Apparatus and method for improving a time domain reflectometer

• US 5,461,318 A
• Filed: 06/08/1994
• Issued: 10/24/1995
• Est. Priority Date: 06/08/1994
• Status: Expired due to Fees

• Current Assignee: Douglas A. Hartzell, Edward J. Thomassen, Lee M. Rezac, Marshall B. Borchert
• Original Assignee: Douglas A. Hartzell, Edward J. Thomassen, Lee M. Rezac, Marshall B. Borchert
• Inventors: Borchert, Marshall B., Rezac, Lee M., Thomassen, Edward J., Hartzell, Douglas A.
• Primary Examiner(s): Regan, Maura K.
• Application Number:
  US08/255,352
• Time in Patent Office: 503 Days
• Field of Search: 324/522, 324/527, 324/525, 324/532-535, 324/541, 324/543, 324/544, 324/551, 379/26
• US Class Current: 324/533
• CPC Class Codes: G01R 1/025 concerning dedicated user interfaces, e.g. GUI, or dedicated keyboards G01R31/31912 takes precedence
• CPC Class Codes: G01R 31/11 using pulse reflection methods

Abstract

A method for detecting impedance discontinuities in two-conductor cable includes the initial step of transmitting a pulse of energy onto the cable and receiving any reflected pulses at a base location. The distance to the discontinuity is calculated by measuring the elapsed time between the transmitted and received pulses. A waveform is created on a display screen to shown the transmitted and reflected pulses, by taking a plurality of horizontal samples along the cable, and calculating a vertical value for each horizontal sample taken. Each horizontal sample is then converted to digital form and displayed on the screen. Another step in the method includes determining the gauge of the cable and then subtracting the exponential decay of the transmitted pulse waveform based upon that determined cable gauge so as to create a modified transmitted pulse which is displayed on the screen. The method also includes the step of adjusting the calculation of the distance to the discontinuity so as to account for a decrease in the velocity of propagation of the transmitted and received pulses over the length of the cable. A method for detecting a bridge tap in a twisted pair cable includes the steps of transmitting a pulse of energy onto the cable and receiving any reflected energy pulses at a base location. The gauge of the cable is then determined and the phase of any reflected energy pulses are determined. The amplitude and distance from the base location is determined for each reflected pulse which is out of phase relative to the transmitted energy pulse, to create pulse values. These pulse values are then compared with predetermined pulse values for the particular cable gauge and type to identify the location of a pulse value which is within a predetermined range of pulse values for a bridge tap discontinuity.

Claims

1. A method for detecting impedance discontinuities in two-conductor cable and displaying their location, comprising the steps of:

transmitting a pulse of energy on to the cable at a base location;

receiving any reflected pulses at the base location;

measuring the elapsed time from the transmission of the pulse to the receipt of any reflected pulses;

calculating the distance from the base location to a discontinuity causing a reflected pulse;

determining the gauge of the cable;

determining the exponential decay of the waveform of the transmitted pulse based upon the determined cable gauge;

subtracting the exponential decay from the value of the transmitted pulse to create a modified transmitted pulse value; and

creating a waveform on a display screen showing the modified transmitted pulse and any reflected pulses.

2. The method of claim 1, wherein the step of determining the cable gauge includes the steps of:

(a) taking a predetermined number of horizontal samples along the cable to fill a horizontal length of a display screen;

(b) determining a value for a baseline ahead of the transmitted pulse waveform;

(c) determining a preliminary initial value of the first horizontal sample on the following side of the transmitted pulse waveform;

(d) selecting a decay slope from a plurality of predetermined decay slopes, based upon the preliminary initial value; and

(e) selecting a cable gauge by matching said decay slope one of a plurality of decay slopes in a look up table having different decay slopes based upon a variety of initial values and wire gauges for various pulse widths.