Line shunt and ground fault apparatus method

• US 6,292,541 B1
• Filed: 11/10/1998
• Issued: 09/18/2001
• Est. Priority Date: 11/10/1998
• Status: Expired due to Term

• Current Assignee: Pittway Corporation (Honeywell International Inc.)
• Original Assignee: Pittway Corporation (Honeywell International Inc.)
• Inventors: Tice, Lee D., Clow, Robert J., Keeler, Manley S.
• Primary Examiner(s): TIEU, BINH KIEN
• Application Number:
  US09/189,393
• Time in Patent Office: 1,043 Days
• Field of Search: 379/1, 379/2, 379/6, 379/8, 379/24, 379/25, 379/26, 379/27, 379/29, 379/31, 379/34, 340/511, 340/661, 340/590, 340/825.36, 340/870.04, 324/528, 324/530
• US Class Current: 379/22.03
• CPC Class Codes: H04B 3/46 Monitoring; Testing

Abstract

A system and method to detect ground faults in a multi-processor communication system that includes a communications link that extends between the processors. The processors isolate different sections of the link. Measurements made with different isolated sections establish the location of the fault. The processors can also make measurements of the link to establish the magnitude of a shunt impedance on the link. Where an abnormal value of shunt impedance is detected, the respective devices can activate or deactivate solid state isolation circuitry to disconnect a section of the link exhibiting the abnormal level of shunt impedance.

Claims

1. A method of determining the location of a ground fault on a communication line having a plurality of substantially identical operational units couple thereto wherein the units carry out a non-test function and wherein the line is adapted to be independently open circuited at a plurality of spaced apart locations by the units, the method comprising:

selecting a location displaced from at least one end of the line thereby forming two segments;

open circuiting the line at the selected location using at least one unit adjacent to the location;

testing at least one contiguous line segment by applying at least one selected test voltage at the location to determine which segment includes the fault;

relative to the segment with the fault, repeating the above steps, successively shortening the segment which includes the fault until the fault has been located.

2. A method as in claim 1 wherein the segment lengths are succesively shortened using a binary search pattern until the location of the fault can be established.

3. A method as in claim 1 which includes selecting an end of the line and wherein the testing step indicates if the fault is located between the selected end and the displaced, selected location.

4. A method as in claim 3 wherein the location of the fault can be established relative to an open circuit.

5. A method as in claim 3 wherein a detected test current is compared to an expected test current to identify a segment having a fault.

9. A method as in claim 3 wherein a binary search pattern is used to successively shorten the segment lengths.

36. A method as in claim 1 wherein the operational units comprise ambient condition detectors and including:

monitoring respective ambient conditions adjacent to the units.

6. A method of determining the location of a ground fault on a communication line having a plurality of stanstially identical operational units coupled thereto wherein the units carry out a non-test function and wherein the line is adapted to be independently open circuited at a plurality of spaced apart location by the units, the method comprising:

selecting a plurality of locations displaced from at least one end of the line thereby forming a segment;

open circuiting the line at the plurality of displaced locations using at least one unit adjacent to each of the locations;

testing at least one contiguous line segment by applying at least one selected test voltage at one of the locations and attempting to initiate a current flow between an earth ground, via a ground fault, and a portion of the open circuited line whereby the location of the ground fault is established by the location of the portion of the open circuited line; and

relative to the segment with the fault, repeating the above steps, successively shortening the segment which includes the fault until the fault has been located.

7. A method as in claim 6 wherein the current flow is initiated at the earth ground.

8. A method as in claim 6 wherein the current flow is initiated by a voltage source coupled across first and second conductors wherein one conductor is the open circuited line.

10. A method of determining the location of a ground fault on a multi-conductor communication link having first and second ends, the method comprising:

open circuiting one conductor of the link at a plurality of locations between the ends;

applying a test voltage at at least one location and attempting to cause a test current to flow between another conductor of the link and an earth ground; and

establishing the location of the fault in response to a detected current flowing through the fault.

11. A method as in claim 10 wherein members of a plurality of electrical devices are coupled across the first and second conductors and wherein at least one of the devices attempts to couple at least part of the test current to the second conductor by impressing a selected voltage across the first and the second conductors.

12. A method as in claim 10 wherein the detected fault will be located adjacent to at least one electrical device which detects a flow of at least part of the test current.

13. A method as in claim 10 wherein the test voltage is applied between the second conductor and the earth ground.

14. A method as in claim 10 which includes providing a plurality of electrical devices coupled between the first and the second conductors of the link.

15. A method as in claim 14 where all devices open circuit the first conductor when a predetermined device drives a voltage across the conductors.

16. A method as in claim 14 where only predetermined devices open circuit the communication first conductor when a predetermined device drives a voltage across the conductors.

17. A method as in claim 14 where the voltage across the conductors is a result of sourcing a current across same.

18. A method, as in claim 16 where the predetermined devices are altered in a predetermined pattern to search for the location of the ground fault.

37. A method as in claim 10 further comprising generating a trouble indication on the communication line, after establishing the location of the fault.

38. A method as in claim 37 wherein the trouble indication includes the address of the device proximate the fault.

19. In a two wire communication system with multiple installed devices, a method of determining the location of a ground fault on one of the communication lines comprising:

measuring current flowing from the ground to a selected unit;

open circuiting one of the communication lines at a plurality of locations using the devices installed on the communication wiring between the ends thereof;

determining if the measured current flowing from the ground to the selected unit is coincident with a selected device open circuiting the communication positive wire.

22. A method as in claim 19 where the devices open circuit one of the communication lines in a predetermined pattern to search for the location of the ground fault.

23. A method as in claim 22 where the pattern comprises a binary search pattern.

24. A method as in claim 23 wherein implementing the binary search pattern comprises causing the middle device on a segment to open circuit the line, and if the ground fault disappears, causing the unit that is half way along the segment, in a selected direction to open circuit the line, if the ground fault does not disappear, causing the unit that is halfway on the segment opposite the selected direction to open circuit the communication line, this pattern repeats until the ground fault location is determined.

35. A system as in claim 19 wherein the one communication line is open circuited simultaneously at the plurality of locations.

39. A method as in claim 19 further comprising generating a trouble indication on the communication link, after determining the selected device open circuiting the communication positive wire is coincident with the measured current flowing the ground to the selected unit.

40. A method as in claim 39 wherein the trouble indication includes the address of the device proximate the fault.

20. In a two wire communication system with multiple installed devices, a method of determining the location of a ground fault on one of the communication lines comprising:

measuring current flowing from the ground to a selected unit;

open circuiting one of the communication lines at a plurality of locations, in sequence, starting at a selected location on the lines until the ground fault disappears using the devices installed on the communication wiring between the ends thereof;

determining if the measured current flowing from the ground to the selected unit is coincident with a selected device open circuiting the communication positive wire.

21. A method as in claim 20 which includes locating the ground fault between a) the last device which opened circuited the communication wire, during which time the ground fault disappeared and b) the second to last device which open circuited the communication line during which the ground fault did not disappear.

25. A method of determining the amount of leakage across a pair of conductors using device(s) coupled to the conductors between the ends thereof comprising:

sourcing or driving a current across the conductors in a direction where the device(s) do not interfere with measurements of the conductors;

measuring the voltage developed across the conductors; and

comparing that voltage to a predetermined value stored at the devices that represents excessive shunting across the conductors wherein the devices open circuit sections of at least one of the conductors and make line leakage measurements of the open circuited sections.

27. A method as in claim 25 which includes using field effect transistors to open circuit the sections of the conductors.

28. A method as in claim 25 where the source or drive signal is pulsed on and off at least once.

29. A method as in claim 25 which includes maintaining sections of the at least one conductor in an open circuit condition if an excessive shunt condition is present.

30. A method as in claim 25 which includes incorporating isolation circuitry into at least some of the devices.

31. A method as in claim 30 where all devices of a selected plurality contain isolation circuitry.

26. A method of determining the amount of leakage across a pair of conductors using device(s) coupled to the conductors between the ends thereof comprising:

sourcing or driving a current across the conductors in a direction where the device(s) do not interfere with measurements of the conductors;

measuring the voltage developed across the conductors; and

comparing that voltage to a predetermined value stored at the devices that represents excessive shunting across the conductors where the direction for sourcing or driving a current or voltage is opposite to the direction for powering the devices(s).

32. A communications system comprising:

a communications link;

a plurality of substantially identical electrical units coupled to the link wherein each of the units includes circuitry for carrying out a primary non-test function, circuitry for open circuiting the link and circuitry for testing the link for a fault condition when open circuited.

33. A system as in claim 32 wherein the units are selected from a class which includes fire detectors, motion detectors, position-detectors, gas detectors, and condition indicating output devices.

34. A system as in claim 32 wherein at least some of the units include ambient condition sensors and the primary function comprises sensing the respective ambient condition.