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Maintenance of Aarhus Area ExchangesM AHM, CHIEF ENGINEER, JUTLAND TELEPHONE COMPANY (J.T.A.S.), AARHUS, DENMARKU.D.C. 621.395.722.004.5Six automatic local exchanges and a trunk exchange of L M Ericsson'scrossbar system were opened in the Aarhus area on May 1, 1953. An articlein Ericsson Review No. 311953 gave an account of the design of the system.The present article deals with the methods of maintenance and the results ofoperation for the first six months of 1956.All six local exchanges use the ARF 10 system. The largest is the mainexchange. Centrum, with 20,000 lines. The remaining five, with a total of12,000 lines, are suburban exchanges. The trunk exchange uses the ARM 20system with a capacity of 1.600 trunk and toll lines. It is operated jointly bythe Danish P.T.T. and J.T.A.S.The Centrum and trunk exchanges are installed in the same building. Theequipment rooms are painted with turpentine-free paint, and the floors arecovered with linoleum. The Centrum and trunk switchrooms have air conditioningsystems with humidifiers, while the suburban exchanges have not.Where humidifiers are employed, the relative humidity remains steady at about60 % ; in the suburban exchanges it fluctuates between 30 % and 70 %.During the run-in period, maintenance consisted mainly of periodic routinetests combined with trouble clearing. In course of time routine tests were madeat less frequent intervals, and now, at Centrum, they are performed only asrequired. In the near future the same procedure will be adopted at the suburbanexchanges. A system of qualitative service control, consisting of thecompilation of statistics based on regular traffic tests, congestion metering,alarm panels, and the like, will be introduced. Only if the statistics reveal irreg-V~ r~[if TXFig. IX8013The J.T.A.S. head office in AarhusThe left-hand side of the building houses theCentrum and trunk exchanges.2