CH. IX CONTROL 203 



speed up is well shown. The final current is 18 amperes 

 per motor. 



The mean current for the first four seconds from the 

 moment when the circuit is made appears to be 75 

 amperes. This would give us a total torque per motor 

 (see Fig. 21) of 2,430 inch-pounds. Deducting the frictional 

 torque corresponding to a current of 18 amperes per motor 

 namely, 755 inch-pounds we have 1,675 inch-pounds 

 available for acceleration. Since the weight to be 

 accelerated is 3*4 tons per motor, the acceleration is 

 2 '05 f.p.s. per second. The acceleration curve has been 

 drawn as if the acceleration were constant from the moment 

 of making the current ; this is not strictly correct. The 

 curve should cut the time base about one second from the 

 origin, but it gives a fairly accurate measure of the mean 

 initial acceleration, which by measurement appears to 

 be about 2'1 f.p.s. per second. 



Fig. 52 is the record of a test in which the motors 

 were allowed to speed up in series. The current taken 

 does not appear to have been quite so much as in the 

 case represented in Fig. 51. The form of the current 

 curve is well shown, both with the series and with the 

 parallel connection, and indicates the jerk experienced 

 when the motors are thrown into parallel, the accelera- 

 tion at this point being greater than at the moment 

 of starting. The energy required to attain a speed of 

 35 f.p.s. is less than that required by the method illustrated 

 in Fig. 51. 



The diagrams show a considerable increase in the 

 current taken from the line at the moment when the 

 motors are thrown into parallel connection. It is in- 

 structive to inquire if this increase is necessary, and to 



