Patent GB-253673-A (GB)
Title: Circuit arrangements for selectors in telephone systems
IPC: H04Q3/00
Filed: 1925-05-06
Abstract: 253,673. Siemens Bros. & Co., Ltd., and Humphries, H. E. May 6, 1925. Automatic exchange systems.-The circuits of a group selector are such that the stepping relay is operated at the time when the wipers are brought on to a set of bank contacts and is released to control further hunting if busy earth is found on the test contact. The arrangement may be such that the stepping relay when operated closes a circuit for the rotary magnet and that a circuit over which the test relay may operate in the case of a free trunk is completed just as the wipers move on to a set of contacts. Two arrangements are described in each of which the stepping relay has two windings differentially wound, the relay operating over either winding alone but de-energizing when both windings receive current. First arrangement, Fig. 1. Relay A operating over normal contacts k2, k3 energizes release relay B and. the first impulse is repeated over contacts a1, k1, b3 to vertical magnet VM in series with winding 1 of relay C which operates. Succeeding impulses pass via the front contacts of off-normal spring k1 and contacts d5, b2, c1. At the end of the digit, the relapse of relay C disconnects relay A but completes a holding circuit for relay B in series with winding 1 of stepping relay E which operates and completes a circuit for the rotary magnet RM. Near the end of its stroke the magnet closes its contact rm, thereby connecting winding 2 of relay E to the test wiper, and if this is earthed relay E, receiving current over both windings, releases and opens the circuit of the magnet. The circuit of winding 2 of relay E is opened and the relay energizes again and re-closes the magnet circuit. When an idle trunk is reached, the test relay D operates over contacts rm and relay E releases. All trunks busy. If no idle trunk is found, the wipers pass to eleventh terminals at which relay D operates and springs w1, w2 are closed, whilst a relay Z is energized to operate a meter M. Relay C operates over both its windings and springs w2 and connects relay A to the loop over springs w1. A busy tone and flash circuit BB is connected to the a-wire at springs w1. Second arrangement, Fig. 2. When the selector is seized, relays A, B operate and relay C energizes in series with winding 2 of relay E which also operates, but this circuit is broken as soon as contacts k1 change over. Impulses are repeated by relay A to the vertical magnet VM in series with winding 2 of relay C. At the end of the digit, the relapse of relay C closes a circuit d6, c1, k2, b2, for the rotary magnet RM in parallel with winding 1 of relay E which however does not operate since its winding 2 is energized over contacts rm, k1, d1, c2, e2, b1. The magnet operates and opens the last-mentioned circuit so that relay E operates and opens the magnet circuit. If the first trunk is busy, winding 2 of relay E is energized over contact d1 and test wiper C‹, and the relay releases and causes the hunting magnet to operate again. When a free trunk is reached, test relay D operates in series with relay E and switches through. All trunks busy. The wipers move to eleventh terminals at which springs w1 - - w3 operate, the former energizing a meter M. Relay D operates and connects an interrupted battery circuit LF to winding 1 of relay C which responds to connect intermittent lamp-flashing battery to the a-wire over the last contacts in the bank and wiper A<0>. Spring w3 connects busy tone BB through relay A to the b-wire.