| 摘要 |
A test apparatus for use with cables of the type used in telephone circuits comprising a plurality of two-wire conductive pairs exhibiting fixed resistance and capacitance per unit length. The apparatus can be used to locate a high resistance short involving two conductive wires. A precision a.c. signal or tone at a continuous, fixed frequency is applied to the wires. The phase angle resulting from the conductive and resistive portions of current flowing in the wires relative to the applied signal is determined. Current flow is sensed inductively and the presence of the conductive pair of interest is determined to be at those locations where the measured phase angle is substantially identical. In determining the location of a high resistance short, the current in the pair is sensed along its length and the point of the short is indicated as that point where the measured phase angle makes a substantial change. In the preferred embodiment, matched low-drift oscillator circuits are employed in the tone sending transmitter and the tone receiver. The two circuits are trimmed to be matched in frequency and phase prior to the beginning of the testing such that the two remain in sequence at least for the duration of the testing. The comparison of phase angle in the receiver is between the measured signal and the matched oscillator frequency.
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