CH. IX 



CONTROL 



1*5 



then be no abrupt change in acceleration, and therefore 

 no shock, as there is in the case illustrated in the figure. 

 The car would then be started in 80 seconds, with an ex- 

 penditure of 562 x 1C 4 foot-pounds. This is, therefore, the 

 best method from the point of view of the time occupied. 

 If the motors are allowed to speed up in series after this, 

 there is a small gain in energy but a loss in time. 



The results of the previous calculations may for 

 convenience be arranged in tabular form as follows : 



We shall now illustrate the three methods of control 

 here described by diagrams of current and acceleration 

 obtained in practice. 



In Fig. 49 curves are given showing the variations 

 in the current during the process of starting up a car 

 weighing 6 '25 tons by two different methods of control. 

 The dotted line is the current curve obtained with the 

 parallel method. The first step is irregular, owing to the 

 way in which controlling apparatus is handled. The 

 second step is, on the whole, clearly shown. The full line 



o 2 



