Rad T 290

1

• Rad T 290
• Generators

2
Generator Components

• control console
• kVp adjust
• mA adjust
• time adjust
• transformer
• high voltage (step up)
• filament
• low voltage (step down)
• electronics cabinet
• support circuitry

or mAs adjust
3
Incoming Power

• Line affects generator performance
• diameter of wire
• length or wire
• other devices sharing branch circuit
• Resistance of power line wires can reduce
  generator voltage during exposure affecting
• power available to x-ray tube
• calibration

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Line Voltage Compensation

• Incoming voltage can vary during day
• Generators need to correct for changes in line
  voltage
• power line fluctuations affect calibration

5
Line Voltage Compensation

• Compensation may be
• Automatic
• Almost everything today
• Manual
• user must make adjustment

Line
Line Compensation
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High Voltage Transformer
Rectifier Circuit
Timer Circuit
Auto- trans-former
Line
mA regulator
Filament Transformer
Autotransformer

• High voltage Transformer has fixed ratio
• Autotransformer has variable ratio
• Autotransformer needed to provide variable
  kilovoltage to tube

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Autotransformer
major kV selector
to high voltage transformer primary
Timer Circuit
minor kV selector
to filament transformer primary
mA regulator
Autotransformer does line compensation kVp
selection
8
Generator Voltages

• Input line voltage
• single or three phase
• 115 - 480 Volts AC
• Autotransformer
• provides variable voltage to primary of high
  voltage transformer

1f
3f
Auto Transformer
High Voltage Transformer
Timer Circuit
Power Line
9
High Voltage Circuit

• Supplies high voltage for x-ray tube
• Step-up transformer
• primary from autotransformer
• secondary to rectifier circuit
• mA monitored at center grounded point of secondary

Auto- transformer
Rectifier Circuit
mA
High Voltage Transformer
10
High Voltage Transformer

• Grounded metal box
• filled with oil
• electrical insulator
• Function
• increases or decreases alternating voltage
• Also contains rectifier circuit
• changes alternating current into direct current

11
Fullwave Rectifier

• Four diodes
• 120 pulses/second
• exposure times half of halfwave circuit

Secondary of High Voltage Transformer
Voltage applied to tube (also mA waveform)
12
Fullwave Rectifier
First Half Cycle
Second Half Cycle
13
Full-Wave Rectification

• Rectifiers
• Four diode bridge configuration used with
  single phase
• both - half cycle of high tension transformer
  used
• efficient
• circuit reverses negative half cycle applies to
  x-ray tube

Tube
Output of High Tension Transformer
Applied to X-ray Tube
14
Pulsed Radiation

• single phase input power results in pulsed
  radiation
• Disadvantages
• intensity only significant when voltage is near
  peak
• low voltage heats target and produces low-energy
  photons
• absorbed in tube, filter, or patient
• can contribute to dose

15
Three-Phase Generators

• Commercial power generally delivered as 3 phase
• phases 120o apart

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Three-Phase Generators

• Rectifier circuit
• Inverts negative voltage
• sends highest of 3 phases to x-ray tube

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Three-Phase Generators

• much higher tube ratings than single phase
• more efficient than single phase
• shorter exposures
• lower exposure

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3f Generator Circuits

• pulses
• number of peaks per 1/60 second (16.6 msec) power
  line cycle
• windings
• 3 primary coils (one for each phase)
• 3 or 6 secondary
• with 6 secondaries, 2 secondary coils induced per
  primary

19
Three Phase Transforming

• 3 coils can be hooked up in 2 ways

Delta
Wye
20
3-phase generator

• Primary windings
• generally delta
• Secondary windings
• may be delta or wye

Primary
Secondary
21
3 Phase Generator

• 6-Pulse Twelve Rectifier
• 1 delta primary
• 2 wye secondaries
• 6 secondary windings
• two diodes per winding
• 13.5 ripple

Primary
Ripple
Secondary
Secondary
Three Phase Output
22
3 Phase Generator

• 12-Pulse Twelve Rectifier
• 1 delta primary
• 2 secondaries, 1 wye, 1 secondary
• 30o phase difference between secondaries
• 6 secondary windings
• 2 diodes per winding
• 3.5 ripple

Primary
Ripple
Secondary
Secondary
Three Phase Output
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High Voltage Transformer
Rectifier Circuit
Timer Circuit
Auto- trans-former
Line
mA regulator
Filament Transformer
mA regulator

• Circuitry for mA selection
• Adjusts mA on the fly during exposure.

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High Voltage Transformer
Rectifier Circuit
Timer Circuit
Auto- trans-former
Line
mA selector
Filament Transformer
Filament Transformer
Steps down AC voltage from Autotransformer mA
selector to smaller AC voltage required by
filament (8-12 volts typical)
25
mA selection

• Allows selection from available discrete mA
  stations.
• Applies correct voltage to primary of filament
  transformer.

to filament transformer primary
10 mA
25 mA
mA stabilizer
50 mA
100 mA
200 mA
300 mA
400 mA
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mA Stabilization During Exposure

• On first trigger
• mA regulator supplies anticipated voltage to
  filament transformer primary
• mA monitored during exposure
• Corrections made to filament voltage during
  exposure as necessary
• if mA low, filament voltage boosted
• if mA high, filament voltage lowered

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1f vs. 3f Generators
1f
3f

• Typical home small business power
• inexpensive
• transformer windings
• 1 primary coil
• 1 secondary coil

• Industrial power
• expensive
• transformer windings
• 3 primary coils
• one for each phase
• 6 secondary coils
• 2 secondary coils induced per primary)

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1f vs. 3f Generators
1f
3f

• 100 ripple
• 8 ms minimum exp. Time
• 1/120th second
• lower output intensity
• puts less heat in tube for same technique

• 4-13 ripple
• higher average kVp
• slightly less patient exposure
• lt1 ms minimum exp. time
• higher output intensity
• puts more heat in tube

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Exposure Time Control

• electronic, measuring
• time (crystal)
• power line pulses
• automatic (phototiming)
• terminates exposure based on radiation received
  by receptor

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Phototiming Geometry

• entrance type
• detector in front of film
• detector must be essentially invisible
• exit type
• detector behind film
• obsolete except for mammography
• detector visible because of high contrast image

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Phototiming Radiation Detectors

• ionization chambers
• solid-state detectors

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Ionization Chambers

• Almost always entrance type
• Notes
• thin parallel aluminum plates are electrodes
• voltage applied between plates
• collect ions produced by radiation in air
  between electrodes
• collected ions produce electric current

Photon

-

-
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Solid State Detectors

• PN semiconductor junction generates current when
  struck by radiation
• small
• fast response
• little beam attenuation

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Phototiming Fields

• 1, 2, or 3
• fields may be selected individually or in
  combination
• proper positioning critical

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Phototiming Notes

• must be calibrated for particular film-screen
  system
• some generators allow selection from several
  preset film/screen combinations

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Phototiming Notes

• phototimer must correct for
• rate response
• kVp response of
• film/screen system
• phototiming sensor
• Higher kVp beam more penetrating
• Less attenuated by phototimer detector
• safety
• exposure limited to 600 mAs if phototimer does
  not terminate exposure (2000 mAs for lt 50 kV)