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87 Cards in this Set
- Front
- Back
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two circuits in an xray unit |
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supplies the xray tube with potential difference (kV) |
tube circuit |
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supplies the filament with enough current to thermionically emit the proper amount of electrons |
the filament circuit |
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modifies the incoming power so that the radiographer can control the voltage and exposure time |
tube (main) circuit |
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three main sections of the tube circuit |
1. control console 2. high-voltage section 3. x ray tube |
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where are the main switch and circuit breakers located? |
between incoming current and console |
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control console: |
line monitor and line |
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compensator: |
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what type of transformer is a kVp selector? |
autotransformer |
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example of a rheostat |
mA selector |
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High voltage section: |
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assemblies of an xray tube |
anode assembly cathode assembly |
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six types of exposure timers |
1. mechanical timer 2. synchronous timer 3. electronic timer 4. impulse timer 5. mAs timer 6. AEC |
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makes use of a mechanical device to make and break the circuit across the tube (on/off) |
mechanical timer |
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normally done on the primary side of the high-voltage transformer |
mechanical timer |
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uses a wound spring like a mechanical clock |
mechanical timer |
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timer only used on old portables and dental equipment |
mechanical timer |
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timer that is inexpensive but inaccurate |
mechanical timer |
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mechanical timers are only good for exposures over ___ milliseconds or __ seconds |
250; .25 |
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timer that uses a synchronous motor |
synchronous timer |
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synchronous timers are synchronized at __ Hz current in the US |
60 |
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synch timers rotates shaft at __ revolutions per second |
60 |
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shortest exposure time for synch timers |
1/60th of a second |
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most complicated timer and expensive |
electronic timer |
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most accurate timer |
electronic timer |
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timer that operates by charging a silicon-controlled rectrifier (SCR) which then terminates the exposure |
electronic timer |
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the electronic timer is accurate to _ millisecond or __ second |
1; .001 |
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most common timer used in modern radiographic equipment |
electronic timer |
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counts the number of sine wave pulses in the current before opening the exposure switch |
impulse timer |
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the impulse timer in single phase- _ pulses per cycle- half wave= _ cycles per second. full wave = _ cycles per second |
2;60;120 |
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if impulse timer were set at 1/10th second, it would count __ pulses and then terminate the exposure |
12 |
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minimum exposure time for impulse timers |
1/120th second |
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used in falling load generators and some capacitor discharge units |
mAs timer |
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mAs timers monitor the product of _ and _ to give the mAs desired |
time and mA |
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in mAs timers, the tech sets the mAs and it decides |
what mA and time to use |
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usually designed to give the highest possible mA and shortest time possible without damaging the tube |
mAs timers |
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mAs timers are located on the ___ side of the _____ transformer |
secondary side; high-voltage |
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AEC devices are programmed to automatically terminate the exposure when a predetermined __ has been reached |
density |
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AEC only control the ____ - the ___ and ___ must be set |
exposure time; mA; kVp |
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two types of AECs |
1. phototimer or photomultiplier 2. ionization chamber |
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phototimers are old devices that used a ___ to regulate the exposure |
thyratron |
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where is the phototimer placed? |
under the patient and the cassette |
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in a phototimer, xrays pass through ___,___,and ___ and strike a ___ ___ ___ |
patient, tabletop, and cassette; photo emitting screen |
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in a phototimer, after xrays hit the screen, the light energy is changed into electrons by a ___ |
photomultiplier tube |
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what makes phototimers inaccurate? |
because the photomultiplier is behind the cassette |
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which type of AEC is seldom used today? |
phototimers |
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where is an ionization chamber placed? |
between the patient and the cassette |
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how thin must an ionization chamber be? it must also be what? |
5mm; radiolucent |
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in an ionization chamber, the xrays ionize the ___ in the chamber and the liberated electrons cause a ___. |
gas; current |
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in an ionization chamber, when the predetermined amount of ___ is produced, the exposure is terminated by an ___ |
current;SCR (silicon-controlled rectifier) or thyristor |
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make up the vast majority of AECs today |
ionization chambers |
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the length of time necessary for the AEC to respond to the radiation and for the generator to terminate the exposure |
minimum reaction time |
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phototimers have a min reaction time of |
.05 seconds or 1/20th second |
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ionization chambers have a min reaction time of |
.001 seconds |
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which AEC is more efficient at providing the exact time necessary to produce the density required |
ionization chambers |
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what will cause an AEC not to terminate fast enough? |
a thin body part taken with fast screens and high mA and high kVp |
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will terminate the exposure at a specific time even if the AEC does not read the predetermined density |
backup time |
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the backup time can not excede what? |
the tube limit |
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the backup time is set by |
the technologist |
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what should always be set when using AEC? |
backup time |
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the backup time should be set to what? |
150% of the anticipated manual mAs |
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us public law states that generators must terminate the exposure at ___ mAs for exposures above 50 kVp and __mAs below 50 kVp |
600;2000 |
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in a filament circuit, incoming voltage is stepped down to __ to __ volts |
6;12 |
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amperage in a filament circuit is __ to __ amperes |
3;5 |
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when you set the mA station, you are actually setting what? |
the number of amps flowing through the filament circuit |
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the amperage in a filament circuit is adjusted with a ___ (__)- __ ___ |
variable resistor; rheostat; mA selector |
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all of the tech operated controls are located on the __ __ circuit to minimize the hazard of shock |
low voltage (primary) |
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single phase, full wave rectified current produces _ pulses per cycle or __ pulses per second |
2;120 |
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how many times does the voltage drop to 0 in a single phase generator? |
twice |
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single phase= ___ ripple |
100% |
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the percent drop from peak voltage by generator type |
ripple |
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three staggared sources of AC |
three phase |
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in 3 phase, each out of phase by __ degrees or __ of a cycle |
120; 1/3 |
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in three phase generators, how often does the voltage reach 0? |
never |
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exposure time in three phase is as low as ___ or __ ms |
1/1000 second; 1 |
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which phase generator 1 or 3 has xrays produced with higher average energy? |
3 phase |
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how many rectifiers are required for 3 phase six pulse? |
6 rectifiers |
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how many pulses per cycle for a 3 phase 6 pulse generator? how many per second? |
6 pulses per cycle; 360 per second |
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how many times does the voltage drop to 0 in a 3O, 6 pulse generator? |
never |
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ripple for 3O,6P |
13-25% |
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3,6 pulse never drops below _ to _% of peak voltage |
75;87% |
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3O, 6P produces _ % more average photon energy than single-phase |
35% MORE |
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3O,12P = _ diodes, _ wye, and _ delta connections |
12;1; 2 |
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3O,12P = _ to _% ripple...never drops below _ to _% peak voltage...produces _% more average photon energy than single phase |
4-10% ripple; 90-96%, 41% more |
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high frequency converters (microprocessors) change the frequency of the incoming current from _hz to __ to __hz. |
60;6000;100,000 |
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high frequency generators= _ to _% ripple; about the same as ___ |
3;4%; 3O,12P |
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High frequency generators= _% more average photon energy than 1O. |
45% |
