AUTOMATIC TELEPHONES.

Star (Christchurch), Issue 12761, 3 October 1919, Page 7

AUTOMATIC TELEPHONES.

A NEW SYSTEM FOR CHRISTCHURCH*

VERY INGENIOUS MECHANISM.

The automatic telephones at present in use in Christchurch were installed in order to meet the ever increasing demand for connections with the exchange. It is probable that a more modem system, in connection with which a contract was recently 7 entered into by the Post and Telegraph Department with the "Western Electric Company, will be installed in Christchurch shortly. The new system has already been given a trial in one of the Wairarapa townships, and has , given entire satisfaction. It diifers somewhat from the present, automatic system. The essential difference lies in the method of switching. The chief mechanical work is at present done by means of “selectors” and “connecters,” whereas the Western Electric system is based upon the use of “cams” and “revolving shafts.” The order of the numbers on the dial discs of the -new telephones will be the reverse of the present. The largest exchange for the new system will be installed in a building next to the present automatic ' exchange (which is in the old Government Tourist Department office, Hereford Street). It will be remembered that the foundations of this building were laid a considerable time ago. Other exchanges will bo situated in St Albans and Sydenham. The building for the St Albans exchange was erected in 1916. The Sydenham exchange will be installed in the new post office there. The replacing of the present automatic telephone instruments in houses and offices will be involved, but the same voltage on the wires (50 volts) will be used. It is intended, of course, to connect the new system with the underground cable system, work in connection with which will be undertaken almost immediately. An interesting resume of the development of the telephone and description of the latest automatic system was written by Mr J. N. Wallace, and appeared in the “ New Zealand Journal of Science and Technology.” The includes material culled from the article. While working on multiplex -telegraphy experiments in 1875 Alexander Graham Bell invented the telephone, and gave the first public exhibition of it at tbe Centennial Exposition in Philadelphia in 1876. Since that time the telephone has grown almost out of recognition. Experimental and developmental work on automatic systems was commenced as far back as the time when common battery systems were first being seriously considered; but it is only In the last decade that they have attained such perfection that the British Government has considered it advisable to install such systems in its exchangesIn operating the latest automatic system the subscriber removes his receiver, and thereby causes a certain nyachine in the exchange to become connected with his line. Ho then operated the dial, which controls the operation of one machine after another until the desired connection is secured. The replacing of the receiver on tho switch hook sends all the machinery back to normal. All this is done without the intervention of any operator other than the two f persons who converse. _ Some systems are worked on what is known as tho decimal basis. In such a system— say, for 10,000 lines —the subscribers’ lines are grouped into sets of 100 each; again, ten groups of 100 are arranged in a group of 1000, ten of these in turn being grouped into one lot of 10,000, The calling subscriber, after removing his receiver, is connected by means of trunks to' the correct group of 1000, then of 100, and then the particular group of ten desired. Finally he becomes connected with the particular unit which is the number, or part of the number, of the line desired. The controlling of this selecting is done by the subscriber by means of tho dial on his instrument. In a system of 10,000 lines the lines would he numbered from 0000 to 9999, and it is necessary tor the subscriber to operate_ his dial four times, each time indicating one of tho four digits in the number desired. Upon the removal of the receiver from the hook of an automatic telephone, current flows out from the central office through a relay, through the subscriber’s lino and telephone, and back to the battery at the central office. This relay becomes energised, and in turn closes a local circuit, which starts several line-finders hunting for the particular line calling. The mechanism of the switches and linefinders is vastly . interesting. The switches are of a rotating type, and are driven by means of constantly running vertical shafts, which drive individual horizontal shafts. These shafts are connected to each switch by means of magnetic clutches which are energised when a switch is to be rotated. The line-finder .wipes . connecting brushes over line terminals. A number of lines are accessible to a group of these line-finders, and when one of these_ mechanisms has become connect-i ed with the line calling, connection is continued from the subscriber’s line to another mechanism, known as a groupswitch, which is to be used for selecting a trunk to the particular group of 1000 in which the desired number appears. Attached to the circuit connecting the line-finder and the group switch are a set of registers, and as the subscriber manipulates the dial on his instrument in accordance with the digits of the particular number desired these registers revolve unwl they assume positions corresponding with ' those particular digits. The registers are used to record and store the number in such a way that the further movements of all the mechanisms nefessary in completing the connection «v ill be controlled by the register set An “engaged test” is given if the connection desired is already in use. By no means all the operations of the automatic exchange have been described, but a general idea of its operation has been outlined. The machinery is a triumph in the creation of automatic electric machinery, and gives one the impression that it is possessed of intelligence. Several kinds of special service are provided for. Differentiation between subscribers on party lines is accomplished at the final automatic machine the exchange by means of a certain form of current being connected to ring the called subsenber’s bell, tbe form of current de- 1 pending upon the number called for The final machine also takes care that, in the case of private branch services in offices and warehouses, the fact that the first line called is engaged shall not deter a connection. An automatic test of all the branch wires in the subscriber’s establishment is . made, and .if a free line is found it is connected. •The subscriber dials a certain number for toll service, which connects him with a group of lines running to the toll operator, who then disposes of. his call as in a manual equipment. The calculation of the amount of machinery and equipment necessary, and the manner in which it should be■■ connected is a matter which the electrical engineers have to deal with. They have no light task.