Industrial Electronics N2 Module 1: Atom theory .................................................................................................................... 6 1.1 Introduction................................................................................................................................. 6 1.2 Matter ................................................................................................................................................ 6 1.2.1 Elements ........................................................................................................................................ 7 1.2.2 Compounds ................................................................................................................................. 7 1.2.3 Molecules ...................................................................................................................................... 7 1.3 The atom .......................................................................................................................................... 7 1.4 Covalent bonds.............................................................................................................................. 8 1.5 Electrical current flow ................................................................................................................... 9 Module 2: Direct Current Theory ................................................................................................... 11 2.1 Introduction............................................................................................................................... 11 2.2 Electromotive force (emf) ......................................................................................................... 11 2.3 Definition of the ampere............................................................................................................ 11 2.4 Voltage ........................................................................................................................................... 12 2.4.1 Definition of the volt ................................................................................................................. 12 2.5 Resistance ...................................................................................................................................... 12 2.6 Ohm’s Law ..................................................................................................................................... 13 2.7 Power ............................................................................................................................................... 13 2.8 Resistor circuits .............................................................................................................................. 14 2.8.1 Resistors in series ........................................................................................................................ 14 2.8.2 Resistors in parallel .................................................................................................................... 14 2.8.3 Series-parallel combinations.................................................................................................. 15 2.9 Kirchoff’s laws ................................................................................................................................ 16 2.9.1 Current law (first law) ............................................................................................................... 16 2.9.2 Voltage law (second law) ..................................................................................................... 17 Module 3: Alternating Current Theory.......................................................................................... 20 3.1 Introduction............................................................................................................................... 21 3.2 The cycle ........................................................................................................................................ 21 3.3 Frequency (f) ................................................................................................................................. 21 3.4 Period (t) ......................................................................................................................................... 21 3.5 Instantaneous value .................................................................................................................... 22 3.6 Average and rootmean (RMS) square values of a sinusoidal wave ............................ 24 3.6.1 Mid-ordinate rule method ...................................................................................................... 24 Gateways to Engineering Studies 1 Industrial Electronics N2 3.6.2 Average and RMS value, calculated method ................................................................ 25 3.6.3 Resistor (R), Capacitor (C), Inductor (L) circuits ............................................................... 26 Resistor (R) ............................................................................................................................................. 26 Capacitor (C) ...................................................................................................................................... 26 Inductor (L) ........................................................................................................................................... 27 R-L circuits ............................................................................................................................................. 28 R-C circuits ............................................................................................................................................ 28 R-L-C circuits ......................................................................................................................................... 29 3.7 Phasors ............................................................................................................................................ 29 3.8 Resonance series circuits ........................................................................................................... 29 Module 4: Semi-conductor Diodes .............................................................................................. 37 4.1 Introduction............................................................................................................................... 37 4.2 Silicon and germanium.......................................................................................................... 38 4.3 Valence electrons ....................................................................................................................... 38 4.4 Covalent bonds............................................................................................................................ 38 4.5 Doping............................................................................................................................................. 38 4.6 P-type material ............................................................................................................................. 38 4.7 N-type material............................................................................................................................. 39 4.8 Electron flow .................................................................................................................................. 40 4.9 Hole flow ......................................................................................................................................... 40 4.10 PN junction diode ...................................................................................................................... 41 4.10.1 Forward bias............................................................................................................................. 41 4.10.1 Reverse bias ............................................................................................................................. 42 4.11 Zener diodes ................................................................................................................................ 43 4.11.1 Properties of a zener diode ................................................................................................. 43 4.12 Varactor diodes ......................................................................................................................... 44 4.12.1 Properties .................................................................................................................................. 44 4.13 Photodiode .................................................................................................................................. 45 4.14 Light emitting diodes (LED) ..................................................................................................... 45 4.15 The halfwave rectifier with smoothing capacitor............................................................. 46 4.15 The full wave rectifier ................................................................................................................ 46 4.15.1 The centre tap rectifier without smoothing capacitor ................................................ 46 4.15.2 The centre tap rectifier with smoothing capacitor....................................................... 47 4.16 Bridge type rectifier (Four diodes)......................................................................................... 47 4.16.1 Without smoothing capacitor ............................................................................................. 47 4.16.2 With smoothing capacitor ................................................................................................... 48 Gateways to Engineering Studies 2 Industrial Electronics N2 4.17 Calculations ................................................................................................................................ 48 Module 5: Semi-conductor transistors ......................................................................................... 51 5.1 Introduction............................................................................................................................... 51 5.1.1 NPN transistor ............................................................................................................................. 52 5.1.2 PNP transistor .............................................................................................................................. 52 5.2 Operation of a transistor ............................................................................................................ 52 5.3 Basic amplifier circuit .................................................................................................................. 53 5.3.1 The transistor as a switch......................................................................................................... 54 5.4 Transistor circuit configurations ................................................................................................ 54 5.4.1 Common base .......................................................................................................................... 55 5.4.2 Common emitter ...................................................................................................................... 55 5.4.3 Common collector ................................................................................................................... 55 Module 6: Measuring instruments ................................................................................................ 57 6.1 Introduction............................................................................................................................... 57 6.2 Lenz’s law ....................................................................................................................................... 57 MOVING COIL METER, ANALOGUE TYPE ................................................................................................ 58 6.3 The ampere meter ....................................................................................................................... 58 6.3.1 Internal arrangement of shunt resistor for the ampere meter ..................................... 59 6.3.2 Multi range ampere meter .................................................................................................... 60 6.4 The volt meter ............................................................................................................................... 60 6.4.1Internal arrangement of multiplier for the voltmeter ....................................................... 60 6.4.2 Multi range volt meter ............................................................................................................. 61 6.4 The ohmmeter............................................................................................................................... 61 6.5 The analogue multi-meter ......................................................................................................... 62 6.6 The digital multi-meter ................................................................................................................ 63 Module 7: Transducers ................................................................................................................... 66 7.1 Introduction............................................................................................................................... 66 7.2 Light dependant resistor (LDR) ................................................................................................. 66 APPLICATION CIRCUIT .............................................................................................................................. 68 7.3 Thermocouples ............................................................................................................................. 68 CHARACTERISTIC CURVE .......................................................................................................................... 69 7.4 Bi-metallic strip .............................................................................................................................. 69 7.4.1Temperature sensitive transducer ......................................................................................... 69 7.5 Thermistor........................................................................................................................................ 69 Gateways to Engineering Studies 3 Industrial Electronics N2 Module 8: Syncro systems ............................................................................................................. 72 8.1 Introduction............................................................................................................................... 72 8.2 Lenz’s law ....................................................................................................................................... 72 8.2.1 Applications ............................................................................................................................... 72 8.3 Advantages of synchro systems over mechanical systems ............................................ 73 8.3.1 Acceptable symbols ................................................................................................................ 73 8.3.2 Operation.................................................................................................................................... 73 8.4 Wiring diagrams ............................................................................................................................ 73 Module 9: The decibel ................................................................................................................... 76 9.1 Introduction............................................................................................................................... 76 9.2 Formula ........................................................................................................................................... 76 Gateways to Engineering Studies 4 Industrial Electronics N2 Icons used in this book We use different icons to help you work with this book; these are shown in the table below. Icon Description Icon Description Assessment / Activity Multimedia Checklist Practical Demonstration/ observation Presentation/ Lecture Did you know? Read Example Safety Experiment Site visit Group work/ discussions, role-play, etc. In the workplace Keywords Take note of Theoretical – questions, reports, case studies, etc. Think about it Gateways to Engineering Studies 5 Industrial Electronics N2 Module 1 00 Learning Outcomes When you have completed this module, as a learner you will be able to: Draw sketches of the atomic structure to illustrate universal properties Describe: o Electron shells o Free electrons o Positive and negative charges Give an elementary description of: o Conductors o Insulators o Non-active elements 1.1 Introduction To understand electronics, you must first have an understanding of atoms and basic atomic structure. This module discusses atomic theory and explains the atom and its properties and how this applies to conduction and insulation. 1.2 Matter Matter is anything that has weight and takes up space. Matter cannot be created or destroyed. Matter exists in four different states, solid, liquid, gas and plasma. The earth and anything on it is classified as matter. Examples thereof: Solid matter are wood and stone Liquid matter are water and oil Gas matter are oxygen and helium Plasma consists of ionised particles such as lightning Matter can change its state from one form to another. If ice is heated it will become water and then steam. A solid has changed into a liquid form and then into a gas. Gateways to Engineering Studies 6 Industrial Electronics N2 Figure 1.1 Matter 1.2.1 Elements Elements are used to construct matter. Examples of elements are gold, copper, iron and silicon. 1.2.2 Compounds A compound consists of two or more different types of elements. A compound is formed when one or more elements react in a chemical way. For instance, water is a compound that is made up of the elements oxygen and hydrogen. 1.2.3 Molecules A molecule is the smallest part of a compound that still retains the characteristics of the original compound without breaking up into individual atoms. A water molecule is formed when two hydrogen atoms combine with one oxygen atom. 1.3 The atom The atom is the smallest part of an element that can take part in a chemical reaction. It has a nucleus that is build up of protons and neutrons, and has electrons that revolve around the nucleus in definite orbits or shells. Gateways to Engineering Studies 7 Industrial Electronics N2 Figure 1.2 The electrons in the orbits have a negative charge and they are attracted by the protons in the nucleus, which have a positive charge. Each orbit can take up only a certain number or electrons. The number of electrons in an orbit determined by the formula 2n². If the outermost orbit is incomplete (not completely filled with electrons), then that orbit is called the valency band. The electrons inside the valency band are called the valency electrons. The number of valency electrons in an atom is called the valency number of the atom. The protons in the nucleus have a positive charge, while the neutrons have no charge at all. The number of electrons and protons in a neutral atom are the same. The negative charge of electrons has the same amount of charge as the positive charge of the protons. The atom will thus be electrically neutral. The atomic number always indicates the number of protons or electrons in the atom. If the valency electrons are easily removed from the atom then the element to which these atoms belong is called a conductor. Electrons which have left an atom are called free electrons. When electrons are removed from an atom, the atom becomes positively charged. This positively charged atom is called a positive ion or a cation. When electrons are added to an atom, it becomes negatively charged and is called a negative ion. If electrons of an atom are not easily removable, the element is called an insulator. There exists elements which fall between conductors and insulators, and they are called semiconductors. 1.4 Covalent bonds Some atoms cannot exist on their own as a stable element. Such an atom must combine with another similar atom or with a completely different atom to form a certain type of material. Gateways to Engineering Studies 8 Industrial Electronics N2 When two such atoms combine, a covalent bond is formed. In a covalent bond, the two atoms involved each have one electron in the bond and they share these two electrons with each other. Covalent bonds are very strong and cannot easily be broken up. Figure 1.3 1.5 Electrical current flow Below is a metal bar which is connected to a cell. The chemical reaction that takes place causes the free electrons in the metal bar to be attracted by the positive terminal of the cell and to be repelled by the negative terminal. This causes an electrical current to flow from the negative terminal of the cell to the positive terminal. This type of current flow is referred to as electron current flow. When referring to current flow as being from positive to negative, it is called conventional current flow. Figure 1.4 Activity 1.1 1. Define the following: a. Matter b. Elements c. Compounds Gateways to Engineering Studies 9 Industrial Electronics N2 d. Molecules e. The atom f. Nucleus g. Electrons h. Conductor i. Insulator j. Covalent bond 2. Draw a model of an atom with an atomic number 28. 3. Draw a model of an atom which has 3 valence electrons. 4. Sketch two atoms in a covalent bond. Self-Check I am able to: Yes No Draw sketches of the atomic structure to illustrate universal properties Describe: o Electron shells o Free electrons o Positive and negative charges Give an elementary description of: o Conductors o Insulators o Non-active elements If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 10 Industrial Electronics N2 Module 2 Learning Outcomes When you have completed this module, as a learner you will be able to Describe and illustrate circuit diagrams and calculations of current, voltage and power for resistors in: o Series o Parallel o Series – parallel combinations Explain the definitions of Kirchhoff’s first and second laws Draw circuit diagrams of Kirchhoff’s first and second laws 2.1 Introduction Direct current can be defined that there is a fixed polarity of applied voltage and the current flows in one direction. The unit of electrical current is the ampere (A).Current flow is indicated by (I). Definition: Potential Difference (PD) The pd is the electrical pressure between any two points in a closed circuit. 2.2 Electromotive force (emf) The emf is that force that has the potential electrical energy to produce a current flow in a circuit. EMF is measured in an open circuit. An open circuit does not produce current flow. 2.3 Definition of the ampere There are two common definitions for the ampere: 1. If a current of one ampere flows through a conductor 6,25 x 1018 electrons will pass any point in one second. 2. One ampere is the constant current which, if maintained in two parallel conductors of infinite length and one metre apart in a vacuum, will exert a force of 2 x 10-7 newtons per metre. Gateways to Engineering Studies 11 Industrial Electronics N2 Basic unit Unit for small amounts Unit for large amounts Pronounced Ampere Abbreviation Multiplier Table 2.1 A 1 Milliampere mA 1 x 10-3 Kiloampere kA 1 x 103 Microampere 𝜇𝐴 1 x 10-6 Megaampere MA 1 x 106 Take Note: 1018 is a simple way of writing 1 followed by 18 zeroes which would be written as 1, therefore, if a current of 1 Ampere is flowing through a conductor the number of electrons passing a point every second would be 6,250,000,000,000,000,000 or 6,25 x 1018. 6,25 x 1018 electrons is called 1 coulomb (C) of electric charge. 1 ampere is therefore 1 coulomb per second. 2.4 Voltage Voltage is a general term for emf and pd, and are measured in volts (V). Voltage is usually indicated by E or V in a circuit. 2.4.1 Definition of the volt There are also two common definitions for the volt: 1. One volt is the pd between two points of a conducting wire carrying a constant current of one ampere when the power dissipated between these points is equal to one watt. 2. One volt is the potential difference across a resistance of one ohm when a current of one ampere is passed through it. Basic unit Pronounced Abbreviation Multiplier Table 2.2 Volt V 1 Unit for small amounts Unit for large amounts Milli-volt mV 1 x 10-3 Kilo-volt kV 1 x 103 Micro-volt 𝜇𝑉 1 x 10-6 Mega-volt MV 1 x 106 2.5 Resistance The process where an electron travels slowly and with difficulty in a conductor, is known as resistance. Resistance is expressed by R in a circuit and the unit of resistance is the ohm (Ω). Definition: Ohm One ohm is the electric resistance between two points of a conductor when a constant potential difference of one volt applied between Gateways to Engineering Studies 12 Industrial Electronics N2 these two points, produces a current flow of one ampere, and the conductor is not the source of any emf. 2.6 Ohm’s Law The amount of current flowing in any closed circuit is directly proportional to the applied voltage and inversely proportional to the resistance. Ohm`s law can be stated as a formula: V I R I is the amount of current in ampere (A). V the applied voltage in volts (V). R the resistance in ohms (Ω). Basic unit Unit for small amounts Unit for large amounts Pronounced Ohm Milli-ohm Micro-ohm Kilo-ohm Abbreviation Multiplier Table 2.3 Ω 1 mΩ 1 x 10-3 𝜇𝛺 1 x 10-6 kΩ 1 x 103 Megaohm MΩ 1 x 106 2.7 Power The amount of work done per second in an electrical circuit. The unit is watts (W), the symbol is (P). Power is generated by the applied voltage to a resistive circuit producing a current flow. The current produces heat in the resistor which is referred to as power dissipated in the resistor. P VI P I2 R V2 P R Definition: Watt One watt is the power which results in the production of energy at a rate of one joule per second. Basic unit Pronounced Abbreviation Multiplier Table 2.4 Watt W 1 Unit for small amounts Unit for large amounts Milli-watt mW 1 x 10-3 Kilo-watt kW 1 x 103 Micro-watt 𝜇𝑊 1 x 10-6 Gateways to Engineering Studies 13 Mega-watt MW 1 x 106 Industrial Electronics 2.8 Resistor circuits 2.8.1 Resistors in series RTOTAL = R1 + R2 + ....... R1 R2 Figure 2.1 Worked Example 1 Find the total resistance of the circuit shown. 4 5 3 Figure 2.2 Solution: RT = R1 + R2 + R3 =5 +4 +3 = 12 2.8.2 Resistors in parallel 1 1 1 R T R1 R 2 OR R T R1 R 2 R1 R 2 R1 R2 Figure 2.3 Worked Example 2 Find the total resistance of the circuit shown. Gateways to Engineering Studies 14 N2 Industrial Electronics N2 5 10 Figure 2.4 Solution: 1 RT 1 RT RT 1 1 10 5 0,3 3,33 RT OR RT 10 5 10 5 50 15 3,33 = 2.8.3 Series-parallel combinations Worked Example 3 Find the total resistance of the circuit shown as well as the current flow through the circuit. Also calculate the total power as well as the voltaqge and power through the 3 Ω resistor. 4 5 2 I2 I1 6 3 ITOTAL 10V Figure 2.5 Series circuit RS 23 5 Gateways to Engineering Studies 15 Industrial Electronics RS N2 45 9 Parallel circuit RP RT 9 6 9 6 3,6 3,6 5 8,6 Total current flow VT RT 10 8,6 1,16 A IT PT Total power VT I T 10 116 , 11,6 W I T RT or PT 2 116 , 2 8,6 11,6 W Voltage across 3Ω resistor V3 I R 116 , 3 Power across 3Ω resistor P3 3,48 V I2 R 116 , 23 4,04 W 2.9 Kirchoff’s laws 2.9.1 Current law (first law) The algebraic sum of the currents flowing towards a point, is equal to the algebraic sum of currents flowing away from that point. Gateways to Engineering Studies 16 Industrial Electronics I1 ITOTAL I2 I3 Figure 2.6 It =I1 +I2 +I3 2.9.2 Voltage law (second law) The sum of voltage drops in a closed circuit is equal to the supply voltage. R1 R2 R3 V1 V2 V3 VTOTAL Figure 2.7 Vt = V1 + V2 + V3 Activity 2.1 1. Define the following 1.1 DC 1.2 EMF 1.3 PD 1.4 The ampere 1.5 Resistance 1.6 Ohm`s law 1.7 Power 1.8 Kirchoff`s laws 2. In the circuit shown in Figure 2.8, calculate the following: 2.1 the total resistance [1,53Ω] 2.2 the total current flow [6,52A] 2.3 the total power in the circuit [65,15 W] Gateways to Engineering Studies 17 N2 Industrial Electronics 2.4 2.5 2.6 2.7 2.8 2.9 2.10 N2 the voltage across the 3Ω resistor [4,55 V] the current through the 3Ω resistor [1,52 A] the power consumed in the 3Ω resistor [6,91 W] the voltage across the 6Ω resistor [5,45 V] the current through the 6Ω resistor [0,908A] the power consumed in the 6Ω resistor [4,95 W] the current through the 2Ω resistor [5 A] 3 5 6 10V 2 4 ITOTAL Figure 2.8 3. Draw a fully labelled circuit diagram of a direct current power supply using two diodes, a centre lap transformer and filter capacitor. Clearly show the output waveforms before and after the filter capacitor. 4. Draw a labelled circuit diagram of a full-wave low voltage DC power supply by using a step down transformer, four diodes, a filter circuit and a load resistor. Show the polarities over the load resistor as well as the electron flow. 5. Refer to Question 4 and draw three labelled graphs indicating the waveforms before the diodes, directly after the diodes and the output over the load. 6. Refer to Figure 2.9 and determine the following: 6.1 The total resistance of the circuit [4Ω] 6.2 The total current of the complete circuit [3A] 6.3 The current I2 [1A] 6.4 The voltage over R2 [4] 6.5 The power consumed by the whole circuit [36W] Figure 2.9 Gateways to Engineering Studies 18 Industrial Electronics N2 Self-Check I am able to: Yes No Describe and illustrate circuit diagrams and calculations of current, voltage and power for resistors in: o Series o Parallel o Series – parallel combinations Explain the definitions of Kirchhoff’s first and second laws Draw circuit diagrams of Kirchhoff’s first and second laws If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 19 Industrial Electronics N2 Module 3 Learning Outcomes When you have completed this module, as a learner you will be able to: Demonstrate understanding by means of a graphical representation the sine-wave with the aid of a rotating phasor Demonstrate calculations and definitions of: o Frequency o Peak value o Peak to peak value o RMS value o Average value o Crest factor o Form factor Demonstrate calculations of instantaneous values with the aid of the following formulae: o e = 3m Sin 2 𝜋ft volts o i = Im Sin 2 𝜋ft amps Demonstrate understanding by means of graphical representations and calculations of non-sinusoidal quantities by means of the mid-ordinate rule Demonstrate understanding by means of graphical and phasor representations of voltage and current to illustrate the effects with an alternating current is applied to: o Resistors o Inductors o Capacitors Explain by means of phase diagrams and calculations for a series circuit containing R, L and C o Current o Voltage o Impedance o Resonant frequency o Inductive reactance and o Capacitive reactance Gateways to Engineering Studies 20 Industrial Electronics 3.1 N2 Introduction When a conductor is rotated in a magnetic field as illustrated in Figure 3.1, an emf will be induced. This emf will have a pulsating affect which is referred to as alternating current. The current thus moves forwards and backwards, which produces a continuous change of polarity. This effect makes ac ideal for the operation of transformers. Armature Brushes Sliprings Galvanometer Figure 3.1 3.2 The cycle One complete revolution of the conductor or armature 0º to 360º will produce a cycle. One positive and one negative half cycle. 3.3 Frequency (f) The number of cycles produced or generated in one second is known as frequency. Frequency is measured in hert (Hz) or cycles per second. (c/s) 3.4 Period (t) The time taken to produce one cycle is called a period. Formula 1 t 1 f Period (t) is measured in seconds. Gateways to Engineering Studies 21 Industrial Electronics N2 +V VP 360o O VP-P -V t Figure 3.2 Vp-p = Voltage peak to peak. t = period. Vp = Vm = Peak Voltage or Maximum voltage. = Lamda. Lamda is the length of a cycle and is measured in metre (m). + V = Positive voltage -V = Negative Voltage. 3.5 Instantaneous value When a cycle is produced, the armature of a generator rotated through an angle of 360º or 2𝜋 radians. If the frequency is f, then the rotational frequency is 2𝜋f, radians per second. Therefore () omega is the rotational speed of a armature or axle. 2 f . 1800 To convert radians to degrees, multiply by If an armature rotates through an angle of 00 in (t) seconds, then the instantaneous value, voltage or current can be calculated. Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 e Em Sin 2 ft 1800 e Em Sin 0 1800 1800 2 ft t Em = Maximum voltage value (V). e = Instantaneous voltage (V). 1800 i Im Sin 2 ft o i Im Sin Im = Maximum current value (A). i = Instantaneous current value (A). t = Time in seconds (s). Gateways to Engineering Studies 22 Industrial Electronics N2 Worked Example 1 A sinusodal wave has a frequency of 45Hz , and a maximum value of 20A. Calculate 1. The angle of the armature 10ms after 00. 2. The instantaneous value 10ms after 00. 3. The time elapased at an angle of 360. 4. The current value at 360. Solution: 1. 1800 2 ft 2 4510 103 2,827 1800 180 0 = 1620 2. i Im Sin o = 20 Sin 1620 = 6,18A 3. = 2ft = 36 = 36 = 0,628 radians 180 2f 0,628 = 2 ( 45) t = 0,0022s = 2,2 ms 4. i Im Sin o i = 20 Sin 36 = 11,76A Gateways to Engineering Studies 23 Industrial Electronics N2 3.6 Average and rootmean (RMS) square values of a sinusoidal wave 3.6.1 Mid-ordinate rule method 200V 00 300 600 900 1200 1500 1800 V 1 V2 V 3 V4 V 5 V6 Figure 3.3 Divide 180 of the sinusoidal wave into equally spaced ordinates as illustrated and let n be the number of ordinates. Sample the value of the voltage or current at each ordinate intersection. Table the results. Worked Example 2 A sinusodal value has the following information. Angle voltage 00 0 V1 = 45V V2 = 120V V3 = 190V 300 76 600 152 900 200 1200 175 1500 70 1800 0 V4 = 194V V5 = 126V V6 = 30V Solution: From this information V(AVE) and V(RMS) can be calculated. (1) VAVE V1 V2 V3 V4 V5 V6 n 45 120 190 194 126 30 6 = 117,5V V1 V2 V3 V4 V5 V6 n 2 (2) V( RMS) 2 2 2 2 2 Gateways to Engineering Studies 24 Industrial Electronics N2 452 1202 1902 194 2 1262 302 6 = 133,5V The same procedure is used to determine I(ave) and I(rms) values. V ( RMS ) Formula 1 Formula 2 I AVE I1 I 2 I 3 I 4 I 5 ....... I n n I1 I 2 I 3 I 4 _ _ _ _ _ I n n 2 I ( RMS) 2 2 2 2 3.6.2 Average and RMS value, calculated method Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6 V(ave) = Vm x 0,637 I(ave) = Im x 0,637 I(ave) = I(dc) V(rms) = Vm x 0,707 I(rms) = Im x 0,707 RMSvalue Form factor = AVEvalue Maximum value Crest factor = RMSvalue A wave which has a form factor and crest factor value of less than 1,11 and 1,44 respectively is called a flat wave. Worked Example 3 A sinusodal wave has the following information e = 120 sin 311,17t V. Calculate 1. The maximum voltage value. 2. Vp-p 3. Vave 4. Vrms 5. Frequency (f) 6. Period (t) Answers: 1. Vm = Vp = 120V 2. V(p-p) = 120 x 2 = 240V Gateways to Engineering Studies 25 Industrial Electronics 3. VAVE N2 VM 0,637 120 0,637 4. VRMS 76,44 V VM 0,707 120 0,707 84,84 V 2 311,17 2 50Hz 1 t f 1 50 0,02 5. f 6. 20 ms 3.6.3 Resistor (R), Capacitor (C), Inductor (L) circuits These components behave differently in an ac circuit. Resistor (R) Current and voltage are in phase. Ohms law will apply in these circuits. V Formula 1 R I V R OO I I 18O 36O O O VS Figure 3.4 Capacitor (C) In a pure capacitor circuit, the current leads the voltage by 90º. 1 Formula 1 Xc 2fc Where C = Capacitance in farads (F). Xc Capacitive reaction is the resistance a capacitor offers a circuit at a specific frequency. Gateways to Engineering Studies 26 Industrial Electronics C N2 x 90O I y V VS I Figure 3.5 Inductor (L) In a pure inductor circuit, the voltage leads the current by 90º. Formula 1 XL = 2fL Where L = Inductor value in Henry`s (H) XL = Inductive reaction in ohms (Ω). Inductive reaction is the resistance an inductor offers a circuit at a specific frequency. L V I 0 I 0 90 0 180 V 0 270 0 900 360 0 I VS Figure 3.6 Definition: Impedance (Z) The total resistance offered to a circuit by the reactance of an inductor, a capacitor and a resistor and is measured in ohm. Gateways to Engineering Studies 27 Industrial Electronics R-L circuits R L ITOTAL VS Figure 3.7 Formula 1 Z R2 XL Formula 2 2 Vs Z Z = Impedance (Ω) and Vs = Supply voltage (V) I Where Formula 3 VS VR VL 2 Formula 4 Formula 5 Formula 6 2 VL = It x XL VR = It x R Tan1 XL R R-C circuits C R ITOTAL VS Figure 3.8 Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Z R2 XC 2 Vs Z It Vc = It x Xc VS VR VC X Tan1 C R Gateways to Engineering Studies 28 2 2 N2 Industrial Electronics N2 R-L-C circuits C L R VS Figure 3.9 Formula 1 Z R L X L XC 2 Formula 2 It Formula 3 Formula 4 2 Vs Z VS VR VL VC Tan1 2 2 XL XC R 3.7 Phasors Phasor diagrams are used to illustrate the relationships between the voltages, currents or impedances and reactances in a circuit. There are basically three types or illustrations or phasors. XL IC VL Z R VR IR VT XC VC IL IT Figure 3.10 3.8 Resonance series circuits Resonance is a condition that exists in a series RLC circuit when XL = XC, and R = Z, VL = VC, the current and voltage will be in phase. Formula 1 fR 1 2 LC Gateways to Engineering Studies 29 Industrial Electronics N2 Resonant frequency (FR) is the frequency where XL=XC. In a series R=Z. Current will be at maximum value. No phase shift 𝜃 = 0º. Worked Example 4 For the circuit shown in Figure 3.11, calculate: 1. Z 2. It 3. VR 4. Vc 5. The phase angle 𝜃 6. Draw the phasor diagram. (XC; R; Z) 7. Draw the phasor diagram (VC; VR; Vs) 20 ITOTAL 100F VS=220V f=50HZ Figure 3.11 Solution: 1. XC 1 2 fc 1 2 (50)(100 106 ) 31,83 Z R 2 XC 2 202 31,832 37,59 2. VS Z 220 37,59 5,85 A It 3. VR = It x R = 5,85 x 20 = 117,05V 4. Vc = It x Xc = 5,85 x 31,83 Gateways to Engineering Studies 30 Industrial Electronics = 186,21V 5. XC R 1 31,83 Tan 20 57,86 o Tan 1 6. 20 = 57,86 R 0 31,83 Z XC 7. VR=117,05V = 57,860 VS=220V VC=186,21V Worked Example 5 Determine the following for the circuit shown in Figure 3.12. 1. Xc 2. XL 3. Z 4. It 5. VC 6. VL 7. VR 8. Phase angle 𝜃 9. Draw the phasor diagram (XL; Xc; R; Z) Gateways to Engineering Studies 31 N2 Industrial Electronics C 200F L R 100mH 20 Ib VS=220V f=50Hz Figure 3.12 Solution: 1. XC 1 2 fc 1 2 (50)(200 106 ) 15,92 2. XL = 2fL = 2(50) (100 x 10 ) = 31,4 -3 3. Z R 2 X L X C 2 20 2 31,4 15,92 25,29 4. It 5. Vs Z 220 25,29 8,7A Vc = It x Xc = 8,7 x 15,92 = 138,18V 6. VL = It x XL = 8,7 x 31,4 = 273,18V 7. VR = It x R = 8,7 x 20 = 174V 8. Tan 1 XL XC R Tan 115,48 20 37,740 Gateways to Engineering Studies 32 2 N2 Industrial Electronics 9. XL XL-XC=15,48 Z R 20 XC Activity 3.1 1. Refer to the circuit and determine the following: 1.1 Xc [159,15] 1.2 Z [187,96] 1.3 It [1,17A] 1.4 VR [117V] 1.5 Vc [186,21V] C 20F R 100 VS=220V f=50HZ Figure 3.13 2. Determine the following: 2.1 Vs [28,28V] 2.2 L [23mH] 2.3 C [63,3] 2.4 R [10] 2.5 Z [14,14] Gateways to Engineering Studies 33 N2 Industrial Electronics R C L VR=20V VL=30V VC=50V IT=2A V S= f=100HZ Figure 3.14 3. Determine the following: 3.1 3.2 3.3 3.4 3.5 R [3,75] C [1273 F] L [15,91mH] FR [35,4Hz] Draw the XL; XC; R; Z phasor diagram. C R L VC=10V VR=15V VL=20V IT=4A f=50HZ XL XL- XC =2,5 Z 3,75 R XC Figure 3.15 4. Determine the following for the circuit shown in Figure 3.16. 4.1 Z [161,9] 4.2 IT [O,62A] 4.3 VR [62v] 4.4 VC [78,94v] 4.5 Phase angle [51,85O] Gateways to Engineering Studies 34 N2 Industrial Electronics R=100 N2 C=25F IT VS=100V f=50HZ Figure 3.16 5. Draw and label a sine wave of 720º with a peak value of 141,4 V and a frequency of 100 Hz. 6. Calculate the following for the sine wave in Question 5: 6.1 Peak to peak value 6.2 The RMS value 6.3 Time (period of one cycle in seconds) 7. The equation for a certain alternating wave is given by the formula 3 = 150sin31,41tV. Use the formula to calculate the following: 7.1 The maximum or peak value for voltage [150V] 7.2 The average and RMS values [95,55V; 106,05] 7.3 The form and crest factors [1,11; 1,414] 7.4 The frequency of the waveform [5 Hz; 28,110 8V] 7.5 The instantaneous value of the voltage 6 and 12 milliseconds after zero [55,225 5V] Self-Check I am able to: Yes Demonstrate understanding by means of a graphical representation the sine-wave with the aid of a rotating phasor Demonstrate calculations and definitions of: o Frequency o Peak value o Peak to peak value o RMS value o Average value o Crest factor o Form factor Demonstrate calculations of instantaneous values with the aid of the following formulae: o e = 3m Sin 2 𝜋ft volts o i = Im Sin 2 𝜋ft amps Demonstrate understanding by means of graphical representations and calculations of non-sinusoidal quantities by means of the mid-ordinate rule Gateways to Engineering Studies 35 No Industrial Electronics N2 Demonstrate understanding by means of graphical and phasor representations of voltage and current to illustrate the effects with an alternating current is applied to: o Resistors o Inductors o Capacitors Explain by means of phase diagrams and calculations for a series circuit containing R, L and C o Current o Voltage o Impedance o Resonant frequency o Inductive reactance and o Capacitive reactance If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 36 Industrial Electronics N2 Module 4 Learning Outcomes On completion of this module, students should be able to: 4.1 Demonstrate the crystal structure of pure germanium and silicon using diagrams Describe: o Valency electrons o Doping o Forming of P- and N-type materials o Electron flow o Hole flow o Covalent bonds Describe with the aid of diagrams the PN-junction as applicable to diodes when considering forward bias and reverse bias conditions Illustrate the difference between germanium and silicon diodes using characteristic curves Describe the properties and characteristics of: o Zener diodes o Varactor diodes o Photo diodes o Light-emitting diodes Explain with the use of circuit diagrams the input and output wave forms o the diode as: o Half wave rectifier with a capacitor as a filter component o Full wave rectifier using two and four diodes that include a capacitor as a filter component Introduction Semiconductors are materials that are neither good conductors of electricity nor are they insulators. The conductance of electricity is achieved by means of thermally generated electrons and is controlled solely by the temperature of the pure ‘intrinsic’ semiconductor material. Gateways to Engineering Studies 37 Industrial Electronics N2 A semiconductor is a material having an electrical resistance higher than that of good conductors such as copper or iron, but lower than that of insulators such as glass or rubber. A semiconductor has the following properties: As the temperature of the semiconductor rises, its electrical resistance changes. When certain other substances are mixed with it, its electrical conductivity rises. When struck by light, its resistance changes, and it emits light when an electrical current is passed through it. 4.2 Silicon and germanium Silicon (Si) and germanium (Ge) are the two most important semiconductors used in the manufacturing of electronic components. The atoms of both these materials are tetravalent. Tetravalent means that these atoms have four valency electrons each. Pure or undoped semiconductor material is known as intrinsic. 4.3 Valence electrons Valence electrons are electrons found in the outermost unfilled electron shell of a atom. 4.4 Covalent bonds Covalent bonds are the sharing of the valence electrons between two atoms. THE CRYSTAL LATTICE STRUCTURE Figure 4.1 4.5 Doping When semiconductor material is mixed with other chemicals to produce P-type or N-type material. This is known as extrinsic or impure semi-conductor material. 4.6 P-type material If a trivalent atom (an atom with three valence electrons) such as boron (B) or indium is mixed with silicon or germanium, P-type material is produced. P-type Gateways to Engineering Studies 38 Industrial Electronics N2 material is positive type material and is known as acceptor atom because it will accept or attract electrons. P-TYPE SEMICONDUCTOR CRYSTAL LATTICE STRUCTURE Figure 4.2 4.7 N-type material If a pentavalent atom, such as phosphorus (P) or arsenic, is mixed with silicon or germanium, N-type material is produced. Definition: Pentavalent An atom with five valence electrons. N-type material is negative type material and is known as donor atoms, because they will donate or give free electrons off to atoms attracting them. Free electrons are electrons not joined in a atom structure. Free electrons are free to conduct in current flow. Free electron N-TYPE SEMICONDUCTOR CRYSTAL LATTICE STRUCTURE Figure 4.3 Gateways to Engineering Studies 39 Industrial Electronics N2 4.8 Electron flow Figure 4.4 Electrons (é) have a negative charge and are attracted to the (+) side of a cell. For every electron leaving the metal above one is give off or is replaced by the (-) side of the cell. 4.9 Hole flow Figure 4.5 Holes (+) are positions where electrons are housed. These holes (+) will attract electrons. The hole does not move but electrons leaving a hole and filling another gives the impression that holes are moved, thus hole flow. Gateways to Engineering Studies 40 Industrial Electronics N2 4.10 PN junction diode Figure 4.6 When P- and N- type material is joined to form one crystal structure. This PN junction possesses rectification properties, and is known as a diode. 4.10.1 Forward bias Figure 4.7 When a PN junction is forward biased, the depletion region disappears. The battery is connected as illustrated. Conduction takes place due to electron flow and hole flow. The forward voltage of a silicon diode is ± 0,6V and a germanium diode is ± 0,3V. This is known as the threshold voltage. The threshold voltage is the voltage required to overcome the virtual battery generated inside the PN junction. Gateways to Engineering Studies 41 Industrial Electronics N2 4.10.1 Reverse bias When the PN junction is reverse biased, the depletion region increases. The battery is connected as illustrated. No conduction takes place. No current can flow. A diode which is reversed biased can be used as protection against polarity reversal in electronic circuitry. Avalanche breakdown, is achieved when the diode is forced into conduction by reverse biasing the diode with a high voltage. This will destroy the diode. Figure 4.8 Ge Si Figure 4.9 PN Junction diode characteristic curve Uses 1. Rectification. 2. Polarity reversal protection. 3. Filter circuit. 4. Back emf protection. Symbol Gateways to Engineering Studies 42 Industrial Electronics N2 Figure 4.10 4.11 Zener diodes A zener diode is a special diode that serves as a voltage (pressure) relief valve. It will conduct current, normally when forward biased. It will block current when reversed biased. However, when a specific reverse bias voltage is reached, the zener diode will conduct current. Vz = Zener voltage -V = Reverse bias area SR = Safe conduction region I CHARACTERISTIC CURVE Figure 4.11 4.11.1 Properties of a zener diode This diode is used in reverse bias only. Uses or application Reference voltage or voltage regulation, eg if 9,1V zener diode is reverse biased 9,1V will be measured across the diode at all times. Gateways to Engineering Studies 43 Industrial Electronics N2 RS + VS=12V RL - VZ=9V=VRL APPLICATION CIRCUIT Figure 4.12 Symbol Figure 4.13 4.12 Varactor diodes C = Capacitance value in F -V = Reverse biased 25 Characteristic curve F 100 -V Figure 4.14 4.12.1 Properties This diode is always reversed biased. To vary the reverse biased voltage will vary the depletion area which will vary the capacitance value between the walls of the depletion region. The larger the reverse voltage the lower the capacitance value in (F) farads. Uses Tuning circuits such as in a (TV) television set. Symbol Figure 4.15 Gateways to Engineering Studies 44 Industrial Electronics N2 4.13 Photodiode These diodes are reversed biased. This diode is so constructed that a window allows incident light to fall on the PN junction. In no light conditions, no current will flow. When light falls on the junction, the photodiode allows current to flow. Symbol A C Figure 4.16 Application circuit Figure 4.17 Uses Light sensitive circuits, eg street lights, darkrooms etc. 4.14 Light emitting diodes (LED) These diodes when forward biased give off light. When free electrons move from one energy level to another they give off energy in the form of light known as photons. Symbol Figure 4.18 Uses (1) Indication circuits, e.g. on/off indications. (2) 7-Segment display. Application circuit Gateways to Engineering Studies 45 Industrial Electronics Figure 4.19 4.15 The halfwave rectifier with smoothing capacitor Figure 4.20 Uses Rectification properties. To convert ac to dc. 4.15 The full wave rectifier 4.15.1 The centre tap rectifier without smoothing capacitor Figure 4.21 Gateways to Engineering Studies 46 N2 Industrial Electronics N2 4.15.2 The centre tap rectifier with smoothing capacitor Note that the current flows through the load resistor in the same direction, therefore the polarity over RL is the same continuously. Figure 4.21 4.16 Bridge type rectifier (Four diodes) When the current source causes electrons to flow in a through the positive side as show, the current will flow through D2, through the load (resistor). Through D4 and back to the negative side of the source. The other two diodes are reversed biased and will block current flow. 4.16.1 Without smoothing capacitor Figure 4.22 Gateways to Engineering Studies 47 Industrial Electronics N2 4.16.2 With smoothing capacitor Figure 4.23 4.17 Calculations FORMULA: (1) Halfwave Rectifier. Vdc = Vp x 0,318 (11) Fullwave Rectifier. Vdc = Vp x 0,637 Worked Example 1 A Bridge type rectifier has a Vp = 20 V, calculate the VDC. Solution: VDC = Vp x 0,637 = 20 x 0,637 = 12,74 V Worked Example 2 A halfwave rectifier has a VDC value of 13,5 V. Calculate the Vp over the secondary side of the transformer. Solution: VDC = Vp x 0,318 Vdc VP 0,318 13,5 0,318 42 ,45V Gateways to Engineering Studies 48 Industrial Electronics N2 Activity 4.1 1. Define the following : 1.1 Photo diodes 1.2 Doping 1.3 Light-emitting diodes 1.4 Free electrons 1.5 Valency electrons 1.6 Threshold voltage 1.7 Forward bias 1.8 Avalanche breakdown 1.9 Reverse saturation current 1.10 Reverse bias 1.11 Extrinsic semi-conductor 1.12 Intrinsic semi-conductor 2. Draw and label the characteristic curve of a 12V zener diode and explain four of its characteristics. 3. Draw and label a circuit diagram of a half-wave rectifier fitted with a load resistor of 100 Ω (RL) and a filter capacitor of 100 F (C). Show at least 720º of the sinusoidal input and output waveforms. 4. Draw the characteristic curves of the following diodes: 4.1 Silicon diode 4.2 Varactor diode 5. Draw the symbols of the following diodes and state one function of each: 5.1 Zener diode 5.2 Varactor diode 6. Define the following terms: 6.1 Intrinsic semi-conductor 6.2 Extrinsic semi-conductor 7. Draw a labelled diagram indicating the biasing and current flow of an NPN transistor. Self-Check I am able to: Yes Demonstrate the crystal structure of pure germanium and silicon using diagrams Describe: o Valency electrons o Doping o Forming of P- and N-type materials o Electron flow o Hole flow o Covalent bonds Gateways to Engineering Studies 49 No Industrial Electronics N2 Describe with the aid of diagrams the PN-junction as applicable to diodes when considering forward bias and reverse bias conditions Illustrate the difference between germanium and silicon diodes using characteristic curves Describe the properties and characteristics of: o Zener diodes o Varactor diodes o Photo diodes o Light-emitting diodes Explain with the use of circuit diagrams the input and output wave forms o the diode as: o Half wave rectifier with a capacitor as a filter component o Full wave rectifier using two and four diodes that include a capacitor as a filter component If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 50 Industrial Electronics N2 Module 5 Learning Outcomes By the end of the module you should be able to: Demonstrate understanding of the transistor as a PNP or NPN junction with the use of sketches Explain the concepts of forward and reverse biasing as applicable to emitter, base and collector Explain the operation of the transistor with the aid of I e = Ib + Ic (No calculations) Demonstrate with diagrams how the transistor is employed as an amplifier in the following configurations: o Common emitter o Common collector o Common base 5.1 Introduction A transistor regulates current or voltage flow and acts as a switch or gate for electronic signals. A transistor consists of three layers of a semiconductor material, each capable of carrying a current. A semiconductor is a material such as germanium and silicon that conducts electricity in a "semi-enthusiastic" way. It's somewhere between a real conductor such as copper and an insulator (like the plastic wrapped around wires). Gateways to Engineering Studies 51 Industrial Electronics N2 5.1.1 NPN transistor Figure 5.1 VCC = Voltage closed circuit. (The supply voltage) The transistor consists of three semiconductor layers. The base (B) and emitter (E) must always be forward biased and the collector (C) reversed biased. This is for both NPN and PNP transistors. 5.1.2 PNP transistor Figure 5.2 5.2 Operation of a transistor The current flows from the emitter (E) to the collector (C) and the amount of current passing to the collector is controlled by the base (B). Formula: I E = IB + IC. Another explanation for understanding purposes can be done by using a water tap. The water flowing from the supply to the bucket is controlled by the tap. Gateways to Engineering Studies 52 Industrial Electronics N2 Figure 5.3 5.3 Basic amplifier circuit To open and close or vary the current flow from the emitter to the collector, vary the voltage VBE (Voltage base, emitter) between +0,4V to +0,9V, as illustrated. 5V 0,7V Vce Vrb 0,6V 4V 0,5V Figure 5.4 The value of RB is such that the DC voltage drop across RB is 0,6 V. If a person speaks into the microphone (M) the microphone will produce a varying loss of current which can be illustrated by VRB. This current is applied to the base of the transistor which in turn will vary the flow of current through the transistor from the emitter to the collector and will produce a current to flow through loudspeaker illustrated by VCB. The current produced will effect a sound in the loudspeaker which would be amplified by the amplifier circuit. Gateways to Engineering Studies 53 Industrial Electronics Input voltage Vbe = Outputt voltage Vce = N2 0,7 - 0,5 = 0,2V 6 - 4 = 2V Voltage gain of the amplifier is Gi = N Vo 2 10( timesofgainof ) Vi 0,2 Vo 2 20Log 20Log 20dB Vi 0,2 The input signal is small and the output signal large. The amplifier has amplified the signal. 5.3.1 The transistor as a switch Figure 5.5 If the switch is closed the VBE is forward biased and the transistor will conduct. The globe will light up. The transistor is saturated. This means that maximum current will flow through the transistor. In an amplifier circuit, the current varies through the transistor, and is not in saturation. 5.4 Transistor circuit configurations There are three basic configurations in which a transistor can be used. Gateways to Engineering Studies 54 Industrial Electronics 5.4.1 Common base Figure 5.6 Applications This circuit is used in voltage amplifier circuits. 5.4.2 Common emitter Figure 5.7 Applications This circuit is used in a power amplifier circuit. 5.4.3 Common collector Figure 5.8 Gateways to Engineering Studies 55 N2 Industrial Electronics N2 Applications This circuit is used as a current amplifier circuit. Activity 5.1 1. Draw and label the block diagram of a PNP transistor. Label the charge carriers and explain the equation, IE = IB + IC. 2. Draw and label the circuit diagram of an NPN transistor in a common collector amplifier circuit. 3. Draw and label a common base amplifier using an NPN transistor, showing the most essential components. 4. Draw and label a single-stage NPN-transistor amplifier in a common emitter configuration. A microphone and a loudspeaker must be connected to the input and output terminals. Self-Check I am able to: Yes No Demonstrate understanding of the transistor as a PNP or NPN junction with the use of sketches Explain the concepts of forward and reverse biasing as applicable to emitter, base and collector Explain the operation of the transistor with the aid of Ie = Ib + Ic (No calculations) Demonstrate with diagrams how the transistor is employed as an amplifier in the following configurations: o Common emitter o Common collector o Common base If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 56 Industrial Electronics N2 Module 6 Learning Outcomes By the end of the module you should be able to: 6.1 Describe, by means of a sketch, how the moving coil meter is employed as a volt meter and an amp meter Demonstrate how to change the range of the above-mentioned metres using circuit diagrams and calculations of resistor values Demonstrate a circuit diagram that is suitable for measuring resistance Demonstrate by means of a circuit diagram of an analogue multi-meter with a maximum of three scales per quantity to measure the following: o Current o Voltage o Resistance Describe an introduction of the digital metre in respect of: o Advantages o Uses o Scales Introduction A measuring instrument is a device which is used to evaluate an unknown quantity. 6.2 Lenz’s law The direction of an induced emf is always such that it tends to set up a current opposing the motion and the change of magnetic flux responsible for producing that emf. Gateways to Engineering Studies 57 Industrial Electronics N2 MOVING COIL METER, ANALOGUE TYPE Figure 6.1 The value under test is passed through the coil which interrupts the magnetic flux of the magnet, which forces the pointer to a different position. The scale is calibrated to read off the correct value. 6.3 The ampere meter An ampere meter is a meter which is used to measure the amount of current flowing in a circuit. The current that will give a full scale deflection (fsd) will normally be between 1mA and 20mA. A shunt resistor (RSH) will be placed in parallel to the coil winding to prevent damage to the meter if a large current (IT) is to be measured. The shunt resistor is usually composed of a few resistors placed on parallel and is selectable so as to vary the range of the ampere meter. The shunt resistor (RSH) value can be calculated as follows: Formula (1) RSH IM RM ISH Rsh = Shunt resistor Im = Current through the meter (2) Ish = It - Im Rm = Internal resistance of the meter (3) RSH IM RM IT IM Ish= Current through Rsh It = Current being measured Gateways to Engineering Studies 58 Industrial Electronics N2 6.3.1 Internal arrangement of shunt resistor for the ampere meter Figure 6.2 An ampere meter is always connected in series with the circuit. Worked Example 1 A current value of 7A is to be measured. The ampere meter has a internal resistance of 2Ω and a full scale deflection of 10mA. Calculate: 1. the value of the shunt resistor. 2. the value of current through the shunt resistor. Solution: It = 7A Rm = 2 Im = 10mA = 10 x 10-3 (1) the value of the shunt resistor RSH IM RM IT IM 10 103 2 7 10 103 0,02 6,99 2 ,86m (2) the value of current through the shunt resistor ISH = IT - IM = 7 - (10 x 10-3) = 6,99mA Gateways to Engineering Studies 59 Industrial Electronics N2 6.3.2 Multi range ampere meter It I1 I2 Rsh2 Rsh1 Im I4 I3 Rsh4 Rsh3 M A mA A nA Figure 6.3 6.4 The volt meter A volt meter is always connected in parallel with the circuit under test. The same type of moving-coil meter is used as in the ampere meter. A resistor connected in series to the meter is to prevent the current from exceeding the full-scale current rating and damaging the meter. This resistor is called a multiplier and is used to make the meter Multi-rangeable. The multiplier can be calculated as follows. Formula (1) R S VT RM IM RS = Multiplier VT = Voltage under test IM = Current through coil (2) VT = IM (RS + RM) RM = Resistance or coil 6.4.1Internal arrangement of multiplier for the voltmeter Figure 6.4 Gateways to Engineering Studies 60 Industrial Electronics N2 Worked Example 2 A voltmeter has a full scale deflection of 15mA and a internal resistance of 5 Ω. Calculate the value of the resistor to measure a full scale voltage of 50V. Solution: VT = 50V, RS RM = 5Ω, IM = 15mA = 15 x 10-3A VT RM IM 50 5 15 103 3333,33 5 3328,3 3,328k 6.4.2 Multi range volt meter Rs1 V mV Rs2 S1 + V Im Rs3 M _ Figure 6.5 6.4 The ohmmeter A moving - coil meter can be used to measure the value of an unknown resistance (Rx). Gateways to Engineering Studies 61 Industrial Electronics N2 Figure 6.6 Rl = Current limiting resistor. Ro = Variable zero adjustment resistor. Rx = Resistance under test. B = Battery or power source of meter. 6.5 The analogue multi-meter This analogue can be used as a multipurpose meter to measure current, voltage and resistance with multi- ranging selectivity. The meter is also known as a (AVO meter). V S1 R1 mV R2 V V R3 S1 A A R4 S4 + x7 R5 R6 R7 Rv B x10 S3 R8 A mA S2 x100 R9 _ Figure 6.7 Gateways to Engineering Studies 62 A M Industrial Electronics N2 Caution: When using a multi-meter for testing current in a circuit Multi-meters have a small internal resistance in the circuit for measuring electric current. Therefore, a multi-meter should never be connected in parallel to a circuit as a large amount of current will flow and destroy the multi-meter. The multi-meter must be connected in series with the circuit. Precautions to be taken when using an analogue meter Always select the highest scale first and then decrease the scale if necessary. Never leave the meter on the ohm scale. This could cause the batteries to run down. Before any measurements are made, the meter must be set to zero. Prevent polarity reversal. Caution: When using a multi-meter for testing voltage in a circuit Multi-meters, when used to measure voltage, have a high internal resistance, therefore, a multi-meter should never be connected in series to a circuit. The multi-meter must be connected in parallel with the circuit. Caution: When using a multi-meter for measuring resistance in a circuit Multi-meters, when used to measure resistance, can be damaged if the current in the circuit is flowing. Therefore the current must be switched off or the voltage disconnected. 6.6 The digital multi-meter This type of multi-meter uses a numerical readout. The display is usually a LCD (liquid crystal display) or 7 segment LED (Light emitting diodes). This meter has a high level of accuracy, and can automatically select a suitable range. Uses Current meter Volts meter Ohms meter Continuity tester Diode tester Test (HFE) current gain of transistors Scales Auto-ranging = automatically selects a suitable range. Advantages Advantages of the digital multi-meter over a analogue multi-meter. Gateways to Engineering Studies 63 Industrial Electronics N2 Zero - adjustment is not necessary. Indicates polarity reversal. Polarity reversal protection. Overload protection. Auto-ranging High degree of accuracy. Response speed is increased. More robust. Activity 6.1 1. Name two advantages of a digital- multi-meter over an analogue multimeter and three uses thereof. 2. A moving coil meter has a full-scale deflection of 10 mA and an internal resistance of 200 Ω. Draw the circuit diagram and calculate the value of the multiplier resistor that would enable the meter to measure 20 V. [1800 Ω]. 3. Mention three precautions to be taken when using an ohmmeter. 4. A meter has a full scale deflection of 15mA and an internal resistance of 15 0Ω. Calculate: (a) Value of the multiplier resistor to measure a full scale voltage of 200V. (b) Draw and label the circuit. [Rs = 14,52kΩ]. + Vt=220V Rs=14,52 k Im=15mA Rm=150 V _ Figure 6.8 5. A current of 45A must be measured. The meter has a internal resistance 150Ω and a scale deflection of 20mA. Calculate: (a) The value of the shunt resistor. [66,696mΩ]. (b) The value of the current through the shunt. [44,98A] (c) Draw the circuit. Gateways to Engineering Studies 64 Industrial Electronics + N2 It Im=20mA Rsh Rm=150 _ Figure 6.9 Self-Check I am able to: Yes No Describe, by means of a sketch, how the moving coil meter is employed as a volt meter and an amp meter Demonstrate how to change the range of the abovementioned meters using circuit diagrams and calculations of resistor values Demonstrate a circuit diagram that is suitable for measuring resistance Demonstrate by means of a circuit diagram of an analogue multi-meter with a maximum of three scales per quantity to measure the following: o Current o Voltage o Resistance Describe an introduction of the digital metre in respect of: o Advantages o Uses o Scales If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 65 Industrial Electronics N2 Module 7 Learning Outcomes By the end of the module you should be able to: 7.1 Describe the operating principle, construction and characteristic curves of: o Light dependant resistors (LDR) o Thermo couples o Bi-metallic strip o Thermistors Introduction A transducer is a device that converts one form of energy to another. Some common everyday transducers used around the house are an electric stove, fridge, kettle, microwave oven, motor car etc. 7.2 Light dependant resistor (LDR) This is a light sensitive resistor. The resistance varies with a change in light intensity. This component is made from photo-conductive semi-conductive materials such as cadmium selenide (CdSe), Cadmium sulfide (Cds) and lead sulfide (infra - red sensitive). Figure 7.1 Components Gateways to Engineering Studies 66 Industrial Electronics N2 The resistance value of a LDR varies with the amount of light that falls on it. A LDR is a light dependant resistor. It is used for external lighting systems that are only activated at night, camera light meters, etc. The LDR has a ‘window’ under which lies a grid of material that is sensitive to light. R Light intensity Figure 7.2 Characteristic curve Figure 7.3 Symbol Gateways to Engineering Studies 67 Industrial Electronics N2 APPLICATION CIRCUIT Figure 7.4 When light falls on the (LDR) its resistance decreases, causing the transistor to conduct, the relay operates and the high current light will switch on. This simple circuit is used in street lighting, or to switch on a light when the sun goes down. 7.3 Thermocouples A temperature sensitive transducer. This transducer consists of two different metals such as nickel- chrome and nickel- aluminium. If the two metals are joined together, as illustrated and the two junctions are at different temperatures, a potential difference exists between two metals. The value is dependant on the temperature differences. The voltage value is in the region of a few milli-volts. A voltmeter, which is calibrated in ºC is used to indicate the temperature. Figure 7.5 Construction Gateways to Engineering Studies 68 Industrial Electronics N2 CHARACTERISTIC CURVE Figure 7.6 7.4 Bi-metallic strip 7.4.1Temperature sensitive transducer Two metals, iron and brass, riveted together at room temperature. These two metals have different expansion coefficients. When the metals are heated, the device bends to one side, when chilled in bends to the other side. If an indicator is attached to the device and a scale is used, calibrated to read temperature, we have the oldest temperature transducer ever used. Construction Figure 7.7 Uses A simple circuit can be build using the bi-metallic strip to close an alarm circuit when a fire breaks out. 7.5 Thermistor A temperature sensitive resistor. This components resistance varies with a charge of temperature. The component is either (NTC) negative temperature coefficient, resistance decreases if temperature increases, or (PTC) positive temperature coefficient, resistance increases with a increase in temperature. Gateways to Engineering Studies 69 Industrial Electronics N2 Figure 7.8 Characteristic curve Figure 7.9 Symbol Application In this application the thermistor is mounted to the heat-sink of the transistor and prevents thermal runaway of the amplifier and causes distortion. Figure 7.10 Activity 7.1 1. Define a transducer. 2. Describe each of the following transducers: 2.1 bimetal strip 2.2 thermistor 2.3 LDR Gateways to Engineering Studies 70 Industrial Electronics N2 2.4 thermocoule 3. Draw, label and explain application circuits of the transducers in Question 2. 4. Describe briefly, by using labelled sketches, the difference between a bimetallic strip and a thermocouple transducer. 5. Draw labelled circuit diagram symbols of the LDR and the photo diode. Briefly describe the main differences between them and the working principle of each. Self-Check I am able to: Yes No Describe the operating principle, construction and characteristic curves of: o Light dependant resistors (LDR) o Thermo couples o Bi-metallic strip o Thermistors If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 71 Industrial Electronics N2 Module 8 Learning Outcomes By the end of the module you should be able to: Explain the definition of Lenz’s Law Describe the properties, uses, operating principles and draw a circuit diagram of a synchro system with standard coupling Draw circuit diagrams of a synchro system illustrating the couplings for: o 180 phase shift o 240 phase shift o Rotors that rotate in opposite directions 8.1 Introduction A syncro system is the electrical equivalent of the transferring of mechanical displacement over a distance. A synchro system synchronises two or more systems by one control over a distance by an electrical signal. An example of this is a transmitter and receiver of a model, remote controlled aeroplane. The transmitter or controller controls the flight of the aeroplane. If the rotor in the transmitter is moved, the magnetic field on the rotor is affected and in turn transmits an error signal to the receiver which forces the rotor of the receiver to the desired position. 8.2 Lenz’s law When a magnetic field cuts through a coil it induces a current to flow which will generate a magnetic field. This magnetic field will oppose the original field. 8.2.1 Applications Remote controlled model aeroplane. Control of dam sluice gate. Control of ships rudder. Control of space ships. Remote control of microwave dishes. Gateways to Engineering Studies 72 Industrial Electronics N2 8.3 Advantages of synchro systems over mechanical systems The transmitter and receiver can be far apart. Contact between the transmitter and receiver can be over electrical wires, radio frequency, radar, microwave and infra-red. Very little electrical energy is used. No mechanical friction between transmitter and receiver. 8.3.1 Acceptable symbols Always label all the diagrams in full. 0 Figure 8.1 8.3.2 Operation Control between the transmitter and receiver is done by means of a magnetic field. If the rotor of the transmitter is moved, a magnetic field forces the receiver to move. The direction of the resultant movement by the receiver will depend on the wiring of the rotor (R) and the stators (S). 8.4 Wiring diagrams Tx Rx Figure 8.2 In-phase displacement If the transmitter is turned 45º clockwise the receiver will follow and also turn 45º clockwise. Gateways to Engineering Studies 73 Industrial Electronics Tx Tx N2 2400 PHASE SHIFT DISPLACEMENT Tx Rx Figure 8.2 240º phase shift displacement This can be achieved by connectors as illustrated Tx Rx Figure 8.2 Opposite direction phase shift displacement If S1 and S3 are connected between the transmitter and receiver this will give an opposite direction displacement. When the transmitter is turned 45º clockwise, the receiver will turn 45º anticlockwise. Tx Tx Figure 8.2 180º phase shift displacement This is achieved by connecting R1 and R2 between the transmitters. If the transmitter’s rotor is held at 0º the receiver will be on 180º. If the transmitter is moved 45º clockwise, the receiver will follow and move 45º clockwise to the position (180º + 45º) = 225º. Activity 8.1 1. Define Lenz`s law. 2. Define a synchro system. Gateways to Engineering Studies 74 Industrial Electronics N2 3. Give three advantages of a synchro system with reference to a mechanical system. 4. Name three applications of syncro systems. 5. Explain in your own words why Lenz`s law is applicable to syncro systems. 6. Draw and label a sketch of a syncro system to illustrate 240º displacement between the transmitter and receiver. 7. Draw the acceptable symbols of syncro systems. 8. Make a neat sketch showing the coupling between a transmitter and an indicator to give a 180° phase shift. 9. State two requirements of a synchro-system to operate successfully. Self-Check I am able to: Yes No Explain the definition of Lenz’s Law Describe the properties, uses, operating principles and draw a circuit diagram of a synchro system with standard coupling Draw circuit diagrams of a synchro system illustrating the couplings for: o 180 phase shift o 240 phase shift o Rotors that rotate in opposite directions If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 75 Industrial Electronics N2 Module 9 Learning Outcomes By the end of the module you should be able to: Describe the definition of a decibel Calculate gains and losses in terms of : o Power o Voltage o Current 9.1 Introduction The unit (dB) decibel is 1/10 of a Bel. This unit is used to express the ratio between two signals, output and input signal. If the output signal is larger than the input signal, the signal has been amplified. If the output signal is smaller than the input signal, the signal has been attenuated. PI N PO N = Amplifier or attenuater P = Power 9.2 Formula N 10 log PO Pi Worked Example 1 An electronic network has a output power of 60mW and a input power of 16mW. Calculate the gain or loss of the network. N 10 log PO Pi Gateways to Engineering Studies 76 Industrial Electronics N2 60 10 -3 10 log 16 10 -3 = 10 log 3,75 = 5,74 dB The circuit is an amplifier and the signal has undergone a gain. Worked Example 2 An electronic network has a output voltage of 2,5V and a input voltage of 12V. The input and output impedance is 600. Calculate: (a) Po (b) Pi (c) Io (d) Ii (e) The gain or loss of the amplifier in (dB) R1 = R0 = 600 V1 = 12V, V0 = 2,5V a) 2 P0 V0 RO 2,52 600 0,0104W 10,4 mW (b) 2 Pi V1 R1 12 2 600 = 0,24W = 240mW (c) I0 V0 R0 2,5 600 = 4,167mA (d) Gateways to Engineering Studies 77 Industrial Electronics I1 N2 V1 R1 12 600 = 20mA (e) PO Pi 10mW 10 log 240mW N 10 log = (-) 13,80 dB The electronic network is a attenuator, (dB) is a ratio and is never express as (-). Worked Example 3 A electronic network has a gain of 26 dB. Calculate the output power (Po). P N 10 log O Pi PO 26dB 10 log 27 mW PO 26 log 10 2,7 10 3 PO anti log 2,6 2,7 10 3 PO 398,11 2,7 10 3 PO 398,11 2,7 10 3 The input power (Pi) = 27mW. 1,07W Activity 9.1 1. Define the decibel. 2. A 200 mV input to an amplifier produces a current of 2 A in a loudspeaker which has a 4Ω impedance. The input impedance is 300 Ω. Calculate: 2.1 The input power (Pi) [0,133mW] 2.2 The output power (Po) [16W] 2.3 The input current (Ii) [0,66mA] 2.4 The output voltage (Vo) [8V] 2.5 The gain of the amplifier in dB (N) [50,79dB] Gateways to Engineering Studies 78 Industrial Electronics N2 3. A 20mV input to an amplifier produces a current of 200mA in a loudspeaker which has a 4Ω impedance. The input impedance is 30 Ω. Calculate the gain of the amplifier in dB(N) [N = 40,8dB] 4. An amplifier has an output of 10 w and an input power of 10 mW. Calculate the gain or loss of the amplifier in decibel (dB). [N = 30dB (gain)] 5. An amplifier has a gain of 100. Determine this gain in the unit decibel. [N = 20dB] Self-Check I am able to: Yes No Describe the definition of a decibel Calculate gains and losses in terms of : o Power o Voltage o Current If you have answered ‘no’ to any of the outcomes listed above, then speak to your facilitator for guidance and further development. Gateways to Engineering Studies 79 Industrial Electronics N2 Table of C Past Examination Papers APRIL 2012 NATIONAL CERTIFICATE INDUSTRIAL ELECTRONICS N2 (8080602) 28 March (X-Paper) 09:00 – 12:00 This question paper consists of 5 pages, a 1-page diagram sheet and a 3-page formula sheet. Gateways to Engineering Studies 80 Industrial Electronics N2 TIME: 3 HOURS MARKS: 100 __________________________________________________________________ INSTRUCTIONS AND INFORMATION 1. Answer ALL the questions. 2. Read ALL the questions carefully. 3. Number the answers according to the numbering system used in this question paper. 4. Keep subsections of questions together. 5. RULE OFF on completion of each question. 6. Use ONLY IEC symbols and units when answering the question paper. 7. ALL sketches must be neat and labelled, using a pencil and a ruler (NOT freehand sketches). 8. NO red or green ink may be used. 9. Use 𝜋 as 3,142 and NOT as 22 7 10. Write neatly and legibly. ___________________________________________________________________ Gateways to Engineering Studies 81 Industrial Electronics N2 QUESTION 1 1. Define the following terms: 1.1 Matter (2) 1.2 Conductor (2) 1.3 Covalent bond (2) 1.4 Resonance (2) 1.5 Thermistor (2) [10] QUESTION 2 2. Refer to FIGURE 1 (on the attached DIAGRAM SHEET) and calculate the following: 2.1 The value of the resistor R1 (2) 2.2 The power consumed by the resistor R2 (2) 2.3 The total resistance of the circuit (6) [10] QUESTION 3 3 Refer to FIGURE 2 (on the attached DIAGRAM SHEET) and calculate the following: 3.1 The value of the capacitor (2) 3.2 The value of the inductor (2) 3.3 The total impedance of the circuit (3) 3.4 The total current (2) 3.5 The voltage drop across the capacitor (2) 3.6 The phase angle (3) [14] QUESTION 4 Gateways to Engineering Studies 82 Industrial Electronics 4.1 N2 An alternating current waveform has a peak-to-peak value of 300 V Calculate the following: 4.2 4.1.1 The maximum or peak value for voltage (2) 4.1.2 The average and RMS values (2) 4.1.3 The form and crest factors (2) The equation for a certain alternating wave is given by the formula: e = 150 sin 3,41 tV. Use the formula to calculate the following: The instantaneous value of the voltage 6 and 12 milliseconds after zero. (6) [12] QUESTION 5 5.1 5.2 Draw the symbols of the following diodes and give ONE use of each: 5.1.1 Zener diode (2) 5.1.2 Varactor diode (2) Draw and label the expected Input and output waveforms of the rectifier in FIGURE 3 (attached DIAGRAM SHEET). The transformer is connected to 220 V/50 Hz. (6) [10] QUESTION 6 6.1 An ammeter can measure 500 mA full scales. The meter movement requires a current of 1 mA to show a full-scale deflection. The internal resistance of the meter is 500 Ω. 6.1.1 Calculate the shunt resistance (up to THREE decimal points). (3) 6.1.2 Draw and label the circuit of the ammeter described in QUESTION 6.1. (5) 6.2 State THREE precautions which must be taken when measuring current with an ammeter. (3) [11] Gateways to Engineering Studies 83 Industrial Electronics N2 QUESTION 7 With reference to the theory of TRANSISTORS, answer the following questions: 7.1 Draw a labelled circuit symbol for an NPN and a PNP transistor. (6) 7.2 Name THREE types of amplifiers. (3) [9] QUESTION 8 8.1 Define a transducer. 8.2 Discuss the operating principle of the following transducers: 8.3 (2) 8.2.1 Thermistor (2) 8.2.2 Bimetal strip (2) Calculate the gain of an amplifier that produces a voltage of 10 V over a 15 Ω loudspeaker when a current of 12 mA is applied to the input. The input impedance of the amplifier is 10 000 ohms (6) [12] QUESTION 9 9.1 Define Lenz's Law. (5) 9.2 Make a neat labelled sketch of a synchro system showing the connections for the transmitter and receiver to turn in the same direction. (6) State THREE advantages of a synchro system over a mechanical system. (3) 9.3 [12] TOTAL: 100 Gateways to Engineering Studies 84 Industrial Electronics DIAGRAM SHEET Gateways to Engineering Studies 85 N2 Industrial Electronics INDUSTRIAL ELECTRONICS N2 FORMULA SHEET Gateways to Engineering Studies 86 N2 Industrial Electronics Gateways to Engineering Studies 87 N2 Industrial Electronics Gateways to Engineering Studies 88 N2 Industrial Electronics Marking Guidelines APRIL 2013 NATIONAL CERTIFICATE INDUSTRIAL ELECTRONICS N2 (8080602) This marking guideline consists of 6 pages Gateways to Engineering Studies 89 N2 Industrial Electronics N2 QUESTION 1 1.1 Matter is anything that has weight and takes up space and cannot be created or destroyed. √√ (2) 1.2 Material that allows current to flow through it. √√ (2) 1.3 The sharing of valency electrons by two atoms. √√ (2) 1.4 When XL= X. In a series circuit R = Z and the current will be at its maximum value. √√ (2) 1.5 A thermistor is a temperature-sensitive resistor. √√ (2) [10] QUESTION 2 𝑉 12 2.1 𝑅1 = 2.2 𝑃 = 𝑉 𝑥 𝐼 = 12 𝑥 0,6 = 7,2 𝑊 √√ 2.3 𝑅2 = 0,6 = 20 𝛺 √ 𝐼 (2) = 1,2 = 10 𝛺 √√ (2) 12 𝑉5 = 𝑉𝑡− (𝑉3 + 𝑉4 ) = 12 − (1,2 + 3,6) = 7,2 𝑉 √ 7,2 𝑅5 = 0,6 = 12 𝛺 √ 6 𝑅 = 2 + 12 + 20 = 10 𝛺 √ 𝑅𝑡 = 10//10 = 5𝛺 √√ (6) NOTE: double ticks at the end of the ANSWER imply a tick for the preceding step. [10] QUESTION 3 3.1 3.2 1 2𝜋𝑓𝑐 1 63,662 = 2𝜋 𝑥 50 𝑥 𝐶 √ 𝐶 = 50 𝜇𝐹 √ 𝑋𝑐 = (2) 𝑋𝐿 = 2𝜋 𝑓𝑙: 15,708 = 2𝜋 𝑥 50 𝑥 𝐿 √ 𝐿 = 15,708 / 314,159 = 0,05 𝐻 √ 2 3.3 𝑍𝑇 = √102 + (63,662 − 15,708) = 48,985 𝛺 √√√ 3.4 𝐼𝑇 = 3.5 𝑉𝑐 = 𝐼𝑡 𝑥 𝑋𝑐 = 2,04 𝑥 63,662 = 129,96 𝑉 √√ 𝑉1 𝑍1 = 100 48,985 = 2,04 𝐴 √√ Gateways to Engineering Studies 90 (2) (3) (2) (2) Industrial Electronics 3.6 𝜃 = cos −1 10/48,985 √√ = 78,56° √ N2 (3) [14] QUESTION 4 4.1.1 Maximum peak = 300/2 = 150 V √√ (2) 4.1.2 RMs = 0,707 x maximum = 0,707 x 150 = 106,05 V √ Average value = 0,637 x maximum = 0,637 x 150 = 95,55 V √ (2) Form = 106,05/95,55 = 1,11 √ Crest = 150/106,05 = 1,414 √ (2) 4.1.3 4.2 𝑒6𝑚𝑠 = 150 sin 31,41 𝑥 6 𝑥 10−3 𝑥 180 𝑒12𝑚𝑠 = 150 sin 31,41 𝑥 12 𝑥 10−3 𝑥 = 28,08 𝑉 √√ 𝜋 180 𝜋 = 55,12 𝑉 √√ (6) [12] QUESTION 5 5.1.1 (2) 5.1.2 (2) Gateways to Engineering Studies 91 Industrial Electronics N2 5.2 (6) [10] QUESTION 6 6.1.1 (3) 6.1.2 (5) 6.2 Connect in series with load Observe correct polarities Start with highest scale Switch off power before connecting meter Never touch probes at tips, only at insulation. (3) (Any THREE) [11] Gateways to Engineering Studies 92 Industrial Electronics N2 QUESTION 7 7.1 (6) 7.2 Common emitter Base Collector (3) (ONE mark each) [9] QUESTION 8 8.1 A device that converts one form of energy into another. √√ (2) 8.2.1 The resistance will decrease as the temperature increases. √√ (2) 8.2.2 When heating two different types of metal which are fastened on top of each other, the combined metal strip will bend because of the change in temperature. √√ (2) Po = V2/R = 102/15 = 6,67 W √√ Pin = 12 x R = (12 x 10-3)2 x 10 000 = 1,44 W √√ N = 10 Log Po/Pin = 10 Log (6,67/1,44) = 10 Log 4,632 = 6,657 db √√ (6) 8.3 [12] QUESTION 9 9.1 Whenever a magnetic field cuts through a coil and induces a voltage in the coil, causing a current to flow, that current will in turn generate its own magnetic field which will oppose the original induced magnetic field. Gateways to Engineering Studies 93 (3) Industrial Electronics N2 9.2 (6) 9.3 Transmitter and receiver can be far apart. Very little electrical energy is used. Contact between the two systems can be by means of radio, telemetering or wires. Quantity can be controlled. Large values can be transmitted when it is combined with a server system. √√√ (Any THREE) (3) [12] TOTAL: 100 Gateways to Engineering Studies 94 Industrial Electronics N2 Table of C Past Examination Papers NOVEMBER 2012 NATIONAL CERTIFICATE INDUSTRIAL ELECTRONICS N2 (8080602) 9 November (X-Paper) 09:00 – 12:00 Gateways to Engineering Studies 95 Industrial Electronics N2 This question paper consists of 5 pages, a 1-page diagram sheet and a 3-page formula sheet. TIME: 3 HOURS MARKS: 100 __________________________________________________________________ INSTRUCTIONS AND INFORMATION 1. Answer ALL the questions. 2. Read ALL the questions carefully. 3. Number the answers according to the numbering system used in this question paper. 4. Keep subsections of questions together. 5. RULE OFF on completion of each question. 6. Use ONLY IEC symbols and units when answering the question paper. 7. ALL sketches must be neat, using a PENCIL and a ruler. NOT freehand. 8. NO red or green ink may be used. 9. Use 𝜋 as 3,142 and NOT as 10. 22 7 Write neatly and legibly. ____________________________________________________________ Gateways to Engineering Studies 96 Industrial Electronics N2 QUESTION 1 1. Define the following: 1.1 Impedance (2) 1.2 Photodiodes (2) 1.3 Doping (2) 1.4 Threshold voltage (2) 1.5 Covalent bonds (2) [10] QUESTION 2 2 Refer to FIGURE 1 (on the attached DIAGRAM SHEET) and calculate the following: 2.1 The total current flowing in the circuit (5) 2.2 The voltage drop across the R1 resistor (4) 2.3 The current flowing through R2 resistor (2) 2.4 The power used in the 2 0 resistor (2) [13] QUESTION 3 3 A 10 0 resistor, 198 IJF capacitor and 10 mH inductor are connected in series. The circuit is connected to a 50 V/50-Hz supply. Calculate the following: 3.1 The inductive reactance (2) 3.2 The capacitive reactance (2) 3.3 The impedance of the circuit (2) 3.4 The current flowing in the circuit (2) 3.5 The phase angle between the voltage and current (2) [10] Gateways to Engineering Studies 97 Industrial Electronics N2 QUESTION 4 4.1 Draw and label a sine wave of 720° with an RMS value of 220 V with a frequency of 50 Hz. (4) 4.2 Calculate the following for the sine wave in QUESTION 4.1: 4.2.1 The maximum value (2) 4.2.2 The average value (2) 4.2.3 The peak-peak value (2) 4.2.4 The time period in seconds (2) [12] QUESTION 5 5.1 Draw labelled circuit symbols for the following: 5.1.1 A PN-junction diode (2) 5.1.2 Zener diode (2) 5.1.3 Varactor diode (2) 5.2 With the aid of neat labelled circuit diagrams, explain the following as applicable to PN-junction diodes: (4) Forward bias 5.6 Draw a fully labelled circuit diagram of a half-wave rectifier using a step down transformer, a diode, capacitor and a load resistor. (6) [16] QUESTION 6 6.1 6.2 State FOUR advantages of the digital meter as compared to the analog meter. (4) State THREE precautions which must be taken when measuring voltage with a multimeter. (3) [7] QUESTION 7 Gateways to Engineering Studies 98 Industrial Electronics N2 With reference to the theory of TRANSISTORS, answer the following questions: 7.1 7.2 Draw and label a single-stage NPN transistor amplifier in a common emitter configuration. A microphone and a loudspeaker must be connected to the input and output terminals. (6) Name the THREE classes of amplifiers. (3) [9] QUESTION 8 8.1 Name THREE most commonly used examples of transducers. (3) 8.2 Describe the difference between a light dependent resistor and a thermistor. (4) 8.3 The input power to a system is 100 mW and the power it delivers at the output is 10 mW. Calculate the system's power loss. (6) [13] QUESTION 9 9.1 9.2 Draw the TABLE in FIGURE 2 on the attached DIAGRAM SHEET A in the ANSWER BOOK and show the coupling between the transmitter and receiver for a 240° phase shift. (6) State FOUR applications of synchronous systems. (4) [10] TOTAL: 100 Gateways to Engineering Studies 99 Industrial Electronics DIAGRAM SHEET A Gateways to Engineering Studies 100 N2 Industrial Electronics INDUSTRIAL ELECTRONICS N2 FORMULA SHEET Gateways to Engineering Studies 101 N2 Industrial Electronics Gateways to Engineering Studies 102 N2 Industrial Electronics Gateways to Engineering Studies 103 N2 Industrial Electronics Marking Guidelines NOVEMBER 2012 NATIONAL CERTIFICATE INDUSTRIAL ELECTRONICS N2 (8080602) This marking guideline consists of 6 pages. Gateways to Engineering Studies 104 N2 Industrial Electronics N2 QUESTION 1 1.1 1.2 1.3 1.4 1.5 Impedance is the total resistance offered to a circuit by the inductor, capacitor and resistor. √√ (2) Photodiodes are diodes which offer a high resistance in the dark, but when incident, light falls onto the pn-junction, the diodes resistance decreases. √√ (2) A process achieved by adding impurity atoms to silicon or germanium to increase the materials conductivity. √√ (2) The forward bias voltage required to overcome the depletion region of the diode for silicon diodes its 0, 6. √√ (2) Covalent bonds is the sharing of valency electrons by two atoms. √√ (2) [10] QUESTION 2 2.1 𝑅// = 𝑅// = 2.2 15 𝑥 10 15+10 20 𝑥 20 20+20 10 𝑥 6 = 6𝛺 √ = 10𝛺 √ 𝑅// = 10+6 = 3,75 𝛺 √ 𝑅𝑇 // = 3,75 + 2 = 5,75 𝛺 √ 12 𝐼𝑇 = 5,75 = 2,08 𝐴 √ (5) 𝑉3 = 2,08 𝑥 2 = 4,174 𝑉 √√ Voltage across 𝑅1 = 12 − 4,174 = 7,826 𝑉 √√ (4) 7,826 2.3 𝐼2 = 2.4 𝑃 = 2,08 𝑥 2 = 4,16 𝑊 √√ 20 (2) = 0,391 𝐴 √√ (2) [13] QUESTION 3 3.1 𝑋𝐿 = 2𝜋𝜋𝑓𝑥 2𝜋 𝑥 50 𝑥 10 𝑥 10−3 = 3,14 𝛺 √√ 3.2 𝑋𝐶 = 3.3 𝑍𝑇 = √102 + (16,08 − 3,14 = 167,557 𝛺 √√ 3.4 𝐼𝑇 = 𝑉𝑡 𝑍𝑡 1 2 𝑥 3,141 𝑥 50 𝑥 198 𝑥 10−6 = 50 167,557 = 0,298 𝐴 (2) = 16,08 √√ (2) 2 (2) √√ Gateways to Engineering Studies 105 (2) Industrial Electronics 3.5 𝑅 10 𝑧 167,557 𝜑 = cos−1 = cos−1 = 86,57 √√ N2 (2) [10] QUESTION 4 4.1 (4) 4.2.1 RMS = 0,707 x Maximum = 0,707 x Max 220 = 0,707 x Max Max = 220,0,707 = 311,174 V √√ (2) 4.2.2 Average value = 0,637 x Maximum = 0,637 x 311,174 V = 198,217 V √√ (2) 4.2.3 Peak to Peak = 2 x Maximum = 2 x 311,174 = 622,348 V √√ (2) 4.2.4 𝑡= 𝐼 𝑓 = 𝐼 50 = 0,02 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 √√ (2) [12] QUESTION 5 5.1.1 (2) 5.1.2 (2) 5.1.3 (2) 5.2 Forward bias Gateways to Engineering Studies 106 Industrial Electronics N2 Positive terminal connected to the anode and negative terminal to the cathode, cause current flow through the diode. (4) 5.3 (6) [16] QUESTION 6 6.1 5.2 They are more robust/More accurate; No parallax error A constant high impedance is offered on all voltage ranges Overload is indicated/Reverse polarity is indicated/Auto ranging available (4) Always connect a voltmeter across the component/The correct polarity should always be observed/Always take loading effect of voltmeter into account If uncertain use highest scale and decreases if necessary (3) [7] QUESTION 7 7.1 (6) 5.2 Class A, B and C (3) [9] Gateways to Engineering Studies 107 Industrial Electronics N2 QUESTION 8 8.1 8.2 A loudspeaker A microphone A solar cell (3) LDR – This is a light sensitive resistor. The resistance varies with change in light intensity. √√ Thermistor – This is a temperature sensitive resistor. The resistance varies with a change in temperature. (NTC or PTC) √√ 8.3 𝑁 = 10 𝐿𝑜𝑔 (4) 𝑃0 𝑃1 10 𝑚𝑊 = 10𝐿𝑜𝑔 100 𝑚𝑊 √√ = −10 𝑑𝐵(𝑙𝑜𝑠𝑠 𝑜𝑟 𝑛𝑒𝑔𝑎𝑡𝑖𝑣𝑒 𝑔𝑎𝑖𝑛) √√√√ (6) [13] QUESTION 9 9.1 5 marks for each correct coupling. 1 extra mark if all correct – 6 marks 9.2 (6) Control of power tools/Control positioning of gun turrets/Control of dam sluice gates Remote positioning of communication systems/Remote control of model cars Angular displacement of ships rudder/Rapid and accurate transmission of information between/Equipment and stations/Control the course of missiles (4) [10] TOTAL: 100 Gateways to Engineering Studies 108 Industrial Electronics Table of C N2 Past Examination Papers APRIL 2012 NATIONAL CERTIFICATE INDUSTRIAL ELECTRONICS N2 (8080602) 22 March (X-Paper) 09:00 – 12:00 Gateways to Engineering Studies 109 Industrial Electronics N2 This question paper consists of 5 pages, 1 diagram sheet and a 3-page formula sheet. TIME: 3 HOURS MARKS: 100 __________________________________________________________________ INSTRUCTIONS AND INFORMATION 1. Answer ALL the questions. 2. Read ALL the questions carefully. 3. Number the answers according to the numbering system used in this question paper. 4. Keep sub-sections of questions together. 5. Rule off across the page on completion of each question. 6. Use only IEC symbols and units throughout. 7. ALL sketches must be neat, using a pencil and a ruler NOT freehand. 8. NO red or green ink may be used. 9. Use 𝜋 as 3,142 and NOT as 10. Write neatly and legibly. ______________________________________ 22 7 Gateways to Engineering Studies 110 Industrial Electronics N2 QUESTION 1 1. Indicate whether the following statements are TRUE or FALSE. Choose the answer and write only 'true' or 'false' next to the question number (1.1 - 1.10) in the ANSWER BOOK. 1.1 A decibel is one tenth of a bel. (1) 1.2 A synchro system is the electrical equivalent of mechanical transfer of information over a long distance. (1) 1.3 The voltmeter must always be connected in parallel with the load. (1) 1.4 The resistance of the NTC thermistors decreases as the temperature increases. (1) 1.5 The common emitter amplifier has a 180° phase shift. (1) 1.6 The mid-ordinate rule is used to calculate the RMS values of sinusoidal wave forms. (1) The sum of the currents flowing towards a point is equal to the sum of the currents flowing away from the same point. (1) 1.8 Electrons on the outer energy level are called valence electrons. (1) 1.9 Varactor diodes are most commonly used in FM and TV receiver circuits. (1) 1.10 Doping is the addition of impurities to pure semi-conductor materials. (1) 1.7 [10] QUESTION 2 2. Refer to FIGURE 1 (attached DIAGRAM SHEET) and calculate the following: 2.1 The total resistance of the circuit (4) 2.2 The current flowing through the 100 Ω resistor (4) 2.3 The voltage drop across the 20 Ω resistor (3) 2.4 The total power consumed by the circuit (3) [14] QUESTION 3 3. Refer to FIGURE 2 (attached DIAGRAM SHEET) and calculate the following. Gateways to Engineering Studies 111 Industrial Electronics N2 3.1 The value of the capacitor (3) 3.2 The value of the inductor (3) 3.3 The resonant frequency (4) 3.4 The voltage drop across the inductor and the capacitor (4) [14] QUESTION 4 4.1 4.2 Draw neat, labelled characteristic curves of the silicon and germanium diodes on the same axis. (6) Draw a fully labelled circuit diagram of a direct current power supply using FOUR diodes, step down transformer and filter capacitor. (5) [11] QUESTION 5 5. Refer to the table below and make use of the mid-ordinate rule to determine the following: 5.1 The mid-ordinates of the voltage (3) 5.2 The average value (3) 5.3 The RMS value (3) 5.4 The crest factor (2) 5.5 The form factor (2) (The above values are ordinates and not the mid-ordinate values) [13] QUESTION 6 6.1 State TWO precautions when using an ampere meter. (2) 6.2 State THREE advantages of digital meters over analogue meters. (3) 6.3 A Voltmeter has a full scale defection of 5 mA and an internal resistance of 100 ohms. Calculate the value of the resistor that would enable the meter to Gateways to Engineering Studies 112 Industrial Electronics N2 measure a voltage of 5 V. Also draw a neat, labelled circuit diagram to show where this resistor should be connected. (5) [10] QUESTION 7 7. Answer the following questions with reference to transistor theory. Write only the answer next to the question number (7 .1 - 7.3) in the ANSWER BOOK. 7.1 Draw and label a circuit symbol of a PNP silicon transistor. (3) 7.2 Name the THREE classes of transistor amplifiers. (3) 7.3 Draw a labelled circuit diagram of a common BASE amplifier circuit which uses an NPN transistor. (3) [9] QUESTION 8 8.1 5.2 Explain the operation of the following transducers: 8.1.1 Thermo couple (3) 8.1.2 Bi-metal strip (3) Calculate the gain or loss of an amplifier with an input of 1 W and an output of 100 mW. (4) [10] QUESTION 9 9.1 Define Lenz's law. (5) 9.2 Draw a neat, labelled symbol of a synchro. (3) 9.3 State THREE advantages of synchro-systems over mechanical systems. (3) [9] TOTAL: 100 DIAGRAM SHEET Gateways to Engineering Studies 113 Industrial Electronics Gateways to Engineering Studies 114 N2 Industrial Electronics INDUSTRIAL ELECTRONICS N2 FORMULA SHEET Gateways to Engineering Studies 115 N2 Industrial Electronics Gateways to Engineering Studies 116 N2 Industrial Electronics Gateways to Engineering Studies 117 N2 Industrial Electronics Marking Guidelines APRIL 2012 NATIONAL CERTIFICATE INDUSTRIAL ELECTRONICS N2 (8080602) The marking guideline consists of 5 pages. Gateways to Engineering Studies 118 N2 Industrial Electronics N2 QUESTION 1 1.1 True (1) 1.2 True (1) 1.3 True (1) 1.4 True (1) 1.5 True (1) 1.6 False (1) 1.7 True (1) 1.8 True (1) 1.9 True (1) 1.10 True (1) [10] QUESTION 2 2.1 20 𝑥 5 𝑅// = 20 ÷5 = 4𝛺 √ 𝑅𝑆 = 4 𝛺 + 60 𝛺 + 36 𝛺 = 100 𝛺 √ 𝑅// = (100 𝑥 100)/200 = 50𝛺 √ 𝑅𝑡 = 50 𝛺 + 50 𝛺 = 100 𝛺 √√ 𝐼𝑇 = 50/100 = 0,5 𝐴 (4) 2.2 I2 = It − I4 = 0,5 A − 0,25 A = 0,25 A √√√√ (4) 2.3 𝑉20𝛺 = 𝐼 𝑥 𝑅 = 0,05 𝑥 20 = 1𝑉 √√√ (3) 2.4 𝑃 = 𝐼 2 𝑥 𝑅 = 0,52 𝑥 100 = 25 𝑊 √√√ 𝑃 = 𝑉 2 /𝑅 = 502 /100 = 25 𝑊 (3) [14] QUESTION 3 3.1 𝑋𝑐 = 1/2𝜋𝑓𝑐 𝐶 = 1/2𝜋𝑋𝑐 = 1/2𝜋𝑥50𝑥10 = 318,59𝜇𝐹 √√√ (3) 3.2 𝑋𝐿 = 2𝜋𝑓𝐿 𝐿 = 10/2𝜋𝑥50 = 31𝑚𝐻 √√√ (3) Gateways to Engineering Studies 119 Industrial Electronics 3.3 𝑓𝑜 = 3.4 𝐼𝑇 = 1 2𝜋√𝐿𝐶 𝑉𝑡 𝑍𝑡 = 1/0,01997 = 50𝐻𝑧 𝑋𝐶 = 𝑋𝐿 = 200/100 = 2𝐴 √√ N2 (4) (4) 𝑉𝐿 = 2𝑥10 = 20𝑉 √ 𝑉𝑐 = 2𝑥10 = 20𝑉 √ [14] QUESTION 4 4.1 (6) 4.2 (5) [11] QUESTION 5 5.1 MID-ORDINATES IN VOLT: 11,25/50/112,5/122,5/72,5/25 √√√ (3) 5.2 𝑣𝑅𝑀𝑆/𝐺𝐸𝑀 = 11,25 + 50 + 112,5 + 122,5 + 72,5 + 25/6 = 65,625 𝑉 √√√ (3) 5.3 5.4 1 2 2 𝑣 +𝑣 +𝑉 𝑉𝑊𝐺𝐾 = √ 2 𝑛2 2 = 77,642 𝑉 √√√ Form = 77,64/65,63 = 1,183 √√ Crest = 150/77,64,63=1,932 √√ (3) (2) (2) [13] Gateways to Engineering Studies 120 Industrial Electronics N2 QUESTION 6 6.1 The ammeter must be connected in series with the load. Always start with the highest scale. Switch of the power before measuring. (2) 6.2 More sensitive. More robust. No parallax error. No guessing. Overload indication. (3) 6.3 𝑅𝑆 = 𝑉/𝐼𝑚 − 𝑅𝑚 = 5/5𝑚𝐴 − 100 = 1000 − 100 = 900𝛺 (5) [10] QUESTION 7 7.1 (3) 7.2 A,B AND C (3) 7.3 (3) [9] QUESTION 8 8.1 The thermo couple is a temperature device consisting of two metals joined at the ends. When one end is heated a potential difference is set up across the two ends. This potential difference is proportional to the difference in Gateways to Engineering Studies 121 Industrial Electronics N2 temperature between the two ends. Materials used in the manufacture of thermo-couples include nickel-chrome and nickel-aluminium. √√√ 8.2 The bi-metal strip instead of generating a voltage it indicates only a change in temperature. The two Metals have different expansion coefficients therefore it will bend when it is heated. √√√ 8.3 𝑁 = 10 𝐿𝑜𝑔 𝑃0 𝑃1 (3) (3) (4) = 10𝐿𝑜𝑔 100 𝑚𝑤 = −10 𝑑𝐵 √√√√ [10] QUESTION 9 9.1 When a magnetic field cuts through a coil it induces a current to flow which will generate a magnetic field. This magnetic field will oppose the original field. (5) 9.2 (3) 9.3 Receiver and transmitter can be far apart. Contact can be by means of radio, telemetering or wires. Very little energy is used. (3) [9] TOTAL: 100 Gateways to Engineering Studies 122
