Patent GB-382051-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1931-10-10
Abstract: 382,051. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and HART, T., of General Electric Co., Stoke, Coventry. Oct. 10, 1931, No. 28154. [Class 40 (iv).] In a system in which an intermediate selecting stage is omitted for certain calls, the first selector drops back in response to certain first digits and extends the connection over a second set of wipers in response to the second digit, a signal characteristic of the level to which it was initially raised being sent forward to effect wiper discrimination at a subsequent selecting stage. In the 2000 line exchange shown in Fig. 5 and described in detail below, local calls are denoted by the first digit 3 or 4 and are extended by the first selector GS after dropping back over the lower bank, while the remaining levels of the upper bank are available for junction calls and calls to an operator. A signal is sent forward to the final selector FS to select the set of wipers to be used. The scheme may be extended to a 20,000 line exchange, the discrimination being effective either at the second selector or at the final selector, as in Fig. 6. Fig. 4 shows an exchange in which certain local calls may be extended over the upper bank of the first selector DS in the normal manner without discrimination. First selector, Fig. 2. Line and release relays A, B energize and the first train of impulses are repeated to the vertical magnet V and dialling relay C. Relay G energizes at the first step and locks. If the first digit indicates a junction call or a call to an operator, the rotary magnet R is connected up over vertical wiper QW when relay C falls back and interacts with relay G to step the selector in search of an idle outlet such as 9. If the first digit is 3 or 4, denoting a local call, on the relapse of relay C a circuit is closed over vertical wiper QW for relay Y which operates the release magnet Z. Relay X energizes in series with relay Y if the digit is 3. In the normal position of the selector relay YA energizes, connects up the lower set of wipers and releases relay G. The selector now responds to the second dialled digit and hunts in the selected level for an idle final selector. It will be seen that relay YA effects circuit changes whereby the rotary magnet R is connected up when the second digit is 3 or 4. Switching relay H operates in the usual manner. Subsequent trains of impulses are repeated to the final selector bv relay A, relay C being operated during each train to improve the impulse circuit. Final selector, Fig. 3. Line and release relays AF, BF energize and connect up dialling relay CF. The vertical magnet VF responds to the third digit, and the relapse of relay CF connects up change-over relay EF, so that the rotary magnet RF responds to the final digit. At this time, relay H, Fig. 2, is shunted by a resistance 40 if relay X is operated (first digit 3), and relay WF pulls up over the test wire and connects up the lower set of wipers. If relay X is unoperated (first digit 4), relay WF does not pull up and the connection is made over the upper set of wipers. The wanted line is tested in the interval between the relapses of relays CF, EF, and, if it is idle, switching relay HF energizes, applying ringing current over ring-trip relay FF, which operates on reply followed by back-bridge relay DF. The connections of line relay AF are reversed to energize shunt-field relay D, Fig. 2. If the wanted line is busy, relay GF energizes on the relapse of relay EF and sends back a busy signal.