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94 in the nineties constructed small automatic exchanges, one of them having rotating selectors, Fig. i, being exhibited by the Telegraph Administration at the Exhibition of 1900 and obtaining the gold medal. An exchange of this kind was put into service near Stockholm in April 1901 and this type of exchange had, in conformity with the assurance of the two inventors, also attracted such great interest abroad that »several concerns presented themselves as willing to negotiate for the exploitation of the exchange*. Betulander also constructed exchanges with a connecting device working vertically. These exchanges were made at the workshops of the Telegraph Administration and came into use in the beginning of the 20th century at a number of exchanges — one such exchange at Ostanbro, Fig. 2, was in operation right up to June 1936. It was not until about 1910, however, that the question of automatization came under consideration for a large undertaking. That was the year when proposals for the automatization of the Stockholm telephone network were first put forward. At this period the Telegraph Administration had four local exchanges in Stockholm, all arranged for local batter}'. To provide for anticipated increase in subscribers and to facilitate transition to the CB system a manual main exchange was planned on this system. Before the details for this exchange had been settled, however, the question arose whether it would not be advisable to build the exchange for automatic operation. As up to then no automatic exchange of large size had been built in Sweden and consequently experience in the domain was lacking, the then Director of Telephones Axel Hultman and the Line Engineer Herman Olson were instructed by the Administration to investigate in America the economic conditions and the working reliability of automatic telephone plants. This voyage of investigation, undertaken during the first half of 1910, convinced the two envoys of the advantages of the new system from the points of view both of economy and operating reliability particularly as regards large networks. At that time, however, it was considered that the semi-automatic systems were to be preferred, partly because they were cheaper and more reliable in operation than the automatic (the number dials were expensive and functioned with less satisfaction), and partly because they made no demands on the subscribers either in the form of ability or inclination to carry out the impulsing themselves. Both Hultman and Olsson commenced immediately on their return to work on the construction of automatic selectors, each with the Strowger selector as prototype. Olson subsequently changed over to a design in which the wiper was moveable around a fixed point, Fig. 3. Connection was obtained by the wiper being first turned vertically and then sideways along the arcshaped banks of contacts in the field. The banks of contacts in the Olson selector, therefore, took on the form of a section of a sphere, while the banks in the Strowger selector were shaped as parts of a cylinder. The next system of Olson was based on small step-by-step driven selectors, 30 and 10line, operated by DC impulsers from an impulse machine, and finally he settled on the coordinate selector, which the Telegraph Administration later developed further. Hultman too soon abandoned his trials with selectors of the Strowger type and went over to the problem of designing a machine-driven selector. It was obviously the Western Electric Rotary System which gave the impulse tot this aim, but the system which Hultman with, inter alia, Maurits Agrell as collaborator, succeeded in designing differed so essentially from the Rotary System and indeed from any other system that it must be regarded as a new and independent invention. The special feature of the Hultman system is the design of the bank of contacts. In other systems the bank consists either of a separate bank for each selector, the connecting device being moved in one or two directions along the surface of the bank, or of a bank common to several selectors,
in which case the connecting" device moves in one direction only. In the Hultman system, however, the hank is common for several selectors and the connecting device is moved over the bank in two directions. The difference in principle may therefore be stated as that in the Hultman system the bank has extension in three dimensions as against only two in other systems. It was thus the design of the bank which constituted the essentially new in Hultman's invention and which was therefore made the main point in the patent application, first made in Germany on 2nd June, 1913, and later in Sweden among other countries on 23rd February, 1915. Even in its first execution Hultman's connecting bank consisted of bare wires running parallel with one another, supported and insulated from each other by a number of transverse discs of fibre or other insulation material, placed at suitable distances from each other, the wires being drawn through holes in the discs. While the bank has many times being altered since that time, yet this design still persists. The holes in the insulating discs were arranged in two rows, the holes being at equal intervals in each row but one row having double as many holes as the other. The distance between the two rows of holes was large enough for a wiper, provided at its end with three trailing contacts, two on one side and one on the other, to be inserted between the wires drawn through the holes, thus producing the contact connections necessary for switching, The number of wires was governed by the capacity of the bank and their length by the number of selectors which had to work in one and the same bank. A suitable number of bank units made up in this way, was combined to a • frame and placed so that the wipers movably fitted on the selector could be inserted in any frame whatever of the rack. The first selector constructed by Hultman, Fig. 4, was made for a multiple capacity of 10 000 subscriber lines, i. c, the bank comprised 3X10000 or 30 000 wires. The selector consisted of an extended frame fixed on a carriage fitted with four castor wheels for sideways motion. At the top and bottom of the frame were placed two wheels between which the long, double-acting wiper was guided in its up and down movement. The wiper was moreover guided by four wheels fitted in the middle of the wiper and running on vertical tracks on the frame. The selectors were fitted on horizontal beams, along which they could be pulled to right or left from the central normal position by means of cords, while the castors on the abovementioned carriage ran in tracks on the upper 95
Page 3 and 4: ERICSSON REVIEW Responsible Publish
Page 5 and 6: the pioneers of the guild of teleph
Page 7: Fig. 1 XS869 The BetulanderandPehrs
Page 11 and 12: Aktiebolaget Autotelefon Betulander
Page 13 and 14: that the system was not adopted for
Page 15 and 16: All the apparatus necessary for the
Page 17 and 18: Fig. 1 Repeater racks X547T right t
Page 19 and 20: Fiq. 3 & 4 x « Rocks in detail lef
Page 21 and 22: Fig. 6 * 7«i5 General diagram for
Page 23 and 24: x n Fig. 9 Connecting diagram for
Page 25 and 26: \ Fig. 12 xi Intermediate repeater
Page 27 and 28: grasping of the speech from the dis
Page 29 and 30: Portable Telephone Instruments E. B
Page 31 and 32: highest efficiency is obtained with
Page 33 and 34: This is done by pressing in the key
Page 35 and 36: \ Hotel Switchboard K. G. H A N S 5
Page 37 and 38: \ New Ericsson Wireless Receivers B
Page 39 and 40: \ The sensitivity of the apparatus
Page 41 and 42: Ericsson 380, Fig. 6, is a single c
Page 43 and 44: \ For a time gelatine appeared to m
Page 45 and 46: S Recording The attainment of good
Page 48: The Ericsson Group Associated Enter

contents - History of Ericsson - History of Ericsson

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