Patent GB-413701-A (GB)
Title: Improvements in or relating to telephone or like systems
IPC: H04Q3/58
Filed: 1933-01-20
Abstract: 413,701. Exchange systems. STANDARD TELEPHONES & CABLES, Ltd., and GOULD, J. R., Connaught House, Aldwych, London. Jan. 20, 1933, No. 1908. [Class 40 (iv).] Relates to systems in which a number of subscribers' lines are associated at a switching station, having no local source of current, with a single two-wire line to an exchange. In the manual exchange system, Figs. 4, 5, the line terminates in a number of individual calling jacks and a common answering jack. In the case of incoming calls a common switch associates itself with the line and hunts for the individual jack, sending impulses at the same time to a counting chain at the switching station to select the wanted subscriber. Outgoing calls are established in the same way, the operator after answering the call in the common jack, plugging into the calling subscriber's individual jack. In the case of reverting calls the operator then plugs into the wanted jack and removes the plug from the calling party's jack to cause the common apparatus and counting chain to be restored and re-operated. In the automatic exchange system, Figs. 1-3, common apparatus interacts with the counting chain at the satellite and also with a switch which is individual to the line and which on outgoing calls selects the calling party's meter and on incoming calls hunts for the final selector terminals over which the line was seized. The common apparatus also discriminates between reverting calls (21-20) and outgoing calls, discrimination in the case of outgoing calls having the reverting numbers as their first two digits depending on the arrival of a third digit within a definite time interval. The counting chain relays receive current over one line wire, impulses in the form of alternate strong and weak current over the other wire being used for controlling them. Two relays are connected to the impulsing leg and are so associated with rectifiers that one, which remains energized continuously during impulsing, falls back before the other (which repeats the impulses to the counting chain) when the line is disconnected at the exchange. Means are provided for restoring the circuits in the case of premature release. Automatic system-incoming call. The final selector on seizing the line puts ground on PF, Fig. 2, energizing the cut-off relay (not shown) connected to PLS which puts battery on the wire Z to energize CO. CO energizes CA and provided the common equipment; Fig. 3, is idle, the associating relay K. ST in the common equipment pulls up and starts the switch S which continues to advance slowly by interaction with two sluggish relays SA, SZ. In its 1st 2 positions wiper S2 connects strong battery and in its next 2 positions weak battery to the + wire of the line to the switching station and thereafter strong and weak battery in alternate positions. In position 4 and subsequent positions wiper S3 connects battery to the - wire and wiper S4 connects up magnet M of the individual switch so that thereafter switches S, M, step together until wiper M3 encounters the terminal connected to the + terminal with which the final selector has made connection. The next relapse of SA then energizes BB which disconnects the line to the switching station from the common apparatus and connects it instead to a ringing source DRL and relay F. ST, K, SZ fall back and M takes a further step, wiper M2 now engaging the + wire from the final selector previously engaged by M3. In the switching station, Fig. 1, A and B are energized by strong battery on the + wire and only B by weak battery. Battery on the - wire (position 4 of S) energizes NC over its right hand winding. The operation of A in position 5 of S puts MM, MA in series with C and the left hand winding of NC. MA pulls up quickly, short-circuiting MM before it can operate and C disconnects the high resistance winding of NC. When A falls (position 6) MB is operated and short-circuits MA. Similarly in position 7, MC is energized and so on. When the operation of BB at the main office disconnects the line to the switching station B falls quickly and A sluggishly owing to the effect of rectifiers RE1, RE2. C falls back and R pulls up in series with NC, the operated relay MA-MK and the relay F at the main office which is not operated. Ringing current goes to the station selected by the relay MA-MK over the + wire only and when the called party replies the shunting of relays R, NC, MA-MK by the ringing circuit allows F to pull up and substitute AA for the ringing generator. AA energizes AB, FF. Battery over L is now connected to the - wire to energize LR and the appropriate one of relays LA-LK, the former releasing NC, R and the selecting relay and preventing at lr1 the initiation of an outgoing call. At the exchange, AB operates the ring-cut-off relay in the final selector and releases CA which allows I to pull up in series with the back-bridge relay and energize SW which locks and completes a metallic talking circuit. Relays L, AA, AB, I fall back. When the calling party clears PF is disconnected at the final selector and CO, and the out-off-relay (not shown) fall back. BB, F, FF fall back and switch M goes home. Automatic system-outgoing call. When a call is made, the individual line relay LA, LB &c. pulls up in series with L at the exchange. LA &c. makes a new circuit for itself including LR which prevents the operation of any other individual line relay and disconnects relays A, B. In the exchange, L energizes LL which loops the talking circuit to start the line switch and energizes F, FF, IC. When the cut-off relay is energized, CO, CA, K, ST pull up and the common apparatus operates as in an incoming call but since LL is energized, S5 in position 2 energizes PR which locks, arranges for S3 to connect battery to the - wire over a very high resistance RVH in position 3 and alters the connections to the S2 bank so that strong battery is connected up in positions 3, 4 and the even positions and weak battery in the odd positions. At the switching station the individual and common line relays fall back on the operation of K and A, B pull up and remain energized in positions 3, 4. MM alone pulls up in the high resistance circuit over MA, C in position 3 and puts CC (right hand winding) in parallel with A, B. In position 4 the resistance is cut out and MA, C pull up releasing MM, CC however remaining operated over its left hand winding in series with MA, C. NC is unoperated but the building up of the selecting chain now proceeds as in an incoming call until the relay corresponding to the calling line is operated. CT at the exchange which has been unable to operate in series with the selecting relays now finds an operating circuit over a contact such as mb2 and the calling line relay. The latter locks to the line energizing LR to cut-off the selecting and control relays. CT at the exchange energizes CH in two steps, full operation taking place on the relapse of SA. CH energizes BB which removes a short-circuit from AA which energizes AB. CA, LL fall but F, FF are held by BB and IC is held over PLS. CH also energizes AS and drives S rapidly to position 14 in which CT is disconnected but battery is still connected to the - wire via L. The relapse of LL removes a short-circuit from I. Dialling tone which has hitherto been shunted at bb1 now goes back. AS releases CT. During dialling the individual relay and relays LR and L are held in series with the bell. AA repeats the digits to AB which repeats them to the switches, CA being energized during each digit to improve the impulsing loop. AS also responds to the impulses. At its first relapse CS is energized and at the end of the impulse NP pulls up and locks and puts the low resistance winding of CS in parallel with its other winding so that the next impulse energizes S. A single impulse thus produces no effect since CS falls releasing NP. If the 1st digit is greater than 2 the relapse of CS locks NP in series with SZ over S5. K is released and the common equipment is restored. If however the digit is 2, S5 energizes RV which unlocks PR and shunts the high resistance winding of CS by its low resistance winding so that the switch responds to the whole of the next digit. The 2nd digit energizes CS, NP as before and RV is locked until the end of the digit when CS, NP, RV fall back. A circuit is now made for TP from ground pulses on SP. On operating TP locks and connects a 2nd pulse wire ZP to SA. If a third digit comes in TP is unlocked, the switch responds to the digit as far as its last contact and at the end of the digit the common equipment is restored. When the metering impulse is applied to MV by the 1st code selector, the meter selected by M4 on switch M, which was stepped with switch S during the control of the selecting relays, is operated and SW which is energized in parallel, locks up and switches through. Relays L, AA, AB, I fall back and CA pulls up. When the calling party clears CO, IC, SW fall back to release the connection. Reverting call. If the 2nd digit is odd PR is energized and looked and if, after a 1st digit 2, no 3rd digit arrives, SA is operated by the time pulse, energizes SZ and releases CH which releases AS, BB. F, FF fall disconnecting AA, L from the line. AA, L, AB at the exchange and the individual line relay, and LR at the switching station fall back. FR which is energized on the relapse of FF releases the exchange switches and locks itself IC and CO. Strong battery is connected over S2 to the + wire whatever the position of S owing to the co-operation of PR. TP on its release by AS connects battery via CT (upper) to the - wire, and releases SA so that the switch S now advances automatically. At the switching station A, B, C, MA (but not NC) pull up. When S takes its first step A falls and MB pulls up and so on. The local numbers have second digits which are complementary with respect to 11 to the final directory digits. When S reaches its last contacts B