IMAGING EQUIPMENT AND MAINTENANCE. PROF. MITCH

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1. IMAGING EQUIPMENT AND MAINTENANCE MARY MITCHELLE M. PUNO, RRT

2. LESSON: ELECTROSTATICS AND ELECTRODYNAMICS ELECTROSTATICS is the study of stationary electric charges. Electric Ground a reservoir of electric charges. It can always Accept stray electric charges due to its large capacity. e.g. Earth

3. Electrification is the process of losing and accepting electric charges. t he act of electrifying or the state of being charged with electricity.

4. Three Ways to Achieve Electrification Friction – transfer of electrons from one object to another by means of rubbing .    (e.g. combing of hair, walking ) Contact – transfer of electrons from one object that is already negatively charged object ( excessive electrons ) to a positively charged ( lacking/needs electrons ) 

5. Three Ways to Achieve Electrification 3. Induction – electrons move to one part of an object because it is in the electric field of another object.  - electrons are transferred when a charged object is brought near a conducting object .

6. ELECTROSTATIC LAWS Unlike charges attract and like charges repel . Coulomb’s Law   - the electrostatic force (F) of an object is directly proportional ( or equal ) to the product of the electrostatic charges ( Q A & B)  and inversely proportional to the square of the distance ( d ) between them.

7. ELECTROSTATIC LAWS 3. Electric charge distribution is uniform throughout or on the surface .

8. ELECTROSTATIC LAWS 4. The electric charge of a conductor is concentrated along the sharpest curvature.

9. BASICS OF ELECTRICITY: OHM’S LAW Created by Georg Simon Ohm. States that Voltage (V) is equal to the product of electric current (I) and resistance (R). V=IR

10. VOLTAGE or electromotive force It is the potential difference in charge between two points Volt (V) is the unit of electric potential or the stationary charges. Volt = 1 Joule/Coulomb or J/C

11. CURRENT is the rate of flowing or moving charges. Ampere (A) is the unit of electric current or intensity. Ampere = 1 Coulomb / Second or C/s

12. REMEMBER : Voltage CAN exist without current. Current CANNOT exist without Voltage. Because Current is the effect once the Voltage or electric charges start to move .

13. RESISTANCE is the ability of a material to resist or restrict the flow of charge. Ohm (Ω) is the unit of electrical resistance .

14. ELECTRIC CHARGE is measured in Coulomb. 1 Coulomb = 6.3 x 1018  electric charges The smallest unit of electric charge is ELECTRON .

15. ELECTRODYNAMICS is the study of electric charges in motion or electricity . Benjamin Franklin Kite Experiment    Franklin constructed a simple kite and attached a wire to the top of it to act as a lightning rod. To the bottom of the kite, he attached a hemp string, and to that, he attached a silk string. Franklin moved his finger near the key, and as the negative charges in the metal piece were attracted to the positive charges in his hand, he felt a spark .

16. Conclusion: the direction of electric current is always opposite to the direction of electron flow. In electrodynamics, direction of electric current is important.

17. CONDUCTOR is any substance that enables electrons to flow easily. E.g. copper wire (commonly used), water. INSULATOR is any material that does not allow electron flow. E.g. rubber, glass, clay.

18. is a material/substance that behaves as both insulator and conductor under different temperatures. E.g. Germanium and Silicon Basis for microchips and computer panels.  SEMICONDUCTOR

19. SUPERCONDUCTIVITY is the property of some metals to allow electricity to flow without any resistance at certain temperatures also known as Critical Temperatures (Tc) E.g. Niobium and Titanium Critical temperatures starts at 0 Kelvin which are very cold environments 

20. In a series circuit, all circuit elements are connected in a line along the same conductor. ELECTRIC CIRCUIT: SERIES CIRCUIT

21. RULES FOR SERIES CIRCUIT The total resistance is equal to the sum of the individual resistances. The current through each circuit element is the same and is equal to the total circuit current. The sum of the voltages across each circuit element is equal to the total circuit voltage.

22. A parallel circuit contains elements that are connected at their ends rather than lying in a line along a conductor. ELECTRIC CIRCUIT: PARALLEL CIRCUIT

23. RULES FOR PARALLEL CIRCUIT The sum of the currents through each circuit element is equal to the total circuit current. The voltage across each circuit element is the same and is equal to the total circuit voltage. The total resistance is the inverse of the sum of the reciprocals of each individual resistance.

24. DIRECT CURRENT (DC) Electrons flow in one direction along the conductor, in which case the electric current

25. ALTERNATING CURRENT (AC) Electrons flow oscillate back and forth is called alternating current (AC).

26. MAGNETISM

27. MAGNETISM Magnetism is a fundamental property of some forms of matter. Magnetite is an an oxide of iron (Fe3O4 ) It was called a lodestone or leading stone .

28. The magnetic field of a charged particle such as an electron in motion is perpendicular to the motion of that particle .

29. MAGNET Bipolar or dipolar It always has a north and a south pole . The small magnet created by the electron orbit is called a magnetic dipole.

30. ORBITAL MAGNETIC MOMENT Magnetic effect that is established by charged electrons orbiting the nucleus A moving charged particle induces a magnetic field in a plane perpendicular to its motion

31. MAGNETIC DIPOLE Groups of atoms with most of the magnetic moment force in a single or same direction Single Dipole: 10 15 atoms Normal Orientation: randomly oriented FUTURE RRT 2020

32. MAGNETIC DOMAIN An accumulation of many atomic magnets with their dipoles aligned FUTURE RRT 2020

33. MAGNETIC LINES OF FLUX Lines of force, lines of flux or magnetic field Imaginary lines of force of the magnetic field SI Unit: Weber (Wb) 1 Wb = 10 8 lines of flux

34. MAGNETIC PERMEABILITY The ability of a material to attract the lines of magnetic field intensity.

35. THREE PRINCIPAL TYPES OF MAGNETS naturally occurring magnets, artificially induced permanent magnets, electromagnets .

36. Natural Magnet Naturally occurring Example: Earth, Lodestone

37. Artificially Produced Permanent Magnets Permanent magnets are typically produced by aligning their domains in the field of an electromagnet Such permanent magnets do not necessarily stay permanent.

38. Electromagnets Consist of wire wrapped around an iron core The intensity of the magnetic field is proportional to the electric current. The iron core greatly increases the intensity of the magnetic field.

39. FOUR MAGNETIC STATES OF MATTER

40. Diamagnetic Materials Weakly repelled by either magnetic pole. They cannot be artificially magnetized, and they are not attracted to a magnet. Examples: water and plastic.

41. Ferromagnetic Materials These are strongly attracted by a magnet and usually can be permanently magnetized by exposure to a magnetic field. Examples: iron , cobalt, and nickel

42. Paramagnetic Materials Lie somewhere between ferromagnetic and nonmagnetic They are very slightly attracted to a magnet and are loosely influenced by an external magnetic field. Examples: iron , cobalt, and nickel

43. MAGNETIC SUSCEPTIBILITY The degree to which a material can be magnetized MAGNETIC LINES OF INDUCTION The imaginary magnetic field lines

44. MAGNETIC LAWS 1. EVERY MAGNET HAS TWO POLES The imaginary lines of the magnetic field: leave the north pole and enter the south pole .

45. MAGNETIC LAWS 2. REPULSION-ATTRACTION Like poles repel; unlike poles attract

46. 3 . GAUSS LAW GAUSS – is an older unit of magnetic field TESLA – is the SI unit of magnetic field strength 1 T = 10,000 Gauss  

47. ELECTROMAGNETISM Moving electric charge/electric current induces magnetic field ELECTROMAGNETIC INDUCTION Moving/changing magnetic field induces electric current.

48. Fleming’s Right Hand Rule Follows conventional current model. Current flows from POSITIVE to NEGATIVE Direction of magnetic field is being determined Thumb: North pole Little Finger: South pole

49. Fleming’s Left Hand Rule Follows the Electron Flow Model Electron flow flows from NEGATIVE to POSITIVE

50. Michael Faraday Introduced Electromagnetic Induction Producing/inducing electric current through a moving magnetic field. A coil of wire is connected to a current-measuring device called AMMETER.

51. FARADAY’S LAW The magnitude of induced current depends on: STRENGTH of the magnetic field VELOCITY of the magnetic field as it moves past the conductor ANGLE OF THE CONDUCTOR to the magnetic field NUMBER OF TURNS in the conductor

52. HANS OERSTED He demonstrated that electricity can be used to generate magnetic fields

53. HEINRICH LENZ He described the second law of electromagnetic induction States that the induced current flow sets up a magnetic field opposing the action that produced the original current

54. HEINRICH LENZ He described the second law of electromagnetic induction 57

55. LENZ LAW States that induced current flow sets up a magnetic field opposing the action that produced the original current 58

56. ELECTROMECHANICAL DEVICES

57. Electric generator In an electric generator, a coil of wire is placed in a strong magnetic field between two magnetic poles. The coil is rotated by mechanical energy. Because the coil of wire is moving in the magnetic field, a current is induced in the coil of wire . The net effect of an electric generator is to convert mechanical energy into electrical energy .

58. ELECTRIC MOTOR Electric energy is supplied to the current loop (coil of wire) to produce a mechanical motion—that is, a rotation of the loop in the magnetic field that is, a rotation of the loop in the magnetic field. It uses many turns of wire for the current loop and many bar magnets to create the external magnetic field. Used in an x-ray tube – induction motor The net effect of an electric motor is to convert electrical energy into mechanical energy .

59. INDUCTION MOTOR Rotating rotor is a shaft made of bars of copper and soft iron fabricated into one mass; however, the external magnetic field is supplied by several fixed electromagnets called stator Current is produced in the rotor windings by induction. The electromagnets surrounding the rotor are energized in sequence, producing a changing magnetic field. The induced current produced in the rotor windings generates a magnetic field.

60. TRANSFORMERS

61. TRANSFORMERS The transformer does not convert one form of energy to another, it only changes the intensity of electric potential and current. Operates only in alternating current . The change in voltage is directly proportional to the ratio of the number of turns (windings) of the secondary coil (Ns) to the number of turns in the primary coil (Np)

62. transformers Transformers are composed of two coils placed near one another (but without electrical connection). If current is supplied to one coil, the lines of force that are induced will pass through the other coil and induce a flow of electrons. PARTS OF A TRANSFORMER PRIMARY COIL - the coil that is supplied with current. SECONDARY COIL - the coil in which current is induced

63. Types of transformers according to function STEP UP TRANSFORMERS A transformer with a turns ratio greater than 1 The voltage is increased or stepped up from the primary side to the secondary side. Voltage in primary side < secondary side STEP DOWN TRANSFORMERS When the turns ratio is less than1 Voltage in primary side > secondary side

64. TRANSFORMER LAW

65. TYPES OF TRANSFORMERS Closed-core transformer Autotransformer Shell-type transformer

66. The ferromagnetic core is built up of laminated layers of iron. This layering helps reduce energy losses , resulting in greater efficiency

67. AIR CORE TRANSFORMER The simple arrangement of two coils of wire in proximity to facilitate induction, which has been used so far to explain transformer function.

68. OPEN CORE TRANSFORMER If the primary and secondary coils are filled with an iron core, the strength of the magnetic field is greatly increased, forming an open-core transformer

69. Closing the core to form a closed-core transformer (by placing a top and bottom to the cores) will direct the lines of force from primary and secondary cores toward each other and result in a significant system net increase in field strength. CLOSED CORE TRANSFORMER

70. SHELL TYPE TRANSFORMER Great efficiency is obtained by insulating the wiring and wrapping the primary and secondary coils atop one another, thus minimizing the distance between coils and maximizing the coupling effectiveness of the induction. X-ray generators use laminated core, shell-type transformers, which are the most common type in use today

71. AUTOTRTANSFORMER a single coil on a central core. Connections are made along a single coil at different points for primary and secondary. The primary side has a selection of taps available to permit a variable number of turns in the primary coil

72. END

73. I²R loss or copper loss It is caused by the inherent resistance to current flow that is found in all conductors . The power lost due to this resistance is proportional to the square of the current . Lost power is given off as heat. Solutions: Using low resistance wire, such as large-diameter copper , U sing high voltage and low amperage

74. Hysteresis loss (lagging loss) Occurs because energy is expended as the continually changing alternating current magnetizes, demagnetizes , and remagnetizes the core material . Demagnetization leaves some dipoles in the original orientation , and this residual magnetism causes the remagnetic effort to lag , thus producing more heat loss . Solution: Coercivity Coercivity : The magnetic field needed to demagnetize the main magnetic material completely 

75. EDDY CURRENT Eddy current loss in the core is a result of currents opposing the cause that produced them, according to Lenz’s law, as discussed earlier. They are produced in any conducting material subjected to changing magnetic fields . Solution: Laminating the transformer core

76. X-RAY TUBE

77. X-RAY TUBE An electronic vacuum tube that produces x-rays A special type of diode - because it has two electrodes: cathode and anode Contained in a protective housing

78. EXTERNAL COMPONENTS: INTERNAL COMPONENTS: SUPPORT MECHANISM PROTECTIVE HOUSING ENCLOSURE ANODE CATHODE

79. EXTERNAL COMPONENTS

80. SUPPORT MECHANISM Purpose: - for easier operation and manipulation of the X-ray tube. - provide support for the heavy x-ray tube. Types: 1. Ceiling support system 2. Floor-to-ceiling support 3. C-arm support

81. Ceiling support C-arm support Floor-to-Ceiling support

82. CEILING SUPPORT two perpendicular sets of ceiling-mounted rails Allows longitudinal and transverse travel of the x-ray tube. Has a telescoping column that attaches the x-ray tube housing to the rails for variable SID Does not enable the tube to move farther than one meter.

83. PREFERRED DETENT POSITION - Position where the x-ray tube is centered above the examination table at standard SID

84. FLOOR-TO-CEILING SUPPORT A single column with rollers T he x-ray tube slides up and down the column. Allows for variable SID

85. C-ARM SUPPORT C-shaped machine. Provides flexible x-ray tube positioning however, SID variation is very limited. X-ray tube is located below the table Image receptor is located above the table

86. PROTECTIVE HOUSING Lead-lined metal structure Provides solid, stable mechanical support Serves as electrical insulator Serves as a thermal cushion Controls leakage radiation <100 mR / hr Isolates the high voltages

87. PROTECTIVE HOUSING Absorbs off-focus/extra radiation

88. PROTECTIVE HOUSING Do not touch the housing after long “on times” Do not use the high-voltage cables as “handles” for maneuvering the tube

89. ENCLOSURE Glass or metal Contains X-ray tube Entire cathode Anode assembly (except the stator) Maintains high vacuum <10 -5 mm Hg

90. ENCLOSURE GLASS ENCLOSURE METAL ENCLOSURE FUTURE RRT 2020 95

91. TARGET WINDOW Part of the enclosure Exit point of the x-rays produced 5 cm 2 Made thinner than the rest Minimally interfere with (absorb) the x-rays

92. INTERNAL COMPONENTS CATHODE AND ANODE

93. ANODE Positive end of the x-ray tube Provides the target for electron interaction Designed for heat dissipation (thermal conductor)

94. Tube Materials Location Purpose Tungsten Target Filament Increases efficiency of x-ray production Increases heat dissipation Prevents pitting or bubbling Provides higher thermionic emission Rhenium Target Provides greater elasticity Thorium Filament Enhances the efficiency of thermionic emission Increases x-ray tube life Molybdenum Target (under) Anode stem/shaft Focusing cup Mammographic target Makes the anode easier to rotate Slows migration of heat Increases thermal capacity (+graphite) Preventing bearing damage Narrows thermionic cloud Provides useful energy for breast imaging (24-26 kVp ) Graphite Target (under) Makes the anode easier to rotate Slows migration of heat Rhodium Mammographic target Provides useful energy for breast imaging (30 kVp ) Copper Stationary anode` Anode rotor (rotating anode) Provides thermal properties Provides electrical conductive properties

95. ANODE Consists of an induction motor Stator Rotor Designs: stationary & rotating

96. Tungsten is the metal of choice for the source of x-ray photons for three primary reasons: High atomic number High melting point Heat-conducting ability

97. STATIONARY ANODE A tungsten button embedded in a copper rod Used in old tube designs Heat builds up rapidly Limited to low-power functions Applications: Dental x-ray imaging system Portable x-ray imaging system

98. ROTATING ANODE Consists of a rotating disc made of molybdenum as a core material coated with tungsten 50% greater heat load capacity Possible with high tube current and lower exposure times

99. ROTATING ANODE 3400 rpm: most rotating anode (3200-3600 rpm) 10,000 rpm: high capacity x-ray tube (10,000-12,000 rpm)

100. ROTATING ANODE Faster rotation, better heat dissipation Rotated by an electromagnetic induction motor Applications: General-purpose x-ray tubes

101. FOCAL SPOT VS FOCAL TRACK FOCAL SPOT refers to the spot in the stationary anode target where projectile electrons hit. FOCAL TRACK refers to the area in the rotating anode where projectile electrons hit

102. CATHODE Negative end of the x-ray tube Consists of filaments and focusing cup Provides source of electrons Focus the electron stream Most diagnostic x-ray tubes have dual filaments called a dual focus arrangement

103. FILAMENT A coil of wire 7-15 mm long 1-2 mm wide Made up of tungsten High melting point Does not vaporize easily 1-2% thorium Increase thermionic emission Extend filament life

104. Space Charge A cloud of electrons peeled off from the filament They are formed by the repulsion of electrons from the filament

105. SPACE CHARGE EFFECT Negative charges (space charge) begin to oppose the emission of addition electrons Space Charge: electrons within the vicinity of the filament

106. FOCUSING CUP Designed to house the filament Used to narrow the thermionic cloud Directs the thermionic electrons to the focal spot by using the repulsion of negative charges.

107. Saturation current Affects the efficiency of the x-ray tube The filament saturation current has been achieved when there are no further thermionic electrons to be driven toward the anode . At this point an increase in kVp will not increase the tube mA. Further mA increases must be achieved by increasing the filament amperage.

108. grid-controlled X-RAY TUBE Also called grid-pulsed, or grid-biased Quickly regulates the production of electrons producing photons It adds a positive or negative potential difference ( approximately 2,000 volts) at the focusing cup causing the cup to attract or repel the thermionic cloud. This very cleanly removes electrons from use for x-ray production when the focusing cup charge is pulsed from negative to positive in synchrony

109. IMAGING EQUIPMENT AND MAINTENANCE MARY MITCHELLE M. PUNO, RRT

110. X-RAY IMAGING SYSTEM

111. E very x-ray imaging system has three principal parts: 1. the x-ray tube II. the operating console, III. the high-voltage generator.

112. Operating console The operating console allows radiologic technologists to control the x-ray tube current and voltage so that the useful x-ray beam is of proper quantity and quality

113. Radiation quantity = number of x-rays or the intensity of the x-ray beam. Radiation quantity is usually expressed in milligray ( mGya ) or milligray / milliampere -second ( mGya / mAs ). Radiation quality = penetrability of the x-ray beam and is expressed in kilovolt peak ( kVp ) or, more precisely, half-value layer (HVL)

114. the voltage provided to an x-ray unit easily may vary by as much as 5%. Such variation in supply voltage results in a large variation in the x-ray beam, which is inconsistent with production of high quality images

115. LINE COMPENSATOR The line compensator measures the voltage provided to the x-ray imaging system and adjusts that voltage to precisely 220 V.

116. autotransformer The autotransformer has a single winding and is designed to supply a precise voltage to the filament circuit and to the high-voltage circuit of the x-ray imaging system . The autotransformer works on the principle of electromagnetic induction but is very different from the conventional transformer

117. autotransformer Because the autotransformer operates as an, the voltage it receives (the primary voltage) and the induction device voltage it provides (the secondary voltage) are related directly to the number of turns of the transformer enclosed by the respective connections.

118. Adjustment of Kilovolt Peak ( kVp ) Major kVp Selection The major kilovolt peak adjustment and the minor kilovolt peak adjustment represent two separate series of connections on the autotransformer. Minor kVp Selection The minor kilovolt peak adjustment “fine tunes” the selected technique.

119. Adjustment of Kilovolt Peak ( kVp ) I f the primary voltage to the autotransformer is 220 V, the output of the autotransformer is usually controllable from about 100 to 400. This low voltage from the autotransformer becomes the input to the high-voltage step-up transformer that increases the voltage to the chosen kilovolt peak.

120. kVp Meter The kVp meter is placed across the output terminals of the autotransformer and therefore actually reads voltage, not kVp . The scale of the kVp meter, however, registers kilovolts because of the known multiplication factor of the turns ratio

121. Control of Milliamperage ( mA) The x-ray tube current, crossing from cathode to anode, is measured in milliamperes (mA ) The number of electrons emitted by the filament is determined by the temperature of the filament.

122. Control of Milliamperage ( mA) The filament temperature is in turn controlled by the filament current, which is measured in amperes (A). As filament current increases, the filament becomes hotter, and more electrons are released by thermionic emission. Filaments normally operate at currents of 3 to 6 A.

123. X-ray tube current is controlled through a separate circuit called the filament circuit Connections on the autotransformer provide voltage for the filament circuit.

124. Precision resistors A re used to reduce voltage to a value that corresponds to the selected milliamperage . Precision resistors result in fixed stations that provide tube currents of 100, 200, or 300 mA, and higher.

125. FALLING LOAD GENERATOR In a falling load generator, the exposure begins at maximum mA, and the mA drops as the anode heats. The result is minimum exposure time

126. Ma METER X-ray tube current is monitored with an mA meter that is placed in the tube circuit. The mA meter is connected at the center of the secondary winding of the high-voltage step-up transformer the center of this winding is always at zero volts

127. Filament transformer “Filament heating isolation step-down transformer” It steps down the voltage to approximately 12 V and provides the current to heat the filament

128. Filament transformer In the filament transformer, the primary windings are of thin copper and carry a current of 0.5 to 1 A and approximately 150 V. The secondary windings are thick and at approximately 12 V electric potential and carry a current of 5 to 8 A.

129. HIGH VOLTAGE GENERATOR The high-voltage generator may be housed in an equipment cabinet positioned against a wall. The high-voltage generator is always close to the x-ray tube, usually in the examination room responsible for increasing the output voltage from the autotransformer to the kVp necessary for x-ray production.

130. 1. High voltage transformer The high-voltage transformer is a step-up transformer Because transformers operate only on alternating current, the voltage waveform on both sides of a high-voltage transformer is sinusoida

131. VOLTAGE RECTIFICATION Rectification is the process of converting AC to DC . The electronic device that allows current flow in only one direction is a rectifier. Although transformers operate with alternating current, x-ray tubes must be provided with direct current.

132. TYPES OF VOLTAGE RECTIFICATION Half wave rectified Full wave rectified

133. HALF WAVE RECTIFICATION H alf-wave rectification occurs when only half of the incoming alternating current is being converted to pulsating direct current. The opposing half of the flow is simply ignored and not utilized. The electrons simply cease moving and stop transferring energy

134. FULL WAVE RECTIFICATION This is done through an ingenious arrangement of four rectifiers in a bridge circuit called a full-wave rectification circuit It converts the opposing half of the incoming electron flow so that electrons are always moving in the same direction, instead of discarding half the cycle by suppression.

135. Types of generators According to voltage ripple

136. Voltage ripple It is the variation in the output voltage from its nominal value. Ripple voltage is the amount of AC voltage that remains in the output of a rectifier circuit after filtering.

137. Types of generators SINGLE PHASE GENERATOR HALF WAVE RECTIFIED FULL WAVE RECTIFIED THREE PHASE GENERATOR SIX PULSE (SIX RECTIFIERS) SIX PULSE (TWELVE RECTIFIERS) TWELVE PULSE (TWELVE RECTIFIERS)

138. SINGLE PHASE GENERATOR Single-phase power permits the potential difference to drop to zero with every change in the direction of current flow represented by the symbol 1φ

139. A. 1φ HALF WAVE RECTIFIED Single waveform Positive only 60 pulses per second Voltage ripple: 100% Voltage output: 0-100V

140. A. 1φ full WAVE RECTIFIED One full cycle waveform Positive only 120 pulses per second Voltage ripple: 100% Voltage output: 0-100V

141. Three phase generator Multiple voltage waveforms are superimposed on one another, resulting in a waveform that maintains a nearly constant high voltage . Overall waveform never reaches zero

142. a . THREE PHASE SIX PULSE (SIX RECTIFIERS) Has 3 sets of primary winding and 3 sets of secondary winding in the STEP UP (High voltage) TRANSFORMER 1/60 seconds Has 6 positive half cycles 360 pulses per second 13.5 % voltage ripple 86.5-100% voltage output

143. a. THREE PHASE six PULSE (twelve RECTIFIERS) 3 sets of primary winding and 6 sets of secondary winding (two wires). Connected to an electric ground Allows 150 kV generator to have a transformer that provides voltage of -75kV to 75kV Has insulating requirements

144. a. THREE PHASE 12 pulse PULSE (12 RECTIFIERS) 3 sets of primary winding (delta) and 6 sets of secondary winding (two wires) (delta and wye) When delta and wye are connected in the secondary winding, the output of the delta winding will LAG the WYE by 30 % This will result in overlapping ripples This allows the formation of 12 pulses

145. a. THREE PHASE 12 pulse PULSE (12 RECTIFIERS) 1/60 seconds – 12 positive half cycle 720 pulses per second 3.5% voltage ripple 96.5 – 100 Voltage output

146. Three-phase, six-pulse power produces voltage with only approximately 14% ripple; consequently, the voltage supplied to the x-ray tube never falls to below 86% of the maximum value.

147. Three-phase, 12-pulse power results in only 4% ripple; therefore, the voltage supplied to the x-ray tube does not fall to below 96% of the maximum value. High-frequency generators have approximately 1% ripple and therefore greater x-ray quantity and quality.

148. Power rating Transformers and high-voltage generators usually are identified by their power rating in kilowatts (kW).

149. RATING CHARTS

150. RATING CHARTS Three types of x-ray tube rating charts are particularly important: the radiographic rating chart, the anode cooling chart, T he housing cooling chart.

151. Radiographic Rating Chart Conveys which radiographic techniques are safe and which techniques are unsafe for x-ray tube operation For a given mA, any combination of kVp and time that lies below the mA curve is safe. Any combination of kVp and time that lies above the curve representing the desired mA is unsafe. If an unsafe exposure was made, the tube might fail abruptly

152. ANODE COOLING CHART The thermal capacity of an anode, and its heat dissipation characteristics are contained in a rating chart called an anode cooling chart In x-ray applications, thermal energy is measured in heat units (HUs) or Joules (J). One heat unit is equal to the product of 1 kVp , 1 mA, and 1 s. One heat unit is also equal to 1.4 J . 1 HU = kVp x mA x s

153. ANODE COOLING CHART

154. HOUSING COOLING CHART The cooling chart for the housing of the x-ray tube has a shape similar to that of the anode cooling chart is used in precisely the same way. Radiographic x-ray tube housings usually have maximum heat capacities in the range of several million heat units. Complete cooling after maximum heat capacity requires from 1 to 2 hours.