RAD 262 Ch. 11 quiz

what does a transformer need to function?

AC

what is rectification?

changing alternating current into direct current

what kind of voltage does the x-ray tube need to function?

high

when does the x-ray tube function most efficiently?

with direct current

what happens to the cathode and the anode during the negative half-cycle?

the cathode becomes positive and the anode becomes negative

is there a current during the negative half-cycle? why?

no, there is no space charge near the target

why is the x-ray tube sometimes called a vacuum tube?

all of the air has been expelled from the tube

what are two other names for self-rectification?

half wave or one pulse

what is the cathode made of?

tungsten filament

what is the anode made of?

tungsten target

how hot does the filament circuit heat up to?

to the point of incandescence

what happens after the filament circuit is heated to the point of incandescence?

thermionic emission - electrons are being boiled off filament which hover in a cloud above the filament called a space charge

is the x-ray tube considered efficient?

yes

what happens after thermionic emission?

step-up transformer gives the circuit the kv we need, which makes the cathode very negatively charged and the anode very positively charged

what happens to the electrons in the space charge once the cathode is very negative and the anode is very positive?

they leave the filament side striking the target at a high speed and interacts with the atoms of the target to produce heat and x-ray photons

when the electrons strike the target, what is the ratio of heat to x-ray photons produce?

99% heat and 1% x-ray photon

describe self-rectification:

no rectifier circuit, low heat loading capacity, we have to use low techniques to avoid melting the target

what does a diode do?

prevents the negative half-cycle from going to the x-ray tube

what is a diode?

small glass tube with a cathode and anode

what upgrade does a diode offer?

only allows current to travel from cathode to anode, which gives us a greater heat technique

what is the difference between one diode and two diodes?

still half wave and one pulse, two diodes just allows for a higher heat technique

what is the difference between 1 or 2 diodes and 4 diodes?

4 diodes forces negative half-cycle to move from cathode to anode, gives us full wave and two pulse rectification

in conductivity of matter, where do electrons normally sit?

in the valency band

in the conductivity of matter, what is the forbidden band?

gap between the valence and conductor band

describe the band layout for a conductor:

valency band and conduction band overlap

describe the band layout for an insulator:

valency band and conduction band are far apart

describe the band layout for semiconductors:

valency band and conduction band have small gap, the forbidden band is small

how does current flow in a silicon rectifier?

from N-silicon to P-silicon only

what are two other names for silicon rectifiers?

solid state diode and stick rectifier

what advantages does a silicon rectifier give?

smaller in size, no filaments, low voltage drop, low reverse current, and long life due to rigid construction

how fast does a generator run?

60 Hz

how many alternations per cycle on a generator?

2

how many alternations per second on a generator?

120

what are the two clues to rectifier failure?

images are underexposed, the milliammeter detector reads half of what is set on the control panel

how many dots should there be on an x-ray image for one full second on the spinning top test?

120

what does each autotransformer control in relation to the three phase equipment?

one delta

how do they put together the three single phase currents?

it is three single phase currents combined out of step with each other by 1/3

what is the advantage to the three single phase currents combining?

less voltage ripple and more high voltage

what are the two types of 3 phase generators?

3 phase 6 pulse, and 3 phase 12 pulse

how many autotransformers are needed for a three phase current?

3

what is the job of the delta or star?

combine three single phase currents into a three phase current

what shape does the primary coil of a three phase generator have to be?

delta

what shape can the secondary coil of a three phase generator be?

star or delta

what is the voltage ripple for a 1 phase 2 pulse generator?

100%

what is the voltage ripple for a 3 phase 6 pulse generator?

13-25%

what is the voltage ripple for a 3 phase 12 pulse generator?

4-10%

what is the voltage ripple for a high voltage generator?

less than 2%

what kind of voltage is needed for diagnostic images?

high - low voltage is useless

as we go down in voltage ripple what also goes down?

patient exposure

which generator has the smallest voltage ripple?

high voltage

which generator has the highest effective Kv?

high voltage

which generator has the highest tube rating?

high voltage

what are the advantages of using high frequency?

shortest exposure times available, can set highest Kv and mA with shortest exposure times, waveform is virtually ripple free, conversion of AC to DC immediately smoothing variation and line voltage