(1) Some x-ray unit circuits must be supplied with a specific voltage for
proper operation. Adjustments, therefore, are required to compensate for variations. If
no attempt is made to correct for line variation, the penetrating ability of x-radiation
produced would be variable due to the changing voltage applied to the circuit.
(2) Hence, the "line-to-autotransformer" circuit must have some adjustment
to compensate for different line voltages. Later, in figure 3-3, you will notice a line
voltage compensator, which is used to correct variations.
b. To supply the various circuits in the x-ray unit with the proper voltages, the
volts-per-turn ratio of the autotransformer must be controlled. A voltmeter across a
certain number of turns of the transformer is used to indicate when the volts-per-turn
ratio is proper. When the voltmeter indicates a predetermined value, the volts-per-turn
ratio of the autotransformer is proper for the unit's operation.
c. The prereading voltmeter (PRV) and the line voltage compensator permit
adjustment of the volts-per-turn ratio of the autotransformer. There is a single line on
the face of the meter. By manipulating the line compensator, the x-ray specialist adjusts
the circuit until the pointer is aligned with this line, thus ensuring the proper volts-per-
turn ratio of the autotransformer. In some equipment, this is accomplished
automatically by regulating circuits.
d. The line strap is a major adjustment to be made by the medical equipment
repairman at the time of installation. This adjustment is not available to the x-ray
e. A main switch is used to connect or disconnect the unit from the service line.
The switch has two sections, one in each side of the incoming line. A ground wire
connects to the frame of the unit. The ground wire will protect the operator from
electrical shock should one of the wires of the incoming line become short-circuited to
the chassis of the unit.
X-RAY TUBE FILAMENT CIRCUIT
The x-ray tube filament, as used in medical radiography, must be heated until
incandescent. The hotter the filament, the larger the number of electrons liberated. A
relatively high current is required to produce the desired temperature. The
autotransformer (figure 3-1) is the power source used by a step-down transformer
(filament transformer) to produce higher current (amperage) at a lower voltage. The
filament transformer also isolates the high voltage, which appears across the x-ray tube,
from the autotransformer.