190 BELL SYSTEM TECHNICAL JOURNAL 



flat characteristic is secured by a compensating network consisting 

 of the resistances Ri, Rz and Ri and the condenser Ci. This com- 

 pensating network feeds back on the grid of tube F4 a portion of the 

 voltage drop across the D.C. winding of inductance Li thereby cor- 

 recting for the "static fluctuation" of the control circuit. By a 

 suitable adjustment of this compensating resistance the control circuit 

 may be arranged to give flat regulation, under regulation or even 

 over regulation if desired. Fig. 7 has been drawn with line voltage 

 as the variable. A similar characteristic is also obtained with load 

 as the variable instead of voltage. 



Q 

 U 

 U 



(0 



-lOl^o 



lOO'/o jp- 



^99^, ^^. 



'UNCOMPENSATED 

 COMPENSATED 



100 120 



LINE VOLTAGE 



Fig. 7 — Performance characteristics of motor. 



An interesting point in connection with this compensation circuit 

 is the necessity for avoiding hunting or surging of the speed. It is a 

 well-known property of all forms of governors that if they are adjusted 

 to too great a sensitivity the speed instead of remaining constant will 

 fluctuate up and down about a mean value. The simplest method of 

 preventing such speed fluctuations is to decrease the sensitivity of 

 the governor allowing a bigger change in speed with load (or voltage) 

 and then compensating for this change of speed or "static fluctuation" 

 by means of a delayed action compensator. This phenomenon is well- 

 known in the mechanical governor art and is described by Trinks in 

 his book "Governors and the Governing of Prime Movers." The 

 electrical equivalent of this mechanical system is obtained by intro- 



