Figure 1-3.Tube head and cylinder (short cone).
The X-ray beam passes from the aluminum filter
through an opening in a lead diaphragm, which
restricts the beam to 2.6 inches at the cylinder tip.
There are two commonly used cylinder lengths. A tube
head with an X-ray source to cylinder end distance of 8
inches is referred to as a "short cone" machine, while a
tube head with an X-ray source to cylinder end distance
of 16 inches is referred to as a "long cone" machine. It
is essential that the technician knows the X-ray source
to cylinder end distance in order to set the appropriate
The tube head is attached to an extension arm. The
extension arm is movable, allowing you to adjust the
position of the tube head for each patient.
The operational controls on the control panel are
covered in the discussion on the operational check.
OPERATIONAL CHECK (WITHOUT
At the beginning of each workday, you should
activate the X-ray machine to ensure that it is working
properly. This operational check is conducted without
a patient in the chair. In order to check the machine,
you must be thoroughly familiar with its operation.
Read the manufacturer's instructions carefully.
Throughout this discussion of the operational
check, refer to figure 1-4. The steps of procedure are:
1. Energize the control panel. The control panel
shown in figure 1-4 has three push buttons in the upper
left corner. By depressing either the 10 mA or the 15 mA
pushbutton, you will energize the machine and select
the milliampere setting at the same time. Once the
button is depressed the "power on" light will glow
amber, indicating that the system is turned on. (A setting
of 10 mA is normally used for intraoral radiographs.)
NOTE: Some machines have separate master
on/off switches. On these machines, you should FIRST
activate the master switch, and then select the
milliamperes (10 mA or 15 mA) setting. A 10 mA
setting is used for most dental radiographs. Some units
use a combination master on/off switch and mA
selector to energize the machine.
2. Set the tube head selector. On units with
multiple tube head capabilities, depress the pushbutton
that corresponds to the tube head to be used, normally