Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Including fault responsive disconnection of tested component
Patent
1994-12-21
1997-02-18
Chin, Wellington
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Including fault responsive disconnection of tested component
379 29, 324522, H04M 124, H04M 308, H04M 322
Patent
active
056047851
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to communications circuits, and especially to maintenance termination units for use in telephone circuits.
2. Introduction to the Invention
In recent years, and especially in view of deregulation of many telephone systems, privately owned communication equipment has increasingly been installed in the premises of subscribers to the system, with the result that it is often necessary to determine whether any fault is located in the telephone line, or in the subscriber's premises, i.e. in the subscriber's equipment or cabling, in order to determine whose responsibility it is to repair the fault. It is highly advantageous economically if this determination can be performed remotely by sending an appropriate signal from the local exchange along the line, thereby obviating the necessity to send any telephone company personnel to the subscriber's premises.
In order to test the telephone line for any faults it is necessary firstly to install a so-called "maintenance termination unit" or MTU in the line at the subscriber's premises which can disconnect the subscriber equipment from the line (often called sectionalizing the line) and connect the a and b or tip and ring lines on receipt of the appropriate signals from the exchange. During the line testing procedure determinations will typically be made of the line to line resistance and of the first and second line to ground resistance. Also the line continuity can be determined by detecting the presence of the MTU electronically.
Various forms of MTU are described, for example, in U.S. Pat. No. 4,710,949 to Om Ahuja. This device comprises a pair of voltage sensitive switches, one located in each of the tip and ring lines, and a distinctive termination connecting the tip and ring lines on the subscriber side of the voltage-sensitive switches. The voltage-sensitive switches may each have a threshold voltage of about 16 volts so that they are closed in normal operation by the 48 volt battery voltage but will open when this is replaced by a test voltage below about 32 volts in order to test the line-to-ground and tip-to-ring impedances. The distinctive termination may, for example, comprise a back-to-back diode and Zener diode which will exhibit an asymmetric resistance when large voltages (higher than the operating voltages) of different polarity are applied.
In addition to the provision of an MTU in a communications system, the system will normally need to be protected against overcurrents and also overvoltages in the communications channel which may, for example, be caused by equipment failure, electromagnetic interference, electrostatic discharge, connection to mains voltage power supply and the like. This is normally achieved by incorporating separate components such as spark gaps, triacs, etc., in the system.
SUMMARY OF THE INVENTION
The present invention is based on the appreciation that it is possible to employ the same switching circuit both as a remotely actuated switch for subscriber isolation, or loop back testing, and also as a device for protecting the subscriber equipment or the exchange equipment from an overcurrent or overvoltage.
Thus, according to the present invention, there is provided a switching arrangement that can be connected in a communications channel comprising a pair of lines, between sets of terminal equipment, which comprises: connected in one of the lines and will open when subjected to an overcurrent in its associated line; and/or between one or both the lines and earth, and will close when subjected to an overvoltage in its associated line; a test signal sent along the channel.
DETAILED DESCRIPTION OF THE INVENTION
The switching arrangement according to the invention has the advantage that a single switch is employed in each signal line (in the case of series switches) to provide two functions, namely remote disconnection and overcurrent protection, thereby improving the reliability of the arrangement, reducing its insertion loss in the lines and reducin
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Challis Michael
Pryor Dennis M.
Bertram Bruce M.
Burkard Herbert G.
Chin Wellington
Gerstner Marguerite E.
Loomis Paul
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