4. Generators

Question 1

What is the generator principle?

Answer 1

A change in magnetic field creates Voltage by using electromagnetic induction

Question 2

What type of generators are the best to create voltage?

Answer 2

High frequency generators

Question 3

Define self rectification in relation to x rays:

Answer 3

-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)

Question 4

Define Rectifiers:

Answer 4

-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

Question 5

What are the 2 classifications of generators?

Answer 5

1. Waveform
2. Rating

Question 6

Define rating:

Answer 6

The max power of the generator.
-The max mA a generator can support at 100kVp for 100ms

Question 7

What are the 5 types of waveforms?

Answer 7

1. Half wave
2. Full-wave
3. 3 phase-six pulse
4. 3 phase-twelve pulse
5. High frequency

Question 8

Describe single-phase generators

Answer 8

-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

Question 9

Describe 3 phase generators

Answer 9

-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

Question 10

What are the 2 types of 3-phase generators?

Answer 10

1. Delta connection
2. Star (Y) connection

Question 11

What are 2 benefits of high f generators in an x-ray?

Answer 11

1. Better beam quality
2. Gives you almost constant voltage

Question 12

What are the 6 steps of the high-frequency from the source to the tube?

Answer 12

1. Rectification: Changes from 60Hz AC to supply DC
2. Smoothing
3. Inverter
4. High tension transformer: Steps up from V to kV and makes even higher frequency
5. Rectification: From AC to DC
6. Smoothing: High f DC kV to constant DC

Question 13

What does an inverter do?

Answer 13

Rapidly switches the polarity of the V and changes DC to AC, makes nearly constant V

Question 14

What does smoothing do?

Answer 14

Capacitors/batteries smooth V to make it constant

Question 15

What is Ripple?

Answer 15

It is the variance of Voltage

Question 16

What are the 2 types of Ripple?

Answer 16

1. Half-wave+Full wave ripple
2. 3 phase and high frequency ripple

Question 17

What does it mean if you have a low ripple in relation to energy of the beam?

Answer 17

It will produce a higher average energy on the beam

Question 18

What are the 5 advantages of high frequency generators?

Answer 18

-Small size
-Efficient
-Better beam quality
-Higher tube ratings
-Gives you almost constant V

Question 19

What are 2 advantages and 2 disadvantages of falling load generators?

Answer 19

Advantages:
-Never exceeds the tube ratings
-Highest mA, shortest exposure time-drops mA

Disadvantages:
-Increased tube wear
-Focal spot blooming

Question 20

What are 2 advantages and 2 disadvantages to capacitor discharge?

Answer 20

Advantages:
-Cheaper
-Light

Disadvantages:
-Voltage drops
-Effects image quality

Question 21

What is 1 advantage and disadvantages of modular generators?

Answer 21

Advantage:
-Cheap
Disadvantage:
-Can only use one room at a time

Question 22

What are the advantages of poly phased generators?

Answer 22

1. Lower ripple
2. Lower patient dose
3. Almost constant V

Question 23

List the various types of generators from highest allowable tube ratings to lowest.

Answer 23

1. High f
2. 3 phase
3. Single phase

Question 24

How do capacitor banks work in high f generators?

Answer 24

-Maintains V by charging and discharging at the same time
-Increases the minimum V to decrease the ripple