rectification rt 244 – lect #2 rev 2012 1. wavelength x-ray is measured in hertz or angstrom...

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RECTIFICATION RT 244 – Lect #2 Rev 2012 1

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Page 1: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

RECTIFICATION

RT 244 – Lect #2 Rev 2012

1

Page 2: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

Wavelength

• X-ray is measured • In HERTZ OR• Angstrom

Elsevier items and derived items © 2009 by Mosby, Inc., an affiliate of Elsevier Inc. 2

XRAY IS MEASURED IN HERTX OR ANGT

Page 3: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

3

Alternating Current - AC• AC is produced when a coil of wire turns in a

magnetic field• ½ turn current is moving in one direction• Then ½ turn it moves in the other direction

• IF 3 coils of wire are wrapped around a core – they rotate 1/3 (120º apart) – then 3 different AC currents are generated

Page 4: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Rectification• Converts AC to DC• Located after Step up Transformer • On secondary side of Circuit• Can be single phase (1Φ) • Or 3 phase (3 Φ )

Page 5: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Rectification

• process of changing AC to pulsed DC• rectifier

– device that allows I to flow in only one direction– types valve tube solid state

Ie

I

+ -

Ie

I

+ -

Page 6: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Rectification

• purpose– convert HV AC to pulsed DC

for x-ray tube

• location– between HV secondary coil &

x-ray tube

• types– full wave -- most common– half wave -- limited use– self -- rarely

TransformerSection

Page 7: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Valve tube (diode) glass vacuum tube w/ 2 electrodes

1) negative electrode -- cathode– thermionic emission of e-

2) positive electrode -- anode– cold metallic plate

cold hot

anode cathode

Page 8: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

8FLOW OF CURRENT

• VALVE TUBE RECTIFIES

Page 9: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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SOLID STATE - DIODES – Semi Conductor

• Allows current to only flow in one direction

• Most common type used in rectifiers

Page 10: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Solid State Rectifier

1) "n-type" material (donor) [similar to cathode]

– contains loosely bound e-

2) "p-type" material (acceptor) [similar to anode]

– spaces in molecular structure to accept e-

3) p-n junctionp-n junction– union of the two types of materials

n-type- - - --

--- - --

--

p-type

p-nj

Page 11: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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TYPES OF RECTIFICATIONSINGLE PHASE

½ RECTIFIED + FULL RECTIFIED

Page 12: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Rectification Process• rectifiers placed in circuit to convert AC

current to pulsed DC• methods

– suppress unwanted part of the AC (half wave rectification)

– redirect unwanted part of AC (full wave rectification)

+

-

+

-

+

-

+

-

V

V

I

I

Page 13: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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AC – single phase

• Only ½ of cycle usable

• By converting other ½ more useful

• Draw back –• 100% ripple • (0-100-0) output

Page 14: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Single Phase – Full rectifiedVoltage

• 1Ø AC has a 100% voltage ripple

+ V

- V

+ V

- V

0 0

Page 15: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Single vs. Three Phase Power (cont.) Three phase (3Ø )

• power supplied/used w/ a new cycle beginning each 120°– results in three overlapping sine waves– 3 + pulses & 3 - pulses occur in the length of time of one complete

cycle (1/60s)– each wave can be rectified (3Ø6p)– pulses overlap reducing voltage ripple & Vmin

1/60s +

-

V

1/60s +

-

V

Page 16: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3 PHASE – MORE EFFICIENT

Page 17: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3Ø comparison to 1Ø

• 3Ø more efficient than 1Ø• 3Ø requires more complex circuitry• 3Ø more expensive to install

Page 18: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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(3 Φ ) 3 PHASE

• LESS RIPPLE • MORE EFFIECIENT OUTPUT

• HIGH FREQUENCY – 1% RIPPLE• MOST EFFIEICENT – VERY EXPENSIVE

Page 19: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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VOLTAGE RIPPLE

Ripple effect differences

• 100 % RIPPLE• 4 – 10 % RIPPLE• 1% RIPPLE

Page 20: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Voltage Waveforms (Bushong)Voltage Waveforms (Bushong)

Single phase

Rectification Type

Ripple

Half wave 100%

Full wave 100%

Rectified 3-phase

Rectification Type

Ripple

Three phase, 6 pulse

13%

Three phase, 12 pulse

4%

Three phase, high frequency

<1%

Page 21: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Generator SummaryType p/c p/s # % Wave Form (2 cycles)

rectifiers Ripple

+

-

+

-

+

-

+

-

+

-

1ØSelf 1 60 0 100%

1Ø1p 1 60 1 or 2 100%

1Ø2p 2 120 4 100%

3Ø6p 6 360 6 or 12 12-15%

3Ø12p 12 720 12 3-5%

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Comparison of X-ray Machines1Ø 3Ø High freq.

V ripple 100% < 15% <1%p/s 60 or 120 720 13,000X-ray Quantity “X” more highestX-ray Quality “X” higher min time 1P (~8 ms) 1 ms machine $ “X” higher highestoperation $ “X” lower ??generator size moderate largest smallest

Page 23: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Ripple Factor (%)• variation in tube V during an exposure• What is the ripple of the following waveform?

1/60s

+

-

V

80 kV

68 kV

= look in book for comparisons

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High Frequency Generators

• x-ray tube nearly constant– ripple <1%

• small in size• Expensive – most efficient

rectifiers smooth choppedHVT rectifiers smooth tube

Page 25: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Full-Wave Rectification

Positive HV pulse Negative HV pulse

+

-

I

+

- I

+

-

+

-

V

+

-

I

Ie

x rays

+

-

I+

-

+

-

V

+

-

I

Ie

x rays

FYI - Don’t need to know the direction of the current

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High Frequency Power

• machine designed to have a low ripple (<1%) & use 1Ø power

• 1Ø AC rectified then smoothed & chopped into high frequency output (kHz)

Page 27: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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1Ø vs. 3Ø HV Transformers

Each phase must have step-up transformer

primary secondary

primary secondary

Page 28: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3 Transformer Configurations

simple 3 6 pulse: delta/wye () primary secondary

15% voltage ripple

Star Wye or delta

Page 29: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3 Trans. Configurations (cont.)

complex 3 6 pulse: delta/wye/wye () primary secondary

12% voltage ripple

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3Ø Transformer Coils

1/60s +

-

V

Wye -- delayed output

Delta -- either side

Wye -- secondary only

Delta Coils Wye Coils

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3 Rectification• each secondary coil requires 2 rectifiers• 3Ø6 with coils = 6 rectifiers

positive pulse negative pulse

-+

-+

+-

-+

Page 32: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3 Rectification (cont.)

• 3Ø6 with coils = 12 rectifierspositive pulse negative pulse

-+

-+

-+

-+

-+

-+

Page 33: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3 Rectification (cont.)

• 3Ø12 with coils = 12 rectifiers

positive pulse negative pulse

-+ -

+

+ -

-+ -

+

+ -

Page 34: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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A star or delta connection is used to ?

Page 35: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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3 Transformer Configurations

simple 3 6 pulse: delta/wye () primary secondary

15% voltage ripple

A star or delta connection is used to combine three-phase current

Page 36: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Rectification• AC to DC• Keeps e- flowing from

cathode to anode• Uses rectifying bridge

between HVT & tube

HVT

tube

HVT

tube

AC DCbridge

Page 37: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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Capacitor Discharge Generator

• capacitor bank charged by rectified high voltage• during exposure capacitors provide kV across tube• problems

– as capacitors drain kV drops (~1 kV/mAs)– any residual charge may shock operator

HVT rectifiers capacitor tube

PLUG IN PORTABLE MACINES

Page 38: RECTIFICATION RT 244 – Lect #2 Rev 2012 1. Wavelength X-ray is measured In HERTZ OR Angstrom Elsevier items and derived items © 2009 by Mosby, Inc., an

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TECHNIQUE CHANGES

• SINGLE PHASE (1Φ) TO • 3 Φ 12 PULSE CUT MAS BY ½

• SINGLE PHASE (1Φ) TO • 3 Φ 6 PULSE CUT MAS BY 1/3

MORE EFFICIENT = LESS MAS NEEDED