2 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



modern cross-bar switching systems. In these, estabhshing a single tele- 

 phone connection between two subscribers makes use, for a very short 

 time interval, of approximately 1,000 relay operations with a total of 

 about 7,000 contacts. 



As the telephone plant has become more mechanized with its local 

 and toll dial systems, automatic message accounting, automatic trouble 

 recorders, etc., the relays have been required to do more things with less 

 trouble. Accordingly, the steady progress which has been made in the 

 automatism of switching equipment has depended upon improving the 

 performance of relays. To provide this improvement, relay design must 

 be guided by a clear understanding of the physical relations among all 

 aspects of performance and the construction specified by the design. 



Some of the recent work in the area of relay design, production, service 

 and measurements is covered by this issue which is devoted entirely to 

 the analysis and measurement of relay performance, and to the economic 

 considerations which govern optimum relay design. It is evident from 

 the typical statistics given, that the successful and economical opera- 

 tion of smtching systems and certain other existing automatic control 

 systems demand the best in relay performance. 



A. C. Keller 



