Fault detection method and apparatus for multiconductor cables

An apparatus of the type employed for detecting the existence of physical faults in a multiconductor cable having paired conductors exhibiting a capacitive effect at the terminations thereof wherein said apparatus includes a relay circuit means, a timing circuit means coupled to said relay circuit means for timing the operation of said relay circuit means, a meter means coupled to said relay circuit means and, a source of battery potential operatively coupled to said meter means to periodically charge and discharge each selected cable pair in accordance with the timing of said relay circuit means by said timing circuit means to cause an average reading on said meter means indicating the magnitude of the capacitance exhibited by the selected pair of conductors, the combination therewith comprising:

• an amplification circuit means and range selector switching means;
• said range selector switching means having a first position coupled to said meter means for connecting said battery potential substantially directly through said meter means and said relay means and for charging said selected pair of cable conductors, and having at least a second position for connecting said battery potential to said amplification circuit means and for connecting said relay means to the input of said amplification circuit means and said meter means to the output of said amplification circuit means so as to amplify the charging voltage periodically applied to the cable pair through said relay means in order to increase the average level of charging current registered by said meter means for relatively short lengths of cable.

A method of detecting the existence of physical faults such as shorts, grounds, opens, crosses, splits and punchbacks in a multiconductor cable composed of paired tip and ring conductors of a telephone transmission system comprising:

• physically connecting a plurality of the pairs of tip and ring conductors to a test instrument;
• selecting individual ones of said pairs of conductors for connection to a test circuit included in said test instrument;
• periodically applying a voltage pulse across said selected tip and ring conductors;
• measuring an average current flow through said tip and ring conductors caused by said periodic application of the voltage charging pulse;
• and
• selectively amplifying said average current flow through said tip and ring conductors as necessary to maintain a reference level of current flow at the selected conductor pair as the length of cable associated with such selected pair decreases with a commensurate decrease in the distributed capacitance associated therewith, whereby the measuring of the average current flow of the periodically applied and selectively amplified voltage pulse across the tip and ring conductors provides the detection of the physical faults.