Patent GB-398542-A (GB)
Title: Arrangement for controlling switching operations in telephone systems
IPC: H04Q1/442
Filed: 1932-03-16
Abstract: 398,542. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. March 16, 1932, No. 7887. Convention date, March 19, 1931. [Class 40 (iv).] In an inter-exchange system a calling exchange sends a train of impulses to the wanted exchange which sets the apparatus thereat into the position for receiving the selecting impulse trains whereupon a control signal is returned to the calling exchange which terminates the calling impulse series and allows the selecting trains to be transmitted. As described, alternating current impulses are used for all signalling purposes. When the junction IL is seized relay AR pulls up and relays R6, R7 and R8 energize. These three relays R6, R7, R8, all of which are of the slow-release type, interact slowly. Relay R5 energizes whilst R6 is up and connects alternating current to the distant exchange. Under normal conditions the apparatus is as indicated in the Figure, so that R10 is energized on the first pulse and R11 pulls up. R11 makes its contacts 31 and 32 only, pulling up completely over 32 when the pulse ceases. Contact 31 closes the starting circuit for register finders RS which hunt to find a free register RE2. Relay R9 energizes when a free register is found and transfers the incoming circuit to RR4 which relay responds to the next calling impulse and drives the sequence switch SO into position 2. When the impulse ceases SO, which moves one step on each energization and on each de-energization of SOR1, moves into position 3 and RR12 pulls up to send an alternating current pulse to the calling exchange. The sequence switch moves into position 7 in which position the circuit for RR12 is broken and the pulse ceases. At the calling station R2 responds to the return signal and R4 pulls up to open the impulse transmitting circuit. Relays KR and R1 energize, KR releasing the impulse transmitter or, in the case of a manual call, indicating to the operator that dialling may proceed. Relay RI repeats the impulses to R5 which transmits them as A.C. pulses over the junction to set registers RM1 .. RM5 in turn. The connection is established in the usual way. When the conversation is ended relay R5 is energized for the release period of R3 to transmit a clearing impulse to the called exchange. R10 responds and as R11 and R13 are both operated, R12 pulls up, breaking the holding circuit of R11 which restores when the pulse ceases to release the connection. If the relay arrangement at ST2 is not in its normal position when the junction is seized, the number of calling pulses necessary to set the incoming apparatus into its receiving position would be other than two. If, for example, the clearing signal had not been received correctly on the preceding call, three pulses would be required, the first releasing relay R11 and the next two performing the normal calling functions. If stray currents had energized R10 so that the register RE2 had been selected then the return signal would be transmitted on the termination of the first pulse ; whilst if the sequence switch is found in a position between 7 and 16, the calling pulses will first set the sequence switch to normal, relay R11 will be released and then a further two pulses will prepare the apparatus to receive the selective impulse trains. The relays R2, R10, RR4, which respond to the A.C. pulses, are each bridged across four rectifiers to allow direct current to pass through the relay windings when the relays are energized.