224 



HANDBOOK OF MECHANICAL DESIGN 



ELECTRIC CONTROL METHODS 



Reel Diameter 



A.C. 

 diagram 



Motor- 



Torque 

 adjusment 

 rheosM 



Fig. 446. — Constant tension with constant peripheral speed is required in this wire-reel 

 application. The application can be used on wire-drawing machines, insulating machines, or 

 any other reeling operation. As the reeling diameter increases, the reel speed decreases, and at 

 the same time the reeling torque is increased. The required constant horsepower characteristic 

 is obtained accurately with a direct-current motor and a regulator type of control on shunt 

 field. An alternating-current wound rotor motor with secondary resistance control approxi- 

 mates ideal conditions. 



Grinding wheel 



Rheosfa-t 



Siiuni field 



o 



Wheel Diameter 



Armalure 



Fig. 447. — For automatically limiting the peripheral speed of a grinding wheel, the truing 

 diamond is mechanically interlocked with the wheel motor field rheostat. The wheel r.p.m. 

 is increased as the wheel diameter decreases. 



