Figure 2-27. Comparison of anode heat patterns with
single-phase and three-phase systems.
f. Special "spin-tops" have been devised to test the capabilities of three-phase
equipment and capacitor discharge units. These special tops operate in a similar
manner as those used for single-phase units. The major difference is that when the top
is spinning at a specific number of revolutions per minute, a strobe disk synchronizes
with the flicker in 60-cycle fluorescent lighting. With this type of spin-top, the time is
determined by measuring the length of the strip exposed. Since the speed of the top is
known, then time can be determined by how far it rotated during exposure. This top can
be used to measure exposure times in the millisecond range.