This document discusses key components of X-ray systems, including vacuum tube diodes that require rectification to convert AC to DC, high voltage transformers to achieve the voltages needed for X-ray production, and various generator designs like single phase, three phase, and constant potential generators. It also covers topics like transformer configurations and efficiencies, rectification circuits, and factors that determine the maximum safe output of X-ray tubes.

2.  Heart and Brain of X-ray System

3.  Needs DC (is in fact a vacuum tube diode)
 Can only conduct in one direction:
 cathode negative with respect to anode
 Because of thermionic emission
 Therefore need rectifiers; convert AC to DC
 Need high voltage for X-ray production
 ½ mv2 into h 
 110 Volts vs 110 thousand volts
 Therefore need transformers (changes voltage)

4. p
s
p
s
N
N
V
V

V i 
V i
p p s s

10.  Battery storage
 Capacitor discharge
 Constant potential gradient (CPG)
 Tetrodes (high voltage vacuum tubes) control kV and exposure
time directly on high voltage side
 Flat waveform but expensive
 High freq nearly as good

11.  Two separate coils of wire
wrapped around closed core
 Many configurations
 Electrical supply connected to 1
 Output device to 2
 Step up or step down

12.  1) Voltage in two circuits proportional to
number of turns in the two coils
 2) Power (Energy) is conserved:
p
s
p
s
V
V
N
N

 As Power (watts) is voltage x current:
 Therefore as voltage increases by turns ratio,
current decreases p p s s V I  V I
s
p
p
s
I
I
N
N


13. Bushberg

14.  Unique single winding design
 Self inductive
 1 & 2 defined by number of turns enclosed by taps
 Variable number of turns from taps allows voltage
control at relatively low potential
 Feeds primary of high voltage transformer and
filament transformer
 Can be both step up and down

15.  Step down transformer drops voltage
 10 V @ 3-5 A
 Filament current (A) indirectly controls tube current (and output
X-ray intensity)

16.  Step up transformer
 > 500 fold voltage increase
 Immersed in dielectric
 Secondary side of autotransformer
 Fixed # of transformer windings
 Grounded at center (mA meter)
 So for 100 kVp, potential on one side is +50,000 V & other is –
50,000 V
 Less of an insulation problem

17.  Converts AC (needed by transformer) to DC
(needed by tube)
 Conduct current in one direction only
 Vacuum tubes (old style) large, bulky, and
burnout
 Solid state semiconductor diodes
 Made of N-P semiconductors
 Conduct only on forward bias

18.  Four diode arrangement to allow current to
flow in one direction through tube regardless
of polarity of secondary side of high tension
transformer
 Full wave rectified generator
 2x as efficient as self (half) wave rectified
 But inefficient compared to high freq & CPG
generators

19.  Single Phase – 100% ripple w/ half or full wave
rectified
 High voltage varies between 0 and max
 For single phase, average voltage is R.M.S.
peak
peak
RM S   0.707
2
. . .

20.  Recall AC power avail. in 3
 3 voltage peaks per 1/60 sec
 3, 6 pulse
 High volt transform & rectify
 13.5% ripple
 3, 12 pulse
 2 different winding config on 2°
▪ Delta and wye
 Another 30° phase shift for 2 halves of output, peaks fill
troughs
 3.5% voltage ripple

21.  Transformer efficiency: V ~ NA
 By increasing frequency, cross sectional area reduced for same power (50kW in tube head!)
 Frequency of invertor ranges from 5-100 kHz!
 Feedback loop controlled – during exposure if kV drops off, increase invertor frequency & kV increases
 Timer accuracy
 Shorter exposures
 (<10 ms)

23. Generator Type / High Voltage Waveform

24.  Tube insert has power/load limit
 Function of heat produced in exposure
 HU = kVp x mA x time x correction factor
 single phase generator – less efficient
 Correction factor cpg generator =1.4
 70 kVp x 100 mA x 0.1 sec = 700 HU (single phase)
 Joules = watts x seconds
 1 W = 1 V x 1 A = 1000 V x 0.001 A = keV x mA!
 assume constant voltage, so divide by correction factor!
 70 kVp / 1.4 x 100 mA x 0.1 sec = 500 J (single phase)
 For cpg is 700 Joules

25. Question:
What is highest kVp can
safely use to get 35 mAs
(350 mA & 100ms)?

26. Question:
What is highest kVp can
safely use to get 35 mAs
(350 mA & 100ms)?
Answer:
Should not exceed 100 kVp

27.  Integrates area under tube rating curve
 Applies highest mA in shortest time, reduces mA
as exposure continues
 Expensive, not used as much with today’s high
output tubes

28.  Single phase seldom at peak voltage, so set higher kVp
 Three phase higher average kVp
 Less ripple means more mR/mAs (shorter exposure time)
 5 mR/mAs single vs. 10 mR/mAs three phase
 Ripple based on some multiple of 60 Hz
 High frequency more common now, smaller and cheaper than CPG

29.  Tube power handling should match generator output
 Rated in kilowatts under load (kVp x mA) @ 100 kVp
 80 kW generator can produce 800 mA at 100 kVp (simultaneously)
 Polydoros 80s, Medio CP80
 Small clinic may have 20kW, 200 mA at most
 Angio/Cardio generators 100 kW and greater
 CT not necessarily high instantaneous, but tube and generator sustain for long
periods