112 



KENNELLY AND VELANDER— POTENTIOMETER 



tor locus M'K'H'U'Q' of Fig. gc. As the capacitance in c varies 

 from o to CO, the impedance in the main circuit varies from OL' to 

 OM', around the circular arc H'Q'. 



The vector OP' =^206.7 \ 20°.26'.49" ohms, is the point of ap- 

 parent resonance or minimum impedance in the main circuit; i.e., 

 maximum main current, as the result of adjusting condenser c. It 

 is not a true resonant point, since there is neither cophase, zero re- 

 sistance, zero susceptance nor equality of undamped frequencies. 



The vectors OK' and OH' are two cophase vectors, at each of 

 which the current in the main circuit is in phase with the main im- 

 pressed e.m.f." In general, there will be either two such cophase 

 points, or none. A single cophase point may, however, present 

 itself as an intermediate case. Such cophase points are, in general, 

 not to be classed as resonance points. 



The vector points, U' and S' , corresponding to U and 5 in Fig. 

 gh, and also to u and .j in Fig. ga, are only of secondary signification 

 in relation to the main-circuit impedance. That is to say, although 

 they correspond to local-circuit resonances in Ic, they do not, in 

 general, represent main circuit resonances. 



Fig. gc. Total impedance of circuit includ- 

 ing / and c in parallel, as obtained from the 

 vector addition of OM to the locus of Fig. gb. 



Fig. gd. Total admittance of circuit 

 as obtained bj- inversion from Fig. gc. 



