322 ELECTRICAL MEASUREMENTS 



if the charging current for the electrometer be neglected, 



V2b = v + ri - (Ri + v + ri) (l -- *) = ^ 



Consequently 



The term is proportional to the instantaneous power; the 



other three terms can be eliminated by properly adjusting r, 

 for if their sum be placed equal to zero, 



n n 



If r be adjusted to this value, 



2KR i 



D = - - 7p I 

 w TJq 



or 



and no correction for the power wasted in R is necessary. 



If the tap be brought out at the middle of ac, n = 2, and no 

 compensating resistance, r, is required. 



If the compensating resistance is not used, (r = 0), 



When small amounts of power at low power factor are measured, 

 the term 



727? n ~ 2 

 / n ^ 



