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
25. To measure tube current, the mA meter must be connected in the main circuit between the ___________________________________ and the ___________________________.
step up transformer, x-ray
26
26. Practice: Make a sketch here of the entire x-ray machine circuit, as best you can,
from memory:
?
27
27. An x-ray machine with no rectifiers in its circuits is referred to as __________-rectified.
self
28
28. In a half-wave rectified system, all the rectifiers do is _________________ those
pulses of electrical current which are going the wrong way.
block
29
29. 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.
doubled
30
30. The average kilovoltage for a single-phase x-ray machine is approximately _____________ of the peak kilovoltage.
one-third
31
31. For three-phase x-ray machines, during an exposure the voltage never drops to ________________.
91%
32
32. For a three-phase x-ray machine, the fluctuation of the voltage between 86% and 100% of the set kVp is called voltage _______________________.
ripple
33
33. For a three-phase x-ray machine, the average voltage is about ____________% of the kVp set.
91
34
34. 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.
penetration
35
35. In addition, because of overlapping pulses of electrical current for a three-phase machine, for a given set mA station the effective mA is ______________________.
increased
36
36. 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.
half
37
37. For a 3-phase, 12-pulse machine, the voltage ripple is reduced to ____________%.
94%
38
38. 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.
500, 25,000 Hz
39
39. 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.
equal
40
40. 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.
short
41
41. 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 ____________________.
kW
42
42. Write here the formulas to calculate the generator power ratings for:
A three-phase x-ray machine: _____________________ A single-phase x-ray machine: _____________________
mA x kVp / 1,000
| 0.7 mA x kVp / 1,000
43
43. Synchronous motor exposure timers have a minimum exposure time of __________ second, and all available exposure times are multiples of 1/60.
1/60th
44
44. ______________________ timers are the most common type and use capacitors to measure the electric charge accumulated.
Manual
45
45. Electronic timers are extremely accurate and can produce exposure times as short
as __________ millisecond.
1
46
46. Commonly found on mobile x-ray units is the _____________ timer.
mAs
47
47. The first automatic exposure terminating device was the _______________________.
Photo timer
48
48. In most automatic exposure control (AEC) systems, the radiation detection device is a gas ____________ _____________________.
ion chamber
49
49. 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.
thyratron
50
50. 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.
electromagnet
51
51. 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.
count
52
52. 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.
rate
53
53. The ______________________ control is the only logical way to alter the resulting exposure while using the AEC.
density
54
54. The “density” control for an AEC system alters the _____________________ higher or lower by set amounts (usually steps of 25%).
thyratron
55
55. 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.
front, behind
