GB326986A - Improvements relating to automatic and semi-automatic telephone systems - Google Patents

Abstract

326,986. Siemens Bros. & Co., Ltd., and Patterson, W. G. March 9, 1929. Automatic exchange systems. - In a selector having two sets of wipers, hunting simultaneously, and two test relays, one or each of these relays has, in addition to its operating winding connected to the associated test wiper, a winding connected to the other test wiper and arranged so that when idle outlets are encountered simultaneously, one test relay is quicker to operate than the other. One relay may have a differential winding connected in series or parallel with a single winding of the other relay so that the first relay will not be operated by its differential winding and will be retarded or prevented from operating when current flows over both windings. The other relay may also have a winding in the operating circuit of the first relay so that it is quicker to operate when current flows over both of its windings. Twogroup selectors are described. Group selector, Fig. 1, testing for battery on idle outlets. Impulse relay A operates over the b wire and change-over relay D pulls up over Di to prepare the circuit VM. At the first vertical step the circuit Di is opened at n3 but this relay holds over Dii during the impulse train, and then falls back to complete the circuit of RM. If test wiper C1 finds battery first, TP operates over i but the current over TSii fails to operate the other test relay which is energized over TSi only when C2 finds battery first. When both test wipers find-battery simultaneously, the windings of TS oppose each other and prevent or retard its operation. The test relays each open the operating circuit of the ether, and have locking windings TPii, TSiii. If all outlets are busy, TP operates over C1 and the last bank contact, and stops the drive. A busy signal may be given. Group selector, Fig. 2, testing for absence of ground. Impulse relay A operates over the calling loop, and energizes B which connects the windings of shunt-field stepping-relay G to the test wipers C1, C2. The impulses are repeated to VM over D, which completes circuits from ground at b2 for both windings of G which lock over g2, g3. When D falls back, RM operates and interacts with G until either or both test wipers fail to find ground. If C1 fails to find ground, TP operates in series with the righthand winding G which remains inert, although its left-hand winding is energized over C2. The other test relay TS has two windings arranged as described with reference to Fig. 1 so that it does not operate when idle outlets are found simultaneously. Each test relay opens the operating circuit of the other. When all outlets are busy, the switch steps on to last contacts, the reoperation of G being prevented and busy tone connected up by cam springs s2, s1 respectively. The last contacts of C1, C2 are grounded to prevent the operation of TP, TS.