LINEAR SERVO THEORY 



625 



transfer stiffness .S", , the voltage output of the control transformer being 

 given by Si{6i — 62). However, as seen from the modified diagram of 

 Fig. 5b, the (3 characteristic is simply — 1, the transfer constant St appearing 

 in the n circuit. Thus if the loop transmission is kept large, the essential 

 relation demanded between ^1 and do does not depend upon the value of St 



Eft^-ste 



,. E E-Ste 



(b) > t » ^ A 



-St 



e e 



M > ^ 



"e 



-p St ^ 

 Fig. 6 — Potentiometer loop. 



E-Rt© 



-Rte 





® -(i"Rt 

 Fig. 7 — Tachometer loop. 



(as is obvious from physical considerations). This result also applies to a 

 radar angle-tracking loop, where the received deviation or error signal is 

 proportional to the difference between the angular coordinate of the target 

 and that of the antenna system. 



Figures 6 and 7 represent two servo systems where the input is electrical 

 and the output mechanical. In Fig. 6 a potentiometer is used as a monitor- 



