328,314. Standard Telephones & Cables, Ltd., and Baker, J. H. E. Dec. 20, 1928. Automatic and semi-automatic exchange systems; party line systems.-A switch in a train of numerical conversational selectors controlled by a common registering mechanism is controlled by this mechanism over a path different from the conversational path between it and a preceding switch. In the system described, the conversational path between two subscribers S1, S2, Fig. 1, comprises line-circuit LC1, finder-selector link F, SS, final selector FS and line-circuit LC2, two-way junctions to a distant manual exchange being also accessible to finder F and selector SS. When a call is initiated by S1, the line relay locks up and S1 may replace, his receiver and await ringing. The finder F of a link circuit LK associated with an idle register-controller RG and allotted by distributor D, hunts for the calling line. The register-controller, Fig. 5, comprises common control relays for the finder and selector, and four single-motion switches R1 r - R4, all the digits being received by switch R1 which moves to intermediate sub-normal positions between the digits. After, the first digit has been registered, R2 moves to the first contact of the group marked by R1 and hunts for an idle final selector FS in the group or for an idle junction. Switch R3 is moved to the first contact of the required tens group and subsequently to terminals of the wanted line in accordance with the setting of R1 for the second and third digits. The marking bank of R2 is multipled to a bank of the selector or SS (a non-homing switch) and also of register switch R4, and after reception of the third digit in the case of a local call, SS and R4 hunt for the terminals marked by R2 and make connection with outlets leading to the final selector FS, R4 being a relief switch for R2 to extend additional controlling leads to FS. The final selector is also a non-homing switch and is first driven home and then stepped by impulses from the register-controller over a wiper of R4 in synchronism with the stepping of R3 to normal. The system described is a party-line system, and the appropriate ringing current is connected up by R1 in response to a fourth digit. In the case of a reverting party-line call, a digit 9 is dialled followed by the ringing digit. In response to the first digit R1 completes a circuit for stepping the selector SS to its last (unused) outlets and R1 is then driven through to the position for receiving the ringing digit The calling party, after dialling this digit, replaces his receiver and ringing current is sent back over the calling line. The registercontroller also comprises a time switch PS, Fig. 5, which controls arrangements for dealing with various abnormal conditions which may arise. The Provisional Specification describes a system which differs from the above in the manner of access to idle link circuits and in respect of reverting party-line calling arrangements. Local call; seizure of link-circuit and register. Line relay L, Fig. 2, locks to ground at l1, and operates Y, Fig. 3, of the distributor which engages K, Fig. 4, of the link-circuit, on which the distributor is standing. Relay K grounds lead 5 to operate LG, Fig. 5, which energizes S, SA and holds over lg4, t6, lg2, s4. The driving circuit of finder F is completed over lead 8, and when the calling line is found KK, Fig. 2, operates over lead 7 in series with T, Fig. 5, which stops the drive. Relay KK locks up, and releases L, which releases Y, relay K remaining held over lead 11, and wipers PS4. R1c. Ground on lead 4 at the register steps the distributor. Ground from any idle register-controller is connected over lead 3 to the last contact of D so that the distributor normally passes this contact. If all the registercontrollers are busy, D is held up until one becomes free. Relay T releases LG which completes the ringing contact (source RCS1, R1a, F, lead 9, calling line, lead 10, t2, f7, battery). When the calling party responds, F operates, locks and extends the line to impulse relay AA which operates BB, BA, and BA completes circuits for AA independent of D. Dial tone is sent out from DT. It may be made compulsory for the calling party to await ringing. In this case the dotted line connections at lg1, Fig. 5, are used so that LG locks up over the loop when T operates and is only released when the calling party replaces his receiver. Registration of numerical digits and setting switches R2, R3, R4. All digits are registered on R1 which proceeds to intermediate positions HI, H2, H3 after the registration of each digit. In response to the first digit, R1 steps in a circuit including CC and wiper R1d, and CC operates CA which releases F. When R1 goes off normal, ground on wiper R1c completes a self-interrupting circuit for R2 and when wiper R2c reached the first contact of the group marked by R16, relay MM pulls up and stops R2. As CO and CA relapsed at the end of the digit, DD operates to the ground on R1c, locks to s6, releases MM, and completes (1) a stepping circuit for R1 which moves to its 9th contacts, and (2) a stepping circuit (r2., dd11, hh2) for R2 which hunts for a free final selector such as FS, Fig. 6, which has battery over non- induction winding of HK connected to lead 20. When R2 reaches FS, this battery is extended over R2a to test relay HH which opens the drive. Relay U pulls up, locks, and completes circuits over R1c for stepping R1 to position HI. Relay HH is short-circuited at u5 and R3c (normal and falls back, while ground over u5, R2a, conductor 20, busies FS to other register-controllers. In response to the second digit, R1 steps as before but R3 now follows and when R3b encounters the lead XX connected to the first contact of the group marked by R1b, MM opens the drive and operates E which locks to s6, while R1 runs to position H2 and MM falls back. The leads YY in the bank of R1b are multipled to each tens group in the bank of R3 so that when R1 responds to the third digit, R3 steps on until its circuit is opened by MM operating over R3a, R1b. Relay J operates, locks to s6, and completes a circuit for stepping R1 to position H3. Register R4, a relief to R2, hunts for the terminal marked by R2c in the bank R4d, relay G being operated in parallel with R4. Relay MM engages over o3, e6, j6, kb2, g5 and marked lead Ml, opens the circuit of R4, and, before G falls back, completes the circuit of KB which locks to s6, releases MM, and connects this relay to lead 16 and marking wiper of group selector SS. Operation of group and final selectors SS. FS. The terminals in fourth bank of selector SS are multipled by leads such as Ml to the banks R2c and R4d of the registers. Relay KB, operated as described in the preceding paragraph completes the circuit of magnet S of SS over lead 15, and when the marked terminal is encountered MM operates, stops the selector, and energizes LK which locks s6, and releases MM. The final selector, Fig. 6, is normally in the position in which it was set for a previous call and its driving circuit over lead 18 is now completed in parallel with a circuit for G. When it reaches home, MM operates from ground at H, Fig. 6, over 21, R2b, and opens the driving circuit and, during the release period of G, N pulls up, locks to s6 and completes a circuit for X over interrupter springs of R3, and homing bank R3c. R3 interacts with X and steps to normal and, during the stepping, impulses are sent from x2 over R4b and lead 17 to magnet FS so that when R3 reaches home X falls back and the final selector stands on the wanted line. When the final selector moves off normal MM relapses and operates G over R3c. the circuit of G being opened when R3 reaches home. Testing: ringing, completion of connection. During the relapse of G the wanted line is tested. If free, battery over both windings of cut-off relay corresponding to KK, Fig. 2, over lead 19, R4a is connected over HH to ground at R3c. Relay HH operates V which locks to s6 and completes an operating circuit for HK, Fig. 6, over 21, R2b and this relay temporarily locks over 19, R4a to ground at v6, this ground marking the line busy. The final or ringing digit had stepped R1 from position H3 to one of the next six contacts and code ringing is now sent out from one of leads RCS2 - - 8 over R1a, f<5>, F, 14, wanted line 13, v2 to battery. When the called party replies, F trips the ringing and releases V which connects ground from s6 over lead 12 to operate B, Fig. 4, which at b7, b8 holds relay HK, Fig. 6, the cutoff relays KK, busies the lines, and connects up the feed relays A, D. Relay K in the link falls back and B locks to a2 or d2. Busy signal. If the wanted line is busy HH fails to operate and when G has relapsed, P is operated by ground on the test wire and connects up busy tone from BT. All final selectors busy; first digit incorrect. The last contacts of the groups in R2a are connected to relay W so that if all final selectors in the group are busy, ground from u5 over HH, sa2. lk1, dd5 operates W which connects up tone from NUT. Terminals of unused groups in R2a are also connected to W so that if a first digit corresponding to these groups is dialled, NU tone is also connected up. Release of registers. The relapse of K in the link circuit releases S, SA, and operated relays in Fig. 5. R1 homes over sa7, ba5, R1d, s7 or sa4, sa8, aa1, R2 homes over an obvious circuit, R3 homes over j5, o5, sa9, R3c, while R4 remains as set. Reverting party-line calls. A calling party dials 9 and steps R1 accordingly so that R2 steps to its last contacts and MM operates over R2c, R1b. Relay RC operates over R1b, DD operates over R1c and both lock to s6. Relay MM falls back. Relay DD closes a circuit for HH over R2a and the non-inductive winding of W, the operating circuit of which is open at rc2. Relay HH energizes U and O which lock to s6, U being slow-to-operate. Relay 0 closes a circuit for d