Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Patent
1988-08-25
1990-01-23
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
324536, 377 26, G01R 3108
Patent
active
048961140
DESCRIPTION:
BRIEF SUMMARY
Method and means for detecting a fault, e.g. a short circuit, break or leakage, in an electric cable or conductor, whereby two conductor pairs, one of which comprises the faulty conductor, are connected in such a way as to form a double loop, a voltage pulse being applied to one of the loops to locate the fault.
As the density and rates of traffic increase, especially in cables for data communication, maintaining the quality and reliability of cables requires a great deal of attention. It is important that cable faults be quickly and reliably located.
At present, accurate methods for detecting cable faults exist, in which a detector is connected to a pair in which one conductor is faulty and the other one intact, cable faults being generally due to discharges between the condcutors of a given pair. Voltage pulses are then fed into the conductor pair to `burn` through the defective area, producing a permanent short circuit, whereupon the distance of the fault from the detector can be calculated from a simple equation by using a Wheatstone bridge balanced with a precision potentiometer, the total length of the conductor being known.
`Conductor pair` in this context refers both to pairs consisting of ordinary conductors and to pairs consisting e.g. of one of the conductors in a coaxial cable and the cable shield acting as the other conductor.
While faults can be accurately located by this type of methods, they have the significant drawback that burning through the defective area involves a considerable risk of destroying other conductors in the vicinity of the pair under treatment, in which case several pairs or even the whole cable have to be replaced. For this reason and also because the detector used for indicating the measurement result, frequently a precision potentiometer, has to be correctly calibrated, reset and used with great precision to ensure correct results, applying such methods requires great skill.
The object of the present invention is to create a simple method and means by which cable faults can be located without the disadvantages mentioned. To achieve this object, the method of the invention is characterized in that a voltage pulse is applied to the intact branch of the double loop formed, the pulse voltage being adjusted according to the nature of the fault to a level sufficient to produce a malfunction, e.g. sparking, in the faulty loop, whereupon the current pulses produced at the ends of this loop are detected and the ratio of these current values is measured and translated into a distance of the fault from the detector.
The invention offers the advantages that the measuring equipment is light and simple, the measurement is easy to perform, the conductors are not subjected to long high-voltage pulses to produce a full short circuit condition between them, but instead a high-voltage pulse is fed into the intact loop, from which it jumps over via the defective area to the faulty conductor.
The device applying the method of the invention, consisting of a high-voltage pulse generator and circuits for measuring the currents produced in the defective conductor, is characterized in that the characteristic values of the current pulses produced in the defective loop and converted into voltages by means of resistors can be sensed at both ends of the loop by means of detectors, which feed the inputs of a digital voltmeter with voltages proportional to the characteristic values of the current pulses to indicate the ratio between them.
Other advantageous embodiments of the invention are characterized by what is presented in the claims to follow.
In the following, the invention is described in detail by the aid of an example, reference being made to the drawing attached, wherein:
FIG. 1 presents a typical form of the current pulses to be measured.
FIG. 2 presents the circuit principle of the device applying the method of the invention.
To measure the current pulse shown in FIG. 1, produced in the defective area of the conductor by an external high-voltage pulse, two methods as provided by the inven
REFERENCES:
patent: 1865687 (1932-07-01), Graf
patent: 3248646 (1966-04-01), Brazee
patent: 3284704 (1966-11-01), Lamont
patent: 4241305 (1980-12-01), Dickerson
patent: 4278931 (1981-07-01), Huggins
patent: 4424479 (1984-01-01), Brown
patent: 4446421 (1984-05-01), Berde
Eisenzopf Reinhard J.
Mueller Robert W.
Oy Elecid Ab
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