Figure 2-25. Patterns of voltage ripple.
a. Voltage ripple affects certain aspects of tube operation. One factor that it
influences is the speed of the electrons across the x-ray tube.
(1) Consider figure 2-26, which shows a wave pattern produced in a single-
phase generator and another produced in a three-phase, 12-pulse generator. With the
2-pulse wave, the voltage value rises to a peak and then falls to zero (100 percent
ripple). This rise and fall of the voltage causes the kinetic energy of the electrons across
the tube to vary accordingly. Consequently, if 100 kVp were applied to the x-ray tube,
the kinetic energy of the electrons would theoretically range from zero, when the voltage
value is at zero, to 100 keV, when the voltage value is at its peak.
(2) The 12-pulse wave from a three-phase generator does not drop to zero,
as stated earlier. It only drops 3.4 percent below peak value. As a result, the kinetic
energy of the electrons only drops 3.4 percent below peak kV value. In other words, the
kinetic energy of electrons (at 100 kVp) in a 12- pulse system theoretically will range
from 96.6 keV to 100 keV. This means that the average kinetic energy imparted to the
electrons is much higher in the 12-pulse system than in the 2-pulse system.