Telephone system open switching interval protection circuit

Details Telephone system open switching interval protection circuit Telephone system open switching interval protection circuit

1978-07-14

1979-06-19

Claffy, Kathleen H.

H04Q 518

Patent

active

041587553

ABSTRACT:
A circuit which can be appliqued to external terminals of a prior art key telephone line circuit to protect the circuit from prematurely cancelling a customer-applied holding condition when the central office exhibits an open switching interval (OSI) condition is described. The appliqued circuit monitors a contact of the key system hold relay, and when that relay is released by the appearance of an OSI condition, temporarily reconnects the winding of the hold relay across the line so that the hold relay can respond to the reappearance of central office line current if it appears after a normal OSI interval and which disconnects the hold relay if line current does not appear as during a permanent signal condition.

REFERENCES:
patent: 3764752 (1973-10-01), Yachabach
patent: 3840710 (1974-10-01), Limiero et al.
patent: 3857072 (1974-12-01), James et al.
patent: 3895192 (1975-07-01), Angner et al.
patent: 3996426 (1976-12-01), Lancaster
patent: 4064373 (1977-12-01), Pinede et al.
patent: 4093830 (1978-06-01), Pappas

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