# Circuitry & Function Let’s go back to the starting point

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Circuitry & Function Let’s go back to the starting point
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.

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.

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

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.

Control Panel Circuit Elements
POWER SUPPLY 60 Hz AC to 480 V Panel Power On/Off AUTOTRANSFORMER 1. line compensation a. line meter b. primary side adjustments 2. kVp selection a. secondary side adjustments variable turns ratio 3. filament circuit power 2a. 1a. 2a. 3. 1b.

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.

How the current gets to the TUBE

Generator+ Tranformers (where the power comes from)

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-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

3 Divisions of Circuit Board
PRIMARY (CONTROL PANEL) yellow SECONDARY (HIGH VOLTAGE) blue FILAMENT (LOW CURRENT) purple

X-Ray Machine Circuit

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.

Functional Position Control Console Transformers Tube

Complete Single-Phase Rectifier Circuit
high voltage, low current Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126. 18 © UW and Brent K. Stewart PhD, DABMP

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

© UW and Brent K. Stewart PhD, DABMP
high voltage, low current Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 126. 22 © UW and Brent K. Stewart PhD, DABMP

A

Name the parts of the Circuit board # A
TIMER KVP METER MA OR AMMETER RECTIFIER MA SELECTOR LINE COMPENSATOR INCOMING POWER MAIN BREAKER – VOLTS LINES 9.AUTOTRANSFORMER STEP DOWN TRANS FOCAL SPOT SELECTOR STEP UP TRANSFORMER MINOR KVP SELECTOR MAJOR KVP SELECTOR X-RAY TUBE

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

5 6 4 7 8 #1 3 9 mA selector 10 2 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

Current from the outlet

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

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

Line Compensator

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
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 volts AUTO TRANSFORMER Through 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 Through 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.

AUTOTRANSFORMER

AUTOTRANSFORMER RAISES OR LOWERS THE VOLTAGE KVP TAPS LOCATED
220 VOLTS INCOMING CONVERTED FROM 100 T0 300 VOLTS VOLTMETER LOCATED - OFF OF AUTOTRANSFORMER

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)

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

Autotransformer A’s = primary connections & power into the transformer
Other connections allow for variations of voltages

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

kVp selection

Filaments Operate at currents of 3 to 6 amperes (A)
Current comes from Autotransformer Controls the Ma selection Focal Spot Selector Switch located here

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

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?

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?

mA selection

FILAMENT CURRENT MA METER vs AMMETER ??
MEASURE THE MA GOING TO THE XRAY TUBE

RHEOSTAT VARIABLE REISITOR
regulate the amount of resistance in a circuit mA control is found between the AMMETER

Generator+ Tranformers (where the power comes from)

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

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

Transformers Autotransformer HV Filament 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 e- emission

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.

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

INDUCTION MUTUAL INDUCTION is the? SELF INDUCTION is the
A transformer must have ________to produce an electric or magnetic current ?

MUTUAL INDUCTION (STEP UP & DOWN TRANSFORMERS)

AC Amplitude and polarity of the current vary with time
AC – sinusoidal wave AC varies amplitude and periodic reversal of polarity

STEP UP TRANSFORMER

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

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

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

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

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?

How do you convert msec to sec?
1000ms = 1 sec 100ms = 0.1 sec 10 ms = 0.01 sec

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

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

TIMER SWITCH Timer switch ends exposure
Timer – length of exposure set at control panel

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.

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

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

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.

EXPOSURE SWITCH TIMER

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 (?)

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.

APR

Generator+ Tranformers (where the power comes from)

generator A generator is a device that converts
mechanical energy into electrical energy

X-ray Generator Transformers Rectification Connection to tube
HV (step-up) Filament (step down) Rectification Connection to tube cathode anode F diodes HV

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

GENERATOR THAT CREATE AN ALTERNATING CURRENT ARE CALLED:
AN ALTERNATOR – CONVERT MECHANICAL ENERGY INTO ELECTRICITY

WHAT MEASURES ELECTRIC POTIENTAL = VOLT
CURRENT = AMP ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT

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

High voltage transformer
Or step up transformer Connected to the Major and Minor kVp selector Increases the volts from the autotransformer to kilovolts

Step Up Transformer

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

Voltage Rectification

X-Ray Tube Circuit

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

Filament transformer Or step down transformer
Reduces the current to the filament

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

Single Phase Power = Pulsating X-ray beam
What are the 2 types?

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

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

Three-Phase Power : 6 pulse or 12 pulse
Results in higher quality and quantity photons

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

High Frequency

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

Voltage Ripple High-frequency power has 1% ripple
Voltage to the tube never falls below 99% What does this mean for x-ray photon?

Voltage generators (power supply)

Ripple effect differences
VOLTAGE RIPPLE Ripple effect differences

? What is missing?

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

Review Handouts Circuit Board Symbols Function

Questions on imaging systems?

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