X-ray Circuit and Generator Flashcards
What is a rectifier used for?
To convert the incoming AC current to DC for the x-ray tube
Where in the circuit would you find a step-down transformer and why?
At the filament circuit, because a step-down/filament transformer increases current (at the cost of decreasing voltage). A high current (between 3-6A) is required to heat the filament and induce thermionic emission.
Where in the circuit would you find a step-up transformer and why?
In the tube circuit. This increases by mains/industrial voltage (240/400V) into high voltage (20,000-150,000V) required for X-ray production.
What is the filament current?
The filament current is the current passed through the filament. It is usually between 3-6A and affects the size of the space charge and the tube current.
What is the tube current?
The tube current is the number of electrons leaving the space charge and travelling towards the anode. It’s measured in mA and is directly proportional to the size of the filament current.
Where is the autotransformer found and what are its functions?
It’s found at the beginning of the tube circuit.
It:
- Compensates for any voltage fluctuations to maintain a constant voltage
- Allows variable voltage selection to alter kVp
How does a transformer work?
They contain two electromagnets with varying numbers of coils. In a step-up transformer, a current is passed through the electromagnet with least coils, and this influences (via magnetism) the second electromagnetic to generate a current which is greater due to the higher number of coils. The reverse happens in a step-down transformer.
What are the two most common envelope materials?
Pyrex due to having good thermal expansion
Metal ceramic due to having good electrical insulation
What are some methods of heat dissipation in an x-ray tube?
- Via conduction to the oil heat sink encasing the tube
- Via conduction to the glass/metal ceramic envelope
- Via conduction to the rotating shaft
