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X-RAY CIRCUITY RT 244 – 2012 Circuitry & Function Let’s go back to the starting point Contributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW. 1 The Control Console • The control console is device that allows the technologist to set technical factors (mAs & kVp) and to make an exposure. • Only a legally licensed individual is authorized to energize the console. 2 Operating Console has meters to measure • kVp, mA, & exposure time • Modern units only display mAs • Units with ACE’s will have a separate meter for mAs 3 Control Panel • All the electric circuits connecting the meters and controls are at low voltage to minimize the possibility of shock. 4 Technique selection • The process begins at the control panel such as the one shown. • The technologist selects a technique which will specify the kVp, mA, exposure time, and focal spot . • When the exposure switch is depressed, manipulation of electricity to produce x-rays begins. • It is necessary to follow the sequence of events in two parts. • the voltage through to the x-ray tube, • then go back and follow the voltage and current through to the filament. Control Panel Circuit Elements POWER SUPPLY – – 2a. 60 Hz AC 120 to 480 V Panel Power On/Off AUTOTRANSFORMER 1. line compensation 1a. 2a. a. line meter b. primary side adjustments 2. kVp selection a. secondary side adjustments variable turns ratio 1b. 3. 3. filament circuit power 6 Operating Console Controls: • Line Compensation • Quantity = # of x-rays – Milliroentges (mR) or (mR/mAs) • Quality = the pentrability – Kilovolts peak (kVp) or HVL 7 Electric Circuits • Modifying electric flow and controlling electricity results in an electric circuit. 8 How the current gets to the TUBE 9 Generator+ Tranformers (where the power comes from) 10 Circuitry: Source: Carlton & Adler (1996). Principles of radiographic imaging: An art and a science. (96-99). • MAIN CIRCUIT Modifies incoming current to produce x-rays Boosts voltage to range necessary produce x-rays. Modifies incoming line power to produce thermionic emission from the filament wire. FILAMENT CIRCUIT • Filament circuit adjusts to mA ratings (50, 100, 200, etc.). • After mA selection, current sent to step down transformer to modify amps that reach filament on x-ray tube 11 3 Divisions of Circuit Board • PRIMARY (CONTROL PANEL) yellow • SECONDARY (HIGH VOLTAGE) blue • FILAMENT (LOW CURRENT) purple 12 13 X-Ray Machine Circuit 14 Functional Position Control Console Transformers Tube 16 17 Complete Single-Phase Rectifier Circuit high voltage, low current Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126. © UW and Brent K. Stewart PhD, DABMP 18 18 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. MAINBREAKER AUTOTRANSFORMER – KVP - Meter EXPOSURE SWITCH TIMER CIRCUIT HIGH VOLTAGE STEP UP TRANSFORMER RECTIFIER - Ma Meter FILAMENT CIRCUIT VARIABLE SELECTPR FILAMENT STEP DOWN TRANSFORMER X-RAY TUBE ROTOR / STATOR 19 20 21 high voltage, low current Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126. © UW and Brent K. Stewart PhD, DABMP 22 22 23 Name the parts of the Circuit board # A 1. 2. 3. 4. 5. 6. 7. 8. TIMER KVP METER MA OR AMMETER RECTIFIER MA SELECTOR LINE COMPENSATOR INCOMING POWER MAIN BREAKER – 2 - 110 VOLTS LINES 9.AUTOTRANSFORMER 10. STEP DOWN TRANS 11. FOCAL SPOT SELECTOR 12. STEP UP TRANSFORMER 13. MINOR KVP SELECTOR 14. MAJOR KVP SELECTOR 15. X-RAY TUBE 24 Important Parts Of The Circuit Board TO ID • • • • • • • • • • • 1 2 3 4 No # 5 6 7 8 9 10 Incoming Line Voltage Autotransformer KVP Selector Timer Ma Selector Primary Side (Low Voltage) Secondary Side (High Voltage) X-ray Tube Rectifier STEP – Up Transformer STEP – Down Transformer 25 5 6 4 8 #1 7 3 9 mA selector 10 2 26 See Circuitry Review handout and chart for numbers • Wavelength is the distance from the peak of one wave to the peak of the next wave. • Frequency refers to the number of waves that go by a specific point in one second. Remember that electromagnetic energy waves all travel at the same speed—the speed of light • Measured in • Hertz or angstrom 27 Current from the outlet 28 Line Compensation • Most imaging systems are designed to operate on 220 V. (some 110 V or 440 V) • However power from the wall is not always accurate continuously 29 Line Compensation • Wired to the autotransformer is the line compensator • Designed to maintain the accurate voltage required for consistent production of highquality images • Today’s line compensators are automatic and are not displayed on the control panel 30 Line Compensator 31 TRANSFORMERS (Step Up or Step Down) • Increases the VOLTAGE going to the ANODE side of the tube OR • 110 volts to 110,000 volts • Decreases the CURRENT going to the CATHODE side of the tube • 5 Amps to 50 milliamps 32 Transformers • Autotransformer • Step Up • Step Down AUTOTRANSFORMER 34 AUTOTRANSFORMER • RAISES OR LOWERS THE VOLTAGE • KVP TAPS LOCATED • 220 VOLTS INCOMING CONVERTED FROM 100 T0 300 VOLTS • VOLTMETER LOCATED OFF OF AUTOTRANSFORMER 35 Autotransformer – Self Induction • There is only one wire – but works like when there are 2 wires = • The windings are used as the primary and secondary coils • The induced voltage varies on where the outside wires are connected (KVP Taps) 36 Autotransformer • The power for the x-ray imaging system is delivered first to the autotransformer • The autotransformer works on the principle of electromagnetic induction • It has one winding and one core • There are a number of connections along its length 37 Autotransformer • A’s = primary connections & power into the transformer • Other connections allow for variations of voltages 38 Autotransformer • Is designed to step up voltage to about twice the input voltage value • The increase in voltage is directly related to the number of turns • Operates on SELF INDUCTION 39 kVp selection 40 Filaments Operate at currents of 3 to 6 amperes (A) • Current comes from Autotransformer • Controls the Ma selection • Focal Spot Selector Switch located here 41 • Nearly all x-ray equipment operates from an incoming line of ____? • The filament circuit in an x-ray tube operates at about what 10 volts of current 42 X-ray tube current or Filament circuit • A separate circuit crossing from cathode to anode • Measured in milliampers (mA) • What determines how many x-rays are created? 43 X-ray tube current or Filament circuit • # of e- is determined by the temperature of the filament. The hotter the filament the more e• Are their any limiting factors to thermionic emission? 44 mA selection 45 FILAMENT CURRENT • MA METER vs • AMMETER ?? • MEASURE THE MA GOING TO THE XRAY TUBE 46 RHEOSTAT • VARIABLE REISITOR • regulate the amount of resistance in a circuit • • mA control is found between the • AMMETER 47 Generator+ Tranformers (where the power comes from) 48 TRANSFORMER • is responsible for supplying a precise voltage to the x-ray machine. 49 TRANSFORMER FORMULAS (STEP UP OR DOWN) • • • • • V = voltage N = # turns p = primary s = secondary I = current • Vp = N p Vs Ns • Vp = I s Vs Ip • Np = I s Ns Ip 50 Transformers Autotransformer Step-up or step-down Variable Turns Ratio Controls kV by varying V sent to HVT • HV – – – – Step-up Fixed TR > 1 (500 to 1000) VS > VP V to kV • Filament – – – – Step-down Fixed TR < 1 IS > IP (VS<VP) I in filament to cause eemission 51 Transformer Efficiency • By design – – – – Shell – most Closed core Open core Air core • Ideal – no loss • Reality best = ~95% induction • Loss due to – Cu resistance • wire diameter – Eddy currents • Laminate core – Hysteresis • core mag. perm. 52 TRANSFORMERS (Step Up or Step Down) • Increases the VOLTAGE going to the ANODE side of the tube OR • 110 volts to 110,000 volts • Decreases the CURRENT going to the CATHODE side of the tube • 5 Amps to 50 milliamps 53 TRANSFORMERS • STEP UP OR DOWN • OPEN CORE, CLOSED CORE OR SHELL TYPE • ABOUT 95% EFFICIENT • AUTOTRASFORMER = _____ induction • Functions to provide ___________ • Both types require AC for operation 54 INDUCTION • MUTUAL INDUCTION is the? • SELF INDUCTION is the • A transformer must have ________to produce an electric or magnetic current ? 55 MUTUAL INDUCTION (STEP UP & DOWN TRANSFORMERS) 56 AC • Amplitude and polarity of the current vary with time • AC – sinusoidal wave • AC varies amplitude and periodic reversal of polarity 57 STEP UP TRANSFORMER 58 Electricity • Is more efficiently tansported over long distances at low currents ahd high voltage in order to avoid large power losses 59 Faraday’s law Regulate the strength of the induced current • Strength of the Magnet • Speed of the motion • Angle of the magnet • Number of turns on the conduction coil 60 ELECTROMAGNETIC INDUCTION 3 WAYS TO CREATE MOTION BETWEEN LINES OF FORCE AND A CONDUCTOR • Move the conductor through mag field • Move magnetic lines of force • Vary the magnetic flux 61 62 FUSES • PREVENT SHOCK FROM A SHORT CIRCUIT – • THE HIGHER CURRENT WILL MELT THE FUSE – STOPPING THE FLOW OF ELECTRICITY • CIRCUIT BREAKERS HAVE REPLACED FUSES - POWER TOO HIGH IT WILL CUT OFF – not damage appliance 63 Question? What is directly proportional to the number of x-rays reaching the IR? 64 How do you convert msec to sec? 1000ms = 1 sec 100ms = 0.1 sec 10 ms = 0.01 sec 65 mAs Timers • Monitors the product of mA and exposure time • Terminates the exposure when the desired mAs value is reached • Located on the secondary side of the highvoltage transformer since actual tube current must be monitored 66 mAs Timers • Designed to proved the highest mA for the shortest exposure • What is the name of this type of imaging system generator? Hint: most modern and most common 67 TIMER SWITCH • Timer switch ends exposure • Timer – length of exposure set at control panel 68 Exposure Timers • The timer circuit is separate from the other main circuits of the imaging system • It is a mechanical or electronic device whose action is to “make” and “break” the high voltage across the x-ray tube • This is done on the primary side of the high voltage transformer. 69 5 types of timing circuits • 2 most common: • Electronic Timer – Computer controlled – allow a wide range of time intervals – are accurate to intervals as small as 1 ms – can be used for rapid serial exposures 70 AEC Control • AEC measure the quantity of radiation reaching the IR • Automatically terminates when the IR has received enough radiation for desired OD • Two types are common 71 EXPOSURE & TIMER SWITCH EXPOSURE SWITCH – BEGINS THE EXPOSURE Timer switch ends exposure (unless exposure button is let go prior to end of exposure because of dead man switch) Timer circuit controls number of photons produced. TYPES: • MECHANICAL – NO LONGER USED • spring wounded, and not very accurate. • Synchronous timers: synchronous motor w/60 revolutions/second; min. exposure time is 1/60 sec, and timer in multipulse • (i.e., 1/30,1/20). • AEC - TIMERS: monitors time and mA and terminates exposure when desired mAs is attained. Designed to provide the highest safe tube current for the shortest time. • mA METER OR AMMETER IS located on secondary side of high voltage section. 72 EXPOSURE SWITCH TIMER 73 Back up time for AEC • P 116 Bushong (8th ed) • Back-up time should be set (electronic timer to 1.5 the expected exposure) • Usually set automatically • Exposure timer as short a 1 ms • *Reg Rev Q: Manual reset timer = 6 sec (?) 74 APR • Anatomically Programmed Radiography (Ch 20) – Radiologic Technologist selects on the console a picture of a written description of the anatomic part to be imaged and the patient body habitus – A computer selects the appropriate kVp and mAs. 75 APR 76 Generator+ Tranformers (where the power comes from) 77 generator A generator is a device that converts mechanical energy into electrical energy 78 X-ray Generator cathode anode F • Transformers – HV (step-up) – Filament (step down) • Rectification • Connection to tube diodes HV 79 generators •An AC generator produces a current that is expressed mathematically as a sinusoidal wave ~ • Function to change mechanical energy in to electrical energy • Electrical current flowing through a conductor in one direction is _______ • A battery is a source of direct current 80 GENERATOR • THAT CREATE AN ALTERNATING CURRENT ARE CALLED: • AN ALTERNATOR – • CONVERT MECHANICAL ENERGY INTO ELECTRICITY 81 • WHAT MEASURES ELECTRIC POTIENTAL = VOLT • CURRENT = AMP • ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT 82 High-Voltage Generator • Responsible for increasing the output voltage from the autotransformer to the kVp necessary for x-ray production • 3 parts: High-voltage transformer, filament transformer and rectifiers 83 High voltage transformer • Or step up transformer • Connected to the Major and Minor kVp selector • Increases the volts from the autotransformer to kilovolts 84 Step Up Transformer 85 Voltage Rectification • Converts AC to DC current • During the negative cycle current can only flow from anode to cathode • E- must travel cathode to anode – DC current keeps e- traveling in the correct direction, cathode to anode • Attracted to the positive anode 86 Voltage Rectification 87 X-Ray Tube Circuit 88 Rectifier tube failure 2 types • A diode electron tube • A vacuum tube • If one rectifier were malfunctioning the inverted voltage would not be rectified - therefore the resulting mAs would be ½ that expected 89 Filament transformer • Or step down transformer • Reduces the current to the filament 90 High-Voltage Generation – converts 110 volts of AC to kilovolts of DC • The generator is a FIXED component of the imaging system, not under the control of the technologist • Three basic types: single phase, three phase, and high frequency • The generator affects the quality and quantity of photons produced 91 Single Phase Power = Pulsating X-ray beam What are the 2 types? 92 Half-Wave Rectification – photons are produced & emitted only during positive cycle • 100% voltage ripple - quality is the same as full-wave rectification but quantity is half 93 Full-Wave Rectification – same as half-wave except there is no dead time • Half the exposure time is needed for fullwave than half-wave 94 Three-Phase Power : 6 pulse or 12 pulse • Results in higher quality and quantity photons 95 96 High-Frequency: nearly constant positive voltage • Less than 1% ripple • Modern X-ray machines have Highfrequency falling-load generator – Automatically adjusts to the highest mA at the shortest exposure time possible 97 High Frequency 98 Voltage Ripple • Single-phase power has 100% ripple – Voltage varies from zero to the maximum value • Three-phase power has 14% ripple – Voltage never falls below 86% of the maximum • Three-phase, 12 pulse has 4% ripple – Voltage never falls below 96% of the 99 Voltage Ripple • High-frequency power has 1% ripple – Voltage to the tube never falls below 99% • What does this mean for x-ray photon? 100 Voltage generators (power supply) 101 102 VOLTAGE RIPPLE Ripple effect differences 103 ? What is missing? 104 • A three-phase generator operates on three single phase currents, each one out of phase by _____ degrees 105 Review Handouts •Circuit Board •Symbols •Function 106 107 108 Questions on imaging systems? 109