Unit 5: Filament Circuit Flashcards
what controls the filament temperature?
filament current
filament current is measured in _____
amperes (A)
What is the typical range of current for the filament current?
3-6 amperes (A)
as filament current increases, the filament gets _______ and more electrons are released by ______________
hotter; thermionic emission
where does the filament circuit receive its voltage from?
what is tube current?
quantity of electrons available to travel from cathode to anode during exposure
what monitors tube current?
the mA meter
what controls tube current?
the filament circuit
what is the rheostat?
a highly precise variable resistor
what does the rheostat do?
it adjusts the levels of voltage coming from the autotransformer after mA selection
what does the rheostat control?
the amount of voltage sent to the primary side of the step-down transformer
what type of transformer is located in the filament circuit?
step-down transformer
what does the step-down transformer do?
it decreases the voltage so that there is necessary current for thermionic emission at the filament
what happens at the filament when there is a decrease in voltage and an increase in current?
the filament will reach higher levels, causing more electrons to be burned off through thermionic emission
what does the exposure timer do?
where is it most always done at?
it “makes” and “breaks” the high voltage across the x-ray tube
on the primary side of the high-voltage transformer where the voltage is lower
list the three types of exposure timers:
electronic
mAs
AEC
which is the most accurate type of exposure timer?
electronic
what can electronic timers be used for?
rapid serial exposures and are suitable for IR
what do mAs timers do?
they monitor the product of mA and exposure time and terminates exposure when desired mAs is attained
where are mAs timers located?
on the secondary side of the high-voltage transformer
when does the AEC terminate the exposure?
when the image receptor has received the required radiation intensity
AEC incorporates a flat, parallel ___________________ positioned between the _______ and the _______
ionization chamber; patient; IR
when radiographs are taken in the AEC mode, the electronic timer should be set to ________ the expected exposure time as a back up timer
1.5 times
the AEC has how many cells?
3; one middle and two outer
