Directional short circuit detection system and method

• US 6,252,409 B1
• Filed: 02/08/1999
• Issued: 06/26/2001
• Est. Priority Date: 02/08/1999
• Status: Expired due to Fees

• Current Assignee: Akira Iijima
• Original Assignee: Akira Iijima
• Inventors: Iijima, Akira
• Primary Examiner(s): Metjahic, Safet
• Assistant Examiner(s): Hollington, Jermele M.
• Application Number:
  US09/246,891
• Time in Patent Office: 869 Days
• Field of Search: 324/529, 324/512, 324/521, 324/750, 361/78, 361/80, 361/83, 361/93.6
• US Class Current: 324/529
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults

Abstract

A unique system has been provided to precisely locate the exact position of a short along a conductor, even if the conductor is co-located with other conductors, even conductors connected to low resistance loads. A combination of low frequency test pulse signals, at low duty cycles, and the use of a directional sensor made with shields, account for accuracy and reliability of the system. The shields are arranged to optimally shield and direct signals at the transmitter test signal frequency. The shields also acts to place the shorted wire an optimal distance from the sensor. A method of short circuit location, using the direction sensor of the above-mentioned detection system, is also provided.

Claims

1. A system for detecting the location of a low resistance short in a conductor comprising:

a transmitter to generate a transmit test signal having a low duty cycle pulse, said transmitter having an output operatively connected to the conductor;

wherein a conductor magnetic field is induced by the transmit test signal;

a manipulable detector having an input to sense magnetic fields along the conductor, said detector having a output to supply a receive test signal responsive to the magnetic fields;

a receiver having an input operatively connected to the output of said manipulable detector, said receiver supplying a receiver output responsive to the receive test signal, whereby said detector is manipulated in response to the receiver output; and

a directional shield having center shield walls at least partially surrounding said manipulable detector and having an opening in said shield walls to expose said manipulable detector, said directional shield minimizing the influence of magnetic fields on said manipulable detector when said directional shield walls are interposed between a magnetic field and said manipulable detector, and said directional shields maximizing the influence of a magnetic field on said manipulable detector when said opening is interposed between a magnetic field and said manipulable detector, whereby a short in a conductor is precisely located through the use of said directional shield in conjunction with the receiver output signal.

2. A system as in claim 1 in which said manipulable detector includes an inductor of approximately 10,000 micro-henries (uH) in parallel with a capacitor of approximately 0.033 microfarads.

3. A system as in claim 1 in which the transmit test signal low duty cycle pulse width generated by the transmitter has a duty cycle of greater than 0.02%.

4. A system as in claim 1 in which said directional shield includes U-shaped center shield walls, with a mouth, said center shield being shaped to locate the conductor a minimum first distance from said manipulable detector and a maximum second distance from said manipulable detector, whereby the test signal transmitted from a conductor is optimally sensed when the directional shield mouth is interposed between the conductor and said manipulable detector.

5. A system as in claim 4 in which said directional shield further includes a non-conductive spacer interposed to maintain the first minimum distance between the conductor and said manipulable detector.

6. A system as in claim 5 in which the first distance is approximately 17 millimeters (mm), and the second distance is approximately 42 mm.

7. A system as in claim 1 in which the transmit test signal low duty cycle pulse has a repetition rate in the range between 0.1 and 100 Hz.

8. A system as in claim 4 in which said directional shield center walls are selected from the group of materials consisting of aluminum, ferrous, and transformer iron, and in which said walls have a thickness greater than approximately 0.8 millimeters.

9. A system as in claim 4 further in which said shield center walls have an interior wall surface adjacent said manipulable detector and an exterior wall surface, and further comprising:

two middle shield walls each having an interior wall surface located adjacent each said exterior center wall surface, each middle shield wall also having an exterior wall surface; and

two outer shields walls each having an interior wall surface located adjacent said middle shield exterior wall surfaces.

10. A system as in claim 9 in which said middle and said outer shield walls have a thickness in the range from approximately 0.4 to approximately 0.6 mm, in which said middle and outer shield wall material is selected from the group of materials consisting of ferrous metal, aluminum, and transformer iron.

11. A method for improved accuracy in the identification of shorts in a conductor with a manipulable detector with a directional shield, the method comprising the steps of:

a) introducing a low duty cycle pulse transmit test signal to the conductor under test, whereby the conductor radiates a field in response to the test signal;

b) maintaining an optimal separation between the manipulable detector and the conductor under test, whereby the accuracy of the field readings is improved;

c) detecting a plurality of fields, radiated by the transmitter test signal in the conductor under test, in response to a corresponding plurality of positions along the conductor;

d) comparing the plurality of fields detected in Step c) to determine a change in detected fields; and

e) establishing a correspondence between change of field detected in Step d) and a position along the conductor under test, whereby the change of field indicates a short in the conductor.

12. A method as in claim 11 wherein the directional shield includes shield walls at least partially surrounding the manipulable detector and includes an opening in the shield walls to expose the manipulable detector, and in which Step b) includes using the directional shield to minimize the influence of fields on the manipulable detector when the shield walls are interposed between a field and the manipulable detector, and using the directional shield to maximize the influence of a magnetic field on the manipulable detector when the opening is interposed between a magnetic field and the manipulable detector, whereby a short in a conductor is precisely located through the use of the directional shield in conjunction with the detection of fields.

13. A method as in claim 12 wherein a non-conductive spacer is interposed between the manipulable detector and the directional shield mouth, and in which Step b) includes interposing the spacer between the conductor under test and the manipulable detector, whereby an optimal spacing is maintained for the sensing of fields emitted by the conductor.

14. A method as in claim 13 in which Step b) includes the spacer being aligned to maintain a minimum distance in the range from 10 to 30 mm between the manipulable detector and the conductor under test.

15. A method as in claim 11 in which the manipulable detector includes an inductor of approximately 10,000 uH in parallel with a capacitor of approximately 0.033 microfarads.

16. A method as in claim 11 in which Step a) includes introducing a low duty cycle pulse transmit test signal having a duty cycle of greater than 0.02%.

17. A method as in claim 11 in which Step a) includes introducing a low duty cycle pulse transmit test signal having a pulse repetition rate of approximately 2 Hz.

18. A method as in claim 12 in which Step b) includes the directional shield being a U-shaped channel of aluminum having inside walls adjacent the manipulable detector, outside walls, and a wall thickness greater than 0.8 mm.

19. A method as in claim 18 in which Step b) includes the directional shield including a pair of middle shields overlying the outside channel walls, with the middle shield material selected from the group consisting of aluminum, ferrous metal, and transformer iron, having a thickness in the range from approximately 0.4 to 0.6 mm, and in which Step b) includes the directional shield including a pair of outer shields overlying the middle shields, with the outer shield material selected from the group consisting of aluminum, ferrous metal, and transformer iron, having a thickness in the range from approximately 0.4 to 0.6 mm.

20. A closed-loop feedback system of detecting short circuits through the continuous interaction of the system with a human operator, the system comprising:

a stimulus generator creating a transmit test signal having a period of about 0.5 seconds with an and an on-time of about 85 microseconds;

a test signal radiator operatively connected to said stimulus generator and including a conductor under test shorted to ground, said test signal radiator creating a magnetic field, responsive to the transmit test signal induced in said electrical conductor under test between said stimulus generator and the short;

a directional sensor to receive the magnetic field with a first strength in a first directional orientation, and with a second strength, less than the first strength, in a second directional orientation, said directional sensor generating a field indicator signal, detectable to the human operator, in response to the strength of the received magnetic signal; and

in which the operator manipulates said directional sensor with respect to said conductor under test to generate a plurality of field indicator signals corresponding to the location of said directional sensor with respect to said conductor under test, whereby the operator is able to accurately locate of the short in said conductor under test.