Patent GB-392288-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/42
Filed: 1932-01-25
Abstract: 392,288. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and HAMILTON, R. M., c/o General Electric Co.,. Stoke, Coventry. Jan. 25, 1932, No. 2201. [Class 40 (iv).] In an automatic exchange system, in the event of a call finding, at any stage in the setting up of the connection, all the outlets busy, the call is routed to a manual operator who completes the connection without any indication of the operator's intervention being given to the calling subscriber. In the event of the outlets being busy at the non-numerical stage, the operator is signalled and connects the call manually to a free first selector, whilst if the condition is encountered at a later stage, the call is extended to registering equipment, which records the remaining digits and displays all the digits dialled to the operator who completes the call manually. The manual operation consists in placing the plug of a preselected link in the jack of the wanted line, the other end of the link comprising a bi-directional backward hunting switch which hunts for the calling circuit. To obviate the need for manual testing, when a wanted number is displayed before the operator, all engaged lines in the hundred containing the wanted circuit are indicated by the illumination of their individual calling signals. Should the wanted line be busy, the busy signal is returned by the operation of a busy key.. Automatic ringing and metering are provided but these may be replaced by manual equipment if desired.. The invention is described as applied to a four digit system. All line finders busy. When a subscriber SUB, Fig. 1, lifts his receiver relay L operates and connects the line finder starting relay SR in series with lamp SL, SR pulling up to,start the line finders, but SL does not energize. If, however, all line finders are busy contact ab is closed connecting a low resistance winding of SR in parallel with the high resistance winding so that SL is illuminated. An operator then plugs PL, Fig. 2, into the jack SJ energizing K and HC in series. relay HC connecting the calling loop through to a first selector permanently associated with PL. Dial tone is returned to the calling line and when the first digit is dialled contact x changes over to put the relay HC under the control of the switch train. Relay HC acts as a supervisory relay and controls the lighting of lamp CF at the termination of the call. Busy condition at first selector stage. The later outlets from the first selector stage are connected to overflow circuits such as 5, 6, 7, Fig. 3, and LD and LE, Fig. 6, operate, followed by M, T, LMA and LCA. Relay LCA disconnects relays LE and LD and connects'the loop to AA. Relay BA pulls up and LMA, LE and T release. Relay S, Fig. 5, pulls up and the level circuit finder LX, on which the distributor DR is standing, starts to hunt for the calling subscriber. Relay SE and magnet VV pull up over DR2 and SD operates. Contacts vv of VV energize SC, over DR4, and VV and SC interact. When the finder reaches the engaged level SC is held over AU and SD falls away, changing over to the rotary magnet R and SG pulls up, followed by SA. Relay SA interacts with magnet R until wiper LX5 finds lead 10 when SB pulls up over DR6 and HB operates. The finder is provided with 2 contact banks and if the calling circuit had been connected to the lower banks LX6 would have found the marked circuit, SA would have remained energized and HA operated instead of HB. Magnet DR is now energized over DR1 and the distributor steps in search of another free cord circuit. Storage and display of wanted number. Whilst the above circuit changes are taking place the calling subscriber. is dialling the remaining digits of the wanted number and these are repeated by AA first to magnet HS of the hundreds selector, then to TS of the tens selector and the third digit to US to step the units selector, CA releasing at the termination of. each train to move the sequence switch SS one step. When the final digit has been. completely stored RA energizes over SS2, provided that similar relays RB, RC and RD (not shown) of similar register groups connecting with the same display panel, Fig. 8, are all de-energized: The stored number is displayed on the number indicator, the correct thousands digit being illuminated over m8 of relay M. In addition the calling lamps SL of all engaged subscribers in the required hundred are illuminated over HS1, the engaged condition being determined by the condition of relay K, and the lamp LY of the selected cord circuit is lit over LX5, 10 and TA. Busy condition at second selector stage. The operation is similar to that described above, except that relay M has two additional contacts m6, m9, m9 stepping SS when LCA pulls up to enable the first digit to be stored on TS and m6 energizing the correct hundreds display lamp. Completion of call ; ringing ; metering. The operator, on seeing the display, plugs PR into the wanted subscriber's line jack such as SJ, Fig. 1. Relays K and H operate, lamp LY is extinguished and TA, Fig. 7, releases, enabling V to operate and lock to the calling line. A, Fig. 4, now pulls up from the calling loop and J energizes, completing the ringing circuit. In the common equipment AA, BA and LCA fall away, the display is extinguished and the register switches home. Relays RA, CA, LD and M release and the sequence switch SS homes. The register is now free to receive another call. When the called subscriber replies F pulls up and locks, switching through the connection. Relay D energizes to reverse the current flow over the calling loop for supervisory purposes, to connected booster battery from BO to the lead 10, and to release J. When J, which falls away slowly, has completely restored the booster battery BO is removed from the test wire and replaced by earth. When the call has terminated A releases followed by HB, and Z energizes to restore the selector to normal. Lamp LY lights, and when the operator removes the plug PR from the jack, H falls away extinguishing the lamp LY and removing the busy marking from DR1. Called subscriber engaged. Should the operator, when attempting to complete the connection, observe that the calling lamp of the wanted subscriber is illuminated, key BS is operated and busy tone is returned over AA to the calling subscriber, relay BA being held over BH.