center and which indicates and measures voltages in either direction. This voltage is known as alternating current voltage and the current produced by an alternating current voltage is called “alternating current.” Figure 19 shows what is known as the ideal alternating current voltage and it is known as the sine wave e.m.f. which is the goal of every A.C. generator designer.
How may we trace a sine wave so that we may use it as a standard for comparison? Let us assume that the maximum voltage produced is 10 volts. In other words, our maximum deflection of the meter away from zero would be 10. Let us take a point as the center and draw horizontally a line divided into 10 equal portions and with a compass--an instrument to draw circles--draw a circle using this line as the radius. (Fig. 19.)
Through the center, draw a perpendicular line, dividing the outside of the circle (its circumference) into 4 parts. Again
Fig. 19
with our compass let us divide this circumference into 4 parts and from these points, draw lines parallel to “y’-y.”
Let us imagine that the point of “O” is the armature shaft and the points 1, 2, 3, 4--up to 16 are the different positions that conductor A is in when the armature is turned around. At position 2, the amount of voltage generated will be represented by the length of the line between point 2 on the circle and the horizontal line. At point 3, the length of the line between 3 and the horizontal line and so forth for the various positions. At positions 1 and 9, the e.m.f. will be zero and they represent the positions of the conductor when moving parallel to the lines of force. Positions 5 and 13 represent the conductor A when in the center of the North and South poles. The voltages below the horizontal line represent the e.m.f. acting in one direction
