Can high frequency generator use single phase power? Yes
Comparison of xray machines – high frequency? Less than 1% voltage ripple; highest quality xrays; xray quantity equal to three phase; highest power rating.
Comparison of xray machines – single phase? 100% voltage ripple; lowest power rating
Comparison of xray machines – three phase? Less than 15% voltage ripple; better quality and higher quantity xrays; average power rating.
Define Reverse Bias When the polarity of the AC reverses there is no flow of electrons across the cathode and anode. Reverse bias holds the device in a non-conductive state until the control voltage is sufficient to bring it to the conductive state when added together. Bias is used mostly in analog devices, such as an audio amplifier, to keep the output voltage constantly in the conductive region of the transistor or tube. It may also be used in a digital circuit to enable the transistor to switch faster because the transistor is “primed.”
Difference between autotransformer and high voltage transformer? Auto: kVp dial selects voltages from different levels on the autotransformer and applies them across primary of high voltage transformer. High Voltage: Provides high voltage required to accelerate the electrons and generate x rays
How do battery powered generators work? 1. Power from NiCd batteries 2. High voltage 500 to 1000 Hertz DC 3. Rectified 1000 to 2000 hertz AC with 100% ripple 4. Smoothed to minimize ripple
How do vacuum tube rectifiers work? 1. Look like tiny x-ray tubes 2. Composed of cathode negative and anode positive
How does a capacitor discharge generator work? 1. Capacitor bank charged by rectified high voltage 2. During exposure capacitors provide kv across tube
How does half wave rectification work? 1. Only half of AC waveform appears 2. The inverse (negative) voltage is removed 3. Current flows through x-ray tube during positive part of the cycle.
How does the n-type of semiconductor work? Negative has loosely bound negative electrons that are relatively free to move about inside the material
How does the p-type semiconductor work? Positive. Has negative electron traps made up of positively charged holes that attract and hold negative electrons
How many waveforms are provided in three phase power? Three waveforms superimposed
How many windings doe the autotransformer have? One
Self rectified circuit? AC voltage is applied directly across the x ray limiting the x ray production to half the AC cycle. NOTE: typical AC cycle is 1 cycle per 1/60 sec.
The x-ray tube circuit aka filament circuit is what type of circuit? Step down circuit
What are the parts of a solid state rectifier? 1. N-type material. Donor. Negative. Similar to cathode 2. P-type material. Acceptor. Positive. Similar to anode 3. P-n junction.
What are the three components of the high voltage generator? 1. High voltage transformer 2. Filament transformer. 3. Rectifiers.
What are the types of rectification? 1. Half wave – just eliminates negative wave 2. Full wave – converts negative to positive wave.
What are the types of rectifiers? 1. Vacuum tube 2. Solid state.
What does kvp control? The energy of the photons
What does ma control do? Controls the number (quantity) of electrons from cathode to anode per second and is measured in ma
What does ma control? The number of the photons
What does the line voltage compensator do? Compensates incoming voltage so that a constant voltage may be used during exposure
What does the step up/high voltage transformer do? 1. Increases voltage 500 to 1000 times 2. Increased voltage to kilovoltage
What effect does single phase power have on the current? Allows incoming power to pulsate due to rise and fall of current
What generator has lowest power rating? Single phase
What is a coil of wire that heats up when a current is supplied and allows electrons to be emitted from the coil? Filament
What is full wave rectification? 1. Converts negative half of AC waveform into positive waveform 2. Must have four rectifiers.
What is self rectification? Similar to half wave rectification
What is the difference between single phase and three phase power? Single phase has one transformer and three phase has three transformers
What is the disadvantage of half wave rectification? Waste of energy
What is the first component to receive power in the x-ray circuit? Autotransformer
What is the main disadvantage of three phase power? Cost
What is the most efficient generator? High frequency generator
What is the problem with a capacitor discharge generator? 1. As capacitors drain kv drops 2. Residual charge could shock operator
What is the purpose of the step down transformer? 1. Control number of x-rays 2. Create thermionic emission at filament 3. Adjusts current to cathode filament to produce heat for thermionic emission.
What is the solid state rectifier composed of? 1. Two types of semiconductors, p type and n type 2. Made of silicon
What is the transformer section immersed in and why? Oil for insulation and cooling
What is the voltage ripple for single phase power? 100% .
What is voltage ripple? 1. Variation in tube voltage during an exposure 2. Lowest voltage ripple has highest quantity and quality
What type of current does the x-ray tube operate on? DC
What type of induction does the autotransformer use? Self induction
What type of rectifier is used currently? Solid state aka solid state diode
What type of waveform is unrectified? Sinusoidal
Where does rectification take place? Between the secondary side of the step up transformer and the x-ray tube
Where is capacitor discharge generator used? Not used any more, was used in some portables
Where is the transformer section located? In a box linked between control console and x-ray tube
Where is there unrectified voltage in the x-ray machine? At the primary and secondary side of the high voltage step up transformer.
Whose law applies to resistors? Ohm’s
Why use rectifiers in high voltage generator? So electrons flow in one direction only in the x-ray tube from cathode to anode