Lesson 1, Topic 1
In Progress

Generators

April 11, 2024

Generators

Learning Objective: Examine single-phase, three-phase, and high-frequency generators.

The x-ray generator delivers the electrical power to energize the x-ray tube and permits the selection of x-ray energy, x-ray quantity, and exposure time. The generator’s major internal components include transformers, diodes and rectifier circuits, filament circuits, timer switches, and kilovolt and milliampere meters. Single-phase, three-phase, and high-frequency generators produce different voltage waveforms (ripple) and x-ray beam spectra.

Single-Phase Generators

Learning Objective: Describe single-phase generators.

Single-phase generators, which are being phased out of operation due to their inefficiency, produce a pulsating current that alternates from negative to positive during the electric cycle, which results in a pulsating x-ray beam (FIGURE 37.14). In a single-phase current with full-wave rectification, 120 pulses of electricity per second create 120 pulses of x-rays per second. Single-phase generators are considered the lowest power and most basic x-ray machines.

FIGURE 37.14  Three-phase power is a more efficient way to produce x-rays than is single-phase power. Shown are the voltage waveforms for unrectified single-phase power, unrectified three-phase power, and rectified three-phase power. From Bushong SC: Radiologic science for technologists: physics, biology, and protection, ed 12, St. Louis, 2021, Mosby.

Three-Phase Generators

Learning Objective: Describe three-phase generators.

Three-phase generators are powered by three separate sources of AC at the same time, which is a more constant and efficient voltage source. AC is generated over three overlapping cycles. When the current is rectified, its waveform appears as a “ripple” with no real low points. In a three-phase current with full-wave rectification, 360 pulses of electricity per second create 360 pulses of x-rays per second. An advantage of a three-phase current is that it is more efficient and produces approximately 40% more x-rays than a single-phase current. This greater output enables exposure times to be decreased by 40%.

High-Frequency Generators

Learning Objective: Describe high-frequency generators.

High-frequency (HF) generators are the most common generators used today (FIGURE 37.15). They produce x-rays much more efficiently than single-phase or three-phase generators. The primary function in the complex HF circuitry is that the 60-Hz full-wave rectified circuit is converted to a significantly higher frequency of about 6000-Hz. The highest-powered HF units can convert the frequency to as high as 100,000 Hz. HF generators produce a near-constant voltage waveform, resulting in even less exposure time than three-phase. They produce the greatest number of x-rays for the same exposure technique. HF generators are also smaller than three-phase and single-phase generators.

37.3

Critical Thinking Application

At WMFM Clinic, the x-ray generator is a high-frequency generator. During Stephanie’s clinical experience during training, she worked with a single-phase generator. She has learned the technical factors using the single-phase generator. What changes will Stephanie need to make to her technical factors now that she is using a high-frequency generator?

FIGURE 37.15  High-frequency voltage waveform. From Bushong SC: Radiologic science for technologists: physics, biology, and protection, ed 12, St. Louis, 2021, Mosby.