Ques. What are its characteristics?
Ans. It is independent of power factor, wave form, and frequency when no iron is used in the motor.
Ques. What meter is chiefly used on A. C. circuits?
Ans. The induction meter.
Fig. 2,537.—Fort Wayne multiphase induction watt hour meter. The construction of the mechanism is essentially two single phase motor elements, one at the bottom of the meter in a suitable position, the other inverted and placed at the top of the meter. Each element acts on a separate cup, but both cups are mounted on a single shaft so that the registration is due to the resultant torque of the two elements. The meter is provided with three supporting lugs, the one at the top being keyholed and one of the bottom two, slotted to facilitate leveling. The registering mechanism is mounted on a cast iron bracket at the middle of the meter between the two motor elements. The supporting bracket is attached to the meter base by two screws and aligned by two dowel pins. The register is of the four dial type, reading in kilowatt hours. Each division of the right hand circle, or that passed over by the most rapidly moving pointer, equals one kilowatt hour in meters without a dial constant. In meters of larger capacities, dial constants of 10, 100 and 1,000 are used, in which case it is only necessary to add one, two or three ciphers to the observed reading.
Principles of Induction Watt Hour Meters.—Every commercial meter of this type is made up of a number of elements, described below. Each of these elements and parts has certain functions, and each is therefore necessary to the successful operation of the meter; moreover, each element, unless correctly designed, may introduce a source of inaccuracy. These elements are:
1. The field producing element; 2. The moving element; 3. The retarding element; 4. The registering element; 5. The mounting frame and bearings; 6. The friction compensator; 7. The power factor adjustment; 8. Frequency adjustment; 9. The case and cover.
