x-ray systems

where is the kV meter

where is the kV meter

on the primary side of the HVT

what does kV control

determines the penetrating quality of the beam

what is the purpose of a step up transformer

increases voltage for x-ray production

where is a step up transformer found

in a high voltage transformer (HVT)

what is the purpose of a step down transformer

adjust current to cathode filament to produce the heat required for thermionic emission of e-; controls number of x-rays; rheostat

where is a step down transformer found

in a filament transformer

what is a variable transformer

operates by self induction, selects a portion of the incoming line voltage

what does mA control

determines the number of e- boiled off at filament (thermionic emmision); quantity

where is mA meter

secondary side of HVT

what is a voltage ripple

variation in peak voltage waveform, less ripple→greater efficiency

what is the semiconductor material used for a n-type solid state rectifier

arsenic

what is the semiconductor material used for a p-type solid state rectifier

gallium

why do we need rectification

converts AC to pulsed DC for the x-ray tube to suppress or redirect unwanted parts of AC and ensure a steady voltage supply.

where does rectification happen

between the HVT and x-ray tube

what is full wave rectification

redirect unwanted part of the AC; requires at least 4 diodes; most common

what is half wave rectification

suppress unwanted part of the AC; limited use

what is self rectification

rarely used

what is automatic exposure control (AEC)

detects radiation that has passed through the patient, terminates exposure after set amount of radiation reaches sensing device; convert radiation into an electrical signal which will be used to automatically stop the exposure when the image receptor has reached the proper density

what is the purpose of positioning cells

three cells (two lateral, one central) that control when radiation is shut off

what is line voltage compensator

measures the voltage and adjusts to precisely 220 V

what is a mechanical timer

inexpensive, inaccurate for times less than 1/20s; used in portable and dental units

what is a synchronous timer

start/stop with AC cycle; 1 cycle=1/60s

what is an impulse timer

1 pulse= 1/120s

what is an electronic timer

when a precise voltage is reached in capacitor, the switch opens and terminates the exposure

what is a mAs timer

exposure is terminated when desired mAs is attained; highest mA shortest time

what are single phase timers (1ø)

mechanical, synchronous motor, impulse

what is a three phase timers (3ø)

electronic

what are the differences between 3ø and 1ø

3ø is more efficient, requires more complex circuitry and is more expensive compared to 1ø

what is the voltage ripple in 3ø 6 pulse

14% ripple

what is the voltage ripple in 3ø 12 pulse

4% ripple

what is the voltage ripple in 1ø

100%

what is the voltage ripple in high frequency

1% ripple

what is the power rating formula

mA • kV= W

what is the power rating formula for 1ø

mA•kV•0.7=W

what is #1

kV meter

what is #2

timer

what is #3

mA meter

what is #4

ammeter

what is #5

line monitor