Method and apparatus for detecting faults and locating conductors in multi-conductor cables

• US 3,882,287 A
• Filed: 04/20/1973
• Issued: 05/06/1975
• Est. Priority Date: 04/20/1973
• Status: Expired due to Term

• Current Assignee: James F. Simmonds
• Original Assignee: James F. Simmonds
• Inventors: Simmonds, James F.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Olms, Douglas W.
• Application Number:
  US05/353,210
• Time in Patent Office: 746 Days
• Field of Search: 179/175.3A 324/66 330/109 325/465,463 328/138
• US Class Current: 379/25
• CPC Class Codes: G01R 31/083 in cables, e.g. underground
• CPC Class Codes: G01R 31/60 Identification of wires in a multicore cable
• CPC Class Codes: H04B 3/46 Monitoring; Testing

Abstract

Detecting faults and identifying conductor parts multiconductor telephone cables is many times necessary in the maintenance of a telephone communication system. The disclosed method and apparatus for this purpose includes a tone generator for connection to a telepone conductor pair at a first location of a cable and a receiver unit having a frequency tunable amplifier, a signal detection pickup coil or probe, and a headset connected to the tunable amplifier for use at a remote cable location to detect tones imposed on the pair at the first location. The method utilizes a tone generator which has a nominal signal frequency for use at the first cable location in conjunction with a pair of cable wires. The receiving unit is temporarily coupled to the wires at the first location so that the amplifier may be tuned to the precise frequency generated by the tone producing device. The receiving unit is then carried to the remote cable position and the probe or pick-up coil is used to sense the presence of signals generated. Because the amplifier has been tuned to the precise frequency of the signal provided by the tone generator, even weak signals may be detected in the presence of considerable interference from external source. A threshold circuit is provided at the output of the tunable amplifier to enable rejection of low level interference signals and to further improve the resolution of the detection equipment.

Claims

1. A method for detecting and locating faults and/or identifying conductors in a multiconductor cable comprising the steps of:

connecting one of a plurality of tone generators all having a known nominal frequency but wherein the precise frequency of any given such generator varies from said nominal frequency and is thus unknown to one or more conductors of the cable at a first location thereon;

temporarily coupling a tunable frequency amplifier having a manual adjustment to said tone generator or to a point adjacent the connection of said generator to said cable;

tuning the tunable amplifier by means of said manual adjustment to the precise frequency emitted by said generator;

decoupling the tunable frequency amplifier from said first location; and

sensing the presence or absence of the applied tone generator signal on said cable at a location remote from said first location by applying a signal from a pick-up means to said tunable frequency amplifier; and

monitoring the amplified output available from said amplifier for the presence or absence of the tone signal at said remote location.

2. The method of claim 1, in which said step of tuning said tunable frequency amplifier comprises the sub-steps of:

converting a second tunable frequency stage of such amplifier to a straight gain stage;

tuning a first stage of said amplifier to match the frequency produced by said tone generators;

reconverting said second stage to a tunable frequency stage and fine tuning said second stage to the precise frequency of said tone generator.

3. Apparatus for detecting faults and/or locating and identifying conductors of a multi-conductor cable in which a signal generator is used for applying low frequency signals to certain conductors of the cable wherein the precise frequency of such signals is unknown, comprising:

a receiving unit adapted to be connected to a pick-up means for sensing the signal applied to the cable conductors and adapted to be connected to an audio transducer means for producing an audible tone in response to a signal sensed by said pick-up means, said receiver unit having a tunable amplifier means for tuning said receiver to receive and amplify only said preecise frequency produced by said tone generator whereby signals of a different frequency are discriminated against by the receiver unit, and a selectable threshold circuit means connected between said tunable amplifier means and an output of said receiver unit for blocking the passage of amplified signals falling below a certain threshold amplitude level and allowing passage of amplified signals lying above said certain threshold amplitude level whereby weak stray signals of said precise frequency can be rejected to facilitate detection of desired tone signals of greater amplitude.

4. The apparatus of claim 3, wherein said tunable amplifier means comprises:

a first tunable amplification stage and a second tunable amplification stage connected in cascade to provide fine tuning of the precise frequency produced by said tone generator, and switching means and circuit means for selectively converting said second stage between a straight gain amplification stage and a tunable frequency selective stage, whereby said second stage may be disposed in a straight gain amplification condition during tuning of said first tunable stage of said amplifier means.

5. The apparatus of claim 3, said threshold circuit means comprising:

a switching means and a diode, said switching means having a first position connecting said diode between the output of said tunable amplifier means and the output of said rEceiver unit, and a second condition in which said diode is bypassed, such that said switching means enables said threshold circuit means when said diode is connected in said circuit and disables such circuit when said diode is bypassed.

6. Apparatus for detecting faults and/or locating and identifying conductors of a multi-conductor cable in which a signal generator is used for applying a low frequency signal to certain conductors of the cable wherein the precise frequency of such signal is unknown, comprising:

a receiving unit adapted to be connected to a pick-up mean for sensing the signal applied to the cable conductors and adapted to be connected to an audio transducer means for producing an audible tone in response to a signal sensed by said pick-up means, said receiver unit having a tunable amplifier means for tuning said receiver unit to receive and amplify only the precise frequency produced by said tone generator whereby signals of a different frequency are discriminated against by the receiver unit, said receiver unit having a gain control stage including first and second variable impedance sections and an amplifier having a feed-back circuit connected therearound, said first impedance section connected to vary the amount of current flow in said feed-back around said amplifier so as to cause a commensurate change in the signal gain provided thereby while maintaining a relatively high input impedance to said gain control stage for certain types of probing operations, and said gain control stage having a second impedance section connected to vary the input impedance to said amplifier causing a commensurate change in the effective gain thereof but also causing a decrease in the input impedance for lower gain settings, whereby the relatively high impedance variable gain control provided by said first impedance section is suitable for use in '"'"''"'"''"'"''"'"'probing'"'"''"'"''"'"''"'"' operations whereas the second impedance section is suitable primarily for '"'"''"'"''"'"''"'"'coiling'"'"''"'"''"'"''"'"' operations.

7. Apparatus for locating faults and identifying conductors of a multi-conductor telephone cable comprising:

a tone generator for connection to certain conductors of said cable at a first location therealong, in which the precise signal frequency developed by said generator is unknown or is subject to variation;

a receiver unit having a manually adjustable frequency tunable amplifier for being initially disposed proximate said generator and manually tuned to the precise frequency produced by said tone generator, said receiver unit having an input adapted to receive a signal from a pick-up means scanning said cable at a remote location from said generator and having an output adapted to be connected to a transducer means for audibly registering an amplified tone signal applied to the receiver unit input;

said frequency tunable amplifier of said receiver unit comprising;

first and second frequency tunable cascaded stages, said first stage providing relatively coarse tuning at the output thereof, and said second stage providing relatively finer tuning at the output thereof by virtue of the frequency selectivity of both said stages, switching means and circuit means for selectively converting said second stage between straight gain amplification and tunable frequency selective amplification, whereby said first stage may be tuned while said second stage is in its straight gain amplification condition, and thereafter said second stage may be tuned while in its tunable frequency selective condition.