Patent GB-191312061-A (GB)
Title: Improved Circuit Arrangements for Telephone Systems.
Filed: 1913-05-23
Granted: 1913-11-20
Abstract: 12,061. Siemens & Halske Akt.-Ges. May 25, 1912, [Convention date]. Automatic exchange systems.-In systems in which first and second preliminary selectors are employed, an outgoing line from a first preliminary selector is rendered non-selectable when the second preliminary selector to which it leads has no disengaged lines, but the blocked line is made once more selectable if all the other lines from the first preliminary selector become either engaged or blocked in the same way. When a line that has been blocked and then rendered selectable again in this manner is seized by a first preliminary selector, the second preliminary selector associated with the line is locked out of action, since it could not serve to extend the call further, and the call is extended through a lateral branch of the blocked line by means of an auxiliary switch of callfinder type, which is only set in action when a call arrives during such overflow periods. The overflow switches may be connected to special supervisory positions or to group selectors or jacks. The invention which has been described above in its application to trunking between non-numerical switches is also applicable to numerical switching. The general lay-out of the trunks interconnecting first and second preliminary selectors IVW, IIVW, and numerical selectors IGW is shown at the right of Fig. 1, and the circuits of one of the second preliminary selectors IIVWI and its connexion with one of the overflow switches SS are shown in greater detail at the left of the Figure. When all the selectors IGW of the group to which the switch IIVWI can obtain access are engaged, a relay G' is energized over the off-normal contacts k and opens the normal test-circuit of the switch IIVWI at the contact 1, so that the switch IIVWI is made non-selectable to the switches IVW. When, however, all the lines v<1>, v<2>, v<3> from a group of switches IVW become either engaged or blocked in this way, a relay F' is energized (because the short-circuits such as r<1>, t<1>, g<1> are all opened by the group relays G' &c. or the cut-off relays T) and prepares at the contact 3 a fresh test-circuit for the line v<1>, rendering it again selectable, so that when a switch IVW next arrives on the terminals of the line v<1> it is brought to a stop by the energization of its test-relay in a circuit through the contacts 2, 3, 5, 6, the relays K, R, and the contact 7. The relay K opens the contact 9 to prevent the switch IIVWI from being set in action. In the meantime the relay F' has also energized a relay J in series with the line relay of the calling line. The relay J locks itself up in series with a relay R', which completes the circuit of the rotary magnet Ds of the switch SS, which rotates until it comes to the terminals of the line v', whereupon a circuit is closed through the test relay V in series with the cut-off relav T and contacts 12, 13. The relay V unlocks the relays J, R' and extends the calling circuit through the contacts 17, 18. The relay T cuts out the relay R, and the relay V remains energized in series with the relay T, contact 29, relay K, contacts 15, 14, and the test relay of the switch IVW. If all the lines v<1>, v<2>, v<3> are engaged, a relay E<1> is energized and opens the circuit of the starting-relay J at the contact 19, and a calling subscriber then receives an engaged signal. A modification is described in which the operation of the switch SS does not involve the energization of the cut-off relay T.