X-RAY MACHINE CIRCUITS AND GENERATORS Ch 8 Flashcards
1
Q
- The main circuit of an x-ray machine is composed of what three general sections:
- __________________________________________
- __________________________________________
- __________________________________________
A
Console
High Voltage
X-ray tube circuit
2
Q
- To protect the entire x-ray machine circuit, a large circuit _____________________ kicks off if there is an overload or short circuit in any part of the system.
A
Breaker
3
Q
- A device which measures the incoming voltage from the power line, and compensates for variations by adjusting the autotransformer slightly up or down, is called the _____________ __________________ __________________________.
A
Line Voltage Compensator
4
Q
- The ____________ (major and minor) controls on the x-ray machine console actually set the autotransformer.
A
kVp
5
Q
- The high voltage transformer is a step-up transformer with a turns ratio normally between ___________ and _____________.
A
500:1, 1,000:1
6
Q
- Before and after passing through the step-up transformer, the only difference in the two AC waveforms for the electricity is the ____________________ of the waves, which indicates increased voltage.
A
amplitude
7
Q
- For full efficiency, a minimum of ____________ diode rectifiers is required in the
rectifier bridge used in a single-phase x-ray machine.
A
4
8
Q
- The modern solid-state diode is constructed by connecting an ________-type
crystal of silicon to a _________-type crystal.
A
N, P
9
Q
- As long as electrons and holes are huddled together along the n-p junction, a _________________________ bridge is formed and electricity can flow through the diode.
A
potential
10
Q
- When AC current reverses direction, it _______________________ the diode with the holes at one end and the electrons at the opposite end, such that electricity cannot flow through the diode.
A
polarizes
11
Q
- It is important that ____________________________ be the last step in preparing high-voltage electricity to enter the x-ray tube.
A
rectification
12
Q
- In Coolidge’s hot-cathode x-ray tube, the process of __________________________ _______________________ frees electrons from the filament wire prior to exposure, which greatly improves efficiency.
A
thermionic emission
13
Q
- To heat the filament wire by friction between electrons, what is needed is high- _______________________ current forced into a very thin wire.
A
amperage
14
Q
- The filament current is applied whenever the _________________ button is held down at the console.
A
rotor
15
Q
- Once the “rotor” button is pushed, a delay is necessary before exposure can be made because it takes a few seconds for the high-amperage current to _______________ the filament.
A
heat
16
Q
- Excessive rotoring can cause unnecessary _______________ and _______________ to the x-ray tube filament, reducing x-ray tube life.
A
wear, tear
17
Q
- The step-down transformer in the filament circuit usually has a turns ratio of
__________ to produce a current of up to 5 amps (at 5 volts).
A
1:44
18
Q
- Because the filament current enters one end of the filament and exits the other (and does not jump across the x-ray tube, it is unnecessary to _______________________ the filament current.
A
rectify
19
Q
- On most x-ray machines, selection of an mA station taps the filament current to pass through a particular electronic ________________________.
A
resistor
20
Q
- Any meter placed in series in a single wire must measure ________________________.
A
amperage
21
Q
- A voltmeter must be connected in parallel because it _______________________ the electrical flow between two points in the circuit.
A
compares
22
Q
- To avoid the hazard of high voltage shock at the x-ray machine console, a ____________________________ voltmeter is used.
A
pre-reading
23
Q
- The mA meter on the console measures the milliamperage of the current which actually flows ___________________ the x-ray tube.
A
across
24
Q
- The number of electrons “boiled off” of the filament and passing across the x-ray tube, (the tube current), is but a _____________________ of the current passing through the filament itself, (the filament current).
A
fraction
25
Q
- To measure tube current, the mA meter must be connected in the main circuit between the ___________________________________ and the ___________________________.
A
step up transformer, x-ray
26
Q
- Practice: Make a sketch here of the entire x-ray machine circuit, as best you can,
from memory:
A
?
27
Q
- An x-ray machine with no rectifiers in its circuits is referred to as __________-rectified.
A
self
28
Q
- In a half-wave rectified system, all the rectifiers do is _________________ those
pulses of electrical current which are going the wrong way.
A
block
29
Q
- Because self-rectified and half-rectified units provide only 60 pulses of current to the x-ray tube per second, radiographic techniques must be ____________________ when compared with a fully-rectified single-phase x-ray machine.
A
doubled
30
Q
- The average kilovoltage for a single-phase x-ray machine is approximately _____________ of the peak kilovoltage.
A
one-third
31
Q
- For three-phase x-ray machines, during an exposure the voltage never drops to ________________.
A
91%
32
Q
- For a three-phase x-ray machine, the fluctuation of the voltage between 86% and 100% of the set kVp is called voltage _______________________.
A
ripple
33
Q
- For a three-phase x-ray machine, the average voltage is about ____________% of the kVp set.
A
91
34
Q
- The increased effective voltage of a three-phase machine provides higher overall _________________________ for the x-ray beam, which results in more exposure reaching the detector plate or cassette.
A
penetration
35
Q
- In addition, because of overlapping pulses of electrical current for a three-phase machine, for a given set mA station the effective mA is ______________________.
A
increased
36
Q
- Combining both of the foregoing, for practical purposes, the mAs may be approximately cut to _________________ for any three-phase machine when compared to a single-phase machine.
A
half
37
Q
- For a 3-phase, 12-pulse machine, the voltage ripple is reduced to ____________%.
A
94%
38
Q
- High-frequency generators alter the waveform of the electrical current and convert it from 60 hertz to a much higher frequency ranging from ________ to ________ Hz.
A
500, 25,000 Hz
39
Q
- For high-frequency mobile x-ray machines, 8 to 10 less kVp can be set for torso procedures because the average kV is nearly _________________ to the kVp set.
A
equal
40
Q
- Higher-power generators with mA stations as high as 800 to 1200 mA are recommended for pediatric and interventional radiography, because they allow exceedingly _________________ exposure times.
A
short
41
Q
- The electrical power rating of a generator or transformer is used as an indication of its overall quality, and is normally expressed in units of ____________________.
A
kW
42
Q
- Write here the formulas to calculate the generator power ratings for:
A three-phase x-ray machine: _____________________ A single-phase x-ray machine: _____________________
A
mA x kVp / 1,000
0.7 mA x kVp / 1,000
43
Q
- Synchronous motor exposure timers have a minimum exposure time of __________ second, and all available exposure times are multiples of 1/60.
A
1/60th
44
Q
- ______________________ timers are the most common type and use capacitors to measure the electric charge accumulated.
A
Manual
45
Q
- Electronic timers are extremely accurate and can produce exposure times as short
as __________ millisecond.
A
1
46
Q
- Commonly found on mobile x-ray units is the _____________ timer.
A
mAs
47
Q
- The first automatic exposure terminating device was the _______________________.
A
Photo timer
48
Q
- In most automatic exposure control (AEC) systems, the radiation detection device is a gas ____________ _____________________.
A
ion chamber
49
Q
- In an AEC circuit, device called a _______________________ presets the amount of charge the capacitor will hold before it is discharged to shut down the exposure.
A
thyratron
50
Q
- The surge of electricity discharged from the capacitor is used to energize an ____________________________ which pulls the switch in the main circuit open to terminate the exposure.
A
electromagnet
51
Q
- The AEC circuit does not “time” anything—all it knows how to do is _________________ electrical charge, and shut off the exposure when the pre-set amount is reached.
A
count
52
Q
- Anything which reduces the ________________ of x-rays reaching the detectors behind the patient, such as rolling the patient onto his/her side, results in a longer time for the charge limit to be reached.
A
rate
53
Q
- The ______________________ control is the only logical way to alter the resulting exposure while using the AEC.
A
density
54
Q
- The “density” control for an AEC system alters the _____________________ higher or lower by set amounts (usually steps of 25%).
A
thyratron
55
Q
- The AEC system can automatically compensate for any changes that occur in ____________________ of the tabletop, but has no way of “knowing” when grids, cassettes, and detector plates that lie ____________________ the AEC detectors have been changed.
A
front, behind
