A Governor for Telephone Dials 



Principles of Design 



By W. PFERD 



(iManuseript received July 29, 1954) 



This is a report on the development of a new type of governor for regulating 

 the speed of rotary dials. The paper includes derivation of the equations of 

 motion which determine the theoretical speed of the governor during dial 

 run-down and an analysis of the operating characteristics of the governor as 

 influenced by vanjing friction and input torque. Experimental verification 

 of the relations is presented. A theoretical analysis which explains "governor 

 chatter^' or positional instability for friction-centrifugal governors is also 

 given. 



INTRODUCTION 



Machine switching telephone systems depend on the telephone dial 

 for originating information used in completing a call. During run-down, 

 the dial originates current pulses which operate step-by-step switching 

 etiuipment or are registered for use in common-control panel or crossbar 

 systems. For reliable functioning of dial pulse controlled switching ecjuip- 

 ment, the pulses must be closely controlled in frequency and form. Since 

 the pulses are produced during run-down of the dial after release by the 

 customer, the run-down speed most be constant. Friction-centrifugal 

 governors are commonly used to provide this required control of speed. 



If the pulses reaching the central office were exactly like those gen- 

 erated by the dial, the designers of dials and central office switching ap- 

 paratus and circuits would find themselves far less restricted. Unfor- 

 tunately the dial pulses are distorted by the electrical characteristics of 

 the customer's loop. To compensate for this distortion and insure ac- 

 curate registration of the pulses at the central office, the dial and central 

 office efiuipment must be designed to operate to close limits of perform- 

 ance. The designs must also be such that there is negligible change of 



1267 



