MACHINE SWITCHING TELEPHONE SYSTEM 87 



tandem office and other offices through which the call may pass, to 

 the desired local office and subscriber's line. 



Many different combinations of the above are possible and arc 

 employed when desired. 



Maintenance 



As will have become apparent from the description already given 

 there is, in the machine switching telephone central office, a large 

 amount of apparatus which, in order to insure service of good quality, 

 must be maintained in proper working condition. Consequently, 

 the subject of maintenance has been very carefully kept in mind 

 throughout the design of the system. For instance, all new pieces 

 of apparatus used in this system have been subjected to the most 

 rigid tests to insure that they will have a satisfactory life and that 

 their margins of adjustment will be adequate. 



When maintaining machine switching equipment, the main reli- 

 ance is placed on preventive measures, so that incipient faults will 

 be detected and corrected before they have got to the point of inter- 

 fering with service. Ingenious automatic testing arrangements have 

 been designed to aid in this preventive maintenance work. They 

 subject the various circuits in the exchange to routine tests, and are 

 arranged so that they will automatically test all of the circuits, one 

 by one, under conditions more severe than they will ever be called 

 upon to meet in service. In case some feature of any circuit has 

 deteriorated from its normal standard of adjustment — which includes 

 a wide margin — so that it will not meet this severe testing condition, 

 the testing apparatus automatically stops and by supervisory lamps 

 indicates the location of the trouble. An audible alarm is also sounded 

 which notifies the maintenance man responsible that something 

 requiring his attention has been found. The circuit in trouble may 

 still be capable of giving service, but is below the standard set and 

 may soon give service trouble if not corrected. 



As applied to the sender, for example, the automatic routine test 

 equipment picks up each sender in turn and puts it through its regular 

 process of operation, under conditions more severe than are en- 

 countered in practise. If the sender under test meets the operating 

 conditions without failure, the sender is dropped and the test equip- 

 ment moves to the next sender. If any trouble develops an alarm 

 is given, which summons the maintenance man who is able to de- 

 termine by the condition of the apparatus the location of potential 

 trouble. 



