Power Supplies- Quizzes

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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

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    Ultraviolet imaging may provide metabolic map of brain tumors
    Neurosurgeons and researchers at Cedars-Sinai Medical Center in Los Angeles are adapting an ultraviolet camera to possibly bring the technology into the operating room.

    If the system works when focused on brain tissue, it could give surgeons a real-time view of changes unapparent with current imaging systems. The pilot study seeks to determine if the camera provides visual detail that might help surgeons distinguish areas of healthy brain from gliomas, which have irregular borders as they spread into normal tissue.

    Gliomas’ far-reaching tentacles represent a balancing act for neurosurgeons: Taking out too much normal brain tissue can have catastrophic consequences, but stopping short of total removal gives remaining cancer cells a head start on growing back. Delineating the margin where tumor cells end and healthy cells begin never has been easy, even with recent advances in medical imaging systems, said Keith L. Black, MD, chair of the department of neurosurgery, said in a release.

    But the ultraviolet camera might be able to see below the surface, he said. Because tumor cells are more active and require more energy than normal cells, the chemical—nicotinamide adenine dinucleotide hydrogenase (NADH)—accumulates in tumor cells but not in healthy cells. NADH emits ultraviolet light that may be captured by the camera and displayed in a high-resolution image.

    “The ultraviolet imaging technique may provide a ‘metabolic map’ of tumors that could help us differentiate them from normal surrounding brain tissue, providing useful, real-time, intraoperative information,” said Ray Chu, MD, a neurosurgeon leading the study, said in the release.

    In the clinical trial, neurosurgeons will study 20 patients, placing the camera near the surgical field and recording images as the tumor is exposed and removed. Images will not be used in decision-making or surgical technique but later will be correlated with tumor appearance, laboratory findings and MRI and CT scans to assess the ultraviolet technology’s value in the operating room.

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