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Browse Prior Art Database

Capacitance Check for Cable Integrity

IP.com Disclosure Number: IPCOM000106411D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 4 page(s) / 90K

Publishing Venue

IBM

Related People

Donovan, PA: AUTHOR

Abstract

A method using capacitance to test a cable consisting of multiple twisted pairs is disclosed. An example of such a cable is shown in Figs. 1 and 2. Fig. 1 depicts a cable which consists of a D-shell connector and eight Twin-X connectors joined together by eight twisted pairs of wire. Fig. 2 shows a cross sectional view of the same cable. Although these figures represent a specific cable configuration, the method can be applied to any cable of similar construction.

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Capacitance Check for Cable Integrity

      A method using capacitance to test a cable consisting of
multiple twisted pairs is disclosed.  An example of such a cable is
shown in Figs. 1 and 2.  Fig. 1 depicts a cable which consists of a
D-shell connector and eight Twin-X connectors joined together by
eight twisted pairs of wire.  Fig. 2 shows a cross sectional view of
the same cable.  Although these figures represent a specific cable
configuration, the method can be applied to any cable of similar
construction.

      Fig. 3 depicts the cable shown in Fig. 1 as having a wiring
fault.  The fault being the A4 and A5 connections are swapped along
with the A4' and A5' connections.  If this cable is tested using only
resistance measurements, it will test good.  Subsequently the faulty
cable gets installed into a product and the equipment attached to
connectors 4 and 5 fails to operate properly.  The failure is due to
cross coupling of signals between twisted pairs 4 and 5.  This leads
to signal degradation and a noisy operating environment for equipment
connected to those terminals.

      Since capacitance between two conductors is inversely
proportional to the distance between them, a faulty cable can be
detected by making capacitance measurements across each set of
twisted pair terminals.  Referring to Fig. 3, the capacitance between
A2 and B2 will be more than the capacitance between A4 and B4 or A5
and B5.  This is because the distance between the two...