Ch. 10 - Production and Control of High Voltage / Regulation of Current in the X-ray Tube

What is a transformer?

a device that changes alternating current from low voltage to high voltage or high voltage to low voltage; converts volts into kilovolts

What principle does a transformer operate on?

mutual induction

What is an air core transformer?

two coils of wire side by side

What is transformer law?

emf induced in a secondary coil is to the emf in the primary coil, as the number of turns in the secondary coil is to the number of turns in the primary coil

What is a step-up transformer?

the secondary side has more turns; increases voltage and decreases current

What is a step-down transformer?

the primary side has more turns; decreases voltage and increases current

What is the equation for transformer law?

Vs/Vp = Ns/Np

In a diagnostic x-ray machine, what units do we use?

kilovolts (kV) and milliamperage (mA)

What is an open core transformer?

two coils side by side with an iron core within each of them

What is flux leakage?

when magnetic lines of flux are leaking out into the air causing a loss of power

What is a closed core transformer?

one continuous core

What type of current does a closed core transformer have?

eddy current

How does a closed core transformer minimize eddy current?

core is laminated and made of silicon steel

What is a shell type transformer?

two rectangular cut outs where the central area has a primary and secondary coil wound around the core

Which type of transformer is used in the x-ray machine?

close core transformer

Which type of transformer is used for commercial or industry use?

shell type transformer

Are transformers considered to be highly efficient?

yes

Copper Loss

power loss due to the resistance of the coil; minimized my an adequate diameter

Which side do you want to have a thicker diameter for copper loss?

the side with a higher current; example: in a step-up transformer, the primary coil should have a thicker diameter because it has lower voltage but higher current

Eddy Current Loss

swirling current set up in the core because of electromagnetic induction; this causes a waste of power; minimized by laminated sheets made of silicon steel

Hysteresis Loss

because the current is alternating the magnetic lines of flux are constantly changing direction, causing the domains to continually rearrange. There is a certain amount of resistance to this because magnetized material has a tendency to stay magnetize, so energy must be used to overcome this opposition to change each time ; minimized by laminated sheets of silicon steel

Autotransformer

kV selector; either increases or decreases the voltage from the incoming power supply and then send it to the step up transformer, the step up transformer has an unchangeable ratio so the autotransformer adjusts the voltage that is fed into it, so that the desired kilovoltage is produced

What principle does an autotransformer operate on?

self-induction

Where is the autotransformer located in the x-ray machine?

between the incoming power supply and the primary coil of the step-up transformer

What is the formula for autotransformer?

Vs/Vp = T/P

Main Circuit

high voltage current that produces the big potential difference across the tube that enable x-ray production

Filament Circuit

low voltage current used to heat the filament

Tube Current

the actual electrons that are traveling from cathode to anode

Filament Current

the current that is heating the filament

What is the relationship between filament current and tube current?

the small change in filament current, produces a large change in tube current

Choke Coil

coil of wire with a removable core; operates on the principle of self-induction

Rheostat

variable resistor that is used to regulate filament current (mA selector); the more resistance, the less current will flow