~Ques. What is the strength of the rotating field with 90 degrees phase difference between the currents?~
Ans. It is proportional to the product of the currents in the two coils and therefore proportional to the product of current and voltage in the metered circuit.
At any other power factor the field is proportional to this product multiplied by the sine of the angle of phase difference between the two meter currents. If the current in the voltage coil be in quadrature with the voltage of the metered circuit, at any power factor the sine of the angle of phase difference between the currents in the meter circuits will be equal to the cosine of the angular displacement between the current and voltage in the metered circuit. Under these conditions therefore the strength of the shifting field is proportional also to the power factor of the circuit. In other words, the strength of the rotating field is proportional to the product of the volts, amperes and power factor and is therefore a measure of the actual power.
[Illustration: FIG. 2,545.--Sangamo single phase induction watt hour meter; view with cover removed showing mechanism.]
~Ques. In what part of the meter is energy consumed?~
[Illustration: FIG. 2,546.--Main grid or supporting frame of Sangamo single phase induction watt hour meter. The grid is of cast iron and its design is such that the weight of the permanent magnets, series laminated element and return plate are carried on the main portion, the smaller projecting brackets carrying no weight except that of the moving system. The supporting grid is removed by taking out the three screws locating and holding it in position, to the iron base, also removing at the same time the screws connecting the leads of the series coils to the binding posts at the bottom. The meters are all built with four binding posts so that they may be connected either with two series leads and a tap for the pressure connection or with both sides of the circuit carried through the meter. The wire meters employ a 220 volt shunt coil, connected across the binding posts within the meter, one series coil being in each of the outer lines of the three wire system. This renders unnecessary the use of a pressure tap.]