Key system protective apparatus

Details Key system protective apparatus Key system protective apparatus

1978-11-29

1980-03-18

Brigance, Gerald

179 81R, 179 16E, H04M 100, H04Q 518

Patent

active

041940938

ABSTRACT:
A circuit for apparatus to be used with a key system line card for providing electrical isolation between the line circuit and the central office. The adapter responds to ring current from the central office to close a path to the line circuit to cause the line circuit to respond. The circuit provides two-way supervision responding to change of conditions either at the station or at the central office, and also provides a time delay to prevent the circuit from entering the hold condition improperly.

REFERENCES:
patent: 2830128 (1958-04-01), Radcliffe, Jr. et al.
patent: 3166642 (1965-01-01), Abbott
patent: 3925624 (1975-12-01), Earle et al.
patent: 3996426 (1976-12-01), Lancaster
patent: 4039763 (1977-08-01), Angner et al.
patent: 4057693 (1977-11-01), Angner et al.
patent: 4101740 (1978-07-01), Barsellott
patent: 4103112 (1978-07-01), Korsky
patent: 4132870 (1979-01-01), Liu
patent: 4145579 (1979-03-01), Angner et al.

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