| 摘要 |
<p>566,779. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., BAKER, G. T., and TAYLOR, R. July 8, 1943, No. 11075. [Class 40 (iv)] A selector is started by a subscriber who receives an audible signal at each step and stops it in the appropriate position. In the ten-line P.A.X. shown, the subscribers have voice-powered transmitters and a key PB1 on the hand-set for bridging the line wires. A call is initiated by operating this key, whereupon line relay C steps the forward-drive switch SS one step off normal and so energizes H. The key is then released, C falls and H holds momentarily over pulse wire IPL and then connects this wire to the stepping magnet SSM over the off-normal bank. At each step, a tone signal is given from wire ITL which receives pulses of tone current synchronous with the driving pulses on IPL from a neon tube generator. When the switch has made the desired number of steps, the key is operated again and C pulls up to stop it. If the line is idle, H pulls up also over the zero contact of the wanted line in series with H of the wanted circuit and the latter connects up calling tone from CTL. When the subscriber replies, his relay C moves his switch one step off-normal to cut off the calling tone. If the line is busy, H is unoperated and the caller continues to hear the tone signals. At the end of a conversation or when the call is abandoned, the key contacts are opened again and the switch is stepped on to its home position. It can be stopped if desired before reaching this position by re-operating the key. One of the switch positions may be devoted to a conference circuit. Subscribers are given the facility of breaking in on busy lines by bridging their h3 contacts. A non-linear resistance shunt, e.g. a dry rectifier, may be put across the receiver to prevent its actuation by the calling tone, the calling signal in this case being given out by the transmitter. In a modification, the key contacts PB1 are replaced by cradle switch contacts and a further switch on the hand-set with its contacts normally closed is used to give the temporary interruption necessary to drive the switch to the wanted line. The invention is stated to be applicable to larger systems.</p> |
