ELECTRICITY & ELECTROMAGNETISM TRANSFORMERS + ETC

Transcription

1 Circuitry, Formulas & Electricity Ch5 Bushong RT Lect # 3 1 RT 244 WEEK 10 rev LECTURE # 3 ELECTRICITY & ELECTROMAGNETISM TRANSFORMERS + ETC BUSHONG CH. 4 & 5 REF: CARLTONS CH 3, 4 & 5 & PHYSICS CD 4 & 5 1

2 Wavelength is the distance from the peak of one wave to the peak of the next wave. Frequency refers to the number of waves that go by a specific point in one second. Remember that electromagnetic energy waves all travel at the same speed the speed of light 3 Measured in Hertz or angstrom 4 2

3 Electric Circuits 5 Modifying electric flow and controlling electricity results in an electric circuit. Electric Potential 6 Energy =?* Electric charges have potential energy, when positioned close to each other. * EMF 3

4 Capacitors A device that is capable of accumulating and storing an electrical charge 7 A parallel plate capacitor ELECTRIC POTENTIAL (EMF) Potential difference between two charges that makes the current flow (there does not have to be an actual flow just the potential difference The force or strength of electron flow Voltage is an expression of electric potential. electric potential is the ability to do work due to separation of charges The volt is equal to the amount of work (joules) that can be done per unit of charge 220 volts sent to x-ray machines Joule is the SI unit for both mechanical energy and work Work of a battery 8 4

5 VOLT= THE POTIENTAL DIFFERENCE Voltmeter measures the voltage across the circuit 9 Ammeter measures current Ohmmeter- measures resistance of one resistor in circuit switch must be closed for current to flow Properties Of Electricity Voltage Current Resistance the units of measure for electric potential (kev) = voltage current = amperage are the same units we use as technologists to express technical factors on the x-ray machine operating console. kvp is kilovoltage peak and ma is milliamperes. 10 5

6 CURRENT Rate of Electron Flow Ampere or Amp 1 Amp = 1 Coulomb Flowing In 1 Sec Ac = 60 Cycles Per Sec (50 cycles in Europe) People sometimes mistakenly use the word "volt" as if it referred to the current passing through a conductor. the Volt refers to the difference in electric potential between the two charges that make the current flow. The actual flow of electrons is current CURRENT (ma) The # of electrons flowing past a given point per unit of time. AC Alternating current when electrons flow in one direction and then the other DC when electrons all flow in one direction 6

7 Current flows in opposite direction of the electrons 13 AC electrons Flow Alternately DC electrons Flow in one direction Amperes = columbs/sec One ampere equals one coulomb flowing by in one second: Voltage and amperes are related in terms of how they affect the strength of an electric current. 1. A low-voltage, high-amperage current has many electrons moving 2. A low-amperage, high-voltage current with fewer electrons moving may be just as powerful because of the higher potential. Which one of the above describes the X-ray machine? 14 7

8 Resistance Ω ( OHM) Resistance is the property of an element in a circuit that resists or impedes the flow of electricity 15 The amount of opposition to flow Conductor material that permits electrons to flow easily Insulator - inhibits the flow of electrons OHM S LAW: V= IR States that the potential difference (voltage) across the total circuit or any part of that circuit is equal to the current (amperes) times the resistance. V = Potential difference in volts I = Current in amperes R = Resistance in ohms ( ) 16 V= IR I =V/R R=V/I 8

9 17 ELECTRIC CIRCUIT IS THE PATHWAY FOR ELECTRIC CURRENT What measures Electric potiential? Current? What are the definitions of each? State the meaning of Ohms Law V = IR 18 The voltage across the total circuit or any portion of the circuit is equal to the current times the resistance. According to Ohm s Law, what would the voltage be if the resistance is 2 and the current is 4 ampere? A. 2 volt B. 4 volt C. 8 volt D. 10 volt 9

10 R = V/I 19 The resistance in a circuit is equal to the voltage divided by the current According to Ohm s Law, what would the resistance be if the voltage is 110 volt and the current is 5 ampere? A. 22 B. 55 C. 220 D. 550 I = V/R 20 The current across a circuit is equal to the voltage divided by the resistance. According to Ohm s Law, what would the current be if the voltage is 12 volt and the resistance is 1.5? A. 2 Ampere B. 4 Ampere C. 6 Ampere D. 8 Ampere 10

11 According to Ohm s Law, 21 what would the resistance be if the voltage is 220 volt and the current is 10 ampere? volts of potential difference causes a current of 2 ohms resistance What amperage is produced? 11

12 Transformers & Formulas Autotransformer Step Up Step Down TRANSFORMER FORMULAS (STEP UP OR DOWN) 24 V = voltage N = # turns p = primary s = secondary I = current Vp = N p Vs Ns Vp = I s Vs Ip Np = I s Ns Ip 12

13 Transformer Review 25 Turns Ratio N N S P Transformer Law N N S P V V S P I I P S The number of turns in the primary and secondary coils of a transformer determines whether it will increase or decrease voltage and by how much. In other words, the number of turns in the coil "cut" by this magnetic field determines the magnitude of the induced voltage as reflected by the transformer law formula: 26 Example: A transformer has 100 turns in the primary coil and 10,000 turns in the secondary coil (a turns ratio of 10,000/100 or 100/1). If 500V is applied to the primary side, what will the output voltage be? Calculate as follows: Vs/500V = 10,000/100 Vs/500V = 100/1 Vs = 500V x 100 = 50,000V Simply stated, if there are more turns in the secondary coil than in the primary coil, voltage will be increased. The opposite is also true: If there are more turns in the primary coil than in the secondary coil, voltage will be reduced. 13

14 Vp = N p Vs Ns 27 Transformer has a turns ratio of 1 to 200. There are 250 volts on the primary side, what is the voltage on the secondary side? 28 The Transformer has 100 turns on the Primary side, 100 volts and 10 amps. The secondary side has 50,000 turns of wire. What is the current AND voltage supplied to the secondary side? volts = kvp amps = ma 14

15 29 A radiograph using 200 ma 1/20 sec 55 kvp of a hand was taken in a 3Ø 12p room. What do you use in a single phase room? PROBLEM: 30 A TRANSFORMER HAS A TURNS RATIO OF 1:500 With a supply of 220 V and 50 Amps What is the KVP + MA supplied to the tube? 15

16 = 1 x = 110,000 volts x 500 x = 110 kvp (volts to Kilovolts remove 3 0 s - or move 3 spaces to the left) 1 = x x =.01 Amp or 100Ma = 100 (amps to milliamps move 3 spaces to the rt) X-Ray Tube Circuit 32 What is the turns ratio? 16

17 Vp = N p Vs Ns v = N p v Ns 500 Turns Ratio Transformer Review N N S P Step Up V I 34 Transformer Law NS VS IP N V I P P S Step Down V I 17

18 Transformer Law N N S P V V S P I I P S 35 The Transformer has 100 turns on the Primary side, 100 volts and 10 amps. The secondary side has 50,000 turns of wire. What is the current AND voltage supplied to the secondary side? volts = kvp amps = ma 36 What is responsible for supplying a precise voltage to the x-ray machine? THE TRANSFORMER 18

19 The Earth 37 A huge reservoir of stray electric charges electric ground 38 ELECTRIFICAITON OF OBJECTS FRICTION CONTACT INDUCTION ELECTRIFICATION BY CONTACT ELECTRONS LEAVE YOUR BODY CONTACT THE BALLOON 19

20 Electrification 39 Electrification = process of electrons being added or subtracted from an object Balloon rubbed against your head (Friction) Collects electrons from you - sticks to the wall that has a positive charge Shuffling across wool rug e on shoes Touch door handle e s want to escape (Contact) Induction electrical fields acting upon each other like in the circuitry of the x-ray equipment X-ray Tubes have complicated wiring 40 SERIES CIRCUIT (all circuit elements are connected in a line along the same conductor PARALLEL CIRCUIT (elements bridge the circuit rather than lie in a line along the conductor) 20

21 PARALLEL & SERIES circuit 41 EX: CHRISTMAS LIGHTS One line all bulbs go out Separate lines Only bulb burns out Rules for Simple Series Circuits 42 The total resistance is equal to the sum of the individual resistances. The current through each circuit element is the same and is equal to the total circuit current. The sum of the voltages across each circuit element is equal to the total circuit voltage. 21

22 43 Rules for Parallel Circuit The sum of the currents through each circuit element is equal to the total circuit current. The voltage across each circuit element is the same and is equal to the total circuit voltage. The total resistance is the inverse of the sum of the reciprocals of each individual resistance

23 Series Circuit Formula: 45 Current: I T = I1 =I2 =I3 Voltage: V T = V1 + V2 + V3 Resistance: RT = R1 + R2 + R3 Current: IT = I1 + I2 + I3 Voltage: Resistance: Parallel Circuit Rules VT = V1 = V2 = V RT = R1 + R2 + R3 (REMEMBER TO FLIP SIDES RT/1) 46 23

24 Review Problems on Handout Set up the formulas What is the total current in a series circuit with 3 resistances, each supplied with 10 amperes? 5. What is the total voltage in a series circuit with 3 resistances, each supplied with 10 volts? 6. What is the total resistance of a series circuit with resistances of 2.5, 4.2, 6.8? Review Problems on Handout Set up the formulas amperes volts , 4.2, 6.8 =

25 Review Problems on Handout Set up the formulas What is the total current in a parallel circuit with 3 resistances, each supplied with 10 amperes? 8. What is the total voltage in a parallel circuit with 3 resistances, each supplied with 10 volts? 9. What is the total resistance of a parallel circuit with resistances of 2.5, 4.2, 6.8? Review Problems on Handout Set up the formulas amperes volts 9. 1/2.5, 1/4.2, 1/ 6.8 = =.79/1 =

26 Find the Resistance: 51 What is the total resistance of a parallel circuit with resistances of 10, 10, 20? What about a series circuit? What type of circuit is this? 52 26

27 CIRCUITS 53 Short Circuit Resistance = Reduces The Flow Of Electricity (Too Much Will Blow Out Circuits) HIGHER RESISTANCE=LOWER FLOW Of Electrons FUSE ENCASED IN GLASS IN THE CASE OF A SHORT CIRCUIT THE HIGHER CURRENT WILL MELT THE FUSE STOPPING THE FLOW OF ELECTRICITY CIRCUIT BREAKERS HAVE REPLACED FUSES - POWER TOO HIGH IT WILL CUT OFF not damage appliance 54 27

28 55 A circuit breaker acts in the same manner as a fuse. If the current flowing through it rises above a certain level, the circuit breaker flips its internal switch to open the circuit and stop the electric flow. Any short circuit that lets the current rise to a dangerously high level will "trip" the circuit breaker and shut the system down. After the problem is corrected, the circuit breaker can be switched back on. ELECTRIC GROUND 56 2 WIRES CONDUCT CURRENT 3 RD WIRE CONNECTED TO A GROUND SOURCE KEEPS CURRENT FROM A LOOSE WIRE GOING DIRECTLY TO PERSON CURRENT ESCAPES THROUGH YOU 28

29 Ground to prevent shock - if there is a lose wire without a ground the electrons try to escape through your body Ground 57 A type of protection comes from a way of wiring circuits with an electric ground. Grounding is a process of connecting the electrical device to the earth via a conductor. X-ray imaging system 58 Convert electric energy to electromagnet energy. A well controlled electrical current is applied and converted to mostly heat and a few x-rays. 29

30 ELECTROMAGNETISM Electrodynamics study of electric charges in motion Conductor = electrons flow easily Insulator = electrons do not flow Semiconductors = some conditions behaves as an insulator and others a conductor. How the current gets to the TUBE Insulated cables 59 Magnetic force similar to electric force = Electric fields = exists around any charged particle Electromagnetism = fields When charged particles move = a magnetic field is induced Every moving charges produces a magnetic field 60 30

31 FERROMAGNETIC OBJECTS THAT CAN BE MAGNETIZED (IRON, COBALT, NICKEL) SIMILAR TO BALLOON 3 TYPES OF MAGNETS LODESTONE NATURAL (PERMANENT) ARTIFICAL N & S INDUCED ELECTROMAGNET temporary magnets produced by moving electric current 61 Ferromagnetic material such as iron attracts magnetic lines of induction, whereas nonmagnetic material such as copper does not. MAGNETS 62 USUALLY MADE OF IRON EVERY MAGNET HAS A NORTH AND SOUTH POLES LIKE SIMILAR CHARGES REPEL OPPOSITES ATTRACT 31

32 63 TESLA measurement of magnetic strength - used in MRI Demonstration of magnetic lines of force with iron filings 64 NORTH & SOUTH POLES If a single magnet is broken into smaller and smaller pieces, baby magnets result 32

33 65 A moving charge creates a magnetic field When a charged particle is in motion a magnetic force field perpendicular to the motion is created Solenoid & Electromagnet A coil of wire is a helix Supplied with current it is a solenoid SOLENOID: Current flowing through a wire coil of wire Add an iron core simple form of ELECTROMAGNET Putting a magnet in the middle of the coil of wire increases the strength if the electromagnet s magnetic field 66 33

34 ELECTROMAGNETISM 67 A MOVING CHARGE CREATES A MAGNETIC FIELD In Electromagnetism - MOVEMENT OF ELECTRONS IN A ELECTRIC CURRENT THAT CREATS AN ELECTRIC FIELD SEEN ON A COMPASS RT HAND RULE 68 Current flow direction of thumb Magnetic filed fingers An electric current is considered to be a + flow The negatively charged electrons are moving in the direction opposite to the current flow 34

35 RT HAND RULE 69 Direction of magnetic current lines When wire is looped magnetic field is strengthened = 2x more Adding more loops increases strength Magnetic lines curve around to other pole TRANSFORMER PRINCIPLE 70 When the wire that is conducing the current is looped The magnetic field is strengthened It is now 2x as strong The MORE the LOOPS The STRONGER the field INCREASE # OF COILS OF WIRE INCREASES THE VOLTAGE 35

36 Armature 71 A coil of wire that is rotated in a magnetic field More turns of coil the higher the voltage Look at diagram of x-ray tube Armature surrounds neck of anode How Electric & Magnetic Fields Interact 72 Faraday discovered that the magnetic lines of force and the wire must have a motion relative to each other to induce an electrical current 36

37 ELECTROMAGNET INDUCTION 73 Moving a wire through a magnetic field will induce a current (Faraday) Wire or field can move Moving a magnet through a coil of wire will induce an electrical current Faraday s Laws : or how to increase the strength of the induced current Increase the Strength of field or size of magnet Increase the SPEED of motion Change the ANGLE (more perpendicular) Increase the Number of Turns of coil 74 37

38 ELECTROMAGNETIC INDUCTION 75 3 WAYS TO CREATE MOTION BETWEEN LINES OF FORCE AND A CONDUCTOR Move the conductor through mag field Move magnetic lines of force Vary the magnetic flux 76 ELECTROMAGNET INDUCTION MOVING A BAR MAGNET THROUGH A COIL OF WIRE WILL INDUCE A CURRENT TO FLOW THROUGH THAT WIRE 38

39 INCREASING VOLTAGE 77 Increasing the number of coils of wire will increase magnetic field strength Increasing the number of coils moving in a magnetic field will increase the voltage induced Doubling the # of turns of wire = Doubles the Voltage INCREASING CURRENT 78 Increasing the strength (size of bar) of the magnetic field will increase the current Increasing speed of motion through wires will increase current 39

40 Increasing Current 79 2 turns of coil and moved 1 / sec 4 turns of wire (2x more) and moved 3/sec How much stronger is current? 2 x 3 = 6 times stronger Angle of motion 80 Motion of the wire perpendicular to the magnet (magnetic field) produces more current than a magnet that is at an oblique angle 40

41 Faraday s law? 81 Regulate the strength of the induced current BY INCREASING: of the Magnet of the motion of the magnet on the conduction coil Faraday s law 82 Regulate the strength of the induced current Strength of the Magnet Speed of the motion Angle of the magnet Number of turns on the conduction coil 41

42 AC magnetic field moves in and out MUTUAL INDUCTION 83 MUTUAL INDUCTION (STEP UP & DOWN TRANSFORMERS) 84 42

43 pg 95 Transformer Design 85 Closed core (open) auto Shell type SELF INDUCTION SIMILAR TO 2 COILS WRAPPED ON ONE CORE (Self induction occurs in single coil of wire the flow of electrons in one direction produces a current (in the same wire) then when flow of current changes polarity of magnet changes) 86 43

44 AUTOTRANSFORMER Autotransformer Self Induction There is only one wire but works like when there are 2 wires = The windings are used as the primary and secondary coils The induced voltage varies on where the outside wires are connected (KVP Taps) 44

45 TRANSFORMERS 89 STEP UP OR DOWN OPEN CORE, CLOSED CORE OR SHELL TYPE ABOUT 95% EFFICIENT AUTOTRASFORMER = induction Functions to provide Both types require AC for operation 90 A transformer with more secondary windings than primary windings. 1. has a greater secondary voltage 2. has a greater power output than input 3. is a step-down transformer 4. none of the above 45

46 Transformer Efficiency All transformers must operate on AC to provide the collapsing magnetic fields that induce the voltage changes in the secondary coil Ideal Effciency no loss Reality best = ~95% induction Loss due to Cu (copper) resistance (Copper loss) resistance to flow in a conductor (lg) wire diameter will reduce loss Eddy currents Laminating the core reduces eddy loss Hysteresis occurs in the core due to the loss of energy because of constant changing AC current) Improved using silicon core material A C ELECTRONS SWITCH DIRECTIONS OF FLOW RECTIFIED = DC A LOOP OF WIRE ROTATED IN A MAGNETIC FIELD = PRODUCES A CURRENT WIRE FLIPS BACK & FORTH 46

47 Electric Motor 93 Current supplied creates and electric field around the coils are moved by the magnetic field. The motion makes the motor turn Direct Current makes sure the motor only turns in one direction An electric generator produces an electrical current by rotation loops of wire through a fixed magnetic field 94 47

48 Examples of Electric Circuit Elements 95 Generatorsconvert mechanical energy to electrical energy High Voltage Increases the output voltage from autotransformer to the kvp Falling Load Type of generator used in capacitor discharge Voltage falls approx 1 kvp/mas operates at shortest time + highest ma uses series of steps (ma + t) to achieve mas Where are these used? 96 48

49 High Voltage generator 97 THAT CREATE AN ALTERNATING CURRENT ARE CALLED: AN ALTERNATOR CONVERT MECHANICAL ENERGY INTO ELECTRICITY generators 98 Function to change energy in to energy Electrical current flowing through a conductor in one direction is A battery is a source of direct current 49

50 Control Console Line monitor Autotransformer Line compensator kvp selection ma Selection Timing circuit Time selection Circuit Sections 99 High Voltage X-Ray Tube Circuit Step-up transformer Rectification circuit ma meter X-ray tube Filament Circuit Step-down transformer Focal spot selection Filaments

51 101 Circuit Diagram of Imaging System