2 Flashcards
measure the voltage provided to the xray imaging system and adjusts the voltage to precisely 220V
line voltage compensator
older models require manual adjustment of the line voltage compensator and incorporates a
line voltage meter
adjusts the voltage supplied to specific circuit of the xray machine
autotransformer
allow the radtechs to select the voltage and control the amount of voltage that will flow across the xray tube
kVp selectors
kVp selector can be a ____
major- increment of __ kVp
minor- increment of __ kVp
major or minor kVp selector
10, 1
placed across the output terminals of the autotransformer and actually reads voltage in the primary circuit and not the kVp
kVp meter
consists of electronic device whose action is to make or break the high voltage across the tube
timer circuit
automatically terminate the exposure after prescribed time, usually 6 s
guard timer
4 types of timing circuits
synchronous timer, electronic timer, mAs timer, automatic exposure control
make use of synchronous motor
synchronous timer
device designed to drive a shaft at precisely 60 revolutions per second based on frequency of the supplied current
synchronous motor
minimum exposure time is set at 1/60 seconds and timing intervals increases by multiples thereof, 1/30, 1/20, etc
synchronous timer
needs to be reset after each exposure and therefore cannot be used for multiple exposures
synchronous timer
uses a rather complex circuitry, most accurate xray exposure timers
electronic timer
allows a wide range of time intervals to be selected as small as 1 ms
electronic timer
suitable for rapid serial exposure such as required in interventional radiology procedures
electronic timer
monitors the product of mA and exposure rime snd terminates exposure when the desired mAs value is attained.
mAs timer
designed to provide the highest safe tube current for the shortest exposure time
mAs timer
this timer is located on the secondary circuit as it must monitor the actual tube current
mAs timer
device that measures the quantity of radiation that reaches the image receptor and automatically terminates the exposure when the image receptor has received the required radiation intensity
automatic exposure control AEC
now widely used but it is just an addition to an electronic timer, manual to automatic control of exposure
AEC
increases the voltage that will be supplied into the xray tube from hundreds to thousands of volts
step-up transformer
monitors the xray tube current. connected to the center of the secondary winding of the step down transformer
mA/s meter
converts ac to dc, ensures one direction of flow, cathode to anode
rectifiers
diodes used for xray machines are solid state diodes made of
silicon
can be half wave rectified or full wave rectified
xray machines
used for portable xray machines and dental xray machines
half-wave rectification
can be made of 0 (self-rectified), 1 or 2 diodes
half wave rectification
half-wave rectification-
xray output pulsates, producing ___ or ____ pulses each second
50 or 60
inefficient because it waste half of the supply of power
half-wave rectification
also requires half of the exposure time
half wave rectification
used for most permanent radiographic unit
full wave rectification
usually made of 4 diodes
full wave rectification
full wave rectification- the pulsed output occurs ___ times each second
120
why full wave rectification is more efficient than half way rectified unit?
negative half cycle of the input voltage is converted to positive cycle
time of exposure is also cut in half
full wave rectification
voltage waveform with positive and negative cycle. Voltage is pulsating and swings from zero to maximum potential
single-phase voltage waveform
the negative half cycle of the waveform is suppressed
single phase half wave rectified voltage waveform
voltage waveform wherein the negative half cycle is converted to positive cycle by rectifiers. voltage is still pulsating
single phase full wave rectified voltage waveform
this voltage waveform is composed of three simultaneous voltage waveforms that are out of step with one another. With three phase voltage waveform, voltage no longer drops to 0
three phase voltage waveform
in this voltage waveform,a nearly const high voltage is supplied to the xray tube
three phase six pulse voltage waveform (full wave rectified)
additional component is added to further improve the number of pulses in a cycle
three phase 12 pulse voltage waveform
in this voltage waveform, the usual frequency (50 or 60 hz) before converting to high voltage. This produces nearly constant potential voltage waveform, improving image quality at lower patient dose.
high frequency voltage waveform (constant potential)
part of the high voltage circuit. the circuit is completed once the electrons produced on the filament travel from cathode to anode. However, the reverse is not possible as anode cannot produce electrons.
X-ray tube
controls the filaments current that will be supplied to the filament of the xray tube. This current controls the temperature of the filament
The Filament Circuit
As filament current increases, the filament becomes hotter, and more electrons are released by thermionic emission
filament circuit
as filament current increases
filament becomes hotter and more electrons are released
it is measured in amperes (A). Filament operates ar currents between 5 to 7 A
filament circuit
filament circuit consists of
mA selector (Rheostat, focal spot selector, step down transformer
reduces the voltage supply from the autotransformer by varying the resistance through the circuit
mA selector / Rheostat
controlled by the mA selector on the opera console. The higher the mA station, the lower the resistance. The lower the mA station, the higher the resistance
mA selector / rheostat
the higher the mA station
the lower the resistance
lower the mA station
higher the resistance
current of about 0.5 to 1 A is supplied to the primary side of the transformer
mA selector / rheostat
selects the filament (small or large) that will be heated, which corresponds to the focal spot size
focal spot selector
connected to the primary windings of the step down transformer
focal spot selector
decreases the voltage and increases the current that is supplied to heat the filament of the xray tube
step down transformer
the primary windings carry a voltage of 150 V at a current of 0.5 to 1 A, and the secondary windings carry a voltage of 12 V at a current of 5 to 8 A
step down transformer
