X-ray generators

Question 1

What is the purpose of an electrical transformer?

Answer 1

To change the voltage of a current?

Question 2

How do electrical transformers work?

Answer 2

There are two coils with a different number of twists/ turns in each.

A current is run through one of the coils. The current running through the coil generates a changing magnetic field.

This changing magnetic field generates a current in the other wire.

The relative voltage of the currents is proportional to how many twists/ turns there are in the coils.

Question 3

What is the first law of transformers?

Answer 3

Secondary voltage (output) is related to primary voltage (input) by the ratio of the number of turns (N) on the coils.

Question 4

What is the second law of transformers

Answer 4

Product of voltage and current in the two circuits must be equal

Question 5

What is the problems with using alternating current for x-ray generation?

Answer 5

1. It’s only positive half the time (so it only generates x-rays half the time)
2. It’s negative half the time (can cause damage to stuff)
3. it varies a lot in it’s intensity

Question 6

What device lets through only the positive part of an alternating current?

Answer 6

Rectifier

Question 7

What device reverses the negative part of an alternating current?

(to make the whole thing positive)

Answer 7

bridge rectifier

Question 8

What is fluctuation in the electrical output of current called?

Answer 8

ripple

Question 9

How is ripple calculate

Answer 9

difference between max and minimum voltage reached (out of max voltage)

Question 10

What is the waveform of an alternating current that’s been modulated by a rectifier called?

Answer 10

a half-wave rectified waveform

Question 11

What is the waveform of an alternating current that’s been modulated by a ‘bridge rectifier’ called?

Answer 11

a full-wave rectified waveform

Question 12

What device reduces the ripple of a full rectified waveform current further?

Answer 12

a three phase generator

Question 13

how does a three phase generator work?

Answer 13

each current is out of sync with the others by 1/3 of a cycle (120 degrees).

The currents are added so that the minimum voltage never gets that low (but the maximum doesn’t increase at all)

Question 14

What is a high-frequency inverter generator?

Answer 14

a new device that lowers ripple, it’s complicated how it works.

Rectifies current to be a had wave rectified current
Smooths the current to be pretty similar to direct current
Uses inverter to turn into a very high frequency alternating current
rectified this current to be a very high frequency positive only current
Then smooths this current to be a pretty low ripple current

Question 15

How much ripple would you expect on a three phase, 6-pulse or medium frequency inverter?

Answer 15

~15%

Question 16

How much ripple would you expect on a three phase, 12-pulse or high frequency inverter?

Answer 16

~4%

Question 17

What effect does ripple have an the spectrum of x-rays produced?

Answer 17

lowers the overall quantity

lowers the average energy of x-rays produced

Question 18

What does AEC stand for in x-ray production?

Answer 18

Automatic Exposure Control

Question 19

What does Automatic Exposure Control do?

In x-ray production?

Answer 19

stops production of x-rays when:
1. enough have been produced for a good image

OR

2. Not enough X-rays are getting through

OR

3. If settings are grossly wrong

OR

4. Set time has passed