1. Stacy Kopso, M.E.d, RT (R)(M)
The X-ray Circuit
Stacy Kopso, M.E.d, RT (R)(M)

2. Nature of Electricity
Electrostatics- the study of stationary electric charges
Electrodynamics- the study of electric charges in motion
Electric charge is a property of matter
Electrons and protons have charges
Electrons- negative electrical charge
Protons- positive electrical charge

3. Coulomb’s Law Electrical charges unit of measure is Coulomb (SI unit)
1 coulomb= 6.25 x electrons
Movement of electrons causes electricity
Coulombs Law
The electrostatic force between positive & negative charges is directly proportional to the product of their quantities
Increase the quantity, increase the force
Its inversely proportional to the square of the distance between them
Increase the distance, decrease the force
Move the two charged objects three times as far apart, and the force will be one-ninth of what it was when it was closer.
More of them, more force
Further away, less force

4. Electrostatics
Electric charges reside only on the external surface of conductors
The concentration of charges on a curved surface of a conductor is greatest where the curvature is greatest
Only negative charges (electrons) are free to move in solid conductors
Like charges repel/ unlike charges attract

5. Electrostatics
Electrification of objects occurs when they gain either a net positive or net negative charge (electron movement)
Friction
occurs when electrons are rubbed off one object and deposited on another (balloon on hair)
Contact
occurs when a charged object touches an uncharged object and the latter acquires the same charge (rub across carpet/touch something metal/spark)
Induction
Induction occurs as a result of the interaction of the electric fields around two objects that are not in contact.

6. Electrodynamics Electrical charges in motion
For electric current to move, an electric potential must exist.
Electric potential is the ability to do work due to separation of charges (positive and negative ends)
An electric current, or a flow of electrons, occurs in a conductive metal or other substance when an electric potential exists
A conductive substance is one with free electrons that allow the flow of a current.

7. Voltage Voltage Measured in volts Volts kVp
Expression of electric potential
The ability to do work because of separation of charges
Measured in volts
Volts
The expression of the difference in electric potential between two points
The amount of work that can be done per unit of charge
Volt=joules/coulombs
kVp
Radiographer is selecting the thousands of volts (kilovolts)that will be applied to produce x-rays
Beam energy
Affects contrast
Work= force x distance

8. Work it Out
Volt=joules/coulombs
What is the voltage of a battery that uses 6 joules of energy to move 1 coulomb of charge
6 volts
6 volt

9. Current Current The flow of electrons in a conductor
Measured in amperes
Amps=coulombs/seconds
Electrons flow from a negative charge to a positive charge as long as an electric potential difference exists
Required for current to flow
An electric potential
Conductor
pathway for the electrons to travel

10. Current
Vacuum tube
The medium in which current travels in the x-ray tube
Electrons jump the gap between oppositely charged electrodes (within the x-ray tube)

11. Current Direct current (DC) Alternating current (AC)
Flows in only 1 direction (battery)
Electrons flow from negative(cathode) to positive(anode)
Alternating current (AC)
Changes direction in cycles
Negative and positive terminals alternate
United states electricity= AC 60 cycles /second
60 Hz= Frequency of 60 cycles per second

12. Resistance Resistance
Property of an element in a circuit that resists or impedes the flow of electricity
Dependent upon material, length, area, temperature
Inverse relationship between current and resistance
The higher the resistance, the lower the current
Measured in Ohms

13. Resistance Ohms Law V=IR
The potential difference (voltage) across the total circuit or any part, is equal to the current(amps)multiplied by the resistance.
V=IR
V=voltage(electric potential)
I= current(amps)
R=resistance (ohms)

14. Work it Out
How much voltage will be required to move a current measuring 5.6 amperes through a simple circuit containing a resistance of 3.85 ohms?
volts
Determine current
5.6amps
Determine resistance
3.85 current

15. Conductors & Insulator
Materials that allow a relatively free flow of electricity
Metals such as copper
Insulators
Elements with virtually no free electrons therefore do not conduct electricity well. Restrict the flow of electricity.
Contain the flow of electricity (insulate)
Covering a wire with plastic/rubber
Glass x-ray tube

16. Class work Part 1

17. Circuit
Electric circuit is a closed pathway composed of wires and circuit elements through which electricity may flow
closed circuit -Pathway must be closed for electricity to flow
Open circuit- the pathway is broken
On/off switch
Turning the switch off, opens the pathway

18. Circuit Protective devices
Act as emergency devices that open(break) the circuit if there is a sudden surge of electricity to the circuit.
Fuse
Wire encased in glass that quickly melts if the current flow rises excessively, thus opening the circuit.
Circuit breaker
Internal switch is tripped (opened), stopping the flow of electricity.

19. Grounding
Connecting the electrical device to the earth via a conductor (protective measure)
Any charged object can be neutralized if it is grounded to the earth (reservoir of electrons)
Positive charged objects take on electrons
Negative charged objects give up electrons until neutral

20. Circuit Battery Capacitor Diode
Produces electrons though a chemical reaction, stores an electric charge for the long term and provides an electric potential
Capacitor
Stores an electric charge only temporarily
Diode
Allows electrons to flow in one direction only
One way valve

21. Circuit Switch Resistor
Opens the circuit (breaks the pathway)
Resistor
Inhibits the flow of electrons, regulates the flow of electricity wherever it is placed
Rheostat
An adjustable form of a resistor
Transformer
Increases or decreases voltage

23. Magnetism

24. Electromagnetism Electricity and magnetism=electromagnetism Magnetism
The ability of a material to attract iron, cobalt or nickel
Magnetic field
Lines of force in space called flux
Flux
Lines travel from the south to north pole inside the magnet
Lines travel from north to south pole outside the magnet
Create elliptical loops

25. Electromagnetism Electromagnetic
An iron bar wrapped with a wire carrying electric current
This creates a temporary magnetic field by the flow of electricity and is only magnetic while electricity is flowing
2 forms in x-ray machines
Mutual induction
Self-induction

26. Self Induction Lenz’s law
States that an induced current flows in a direction that opposes the action that induced it
Results in a fluctuating magnetic field cutting back and forth through a single coil, inducing a constant secondary current that opposes the original.
Autotransformer

28. Mutual induction
The induction of electricity in a secondary coil by a moving magnetic field
The more coils cut by the magnetic field, the greater the induced voltage.
Step up and step down transformer
Coil A is the primary coil connected to an AC power
When placed next to Coil B, secondary coil, electricity is induced to flow in that coil (also AC)

30. Class work Part 2

31. Generators Electric generators
Devices that convert some form of mechanical energy into electrical energy
Ex., wind turning a windmill turbine
As the loop is rotated in the magnetic field, a current is induced in the loop

32. Motors
Convert electrical energy to mechanical energy through electromagnetic induction

33. Transformers
Devices used to increase or decrease voltage/current through electromagnetic induction
Voltage and current have an inverse relationship
Step up transformer
Increases voltage
Decreases current
Step down transformer
Decreases voltage
Increases current

34. Transformers Difference in voltage
Depends on the ratio of the number of turns of wire in the 2 coils
Twice as many turns in the secondary coil= voltage is twice that of the primary coil

35. Transformers
X-ray equipment used closed-core and shell-type transformers to maximize efficiency

36. Transformers
Principle function is the conversion of incoming low voltage (220 volts) into high voltage necessary to produce x-rays
Regulate voltage within the circuit
Operate on the principle of electromagnetic induction(self and mutual) and require alternating current to operate
Create an electromotive force (EMF) or potential difference (voltage) within a conductor material that cuts across magnetic lines of force

37. Transformers 3 ways to induce an electromotive force (EMF)
A wire moves across a stationary magnetic field
A stationary wire is placed within a moving magnetic field
A magnetic field that varies in intensity while a stationary wire lies within the magnetic field

38. Transformers
Factors that determine the strength of the EMF induced within the conductor material
SPEED with which the conductor material cuts the magnetic lines of force
STRENGTH of magnetic field
ANGLE between the conductor and the direction of the magnetic field
NUMBER of turns of the conductor material

39. Transformers Air Core Simplest type
2 highly insulated coils of wire side by side
Primary coil is supplied with AC
Secondary coil develops AC by mutual induction

40. Transformers Open Core Closed core Shell core
Iron core is inserted into each
Significant increase in the magnetic force
Closed core
Primary and secondary coils are wrapped around each end of a square
Shell core
Contains 2 closed cores
Primary and secondary are wrapped around a central portion of the core
Most efficient and commonly used

41. Transformers As the number of turns increase, so will the voltage
Auto transformer
Single coil
Step up
increase in turns on secondary side
Step down
Decrease in turns on secondary side

42. Transformers
Class work part 3

43. Class Presentations
List parts and their function/illustrate where they are located
Primary Circuit
Secondary Circuit
Filament Circuit

45. X-ray Circuit Primary circuit
Main power switch (on-off for the unit) connected to the power supply of the facility
Line compensator used to adjust the power supplied to the x-ray machine to 220 volts
Circuit breakers protect against short circuits and electric shock

46. Transformers Autotransformer
Operates on the principle of self-induction
Only one coil of wire around a magnetic core

47. Autotransformer
Autotransformer- an adjustable transformer controlled by the kilovoltage peak (kvp) selector on the console controlled by the operator
Operates on principle of self induction
kVp setting determines the number of turns of the secondary side
Primary purpose of autotransformer is to provide voltage that will be increased by the step up transformer to produce the actual selected kilovoltage at the operating console
Aka….kVp selector

49. Step-up transformer
Step-up transformer- used to increase the voltage from the autotransformer to the kilovoltage necessary for x-ray production
Dividing line between primary & secondary circuit
Primary coil is in the primary circuit
Secondary coil is in the secondary circuit
Not adjustable/increases the voltage from the autotransformer by a fixed amount

51. Timer Timer circuit Exposure timer
Located in the primary circuit because the voltage is still low here
It is easier to control (turn on and off) a low voltage than a very high one

52. Exposure timers Variations of Exposure timers Synchronous timer
Turns at 60 revolutions/second
The exposure time selected determines the reduction gear used & therefore the time it takes the disk to move from the on switch to the off switch
Electronic timer
Most widely used
Based on the time it takes to charge a capacitor through a variable resistor
Once the capacitor reaches its preprogrammed charge, it terminates the exposure
mAs timer
Variation of the electronic timer
Monitors the current passing through the x-ray tube and terminates the exposure when the desired mAs is reached
LOCATED ON SECONDARY CIRCUIT

53. AEC Automatic exposure control (AEC)
Used the patients body part of interest as the variable in determining when to terminate exposure
Uses a device called ionization chamber
Radiolucent device placed between the patient and the image receptor
When x-rays interact with this chamber, its atoms are ionized(electrons removed), creating an electric charge
This charge becomes a signal that terminates the exposure

54. AEC , cont
The AEC can be adjusted so that more or less of a charge is needed before the signal to terminate the exposure is sent
Increase in density (+or – 1) big personal, little person
If you have to consistently change the density, AEC needs to be recalibrated
As x-rays exit the patient they pass through the ionization chamber, causing ionization
Once the preprogrammed magnitude of electric charge is reached, the exposure is terminated
The lengthy of the exposure is determined by the thickness and density of the area of the patient placed over the chamber
Longer exposure time for larger patient. Takes longer for the x-rays to exit the larger patient and create the signal in the chamber
Affects quantity of radiation reaching the image receptor

57. Primary Circuit Class Work

58. Secondary Circuit

59. Secondary Circuit Step-up transformer secondary coil mA meter
Monitors xray tube current
Rectifiers
Convert AC to DC
AC is needed to operate transformers( need a moving magnetic field)but can not travel to xray tube
DC for x-ray tube
Electrons must always flow from cathode to anode

60. Rectifiers Solid-state rectifier Most commonly used
Made of 2 semiconducting crystals
One has an abundance of “electron traps” (p)crystal
Other has an abundance of freely moving electrons (n) crystal
The 2 crystals are joined to form a solid-state diode

61. Rectifiers
When a +charge is placed on (p) crystal and –charge on (n) crystal, the solid-state diode will conduct electricity
In order to conduct electricity both the traps from the p-crystal and the electrons from the n-crystal move toward and across the junction allowing current to flow.

62. Rectifiers
When the AC cycle reverses, the p-type crystal receives the negative charge and the n-type crystal receives the positive charge
solid-state diode will not conduct electricity
The traps and electrons do not move to the junction

63. Rectifiers
To best use rectifiers, they must be arranged in the circuit to work in pairs.
Symbol
Current flow is with the direction of the arrow and electron flow is against the direction of the arrow of this symbol.

64. Rectifiers Half-wave rectification Use of only 2 rectifiers
½ of the AC cycle flows through the x-ray tube and the other half is suppressed

65. Rectifiers Single phase full-wave rectification
4 rectifiers used by inverting the negative half of cycle
X-rays vary in energy from the kVp selected on the operating console to zero
Not getting the full kVp that you selected
Ripple-Energy fluctuates from zero to the maximum voltage (100%)

66. Rectifiers Three Single-Phase waveform
Once each AC waveform is rectified, the ripple decreases from 13% (3 phase 6 pulse) to 3.5%
(3 phase 12 pulse)

67. Rectifiers 3 phase 6 pulse 3 phase 12 pulse 13% ripple
87%-100% of the kVp selected
Want the penetration of 70kVp must use around 80 kVp
3 phase 12 pulse
3.5% ripple
96.5%-100% of the kVp selected

68. Rectifiers
High frequency generators in place of standard 60-Hz generators
Reduces the ripple to 1%

71. Filament Circuit

72. Filament Circuit Rheostat Variable resistor (amount of resistance)
Controlled by the mA (milliampere) selector on console
Milliampere
Tube current
Reflects the rate of flow of electrons passing through the x-ray tube
The higher the mA station, the lower the resistance

73. Filament Circuit
The goal of the filament circuit is to boil electrons out of the filament wire
If the current is too high, this tiny wire will be damaged or destroyed
mA selector
The rheostat directly determines the current that is ultimately applied to the selected filament & the number of electrons boiled off and available for x-ray production

74. Filament Circuit Rheostat Timer
Controls filament temperature and the rate at which electrons are boiled off of the filament
Timer
Determines the duration of this process

75. Filament Circuit Step down transformer Filaments
Increase the current by reducing the voltage that is applied to the filament
Current to the filament
Filaments
2 tiny coils of wire housed in the cathode of the x-ray tube
Large and small focal spot

79. Principles of Operation
Operating console
kVp mA
Exposure time
Focal spot size
Automatic Exposure Control (AEC)
Anatomically programmed radiography(APR)
Wall or table bucky selection

80. Principles of Operation
kVp
Adjusts the autotransformer and determines the # of turns on the secondary side necessary to produce a voltage (through self induction) that will be sent to the step-up transformer
Step up transformer increases this voltage by a fixed amount and through mutual induction, produces the kilovoltage selected on the operating console
Transition from primary circuit to secondary circuit

81. Principles of Operation
Once kVp is selected, it must be rectified for the x-ray tube
The electrons must always flow from cathode (-) to anode (+)
Solid state rectifiers are used to route electricity through the x-ray tube correctly

82. Principles of Operation
The filament circuit draws electricity from the autotransformer, when then travels to the rheostat
The rheostat is a variable resistor controlled by the mA selector on the operating console and is tied to the focal spots
The focal spot selector represents the two filaments in the x-ray tube (large & small)

83. Principles of Operation
When the mA station was selected, the appropriate filament was also selected (small for small mA stations)
The selected mA station sets the resistance in the filament circuit
From the rheostat, electricity then travels to the step-down transformer (current increases/voltage decreases)
The adjusted current then travels directly to the filament located within the focusing cup of the cathode
This current heats the filament to the point at which electrons boil off

84. Principles of Operation
A group of electrons is created by the filament circuit
The kv applied to the xray tube creates a + charge on anode, - charge on cathode
The positive charge attracts the electrons boiled off the filament, giving them kinetic energy
Opposites attract
The electrons from the filament reach speeds of about ½ the speed of light

85. Principles of Operation
The large negative charge on the cathode serves to keep the electrons crowded together
The electrons travel across to the anode and interact there to produce x-rays until the timer circuit terminates the process

86. break
1. Class work part 3
2. Label circuit diagram