128 KENNELLY AND VELANDER— POTENTIOMETER 



In this expression, if 3' varies circularly, so does its reciprocal, and 

 therefore so does Z. Consequently, if the sending-end impressed 

 voltage is held constant, and y is varied circularly, the current deliv- 

 ered to the load at the receiving-end will undergo a circular varia- 

 tion. From similar considerations, it may be seen that if the sending- 

 end impressed current is held constant, the voltage at receiving 

 terminals will also undergo circular variation, when y is varied 

 circularly. 



We have hitherto considered the efifect of a circularly varied 

 load at the receiving terminals CD, in producing circular variations 

 of impedance, voltage, and current, both at those terminals and at 

 the sending terminals A B. We may now consider, in like manner, 

 the effect of circularly varied impedance, voltage and current at the 

 sending end. 



Referring to Fig. 16b, let the receiving terminals DC be con- 

 nected through a fixed impedance load a ohms Z , such that 



P2 + 0- = So = — ohms Z . 



Then the total admittance at will be g,- -\- y., mhos Z • The total 

 mipedance at the terminals A B is then p^ -f- [^/{gj,-}- yo)] ohms Z. 

 Let an e.m.f. of fixed frequency and constant vector value E be 

 applied at the terminals A B, through an impedance r^ ohms Z , 

 which impedance is varied circularly. Then the total impedance Z ^ 

 of the circuit at the sending-end is 



Za= ZI + pi-\- ohms Z (26) 



gr + yi 



Since z.^ is supposed to be the only variable, the circular variation 

 of ^1 causes circular variation in Z^; so that the current entering 

 the network a.t A B is circularly varied under constant e.m.f. E ; 

 or, if the entering current should be maintained constant, the im- 

 pressed voltage E must be varied circularly to correspond. 

 The entering current cct A B being 



E E(g , -\- y.j) 



za~ (si+pi)(gr+>'2)+i 



