ELECTRICITY METERS 



483 



fastened to the same shaft. The driving torque is therefore the 

 sum of the torques due to the two members; that is, it is propor- 

 tional at any instant to the power in the circuit. The retarding 



1.06 

 1.04 

 1.02 



ri.oo 



Induction Watt-hour Meter 



Effect of Voltage Variation 



Frequency = 60 Cycles 



Smooth Waves 



90 100 110 120 130 140 150 

 Volts 



50 60 70 



FIG. 276. Showing effect of voltage variation on induction watt-hour meter. 



FIG. 277. Polyphase watt-hour meter, Westinghouse Co. 



torque is furnished by two sets of drag magnets, one applied to 

 each disc. Of course, there must be no interference between 

 the two elements. 



