| 摘要 |
PURPOSE:To ensure both the office call and the extension call with the minimum number of insulated conductors and independently from each other 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:Main wires L1 and L2 plus office call line 41 within the key telephone system form a DC loop each and also isolated from each other in terms of DC. These wires and line are furthermore connected to each other in terms of AC, and at the same time the branch connection is secured between line 41 and each of slave units 20 and 30. In addition, current supply means B2, CH10 and C10 are provided to the main device in order to supply the DC current to the neutral point of line 41. At the same time, the following means are provided to each slave unit: current extracting means CH21 and C21 which extract the DC from other neutral points of line 41; and control means 22, 23, 24 and 25 which give the necessary control each by the current extracted through the current extracting means. |
