520 



ELECTRICAL MEASUREMENTS 



the maximum demand in kilowatts. It gives no indication of 

 the time when the maximum occurred. 



Though the principle on which it works is entirely different, 

 this instrument is purposely designed to have the same general 

 operating characteristics as the Wright demand indicator. This 

 will be seen by reference to Fig. 306, which shows the motion of 

 the pointer from its zero position after turning on the current. 



FIG. 307. Ingalls relay demand indicator. 



Ingalls Relay Demand Indicator. 13 This device may be re- 

 garded as an auxiliary to the watt-hour meter by means of which 

 the number of revolutions made by that instrument in a given 

 time (half an hour) may be obtained from a record impressed 

 on a uniformly moving paper tape. From this record, knowing 



