DC signaling circuit for use in conjunction with isolation trans

Details DC signaling circuit for use in conjunction with isolation trans DC signaling circuit for use in conjunction with isolation trans

1977-05-31

1978-10-03

Claffy, Kathleen H.

179 16A, 179 78A, H04M 318, H04M 118

Patent

active

041186036

ABSTRACT:
The present invention relates to a DC signaling circuit operatively associated with a communication system having an isolation transformer interconnected between a central communication exchange center and a station site such as a power substation or generating plant where high voltage potential exists. The isolation transformer provides protection from fault conditions that could apply hazardous voltage to a cable pair entering the station. Because of the presence of the isolation transformer, there is no direct path for DC signal functions to pass from the station to the central communication exchange center. Thus, the DC signaling circuit of the present invention is designed to simulate and transfer the simulated DC signals across the isolation transformer to a line side of the communication system leading to the central communication exchange center. DC signals and logic information generated by a signal source such as a telephone on the station side of the isolation transformer can thusly be effectively transferred across the isolation transformer exactly as generated and in a clear and undistorted manner due, at least in part, to provisions in the DC circuit that shunt the windings of the isolation transformer during time intervals when DC signals are generated and communicated to the line side of said communication system.

REFERENCES:
patent: 2938955 (1960-05-01), Molnar
patent: 3166642 (1965-01-01), Abbott
patent: 3538260 (1970-11-01), Brouwer
patent: 3723662 (1973-03-01), Macrander
patent: 3746795 (1973-07-01), Fitzsimons et al.
patent: 3798379 (1974-03-01), Brooks
patent: 3932804 (1976-01-01), Allen
patent: 3968408 (1976-07-01), Allen
Straw & Tilford, "System 731 - Telephone System for Mines", Plessey Systems Technology, Nov. 1977, No. 27, pp. 35-40.

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