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United States Patent | 4,194,230 |
Danford | March 18, 1980 |
A safety circuit for protective operation at the interface between certain customer premises telephone installations and the external telephone distribution lines. The protection circuit includes a means for discriminating any voltages of sufficient magnitude having a frequency at or near 60 Hz., and upon such detection, a reactance means is responsive to open the connection between the premises telephone installation and the external telephone distribution line.
Inventors: | Danford; Glenn S. (Oklahoma City, OK) |
Assignee: |
Southwest Utilities, Inc.
(Oklahoma City,
OK)
|
Appl. No.: | 05/941,068 |
Filed: | September 11, 1978 |
Current U.S. Class: | 361/1 ; 307/129; 327/47; 361/113; 361/182; 379/412 |
Current International Class: | H02H 3/50 (20060101); H02H 003/04 (); H02H 007/26 () |
Field of Search: | 361/1,113,182 179/78A 307/233R,129 328/138,140 |
1377573 | May 1921 | Fortescue |
3940698 | February 1976 | Itoh |
"A Circuit for Protecting Transister Amplifiers from Extraneous Currents," _Khrennikova, Telecommunication & Radio Eng., vol. 27, No. 2, pp. 36-39, 2/1973.. |
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