INSTRUMENTS FOR THE NEW TELEPHONE SETS 



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There is a value of polarizing flux for which the force factor of the 

 given magnetic circuit is a maximum. The rate at which the force 

 factor falls off above and below this optimum value of flux is a function 

 of the magnetic characteristics of the materials employed, the length 



Fig. 10 — Force-to-mass ratio as a function of diaphragm thickness and pole-piece area. 



of the air-gaps, etc. Without exception the more efficient magnetic 

 circuits have been found to be the most critical as regards polarizing 

 flux. Hence, if wide variations in the efficiency of the product 

 receivers are to be avoided and serious losses due to subsequent demag- 

 netization in service prevented, means must be provided not only for 

 bringing the flux in each receiver to the optimum value, but also for 

 insuring that it remain at this value during the life of the instrument. 

 In order to accomplish this result the magnets of the new receiver are 

 so designed as to overpolarize the magnetic circuit when they are fully 

 magnetized. Equipment is provided for demagnetizing each receiver 

 to its optimum flux value during the assembly process. Receivers 



