Physics Test part 4

Question 1

Rectification

Answer 1

the process of changing alternating current into a pulsating direct current.

Question 2

X-ray circuits

Answer 2

Functions to convert electrical energy into electro-magnetic energy (x-rays). There are 3 main types.

Question 3

Single phase

Answer 3

Uses a single source of alternating current (voltage waveform is to the right).
There are two different types of single-phase x-ray machines:
1) Half wave rectified
2) Full wave rectified

Question 4

1/2 wave, 1-pulse, or self rectified

Answer 4

Uses only one half of the normal alternating current wave.
This is accomplished by the x-ray tube itself doing the rectifying or using 1 or 2 rectifiers. Takes longer to expose, only found in dental or small portables.

Question 5

Full-wave rectified or 2-pulse

Answer 5

Uses the full alternating current wave by incorporating 4 rectifiers that channel the pulses through the x-ray tube in the same direction. Twice as many xrays produced over 1/2 wave.

Question 6

3-phase (3Φ

Answer 6

This type of x-ray unit is powered by three separate sources of alternating current that are out of phase with each other by 120 degrees or 1/3 of a cycle. Voltage never drops to 0, shorter exposure times, less mA can be used.

Question 7

Disadvantages of 3 phase units

Answer 7

higher capital and installation costs (generally 3 times or more) and the larger size of the equipment due to the additional electronic components required.
3Φ units also generate more heat during x-ray production, so high-capacity rotating anode tubes must be used.

Question 8

3Φ, 6-pulse

Answer 8

Requires 6 rectifiers and rectifies ½ of the 3Φ alternating current so that 6 individual pulses pass through the x-ray tube each cycle for a total of 360 pulses/sec.

Question 9

. 3Φ, 12-pulse

Answer 9

Requires 12 rectifiers to operate which rectifies all of the 3Φ alternating current, resulting in 12 pulses or current passing through the x-ray tube per cycle or 720 pulses/sec.

Question 10

High Frequency Systems

Answer 10

These systems were created in the late 1980’s and have replaced most 1Φ systems in private offices and clinics.
This unit can be supplied with either a single phase or 3-phase AC that is sent into a microprocessor circuit prior to entering the high voltage section. These cans be smaller in size and less expensive.

Question 11

Voltage ripple

Answer 11

the amount of variation from the maximum or peak voltage that occurs during x-ray production: smaller number means more efficient

Question 12

1 phase voltage ripple

Answer 12

always 100% since the voltage falls from its peak all the way to zero and back to the peak value (it covers 100% of all possible values)

Question 13

3 phase 6 pulse voltage ripple

Answer 13

13 to 14 % since another peak is rising before the other can drop all the way to zero.

Question 14

3 phase 12 pulse voltage ripple

Answer 14

– 3.5 to 4%

Question 15

High frequency

Answer 15

– can range from <1% to 15% (comparable to 3Φ) depending on model).

Question 16

Control console

Answer 16

contains all controls for operating the x-ray tube and accessories, as well as various meters to monitor operation.

Question 17

High voltage or xray generator

Answer 17

contains the transformers and rectifiers

Question 18

Xray tube and accessories

Answer 18

Last xray circuit component

Question 19

Circuit breaker

Answer 19

Prevents circuit overload and required by federal law.
Often separate from the main unit.

Question 20

On/off switch

Answer 20

Federal law mandates a single throw-double blade or pole switch to prevent arcing.

Question 21

kVp selector

Answer 21

Made up of an autotransformer (also called a variac) and selects that proper voltage that will be fed to the step-up transformer.

Question 22

Line voltage compensator

Answer 22

Functions to keep the line voltage constant during x-ray production, since the line voltage can vary as much as 5% throughout the day.

Question 23

mA selector

Answer 23

Selects the amount of current to the filament of the x-ray tube.
Can consist of either a rheostat, choke coil, saturable reactor, or high frequency circuit, depending on the type of unit.

Question 24

Filament ammeter

Answer 24

Measures the number of amperes being sent to the filament of the x-ray tube and found only on older units.

Question 25

Exposure switch

Answer 25

Designed to begin the exposure but not end it (accomplished by a timer circuit).
For this reason, whenever the exposure switch is depressed, it must be held until both the audible and visible indicators have ceased.

Question 26

thyratron tube

Answer 26

is a triode (meaning 3 internal components) vacuum tube containing a cathode, anode, and grid. The grid normally contains a negative charge that will repel electrons from the cathode and prevent them from traveling to the anode.

Question 27

thyrister or microprocessor circuit

Answer 27

New units use this

Question 28

Timer Circuit

Answer 28

Functions to end the exposure at an accurately measured, preset time.
Timer circuits can be found in 7 basic types: