CABLE TESTING CIRCUIT EMPLOYING A PAIR OF DIODES TO DETECT SPECIFIC CONDUCTOR PAIR CONDITIONS

• US 3,818,329 A
• Filed: 08/01/1972
• Issued: 06/18/1974
• Est. Priority Date: 08/01/1972
• Status: Expired due to Term

• Current Assignee: AT&T, Inc.
• Original Assignee: Reaves A. Lee Jr
• Inventors: Reaves, A. Lee Jr.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US05/277,055
• Time in Patent Office: 686 Days
• Field of Search: 324/51,66,73,110,119,132,133,72.5
• US Class Current: 324/540
• CPC Class Codes: G01R 31/58 Testing of lines, cables or conductors testing of electric windings G01R31/72

Abstract

A test circuit in which the difference between the junction resistances of a pair of semiconductor diodes when forward biased and when reverse biased is employed to detect whether a conductor pair of an electrical cable is good, open, shorted, or reversed. A first and a second test bridge, one including a first of the diodes, a potential source, and a current level indicator, the other including only the second diode, are connected across the ends, respectively, of the conductor pair under test. The functional state of the conductor pair is read from the current level indicated.

Claims

1. An electrical test circuit comprising a first test bridging circuit adapted to bridge one end of a conductor pair, said first bridging circuit and said one end of said conductor pair each having electrical terminal means for completing a conducting path including the ends of said first bridging circuit and the one ends of the conductors of said conductor pair, respectively, said first bridging circuit comprising a source of potential, a first diode having a first resistance when forward biased and a second resistance when reverse biased, and current level sensing means;

and a second test bridging circuit adapted to bridge the other end of said conductor pair, said second bridging circuit and said other end of said conductor pair having electrical terminal means for completing a conducting path including the ends of said second bridging circuit and the other ends of the conductors of said conductor pair corresponding to said one ends of said conductor pair, respectively, said second bridging circuit comprising a second diode also having a first resistance when forward biased and a second resistance when reverse biased, said first and second bridging circuit and said conductor pair defining a first electrical circuit having a current present therein having levels as determined by the continuity of said conductor pair when said first and second diodes are forward biased and the reversal of said conductor pair when said second diode is reverse biased, said first bridging circuit and portions of said conductor pair defining a second electrical circuit shunting said second diode having a current present therein having a level as determined by the presence of a short between the conductors of said conductor pair.

2. An electrical test circuit as claimed in claim 1 in which said first test bridging circuit also comprises potentiometer mEans for calibrating said current level sensing means.

3. An electrical test circuit as claimed in claim 2 in which said current level sensing means comprises an ammeter means.

4. An electrical test circuit for testing an electrical cable having a plurality of conductor pairs comprising a first and a second test bridging circuit each including a unilateral conducting element having a first resistance when forward biased and a second resistance when reverse biased, said first bridging circuit also including a potential source and current level sensing means, and switch means for selectively connecting said first and second bridging circuits across one and the other end, respectively, of individual ones of said conductor pairs, said first and second test bridging circuit completing a first electrical circuit including a particular individual one of said conductor pairs having a current present therein of a level as determined by the continuity or reversal of said last-mentioned individual one of said conductor pairs, said first test bridging circuit completing a second electrical circuit including portions of said last-mentioned individual one of said conductor pairs having a current present therein of a level as determined by the presence of a short between the conductors of said last-mentioned individual one of said conductor pairs.

5. An electrical test circuit as claimed in claim 4 in which said unilateral conducting elements of said first and second test bridging circuit each is of the semiconductor junction type.

6. Electrical test circuit apparatus for testing a conductor pair comprising a first and a second test bridging circuit each including a unilateral conducting element having a first resistance when forward biased and a second resistance when reverse biased, said first bridging circuit also including a potential source and current level indicating means, and means for connecting said first and second bridging circuits across one and the other end, respectively, of said conductor pair to cause a current in said indicating means as determined by said resistances of said unilateral conducting elements, said indicating means indicating:

a first current level when each of said unilateral conducting elements is forward biased when said conductor pair is electrically continuous and parallel;

a second current level when said conductor pair is shorted and one of said unilateral conducting elements is shunted;

a third current level when one of said unilateral conducting elements is reverse biased when said conductor pair is reversed; and

a fourth current level when either or both of the conductors of said conductor pairs are electrically open.

7. Electrical test circuit apparatus as claimed in claim 6 in which said connector means includes switch means for selectively connecting said first and second bridging circuits across said ends, respectively, of individual ones of a plurality of conductor pairs.

8. Electrical test circuit apparatus as claimed in claim 7 in which said first bridging circuit also includes resistance adjusting means for calibrating said current level indicating means.