Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Testing of subscriber loop or terminal
Utility Patent
1998-09-01
2001-01-02
Kuntz, Curtis A. (Department: 2743)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Testing of subscriber loop or terminal
C379S029010, C379S030000, C324S519000
Utility Patent
active
06169784
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
A need is arising for a low cost means of testing the impedance presented by a two-wire telecommunications line. This could be used to determine line leakage or detect the presence of terminating equipment (e.g. a telephone). This could also detect fault conditions such as open or short circuits.
A proposed situation where this could be useful is where an Integrated Services Digital Network (ISDN) line is terminated to provide an ISDN connection together with a 2-wire analogue connection.
The detection of the presence of a telephone connected to a 2-wire analogue port is regarded as being where the real part of the load impedance is 300 Kohm or less.
The circuit component which interfaces from an exchange to a 2-wire connection is a subscriber line interface circuit (SLIC) which is normally located at the exchange or a remote concentrator. A SLIC is commonly an integrated circuit and has a line reversal function and a means of disconnecting one of the 2-wire connections. An example of a SLIC is described in Patent No. GB 2093314B.
One method by which a telephone subscriber loop may be tested is described in Patent Application No. GB2269073 where an electrical impulse is applied across the legs of the loop and the nature of the resulting transient voltage due to current in the loop is determined. The impulse may be provided by reversing the polarity of a power supply to the loop. The transient can be measured by a differential amplifier coupled across a resistor in series with the loop. Typically the maximum voltage, the time taken for the voltage to decay to a particular fraction of the maximum and the long term residual voltage are measured. These measurements are returned to the exchange to identify fault conditions in the loop. The disclosure require series resistors in the connecting legs and the addition of a relay to provide switching.
SUMMARY OF THE INVENTION
According to the present invention there is provided a connection from a telephone exchange to a subscriber, the connection being made via a subscriber line interface circuit (SLIC) and a termination box, there being a 2-wire connection between the SLIC and the subscriber, the termination box having a capacitor and a resistor connected in series between the two wires of the connection and between the SLIC and the subscriber, the SLIC including a switch for disconnecting one wire of the 2-wire connection and a further switch connected to the said one wire and to a SLIC supply rail and having a current monitoring point in series therewith, whereby the time required to discharge the capacitor may be monitored enabling determination of the impedance between the two wires of the connection.
REFERENCES:
patent: 4373121 (1983-02-01), Sartori et al.
patent: 4550223 (1985-10-01), Poitevin
patent: 6084946 (2000-07-01), Beierle
patent: 2 269 073 (1994-01-01), None
Kirschstein, et al
Kuntz Curtis A.
Marconi Communications Limited
Nguyen Duc
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