Presentation on theme: "Circuitry & Function Let’s go back to the starting point"— Presentation transcript:
1 Circuitry & Function Let’s go back to the starting point X-RAY CIRCUITY RT 244 – 2012Circuitry & FunctionLet’s go back to the starting pointContributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW.
2 The Control ConsoleThe 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.
3 Operating Console has meters to measure kVp, mA, & exposure timeModern units only display mAsUnits with ACE’s will have a separate meter for mAs
4 Control PanelAll the electric circuits connecting the meters and controls are at low voltage to minimize the possibility of shock.
5 Technique selectionThe 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.
6 Control Panel Circuit Elements POWER SUPPLY60 Hz AC to 480 VPanel Power On/OffAUTOTRANSFORMER1. line compensationa. line meterb. primary side adjustments2. kVp selectiona. secondary side adjustmentsvariable turns ratio3. filament circuit power2a.1a.2a.3.1b.
7 Operating Console Controls: Line CompensationQuantity = # of x-raysMilliroentges (mR) or (mR/mAs)Quality = the pentrabilityKilovolts peak (kVp) or HVL
8 Electric CircuitsModifying electric flow and controlling electricity results in an electric circuit.
10 Generator+ Tranformers (where the power comes from)
11 Circuitry: Source: Carlton & Adler (1996) Circuitry: Source: Carlton & Adler (1996). Principles of radiographic imaging: An art and a science. (96-99).MAIN CIRCUIT Modifies incoming current to produce x-raysBoosts voltage to range necessary producex-rays. Modifies incoming line power to produce thermionic emission from the filament wire.FILAMENT CIRCUITFilament 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
15 In section two of this module, the components of the filament circuit were given. One of the components in that list was the rheostat. Click on the image to see the location of the rheostat.A rheostat is a variable resistor. Just as the autotransformer (discussed in Section 3) can adjust output voltage, the rheostat can vary the amount of resistance in a particular part of a circuit. In the filament circuit section of the x-ray circuit, we are controlling the current that is applied to the filament of the x-ray tube by changing resistance. The x-ray tube will be discussed in detail in Module 7. In Section 6 of this module, we will pull all of the parts of the x-ray circuit together and discuss how they work as one circuit to produce x-rays. But first it is important to understand the role of the rheostat.The technologist has direct control over the rheostat through the mA stations on the control panel. When different mA stations are selected, the amount of resistance in the filament circuit is changed, resulting in a direct control of the current supplied to the filament. The higher the mA station number, the lower the resistance. A 1000 mA station will have very little resistance to the flow of electricity, while a 100 mA station will have considerable resistance.
24 Name the parts of the Circuit board # A TIMERKVP METERMA OR AMMETERRECTIFIERMA SELECTORLINE COMPENSATORINCOMING POWERMAIN BREAKER –VOLTS LINES9.AUTOTRANSFORMERSTEP DOWN TRANSFOCAL SPOT SELECTORSTEP UP TRANSFORMERMINOR KVP SELECTORMAJOR KVP SELECTORX-RAY TUBE
25 Important Parts Of The Circuit Board TO ID 1 Incoming Line Voltage2 Autotransformer3 KVP Selector4 TimerNo # Ma Selector5 Primary Side (Low Voltage)6 Secondary Side (High Voltage)7 X-ray Tube8 Rectifier9 STEP – Up Transformer10 STEP – Down Transformer
26 56478#139mA selector102See Circuitry Review handout and chart for numbers
27 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 lightMeasured inHertz or angstrom
29 Line CompensationMost 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
30 Line Compensation Wired to the autotransformer is the line compensator Designed to maintain the accurate voltage required for consistent production of high-quality imagesToday’s line compensators are automatic and are not displayed on the control panel
32 TRANSFORMERS (Step Up or Step Down) Increases the VOLTAGE going to the ANODE side of the tube OR110 volts to 110,000 voltsDecreases the CURRENT going to the CATHODE side of the tube5 Amps to 50 milliamps
33 Transformers Autotransformer Step Up Step Down The primary circuit is made up of the main power switch (connected to the incoming power supply), circuit breakers , the autotransformer , the timer circuit , and the primary side of the step-up transformer (high tension transformer ). The main power switch is simply the "on/off" switch of the machine and is connected to the power supply of the facility. Circuit breakers are included in the primary circuit to protect against short circuits and electric shock. They are simply switches that open and break the flow of electricity in the event of a surge in power. Because the incoming power supply to the facility is not a consistent 220 volts, a line compensator is also utilized. This device is usually wired to the autotransformer (discussed later) and automatically adjusts the power supplied to the x-ray machine to 220 voltsAUTO TRANSFORMERThrough self-induction , the autotransformer selects the number of turns on its secondary side necessary to produce a voltage that, when increased about 500 times, will become the kVp selected. This voltage is then sent to the step-up transformer (high tension transformer). The step-up transformer will increase the voltage applied to its primary side by about 500 times to one kilovoltage on the secondary side through mutual induction. This transformer represents the transition from the primary section to theThrough self-induction , the autotransformer selects the number of turns on its secondary side necessary to produce a voltage that, when increased about 500 times, will become the kVp selected. This voltage is then sent to the step-up transformer (high tension transformer). The step-up transformer will increase the voltage applied to its primary side by about 500 times to one kilovoltage on the secondary side through mutual induction. This transformer represents the transition from the primary section to the secondary section of the x-ray circuit.
35 AUTOTRANSFORMER RAISES OR LOWERS THE VOLTAGE KVP TAPS LOCATED 220 VOLTS INCOMING CONVERTED FROM100 T0 300 VOLTSVOLTMETER LOCATED - OFF OF AUTOTRANSFORMER
36 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 coilsThe induced voltage varies on where the outside wires are connected (KVP Taps)
37 AutotransformerThe power for the x-ray imaging system is delivered first to the autotransformerThe autotransformer works on the principle of electromagnetic inductionIt has one winding and one coreThere are a number of connections along its length
38 Autotransformer A’s = primary connections & power into the transformer Other connections allow for variations of voltages
39 AutotransformerIs designed to step up voltage to about twice the input voltage valueThe increase in voltage is directly related to the number of turnsOperates on SELF INDUCTION
46 FILAMENT CURRENT MA METER vs AMMETER ?? MEASURE THE MA GOING TO THE XRAY TUBE
47 RHEOSTAT VARIABLE REISITOR regulate the amount of resistance in a circuitmA control is found between theAMMETER
48 Generator+ Tranformers (where the power comes from)
49 TRANSFORMERis responsible for supplying a precise voltage to the x-ray machine.
50 TRANSFORMER FORMULAS (STEP UP OR DOWN) V = voltageN = # turnsp = primarys = secondaryI = currentVp = N pVs NsVp = I sVs IpNp = I sNs Ip
51 Transformers Autotransformer HV Filament Step-up or step-down Variable Turns RatioControls kV by varying V sent to HVTHVStep-upFixed TR > 1 (500 to 1000)VS > VP V to kVFilamentStep-downFixed TR < 1IS > IP (VS<VP)I in filament to cause e- emission
52 Transformer Efficiency By designShell – mostClosed coreOpen coreAir coreIdeal – no lossReality best = ~95% inductionLoss due toCu resistance wire diameterEddy currentsLaminate coreHysteresis core mag. perm.
53 TRANSFORMERS (Step Up or Step Down) Increases the VOLTAGE going to the ANODE side of the tube OR110 volts to 110,000 voltsDecreases the CURRENT going to the CATHODE side of the tube5 Amps to 50 milliamps
54 TRANSFORMERS STEP UP OR DOWN OPEN CORE, CLOSED CORE OR SHELL TYPE ABOUT 95% EFFICIENTAUTOTRASFORMER = _____ inductionFunctions to provide ___________Both types require AC for operation
55 INDUCTION MUTUAL INDUCTION is the? SELF INDUCTION is the A transformer must have ________to produce an electric or magnetic current ?
63 FUSES PREVENT SHOCK FROM A SHORT CIRCUIT – THE HIGHER CURRENT WILL MELT THE FUSE – STOPPING THE FLOW OF ELECTRICITYCIRCUIT BREAKERS HAVE REPLACED FUSES - POWER TOO HIGH IT WILL CUT OFF – not damage appliance
64 What is directly proportional to the number of x-rays reaching the IR? Question?What is directly proportional to the number of x-rays reaching the IR?
65 How do you convert msec to sec? 1000ms = 1 sec100ms = 0.1 sec10 ms = 0.01 sec
66 mAs Timers Monitors the product of mA and exposure time Terminates the exposure when the desired mAs value is reachedLocated on the secondary side of the high-voltage transformer since actual tube current must be monitored
67 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
68 TIMER SWITCH Timer switch ends exposure Timer – length of exposure set at control panel
69 Exposure TimersThe timer circuit is separate from the other main circuits of the imaging systemIt is a mechanical or electronic device whose action is to “make” and “break” the high voltage across the x-ray tubeThis is done on the primary side of the high voltage transformer.
70 5 types of timing circuits 2 most common:Electronic TimerComputer controlledallow a wide range of time intervalsare accurate to intervals as small as 1 mscan be used for rapid serial exposures
71 AEC Control AEC measure the quantity of radiation reaching the IR Automatically terminates when the IR has received enough radiation for desired ODTwo types are common
72 EXPOSURE & TIMER SWITCH EXPOSURE SWITCH – BEGINS THE EXPOSURETimer 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 USEDspring 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 AMMETERIS located on secondary side of high voltage section.
74 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 automaticallyExposure timer as short a 1 ms*Reg Rev Q: Manual reset timer = 6 sec (?)
75 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 habitusA computer selects the appropriate kVp and mAs.
77 Generator+ Tranformers (where the power comes from)
78 generator A generator is a device that converts mechanical energy into electrical energy
79 X-ray Generator Transformers Rectification Connection to tube HV (step-up)Filament (step down)RectificationConnection to tubecathodeanodeFdiodesHV
80 generatorsAn AC generator produces a current that is expressed mathematically as a sinusoidal wave ~Function to change mechanical energy in to electrical energyElectrical current flowing through a conductor in one direction is _______A battery is a source of direct current
81 GENERATOR THAT CREATE AN ALTERNATING CURRENT ARE CALLED: AN ALTERNATOR –CONVERT MECHANICAL ENERGY INTO ELECTRICITY
82 WHAT MEASURES ELECTRIC POTIENTAL = VOLT CURRENT = AMPELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT
83 High-Voltage Generator Responsible for increasing the output voltage from the autotransformer to the kVp necessary for x-ray production3 parts: High-voltage transformer, filament transformer and rectifiers
84 High voltage transformer Or step up transformerConnected to the Major and Minor kVp selectorIncreases the volts from the autotransformer to kilovolts
86 Voltage Rectification Converts AC to DC currentDuring the negative cycle current can only flow from anode to cathodeE- must travel cathode to anode – DC current keeps e- traveling in the correct direction, cathode to anodeAttracted to the positive anode
89 Rectifier tube failure 2 typesA diode electron tubeA vacuum tubeIf one rectifier were malfunctioning the inverted voltage would not be rectified - therefore the resulting mAs would be ½ that expected
90 Filament transformer Or step down transformer Reduces the current to the filament
91 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 technologistThree basic types: single phase, three phase, and high frequencyThe generator affects the quality and quantity of photons produced
92 Single Phase Power = Pulsating X-ray beam What are the 2 types?
93 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
94 Full-Wave Rectification – same as half-wave except there is no dead time Half the exposure time is needed for full-wave than half-wave
95 Three-Phase Power : 6 pulse or 12 pulse Results in higher quality and quantity photons
97 High-Frequency: nearly constant positive voltage Less than 1% rippleModern X-ray machines have High-frequency falling-load generatorAutomatically adjusts to the highest mA at the shortest exposure time possible
99 Voltage Ripple Single-phase power has 100% ripple Voltage varies from zero to the maximum valueThree-phase power has 14% rippleVoltage never falls below 86% of the maximumThree-phase, 12 pulse has 4% rippleVoltage never falls below 96% of the maximum
100 Voltage Ripple High-frequency power has 1% ripple Voltage to the tube never falls below 99%What does this mean for x-ray photon?