A DYNAMOMETER METHOD. 



191 



The two coils of the dynamometer can, however, be separated, 

 and two independent currents be sent through them. The reading 

 is then proportional to 



/1/2 COS 9 



where /i, / 2 are the E.M.S. values of the currents, and the phase- 

 difference between them. When used in this way, it is called 

 a split, or divided coil, dynamometer. 



Let, in Fig. 80, BC be the inductive circuit, the power given to 



B 



'c 



FIG. 80. 



which is to be measured. Let r be a non-inductive resistance, J)\ 

 a dynamometer, Z> 2 a split dynamometer. 



Let i, ii, and i& be the corresponding instantaneous currents in 

 the main circuit, the resistance r, and the circuit BC respectively, 

 then 



therefore 



But r, ii, i-2 is the instantaneous power given to BC, therefore the 

 power, W, given to BC is 



w = 



= rD 2 - rD l = r(D 2 - D^ 



where T is the periodic time of the currents, and D\, D 2 the 

 readings of the two dynamometers. 



