| 摘要 |
<p>1490869 Substation circuits WESTERN ELECTRIC CO Inc 9 Dec 1974 [12 Dec 1973] 53237/74 Heading H4K A key telephone substation includes a relay which is normally short-circuited but which is permitted to operate in series with the loop through the subset transducer circuitry and then hold via one of its own contacts when a line-hold key is operated. Any one of the stations, e.g. S1, connected to an exchange line, e.g. L1, may respond to ringing by going off-hook, thereby closing his hook switch contacts SH and operating his line key so as to place the contacts 1PU in their rest condition. Consequently the light indicators LED-1 in each station glow continuously. If the responding station, e.g. S1, wishes to have a private conversation in his office or to communicate over another line he presses his hold key thereby opening contact 1H-1 and thus removing a short-circuit from relay 1B. The latter operates in series with the subset transducer circuitry and then holds via its make contact 1B-1. The line L1 is thus terminated via a suitable impedance and the substation circuit is short-circuited. If the station goes on-hook or operates his line key thus opening contacts 1SH or transferring the 1PU contacts to their make side, the line remains held with the lamps LED glowing. If any station wishes to break-in by going off-hook and operating his line key, i.e. contacts 2PU or 3PU in their rest state, or, if the original station releases his hold key, the holding relay 1B is once more short-circuited and thus falls back to release the hold condition.</p> |
