Rad T 290 - PowerPoint PPT Presentation

1 / 36
About This Presentation
Title:

Rad T 290

Description:

... of high contrast image Exit type Sensor Grid Film Entrance type Sensor Phototiming Radiation Detectors ionization chambers solid-state detectors Ionization ... – PowerPoint PPT presentation

Number of Views:42
Avg rating:3.0/5.0
Slides: 37
Provided by: Georg224
Category:

less

Transcript and Presenter's Notes

Title: 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

4
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
6
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

7
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

16
Three-Phase Generators
  • Rectifier circuit
  • Inverts negative voltage
  • sends highest of 3 phases to x-ray tube

17
Three-Phase Generators
  • much higher tube ratings than single phase
  • more efficient than single phase
  • shorter exposures
  • lower exposure

18
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
23
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.

24
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
26
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

27
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)

28
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

29
Exposure Time Control
  • electronic, measuring
  • time (crystal)
  • power line pulses
  • automatic (phototiming)
  • terminates exposure based on radiation received
    by receptor

30
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

31
Phototiming Radiation Detectors
  • ionization chambers
  • solid-state detectors

32
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

-

-
33
Solid State Detectors
  • PN semiconductor junction generates current when
    struck by radiation
  • small
  • fast response
  • little beam attenuation

34
Phototiming Fields
  • 1, 2, or 3
  • fields may be selected individually or in
    combination
  • proper positioning critical

35
Phototiming Notes
  • must be calibrated for particular film-screen
    system
  • some generators allow selection from several
    preset film/screen combinations

36
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)
Write a Comment
User Comments (0)
About PowerShow.com