Transformers in X-ray Machines

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Questions and Answers

What is the primary purpose of a high tension transformer in an x-ray machine?

To supply high voltages necessary for x-ray production (correct)

To allow for kVp selection

To increase current for the filament circuit

To provide low voltage for thermionic emission

Which transformer type is used to supply the filament circuit and ensure thermionic emission occurs?

Step up Transformer

Autotransformer

Filament Transformer (correct)

High Tension Transformer

In the context of mutual induction, what causes an electromotive force (E.M.F.) to be induced in one coil?

Inductive reactance of the circuit

Current flow in the same coil

Current change in a neighboring coil (correct)

Resistance in the circuit

How does an autotransformer function within an x-ray machine?

It provides high and low voltage options for different circuit needs Signup and view all the answers

What is the relation between the primary and secondary winding numbers in a step-up transformer?

The secondary number is more than the primary Signup and view all the answers

What is the primary function of a high tension transformer in an x-ray machine?

To change low voltage into high voltage Signup and view all the answers

How does an autotransformer function in an x-ray machine?

It supplies varying levels of filament current Signup and view all the answers

What is the role of a filament transformer in the x-ray system?

To supply the necessary current for heating the x-ray tube filament Signup and view all the answers

What is a key characteristic of transformers in an x-ray machine?

They change voltage levels without changing frequency Signup and view all the answers

What is the main function of the high tension transformer as mentioned in the content?

To supply high voltage required for x-ray photons Signup and view all the answers

Which transformer is located within the control panel of the x-ray machine?

Autotransformer Signup and view all the answers

Which of the following describes a benefit of using a filament transformer?

It ensures consistent filament temperature Signup and view all the answers

What does the term 'radiation quality' in x-ray systems refer to?

Penetrating ability of x-ray photons Signup and view all the answers

Which factor influences both radiation quantity and quality in an x-ray system?

kVp setting Signup and view all the answers

What is measured by the HVL in x-ray systems?

Penetrating power of x-ray photons Signup and view all the answers

Study Notes

Principle of operation

Based on mutual induction
An electromotive force (EMF) is induced in a coil
When current in a neighboring coil changes

Constructional detail: Shell type

Windings are wrapped around the center leg of a laminated core

Core type

Windings are wrapped around two sides of a laminated square core

Transformers in x-ray machine

High tension transformer:
- Step-up transformer
- Primary winding number lower than secondary winding
- Supplies the anode circuit
- Responsible for producing high voltages needed for X-ray production
- Typical turns ratio 1:500 or 1:1000
Filament transformer:
- Step-down transformer
- Secondary winding number lower than primary winding
- Supplies the filament circuit
- Low voltage and high current
- Allows thermionic emission to occur at the filament
Autotransformer:
- Single-coil transformer
- Provides means for kVp selection
- Supplies power to other parts of the X-ray circuit
- Tube current is approximately 3 to 5 amps, depending on the filament temperature

Autotransformer – Example Calculation

Transformer input voltage (vin)
Output voltage (vout) can be switched between 0 and 120 VRMS
Turns ratio is 1500
Formula: vout/vin = NS/NP = turns ratio
Rearranging the formula: vout = vin × turns ratio
Substitute: vout-min = 0 V × 1500, vout-max = 120V × 1500
Answer: vout has a range of 0 V to 180,000 V (RMS)

Autotransformer Continued

Consists of a single coil of wire wrapped around an iron core

Operating Console

Console controls voltage (kVp) and current (mAs)
Radiation quantity:
- Total number of X-ray photons in the diagnostic beam
- Depends on kVp and mAs
- Usually expressed in mR or mR/ mAs, where R = roentgen (for US systems)
- Also expressed as ionizing charge per unit mass of air (SI unit), with 1 R = 2.58  10-4 C/kg
Radiation quality:
- Refers to the penetrating ability of the X-ray photons
- Determined by kVp
- Measured by HVL (Half Value Layer)

Mains Power

Mains power in the UAE is 220 VRMS
An X-ray set requires a large DC voltage
Generated from mains by rectification, amplification, and smoothing
Power system can be single-phase or 3-phase

Transformers in X-ray Machine

High tension transformer and filament transformer are inside the high tension tank
Autotransformer located in the control panel

Transformer

An AC device used to change high voltage, low current AC into low voltage, high current AC and vice versa without changing the frequency
It transfers electrical power from one circuit to another without a change of frequency
It accomplishes this by electromagnetic induction
There is no voltage loss in the remaining parts of the circuit
Formula: vout/vin = NS/NP = turns ratio
To power a 125 kVp x-ray tube, the transformer windings ratio is 403

Rectification

Converts AC voltage to a unidirectional voltage (all positive)
Done using a full-wave rectifier (diode bridge)
In the UAE, the period of the mains power is 1/50 seconds

Process of Rectification

Conversion of AC to DC
Half-wave rectification
Full-wave rectification
Dedicated circuits
- Contain diodes:
  - Semiconductor
  - Thermionic
- Power rating: Supply current to circuits

Half-wave Rectification

Only the positive half-cycle of the AC supply is allowed to pass

Half-wave Rectifier Circuit

Simple! Single diode
‘Load’: DC circuit; not truly getting DC

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Description

Explore the role of different transformers used in X-ray machines. This quiz covers high tension, filament, and autotransformers, including their operational principles and construction details. Test your knowledge on how these transformers function and contribute to X-ray production.