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 10 18 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 = I 2 R 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 highfrequency 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