Transcript Rad Tech 110

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
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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