CHAPTER XI 



GRAPHIC RECORDING OR CURVE-DRAWING 

 INSTRUMENTS 



Graphic recording instruments are those which automatically 

 record their indications on a uniformly moving strip, or circular 

 sheet, of paper. Continuous and permanent records of the quan- 

 tity which the instruments are adapted to measure are thus 

 obtained. 



Such instruments are extremely useful in investigating the 

 power conditions in factories and in studying the cycle of opera- 

 tions of single machines. In many cases the load fluctuates so 

 rapidly that to obtain equivalent data by using indicating in- 

 struments would necessitate the observers remaining continu- 

 ously at their posts taking frequent readings at noted times. 

 Afterward, these readings must be plotted and the best repre- 

 sentative curve drawn. This is a time-consuming operation. 



Continuous records are frequently important in central- 

 station work. For instance, a registering ammeter in a feeder 

 gives a record of the current and shows, if the clock be of good 

 quality and properly regulated, when the feeder is put in and 

 taken out of service, as well as the time when any abnormal 

 conditions arise. Such data, if systematically kept, may be of 

 great importance as evidence in adjusting disputes arising from 

 accidents. Again, a continuous record of the potential on a 

 lighting circuit contributes to the life of the incandescent lamps 

 by directing the attention of the operator toward constancy of 

 voltage. The records obtained by a registering wattmeter show 

 the customer's power consumption throughout the day and are 

 useful in determining rates. 



Fig. 337 illustrates the application of an instrument of this 

 class to the study of a particular machine. It shows the current 

 taken by a direct-current motor driving a roughing lathe. The 

 cycle of operations is to be referred to Fig. 336 which shows 



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