| 摘要 |
PURPOSE:To switch two kinds of telephone set circuits automatically by supplying power to a key telephone set from a changeover circuit of a master set side via one side line of two couples of transmission lines at the restoration of power supply and connecting the changeover circuit of the key telephone set side switchingly when a 1st telephone set circuit is connected to the changeover circuit of the key telephone set at the time of normal power supply. CONSTITUTION:In the state of power failure, a 2nd telephone set circuit 5-7 is connected to a subscriber line 1 through one-side lines 3b, 4b of a transmission line 3-4. When power failure is restored and the 2nd telephone set circuit 5-7 is not in the talking state on the other hand, a relay 2-6 is activated and contact points 2-3, 2-4 are changed over to positions opposite to those shown in the figure. Then a +24V power supply and a ground potential are supplied to the key telephone set 5, then a relay 5-3 is operated and contact points 5-8, 5-9 are changed over to positions opposite to those shown in the figure. Thus, the 1st telephone set circuit 5-6 is connected to the transmission line 4 via a transformer 5-5. Thus, two kinds of telephone set circuits are used switchingly automatically in response to the state at the time of power failure and power failure restoration with comparatively simple constitution.
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