ELECTRICITY METERS 



527 



the usual four-dial register, from which the kilowatt-hours are 

 read. The auxiliary disc is a metal sector which forms the mov- 

 able element of an induction wattmeter, the spiral spring furnish- 

 ing the control. Both discs move in the same air gap, and so are 

 actuated by the same set of current and potential coils (not shown 

 in the figure). 



The auxiliary disc is connected by means of the spindle and 

 gears 1, 2, 3, 4, with the dog which drives the demand pointer. 

 When this disc, and consequently the gear 4, deflects from the zero 



r-Splral Spring 



Trip- 



Main Paw 



Pointer 



" A 1 LDouble I Q 



Light Spring g p . vot 



Bearing 



Ball Bearing^ 



FIG. 313. Diagram for Westinghouse R.O. demand indicator. 



position the dog pushes the pointer up the scale. If the aux- 

 iliary disc returns toward zero, the driving arm leaves the dog and 

 the pointer remains stationary, its position being maintained by 

 the ratchet and light spring. The maximum deflection is thus 

 registered. 



The time element is introduced as follows: Attached to the 

 spindle of the wattmeter element is an arm carrying the main 

 pawl. This pawl rests on the ratchet wheel, the hub of which 

 carries the gear 5 and is loose on the spindle. The gear 5 meshes 

 with 6, and is thus connected to the escapement wheel. The 

 escapement is oscillated by an eccentric, the rate of oscillation 

 being controlled from the worm shaft by means of the timing 

 gears. 



