Conversion of paris telephone system to automatic

This conversion was decided upon in October, 1926, and put in hand during 1927. The number of subscribers at the commencement was about 150,000, which will have increased to about 400,000 by the completion in about ten years. About 40,000 lines per year are to be equipped for automatic operation. An improved form of the rotary system has been adopted, providing for dialing the first three letters of the exchange name. The corresponding setting of the register is translated into a series of route-determining code trains; 100-point line-finders and 300-point selectors (30 links per level) are employed. In these new switches commutator type interrupters are substituted for the contact type for sending the reverted impulses, and gear meshed driving clutches replace the earlier friction clutches. The sequence switches have horizontal instead of vertical shafts. Automatic to manual connections arc to be dealt with by call-indicators either at the manual exchanges or on tandem positions from which the call is extended by ordinary manual order wire working. Manual to automatic traffic is to be handled by "direct selection" (key sending and individual jacks on the "A" positions) with automatic selection of a free junction or by semi-automatic "B" positions. Connections with suburban manual exchanges are to be completed via four junction centres provided with call indicators and semi-automatic key-sending positions. This equipment in the junction centres may, as the conversion proceeds, be replaced by tandem selectors.