Electrical Transformers and X-ray Circuit Components: Key Concepts and Formulas

What type of device converts mechanical energy to electrical energy?

generator

An electromagnetic device that changes AC from low voltage to high voltage and from high voltage to low voltage is termed a

transformer

The step-up transformer increases voltage and decreases amperage; therefore, it is used on the ________ side of the XR tube

anode

The step-down transformer decreases voltage and increases amperage; therefore, it is used on the _______ side of the XR tube

cathode

A transformer that converts high voltage to low voltage is

step-down transformer

A step-down transformer converts ____ to ___ volts for the cathode for thermionic emission

120; 10

A transformer that converts low voltage to high voltage is

step-up transformer

A step up transformer converts _____ to __________ volts for the anode

120; 120,000

A transformer works on the principal of ____________ induction

electromagnetic

What is the formula for a transformer

(Np/Ns) = (Vp/Vs)

What is the formula for current in a transformer

(Np/Ns) = (Is/Ip)

What is the formula for current and voltage

(Vp/Vs) = (Is/Ip)

What is the power loss formula

P = I2 x R

Voltage and amperage are _________ proportional to each other

inversely

Name the four types of transformers

air core type (the least efficient), open core type, closed core type, and shell core type (the most efficient)

Which type of transformer is this

air core

Which type of transformer is this

open core

Which type of transformer is this

closed core

Which type of transformer is this

shell type

To prevent power losses in two of the types of transformers, how are they constructed? Name the transformers

laminated steel plates for closed-core and shell-type transformers

Name the three types of power losses in transformers

copper losses, hysteresis, and eddy currents

Copper losses are due to

how thick the copper wire is (thicker the wire = less resistance)

Hysteresis power loss is due to

magnetic domains; lining up the atoms all at the same time and electrons become lazy/distracted

Eddy currents occur from

swirling currents of the magnet dipoles

WHICH TYPE OF LOSS HAS TO DO WITH SWIRLING CURRENTS?

Eddy currents

The whole purpose of step-up transformers is to increase the amount of voltage to...

kilovoltage for X-ray, done with 1000 turns on the secondary side of the transformer (low AC in and high AC (kV) out

What device allows you to determine the amount of kilovoltage that is needed for that particular type of exam?

the autotransformer

The autotransformer works on the process of _____ induction

self

An autotransformer has

one coil of wire and one magnet

Where is the autotransformer located within the circuit?

low voltage side or primary side

what is the sole purpose of the autotransformer?

It is the kVp selector, it sends the selected voltage to the step-up transformer to be converted to 1000 volts

kVp major

goes up or down by tens (50,60,70,80 etc.....)

kVp minor

goes up or down by single digits (1,2,3,4,5, etc.....)

When the voltage in the circuit increases, what happens to the amperage?

amperage is decreased to milliamps on the secondary side of the step-up transformer

What is the sole purpose of the step-down transformer? (give the amounts that the tube runs on)

step-down transformer decreases the voltage to 10 V and increases the amperage to 3-5 A for thermionic emission of the cathode

What are the three devices that control filament current?

rheostat, choke coil, and high frequency

What is a rheostat

variable resistor (mA selector) for small or large focal spot

What does a choke coil run on

self-induction (one coil, one magnet)

High frequency runs on __ for battery-operated devices

DC

Filament current is known as tube current, which is what setting on the control panel?

mA selector (small or large focal spot size)

Small focal spot is an mA that is

below 100 (small parts and breathing techniques)

Large focal spot is an mA that is

above 100 (big parts)

Which device is used to regulate the amount of voltage and amperage due to the amount of resistance on the line? (variable resistor)

rheostat

________ ____ control of filament current is used to maintain a constant potential across the line with little resistance

high frequency

Is high-frequency control used in single-phase or three-phase equipment?

triple phase (3 waves of current with 12 pulses and a dc chopper)

Which ancillary departments use high frequency generators to maintain a constant voltage and current output with a voltage ripple of less than 1%?

cardiac cath, interventional radiography, mammography, and some fluoro machines

Where in the X-ray circuit is the step-down transformer located?

in the filament circuit

A high frequency current works on the process of _______induction

mutual

High frequency requires ___ transformers

3

Transformers will operate only on what type of current?

AC, or they will explode with DC due to the excessive amount of heat

A transformer that has a turn ratio of 20: 1 is known as what type of transformer?

step-down transformer.

A transformer that has a turn ratio of 10: 100 is known as what type of transformer?

step-up transformer

In a shell type of transformer, the primary and secondary coils are wrapped how?

in the middle of the main core

Electrons from the filament are focused to the anode by what means?

by the focusing cup and the electrical potential difference between the anode and the cathode

What device is located on the outside of the X-ray tube?

Stator (electromagnetic induction motor)

Which device is used to convert AC to DC?

rectification unit with the use of diodes

How are step-up transformers arranged?

star, delta, y for a 3-phase unit

What are the two devices of rectification?

valve tubes and solid-state diodes

Where are all rectification systems located in the X-ray circuitry?

high-voltage side, after the secondary side of the step-up transformer and before the X-ray tube

Which type of rectification has only one diode?

self

Which type of rectification has two diodes?

half

Which rectification type(s) are the least efficient and can cause backflow to the X-ray tube?

self and half (both)

What are the three types of full-wave rectification?

Full-wave (single-phase), 3-phase 6-pulse, 3-phase 12-pulse (including HF)

Single-phase rectification has how many diodes?

4

Single-phase rectification is ____ phase, ____ pulse

1; 2

What is the efficiency factor for single-phase rectification

1.00

Voltage always drops to what for single-phase rectification?

zero

What is single-phase rectification's percentage of voltage drop?

100% (always drops

Three-phase, 6-pulse rectification has how many diodes?

6

True/false: three-phase, 6-pulse prevents voltage from dropping to zero

true

What is the efficiency factor for three-phase, 6-pulse rectification?

1.35

What is three-phase, 6-pulse rectification's efficiency %

87%

Three-phase, 12-pulse rectification has how many diodes?

12 diodes

What is the efficiency factor for three-phase, 12-pulse rectification?

1.41

What is the voltage ripple of three-phase, 12-pulse rectification?

3-5%

What is three-phase, 12-pulse rectification's efficiency %

95-97%

Three-phase generators are placed in what types of patterns?

star, delta, y

The most efficient type of rectification is known as

HF since its voltage ripple drops < 1% and runs at an efficiency of >99%

High frequency rectification of less than _____ percent of voltage drop/ripple

1

Which type of rectifiers do we use in modern x-ray equipment + why?

solid-state diodes because they are more efficient and use silicon to dissipate the heat

Solid-state diodes are made of what type of substance

silicon

Does an n-type compound have an extra electron or is it missing an electron?

Extra electron (n-type means negative charge)

Does a p-type compound have an extra electron or is it missing an electron?

missing an electron (p-type means positive charge)

An atom that has ______ electrons in its outer shell is known as neutral or stable.

8 (octet rule)

An atom that has an extra electron or is missing an electron is known as a

negative charge or an anion

What type of test determines the function of the rectifiers?

spinning top test for the timer

In a spinning top test, if dots are evident, it is what type of rectification?

single-phase: half-wave (60 dots for each hump or pulse of current) or full-wave (120 dots for each hump or pulse of current)

In a spinning top test, if an arch is evident, what type of rectification is it?

triple phase: 3 waves of 120 pulses, which = 360 degrees, or an arch (full circle)

If one rectifier is not working, the mAs will be what?

½ the amount of mas

And 55 kVp is really how many volts and how many milliamps?

55,000 volts and 0.2 amps

P-type and n- type semiconductors are a part of which rectification type?

solid-state diodes, modern equipment

If converting from a single-phase unit to any three-phase unit, what happens to your kVp?

decrease it by 12% in kVp

If converting from a single-phase unit to a three-phase 6-pulse unit, what happens to your mAs?

decrease it by 1/3 the mAs

If converting from a single-phase unit to a three-phase 12-pulse unit, what happens to your mAs?

decrease the mAs by half

Going from a single-phase unit to a three-phase 12-pulse unit

½ the mAs

Going from a three-phase 12-pulse unit to a Single-Phase unit

2x the mAs

Going from a Single-Phase unit to a 3 Phase 6-pulse unit

decrease by 1/3 mAs

Going from a 3 Phase 6-pulse unit to a single-phase unit

increase by 1/3 mAs

Going from a Single phase to a 3 phase(anything)

decrease by 12% kVp

Going from a 3 Phase (anything) to a single-phase

increase by 12% kVp