basic circuitry and x‐ray...

Basic Circuitry and

X‐ray Production

Lynn C. Sadler, MSRS, R.T.(R)(QM)

President, WCEC, Inc.

X‐Ray Production

• What are X‐Rays?

• Where do they come from?

• What are some characteristics of x‐radiation?

• How are x‐rays produced?

From the Beginning…….

• Why learn this “stuff”?

• Understanding circuits and electricity makes x‐ray production more understandable.

• Understanding x‐ray production and the characteristics of x‐radiation will make you a better technologist.

– How?

Circuit

• The path over which an electric current flows.

• Consists of a source of energy, a conductor, and a load or resistor(s) ‐ (something that utilizes the electricity).

Circuit

• Source of energy?

– Battery

– Generator

– Outlet in wall????

• Conductor?

– Gold

– Silver

– Copper

Types of Circuits

• Series

– Type of circuit where electron flow has only one path from beginning to end.

Types of Circuits

• Parallel

– Circuit has branches…. Electron flow has more than one path to take.

Factors in an Electric Circuit

• Potential Difference or Electromotive Force

– Volt

• Current

– Ampere

• Resistance

– Ohm

Potential Difference

• Potential Difference is the force that “drives” electron movement in an electric circuit– Sometimes shortened to PD

– Also referred to as “emf” or electromotive force

• The unit of potential difference is the “volt”– Voltage is used to measure potential difference

– The higher the voltage, the greater the potential difference or emf, the greater “speed” at which electrons “move” through the circuit.

Current

• Current is the number of electrons passing a given point per second in an electric circuit.– Is referred to as the “strength” or intensity of the circuit. (it’s a numbers thing)

• The unit of current is the ampere.– The higher the amperage the more electrons that pass a given point in the circuit every second.

– One ampere is equal to 6.25 x 1018

electrons flowing per second.

– That’s 6,250,000,000,000,000,000 electrons

Resistance

• Resistance is the property of an electric circuit that hinders or opposes the flow of electrons

• The unit of resistance is the ohm

• The four things that determine the resistance of a conductor are:

• Material

• Length

• Cross‐sectional area

• Temperature

Factors in a cirucit

• Potential difference, current, and resistance are inter‐related in a circuit.

• Changing one factor will have an effect on another factor.

• Ohm’s Law shows that relationship between voltage, amperage, and ohms.

Ohm’s Law

• Voltage = Amperage x Resistance (V = I x R)

– Remember this is a Very Important

Rule

V

I R

Ohm’s Law

• If voltage is increased, and resistance is constant, what would happen to amperage?

• If voltage is constant, and the resistance is increased, what would happen to amperage?

• If voltage is constant, and the amperage is increased, what would happen to resistance?

Ohm’s Law

• If the total voltage is 60 volts, and the total resistance is 20 ohms, what is the value of the current flowing through the conductor?

• If the total resistance is 10 ohms and the value of the current is 6 amps, what is the total voltage?

But Wait…… There’s More!

• One can also talk about current or a circuit in terms of power.

• Electrical energy, just as any other form of energy can perform work.

– Electrical energy is convertible to a definite amount of work and/or heat.

– The power of a circuit is a measure of the amount of work or heat produced.

– The unit of power is the watt.

Power of a Circuit

• P = IV or IV = P

– Power (in watts) is equal to amps x volts

– Remember IVP

• P = I2R

– Since V = I x R, one can replace the V in P = IV with I x R. That’s how we get this other formula.

– Power (in watts) is equal to amps squared x resistance

– Amperage produces a lot of heat. This formula is usually referred to as “power loss”

Power of a Circuit

• Power delivered to the x‐ray generator is essentially constant.

• One can not vary the wattage of the x‐ray circuits, but can manipulate the values of amperage and voltage and/or resistance.

• Just remember that amps x volts has to equal the wattage of the circuit.

The Basic X‐Ray Circuit

• Two Circuits

– Tube Circuit

• Provides all the wiring for the production of x‐rays

– Filament Circuit

• Provides a source of electrons so x‐rays can be produced

Tube Circuit

• Source:

– Alternating current outlet (AC)

– 220 Volts

– Line voltage compensator adjusts incoming voltage so that 220 volts is always delivered to tube circuit.

Tube Circuit Source

Main switch

AC Source

Image from: Stewart Bushong’s Radiologic

Science for Technologists

Tube Circuit

• Autotransformer

– Also known as the kV selector

– Allows you to vary the voltage sent to the rest of the tube circuit.

–Works on the principle of electromagnetic self‐induction

Autotransformer

Transformer Law

Ns Vs=

Np Vp

Image from: Stewart Bushong’s Radiologic Science for Technologists

Tube Circuit

• Exposure timers

– Determines the amount of time the tube circuit is energized.

– Five main types:

• Mechanical ‐ obsolete

• Synchronous ‐ obsolete

• Electronic

• mAs timers

• Automatic exposure controls (AEC)

Tube Circuit ‐ Exposure Timers


Tube Circuit

• High Voltage Generator

– Is a step‐up transformer

– Increases voltage values to kilovoltage values

–Works on the principle of electromagnetic mutual induction

Tube Circuit High Voltage Generator

Primary Side Secondary

Side


Tube Circuit

• Rectification System

– Changes alternating current (AC) to pulsating direct current (DC)

–Why? ? ? ?

Image from: Stewart Bushong’s Radiologic

Science for Technologists

Tube Circuit

• X‐Ray Tube

–Where x‐ray production takes place.

Filament Circuit

• Source

– Same AC outlet as for tube circuit


Filament Circuit

• “Rheostat”

– Is a variable resistor used to regulate the filament current

– Known as the mA selector

–Modern tubes don’t use this anymore but utilize a high‐frequency circuit to control filament current.

mA Selector in Filament Circuit


Filament Circuit

• Filament Transformer

– Is a step‐down transformer

– Reduces the voltage and raises the amperage in the filament circuit

PrimarySecondary


Filament Circuit

• Filament

– Current of the filament circuit passes through the filament in the x‐ray tube.

– High amperage of filament circuit causes the filament to become very hot.

– Electrons are “boiled off” of the filament in a process called thermionic emission.

Filament of X‐Ray Tube

Putting It All Together!!


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