Basic Aircraft Maintenance Training Manual 3.10 Magnetism PDF

GMR Air Cargo and Aerospace Engineering Limited, Hyderabad, Telangana, India. Website: www.gmrschoolofaviation.com Email: [email protected] BASIC AIRCRAFT MAINTENANCE...

GMR Air Cargo and Aerospace Engineering Limited, Hyderabad, Telangana, India. Website: www.gmrschoolofaviation.com Email: [email protected] BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL MODULE 3 - ELECTRICAL FUNDAMENTAL SUBMODULE 3.10 – MAGNETISM CATEGORY: B1.1/B2/B1.1+B2 ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 1 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 8.3 PRINCIPLE OF OPERATION: -............................................................ 19 TABLE OF CONTENTS 8.4 VARIOUS TYPES OF ELECTROMAGNETS....................................... 19 FOREWORD.................................................................................................... 3 9. HAND CLASP RULES TO DETERMINE MAGNETIC FIELD AROUND COPYRIGHT NOTICE...................................................................................... 3 CURRENT CARRYING CONDUCTOR.......................................................... 20 BASIC KNOWLEDGE REQUIREMENTS........................................................ 4 9.1 LEFT-HAND RULE................................................................................ 20 KNOWLEDGE LEVELS – CATEGORY A, B1, B2, B3 AND C AIRCRAFT 9.2 RIGHT HAND THUMB RULE............................................................... 20 MAINTENANCE LICENCE............................................................................... 5 10. MAGNETOMOTIVE FORCE............................................................... 21 LEVEL 1........................................................................................................ 5 11. MAGNETIC FIELD STRENGTH......................................................... 21 LEVEL 2........................................................................................................ 5 12. MAGNETIC FLUX DENSITY............................................................... 21 LEVEL 3........................................................................................................ 5 13. MAGNETIC PERMEABILITY.............................................................. 21 ABBREVIATIONS............................................................................................. 6 13.1 FACTORS AFFECTING MAGNETIC PERMEABILITY...................... 21 1. MAGNETISM............................................................................................ 7 13.2 MAGNETIC PERMEABILITY FORMULA........................................... 21 1.1 THEORY OF MAGNETISM.................................................................... 7 14. THE HYSTERESIS LOOP.................................................................. 22 2. PROPERTIES OF A MAGNET............................................................... 10 15. EDDY CURRENTS............................................................................. 23 3. ACTION OF MAGNETS SUSPENDED IN THE EARTH MAGNETIC FIELD.............................................................................................................. 12 16. PRECAUTIONS FOR CARE AND STORAGE OF MAGNETS.......... 24 4. MAGNETISATION AND DEMAGNETISATION..................................... 13 4.1 MAGNETIZATION:............................................................................... 13 4.2 DEMAGNETIZATION: -........................................................................ 13 5. MAGNETIC SHIELDING........................................................................ 14 6. VARIOUS TYPES OF MAGNETIC MATERIAL...................................... 15 6.1 TYPES OF MAGNETS......................................................................... 16 7. ELECTROMAGNETISM......................................................................... 17 8. ELECTROMAGNET............................................................................... 19 8.1 INTRODUCTION.................................................................................. 19 8.2 ELECTROMAGNET CONSTRUCTION............................................... 19 ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 2 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM FOREWORD It is important to note that the information in this book is for study/ training purposes only and no revision service will be provided to the holder. When carrying out a procedure/ work on aircraft/ aircraft equipment you must always refer to the relevant aircraft maintenance manual or equipment manufacturer's handbook. For health and safety in the workplace you should follow the regulations/ guidelines as specified by the equipment manufacturer, your company, national safety authorities and national governments. COPYRIGHT NOTICE © Copyright. All worldwide rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form by any other means whatsoever: i.e., photocopy, electronic, mechanical recording or otherwise without the prior written permission of GMR School of Aviation. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 3 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM BASIC KNOWLEDGE REQUIREMENTS These Study Notes comply with the syllabus of DGCA Regulation, CAR-66 (Appendix I) and the associated Knowledge Levels as specified. These Study Notes comply with the syllabus of EASA Regulation (EU) No. 1321/2014 Annex (Part-66) Appendix I and the associated Knowledge Levels as specified below: CAR 66/ Level Objective PART 66 Reference B1.1 B2 Magnetism (a) Theory of magnetism; Properties of a magnet; Action of a magnet suspended in the Earth's magnetic field; Magnetisation and demagnetisation; 2 2 Magnetic shielding; 3.10 Various types of magnetic material; Electromagnets construction and principles of operation; Handclasp rules to determine: magnetic field around current carrying conductor; (b) Magnetomotive force, field strength, magnetic flux density, permeability, hysteresis loop, retentivity, coercive force reluctance, saturation point, eddy currents; 2 2 Precautions for care and storage of magnets. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 4 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM KNOWLEDGE LEVELS – CATEGORY A, B1, B2, B3 AND C AIRCRAFT MAINTENANCE LICENCE Basic knowledge for categories A, B1, B2 and B3 are indicated by the allocation of knowledge levels indicators (1, 2 or 3) against each application subject. Category C applicants must meet either the category B1 or the category B2 basic knowledge levels. The knowledge level indicators are defined as follows: LEVEL 1 A familiarization with the principal elements of the subject. Objectives: The applicant should be familiar with the basic elements of the subject. The applicant should be able to give a simple description of the whole subject, using common words and examples. The applicant should be able to use typical terms. LEVEL 2 A general knowledge of the theoretical and practical aspects of the subject. An ability to apply that knowledge. Objectives: The applicant should be able to understand the theoretical fundamentals of the subject. The applicant should be able to give a general description of the subject using, as appropriate, typical examples. The applicant should be able to use mathematical formulae in conjunction with physical laws describing the subject. The applicant should be able to read and understand sketches, drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using detailed procedures. LEVEL 3 A detailed knowledge of the theoretical and practical aspects of the subject. A capacity to combine and apply the separate elements of knowledge in a logical and comprehensive manner. Objectives: The applicant should know the theory of the subject and interrelationships with other subjects. The applicant should be able to give a detailed description of the subject using theoretical fundamentals and specific examples. The applicant should understand and be able to use mathematical formulae related to the subject. The applicant should be able to read, understand and prepare sketches, simple drawings and schematics describing the subject. The applicant should be able to apply his knowledge in a practical manner using the manufacturer’s instructions. The applicant should be able to interpret results from various sources and measurements and apply corrective action where appropriate. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 5 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM ABBREVIATIONS ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 6 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 1. MAGNETISM 1.1 THEORY OF MAGNETISM Theory of magnetism is given by a scientist Weber, and hence it is also called as Weber’s theory. From the concept of this theory, we can say that all the substances having properties of the magnet are made up of smaller magnets present in a large number. The molecules of the un-magnetized body have magnet properties, and due to which magnetic forces arise, these magnetic forces are made neutral by the neighbouring molecules because it also has magnetic force but not in the same direction as that of its adjacent molecule because of which there is no magnetic effect present. Whereas in a magnetized body the directions of tiny magnets are in such a way that all the tiny magnets are headed towards the north pole, and the other direction is called the south pole which faces another side of the magnetic molecules. Figure 1 ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 7 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM If the material is ferromagnetic, then it will act as a permanent magnet if it is placed in a magnetic field for a particular time because its molecules are aligned in the direction of magnetic field permanently and do not change ever after it is removed from the magnet. Therefore, based on the above explanation, we can say that a magnetic material must have a north pole and a south pole. Note: We can note that both magnetized and unmagnetized material has small magnetic molecules, but due to their alignment and resultant of magnetic force, their magnetic property as a whole is defined. The presence of the magnetic force or field around a magnet can best be demonstrated by the experiment illustrated in Figure 2. A sheet of transparent material, such as glass or Lucite TM, is placed over a bar magnet andiron filings are sprinkled slowly on this transparent shield. If the glass or Lucite is tapped lightly, the iron filings will arrange themselves in a definite pattern around the bar, forming a series of lines from the north to south end of the bar to indicate the pattern of the magnetic field. Figure 2 As shown, the field of a magnet is made up of many individual forces that appear as lines in the iron filing demonstration. Although they are not " lines" in the ordinary sense, this word is used to describe the individual nature of the separate forces making up the entire magnetic field. These lines of force are also referred to as magnetic flux. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 8 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM They are separate and individual forces, since one line will never cross another; indeed, they actually repel one another. They remain parallel to one another and resemble stretched rubber bands, since they are held in place around the bar by the internal magnetizing force of the magnet. The demonstration with iron filings further shows that the magnetic field of a magnet is concentrated at the ends of the magnet. These areas of concentrated flux only are called the north and south poles of the magnet. There is a limit to the number of lines of force that can be crowded into a magnet of a given size. When a magnetizing force is applied to a piece of magnetic material, a point is reached where no more lines of force can be induced or introduced. The material is then said to be saturated Magnetic phenomena result from the movement of electrical charges. The vector quantity of the magnetic induction field is represented by “𝐵” and depends on the movement of these charges. The vector magnetic field is indicated by “H” it also reflects the influence of the environment. In common materials, the vectors 𝐵 and H are collinear or tangential. MAGNETIC QUANTITIES Magnetic field “H” This is the space around a magnet or a coil in which its influence is felt. The field lines move from the north pole to the south pole outside the magnetised material. It is expressed in A/m Magnetic induction field “𝑩” This is the value of a magnetic field at a point in space. The value of the magnetic induction field “𝐵” depends on the shape and on the magnetic material. 𝐵 = 𝜇0. 𝜇𝑟. 𝐻 where: 𝐵: in Tesla T, 𝜇0: vacuum permeability, 𝜇𝑟 : relative permeability. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 9 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 2. PROPERTIES OF A MAGNET We already know that magnets are made up of the magnetic substance. Magnets have certain important properties. They are, ATTRACTIVE PROPERTY – Magnet attracts ferromagnetic materials like iron, cobalt, and nickel. REPULSIVE PROPERTIES – Like magnetic poles repel each other and unlike magnetic poles attract each other The two like poles repel one another because the lines of force will not cross each other. As the arrows on the individual lines indicate, the lines turn aside as the two like poles are brought near each other and travel in a path parallel to each other. Lines moving in this manner repel each other, causing the magnets as a whole to repel each other. By reversing the position of one of the magnets, the attraction of unlike poles can be demonstrated, as shown in Figure. Figure 3 DIRECTIVE PROPERTY – A freely suspended magnet always points in a north-south direction also, A magnetic pole can never be isolated; Magnetisation can be permanent or temporary. If a magnet is broken, we get two magnets, each having a south pole and a north pole. This feature supports the theory that each molecule is a magnet, since each successive division of the magnet produces still more magnets. Between two poles of horse shoe magnet uniform field exists. A free magnet will have expanding magnetic field from one pole to other Figure 4 (Creation of pole pairs through single magnet) ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 10 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM ORIENTATION OF A MAGNET The direction of a moving magnet is roughly that of True North in the Earth’s magnetic field. A pole exerts a magnetic force on any other pole. Like poles repel each other and opposite poles attract each other Figure 5 Figure 6 (Attractive property of magnet through insulator) Specific features of a magnet are that a magnetic pole attracts only certain materials: iron, nickel, cobalt. These materials are said to be magnetic or ferromagnetic. Its action is felt, even though a plate of glass, cardboard or another insulator. There is no known insulator for magnetic flux, or lines of force, since they will pass through all materials. However, they will pass through some materials more easily than others. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 11 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 3. ACTION OF MAGNETS SUSPENDED IN THE EARTH MAGNETIC FIELD Magnetism is an invisible force, the ultimate nature of which has not been fully determined. It can best be described by the effects it produces. Examination of a simple bar magnet similar to that illustrated in Figure 7 discloses some basic characteristics of all magnets. If the magnet is suspended to swing freely, it will align itself with the earth's magnetic poles. One end is labelled "N," meaning the north seeking end or pole of the magnet. If the "N" end of a compass or magnet is referred to as north seeking rather than north, there will be no conflict in referring to the pole it seeks, which is the north magnetic pole. The opposite end of the magnet marked "S" is the south seeking end and points to the south magnetic pole. Since the earth is a giant magnet, its poles attract the ends of the magnet. These poles are not located at the geographic poles and termed as magnetic north and true north. The difference between True North and magnetic north is called magnetic variation. Figure 7 (One end of magnetized strip points to the magnetic north pole) ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 12 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 4. MAGNETISATION AND DEMAGNETISATION 4.1 MAGNETIZATION: Magnetization is the change of magnetic moment of a magnetic per unit volume, whereas demagnetization is the removal of the magnetic property of the magnet. 4.2 DEMAGNETIZATION: - Demagnetization is the creation of a magnetic field by the magnetization in a magnet. This state can be defined as the alignment of domains which has been subdivided into smaller domains having random directions of magnetization. The process of demagnetization is also known as magnetic cleaning, degaussing, etc., which refers to the returning of a magnetic to a neutral state. We can achieve this state with the use of an alternating magnetic field for the removal of evenly aligned elementary magnets into a homogenous disorder. Over time, demagnetization can occur naturally. The speed of this process usually depends on the material, the temperature, and some other factors. Moreover, this can occur by accident as well. However, it is typically performed intentionally upon the magnetization of parts of metals and when there is a requirement to destroy magnetic-encoded data. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 13 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 5. MAGNETIC SHIELDING To avoid that the insulation does not work or works only to a limited extent, materials from the following list of materials should ideally be Since the magnetic lines of force form a continuous loop, they form a used for magnetic field shielding: magnetic circuit. It is impossible to say where in the magnet they originate or start. Arbitrarily, it is assumed that all lines of force leave the MU metal north pole of any magnet and enter at the south pole we have already Soft iron studied that there is no known insulator for magnetic flux, or lines of Silicon iron force, since they will pass through all materials. However, they will pass through some materials more easily than others. Shielded cables: used at wiring level to avoid interference with the signal transmitted or received; Thus, it is possible to shield items such as instruments from the effects of the flux by surrounding them with a material that offers an easier path for the lines of force. Magnetic shielding describes a process in which a magnetic field is excluded from a certain area by deliberately redirecting its field lines. For this purpose, permanent magnets are usually used, or so-called opposing fields are induced. In certain cases, a sufficiently large distance can also be sufficient to achieve a shielding effect. Figure 9 shows an instrument surrounded by a path of soft iron, which offers very little opposition to magnetic flux. The lines of force take the easier path, the path of greater permeability, and are guided away from the instrument. Figure 9 (Shielded cables) Figure 8 (Magnetic shield) ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 14 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 6. VARIOUS TYPES OF MAGNETIC MATERIAL Materials such as soft iron and other ferrous metals are said to have a high permeability, the measure of the ease with which magnetic flux can penetrate a material. The permeability scale is based on a perfect vacuum with a rating of one. Air and other nonmagnetic materials are so close to this that they are also considered to have a rating of one. The nonferrous metals with a permeability greater than one, such as nickel and cobalt, are called paramagnetic. The term ferromagnetic is applied to iron and its alloys, which have by far the greatest permeability. Any substance, such as bismuth, having a permeability of less than one, is considered diamagnetic. Figure 11 Figure 10 ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 15 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 6.1 TYPES OF MAGNETS Magnets can be made in many different shapes, such as balls, cylinders, or disks. One special type of magnet is the ring magnet, or Gramme ring, Magnets are either natural or artificial. Since naturally occurring magnets often used in instruments. This is a closed loop magnet, similar to the or lodestones have no practical use, all magnets considered in this study type used in transformer cores, and is the only type that has no poles. are artificial or manmade. Artificial magnets can be further classified as permanent magnets, which retain their magnetism long after the Sometimes special applications require that the field of force lie through magnetizing force has been removed, and temporary magnets, which the thickness rather than the length of a piece of metal. Such magnets quickly lose most of their magnetism when the external magnetizing are called flat magnets and are used as pole pieces in generators and force is removed. Modern permanent magnets are made of special motors. alloys that have been found through research to create increasingly better magnets. The most common categories of magnet materials are made out of Aluminium-Nickel-Cobalt (Alnicos), Strontium-Iron (Ferrites, also known as Ceramics), Neodymium-Iron Boron (Neo magnets), and Samarium-Cobalt. Alnico, an alloy of iron, aluminium, nickel and cobalt, and is considered one of the very best. Others with excellent magnetic qualities are alloys such as Remalloy™ and Permendur™. The ability of a magnet to hold its magnetism varies greatly with the type of metal and is known as retentivity. Magnets made of soft iron are very easily magnetized but quickly lose most of their magnetism when the external magnetizing force is removed. The small amount of magnetism remaining, called residual magnetism, is of great importance in such electrical applications as generator operation. Steel is magnetised in a magnetic field created by a solenoid and remains magnetised after the field is removed. The North and South poles formed at the ends of the bar depend on the direction of the current supplying the solenoid. Horseshoe magnets are commonly manufactured in two forms. The most common type is made from a long bar curved into a horseshoe shape, while a variation of this type consists of two bars connected by a third bar, or yoke. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 16 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 7. ELECTROMAGNETISM As long as current flows in the conductor, the lines of force remain around it. (Figure 13) If a small current flow through the conductor, there In 1820, the Danish physicist, Hans Christian Oersted, discovered that will be a line of force extending out to circle A. If the current flow is the needle of a compass brought near a current carrying conductor increased, the line of force will increase in size to circle B, and a further would be deflected. When the current flow stopped, the compass needle increase in current will expand it to circle C. As the original line (circle) returned to its original position. This important discovery demonstrated of force expands from circle A to B, a new line of force will appear at a relationship between electricity and magnetism that led to the circle A. As the current f low increases, the number of circles of force electromagnet and to many of the inventions on which modern industry increases, expanding the outer circles farther from the surface of the is based. current carrying conductor. If the current flow is a steady nonvarying Oersted discovered that the magnetic field had no connection with the direct current, the magnetic field remains stationary. When the current conductor in which the electrons were flowing, because the conductor stops, the magnetic field collapses and the magnetism around the was made of nonmagnetic copper. The electrons moving through the conductor disappears. wire created the magnetic field around the conductor. Since a magnetic field accompanies a charged particle, the greater the current flow, and the greater the magnetic field. Figure12 illustrates the magnetic field around a current carrying wire. A series of concentric circles around the conductor represent the field, which if all the lines were shown would appear more as a continuous cylinder of such circles around the conductor. Figure 13 (Expansion of magnetic field as current increases) Figure 12 ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 17 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM A compass needle is used to demonstrate the direction of the magnetic field around a current carrying conductor. (Figure 10-16) View As how s a compass needle positioned at right angles to, and approximately one inch from, a current carrying conductor. If no current were flowing, the north seeking end of the compass needle would point toward the earth's magnetic pole. When current flows, the needle lines itself up at right angles to a radius drawn from the conductor. Since the compass needle is a small magnet, with lines of force extending from south to north inside the metal, it will turn until the direction of these lines agrees with the direction of the lines of force around the conductor. As the direction of the compass needle is moved around the conductor, it will maintain itself in a position at right angles to the conductor, indicating that the magnetic field around a current carrying conductor is circular. As shown in View B of Figure 10-16, when the direction of current f low through the conductor is reversed, the compass needle will point in the opposite direction, indicating the magnetic field has reversed its direction. Figure 14 (Magnetic field around a current-carrying conductor) ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 18 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 8. ELECTROMAGNET 8.1 INTRODUCTION 1. It is defined as a magnet that is driven by electricity. 2. It can be adjusted by altering the amount of electric current flowing through it. 3. The property of magnetism is lost when the current flow is interrupted 8.2 ELECTROMAGNET CONSTRUCTION It consists of a long coil of insulated copper wire wrapped around a soft iron core that is magnetized only when an electric current passed through the coil. To make an electromagnet, one required a rod of soft iron and wind a coil of insulated copper wire around it. When the two ends of the copper coil are connected to a battery, an electromagnet is formed. 8.3 PRINCIPLE OF OPERATION: - As described in preceding topics an electromagnet t works on the principle of the magnetic effect of electric current Electricity passes through coils of wire in electromagnets. An electromagnet behaves like a magnet when it has electric current flowing through its coils, which creates magnetic fields. Electronic devices often use electromagnets when magnetic forces are only applied for a short time. 8.4 VARIOUS TYPES OF ELECTROMAGNETS There are several types of electromagnets Straight with fixed core; Horseshoe with fixed core; With plunger core; With armoured plunger core. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 19 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 9. HAND CLASP RULES TO DETERMINE MAGNETIC FIELD 9.2 RIGHT HAND THUMB RULE AROUND CURRENT CARRYING CONDUCTOR. The Right-hand thumb rule is used to determine the direction of 9.1 LEFT-HAND RULE magnetic field around a current carrying wire. The polarity of the electromagnet is determined by the left-hand rule in The rule states that when an electric current pass through a straight wire the same manner as the polarity of the coil without the core was that is held by the right hand with the thumb pointing upwards and the determined. If the coil is grasped in the left hand in such a manner that fingers curling up the wire, the thumb points in the direction of the the fingers curve around the coil in the direction of electron flow (minus conventional current (from positive to negative), and the fingers point in to plus), the thumb will point in the direction of the north pole. (Figure the direction of the magnetic field. 10-05) Below figure represents the direction of current and magnetic field through a straight current carrying conductor. Figure 15 (Left-hand rule applied to a coil) Figure 16 ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 20 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 10. MAGNETOMOTIVE FORCE 13. MAGNETIC PERMEABILITY The magnetic circuit can be compared in many respects to an electrical Magnetic permeability, also referred to as permeability in circuit. The magnetomotive force, causing lines of force in the magnetic electromagnetism, is a property of a magnetic material which supports circuit, can be compared to the electromotive force or electrical pressure the formation of a magnetic field. The term was coined by Oliver of an electrical circuit. The magnetomotive force is measured in gilberts, Heaviside in the year 1885. Magnetic permeability is a property that symbolized by the capital letter "F." The symbol for the intensity of the basically allows magnetic lines of force to pass through a material. In lines of force, or flux, is the Greek letter phi, and the unit of field intensity other words, the magnetic permeability of a material can also be said to is the gauss. An individual line of force, called a Maxwell, in an area of be its magnetisation capability. This helps in determining how one square centimetre produces a field intensity of one gauss. Using much magnetic flux can the material support, which will pass through it. reluctance rather than permeability, the law for magnetic circuits can be Magnetic permeability is defined as the ratio of the magnetic induction stated: a magnetomotive force of one gilbert will cause one Maxwell, or to the magnetic intensity. It is a scalar quantity and is denoted by the line of force, to be set up in a material when the reluctance of the material symbol μ. Magnetic permeability helps us measure a material’s is one. resistance to the magnetic field or measure the degree to which a 11. MAGNETIC FIELD STRENGTH magnetic field can penetrate through a material. It is a measure of the intensity of a magnetic field in a given area of that If the material has greater magnetic permeability, the greater will be the field. Represented as H, magnetic field strength is typically measured in conductivity for magnetic lines of force. amperes per meter (A/m), as defined by the International System of 13.1 FACTORS AFFECTING MAGNETIC PERMEABILITY Units (SI) Permeability also depends on several factors, such as the nature of the 12. MAGNETIC FLUX DENSITY material, humidity, position in the medium, temperature, and frequency It is amount of magnetic flux through unit area taken perpendicular to of the applied force. Magnetic permeability is always positive and can direction of magnetic flux. Flux Density (B) is related to Magnetic Field vary with a magnetic field. On the other hand, the opposite of magnetic (H) by B=μH. It is measured in Weber per square meter equivalent to permeability is magnetic reluctivity. Tesla [T]. 13.2 MAGNETIC PERMEABILITY FORMULA The magnetic permeability formula is given as follows; Magnetic permeability (μ) = B/H Where B = magnetic intensity and H = magnetising field. The SI unit of magnetic permeability is henry per meter (H/m) or newton per ampere squared (N⋅A−2). ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 21 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 14. THE HYSTERESIS LOOP The coercive force is the magnetizing force in the opposite direction that needs to be applied to remove the retained flux. The coercive force When magnetizing a material, there is a direct relationship between the reluctance of the material is the opposition to giving up the retained intensity of the magnetizing force and the amount of magnetism magnetic flux that remains after the magnetizing force is removed. developed in a material as demonstrated by the amount of flux (flux density) produced. A phenomenon called hysteresis loop reveals more Reluctance, the measure of opposition to the lines of force through a about this relationship. (Figure 17) material, can be compared to the resistance of an electrical circuit. The reluctance of soft iron, for instance, is much lower than that of air. By measuring the magnetic flux of a ferromagnetic material as the magnetizing force applied to the material is manipulated, the loop is drawn. Beginning at the origin for a material which is non-magnetized or has lost nearly all of its magnetism, as the magnetizing force is increased, the flux density (magnetic field) increases. Near point A, increases in magnetizing force produces very little increase in magnetic flux and the material is said to be magnetically saturated. When the magnetizing force is reduced to zero, some magnetic flux remains in the material (point B). This is referred to as a material's retentivity. Application of a reversed magnetizing force removes the flux than remained in the magnetizing material (point C). This is known as coercivity. As the reversed magnetizing force is increased, a similar flux build-up related to the intensity of the magnetizing force occurs with polarity opposite to the original (point D). Again, a point of saturation is reached as further increasing the intensity of the magnifying force produces virtually no change in flux density. When the magnetizing force is removed, retentivity caused some magnetic flux to remain (point E). Then, as the magnetizing intensity is increased in the original direction, the magnetic f lux increases in the Figure 17 (The hysteresis loop) original direction once again until saturation point is reached. (Some of the magnetizing force is used to remove the retentive flux so the flux curve does not pass through the origin.) Thus, a loop is formed that incorporates the hysteresis of the lingering f lux (retentivity) in the magnetized material. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 22 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 15. EDDY CURRENTS Inspection – It helps in the inspection of coating layers in metals and products. It’s a non-contact type of inspection, which does not damage When the magnetic field in a conductor is changed, eddy currents the work. develop. The eddy currents induce their own magnetic fields. The forces oppose their own development or dissipation as well as the development Surface Detection – Eddy current is one among the many methods to and dissipation of the conductor's magnetic field. The faster the change find the irregularity or discontinuity in the surface of the materials. in the conductor magnetic field, the greater the eddy currents and Induction Motor – The induction motor is rotated by employing Eddy associated magnetic fields. currents. It’s done when the induced currents are exposed to the metallic rotor spinning in the magnetic field. So, according to Lenz’s law, the relative motion is reduced between the rotor and the field and rotates in the direction of the magnetic field. Therefore, the induction motor rotates. Figure 18 Eddy currents tend to generate heat and reduce the efficiency of devices that rely on changing magnetic fields. Use of permeable laminations in the magnetic material helps suppress eddy currents. The choice of magnetic core material with low electrical conductivity also helps. One should not paint a picture in mind that eddy current is only a loss, though it affects the magnetic strength but the same property can be used for many applications, some of them related to our curriculum are listed below: - Structure Test – Eddy currents are widely used in structural identification and testing of metallic structures. It’s used to test the structural components of aircraft heat exchange tubes. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 23 of 24  3. ELECTRICAL FUNDAMENTAL BASIC AIRCRAFT MAINTENANCE TRAINING MANUAL 3.10. MAGNETISM 16. PRECAUTIONS FOR CARE AND STORAGE OF MAGNETS While durable permanent magnets are not indestructible, they should be handled with care and kept from being dropped or receiving mechanical shock. 1.Magnets should be stored at room temperature although any temperature below the temperature that they lose their permanent magnetism is acceptable. Most magnets don't lose their permanent magnetism until temperature is elevated above 400 °C. 2.Magnets should be stored in a dry place. Although most common magnets are not susceptible to moisture degradation, neodymium magnets may suffer. Separate storage of magnets is recommended. 3.If magnets are stored together they should be stored with opposite poles next to each other. The use of a keeper across the pole ends of a magnet is also recommended when possible. 4. To store multiple magnets in one place you will need to place them into a non-ferromagnetic container, for example a sealed wooden box or tupper ware. The non-ferromagnetic container helps to stop the magnet from attracting any unwanted metal debris. 5. A magnet’s strength can be weakened by factors such as high temperatures and storing next to high voltage electricity. When the magnet is exposed to factors such as these for a long time, it can become demagnetised. 6. The best way to prevent any loss in a magnet’s magnetic ability is to store it with a keeper. A keeper is a piece of iron that is temporarily added between the north and south poles of a magnet to prevent it from demagnetising by redirecting the magnetic field. If a keeper is not provided with your magnet, then store your magnets on a steel sheet. ISSUE 03, DATED 01 JUL 2024 FOR TRAINING PURPOSES ONLY Page 24 of 24