Rad Tech 110

Circuits

Conditions Necessary X-ray Production

• High voltage– In the kilovoltage range

• Electrons– A supply of electrons– A need to stop the electrons suddenly

Types of Transformers

Shell typeCore type

How do transformers work?

• They can only work using AC current

• On the principle of induction– Mutual– Self

• The basic premise is that AC current ‘induces’ alternating magnetic fields.

Transformers work?

• These alternating magnetic fields are distributed throughout the core of the transformer.

• The alternating magnetic fields ‘induce’ an electrical current in loops (coils) of wire.

What gets transformed?

• Both voltage and current• In a step-up transformer the voltage is

increased– The primary side (incoming) has less coils than

the secondary (outgoing) side.– Because there are more coils on the secondary

side a higher voltage is produced• Increases voltage is reflected as a higher amplitude

of the waveform.

• At the same time as voltage increases the current correspondingly decreases.

• This occurs due to the conservation of energy.– If you increase one aspect, voltage, you have to

decrease the other, current.

– (Voltagep)(currentp)=(voltages)(currents)

Step down transformer

• Here the primary side has more coils than the secondary side.– The result is a decrease in voltage through the

transformer.

The X-ray Circuit

Three sections of the x-ray circuit

• Operating (control) console

• High voltage generator

• X-ray tube

Operating (control) console

• Line voltage compensator

• Autotransformer

• kVp selector

• mA selector

• Timer

• Pre-reading kVp meter

Line voltage compensator

The purpose of the line voltage compensator is to maintain a constant voltage to the system.In the modern system this is done automatically.

Autotransformer

The autotransformer works on the principle of self-induction. It has a single core and is responsible for varying the voltage.Because of its ability to adjust voltage, the autotransformer can be either a step-up or step-down transformer.

kVp selector

• kVp is adjusted at the autotransformer

• Taps are available so that different voltages can be achieved.

Pre-reading kVp meter

• The kVp meter is considered pre-reading because it is not actually measuring kVp but measuring voltage off the autotransformer.– Remember, the autotransformer is used to

adjust voltage.

Timer

• Historically, there have been many types of timers.

• Today, all timers are electronic timers of various types.– mAs– Phototiming (AEC)– Regular electronic

mA selector

• Allows for adjust of the filament voltage– Precision resistors– Choke coil

High Voltage Generator

• Step-up transformer– High voltage transformer– High tension transformer

• Step-down transformer– Filament transformer

• Rectifiers

Step-up Transformer

• This transformer is responsible for producing the high voltages necessary for x-ray production.– Turns ratio of 500:1 or 1000:1

Filament Transformer

• Intended to lower voltage and increase current

• Allows for thermionic emission to occur at the filament

• Ultimately, provides the electrons necessary for x-ray production.– Tube current measured in mA.

Rectifiers• Current traffic cops

– Intended to allow electrons to flow in only one direction

• Provide the mechanism that converts AC to DC current.

• 4 rectifiers are required to fully convert AC to DC.

Types of Circuits

• Single phase– Full wave– Half wave

• Three phase– 6 pulse– 12 pulse

• Medium and High Frequency• Capacitor discharge

– Found predominantly in portables.

Single Phase

• Full

• Half

Three phase

• 6 pulse

• 12 pulse

Three phase transformers

• Three phase units use delta and ‘wye’ transformers

• 6 pulse– 2 ‘wye’ and 1 delta

• 12 pulse– 2 delta and 1 ‘wye’

• They also require 12 rectifiers

Advantages of 3 phase

• Higher beam quantity and quality

• Higher mA stations are also possible

Why higher quantity and quality for three phase?

• Because the voltage ripple is less– Basically when the tube is energized it stays

energized.

full

3 phase 12 pulse

Medium/High Frequency Generator