| 摘要 |
PURPOSE:To reduce the danger of the short-circuit accident of the control lines by using the trunk connection relay of one unit of the power source and the wiring each and without applying the voltage to the control lines under the queuing state. CONSTITUTION:Under the queuing state, call lines 4 and 5 are connected to the extension with control lines 6 and 7 functioning as the earth respectively. When the operator of the key telephone picks up the handset, transistor Tr45 of catching monitor circuit 44 is turned on. Thus Tr48 is turned on to drive oscillator 43. In accordance with the oscillation cycle of ocillator 43, Tr24 and 27 turn on and off to apply the intermittent voltage of + to control line 6. With selection of main wires 8 and 9, Tr31 is turned on when the + voltage is applied since trunk selection key switch 17 is closed. As a result, trunk connection relay 19b operates, and lines 4 and 5 are connected to wires 8 and 9 by switching of contacts 19b-1 and 19b-2. |
