RRL.iyS IX THE BELL SYSTEM IS 



a slight anuHint of dust or corrosion in the arnialiirc slot lr((iiiiiiily 

 made the contact resistance in the slot so hii;h thai tlie lini' ]am|) would 

 fail to light. 



The super\isory relay in the cord circuit also introduces main- 

 tenance charges for the same reason. It had to meet the same re- 

 quirements as the line relay but, in addition, it required a crosstalk 

 proof cover that would also adequately protect the contacts from dust. 



The solution of this problem was ver>- difificult because the only 

 means of obtaining relays of increased sensitivity or greater operating 

 range was to make mechanical refinements, which would increase 

 manufacturing costs quite out of proportion to the advantages ob- 

 tained, to discover new magnetic materials of higher permeability 

 at low flux densities and with a lower remanence characteristic or 

 to develop an entirely new relay structure. To obtain any advan- 

 tage from the development of a new structure built from the same 

 magnetic materials, it would be necessary to design it in such a man- 

 ner as would enable the engineer to obtain the proportion of copper 

 and iron required for maximum efficiency, greatest economy, extreme 

 sensitivity, maximum operating load or any other specific require- 

 ment which was the controlling factor of a particular design. Ana- 

 htical studies had shown that smaller relays with less iron could 

 be substituted for those in use but such a change could not be made 

 without increasing manufacturing costs because a reduction in core 

 diameters would increase breakage during manufacture as well as 

 entail a greater cost of handling the smaller structures. 



The Flat Type Rel.w 



An anaKsis of the manufacturing costs had shown labor costs to 

 be greater than material costs in the production of relays so that 

 any changes which would result in large sa\ings would have to be 

 of such a nature as to reduce labor charges. This could be accom- 

 plished only by changing production methods which had already 

 been established with reference to greatest economy in manufacture 

 considering the volume of production. The demand for relays, 

 however, was increasing steadily and it was evident that with in- 

 creased production the prevailing manufacturing methods would 

 not continue to be economical. With other pieces of apparatus 

 manufiictured in large quantities, it had been found that production 

 costs could be reducerl to a minimum by designing a unit which could 

 be assembled from interchangeable parts stamped out by a punch 

 press and formed in bending fixtures to the desired shapes. To ac- 

 complish this for relays, it was first necessary' to conceive of an 



