524 ELECTRICAL MEASUREMENTS 



circuits, a contact on the registering train of the watt-hour 

 meter closes the circuit of the operating coil every time the 

 registration of a definite number of kilowatt-hours has been 

 completed. When the armature is attracted, the dog is advanced 

 by the ratchet and pushes the friction pointer before it. 



To introduce the time element, the clutch (a sliding gear) is 

 controlled by the trip levers which in turn are controlled by a 

 cam arrangement driven through a system of gearing from a 

 constant-speed motor. The trip levers are thus operated period- 

 ically, every half hour for instance, and the clutch thrown out of 

 gear, allowing the spiral spring to return the dog to the beginning 

 of its traverse. The friction pointer will thus be left at the end 



FIG. 311. Record from General Electric registering demand indicator. 



of the largest traverse of the dog and will indicate the maximum 

 demand. Arrangements are made for regulating the speed of 

 the motor in order that the time element may be adjusted. 



When the indicator is used on a direct-current circuit the 

 clutch is operated by an 8-day clock. 



The General Electric Co. also manufactures a registering 

 demand indicator which is based upon the same principle. An 

 arm, corresponding to the friction pointer, carries a stylus which 

 draws lines on a circular chart which are proportional, when 

 properly scaled, to the demand during the consecutive 30-min. 

 or other period for which the indicator is set. Fig. 311 shows 

 such a record. 



