EXTENSION CALL DETECTING SYSTEM FOR KEY TELEPHONE SYSTEM

摘要

PURPOSE:To ensure both the office call and the extension call independently from each other with the minimum number of insulated conductors for the key telephone system of the branch connection system, by forming the connecting cord for the office n circuit with 2n+2 pieces of insulated conductors. CONSTITUTION:The branch connection is given between extension call lines 42-1 and 42-2 which are used in common for the power supply to slave units 20 and 30 plus office call line 41 in main device 1 and each of slave units 20 and 30. In such key telephone system, signal generator 7 which secures the piling of the high frequency signal on lines 42-1 and 42-2 is provided to main device 1. And element C20 showing a low impedance to the high frequency signal is connected to lines 42-1 and 42-2 each. Then the calling to lines 42-1 and 42-2 is detected via monitor circuit 8.