Patent GB-314465-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems and apparatus therefor
IPC: H04Q3/42
Filed: 1928-03-28
Abstract: 314,465. Standard Telephones & Cables. Ltd., and Gould, J. R. March 28, 1928. Semi-automatic exchange systems. - Trunk offering distributors are arranged to discriminate between calls having different numbers of digits. Three arrangements are described. In the 1st there are fewer than 10,000 5-digit numbers e.g. the lines dealt with may be 2000 - - 4899 and 49000 - - 52099. In addition to the main distributor D1, a 2nd distributor D2 is provided. Both respond to the 1st digit and DI drops back. If this digit denotes a 5-figure number, the 2nd operates only D1, if not it also rotates D2. The position of D2 now determines whether the number is a 5-digit one, in which case D1 responds to the third digit or a 4-digit one in which case D2 switches through. In the 2nd system there are more than 10,000 5-digit lines and a third switch D3 is added. The 1st digit operates D1 and D2 as before and if it denotes a 5-digit number the next two digits go to D3. The other numbers are dealt with by D1 and D2 as in the 1st system. In the 3rd system there are fewer than 10,000 lines all told e.g. in a satellite office. D2, D3 are omitted and DI responds to the 1st digit, which has no selective function and drops back. If the 2nd denotes a 4-figure number the switch takes an automatic rotary step and switches through. Otherwise it responds to the third digit in the ordinary way. 1st and 2nd systems. When the distributor is seized, line relays A, I and release relay B pull up. The first digit is repeated to magnet V of the main distributor D1 and dialling relay C in parallel and to magnet V of the secondary switch D2. Two-step relay DA pulls up its light armature da1 when the springs N change over. On the relapse of C, release magnet Z of the switch D1 is energized and on the restoration of the switch, DA pulls up all its armatures and switches over the impulsing circuit for D2 to its rotary magnet R. If the first digit indicates a 5-digit call and there are more than 10,000 5- digit lines, DB, which pulls up over post springs NP on the relapse of C prevents further impulsing into D2 and connects magnet V of D3 in series with two-step relay DC (lower) to the impulsing circuit for D1. The second digit thus raises the switch D3. DC which pulls up a light armature dc1 on the first impulse and all its armatures when D1 moves off-normal, transfers the impulsing circuits from D1 to D3. If there are not more than 10,000 5-digit lines, the 2nd digit raises D1 since DC, D3 are not provided. If the first digit does not indicate a 5-digit number, DB is not operated, and the 2nd, in addition to raising D1 rotates D2. If the number is a 5-digit one, wiper Z of D2 is now on a terminal connected to battery over a resistance and DB pulls up to prevent further operation of D2. E, which is energized on the relapse of C after the 2nd digit sends the 3rd (in 5-digit calls) into magnet R of D1 or D3, and C on pulling up energizes EA. On the relapse of C after this digit, G is connected to 'wiper Z and, if the connector is busy, pulls up and connects up busy tone. Similarly if after the 2nd digit, D2 is on a busy connector instead of on the terminal indicating a 5-digit call, DB pulls up and is followed by G and busytone goes back. If the connector is idle, in a 5-digit call, the relapse of E when C falls back after the 3rd digit energizes H which extends the impulsing circuits to wipers R, V, marks the connector busy and energizes FS. In the case of 4.digit calls, the non-energization of DB allows EA to pull up on the relapse of C and energization of E after the 2nd digit. EA releases E and H, FS pull up as before, H in this case energizing DB. 3rd system. The circuits are modified by the addition of the leads shown dotted and the removal of those indicated by crosses. The first digit is absorbed as in the other systems and DA connects up the springs NPA which are operated on the levels corresponding to the 2nd digits of 5-figure numbers to cause the relapse of C to energize DB which disconnects CI. The switch then responds to the 3rd digit. If the springs NPA are not operated, the relapse of C and energization of E energize CI which energizes R to give the wipers a rotary step, and EA to release E. If the wipers are on a busy connector, DB, G pull up to send the busy tone. If not relapse of E energizes H which energizes DB and switches through. Completion of connection and release. The remaining digits go to the connector over wipers V, R. EA is released by the first operation of C and is re-energized at the end of the final digit and energizes RC which locks up and switches the talking circuit through. Assuming the wanted party to be still busy, G pulls up over the test wiper P and keeps I, the first circuit of which is broken by RC, connected to the - wire. The operator then offers the call and when the wanted party releases G, I is dis-connected to inform the operator, who then sets up the call over the regular switches. When the operator unplugs, A and B fall back, a releasing impulse is sent to the connector over FS (lower) and wiper Z. When the connector is restored, FS falls back and the release magnets of switches D1, D2, D3 are operated in turn. Relay A cannot be re-operated after the relapse of B until all the switches are normal.