Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Of trunk or long line
Reexamination Certificate
1998-11-10
2001-09-18
Tieu, Binh (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Of trunk or long line
C379S022070, C379S024000, C379S027060, C379S029010, C324S500000, C340S870030
Reexamination Certificate
active
06292541
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to diagnostic devices and methods for use with communication links. More particularly, the invention pertains to such devices and methods which can be used to determine the presence or absence of shunt impedances as well as the presence or absence of ground faults on communication links.
BACKGROUND OF THE INVENTION
Multiprocessor communication systems which provide bidirectional communication capabilities for each of the processors using a bidirectional communication link are known. Such systems are often associated with alarm or monitoring functions.
One known form of such a system incorporates a common control unit which is connected to a two-wire electrical cable which extends throughout a region to be monitored. A plurality of detectors can be coupled across the wires of the link at locations corresponding to portions of the region to be monitored. Additionally, output devices can also be coupled across the wires of the link and can be used to provide various output functions such as energizing or de-energizing solenoids or energizing or de-energizing audible or visual annunciators.
It has also been recognized that such communication links at times exhibit deteriorating performance due to shunt impedances or ground faults. While there have been approaches developed in the past which attempt to establish the location of one or more such conditions on Class A loops, it would be desirable to ascertain the existence of shunt impedances across the wires of the link or the location of ground faults in other link configurations. Preferably, it would be desirable to provide such functionality without having to substantially increase the base cost of such systems for a given number of detectors. Additionally, it would be preferred if the desired functionality can be provided without substantially increasing system complexity.
SUMMARY OF THE INVENTION
A multi-processor communication system, in one aspect, includes a common communication link which could be implemented as a two-wire cable. Coupled to the link are the members of a plurality of electrical devices some of which might be substantially identical.
Typical electrical devices would include ambient condition detectors such as smoke detectors, position detectors, motion detectors, gas detectors, humidity detectors, and the like. Other types of electrical devices could be used for energizing or de-energizing solenoids so as to implement output functions which could include locking or unlocking, opening or closing doors or windows, energizing or enabling audible or visible output devices of various types to convey messages, warnings or the like. In another aspect, the detectors can be clustered on one communication link, and some of the output devices, if desired, clustered on another communications link.
The electrical devices can each include a local control circuit, which could be implemented as a programmed processor, and associated instructions. In one aspect, the local control circuit is coupled to a solid state or mechanical switch which can be used to open circuit the communication link in the vicinity of the electrical unit. A common control unit, if present, can in turn include similar solid state or mechanical switches which under the control of electrical circuitry therein can isolate the communication link from that control unit.
In order to measure the shunt resistance of the communication line, the devices contain drive circuitry to drive a current across the two wires of the communication line. The current is driven in a manner that the devices connected across the wires will not interfere with the measurement of the shunt resistance across the two wires.
The devices measure the voltage drop produced across the wires by the current and determine if the line shunt resistance is greater than a predetermined value. If the shunt resistance is lower than the predetermined value, a trouble indication can be generated.
In a preferred aspect, the current is driven in a polarity opposite to the polarity present when delivering power to the devices. In this manner, each device appears to be an open circuit or at least a very large impedance when the polarity is reversed. The voltage developed across the line will then be determined by the line shunt resistance.
In another aspect, the current can be driven with the same polarity as the polarity present when delivering power to the devices. However, in this case, it would be driven at very low value such that the voltage developed across the wires of the communication link is less than the voltage value required to deliver power to the devices. Since the devices do not have sufficient voltage to draw power from the line, the voltage on the line will be determined by the line shunt resistance.
In a preferred apparatus, each device also contains an isolation circuit such that it can open circuit the link. The isolation circuit can be implemented using solid state semiconductor switches.
Since each device open circuits the link, each device only checks the portion of the link between itself and an adjacent device. If a shunt resistance across the two wires of the communication link is less than a predetermined value, a trouble indicator can be generated and the device address indicates the location of the shunt resistance. A voltage drive could be substituted for a current drive since these parameters are related.
When a low shunt resistance has been indicated, the device can be commanded to open circuit the link to isolate the section of the communication link that has a low shunt resistance. This will prevent it from adversely affecting the communication process.
In many systems, the communication link is not connected to the earth ground or external shielding around the link. A resistive leakage path, or ground fault, can occur from either or both wires of the communication link to earth ground. This may potentially cause communication problems. It would be desirable to be able to identify that this leakage resistance to earth ground, or ground fault, exists prior to encountering communications problems.
A preferred method includes checking to determine if a link exhibits a ground fault. In one embodiment, the communication link includes two conductors.
One conductor is connected to all devices and cannot be open circuited by the devices. Each device has a capability to open circuit the second conductor.
To test the link, the devices open circuit the second conductor at spaced apart locations on the link. When a respective device is between the ground fault and a predetermined unit, the ground fault will disappear relative to the predetermined unit.
When the ground fault is between the unit and the device, the ground fault will be detected by the unit. By determining which device is closest to the ground fault and still between the ground fault and the unit, the location of the ground fault can be determined.
The predetermined unit can correspond to another device. Alternately, if the system includes a common control unit, coupled to the link, to implement various system-wide communication functions, the predetermined unit can correspond to the common control unit.
A predetermined searching pattern can be used to determine the location of the ground fault. A binary search pattern will find the ground fault with the least number of steps.
One method of locating a ground fault to one of the conductors of a communication link includes selecting an initial location on the link. Where the initial location corresponds to an end of the link, another displaced location on the link is selected. The link is open circuited at the another location.
Each of the segments can then be tested by use of voltage-type test signals to determine which segment includes the fault. Relative of this segment which indicates or includes a fault, another displaced location is selected and the line is open circuited. Each of the shortened line segments is then tested to determine which segment includes the fault. As noted above, a binary search pattern can b
Clow Robert J.
Keeler Manley S.
Tice Lee D.
Pittway Corporation
Rockey Milnamow & Katz Ltd.
Tieu Binh
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