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Unit 1 - RAD 231
X-ray Circuitry
| Question | Answer |
|---|---|
| List physical parts of the x-ray system. | Generator; x-ray tube |
| What are the segments of the x-ray circuit at the x-ray transformer? Describe them. | Primary (low voltage) - connected to primary coil (incoming) includes equipment btwn electrical source and primary coil; 1st circuit in series Secondary (high voltage) - connected to secondary coil (stepped up) includes equipment btwn step up and tube |
| Describe in detail the PRIMARY circuit. | main power switch cxtd to power supply of facility includes circuit breakers, also includes autotransformer (kVp selector on ctrl panel); timer circuitry; kVp prereading meter; ends at primary side of high voltage step-up transformer |
| Describe in detail the SECONDARY circuit. | Begins with secondary side of step-up transformer; fixed ratio; includes rectification (solid state diodes) and milliameter; smaller wires (higher voltage, less current) |
| Define voltage | measure of electrical force or pressure |
| Define resistance. | opposition to current flow; property of an element in circuit that resists/impedes flow; measured in OHMS |
| What is current? | quantity of electrons moving; flow of electrons; measured in AMPERES |
| Define ampere. | unit of electrical current; # of electrons flowing in a conductor |
| Define Conductor. | material in which electrons can move freely; examples ALUMINUM, COPPER, GOLD, SILVER |
| What is a transformer? | electrical devices that change voltage from low to high or vice versa |
| What is a step-up transformer? | transformer includes more turns in secondary winding than in primary winding, which increases voltage |
| What is a step-down transformer? | transformer includes more turns in primary winding than secondary winding, which decreases voltage |
| What is a rectifier? | electrical device that allows current to flow only in one direction (converts AC to DC) |
| What is AC? | alternating current - current flows in positive direction for half the cycle, then negative for other half of cycle; polarity changes |
| What is DC? | direct current - current flows only in one direction (example: battery) |
| What is electrodynamics? p56 Orth p46 Selman | Study of moving electrical charges. electrons can move in vacuum, gas, isotonic solution, metal conductors |
| Explain how current flows. | electrical charges will move when electrical potential difference exists in conductor; a positive charge surface (too many electrons) and a negative charge surface (not enough electrons); electrons move from excess to deficiency |
| What is electrical potential? | ability to do work because of a separation of charges; measured in VOLTS |
| What is an insulator? | material that doesn't permit electron flow; examples RUBBER, GLASS, PLASTIC, WOOD |
| What is a semiconductor/ superconductor? | Semiconductor - material that can act as a conductor or insulator, depending on how it's made and the environment Superconductor - material that allows electrons to move freely w/o resistance when cooled to extremely low temps |
| compare low and high resistance | Low resistance - more free electron movement; shorter length of conductor; larger diameter; low temp High resistance - less electron movement; longer length of conductor; smaller diameter; causes increase in temperature |
| Define OHM | electrical resistance equal to resistance between 2 points along a conductor that, when a potential difference of 1 volt is applied, produces a current of 1 ampere |
| What is Ohm's Law? | states that potential difference (voltage) across total circuit or any part of circuit is equal to current (amperes) multiplied by the resistance I = V / R OR V = I x R |
| Name the specific parts of the x-ray facility | Room Generator X-ray tube Operating console (control panel) |
| What is in the Control Panel? | Control for line voltage compensation (not visible) kVp mA time AEC - chamber/density Fluoro |
| NEED TO KNOW THIS ONE What is the EXACT formula for AMPERE? | one coulomb quantity of electric charge flowing per second 6.25 x 10 (to 18) free electrons per SECOND |
| Define DOPING. | Doping is the process of introducing very small amounts of certain foreign atoms into the crystal lattice structure of semiconductors to alter electrical properties. Create excess or deficiency of electrons around atom. |
| What is N type doping? | Adding atoms w/greater # of valence electrons than silicon to a silicon lattice results in creation of free electrons. IE arsenic, antimony, phosphorus. INCREASES conductivity |
| What is P type doping? | When an atom with one fewer valence electron than silicon is added to a silicon lattice, electron deficiencies are created, called "holes". IE boron, aluminum and gallium DECREASES conductivity |
| Define BATTERY PP p6/Slide 2 Selman p50-51 | a device that produces electrons through a chemical reaction, stores an electric charge long term, and provides electrical potential. a device that acts a source of electric current (wet/dry cell) |
| Define CAPACITOR PP p6/Slide 2 Selman p 56-57/76/168-169 Orth p478 | device like a battery that stores an electric charge, but works differently in that it cannot produce new electrons and stores charge temporarily electrical device used to temporarily store electrical charge |
| Define DIODE PP p6/Slide 2 Selman p | eg Solid State Rectifier one-way valve device, allows electrons flow in only one direction Changes AC to DC |
| Define FUSE PP p6/Slide 3 Selman p150/56 | emergency device that breaks/opens the circuit if there is a sudden surge of electricity; FUSE - section of special wire, usually encased in glass, that quickly melts if current flow rises excessively; one time use |
| Define CIRCUIT BREAKER PP p6/Slide 3 Selman p 155 | additional protection against overloading circuit is provided by circuit breaker (reusable). Usually connected in series w/exposure switch, timer, and RC switch If current flow rises too much, internal switch trips (opens) stopping the flow of energy |
| Define RESISTOR PP p7/Slide 1 | Inhibits the flow of electrons, allowing precise flow of electricity through that specific part of circuit |
| Define RHEOSTAT PP p7/Slide 1 | variable resistor; adjustable form of resistor |
| Define SWITCH-MAIN PP p7/Slide 1 | device that opens the circuit to allow the flow of electricity; usually double blade, single-throw switch |
| Define TRANSFORMER PP p7/Slide 1/3 | device that can increase/decrease voltage by predetermined amt; 2 coils wrapped around an iron core |
| Define LINE COMPENSATOR Selman p151 | Permits adjustment of the line voltage (maintains consistency) to selected value |
| Define AUTO-TRANSFORMER PP p8-9/Slide 3/1 | Self-Induction; also known as variable transformer, variable kVp selector (allows diff kVp to be set); 1 coil of wire wrapped around iron core. Fixed # of turns, 2 lines input side and 1 output side Voltage on 1 side and 2 side are DIRECTLY related |
| Define CHANGE OVER SWITCH Selman p 161 | A special radiographic-fluoroscopic switch that allows the radiologist to do spot-film work automatically. It automatically selects the exposure factors for x-ray. When it is w/drawn, the exposure factors automatically return to fluoro. |
| Define mA SELECTOR Orth p 91 | device in filament circuit that controls the temperature of filament, which determines how many electrons are boiled off (thermionic emission). Temperature is controlled by the current in the filament circuit. It operates at currents of 3-5A |
| Define FILAMENT STABILIZER Selman p156 | a relatively small change in the filament voltage or current causes a large change in electron emission/tube current/mA. it corrects for instantaneous fluctuations in line voltage that may be caused by momentary demand elsewhere on the line. |
| Define RECTIFIER Selman p94-95, 100-106 | a device that changes AC to DC; two types - Self-rectification and Vacuum tube or solid state diode rectification; Located in SECONDARY circuit; changes AC to DC for tube; Self-rectification is basic and not efficient due to gaps between positive phases; |
| Define BACKUP TIMER Selman p154 | a timer that sets max exposure time. It stops the exposure at a predetermined time; may be based on anatomic part or manual. MAXIMUM ALLOWED 600mAs or 1.5 x the expected exposure time in case AEC fails; protects patient and tube |
| Define MECHANICAL TIMER Selman p152 | hand-held timer w/clock mechanism, setting the seconds winds up a spring, and activating the exposure releases the spring, terminating the exposure at preselected time. Accurate to .25secs (used mainly in dental x-ray) |
| What is the Power Formula for A, V, W? | Amps = Watts / Volts Volts = Watts / Amps Watts = Amps x Volts |
| Define SELF RECTIFICATION | x-ray tube acts as a valve permitting the flow of current in only one direction, from cathode to anode. |
| Define SELF INDUCTION PP p7/Slide 2 | Transformer is able to step up/down the voltage within itself; called AUTOTRANSFORMER; VARIABLE kVp SELECTOR |
| Define Lenz Law | Induced currents flow away from action that induced it (changing magnetic fields) |
| Define THYRISTOR Selman p153; handout | solid state device functions like thyratron; much shorter and more accurate exposures. 4 layers of alt N and P type materials. Acts as a switch, conducting when gate receives current pulse, conducts for as long as current is forward biased. (THYRISTORs) |
| What is the formula for Ohm's law? | V = I R V = voltage (unit of electromotive force; POTENTIAL energy) I = current (actual flow of electrons) R = resistance (impedes flow of electrons) |
| What are the three characteristics of electricity in a circuit? | CURRENT, RESISTANCE, and ELECTROMOTIVE FORCE |
| What type of transformer? primary side - high # of coils, secondary side - low # of electrons | Step down |
| What type of transformer? primary side - low # of coils, secondary side - high # of electrons | Step up |
| State the formula for transformer ratio. | # of Turns in Secondary winding / # of Turns in Primary Winding Ns / Np |
| State the formula for determining voltage in secondary coil (Vs) of the transformer when given primary voltage (Vp) and transformer ratio. | Vs = Ns / Np x Vp |
| State the formula for determining amperage in secondary coil (As) of the transformer when given primary amperage (Ap) and transformer ratio. | As = Np / Ns = Ap |
Created by:
Larobbins
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