POWER MEASUREMENT 



319 



If the voltmeters are of the electrodynamometer or the electro- 

 static type, 



P = #iJ>i - K 2 D 2 - K s Ds. (15) 



Load 



FIG. 184. Connections for three-voltmeter method for power measurement. 



For the greatest precision the power wasted in R must be equal 

 to the load. P includes the power in Vs. 



The Split-dynamometer Method. The connections are shown 

 in Fig. 185. 



Load. 



FIG. 185. Connections for split-dynamometer method for power 

 measurement. 



-Da is an ordinary current electrodynamometer with its coils 

 in series. FM is another dynamometer with a non-inductive 

 resistance, R, tapped in between the fixed and movable coils. 



At any instant 



