Lesson 3. X-Ray Circuits and Tubes - Fundamentals of X-Ray Physics

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LESSON 3
X-RAY CIRCUITS AND TUBES
Section I. MAJOR X-RAY MACHINE CIRCUITS
3-1.
INTRODUCTION
The diagram of most medical x-ray units can be reduced to the following four
basic circuits:
a. Line-to-autotransformer circuits, which provides adjustments to overcome
variations of the normal incoming line voltage. It assists the operator to obtain specific
voltages for the unit's operation.
b. X-ray tube filament circuit, primary and secondary, which provides the
electrical power required to heat the x-ray tube filament, and means to vary the x-ray
tube filament temperature as required to control the tube current (quantity of radiation).
c. High-tension circuit, primary and secondary, which permits development of
the required high potential, its application across the x-ray tube, and adjustments which
enable the operator to control kilovoltage peak (quality of radiation).
d. Control circuit (also called the timer circuit or operating circuit, which initiates,
times, and terminates the x-ray production by controlling a switch that connects the
primary circuit of the high-tension transformer to the power source.
e. Other circuits are found in an x-ray machine, but those described here are the
ones essential for operation and control of both the quantity and quality of radiation
produced.
3-2.
LINE-TO-AUTOTRANSFORMER CIRCUIT
Since most practical x-ray units operate from standard service lines, the first
circuit energized in any x-ray unit is the one that connects to the service lines. This is
the circuit used to energize all other circuits in the x-ray unit. Before considering the
circuit, consider the characteristics of the incoming power line.
a. The power source voltage will vary from day to day or even from hour to hour,
depending on the demands placed upon it. At a time when the power drain is great, the
source voltage will be lower than normal. At other times, when demands on the source
are light, the voltage will be higher. The variation that follows the living cycle of the
community is commonly called line variation.
MD0950
3-2

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