492 ELECTRICAL MEASUREMENTS 



test constant 

 Por Sangamo meters, watt-hour constant = Q ann 



o,OUU 



X. p/ = #<# 



71 3,600 t 



For Duncan meters, watt-hour constant = test constant 



AW3,600 



K h = K t P' = 



For Westinghouse meters, watt- hour constant = 



K t _ K t N 



Kh ~ 3,600 t 



t 



test constant 



3,600 



except for type CW 6, for which watt-hour constant = test 

 constant 



, 



The watt-second constant, A",, is the number of watt-seconds 

 of energy necessary to cause one revolution of the movable ele- 

 ment. It is equal to the watt-hour constant multipled by 3,600, 

 the number of seconds in an hour. 



The register constant, K r , is tlie factor by which the reading 

 of the register must be multiplied in order to ascertain the total 

 amount of electrical energy which has been supplied to the load 

 via the meter. For meters of small size, such as are used in the 

 majority of cases, the modern practice is to make this factor unity, 

 for it is likely that the small consumer will fail to understand why 

 the supply company, in making out his bill, should multiply his 

 meter reading by a factor of 2 or 4 for instance. In meters of 

 large size, it is necessary to use register constants of 10, 100 and 

 so on, for otherwise the value in kilowatt-hours of one dial divi- 

 sion becomes too large. 



The register ratio, R r , is the number of revolutions of the 

 wheel meshing with the worm or pinion on the shaft of the movable 

 element, which is necessary to cause the first or most rapidly 

 moving dial hand to make one revolution. 



The gear ratio, R g , is the number of revolutions of the movable 

 element required to cause the first dial hand to make one 

 revolution. 



