4. Generators Flashcards
What is the generator principle?
A change in magnetic field creates Voltage by using electromagnetic induction
What type of generators are the best to create voltage?
High frequency generators
Define self rectification in relation to x rays:
-Since the x-ray tube is AC, and e- can only flow in one direction in the tube, only half the amount of e- are reaching the anode (time would have to be increased to get all e- across)
Define Rectifiers:
-They allow DC through the x-ray tube to end up at the cathode even if the wire is AC
-Electrons travel through the line in the arrow
What are the 2 classifications of generators?
- Waveform
- Rating
Define rating:
The max power of the generator.
-The max mA a generator can support at 100kVp for 100ms
What are the 5 types of waveforms?
- Half wave
- Full-wave
- 3 phase-six pulse
- 3 phase-twelve pulse
- High frequency
Describe single-phase generators
-It is one coil rotating within a magnetic field and uses electromagnetic induction to create voltage in another wire
-It is AC with 60 hz f
Describe 3 phase generators
-3 coils in a magnetic field rotating
-Each are 60Hz but 120 degrees out of phase with the other
-Circuits kept separate until after rectification
What are the 2 types of 3-phase generators?
- Delta connection
- Star (Y) connection
What are 2 benefits of high f generators in an x-ray?
- Better beam quality
- Gives you almost constant voltage
What are the 6 steps of the high-frequency from the source to the tube?
- Rectification: Changes from 60Hz AC to supply DC
- Smoothing
- Inverter
- High tension transformer: Steps up from V to kV and makes even higher frequency
- Rectification: From AC to DC
- Smoothing: High f DC kV to constant DC
What does an inverter do?
Rapidly switches the polarity of the V and changes DC to AC, makes nearly constant V
What does smoothing do?
Capacitors/batteries smooth V to make it constant
What is Ripple?
It is the variance of Voltage
What are the 2 types of Ripple?
- Half-wave+Full wave ripple
- 3 phase and high frequency ripple
What does it mean if you have a low ripple in relation to energy of the beam?
It will produce a higher average energy on the beam
What are the 5 advantages of high frequency generators?
-Small size
-Efficient
-Better beam quality
-Higher tube ratings
-Gives you almost constant V
What are 2 advantages and 2 disadvantages of falling load generators?
Advantages:
-Never exceeds the tube ratings
-Highest mA, shortest exposure time-drops mA
Disadvantages:
-Increased tube wear
-Focal spot blooming
What are 2 advantages and 2 disadvantages to capacitor discharge?
Advantages:
-Cheaper
-Light
Disadvantages:
-Voltage drops
-Effects image quality
What is 1 advantage and disadvantages of modular generators?
Advantage:
-Cheap
Disadvantage:
-Can only use one room at a time
What are the advantages of poly phased generators?
- Lower ripple
- Lower patient dose
- Almost constant V
List the various types of generators from highest allowable tube ratings to lowest.
- High f
- 3 phase
- Single phase
How do capacitor banks work in high f generators?
-Maintains V by charging and discharging at the same time
-Increases the minimum V to decrease the ripple
