| 摘要 |
PURPOSE:To prevent the operation of the whole system from being invalidated by a fault of one interphone by separating an information line and displaying abnomarous state when a channel selection signal is continuously generated for a prescribed period or more. CONSTITUTION:Interphones I1-In are connected in parallel with power supply lines l1, l4, an information line l2, and a call line l3. When the interpone I1 operates a channel selection part 19, a controlling part 20 sends the operated channel selection No. to the line l2 through an output buffer 22, a diode 23 and a contact 18 and turns off a transistor (TR) 4. When the TR4 is turned off, the charge of a capacitor C6 is discharged through resistors 5, 7, 8, but if no signal is outputted from the buffer 22 within the discharging period, the TR4 is turned on and the C6 is charged again. When a signal is generated from the buffer 22 continuously after passing the discharging period, a TR9 is turned off and a TR15 is turned on to actuate a relay 17, so that the contact 18 is opened, the line l2 is separated and an LED26 lights up. |
