Download Basic Circuitry and X‐ray Production

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
Np
=
Vs
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
Image from: Stewart Bushong’s Radiologic Science for
Technologists
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
Image from: Stewart Bushong’s Radiologic Science for
Technologists
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
Image from: Stewart Bushong’s Radiologic Science for
Technologists
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
Image from: Stewart Bushong’s Radiologic Science for
Technologists
Filament Circuit
• Filament Transformer
– Is a step‐down transformer
– Reduces the voltage and raises the amperage in the filament circuit
Primary
Secondary
Image from: Stewart Bushong’s Radiologic Science for
Technologists
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!!
Image from: Stewart Bushong’s Radiologic Science for
Technologists