Chap. 10] 



ELECTRICAL METHODS 



781 



where E is the e.m.f . induced in the coil of the area S and turn number N, 

 and CO is the angular frequency. 



Absolute measurements of field intensity have the disadvantage of de- 

 pending on generator voltage and frequency. Hence, it has become more 

 general practice to measure A.C. fields semiabsolutely, that is, in reference 



fa) 



Fig. 10-102. Larsen compensator with (o) resistance coupled reference, and 

 (6) inductively coupled reference. 



Fig. 10-103. Compensators giving (a) intensity and phase of field and (6) 

 in-phase and quadrature field. 



to generator voltage and phase. With a voltage divider or a transformer 

 (see Fig. 10-102) a portion of the generator voltage is carried to the field- 

 measuring network by a separate cable. Two compensators for the meas- 

 urement of potentials with reference to generator amphtude and phase are 

 described on page 696. Adaptations of these to electromagnetic measure- 

 ments are shown m Fig. 10-102 and 10-103. The Larsen compensator 



