CONTROL PANEL:
- On/off switch
- Exposure timer
- mA Selector
- kV Selector
- kV meter
- Rotor Switch
- Exposure Switch
- Accessory Controls
- AEC
- Many manufacturers produce radiographic
equipment with different characteristics. - Despite variations, most x-ray generators
have common controls for radiographer
selections.
Control panel:
Equipment Variability:
Control Panel Features:
- Modern x-ray generators often have
sophisticated computerized panel displays. - Radiographers need advanced knowledge
and understanding to operate the
equipment.
- Connects electrical power to the radiographic
generator control device. - Prepares the generator unit for x-ray production.
Location and Familiarity: - Usually part of the control console.
- Radiographers must be familiar with its location
ON/OFF SWITCH
- Located on the control panel console.
- Determines the length of time x-rays will be
produced.
EXPOSURE TIMER
Types of Exposure Timers:
- Mechanical
- Synchronous
- Electronic
- Simple type, like a spring-set dial.
- Timer knob is turned to a specific
mark, winding a spring. - During exposure, the spring
unwinds according to the set
time. - Limited to a shortest setting of
1/10 second.
MECHANICAL TIMER
- More advantageous for
radiographic imaging. - Reduces issues with motion of the
body part being examined.
MECHANICAL TIMER
Advantages of Shorter Times:
- Motor-driven devices.
- Utilize the 60-Hertz alternating current in the United States.
- Exposure settings are intervals related to 1/60 second (e.g.,
1/30 sec, 1/20 sec, 1/10 sec). - Shortest available time is 1/120 second.
SYNCHRONOUS TIMERS
ELECTRONIC TIMERS
Advantages:
- Exposure times of less than 1/120 second.
- High reliability.
- Less prone to malfunctions.
- Most common type in radiographic equipment today.
- Designed with sophisticated, complex circuitry.
- Considered the most accurate of exposure timers.
ELECTRONIC TIMERS
EVALUATION OF TIMERS
Importance of Exposure Time:
- Controls the amount of radiation the patient is exposed to.
- Timers must be periodically evaluated for accuracy.
Evaluation of Timers:
- Spinning Top Device
- Oscilloscope
- Pulse Counter Device
- Single-phase, full-wave rectified units using a device
called the spinning top. - Consists of a round disk (approx. 3 inches in diameter)
with a small hole near the edge, resting on a smaller
circular pedestal. - Placed on an x-ray cassette containing unexposed film.
- Set spinning with a flip of the fingers; exposure is made
while it spins.
SPINNING TOP DEVICE
EXPOSURE TEST PROCEDURE:
* Select exposure factors: 1/__, 1/__, or 1/__ second.
* Image produces dashes (or dots).
* Number of dashes relates to the exposure time:
* 1/&_ second: _ dashes
* 1/30 second: _ dashes
* 1/__ second: __ dashes
* For single-phase, full-wave rectified units, one dot
per 1/___ second of exposure.
* Calculate expected dots: multiply exposure time
(seconds) by 120.
EXPOSURE TEST PROCEDURE:
* Select exposure factors: 1/60, 1/30, or 1/10 second.
* Image produces dashes (or dots).
* Number of dashes relates to the exposure time:
* 1/60 second: 2 dashes
* 1/30 second: 4 dashes
* 1/10 second: 12 dashes
* For single-phase, full-wave rectified units, one dot
per 1/120 second of exposure.
* Calculate expected dots: multiply exposure time
(seconds) by 120.
- Three-phase and capacitor discharge units do not produce the same pulsed radiation; spinning top is not suitable for these.
To test a three-phase generator: - Use a calibrated oscilloscope.
- Connect oscilloscope to the primary voltage of the step-up
transformer. - Compare actual exposure time with selected time.
Oscilloscope
Used for both single-phase
and three-phase
generators.
* Placed in the primary x-ray
beam.
* Counts and records pulses
for evaluation.
Pulse counter device
- Controls the amount of electrical current flowing through the cathode
filament. - Current flow through the cathode filament produces heat, causing
thermionic emission.
Thermionic Emission: - Produces a “space charge” as electrons break away from the hot cathode
filament. - During exposure, electrons in the space charge move from the cathode to
the anode
Milliampere Selector
mA SELECTIONS:
* Radiographic units offer mA selections ranging from __ to
____ mA.
Focal Spot Size Determination:
* In many general radiographic units, the selection of mA
determines the focal spot size.
* “L” (Large) indicates selections using the ______ focal spot.
* “S” (Small) indicates selections using the _____ focal spot
mA SELECTIONS:
* Radiographic units offer mA selections ranging from 25 to
2000 mA.
Focal Spot Size Determination:
* In many general radiographic units, the selection of mA
determines the focal spot size.
* “L” (Large) indicates selections using the large focal spot.
* “S” (Small) indicates selections using the small focal spot
- Located on the control console, provides information to the
radiographer. - Indicates the total amount of electrical current passing through the
x-ray tube (from cathode to anode) during exposure.
Total Tube Current (mAs): - Calculated as the product of milliamperes (mA) and exposure
time (seconds). - mAs = mA x Time (seconds)
mA meter/mAs meter
