1. BORROWED FROM: Physics Applied to Radiology RADI R250 -- Fall 2003 CH 9 CIRCUITRY

2. 2 X-Ray Machine Purpose: provide a specific current (mA) & voltage (kV) to the x-ray tube convert electrical energy to electromagnetic energy (x rays) in a controlled manner control the energy of the x-ray photons control the number of photons

3. 3 X-Ray Machine Circuit

4. 4 Main Subcircuits (1) High Voltage Subcircuit gives KE to e -

5. 5 Main Subcircuits (2) Filament Subcircuit thermionic emission of e -

6. 6 Transformer Side Primary SideSecondary Side low voltage high voltage

7. 7 Functional Position Control ConsoleTransformersTube

8. 8 Control Panel Functions 1. ON/OFF 2. Regulate incoming power 3. kVp selection 4. TIME selection exposure control exposure control 5. mA selection FSS selection 1. 2. 3. 4. 5.

9. 9 Control Panel Circuit Elements POWER SUPPLY 60 Hz AC 120 to 480 V Panel Power On/Off AUTOTRANSFORMER 1. line compensation a. line meter b. primary side adjustments 2. kVp selection a. secondary side adjustments variable turns ratio 3. filament circuit power 1a. 1b. 2a. 3.

10. 10 Control Panel Elements (cont.) on secondary side of autotransformer 1.mA selector a.precision resistors b.meter (in  transformer) c.FSS selector 2.kVp selector a.major/minor taps b.meter (pre-reading) 3.time selector a.circuit types b.exposure switch 2a. 2b. 1a. 1b. 3a. 3b.

11. 11 Timer Circuit Types (1  ) mechanical spring action synchronous motor start/stop with AC cycle 60 Hz = 60 start/stop positions shortest time = 1/cycle = 1/60 s impulse start/stop with AC pulse 60 Hz = 120 start/stop positions shortest time = 1/pulse = 1/120 s 1/60 s 1/120 s

12. 12 Timer Circuit Types (3  ) electronic timer operation selecting time = varying resistance in rheostat to control time it takes to charge the capacitor activating exposure also begins storage of charge in the capacitor when a precise voltage is reached in capacitor, the switch opens & terminates the exposure microprocessor computer chip technology shortest time = 1 ms=.001 s= 1/1000 s capacitor rheostat switch

13. 13 Functional Position Control ConsoleTransformersTube

14. 14 Timer Comparison 1  mechanical shortest = 1/4 s250.0 ms synchronous motor shortest = 1/60 s16.6 ms impulse shortest = 1/120 s8.3 ms 3  electronic shortest = 1/1000 s1.0 ms

15. 15 Timer Circuit Types (3  ) (cont.) mAs timer type of electronic timer uses tube current (mA) to charge capacitor time to charge capacitor = time of exposure on secondary side of HV transformer

16. 16 Timer Circuit Types (3  ) (cont.) Automatic Exposure Control (AEC) timers electronic timer detects radiation that has passed through the patient terminates exposure after set amount of radiation reaches sensing device based on light emitted or ionization caused photomultiplier tube (PMT) film/cassette etc. patient film/cassette etc. patient ionization chamber

17. 17 Functional Position Control ConsoleTransformersTube

18. 18 Transformer Section components 1. step-up transformer 2. mA meter 3. rectification circuit 4. step-down transformers location in “box” linked between control console & x-ray tube immersed in oil for insulation & cooling Transformer Section 1. 2. 3. 4.

19. 19 High Voltage Transformer Fixed TR between 500 & 600 Primary Side (power from autotransformer’s secondary output) P S-AT = P P-HV 120V 10A = 120V 10A Secondary Side   V to kV e.g. if TR = 500 & P P-HV = 120 V 10 A then V S-HV = 500 x 120V = 60 kV and I S-HV = 10A  500 =.02 A amplitude of V sine wave  see text Table 7.1, page 173 = = Voltage Sine Wave kVV

20. 20 mA Meter location midpoint of secondary coil of HV transformer face of meter may be on control console grounded safety places 0V in center of coil each wire out of HV transformer carries ½V T operates only during an exposure 0V +½VT+½VT -½VT-½VT

21. 21 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 Transformer Section

22. 22 Rectification process of changing AC to pulsed DC rectifier device that allows I to flow in only one direction typesvalve tube solid state IeIe II +- IeIe II +-

23. 23 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

24. 24 Valve Tube Operation a) AC with + on anode & - on cathode (+ AC pulse) e - flow from cathode to anode = I +- - - - - - - - - - IeIe I + - V + - I +- - - - - - - - - - + - V + - I b) AC with + on cathode & - on anode (-AC pulse)  e- drawn back to filament = no I

25. 25 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 - p-n junction 3) p-n junction union of the two types of materials n-type - - - - - - - - - - - - - p-type p-nj

26. 26 Solid State Rectifier Operation a) AC with + on p-type & - on n-type ( + AC pulse) e - move across junction to the spaces = I + - V + - I b) AC with + on n-type & - on p-type ( - AC pulse) e- drawn away from the junction = no I + - V + - I + - I IeIe - - - - - - - - - - - - - + - - - - - - - - - - - - - -

27. 27 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

28. 28 Full-Wave Rectification Positive HV pulse Negative HV pulse + - I + - II + - + - V + - I IeIe x rays + - II + - + - V + - I IeIe

29. 29 Half-Wave Rectification Positive HV pulse Negative HV pulse + - + - V + - I + - V + - I x-rays  I e  I + - + - + - + - no I e no  I + - + + - - no x-rays + -

30. 30 Self Rectification Positive HV pulse Negative HV pulse + - V + - I + - V no I e no  I + - + - no x-rays  I e  I + - + - + - I + -

31. 31 Step-Down (Filament) Transformer purpose adjust current to cathode filament to produce the heat required for the thermionic emission of e - control # x rays  I F =  heat  heat =  # e -  # e - =  # x rays Transformer Section

32. 32 Filament Transformer (cont.) operation primary current adjusted by precision resistors (Ohm’s Law) fixed TR =.10 to.05 secondary current  to 3 to 5 A required for thermionic emission 2 selectable transformers small filament transformer large filament transformer

33. 33 Voltage Ripple % ripple voltage fluctuation in waveform + V - V + V - V 00

34. 34 Single Phase – Full rectifiedVoltage 1 Ø AC has a 100% voltage ripple + V - V + V - V 00

35. 35 Filament Circuit vs. Tube Circuit I T anode to cathode P from kVp & mA I F around filament P from V & A

36. 36 Circuit Summary 2 major subcircuits filament circuit thermionic emission of e - at filament high voltage circuit PD to accelerate e - from cathode to anode Other circuit parts timing method rectifiers meters

37. 37 Single vs. Three Phase Power Single phase (1 Ø ) power supplied or used one cycle at a time unrectified  200%  + - V  1/60s  V + -  100%   1/60s  rectified 1 or 2 + pulses in each 1/60s cycle 100 % voltage ripple 1 + & 1 - pulse in each 1/60s cycle 200 % voltage ripple

38. 38 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 & V min  1/60s  + - V + - V

39. 39 3Ø Voltage Ripple pulse overlap decreases ripple to 12-15% on 3Ø6p 3-5% on 3Ø12p effective voltage nearly = maximum voltage  1/60s  + - V  12 - 15%

40. 40 X-ray Machine Power Rating kilowatt rating electrical power of the machine power formula adapted to compensate for: dimensional prefixes used in x-ray machines effectiveness of 3  vs. 1 

41. 41 Kilowatt Rating Problem What is the power rating of a 1Ø machine that can operate at 150 kVp and 500 mA? P 1Ø = ?? kVp = 150 mA = 500 P 1Ø = [(kVp x mA) / 1000] x.7 = [(150 x 500) / 1000] x.7 = 52.5 kW = 50 kW

42. 42 3Ø comparison to 1Ø 3Ø more efficient than 1Ø 3Ø requires more complex circuitry 3Ø more expensive to install

43. 43 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)

44. 44 Rectification Review Type # rectifiers % RippleWave Form (2 cycles) 1 Ø Self 0100% 1 Ø 1p1 or 2100% 1 Ø 2p4100% 3 Ø 6p6 or 1212-15% 3 Ø 12p123-5% + - + - + - + - + -

45. 45 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 & V min  1/60s  + - V + - V

46. 46 1 Ø vs. 3 Ø HV Transformers Each phase must have step-up transformer 1Ø1Ø primary secondary 3Ø3Ø primarysecondary

47. 47 3 Ø Transformer Coils  1/60s  + - V Wye -- delayed output Delta -- either side Wye -- secondary only Delta CoilsWye Coils

48. 48 3  Transformer Configurations simple 3  6 pulse: delta/wye (  ) primarysecondary  15% voltage ripple

49. 49 3  Trans. Configurations (cont.) complex 3  6 pulse: delta/wye/wye (  ) primarysecondary  12% voltage ripple

50. 50 3  Trans. Configurations (cont.) 3  12 pulse: delta/wye/delta (  ) primarysecondary 2 secondary waves from each primary  3-5% voltage ripple

51. 51 3  Rectification each secondary coil requires 2 rectifiers 3 Ø 6 with  coils = 6 rectifiers positive pulse negative pulse - + - + + - - +

52. 52 3  Rectification (cont.) 3Ø6 with  coils = 12 rectifiers positive pulse negative pulse - + - + - + - + - + - +

53. 53 3  Rectification (cont.) 3Ø12 with  coils = 12 rectifiers positive pulse negative pulse - + - + + - - + - + + -

54. 54 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

55. 55 Generator Summary Type p/cp/s# % Wave Form (2 cycles) rectifiers Ripple + - + - + - + - + - 1 Ø Self1600100% 1 Ø 1p1601 or 2100% 1 Ø 2p21204100% 3 Ø 6p63606 or 1212-15% 3 Ø 12p12720123-5%

56. 56 Medium/High Frequency Generators x-ray tube nearly constant ripple <1% small in size Expensive – most efficient rectifiers smoothchopped HV T rectifierssmoothtube

57. 57 Comparison of X-ray Machines 1 Ø 3 Ø High freq. V ripple100%< 15%<1% p/s60 or 120 72013,000 X-ray Quantity“X”morehighest X-ray Quality“X”higher  min time1P (~8 ms)1 ms  machine $“X”higherhighest operation $“X”lower?? generator sizemoderatelargestsmallest

58. 58 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 HV T rectifiers capacitor tube

59. 59 Falling-Load Generators operates at shortest time + highest mA uses series of steps (mA + t) to achieve mAs

60. 60 Miscellaneous Terms (cont.) kilowatt rating (review) power output of the generator power that the tube can use power formula