Patent GB-314562-A (GB)
Title: Improvements in and relating to automatic and semi-automatic telephone systems
IPC: H04Q3/58
Filed: 1928-03-29
Abstract: 314,562. Standard Telephones & Cables, Ltd., Hartley, G. C., and Cameron, A. H. March 29, 1928. Automatic and semi-automatic exchange and party line systems.-In a system in which rural offices are spaced along an omnibus junction or group of junctions to a main office, the subscribers set up calls themselves. In the system described, the offices have incoming connecting circuits permanently associated with the junctions and comprising a selector and pilot switch, and connecting circuits for local and outgoing calls comprising a finder, selector and pilot switch. The first 5 impulses of the office digit, which steps the pilot switch, have no selective effect, but initiate the seizure of an idle junction and give time for this and for the distant release relay to soak. The remaining impulses step the incoming pilot switches. This arrangement prevents the seizure of the junction by a faulty line. If the call is local, the pilot switch releases the junction, acts for the 2nd digit as a marking switch to the selector which receives the 3rd directly, and subsequently responds to a 4th to select a ringing code or, if the call is for an exclusive line, moves automatically to connect up the ordinary ringing lead. The establishment of reverting calls depends on the recognition by the connecting circuit that its release coincides with the wanted line's becoming idle. If the call is non-local, the local pilot-switch and those at the not wanted rural offices are unaffected by the subsequent digits, that at the wanted office controlling the establishment of the call similarly to a local pilot-switch. The main office is signalled by dialling O. The operator there, whose circuits, like those at the rural offices, normally clip the first 5 impulses of the office digit is enabled to offer a preferred call by causing the full number to go out. Office selection. Line relav L energizes starting relay Y and magnet R1 drives the finder F of the preselected connecting circuit, Fig. 2, under control of relay T which pulls up when the line is reached in series with cut-off relay K and extends the loop to impulse relay A which energizes release relay B which drives on the allotting switch. The first digit is repeated by A to magnet R2 of the pilot switch P, the first impulse going over a home contact and the others over a contact of the series relay C. On the second step, G is energized and makes a selfinterrupting circuit for magnet R3 of the selector S and the test relay X is connected up. When an omnibus junction is seized, X locks up and T, Fig. 3, pulls up, energizes U to mark it busy locally and switches it over from the incoming to the local connecting circuit. The - wire is thus connected to battery over A-1, G-1 in parallel and relays A, B in all the rural incoming circuits (Fig. 3) and in the main office circuits, Fig. 4, pull up to busy the junction everywhere. If there are no junctions available, the selector is stopped on its 5th terminals by J. G falls back after P has made 5 steps and the remaining impulses are repeated at A-1 over the - wire of the junction. Since the test relay X is disconnected when P receives the 4th impulse the duration of 1¢ impulses at least is allowed between the seizure of the junction and its reception of an impulse. If the call is local, F is energized over P2, releases X to free the junction, locks itself and drives P to its 2nd home position. If not, the relapse of C prevents any further action in the local circuits. In the rural office for which the call is intended. F in the incoming circuit similarly drives the pilot switch to a 2nd home position. In the other offices the relapse of C prevents any further action. If the call is for the main office, (selected by dialling O) the switch DS (Fig. 4) lights a calling lamp LL. Line selection. The pilot switch at the local or incoming office responds to the 2nd digit and on its 2nd step makes a driving circuit R3, J-2, P3 for the selector which is stopped by J when it reaches the beginning of the group indicated by P1. F is held by the series relay until the end of the digit and when it has fallen back and J has operated, K pulls up, and the pilot switch goes to its 3rd home over F-7, J-1, P3. The third digit goes over K-6 to R3. C releases J and holds K until the end of the digit. In the interval between the relapse of C and K, H is connected to the test wiper and if the line is idle pulls up in two steps and locks itself. If the line is busy the relapse of K energizes G which connects up busy tone. Ringing line and signalling reply. If the call is for a party line, the pilot switch receives a 4th digit and selects a -ringing code with its wiper 2. If it is for an exclusive line it moves one step in a circuit R2, F-7, H-6, C, PI to connect up the ordinary ringing lead. Ringing current is cut off when the called party replies, by F which completes the talking circuit. Backbridge relay D in a local call makes a further circuit for B and in an incoming call sends back a reply signal by connecting battery to the + wire; to operate D, Fig. 2, or SR, Fig. 4. Reverting calls. When the calling party hangs up after dialling, R which was energized by K and held after the relapse of K over the test wiper (since the wanted line is busy) is cut off by B but before it can fall a new circuit is made for it by H which switches through and releases G when the line becomes idle. Ringing current is sent out as before and when the line is bridged at the substation, D re-energizes B which releases R. Release. When both parties in a local and the calling party in an inter-office call hang up, B makes driving circuit for the selector, which is stopped in the home position by J which connects R2 in place of R3 to send the pilot switch home. During release, G operates via T-4, B-3 to busy the circuit to the allotting switch. In the case of inter-office calls, the junction is busied locally by U for a short time after its release by T or B. Zero calls. Impulses in the junction step DS, Fig. 4, which, if it receives 5 impulses lights LL. The call is answered by plugging into AJ whereupon S switches the cord through and removes busy tone from the tip spring of the calling jack. Calls from main to rural; preferred calls. The operator plugs. CCP and DP into CJ and DJ of an idle junction. S connects battery over BF to the - wire to operate the distant impulse relays and A and B pull up. A repeats the first digit over C to DS which after 5 steps energizes D to replace BF by a battery connection over A-1. D locks up, and the remaining impulses of this digit and the whole of the subsequent digits are thus repeated over the junction. Owing to the relapse of C the remaining digits do not affect DS. In the case of preferred calls, the operator throws TOK. This enables her if necessary to break into a busy junction by providing a circuit for S, which normally pulls up only if B is unoperated, and energizes D to cause the first digit to go to line unclipped. As a result, F, Fig. 3, at the destination office, pulls up in series with O instead of direct, and if the wanted party is busy, G energizes R over wiper T and completes a, talking circuit independently of H. If the call is accepted both parties hang up, R falls back and H pulls up and the line is rung in the ordinary way.