Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Patent
1987-03-30
1989-05-30
Eisenzopf, Reinhard J.
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
324539, G01R 3102
Patent
active
048354791
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to apparatuses for testing cables. Such an apparatus is particularly useful for the semi-automatic testing of multicore cables.
According to one aspect of the invention, there is provided an apparatus for testing for leakage between cores of a multicore cable, broadly comprising first means for connection to one end of the cable while the other end of the latter remains disconnected, second means for applying a test voltage through the first means to a first cable core for a predetermined period, third means for connecting and setting each remaining cable core in turn through the first means to a predetermined voltage during an initial portion of the predetermined period and for disconnecting each of the said remaining cable cores in turn from the predetermined voltage at the end of the said initial portion of the predetermined period, and fourth means for detecting current in each of the said remaining cores.
Preferably the first means for applying a test voltage comprises a test voltage source and first switch means for connecting in turn each of at least some of the cable cores to the voltage source through a suitable connector constituting the first means. Preferably the fourth or detecting means comprises an ammeter or a voltmeter and second switch means for connecting in turn each of at least some of the cable cores to the ammeter or voltmeter.
The switch means preferably comprise electrically or electronically operable switches, for instance electromagnetic relays, driven by a counter so as to provide automatic switching of the cores. Preferably means are provided for storing and/or displaying an indication of any cores between which leakage is detected.
Preferably the third setting means comprises third switch means for connecting momentarily the second core to a reference potential, for instance earth. Preferably the third switch means is arranged to be actuated immediately after each actuation of the first or second switch means. The third switch means may comprise an electromagnetic relay whose contact is in parallel with a semiconductor switch, for instance a transistor of an optocoupler or opto-isolator.
When testing for leakage or insulation faults in multicore cables, every combination of pairs of cores must be tested. For a cable comprising N cores, the number of combinations of pairs is (N-1)+(N-2)+ . . . +3+2+1=(N.sup.2 +N)/2-N, and manual checking is tedious, laborious, and time-consuming. For a cable of substantial lenght, there is substantial and practically unpredictable capacitance between each pair of cores and, unless care is taken, the effects of this capacitance can upset testing and give rise to spurious and incorrect results.
The apparatus defined above makes it possible to provide automatic or semi-automatic testing of a cable rapidly and reliably. By charging each core fully prior to testing, the cable effects mentioned above are overcome and speed of operation is limited essentially by the period during which the setting means must be allowed to operate in order to permit the core to be reliably charged. The use of a semiconductor switch allows the charging means to begin charging the core very rapidly, and the provision of a parallel relay contact allows charging to be completed beyond the point where, for instance, the finite conduction cut-off collector-emitter voltage would prevent the semiconductor switch from totally charging the core.
According to another aspect of the invention, there is provided an apparatus for testing a multicore cable, comprising a plurality of test resistors of different values and each having a first terminal connected to a common line and a second terminal arranged to be connected to a respective one of at least some of the cable cores at one of the cable, and means for determining whether the resistance between the common line and each of the at least some cores at the other end of the cable is within a predetermined range corresponding to the respective test resistor to which the core is connected.
Preferably th
REFERENCES:
patent: 4015200 (1977-03-01), Strandh
patent: 4384249 (1983-05-01), Medina
patent: 4418312 (1983-11-01), Figler et al.
"Cable Tester" by G. Formica, IBM Technical Disclosure Bulletin, vol. 16, No. 12, (May 1974), pp. 3973-3974.
Eisenzopf Reinhard J.
Regan Maura K.
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