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X-RAY CIRCUITYRT 244 – 2012

Circuitry & Function

Let’s go back to the starting point

Contributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW.

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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.

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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

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Control Panel

• All the electric circuits connecting the meters and controls are at low voltage to minimize the possibility of shock.

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.

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Control Panel Circuit Elements

POWER SUPPLY– 60 Hz AC 120 to 480 V– Panel Power On/Off

AUTOTRANSFORMER1. line compensation

a. line meterb. primary side adjustments

2. kVp selectiona. secondary side

adjustments variable turns ratio

3. filament circuit power

1a.

1b.

2a.

2a.

3.

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Operating Console Controls:

• Line Compensation

• Quantity = # of x-rays– Milliroentges (mR) or (mR/mAs)

• Quality = the pentrability– Kilovolts peak (kVp) or HVL

Electric Circuits

• Modifying electric flow and controlling electricity results in an electric circuit.

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How the current gets to the TUBE

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Generator+ Tranformers(where the power comes from)

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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

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3 Divisions of Circuit Board

• PRIMARYPRIMARY (CONTROL PANEL) yellow

• SECONDARY

(HIGH VOLTAGE) blue

• FILAMENT

(LOW CURRENT) purple

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X-Ray Machine Circuit

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Functional PositionControl Console Transformers Tube

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18© UW and Brent K. Stewart PhD, DABMP© UW and Brent K. Stewart PhD, DABMP

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Complete Single-Phase Rectifier CircuitComplete Single-Phase Rectifier Circuit

Bushberg, et al., The Essential Physics Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126.of Medical Imaging, 2nd ed., p. 126.

high voltage, high voltage, low currentlow current

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1. MAINBREAKER

2. AUTOTRANSFORMER – KVP - Meter

3. EXPOSURE SWITCH

4. TIMER CIRCUIT

5. HIGH VOLTAGE STEP UP TRANSFORMER

6. RECTIFIER - Ma Meter

7. FILAMENT CIRCUIT VARIABLE SELECTPR

8. FILAMENT STEP DOWN TRANSFORMER

9. X-RAY TUBE

10. ROTOR / STATOR

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22© UW and Brent K. Stewart PhD, DABMP© UW and Brent K. Stewart PhD, DABMP

2222 Bushberg, et al., The Essential Physics Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126.of Medical Imaging, 2nd ed., p. 126.

high voltage, high voltage, low currentlow current

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Name the parts of the Circuit board # A

1. TIMER

2. KVP METER

3. MA OR AMMETER

4. RECTIFIER

5. MA SELECTOR

6. LINE COMPENSATOR

7. INCOMING POWER

8. 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

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Important Parts Of The Circuit Board TO ID

• 1 Incoming Line Voltage• 2 Autotransformer• 3 KVP Selector• 4 Timer• No # Ma Selector• 5 Primary Side (Low Voltage)• 6 Secondary Side (High Voltage)• 7 X-ray Tube• 8 Rectifier• 9 STEP – Up Transformer• 10 STEP – Down Transformer

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#1

2

3

4

mA selector

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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

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Current from the outlet

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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

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Line Compensation

• Wired to the autotransformer is the line compensator

• Designed to maintain the accurate voltage required for consistent production of high-quality images

• Today’s line compensators are automatic and are not displayed on the control panel

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Line Compensator

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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

Transformers

• Autotransformer

• Step Up

• Step Down

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AUTOTRANSFORMER

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AUTOTRANSFORMER• RAISES OR LOWERS THE

VOLTAGE• KVP TAPS LOCATED• 220 VOLTS INCOMING

CONVERTED FROM

100 T0 300 VOLTS• VOLTMETER LOCATED -

OFF OF AUTOTRANSFORMER

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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)

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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

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Autotransformer

• A’s = primary connections & power into the transformer

• Other connections allow for variations of voltages

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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

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kVp selection

Filaments Operate at currents of 3 to 6 amperes (A)

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• Current comes from Autotransformer

• Controls the Ma selection

• Focal Spot Selector Switch located here

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• 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

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X-ray tube currentor Filament circuit

• A separate circuit crossing from cathode to anode

• Measured in milliampers (mA)

• What determines how many x-rays are created?

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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?

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mA selection

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FILAMENT CURRENT

• MA METER vs

• AMMETER ??

• MEASURE THE MA GOING TO THE XRAY TUBE

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RHEOSTAT

• VARIABLE REISITOR

• regulate the amount of resistance in a circuit

• • mA control is found between the

• AMMETER

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Generator+ Tranformers(where the power comes from)

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TRANSFORMER

• is responsible for supplying a precise voltage to the x-ray machine.

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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

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Transformers

• 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 e- emission

Autotransformer Step-up or step-down Variable Turns Ratio Controls kV by varying

V sent to HVT

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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.

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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

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

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INDUCTION

• MUTUAL INDUCTION is the?

• SELF INDUCTION is the

• A transformer must have ________to produce an electric or magnetic current ?

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MUTUAL INDUCTION(STEP UP & DOWN TRANSFORMERS)

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AC

• Amplitude and polarity of the current vary with time

• AC – sinusoidal wave

• AC varies amplitude and periodic reversal of polarity

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STEP UP TRANSFORMER

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Electricity

• Is more efficiently tansported over long distances at low currents ahd high voltage in order to avoid large power losses

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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

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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

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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

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Question?

What is directly proportional to the number of x-rays reaching

the IR?

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How do you convertmsec to sec?

1000ms = 1 sec

100ms = 0.1 sec

10 ms = 0.01 sec

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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 high-voltage transformer since actual tube current must be monitored

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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

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TIMER SWITCH

• Timer switch ends exposure

• Timer – length of exposure set at control panel

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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.

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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

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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

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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 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.

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EXPOSURE SWITCH

TIMER

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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 (?)

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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.

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APR

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Generator+ Tranformers(where the power comes from)

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generator

A generator is a device that converts

mechanical energy into electrical energy

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X-ray Generator • Transformers

– HV (step-up)

– Filament (step down)

• Rectification• Connection to tube

HV

F

diodes

anodecathode

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generators

• 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

•An AC generator produces a current that is expressed mathematically as a sinusoidal wave ~

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GENERATOR

• THAT CREATE AN ALTERNATING CURRENT ARE CALLED:

• AN ALTERNATOR –

• CONVERT MECHANICAL ENERGY INTO ELECTRICITY

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• WHAT MEASURES ELECTRIC POTIENTAL = VOLT

• CURRENT = AMP

• ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT

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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

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High voltage transformer

• Or step up transformer

• Connected to the Major and Minor kVp selector

• Increases the volts from the autotransformer to kilovolts

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Step Up Transformer

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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

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Voltage Rectification

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X-Ray Tube Circuit

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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

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Filament transformer

• Or step down transformer

• Reduces the current to the filament

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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

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Single Phase Power= Pulsating X-ray beam

What are the 2 types?

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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

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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

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Three-Phase Power : 6 pulse or 12 pulse

• Results in higher quality and quantity photons

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High-Frequency: nearly constant positive voltage

• Less than 1% ripple

• Modern X-ray machines have High-frequency falling-load generator– Automatically adjusts to the highest mA at the

shortest exposure time possible

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High Frequency

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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 maximum

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Voltage Ripple

• High-frequency power has 1% ripple– Voltage to the tube never falls below 99%

• What does this mean for x-ray photon?

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Voltage generators (power supply)

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VOLTAGE RIPPLE

Ripple effect differences

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? What is missing?

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• A three-phase generator operates on three single phase currents, each one out of phase by _____ degrees

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Review Handouts

•Circuit Board

•Symbols

•Function

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Questions on imaging systems?