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US 3,941,943 AGranted
Privacy circuit for key telephone systems
AssigneeInternational Telephone and Telegraph Corporation
InventorCoy Edwin Matheny
Life of this patent
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AssigneeInternational Telephone and Telegraph Corporation
InventorCoy Edwin Matheny
Estimating the term…
In key telephone systems where a plurality of stations have access to a line by merely depressing a line key, a circuit is provided to prevent that station from entering a busy line. The circuit uses a single relay per station to provide a normal condition of privacy for any line at a station to equipped. The circuit senses the condition of the line and on a busy condition, the station cannot access the busy line. By providing all stations of a key group with privacy circuits, all stations can have complete privacy on line calls. Privacy control is possible on less than all stations of a system and less than all lines by selective deployment of privacy circuits. Optionally, a privacy release button can be provided to allow a station to enable other stations to access that busy line. Protection has been built into the circuit against transient surges and the like.
In a key telephone system in which each station has access to a plurality of lines with each line having loop conductors for completing a talkpath from a line to a station and a control lead conductor, and in which said control conductor is in a first condition when its line is idle and a second condition when its line is busy, means responsive to a line becoming busy for applying said second condition to the control conductor of said line, a privacy circuit for each said station including means for sensing said second condition in said control conductor of a line completed to said station, means for enabling said privacy circuit responsive to a sensed second condition, means for latching said privacy circuit in an enabled condition, means for sensing the presence of line current in a line loop of said completed line for causing the operation of a privacy relay in said privacy circuit only when said privacy circuit is not latched, and contacts of said privacy relay for opening the line loop conductors responsive to operation of said relay to prevent access to said line by the station with its relay contacts open.
A key telephone system having a plurality of stations which may have access to a key system line, in which the line has a pair of loop conductors for completing a speech path from the line to stations having access thereto and a control conductor;
Dependencies are inferred from the claim text.