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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 Core type Shell 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 stepup 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 xray 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