer having a good conductive properties;
(ii) a middle layer having a predetermined dielectric constants that, at highest measuring frequency of said electric field, the middle layer of the object has a conductivity generally equal to that of water;
and
(iii) an outer-most layer having a surface resistance so that, at low frequencies of said electric field, the outer-most layer of the object has a conductivity generally equal to that of water.

11 more elements

Dependencies are inferred from the claim text.

Surveillance system

Life of this patent

Surveillance system

Life of this patent

Abstract

Claims33