Method of performing non-interactive resistive fault location

• US 6,590,962 B1
• Filed: 06/21/2000
• Issued: 07/08/2003
• Est. Priority Date: 06/21/2000
• Status: Active Grant

• Current Assignee: Tollgrade Communications Incorporated (Enghouse Systems Limited)
• Original Assignee: Teradyne Incorporated
• Inventors: Zhang, Yun, Groessl, David J., Schmidt, Kurt E.
• Primary Examiner(s): TIEU, BINH KIEN
• Application Number:
  US09/598,595
• Time in Patent Office: 1,112 Days
• Field of Search: 379/1.01, 379/14.01, 379/12, 379/15.05, 379/22, 379/22.03, 379/27.07, 379/24, 379/25, 379/27.01, 379/29.01, 379/29.03, 379/29.04, 379/29.09, 379/30, 324/500, 324/512, 324/522, 324/525, 324/531
• US Class Current: 379/14.01
• CPC Class Codes: H04M 3/30 for subscriber's lines , for the local loop
• CPC Class Codes: H04M 3/305 testing of physical copper line parameters, e.g. capacitance or resistance locating faults in cables G01R31/08

Abstract

A method and apparatus to non-interactively test telephone networks and more specifically to localize faults such as resistive faults in the subscriber loop of the telephone network is presented. The method and apparatus determine whether the fault is in the tip line or ring line of a phone line. The existence of a fault voltage, if any, is also determined. The resistance of the tip line to ground and the resistance of the ring line to ground is measured. A fault resistance is calculated from this information, from which the location of the fault is determined.

Claims

1. A method of performing non-interactive resistive fault location identification comprising:

connecting a phone line to a test unit, said phone line having a tip line and a ring line;

determining whether the phone line has a resistive fault;

determining the presence of a fault voltage;

computing the resistance of a selected one of the tip line and the ring line between the unit and the fault using the determined fault voltage;

using the computed resistance to determine the length of the selected one of the tip line and the ring line between the test unit and the resistive fault.

2. The method of claim 1 wherein determining whether the phone line has a resistive fault comprises determining if said fault is on said tip line or on said ring line and the selected one of the tip and ring line is the line containing the fault.

3. The method of claim 2 wherein said step of determining if said fault is on said tip line or said ring line comprises:

connecting a voltage source providing a first voltage value to said tip line;

measuring a first current value of said tip line;

connecting a voltage source providing a second voltage value to said tip line and measuring a second current value of said tip line when said first current value of said tip line equals approximately zero;

connecting a voltage source providing a first voltage value to said ring line when said first current value of said tip line is non-zero and connecting a voltage source providing a second voltage value to said ring line when said first current value of said tip line is zero;

measuring a first current value of said ring line;

determining that a fault is on said tip line when either said first current value of said tip line or said second current value of said tip line is greater than said first current value of said ring line; and

determining that said fault is on said ring line when said first current value of said ring line is greater than either said first current value of said tip line or said second current value of said tip line.

4. The method of claim 3 wherein the step of determining the existence of a fault voltage comprises measuring the voltage between the line having the fault and ground.

5. The method of claim 3 wherein said step of computing a resistance between said tip line and said ring line comprises the steps of:

subtracting the fault voltage from a source voltage to obtain a voltage differential;

subtracting the current value of the ring line from the current value of the tip line to obtain a current differential; and

dividing said voltage differential by said current differential.

6. The method of claim 1 further comprising predicting an error based on at least one of said resistance between said tip line and said ring line and an error record database.

7. The method of claim 6 wherein said error record database comprises at least one of a look up table and an expert system.

8. A method of performing non-interactive resistive fault location identification comprising:

selecting a phone line, said phone line having a tip line and a ring line;

determining which of the tip line and the ring line contains a resistive fault;

determining the magnitude of a fault voltage;

applying a voltage to the line containing the resistive fault and measuring the current to thereby determine a line resistance using the determined magnitude of a fault voltage;

computing a fault location from the measured line resistance.

9. The method of claim 8 wherein said step of determining a fault feature comprises determining if said fault is on the tip line or on the ring line.

10. The method of claim 8 wherein said step of determining if said fault is on the tip line or on the ring line comprises:

connecting a voltage source providing a first voltage value to said tip line;

measuring a first current value of said tip line;

connecting a voltage source providing a second voltage value to said tip line and measuring a second current value of said tip line when said first current value of said tip line equals approximately zero;

connecting a voltage source providing a first voltage value to said ring line when said first current value of said tip line is non-zero and connecting a voltage source providing a second voltage value to said ring line when said first current value of said tip line is zero;

measuring a first current value of said ring line;

determining that a fault is on said tip line when either said first current value of said tip line or said second current value of said tip line is greater than said first current value of said ring line; and

determining that said fault is on said ring line when said first current value of said ring line is greater than either said first current value of said tip line or said second current value of said tip line.

11. The method of claim 10 wherein determining the existence of a fault voltage comprises measuring the voltage between the line having the fault and ground.

12. The method of claim 8 wherein said step of computing a fault resistance comprises:

determining the resistance between ground and the line not having a fault;

determining the line resistance from a central office to the fault; and

subtracting the line resistance from the central office to the fault from the resistance between ground and the line not having the fault.

13. The method of claim 8 wherein said step of predicting an error comprises predicting the error based on said resistance between said tip line and said ring line.

14. A method of performing non-interactive resistive fault location identification comprising the steps of:

selecting a phone line having a tip line and a ring line;

determining a fault feature;

determining the presence of a fault voltage;

measuring a resistance from a tip line to ground and from a ring line to ground;

determining the value of the fault voltage;

setting a source voltage to a predetermined value when said fault voltage is equal to approximately zero volts;

setting the source voltage to a value selected from the group consisting of approximately zero volts and the negative value of the fault voltage when said fault voltage is non-zero;

measuring a first ring voltage with a meter having a first impedance;

measuring a second ring voltage with a meter having a second impedance;

determining a final ring voltage from said first ring voltage and said second ring voltage;

measuring a first tip voltage with a meter having a third impedance;

measuring a second tip voltage with a meter having a fourth impedance;

determining a final tip voltage from said first tip voltage and said second tip voltage;

determining the tip resistance and ring resistance between the fault location and the central office from said final ring voltage and said final tip voltage;

computing a fault resistance from said the tip resistance and ring resistance between the fault location and the central office;

predicting an error from said fault resistance;

computing a fault location from said the tip resistance and ring resistance between the fault location and the central office; and

providing said fault location and said error.

15. The method of claim 14 wherein said step of determining a fault feature comprises determining if said fault is on the tip line or on the ring line.

16. The method of claim 15 wherein said step of determining if said fault is on the tip line or on the ring line comprises the steps of:

connecting a voltage source providing a first voltage value to said tip line;

measuring a first current value of said tip line;

connecting a voltage source providing a second voltage value to said tip line and measuring a second current value of said tip line when said first current value of said tip line equals approximately zero;

connecting a voltage source providing a first voltage value to said ring line when said first current value of said tip line is non-zero and connecting a voltage source providing a second voltage value to said ring line when said first current value of said tip line is zero;

measuring a first current value of said ring line;

determining that a fault is on said tip line when either said first current value of said tip line or said second current value of said tip line is greater than said first current value of said ring line; and

determining that said fault is on said ring line when said first current value of said ring line is greater than either said first current value of said tip line or said second current value of said tip line.

17. The method of claim 14 wherein the step of determining the existence of a fault voltage comprises the step of measuring the voltage between the line having the fault and ground.

18. The method of claim 14 wherein said step of determining a final ring voltage comprises the steps of:

obtaining a first value by subtracting said first impedance from said second impedance;

obtaining a second value by multiplying said first ring voltage by said second ring voltage;

obtaining a third value by multiplying said second ring voltage by said first impedance;

obtaining a fourth value by multiplying said second impedance by said first ring voltage;

obtaining a fifth value by multiplying said first value by said second value;

obtaining a sixth value by subtracting said third value from said fourth value; and

obtaining said final ring voltage by dividing said fifth value by said sixth value.

19. The method of claim 14 wherein said step of determining a final tip voltage comprises the steps of:

obtaining a first value by subtracting said third impedance from said fourth impedance;

obtaining a second value by multiplying said first tip voltage by said tip ring voltage;

obtaining a third value by multiplying said second tip voltage by said third impedance;

obtaining a fourth value by multiplying said fourth impedance by said first tip voltage;

obtaining a fifth value by multiplying said first value by said second value;

obtaining a sixth value by subtracting said third value from said fourth value; and

obtaining said final tip voltage by dividing said fifth value by said sixth value.

20. The method of claim 14 wherein said step of determining the tip resistance and ring resistance between the fault location and the central office from said final ring voltage and said final tip voltage comprises the steps of:

obtaining a first value by subtracting said final tip voltage from said final ring voltage;

obtaining a second value by subtracting said ring voltage from a source voltage;

obtaining a third value by multiplying a source impedance by said first value; and

obtaining a final value by dividing said third value by said second value.

21. The method of claim 14 wherein said step of computing a fault location comprises computing the fault location L according to the formula

22. The method of claim 14 wherein said step of computing a fault resistance comprises computing said fault resistance from said tip resistance and ring resistance between the fault location and the central office.

23. The method of claim 22 wherein said step of predicting an error comprises predicting an error from said fault resistance.