| 摘要 |
The invention refers to an electronic device for limiting access to long-distance and trunk-line automatic systems of internal telephone stations and of the operator's circuit, in institutional trunk exchanges. The device is connected to a junction circuit, through which the telephone stations and the operator's circuit are connected to the telephone exchange. The device is made up of a pulsing signal detector (2), followed by a counter (3) and a control circuit (4) which, by means of a cut-off relay (B), disconnects the telephone circuit if the number of digits of the subscriber called exceeds a preset limit. The input to the signal detector (2) is connected to the contact (lm1) of a pulsing signal short-circuiting relay in the junction circuit. The counter (3) is reset by the contact (A1) of a coupling relay that is activated when coupling the junction circuit.
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