| 摘要 |
PURPOSE:To prevent the foul dialing to a private switchboard using the hooking, bu adding a simple pulse correcting circuit to a central office trunk. CONSTITUTION:An extension telephone is connected to terminals A1 and B1 via a link, and a relay A is actuated by a DC loop of the telephone. A relay B works by a contact of the relay A and continues its working during the dialing and calling. When a central office trunk is connected to the extension telephone, a closed circuit of a terminal A2- contact (a)- contact (b)- RET - terminal B2 is formed to the side of a trunk line. Thus the switchboard of the office side is started. A contact of a relay AA connected to the output of a pulse correcting circuit PCU is put into the above-mentioned closed circuit. Therefore a dial pulse given from the extention telephone is received by the realy A, and a pulse which is corrected or converted to a dial pulse of a normal make factor by the PCU is transmitted toward the office through the contact of the relaaly AA. |
