Patent GB-401695-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1932-05-17
Abstract: 401,695. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool, BAKER, G. T., Blackbrook, Caerphilly, Glamorgan, BELAS, F. T., 26, Arlescourt Road, West Derby, and BEALE, C. E., 59, Towers Road, Wavertree, both in Liverpool. May 17, 1932, No. 14073. [Class 40 (iv).] A final selector which is taken into use alternatively by a local or a toll penultimate selector sends back one of two signals thereto according as the wanted line is idle or busy. In a local call, the penultimate selector rings the wanted line or sends back a busy signal, and in the latter case releases the final selector. In a toll call, if the line is idle ringing takes place under the control of the operator, while if the line is busy, a busy signal is sent, and the operator may control the penultimate selector to complete a toll-offering connection, the final selector being held. As described, the final selector is controlled by common apparatus and is adapted for PBX hunting over one set of wipers. Local penultimate selector, Figs. 1 and 2. Line and release relays A, B energize and a guard resistance is included in the incoming test circuit. Relay G, which holds by virtue of a short-circuited winding in parallel with the vertical magnet VM during impulsing, acts as a stepping relay for the rotary magnet RM, being connected to test wiper P1 at each step, and relays HA, HB test in turn the two trunks encountered in each position, being connected to test wipers PI, P2 by the rotary magnet and relay G respectively. When an idle trunk is found, relay HA or HB energizes to battery over the test wiper, switches through and connects up relay J. If all the trunks are busy, cam springs S become operated, and relay F energizes to send back a busy signal. Subsequent impulse trains are repeated over the negative wire to set the final selector. Assuming the wanted line is idle, earth is received back over the positive wire to energize relay SD, which completes the ringing circuit through ring-trip relay F. Upon reply, relay F energizes, followed by back-bridge relay D, which reverses the connections of line relay A and disconnects relay J, whereby booster battery is momentraily connected to the test circuit. Should the wanted line be busy, earth is received back over the test wire, and switching relay HA or HB relapses, connecting up relay F to send back a busy signal and releasing the final selector. To provide for the possibility of the calling party hanging up at the moment of seizure, line relay A has one winding connected to the test circuit. In this case, relay B disconnects relay A and the selector takes a vertical step, whereupon relay B falls back and effects release of the connection. Final selector, Figs. 3, 4. The upper or lower set of wipers is used according to the route of access. Relay K energizes over the test wire in series with wiper-switching relay WS if the lower wiper-set is to be used and associates the selector with the common apparatus. Line relay 1A energizes over the negative wire, and release and dialling relays 1B, 1C pull up, inserting a guard resistance in the test circuits of all the selectors of the group. Relay 1C on relapsing after the penultimate impulse train connects up relays 1E, ER to effect change-over, while on relapsing after the final train it connects test relay HC to the test wiper pending the release of relay IE. If the wanted line is idle, relay HC energizes, disconnects relay ER and applies earth to the incoming positive wire to initiate ringing. Switching relay H energizes over the test wire and locks. A rectifier MRA prevents relay H holding over a busy line during toll offering. Line relay 1A falls back and initiates release of the common apparatus, the connection being held from the group selector. If the wanted line is busy, relay 1E on relapse applies earth to the incoming test wire to cause a busy signal to be sent. Relay ER falls back and the final selector releases. P.B.X. hunting. P.B.X. groups are reached over the lower set of wipers, and hunting is controlled over a bank PBX having two wipers engaging adjacent terminals, all lines of a group except the last being marked by ground over a contact of relay WS. If the first line of the group is busy, relay HS energizes and locks, closing a fresh circuit for the rotary magnet 1RM and relay 1C under the control of relay 1E which acts as a stepping relay. Relay 1C falls back at each step to complete the test circuit, in which relay HC operates when an idle line is found and unlocks relay HS to stop the hunting. If the last line is busy, relay HS is unlocked, and relay 1E on relapse signals a busy condition. If the selector is set to a particular P.B.X. line, no hunting occurs since relay HS is short-circuited over bank PBX. Release of common apparatus if no impulses are received. Relays TP, TZ energize under the control of time pulses and connect up relay HC which sends back a signal to initiate ringing, while battery is connected to the negative wire to operate the ring-trip relay. Line relay 1A is disconnected and the final selector takes a vertical step in order to maintain the busy marking. On the relapse of relay TP, relay H energizes and connects up NU tone. The common apparatus is released. Toll penultimate selector, Figs. 5, 6. The setting operations are substantially the same as those of the local group selector, Figs. 1, 2, except that relay P energizes at the first vertical step, preparing the test circuits and connecting up relay 2SD. Upon operation of test relay HA or HB, relay P is disconnected, but relay 2SD remains held over test wiper P1 or P2, while ring-trip relay F energizes to prevent ringing. If the wanted line is idle, relay SC operates to earth on the positive wire and prepares the ringing circuit. Actuation of the operator's control key grounds the negative wire and energizes differential relay OC, which releases relay F by short-circuiting to effect ringing. If however the wanted line is busy, relay 2SD falls back due to the short-circuiting ground returned over the test wire and connects up relay SE which applies a busy signal. Actuation of the operator's control key now energizes differential relay OC, whereupon relay SC pulls up and completes the talking circuit to enable the operator to offer the call. Back-bridge relay 2D energizes locally, reversing the line relay connections to provide supervision, and relay SE relapses. When the wanted subscriber clears the existing connection, relay 2SD energizes over his cut-off relay and releases relay 2D to give a supervisory signal. Further actuation of the control key effects ringing if necessary. Relay SE is also employed to transmit a busy signal should all trunks be found busy.