| 摘要 |
<p>The system disclosed transiently disconnects a subscriber's telephone equipment and network from the service provider (e.g. telephone company) network for a predetermined period of time in response to a remote switching pulse to facilitate the execution of diagnostic measurements without the necessity of visiting the subscriber's premises. The disconnect action is carried out by a two stage solid state circuit incorporating gate controlled devices such as SCRs together with RC networks whereby a capacitance is charged in response to the remotely originated switching pulse and then discharges to energize a switching relay and so maintain it energized for a predetermined period. In the energized state the switching relay isolates the subscriber network and its equipment from the telephone company network to permit the diagnostic measurements. The circuit design also provides improved noise suppression, as well as protection against spurious switching and certain overvoltage conditions. A modified version also provides means for detecting certain tip short conditions.</p> |
