Chapter 8 - X-Ray Machine Circuits and Generators Flashcards
What are the 3 general sections of the main x-ray circuit?
- control console
- high-voltage section
- x-ray tube circuit
What is a line-voltage compensator?
device that measures fluctuating incoming voltage from the power line and automatically compensates by adjusting the autotransformer slightly up or down to maintain uniform, accurate voltage
What is the typical turns ratio range for the high voltage step-up transformer?
500:1 - 1000:1
What are the 3 general types of exposure timers for manually set techniques? What is the most common?
- synchronous
- electronic (most common)
- mAs
In the high-voltage x-ray machine circuit, what is the very last thing that must be done with the electrical current before it reaches the x-ray tube?
IT MUST BE RECTIFIED SO ELECTRONS ALWAYS ENTER THE TUBE IN THE SAME DIRECTION
The step-up transformer is between the _____ and the _____.
AUTOTRANSFORMER
RECTIFICATION BRIDGE
The step-down transformer is between the _____ and the _____.
RHEOSTAT
X-RAY TUBE FILAMENT
What is the typical range of output voltage from the autotransformer?
100 - 400 volts
What is the typical turns ratio for the step-down transformer in the filament circuit?
1:44
In a solid-state diode, if electrons drift in n-type silicon, what drifts in p-type silicon?
HOLES
Why can’t electricity pass backward through the solid-state diode?
WHEN AC CURRENT REVERSES DIRECTION, THE ELECTRONS AND HOLES ARE NO LONGER REPELLED TO THE N-P JUNCTION AND THE POTENTIAL BRIDGE DISCONNECTS
Why is high amperage, rather than high voltage, needed for heating of the filament?
HIGH AMPERAGE CREATES GREATER FRICTION WHICH EMITS HEAT
After depressing the exposure switch all the way, why does the x-ray machine prevent any exposure until the “ready” light comes on?
THE FILAMENT NEEDS A FEW SECONDS TO HEAT UP FROM THE HIGH-AMPERAGE CURRENT
On most x-ray machines, when the mA station is selected, what particular type of electrical device in the circuit is being selected?
A RESISTOR IN THE RHEOSTAT
When the kVp is selected, what electrical device is being adjusted?
THE AUTOTRANSFORMER
Voltage meters must be connected in which way in the circuit?
IN PARALLEL
Does the mA meter measure the filament current or the tube current?
TUBE CURRENT
What is defined as the “boiling off” of electrons from a heated filament wire?
THERMIONIC EMISSION
Why is self-rectification dangerous to the x-ray tube?
THE ELECTRONS CAN MOVE BAKWARDS FROM ANODE TO CATHODE AND DAMAGE THE FILAMENT
Compared with a 1 phase machine, radiographic techniques can generally be changed by how much for 3 phase and high-frequency machines?
THEY CAN BE HALVED
Higher-power generators are more efficient because they have a lower percentage of what effect in their waveform?
RIPPLE
What is the only logical way for the radiographer to modify the exposure intensity while the AEC is engaged?
ADJUST THE DENSITY CONTROL
Why does the AEC take longer to shut off the exposure when the patient is rolled up onto his/her side, or when a thicker patient is placed in the beam?
THE RATE OF X-RAYS REACHING THE DETECTORS IS REDUCED, SO CHARGING THE CAPACITOR TAKES LONGER
When setting the density control, what specific electrical device is being adjusted?
THE THYRATRON
What are the 3 main components of the high-voltage circuit on an x-ray machine?
- autotransformer
- step-up transformer
- rectifier bridge
What are the 2 main components of the filament circuit?
- resistor bank (rheostat)
- step-down transformer
How many rectifying diodes are at minimum required for full-wave rectification?
4
What percentage of the kVp setting is actually generated as kilovoltage in each of these generators?
- 1 pulse
- 3 phase, 6 pulse
- 3 phase, 12 pulse
- high-frequency
- 33%
- 91%
- 97%
- 99%
How is the power rating for an x-ray machine calculated?
- (max mA)(kVp)/1000
- expressed in kW
- multiply mA and kVp by 0.7 for single phase machines
How does an electronic timer work?
charge is accumulated and stored on a capacitor until a preset limit is reached, the the capacitor discharges electricity to trip a switch
