AUXILIARY APPARATUS 



421 



it serves to show how well the operator has maintained 

 the voltage constant. These meters are excellent for 

 keeping the operator at his task as they infallibly indicate any 

 variations in the station voltage. 



Watt-hour Meter. An integrating meter or watt-hour 

 meter consists essentially of a little motor, the armature of 

 which is attached to a train of gears which operate fingers 

 over properly graduated dials. The motor is so designed 

 that its speed is directly proportional to the power being sup- 

 plied through the line to which it is attached. Hence the 

 number of revolutions through which it turns is propor- 

 tional to the power flowing 

 through the meter multiplied by 

 the time during which this power 

 flows. But the product of 

 power X times = energy, and so 

 the number of revolutions of the 

 meter is proportional to the 

 amount of electrical energy that 

 has i Kissed through it. 



The train of gears is so de- 

 si.miod that the indications of 

 the fingers on the dials are in 

 kilowatt-hours or multiples there- 

 of. As just explained this type 

 of meter gives a reading propor- 

 tiomd to all the energy that has 

 passed through it and from this 



fact it derives its name of " integrating " meter; the name 

 watt-hour meter, however, is preferable. The Thomson 

 watt-hour meter is illustrated in Fig. 277 and Fig. 278 

 shows a watt-hour meter for use in a-c. circuits. 



Frequency Meter. In the operation of alternating current 

 systems it is necessary to maintain the frequency of the 

 system constant. For the purpose of showing immediately 

 if this is so the frequency meter has been designed. 



FIG. 277. A Thomson Watt- 

 hour Meter. The case has 

 been removed to show the 

 working parts. General 

 Electric Co. 



