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A

Project Report

“ELECTROMAGNETIC PISTON”

Submitted to the department o mechanica! en"ineerin"

In partia! u!#!!ment o the re$uirement%

&or the de"ree o

'AC(ELOR O& TEC(NOLOG)

In

MEC(ANICAL ENGINEERING

*nder the "uidence o+ Submitted ',+

Pro- .u!deep %in"h pa! /(-O-0-1 Arjun %harma/22234566751

Pro- An8ur Raj9an%hi Arpit "ar"/222345667:1

Mechanica! En"ineerin" .ai!a%h 8umar/22234566:;1

La9i%h %harma/22234566:<1

Department of Mechanical Engineering

Bharat institute of technology

1

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U.P.T.U. (LUCKN!"

#$%&'%

DECL)*)T+N

We hereby declare that this submission is our own work and that, to the best of

our knowledge and belief, it contains no material previously published or written

by another person nor material which to a substantial extent has been accepted for

the award of any other degree or diploma of the university or other institute of

higher learning, except where due acknowledgment has been made in the text.

Signature: Signature:

Name : Arun Sharma Name : Arpit !arg

"oll No.: ###$%&''(& "oll No.: ###$%&''()

*ate : $#.'&.$'#) *ate : $#.'&.$'#)

Signature: Signature:

Name : +ailash +umar Name: avish Sharma

"oll No.: ###$%&'')- "oll No : ###$%&'')

*ate : $#.'&.$'#) *ate : $#.'&.$'#)

2

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CE*T+,+C)TE

This is to certify that Project Report entitled “ELECTROMAGNETIC

PISTON” which is submitted by Arjun sharma ,Arpit garg, ailash

umar, la!ish sharma in partial ful"llment of the re#uirement for the

award of degree $% Tech% in &epartment of 'echanical (ngineering of

)% P% Technical )ni!ersity, is a record of the candidate own wor

carried out by him under our super!ision% The matter embodied in this

thesis is original and has not been submitted for the award of any

other degree%

Pro-ect ui/e 0ignature1 E2aminer 0ignature1

3D4Director 0ignature 1

*

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)CKN!LEDMENT

/t gives us a great sense of pleasure to present the report of the 0. 1ech 2roect

undertaken during 0. 1ech. 3inal 4ear. We owe special debt of gratitude to our mentor

Mr )n5ur ra-6anshi7 Department of Mechanical Engineering7 Bharat +nstitute f

Technology7 Meerut for his constant support and guidance throughout the course of our

work. 5is sincerity, thoroughness and perseverance have been a constant source of

inspiration for us. /t is only his cogni6ant efforts that our endeavors have seen light of

the day.

We extend our grateful thanks to )sst. Professor )n5ur *a-6anshi7 Department of

Mechanical Engineering7 Bharat +nstitute f Technology7 Meerut for dedicating

his precious time, giving advice and helping us from the beginning to end of this

proect. 1his work would not succeed without his great supports.

We also take the opportunity to acknowledge the contribution of Professor Kul/eep

0ingh Pal7 3ea/ of Department of Mechanical Engineering7 Bharat institute f

Technology7 Meerut for his full support and assistance during the development of the

proect.

We also do not like to miss the opportunity to acknowledge the contribution of all

faculty members of the department for their kind assistance and cooperation during the

development of our proect. ast but not the least, we acknowledge our friends for their

contribution in the completion of the proect.

+

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)B0T*)CT

1he present inventions relates to an electromagnetic piston engine capable of producing

driving power by a reciprocal movement of a piston in a cylinder by electromagnetic

force.1he present invention has the obects to provide the electromagnetic piston engine

which can do without a variety of resistance inherent combustion piston engines, which

reduces the weight corresponding to a rotary assembly portion to a smaller value even if

a great output is produced , which can be readily employed together with power

transmission mechanisms and so on for use with conventional internal combustion

piston engines, and which has a high efficiency in energy consumption.

1he electromagnetic piston engine is provided with the cylinder and the piston madeeach of a magnetic material as well as with as the cylinder electromagnet having the

inner wall of the cylinder magneti6able to a one magnetic pole and with the piston

magneti6ation unit for magneti6ing a portion of the piston engageable with the cylinder

to a single magnetic pole in a fixed manner.

1he magneti6ation of the cylinder electromagnet generates magneticmagnetic attracting

force between the cylinder and the piston to cause the piston to move in a single

direction and thereafter magnetically repellent force to transfer the piston in the opposite

direction. 1his series of the actions are repeated to provide a continual reciprocalmovement of piston.

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-

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CNTENT0

TP+C N)ME

#.' /N1"7*891/7N

$.' 5/S17"4

(.' 5A"*WA" ";8/"<N1

&.' W77* 0AS

).' 91"7<A!N1

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).$ <A!N1

).( <A!N1/>A1/7N

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).) 9A98A1/N! <A!N1/9 37"9

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-.# 2/S17NS 142

.' </9"797N1"7"

.# *S9"/21/7N

%.' ANA7! */!/1A 97N?"1"

@.' S8224 S91/7N

@.# 1"ANS37"<"

#'.' SW/195/N! *?/9S

#'.# ?71A! "91/3/"

##.' "A4S

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#(.' 9A2A9/17"

#&.' "S/S17"

#).' 1"ANS/S17"S

.

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2-6 INTRO0*CTION =

/ere we are discussing to “(0(TR'A34(T5 P56T4”%According tonew research, the e7ciency of (lectromagnetic piston is 89:% ;henwe will <ow A%% current in the coil, Piston will be start to !ibrate%

(lectromagnetic Piston changes electrical energy to mechanicalenergy% ;hen we <ow the current in (lectromagnetic coil which

produce magnate and this magnate push the iron rod%

5ncreasing the e7ciency of reciprocating engines has constantly beenpursued since tto=cycle engines were "rst used as !ehicle powerplants% The important e>ects of fuel consumption on factors such as!ehicle range, operating cost, and !ehicle structures ha!e alwaysbeen important design considerations% &uring the past decade, the

impact o en!ironmental factors and a national interest in energyconser!ation ha!e accentuated the need to produce clean ande7cient engines%

5mpro!ing e7ciency and meeting emissions standards ha!e beentested and reported in the literature? these ideas include using lean

mi@ture ratios, strati"ed charges, and impro!ed mi@ture distribution%

3-6 (ISTOR) =

eanmixtureratio combustion in internal combustion engines has the. 3irst, excess

oxygen in the charge further oxidi6es unburned hydrocarbons potential of producing

low emissions and higher thermal efficiency for several reasons and carbon monoxide.

Second, excess oxygen lowers the peak combustion temperatures, which inhibits the

formation of oxides of nitrogen. 1hird, the lower combustion temperatures increase the

mixture specific heat ratio by decreasing the net dissociation losses. 1he specific heat

ratio increases, the cycle thermal e7ciency also increases% /

fficient leanmixtureratio operation, in t e rms of good vehicle performance, / fuel

economy, and low hydrocarbon emissions, is limited for several reasons. A reduction in

indicated mean effective pressure B/<2C occurs with lean mixtures Brefs. % and $C.

Also, at ultra lean mixture ratios, the cycletocycle and cylindertocylinder variations

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in /<2 are drastically increased, which produces si6able power fluctuations and causes

engine surge and power train vibrations. 9urrent explanations for these variations are

flow velocity perturbations at the spark plug and spatial variations of turbulence in the

combustion chamber. 1hese conditions control the rate of the combustion processD

therefore, leanmixtureratio operation involves cycletocycle and cylindertocylinder

variations in flame speed. /n addition, as the mixture ratio is made leaner, thecombustion process slows and occurs over larger crankangle intervals, thereby causing

hydrocarbon emission levels and fuel consumption to rise.

Also, the thermal boundary layer, or Euenching distance, increases with leaner mixture

ratios, which also causes hydrocarbon emission levels to rise Brefs. 8 and &". ven

though excess oxygen is available to oxidi6e these hydrocarbons, the Euenching effect

of the cylinder wall will still produce a net increase in hydrocarbon emissions. Another

problem is the leanmixtureratio misfire limit, which occurs near the flammabilitylimits of the fuel. 9ycletocycle and cylindertocylinder variations can cause an

individual cylinder to exceed the lean flammability limits and thus misfire. /ncipient

leanlimit misfire is characteri6ed by high hydrocarbon emissions, rough engine

operation, and poor fuel economy.

A review of the literature dealing with the problems of leanmixtureratio operation

shows that a fuel with a low lean flammability limit and a high flame speed might yield

low exhaust emissions at ultra lean conditions. 5ydrogen was identified in reference as having those properties and has been the subect of much investigation. 8sing a small

Euantity, on a weight basis, of hydrogen as a supplement to gasoline was chosen as a

way to extend lean engine operation. 7nboard generation of hydrogen was selected as a

feasible way to use hydrogen in a mobile application. 1he =et 2ropulsion aboratory /

conducted a similar program Brefs. - and C in which hydrogen generated by the partial

oxidation of gasoline was used as a fuel supplement for lean engine operation. ?arious

commercial processes to generate hydrogen were analy6ed for their applicability. 1he

catalytic steam reformation of methyl alcohol BmethanolC using engine exhaust heat was

selected as being the most efficient process to generate hydrogen that was also compact

enough to be carried on a vehicle. 7ne disadvantage is that it would reEuire a second

fuel and a second fuel system.

A research system to generate hydrogen by methanol reformation was built and installed

on a multicylinder engine in an existing engine test setup. An independent and parallel

8

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program on catalyst evaluation was performed but is not part of this report. An engine

test program was conducted using gasoline and additions of gaseous hydrogen and

reformed methanol to evaluate the effects of hydrogengasoline fuel mixtures on

exhaust emissions, extension of lean engine operating limits, and fuel flammability

limits and combustion flame speed.

1his report presents a brief description of the breadboard methanol reformation system

and the results of fuel and engine testing. 1he data were taken in the 8. S. customary

system of units and converted to S/ units for this report. /n 3uture, we will mostly use

1"7<A!N1/9 2/S17N due to its profitable advantages.

7-6 (AR0>ARE RE?*IREMENT =

1% ;ood base

2% Piston

*% 6witching de!ice

+% 6upply section

%(lectromagnetic coil

-% Piston co!er

19

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&.' W77* 0AS /t is the basic structure of our proect and provides the support of the all parts of the

piston assembly ./t consists of ( legs and # base surface which are attached that is

parallel to hori6ontal surface .

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.$ Creating an Electromagnet 9

Wrap

magnet

wire

around

the soft

boltC

iron

core B

Attach wire ends

to your interface

Fve G ve

12

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Things to remem:er a:out electromagnets'

• 1he more coils you make, the stronger the magnet.

• <agnet wire works better, because it is thinner and more

coils you can get.

• A soft iron core will make the magnet work better Ba boltC.

.% !or5ing of the pro-ect '

Now a dayHs diesel, petrol piston is available. 0ut if both are not present

these are not in use. /n this proect change the electric energy through the

electromagnetic coil in to mechanical energy.

/n this proect we develop an electromagnetic piston. When supply on then

piston start move. We generate electromagnetic field and piston move upper

side. 2iston works of the switching in magnetic field.

Note: please works only $' sec maximum.

Advantage

When other fuel option not present then electromagnetic technology is very

useful to continue over speed.

.# M)NET '

5ron "lings that ha!e oriented in the magnetic "eld producedby a bar magnet

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<agnetic field lines of a solenoid which are similar to a bar magnet as

illustrated above with the iron filings

A magnet Bfrom !reek IJKLMOP QRTP, U<agnesian stoneUC is a material or

obect that produces a magnetic field. 1his magnetic field is invisible but is

responsible for the most notable property of a magnet: a force that pulls onother magnetic materials and attracts or repels other magnets. A permanent

magnet is one that stays magneti6ed, such as a magnet used to hold notes on

a refrigerator door. <aterials which can be magneti6ed, which are also the

ones that are strongly attracted to a magnet, are called ferromagnetic. 1hese

include iron, nickel, cobalt, some rare earth metals and some of their alloys,

and some naturally occurring minerals such as lodestone. 1he other type of

magnet is an electromagnet, a coil of wire which acts as a magnet when an

electric current passes through it, but stops being a magnet when the current

stops. 7ften an electromagnet is wrapped around a core of ferromagneticmaterial like steel, which enhances the magnetic field produced by the coil.

2ermanent magnets are made from UhardU ferromagnetic materials which are

designed to stay magneti6ed, while UsoftU ferromagnetic materials like soft

iron are attracted to a magnet but donVt tend to stay magneti6ed.

Although ferromagnetic materials are the only ones strongly enough

attracted to a magnet to be commonly considered UmagneticU, all other

substances respond weakly to a magnetic field, by one of several other types

of magnetism. 2aramagnetic materials, such as aluminum and oxygen are

weakly attracted to a magnet. *iamagnetic materials, such as carbon andwater , which include all substances not having another type of magnetism,

are weakly repelled by a magnet.

1he overall strength of a magnet is measured by its magnetic moment, while

the local strength of the magnetism in a material is measured by its

magneti6ation.

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.#.% Bac5groun/ on the physics of magnetism an/ magnets 9

5.2.2 M AGNETIC FIELD -

1he magnetic fiel/ Busually denoted BC is called a field BphysicsC because it

has a value at every point in space. 1he magnetic field Bat a given pointC is

specified by two properties: B#C its direction, which is along the orientation

of a compass needleD and B$C its magnitude Balso called strengthC, which is

proportional to how strongly the compass needle orients along that direction.

*irection and magnitude makes B a vector , so B is a vector field. BB can

also depend on time.C /n S/ units the strength of the magnetic field is given

in teslas.

5.2.3 M AGNETIC MOMENT -

A magnetVs magnetic moment Balso called magnetic /ipole moment, and

usually denoted μC is a vector that characteri6es the magnetVs overall

magnetic properties. 3or a bar magnet, the direction of the magnetic moment

points from the magnetVs north pole to its south pole, and the magnitude

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relates to how strong and how far apart these poles are. /n S/ units the

magnetic moment is specified in terms of AmX.

A magnet both produces its own magnetic field and it responds to magnetic

fields. 1he strength of the magnetic field it produces is at any given point

proportional to the magnitude of its magnetic moment. /n addition, when themagnet is put into an UexternalU magnetic field produced by a different

source, it is subect to a torEue tending to orient the magnetic moment

parallel to the field. 1he amount of this torEue is proportional both to the

magnetic moment and the UexternalU field. A magnet may also be subect to

a force driving it in one direction or another, according to the positions and

orientations of the magnet and source. /f the field is uniform in space the

magnet is subect to no net force, although it is subect to a torEue.

A wire in the shape of a circle with area A and carrying current I is a magnet,

with a magnetic moment of magnitude eEual to IA.

5.3 M AGNETIZATION -

1he magneti;ation of an obect is the local value of its magnetic moment

per unit volume, usually denoted M, with units AYm. /t is a vector field ,

rather than ust a vector Blike the magnetic momentC, because the different

sections of a bar magnet generally are magneti6ed with different directions

and strengths Bfor example, due to domains, see belowC. A good bar magnetmay have a magnetic moment of magnitude '.# AmX and a volume of # cmZ,

or '.'''''# mZ, and therefore an average magneti6ation magnitude is

#'',''' AYm. /ron can have a magneti6ation of around a million AYm. Such

a large value explains why magnets are so effective at producing magnetic

fields.

.8.% T<o mo/els for magnets1 magnetic poles an/ atomic currents 9

Magnetic pole mo/el '

Although for many purposes it is convenient to think of a magnet as havingdistinct north and south magnetic poles, the concept of poles should not be

taken literally: it is merely a way of referring to the two different ends of a

magnet. 1he magnet does not have distinct UnorthU or UsouthU particles on

opposing sides. BNo magnetic monopole has yet been observed.C /f a bar

magnet is broken in half, in an attempt to separate the north and south poles,

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the result will be two bar magnets, each of which has both a north and south

pole.

1he magnetic pole approach is used by professional magneticians to design

permanent magnets. /n this approach, the pole surfaces of a permanent

magnet are imagined to be covered with Vmagnetic chargeV, little VNorth poleV particles on the North pole and VSouth polesV on the south pole, that are the

source of the magnetic field lines. /f the magnetic pole distribution is known,

then outside the magnet the pole model gives the magnetic field exactly. 0y

simply supplementing the pole model field with a term proportional to the

magneti6ation Bsee 8nits and 9alculations, belowC the magnetic field within

the magnet is given exactly. 1his pole model is also called the U!ilbert

modelU of a magnetic dipole.[#\ !riffiths suggests Bp. $)%C: U<y advice is to

use the !ilbert model, if you like, to get an intuitive UfeelU for a problem, but

never rely on it for Euantitative results.")mp=re mo/el 9

Another model is the UAmp]re modelU, where all magneti6ation is due to the

effect of microscopic, or atomic, circular U bound currentsU, also called

UAmp]rian currentsU throughout the material. 3or a uniformly magneti6ed

bar magnet in the shape of a cylinder, the net effect of the microscopic

bound currents is to make the magnet behave as if there is a macroscopic

sheet of electric current flowing around the surface of the cylinder, with

local flow direction normal to the cylinder axis. BSince scraping off the outer

layer of a magnet will not destroy its magnetic field, it can be seen that this

is ust a model, and the tiny currents are actually distributed throughout the

materialC. 1he righthand rule due to Amp]re tells which direction the

current flows. 1he Ampere model gives the exact magnetic field both inside

and outside the magnet. /t is usually difficult to calculate the Amperian

currents on the surface of a magnet, whereas it is often easier to find the

effective poles for the same magnet.

.& Pole naming con6entions '

The north pole of the magnet is the pole which, when the magnet isfreely suspended, points towards the Earth's magnetic north pole innorthern Canada. Since opposite poles (north and south) attractwhereas like poles (north and north, or south and south) repel, theEarth's present geographic north is thus actually its magnetic south.

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Confounding the situation further, the Earth's magnetic field hasreersed itself many times in the distant past.

!n order to aoid this confusion, the terms positive and negative polesare sometimes used instead of north and south, respectiely.

s a practical matter, in order to tell which pole of a magnet is northand which is south, it is not necessary to use the earth's magneticfield at all. #or e$ample, one cali%ration method would %e to compareit to an electromagnet, whose poles can %e identified ia the right&hand rule.

. DE0C*+PT+N0 , M)NET+C BE3)>+*0 '

1here are several types of magnetism, and all materials exhibit at least one

of them. 1his section describes, Eualitatively, the primary types of magnetic behavior that materials can show. 1he physics underlying each of these

behaviors is described in the next section below, and can also be found in

more detail in their respective articles.

• 3erromagnetic and ferrimagnetic materials are the ones normally

thought of as VmagneticVD they are attracted to a magnet strongly

enough that the attraction can be felt. 1hese materials are the only

ones that can retain magneti6ation and become magnetsD a common

example is a traditional refrigerator magnet. 3errimagnetic materials,

which include ferrites and the oldest magnetic materials magnetite andlodestone, are similar to but weaker than ferromagnetics. 1he

difference between ferro and ferrimagnetic materials is related to

their microscopic structure, as explained below.

• 2aramagnetic substances such as platinum, aluminum, and oxygen are

weakly attracted to a magnet. 1his effect is hundreds of thousands of

times weaker than ferromagnetic materials attraction, so it can only be

detected by using sensitive instruments, or using extremely strong

magnets. <agnetic ferrofluids, although they are made of tiny

ferromagnetic particles suspended in liEuid, are sometimes considered paramagnetic since they canVt be magneti6ed.

• *iamagnetic substances such as carbon, copper , water , and plastic are

even more weakly repelled by a magnet. All substances not possessing

one of the other types of magnetism are diamagneticD this includes

most substances. Although force on a diamagnetic obect from an

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ordinary magnet is far too weak to be felt, using extremely strong

superconducting magnets diamagnetic obects such as pieces of lead

and even frogs can be levitated so they float in midair.

Superconductors repel magnetic fields from their interior and are

strongly diamagnetic.

..% P3?0+C0 , M)NET+C BE3)>+*0 '

<agnetism, at its root, arises from two sources:

• lectric currents, or more generally moving electric charges, create

magnetic fields Bsee <axwellVs EuationsC.

• <any particles have non6ero UintrinsicU Bor UspinUC magnetic

moments. B=ust as each particle, by its nature, has a certain mass and

charge, each has a certain magnetic moment, possibly 6ero.C

/n magnetic materials, the most important sources of magneti6ation are,

more specifically, the electronsV orbital angular motion around the nucleus,

and the electronsV intrinsic magnetic moment Bsee lectron magnetic dipole

momentC. 1he other potential sources of magnetism are much less important:

3or example, the nuclear magnetic moments of the nuclei in the material are

typically thousands of times smaller than the electronsV magnetic moments,

so they are negligible in the context of the magneti6ation of materials.

BNuclear magnetic moments are important in other contexts, particularly in

Nuclear <agnetic "esonance BN<"C and <agnetic "esonance /magingB<"/C.C

7rdinarily, the countless electrons in a material are arranged such that their

magnetic moments Bboth orbital and intrinsicC cancel out. 1his is due, to

some extent, to electrons combining into pairs with opposite intrinsic

magnetic moments Bas a result of the 2auli exclusion principleD see lectron

configurationC, or combining into Ufilled subshellsU with 6ero net orbital

motionD in both cases, the electron arrangement is so as to exactly cancel the

magnetic moments from each electron. <oreover, even when the electron

configuration is such that there are unpaired electrons andYor nonfilledsubshells, it is often the case that the various electrons in the solid will

contribute magnetic moments that point in different, random directions, so

that the material will not be magnetic.

5owever, sometimes Beither spontaneously, or due to an applied external

magnetic fieldC each of the electron magnetic moents on will be, on average,

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lined up. 1hen the material can produce a net total magnetic field, which can

potentially be Euite strong.

1he magnetic behavior of a material depends on its structure Bparticularly its

electron configuration, for the reasons mentioned aboveC, and also on the

temperature Bat high temperatures, random thermal motion makes it moredifficult for the electrons to maintain alignmentC.

5.5.2 P HYSICS OF PARAMAGNETISM -

/n a paramagnetic material there are unpaired electrons, i.e. atomic or

molecular orbitals with exactly one electron in them. While paired electrons

are reEuired by the 2auli exclusion principle to have their intrinsic BVspinVC

magnetic moments pointing in opposite directions, causing their magnetic

fields to cancel out, an unpaired electron is free to align its magnetic

moment in any direction. When an external magnetic field is applied, thesemagnetic moments will tend to align themselves in the same direction as the

applied field, thus reinforcing it.

5.5.3 P HYSICS OF DIAMAGNETISM -

/n a diamagnetic material, there are no unpaired electrons, so the intrinsic

electron magnetic moments cannot produce any bulk effect. /n these cases,

the magneti6ation arises from the electronsV orbital motions, which can be

understood classically as follows:

When a material is put in a magnetic field, the electrons circling the nucleus

will experience, in addition to their 9oulomb attraction to the nucleus, a

orent6 force from the magnetic field. *epending on which direction the

electron is orbiting, this force may increase the centripetal force on the

electrons, pulling them in towards the nucleus, or it may decrease the force,

pulling them away from the nucleus. 1his effect systematically increases the

orbital magnetic moments that were aligned opposite the field, and decreases

the ones aligned parallel to the field Bin accordance with en6Vs lawC. 1his

results in a small bulk magnetic moment, with an opposite direction to the

applied field.

Note that this description is meant only as an heuristicD a proper

understanding reEuires a Euantummechanical description.

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Note that all materials undergo this orbital response. 5owever, in

paramagnetic and ferromagnetic substances, the diamagnetic effect is

overwhelmed by the much stronger effects caused by the unpaired electrons.

5.5.4 P HYSICS OF FERROMAGNETISM -

A ferromagnet, like a paramagnetic substance, has unpaired electrons.

5owever, in addition to the electronsV intrinsic magnetic moments wanting to

be parallel to an applied field, there is also in these materials a tendency for

these magnetic moments to want to be parallel to each other. 1hus, even

when the applied field is removed, the electrons in the material can keep

each other continually pointed in the same direction.

very ferromagnetic substance has its own individual temperature, called the

9urie temperature, or 9urie point, above which it loses its ferromagnetic

properties. 1his is because the thermal tendency to disorder overwhelms theenergylowering due to ferromagnetic order .

Magnetic Domains

Magnetic /omains in ferromagnetic material '

1he magnetic moment of atoms in a ferromagnetic material cause them to

behave something like tiny permanent magnets. 1hey stick together and

align themselves into small regions of more or less uniform alignment called

magnetic domains or Weiss domains. <agnetic domains can be observed

with a magnetic force microscope to reveal magnetic domain boundaries that

resemble white lines in the sketch.1here are many scientific experiments that

can physically show magnetic fields.

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neighbor is VantialignedV, the substance is antiferromagnetic.

Antiferromagnets have a 6ero net magnetic moment, meaning no field is

produced by them. Antiferromagnets are less common compared to the other

types of behaviors, and are mostly observed at low temperatures. /n varying

temperatures, materials, neighboring electrons want to point in opposite

directions, but there is no geometrical arrangement in which each pair of

neighbors is antialigned. 1his is called a spin glass, and is an example of

geometrical frustration.antiferromagnets can be seen to exhibit diamagnetic

and ferrimagnetic properties.

5.7 P HYSICS OF FERRIMAGNETISM -

.A.% ,errimagnetic or/ering '

ike ferromagnetism, ferrimagnets retain their magneti6ation in the absence

of a field. 5owever, like antiferromagnets, neighboring pairs of electron

spins like to point in opposite directions. 1hese two properties are not

contradictory, due to the fact that in the optimal geometrical arrangement,

there is more magnetic moment from the sublattice of electrons which point

in one direction, than from the sublattice which points in the opposite

direction.

1he first discovered magnetic substance, magnetite, was originally believed

to be a ferromagnetD ouis N^el disproved this, however, with the discoveryof ferrimagnetism.

OTHER TYPES OF A!"ETIS

1here are various other types of magnetism, such as and spin glass

Bmentioned aboveC, superparamagnetism, superdiamagnetism, and

metamagnetism.

97<<7N 8SS 73 <A!N1S

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5ard disks record data on a thin magnetic coating.

• <agnetic recording media: ?5S tapes contain a reel of magnetic tape.

1he information that makes up the video and sound is encoded on themagnetic coating on the tape. 9ommon audio cassettes also rely on

magnetic tape. Similarly, in computers, floppy disks and hard disks

record data on a thin magnetic coating.

• 9redit, debit, and A1< cards: All of these cards have a magnetic strip

on one side. 1his strip encodes the information to contact an

individualVs financial institution and connect with their accountBsC.

• 9ommon televisions and computer monitors: 1? and computer

screens containing a cathode ray tube employ an electromagnet to

guide electrons to the screen. 2lasma screens and 9*s use different

technologies.

• Speakers and <icrophones: <ost speakers employ a permanent

magnet and a currentcarrying coil to convert electric energy Bthe

signalC into mechanical energy Bmovement which creates the soundC.

1he coil is wrapped around a bobbin attached to the speaker cone, and

carries the signal as changing current which interacts with the field of

the permanent magnet. 1he voice coil feels a magnetic force and in

response moves the cone and pressuri6es the neighboring air, thus

generating sound. *ynamic microphones employ the same concept,

but in reverse. A microphone has a diaphragm or membrane attached

to a coil of wire. 1he coil rests inside a specially shaped magnet.

When sound vibrates the membrane, the coil is vibrated as well. As

the coil moves through the magnetic field, a voltage is induced across

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the coil. 1his voltage drives a current in the wire that is characteristic

of the original sound.

<agnetic hand separator for heavy minerals

• lectric motors and generators: Some electric motors Bmuch likeloudspeakersC rely upon a combination of an electromagnet and a

permanent magnet, and much like loudspeakers, they convert electric

energy into mechanical energy. A generator is the reverse: it converts

mechanical energy into electric energy by moving a conductor

through a magnetic field.

• 1ransformers: 1ransformers are devices that transfer electric energy

between two windings of wire that are electrically isolated but are

coupled magnetically.

• 9hucks: 9hucks are used in the metalworking field to hold obects.

<agnets are also used in other types of fastening devices, such as the

magnetic base, the magnetic clamp and the refrigerator magnet.

• 9ompasses: A compass Bor marinerVs compassC is a magneti6ed pointer

free to align itself with a magnetic field, most commonly arthVs

magnetic field.

• Art: ?inyl magnet sheets may be attached to paintings, photographs,

and other ornamental articles, allowing them to be attached to

refrigerators and other metal surfaces.

• Science 2roects: <any topic Euestions are based on magnets. 3or

example: how is the strength of a magnet affected by glass, plastic,

and cardboard_

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<agnets have many uses in toys. <tic uses magnetic rods connected to

metal spheres for construction

• 1oys: *ue to their ability to counteract the force of gravity at close

range, magnets are often employed in childrenVs toys such as the

<agnet Space Wheel to amusing effect.

• <agnets can be used to make ewelry. Necklaces and bracelets can

have a magnetic clasp, or may be constructed entirely from a linked

series of magnets and ferrous beads.

• <agnets can pick up magnetic items Biron nails, staples, tacks, paper clipsC that are either too small, too hard to reach, or too thin for fingers

to hold. Some screwdrivers are magneti6ed for this purpose.

• <agnets can be used in scrap and salvage operations to separate

magnetic metals Biron, steel, and nickelC from nonmagnetic metals

Baluminum, nonferrous alloys, etc#C. 1he same idea can be used in the

socalled Umagnet testU, in which an auto body is inspected with a

magnet to detect areas repaired using fiberglass or plastic putty.

•

<agnetic levitation transport, or maglev, is a form of transportationthat suspends, guides and propels vehicles Bespecially trainsC via

electromagnetic force. 1he maximum recorded speed of a maglev

train is )%# kilometres per hour B(-# mphC

• <agnets may be used to connect some cables to serve as a failsafe if

the cord is pulled.

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0),ET?

5uman tissues have a very low level of susceptibility to static magnetic

fields, and there is no scientific evidence showing a health ha6ard associated

with exposure to these fields. 5owever, if a ferromagnetic foreign body is

present in human tissue, the magnetic field will interact with it, which can pose a serious safety risk.[$\

9hildren sometimes swallow small magnets from toysD and this can be

ha6ardous if two or more magnets are swallowed, as the magnets can pinch

or puncture internal tissuesD one death has been reported.[(\

<A!N1/>A1/7N AN* *<A!N1/>A1/7N

3erromagnetic materials can be magneti6ed in the following ways:

• 5eating the obect above its 9urie temperature, allowing it to cool in amagnetic field and hammering it as it cools. 1his is the most effective

method, and is similar to the industrial processes used to create

permanent magnets.

• 2lacing the item in an external magnetic field will result in the item

retaining some of the magnetism on removal. ?ibration has been

shown to increase the effect. 3errous materials aligned with the earthVs

magnetic field and which are subect to vibration Be.g. frame of a

conveyorC have been shown to acEuire significant residual magnetism.

A magnetic field much stronger than the earthVs can be generated

inside a solenoid by passing direct current through it.

• Stroking An existing magnet is moved from one end of the item to

the other repeatedly in the same direction.

<agneti6ed materials can be demagneti6ed in the following ways:

• 5eating a magnet past its 9urie temperature the molecular motion

destroys the alignment of the magnetic domains. 1his always removes

all magneti6ation.

• 5ammering or arring the mechanical disturbance tends to

randomi6e the magnetic domains. Will leave some residual

magneti6ation.

• 2lacing the magnet in an alternating magnetic field, such as that

generated by a solenoid with an alternating current through it, and

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then either slowly drawing the magnet out or slowly decreasing the

magnetic field to 6ero. 1his is the principle used in commercial

demagneti6ers to demagneti6e tools and erase credit cards and hard

disks, and degaussing coils used to demagneti6e 9"1s.

. T?PE0 , PE*M)NENT M)NET0 '

A stack of ferrite magnets

5.8.1 M AGNETIC METALLIC ELEMENTS -

<any materials have unpaired electron spins, and the maority of these

materials are paramagnetic. When the spins interact with each other in such

a way that the spins align spontaneously, the materials are called

ferromagnetic Bwhat is often loosely termed as UmagneticUC. *ue to the way

their regular crystalline atomic structure causes their spins to interact, somemetals are BferroCmagnetic when found in their natural states, as ores. 1hese

include iron ore Bmagnetite or lodestoneC, cobalt and nickel, as well the rare

earth metals gadolinium and dysprosium Bwhen at a very low temperatureC.

Such naturally occurring BferroCmagnets were used in the first experiments

with magnetism. 1echnology has since expanded the availability of magnetic

materials to include various manmade products, all based, however, on

naturally magnetic elements.

C OMPOSITES

5.8.2 Ceramic or ferrite -

9eramic, or ferrite, magnets are made of a sintered composite of powdered

iron oxide and bariumYstrontium carbonate ceramic. *ue to the low cost of

the materials and manufacturing methods, inexpensive magnets Bor

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nonmagneti6ed ferromagnetic cores, for use in electronic component such as

radio antennas, for exampleC of various shapes can be easily mass produced.

1he resulting magnets are noncorroding, but brittle and must be treated like

other ceramics.

)lnico

Alnico magnets are made by casting or sintering a combination of

aluminium, nickel and cobalt with iron and small amounts of other elements

added to enhance the properties of the magnet. Sintering offers superior

mechanical characteristics, whereas casting delivers higher magnetic fields

and allows for the design of intricate shapes. Alnico magnets resist corrosion

and have physical properties more forgiving than ferrite, but not Euite as

desirable as a metal.

Ticonal

1iconal magnets are an alloy of titanium, cobalt, nickel, and aluminum, with

iron and small amounts of other elements. /t was developed by 2hilips for

loudspeakers.

+n-ection mol/e/

/nection molded magnets are a composite of various types of resin and

magnetic powders, allowing parts of complex shapes to be manufactured by

inection molding. 1he physical and magnetic properties of the product

depend on the raw materials, but are generally lower in magnetic strengthand resemble plastics in their physical properties.

,le2i:le

3lexible magnets are similar to inection molded magnets, using a flexible

resin or binder such as vinyl, and produced in flat strips, shapes or sheets.

1hese magnets are lower in magnetic strength but can be very flexible,

depending on the binder used. 3lexible magnets can be used in industrial

printers.

V"are earthV BlanthanoidC elements have a partially occupied f electron shell

Bwhich can accommodate up to #& electrons.C 1he spin of these electrons can

be aligned, resulting in very strong magnetic fields, and therefore these

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elements are used in compact highstrength magnets where their higher price

is not a concern. 1he most common types of rare earth magnets are

samariumcobalt and neodymiumironboron BN/0C magnets.

S I"!$E % O$E&'$E A!"ETS (S S ) A"* SI"!$E %&HAI" A!"ETS (S& S )

/n the #@@'s it was discovered that certain molecules containing

paramagnetic metal ions are capable of storing a magnetic moment at very

low temperatures. 1hese are very different from conventional magnets that

store information at a UdomainU level and theoretically could provide a far

denser storage medium than conventional magnets. /n this direction research

on monolayers of S<<s is currently under way. ?ery briefly, the two main

attributes of an S<< are:

#. a large ground state spin value BSC, which is provided by

ferromagnetic or ferrimagnetic coupling between the paramagneticmetal centres.

$. a negative value of the anisotropy of the 6ero field splitting B*C

<ost S<<Vs contain manganese, but can also be found with vanadium, iron,

nickel and cobalt clusters. <ore recently it has been found that some chain

systems can also display a magneti6ation which persists for long times at

relatively higher temperatures. 1hese systems have been called singlechain

magnets.

" A"O%STR'&T'RE* A!"ETS

Some nanostructured materials exhibit energy waves called magnons that

coalesce into a common ground state in the manner of a 0oseinstein

condensate.[&\[)\

& OSTS

1he current cheapest permanent magnets, allowing for field strengths, are

flexible and ceramic magnets, but these are also among the weakest types.

Neodymiumironboron BN/0C magnets are among the strongest. 1hese costmore per kilogram than most other magnetic materials, but due to their

intense field, are smaller and cheaper in many applications.[-\

T EPERAT'RE

1emperature sensitivity varies, but when a magnet is heated to a temperature

known as the 9urie point, it loses all of its magnetism, even after cooling

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below that temperature. 1he magnets can often be remagnetised however.

Additionally some magnets are brittle and can fracture at high temperatures.

91"7<A!N1S

An electromagnet in its simplest form, is a wire that has been coiled into

one or more loops, known as a solenoid. When electric current flows

through the wire, a magnetic field is generated. /t is concentrated near Band

especially insideC the coil, and its field lines are very similar to those for a

magnet. 1he orientation of this effective magnet is determined via the right

hand rule. 1he magnetic moment and the magnetic field of the

electromagnet are proportional to the number of loops of wire, to the cross

section of each loop, and to the current passing through the wire.

/f the coil of wire is wrapped around a material with no special magnetic

properties Be.g., cardboardC, it will tend to generate a very weak field.

5owever, if it is wrapped around a UsoftU ferromagnetic material, such as an

iron nail, then the net field produced can result in a several hundred to

thousandfold increase of field strength.

8ses for electromagnets include particle accelerators, electric motors,

unkyard cranes, and magnetic resonance imaging machines. Some

applications involve configurations more than a simple magnetic dipole, for

example Euadrupole and sextupole magnets are used to focus particle beams.UN+T0 )ND C)LCUL)T+N0 +N M)NET+0M '

5ow we write the laws of magnetism depends on which set of units we

employ. 3or most engineering applications, <+S or S/ BSyst]me

/nternationalC is common. 1wo other sets, !aussian and 9!Semu, are the

same for magnetic properties, and are commonly used in physics.

/n all units it is convenient to employ two types of magnetic field, B and 3,

as well as the magneti6ation , defined as the magnetic moment per unit

volume.

#. 1he magnetic induction field B is given in S/ units of teslas B1C. B is

the true magnetic field, whose timevariation produces, by 3aradayVs

aw, circulating electric fields Bwhich the power companies sellC. B

also produces a deflection force on moving charged particles Bas in

1? tubesC. 1he tesla is eEuivalent to the magnetic flux Bin webersC per

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unit area Bin meters sEuaredC, thus giving B the unit of a flux density.

/n 9!S the unit of B is the gauss B!C. 7ne tesla eEuals #'& !.

$. 1he magnetic field 3 is given in S/ units of ampereturns per meter

BAturnYmC. 1he UturnsU appears because when 3 is produced by a

currentcarrying wire, its value is proportional to the number of turnsof that wire. /n 9!S the unit of 3 is the oersted B7eC. 7ne AturnYm

eEuals &` x #'( 7e.

(. 1he magneti6ation is given in S/ units of amperes per meter BAYmC.

/n 9!S the unit of is the emu, or electromagnetic unit. 7ne AYm

eEuals #'( emu. A good permanent magnet can have a magneti6ation

as large as a million amperes per meter. <agnetic fields produced by

currentcarrying wires would reEuire comparably huge currents per

unit length, one reason we employ permanent magnets and

electromagnets.

&. /n S/ units, the relation B μ'B3 G C holds, where μ' is the

permeability of space, which eEuals &` x #' tesla meters per ampere.

/n 9!S it is written as B 3 G &+ . [1he pole approach gives μ' H in

S/ units. A μ' term in S/ must then supplement this μ' H to give the

correct field within , the magnet. /t will agree with the field ,

calculated using Amperian currents.\

<aterials that are not permanent magnets usually satisfy the relation M - 3

in S/, where - is the BdimensionlessC magnetic susceptibility. <ost nonmagnetic materials have a relatively small - Bon the order of a millionthC, but

soft magnets can have - on the order of hundreds or thousands. 3or materials

satisfying M - 3, we can also write B μ'B# G - C3 μ' μr 3 μ3, where

μr # G - is the BdimensionlessC relative permeability and I I'Ir is the

magnetic permeability. 0oth hard and soft magnets have a more complex,

historydependent, behavior described by what are called hysteresis loops,

which give either B vs 3 or vs 3. /n 9!S - 3, but - S/ &+- 9!S, and I

Ir .

9aution: /n part because there are not enough "oman and !reek symbols,there is no commonly agreed upon symbol for magnetic pole strength and

magnetic moment. 1he symbol m has been used for both pole strength Bunit

Am, where here the upright m is for meterC and for magnetic moment

Bunit AmXC. 1he symbol μ has been used in some texts for magnetic

permeability and in other texts for magnetic moment. We will use μ for

magnetic permeability and m for magnetic moment. 3or pole strength we

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will employ .m. 3or a bar magnet of crosssection A with uniform

magneti6ation along its axis, the pole strength is given by .m A, so

that can be thought of as a pole strength per unit area.

F IE$*S OF A A!"ET

3ar away from a magnet, the magnetic field created by that magnet is almost

always described Bto a good approximationC by a dipole field characteri6ed

by its total magnetic moment. 1his is true regardless of the shape of the

magnet, so long as the magnetic moment is non6ero. 7ne characteristic of a

dipole field is that the strength of the field falls off inversely with the cube of

the distance from the magnetVs center.

9loser to the magnet, the magnetic field becomes more complicated, and

more dependent on the detailed shape and magneti6ation of the magnet.

3ormally, the field can be expressed as a multipole expansion: A dipole field, plus a Euadrupole field, plus an octupole field, etc.

At close range, many different fields are possible. 3or example, for a long,

skinny bar magnet with its north pole at one end and south pole at the other,

the magnetic field near either end falls off inversely with the sEuare of the

distance from that pole.

5.9 C ALCULATING THE MAGNETIC FORCE -

9alculating the attractive or repulsive force between two magnets is, in the

general case, an extremely complex operation, as it depends on the shape,

magneti6ation, orientation and separation of the magnets.

,orce :et<een t<o magnetic poles '

1he force between two magnetic poles is given by:

where

F is force BS/ unit: newtonC

.m# and .m$ are the magnitudes of magnetic poles BS/ unit: ampere

meter C

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μ is the permeability of the intervening medium BS/ unit: tesla meter per

ampere, henry per meter or newton per ampere sEuaredC

r is the separation BS/ unit: meterC.

1he pole description is useful to practicing magneticians who design realworld magnets, but real magnets have a pole distribution more complex than

a single north and south. 1herefore, implementation of the pole idea is not

simple. /n some cases, one of the more complex formulae given below will

be more useful.

,orce :et<een t<o near:y attracting surfaces of area A an/ eual

:ut opposite magneti;ations M

where

A is the area of each surface, in mX

is their magneti6ation, in AYm.

I' is the permeability of space, which eEuals &` x #' teslameters per

ampere

,orce :et<een t<o :ar magnets1he force between two identical cylindrical bar magnets placed endtoend

is given by:

[(\

where

,/ is the magnetic flux density very close to each pole, in 1,

A is the area of each pole, in m$,

$ is the length of each magnet, in m,

R is the radius of each magnet, in m, and

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0 is the separation between the two magnets, in m

,' relates the flux density at the pole to the magneti6ation

of the magnet.

@.$ P+0TN '

A piston is a component of reciprocating engines, reciprocating pumps, gas

compressors and pneumatic cylinders, among other similar mechanisms. /t is

the moving component that is contained by a cylinder and is made gastight

by piston rings. /n an engine, its purpose is to transfer force from expanding

gas in the cylinder to the crankshaft via a piston rod andYor connecting rod.

/n a pump, the function is reversed and force is transferred from the

crankshaft to the piston for the purpose of compressing or eecting the fluidin the cylinder. /n some engines, the piston also acts as a valve by covering

and uncovering ports in the cylinder wall.

P+0TN EN+NE0

Main article1 "eciprocating engine

I "TER"A$ &O,'STIO" E"!I"ES

/nternal combustion engine piston, sectioned to show the gudgeon pin.

1he piston of an internal combustion engine is acted upon by the pressure of

the expanding combustion gases in the combustion chamber space at the top

of the cylinder. 1his force then acts downwards through the connecting rod

and onto the crankshaft. 1he connecting rod is attached to the piston by a

swivelling gudgeon pin B8S: wrist pinC. 1his pin is mounted within the

piston: unlike the steam engine, there is no piston rod or crosshead.

1he pin itself is of hardened steel and is fixed in the piston, but free to movein the connecting rod. A few designs use a Vfully floatingV design that is loose

in both components. All pins must be prevented from moving sideways and

the ends of the pin digging into the cylinder wall, usually by circlips.

!as sealing is achieved by the use of piston rings. 1hese are a number of

narrow iron rings, fitted loosely into grooves in the piston, ust below the

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crown. 1he rings are split at a point in the rim, allowing them to press

against the cylinder with a light spring pressure. 1wo types of ring are used:

the upper rings have solid faces and provide gas sealingD lower rings have

narrow edges and a 8shaped profile, to act as oil scrapers. 1here are many

proprietary and detail design features associated with piston rings.

2istons are cast from aluminium alloys. 3or better strength and fatigue life,

some racing pistons may be forged instead. arly pistons were of cast iron,

but there were obvious benefits for engine balancing if a lighter alloy could

be used. 1o produce pistons that could survive engine combustion

temperatures, it was necessary to develop new alloys such as 4 alloy and

5iduminium, specifically for use as pistons.

A few early gas engines had doubleacting cylinders, but otherwise

effectively all internal combustion engine pistons are singleacting. *uring

World War //, the 8S submarine Pompano was fitted with a prototype of theinfamously unreliable 5.7.". doubleacting twostroke diesel engine.

Although compact, for use in a cramped submarine, this design of engine

was not repeated.

<edia related to /nternal combustion engine pistons at Wikimedia

9ommons

@.% Trun5 pistons '

1runk piston for a modern diesel engine

1runk pistons are long, relative to their diameter. 1hey act as both piston and

also as a cylindrical crosshead. As the connecting rod is angled for part of its

rotation, there is also a side force that reacts along the side of the piston

against the cylinder wall. A longer piston helps to support this.

1runk pistons have been a common design of piston since the early days of

the reciprocating internal combustion engine. 1hey were used for both petrol

and diesel engines, although high speed engines have now adopted the

lighter weight slipper piston.A characteristic of most trunk pistons, particularly for diesel engines, is that

they have a groove for an oil ring 1elo2 the gudgeon pin, not ust the rings

between the gudgeon pin and crown.

1he name Vtrunk pistonV derives from the Vtrunk engineV, an early design of

marine steam engine. 1o make these more compact, they avoided the steam

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engineVs usual piston rod and separate crosshead and were instead the first

engine design to place the gudgeon pin directly within the piston. 7therwise

these trunk engine pistons bore little resemblance to the trunk piston: they

were of extremely large diameter and were doubleacting. 1heir VtrunkV was a

narrow cylinder placed mounted in the centre of this piston.

<edia related to 1runk pistons at Wikimedia 9ommons

@.# Crosshea/ pistons '

arge slowspeed *iesel engines may reEuire additional support for the side

forces on the piston. 1hese engines typically use crosshead pistons. 1he

main piston has a large piston rod extending downwards from the piston to

what is effectively a second smallerdiameter piston. 1he main piston is

responsible for gas sealing and carries the piston rings. 1he smaller piston is

purely a mechanical guide. /t runs within a small cylinder as a trunk guideand also carries the gudgeon pin.

0ecause of the additional weight of these pistons, they are not used for high

speed engines.

<edia related to 9rosshead pistons at Wikimedia 9ommons

@.8 0lipper pistons '

A slipper piston is a piston for a petrol engine that has been reduced in si6e

and weight as much as possible. /n the extreme case, they are reduced to the piston crown, support for the piston rings, and ust enough of the piston skirt

remaining to leave two lands so as to stop the piston rocking in the bore. 1he

sides of the piston skirt around the gudgeon pin are reduced away from the

cylinder wall. 1he purpose is mostly to reduce the reciprocating mass, thus

making it easier to balance the engine and so permit high speeds. A

secondary benefit may be some reduction in friction with the cylinder wall,

however as most of this is due to the parts of the piston that are left behind,

the benefit is minor.

<edia related to Slipper pistons at Wikimedia 9ommons

@.& Deflector pistons '

1wostroke deflector piston

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*eflector pistons are used in twostroke engines with crankcase

compression, where the gas flow within the cylinder must be carefully

directed in order to provide efficient scavenging. With cross scavenging, the

transfer Binlet to the cylinderC and exhaust ports are on directly facing sides

of the cylinder wall. 1o prevent the incoming mixture passing straight acrossfrom one port to the other, the piston has a raised rib on its crown. 1his is

intended to deflect the incoming mixture upwards, around the combustion

chamber .[#\ <uch effort, and many different designs of piston crown, went

into developing improved scavenging. 1he crowns developed from a simple

rib to a large asymmetric bulge, usually with a steep face on the inlet side

and a gentle curve on the exhaust. *espite this, cross scavenging was never

as effective as hoped. <ost engines today use Schnuerle porting instead.

1his places a pair of transfer ports in the sides of the cylinder and

encourages gas flow to rotate around a vertical axis, rather than a hori6ontal

axis.[$\

<edia related to *eflector pistons at Wikimedia 9ommons Steam engines

9astiron steam engine piston, with a metal piston ring springloaded against

the cylinder wall.

Steam engines are usually doubleacting Bi.e. steam pressure acts alternately

on each side of the pistonC and the admission and release of steam is

controlled by slide valves, piston valves or poppet valves. 9onseEuently,

steam engine pistons are nearly always comparatively thin discs: their

diameter is several times their thickness. B7ne exception is the trunk engine piston, shaped more like those in a modern internalcombustion engine.C

arly Bc. #%('C piston for a beam engine. 1he piston seal is made by turns of

wrapped rope.

2iston pumps can be used to move liEuids or compress gases.

F OR $I3'I*S

<ain article: "eciprocating pump

F OR !ASES

<ain article: "eciprocating compressor

A/" 9ANN7NS

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1his article contains embedded lists that may :e poorly /efine/7 un6erifie/

or in/iscriminate. 2lease help to clean it up to meet WikipediaVs Euality

standards. Where appropriate, incorporate items into the main body of the

article. ("o4em1er 5//6)

1here are two special type of pistons used in air cannons: close tolerance pistons and double pistons. While in close tolerance pistons, 7rings serve as

a valve, 7rings are not used in double piston types.

9losetolerance pistons have a number of disadvantages: 1hey can swell and

stick, their properties alter due to atmospheric changes, and they fit tightly in

the cylinder with close tolerances. 0acklash may suck some of the bin

material into the valve which can cause the piston to stick.

9ommon features of double piston construction: 1hey cannot swell and

stick, they fit loosely in the cylinder Bno tight tolerancesC, atmosphericchanges do not affect them, and foreign material entering the cylinder

doesnVt cause sticking.

D*)!B)CK0 '

1his section may reuire cleanup to meet !i5ipe/ias uality stan/ar/s.

No cleanup reason has been specified. 2lease help improve this section if

you can. (arch 5//7)

Since the piston is the main reciprocating part of an engine, its movementcreates an imbalance. 1his imbalance generally manifests itself as a

vibration, which causes the engine to be perceivably harsh. 1he friction

between the walls of the cylinder and the piston rings eventually results in

wear, reducing the effective life of the mechanism.

1he sound generated by a reciprocating engine can be intolerable and as a

result, many reciprocating engines rely on heavy noise suppression

eEuipment to diminish droning and loudness. 1o transmit the energy of the

piston to the crank, the piston is connected to a connecting rod which is in

turn connected to the crank. 0ecause the linear movement of the piston must be converted to a rotational movement of the crank, mechanical loss is

experienced as a conseEuence. 7verall, this leads to a decrease in the overall

efficiency of the combustion process. 1he motion of the crank shaft is not

smooth, since energy supplied by the piston is not continuous and it is

impulsive in nature. 1o address this, manufacturers fit heavy flywheels

which supply constant inertia to the crank. 0alance shafts are also fitted to

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some engines, and diminish the instability generated by the pistonVs

movement.

A.$ C*+TE*+) ,* C30+N ) M+C*CNT*LLE*

1he basic criteria for choosing a microcontroller suitable for the application

are:

#C 1he first and foremost criterion is that it must meet the task at hand

efficiently and cost effectively. /n analy6ing the needs of a microcontroller

based proect, it is seen whether an % bit, #-bit or ($bit microcontroller

can best handle the computing needs of the task most effectively. Among the

other considerations in this category are:

BaC 0pee/1 1he highest speed that the microcontroller supports.

BbC Pac5aging1 /t may be a $%pin */2 Bdual inline packageC or a ;32

BEuad flat packageC, or some other packaging format. 1his is important in

terms of space, assembling, and prototyping the end product.

BcC Po<er consumption1 1his is especially critical for batterypowered

products.

BdC 1he number of /Y7 pins and the timer on the chip.

BfC 5ow easy it is to upgrade to higher performance or lower consumption

versions.

BgC Cost per unit: 1his is important in terms of the final cost of the product

in which a microcontroller is used.

$C 1he second criterion in choosing a microcontroller is how easy it is to

develop products around it. +ey considerations include the availability of an

assembler, debugger, compiler, technical support.

(C 1he third criterion in choosing a microcontroller is its ready availability in

needed Euantities both now and in the future.

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A.% DE0C*+PT+N '

1his powerful B$'' nanosecond instruction executionC yet easytoprogram

Bonly () single word instructionsC 9<7S 3AS5based %bit

microcontroller packs <icrochipVs powerful 2/9 architecture into an $%

pin package and is upwards compatible with the 2/9#-9), 2/9#$9and 2/9#-9 devices. 1he 2/9#-3$ features ) channels of %bit Analog

to*igital BAY*C converter with $ additional timers, captureYcompareY2W<

function and the synchronous serial port can be configured as either (wire

Serial 2eripheral /nterface BS2/C or the $wire /nter/ntegrated 9ircuit

B/X9C bus. All of these features make it ideal for more advanced level AY*

applications in automotive, industrial, appliances and consumer applications.

A.%.% DE>+CE 0PEC+,+C)T+N '

3igh Performance *+0C CPU '

7nly () single word instructions to learn

All single cycle instructions except for program branches, which are

twocycle

7perating speed: *9 $' <56 clock input *9 $'' ns instruction

cycle

$+ x #& words of 2rogram <emory, #$% x % bytes of *ata <emory

B"A<C

2in out compatible to 2/9#-9$Y$A and 2/9#-3%$

/nterrupt capability

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ightlevel deep hardware stack

*irect, /ndirect and "elative Addressing modes

Peripheral ,eatures '

5igh SinkYSource 9urrent: $) mA

1imer': %bit timerYcounter with %bit prescaler

1imer#: #-bit timerYcounter with prescaler, can be incremented

during S2 via external crystalYclock

1imer$: %bit timerYcounter with %bit period register, prescaler and

postscaler

9apture, 9ompare, 2W< B992C module

9apture is #-bit, maximum resolution is #$.) ns

9ompare is #-bit, maximum resolution is $'' ns

2W< maximum resolution is #'bit

%bit, )channel analogtodigital converter

Synchronous Serial 2ort BSS2C with S2/ B<asterYSlaveC and /$9

BSlaveC

0rownout detection circuitry for 0rownout "eset B07"C

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CM0 Technology1

ow power, high speed 9<7S 3AS5 technology

3ully static design

Wide operating voltage range: $.'? to ).)?

/ndustrial temperature range

ow power consumption:

'.- mA typical (?, & <56

$' micro A typical (?, ($ k56

# micro A typical standby current

0pecial Microcontroller ,eatures '

#,''' eraseYwrite cycle 3AS5 program memory typical

2oweron "eset B27"C, 2owerup 1imer B2W"1C and 7scillator

Startup 1imer B7S1C

Watchdog 1imer BW*1C with its own onchip "9 oscillator for

reliable operation

2rogrammable code protection

2ower saving S2 mode

Selectable oscillator options

/n9ircuit Serial 2rogramming B/9S2C via $ pins

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2rocessor read access to program memory

P+N D+)*)M , P+C%@,A# '

,ig &. Pin Diagram of Microcontroller

Pin Description

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.$ )N)L'T'D++T)L CN>E*TE* ()4D" MDULE '

1he analogtodigital BAY*C converter module has five inputs for the

2/9#-3$. 1he AY* allows conversion of an analog input signal to a

corresponding %bit digital number. 1he output of the sample and hold is the

input into the converter, which generates the result via successiveapproximation. 1he analog reference voltage is software selectable to either

the deviceHs positive supply voltage B?**C or the voltage level on the

"A(YAN(Y?"3 pin. 1he AY* converter has a uniEue feature of being able

to operate while the device is in S2 mode. 1o operate in S2, the AY*

conversion clock must be derived from the AY*Hs internal "9 oscillator.

1he AY* module has three registers:

AY* "esult "egister A*"S

AY* 9ontrol "egister ' A*97N'

AY* 9ontrol "egister # A*97N#

A device "S1 forces all registers to their "S1 state. 1his forces the

AY* module to be turned off and any conversion is aborted. 1he A*97N'

register, shown in "egister #'#, controls the operation of the AY* module.1he A*97N# register, shown in "egister #'$, configures the functions of

the port pins. 1he port pins can be configured as analog inputs B"A( can

also be a voltage referenceC or a digital /Y7.

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,ig &.%% ) to D *eg%

1he A*"SS register contains the result of the AY* conversion. When the

AY* conversion is complete, the result is loaded into the A*"SS register,

the !7Y*7N bit BA*97N'$C is cleared, and AY* interrupt flag bit

A*/3 is set. 1he block diagram of the AY* module is shown. 1he value in

the A*"SS register is not modified for a 2oweron "eset. 1he A*"SS

register will contain unknown data after a 2oweron "eset. After the AY*module has been configured as desired, the selected channel must be

acEuired before the conversion is started. 1he analog input channels must

have their corresponding 1"/S bits selected as an input. After acEuisition

time has elapsed, the AY* conversion can be started. 1he following steps

should be followed for doing an AY9 conversion:

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#. 9onfigure the AY* module:

9onfigure analog pinsYvoltage reference and digital /Y7 BA*97N#C

Select AY* input channel BA*97N'C

Select AY* conversion clock BA*97N'C

1urn on AY* module BA*97N'C

$. 9onfigure AY* interrupt Bif desiredC:

9lear A*/3 bit

Set A*/ bit

Set !/ bit

(. Wait the reEuired acEuisition time.

&. Start conversion:

Set !7Y*7N bit BA*97N'C

). Wait for AY* conversion to complete, by either:

2olling for the !7Y*7N bit to be cleared 7"

Waiting for the AY* interrupt

-. "ead AY* "esult register BA*"SC, clear bit A*/3 if reEuired.

. 3or next conversion, go to step # or step $ as reEuired. 1he AY*

conversion time per bit is defined as 1A*. A minimum wait of $ 1A* is

reEuired before the next acEuisition starts.

.% +N0T*UCT+N 0ET 0UMM)*? '

ach 2/9#-3$ instruction is a #&bit word divided into an 7297* that

specifies the instruction type and one or more operands that further specify

the operation of the instruction. 1he 2/9#-3$ instruction set summary in

1able below lists :yte'oriente/, :it'oriente/, and literal an/ control

operations. 1able below shows the opcode field descriptions. 3or :yte'

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oriente/ instructions, FfH represents a file register designator and FdH

represents a destination designator. 1he file register designator specifies

which file register is to be used by the instruction. 1he destination designator

specifies where the result of the operation is to be placed. /f FdH is 6ero, the

result is placed in the W register. /f FdH is one, the result is placed in the file

register specified in the instruction. 3or :it'oriente/ instructions, FbH

represents a bit field designator which selects the number of the bit affected

by the operation, while FfH represents the number of the file in which the bit

is located. 3or literal an/ control operations, FkH represents an eight or

elevenbit constant or literal value.

1he instruction set is highly orthogonal and is grouped into three basic

categories:

Byte'oriente/ operations

Bit'oriente/ operations

Literal an/ control operations

All instructions are executed within one single instruction cycle, unless a

conditional test is true or the program counter is changed as a result of an

instruction. /n this case, the execution takes two instruction cycles, with the

second cycle executed as a N72. 7ne instruction cycle consists of four

oscillator periods. 1hus, for an oscillator freEuency of & <56, the normal

instruction execution time is # s. /f a conditional test is true, or the

program counter is changed as a result of an instruction, the instruction

execution time is more.

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.# ENE*)L ,*M)T ,* +N0T*UCT+N0 '

,ig &.%# eneral format

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.$ 0UPPL? 0ECT+N '

.% Transformers

A transformer is a device that transfers electrical energy from one circuit to

another by magnetic coupling without reEuiring relative motion between its

parts. /t usually comprises two or more coupled windings, and, in most

cases, a core to concentrate magnetic flux. A transformer operates from the

application of an alternating voltage to one winding, which creates a time

varying magnetic flux in the core. 1his varying flux induces a voltage in the

other windings. ?arying the relative number of turns between primary and

secondary windings determines the ratio of the input and output voltages,

thus transforming the voltage by stepping it up or down between circuits.

.# Basic principle '

1he principles of the transformer are illustrated by consideration of a

hypothetical ideal transformer consisting of two windings of 6ero resistance

around a core of negligible reluctance. A voltage applied to the primary

winding causes a current, which develops a magnetomotive force B<<3C in

the core. 1he current reEuired to create the <<3 is termed the magnetising

currentD in the ideal transformer it is considered to be negligible. 1he <<3drives flux around the magnetic circuit of the core.

,igure #@1 The i/eal transformer as a circuit element

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An electromotive force B<3C is induced across each winding, an effect

known as mutual inductance. 1he windings in the ideal transformer have no

resistance and so the <3s are eEual in magnitude to the measured terminal

voltages. /n accordance with 3aradayVs law of induction, they are

proportional to the rate of change of flux:

and

Euation A1 EM, in/uce/ in primary an/ secon/ary <in/ings

where:

and are the induced <3s across primary and secondary windings,

and are the numbers of turns in the primary and secondary windings,

and are the time derivatives of the flux linking the primary and

secondary windings

/n the ideal transformer, all flux produced by the primary winding also links

the secondary, and so , from which the wellknown transformer

eEuation follows:

Euation 1 Transformer Euation

1he ratio of primary to secondary voltage is therefore the same as the ratio

of the number of turnsD alternatively, that the voltsperturn is the same in

both windings. 1he conditions that determine 1ransformer working in S12

82 or S12 *7WN mode are:

Ns Np

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Euation 1 Con/iton for 0TEP UP

Ns Np

%$.$ 0!+TC3+N DE>+CE0 '

%$.% *ectifier'

A :ri/ge rectifier is an arrangement of four diodes connected in a bridge circuit

as shown below, that provides the same polarity of output voltage for any

polarity of the input voltage. When used in its most common application, for

conversion of alternating current BA9C input into direct current B*9C output, it is

known as a bridge rectifier . 1he bridge rectifier provides full wave rectification

from a two wire A9 input Bsaving the cost of a center tapped transformerC but

has two diode drops rather than one reducing efficiency over a center tap

based design for the same output voltage.

,igure 1 0chematic of a :ri/ge rectifier

1he essential feature of this arrangement is that for both polarities of thevoltage at the bridge input, the polarity of the output is constant.

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%$.# Basic peration '

When the input connected at the left corner of the diamond is positive with

respect to the one connected at the right hand corner, current flows to the right

along the upper colored path to the output, and returns to the input supply

via the lower one.

When the right hand corner is positive relative to the left hand corner,

current flows along the upper colored path and returns to the supply via the

lower colored path.

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,igure %$1 )C7 half'<a6e an/ full <a6e rectifie/ signals

/n each case, the upper right output remains positive with respect to the

lower right one. Since this is true whether the input is A9 or *9, this circuit

not only produces *9 power when supplied with A9 power: it also can

provide what is sometimes called Ureverse polarity protectionU. 1hat is, it

permits normal functioning when batteries are installed backwards or *9

inputpower supply wiring Uhas its wires crossedU Band protects the circuitry

it powers against damage that might occur without this circuit in placeC.

2rior to availability of integrated electronics, such a bridge rectifier was

always constructed from discrete components. Since about #@)', a single

fourterminal component containing the four diodes connected in the bridge

configuration became a standard commercial component and is now

available with various voltage and current ratings.

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%$.8 utput 0moothing '

3or many applications, especially with single phase A9 where the fullwave

bridge serves to convert an A9 input into a *9 output, the addition of a

capacitor may be important because the bridge alone supplies an output

voltage of fixed polarity but pulsating magnitude.

,igure %%1 Bri/ge *ectifier <ith smoothen output

1he function of this capacitor, known as a Vsmoothing capacitorV Bsee also

filter capacitor C is to lessen the variation in Bor VsmoothVC the raw output

voltage waveform from the bridge. 7ne explanation of VsmoothingV is that

the capacitor provides a low impedance path to the A9 component of the

output, reducing the A9 voltage across, and A9 current through, the resistive

load. /n less technical terms, any drop in the output voltage and current of

the bridge tends to be cancelled by loss of charge in the capacitor. 1his

charge flows out as additional current through the load. 1hus the change of

load current and voltage is reduced relative to what would occur without the

capacitor. /ncreases of voltage correspondingly store excess charge in the

capacitor, thus moderating the change in output voltage Y current.

1he capacitor and the load resistance have a typical time constant R&

where & and R are the capacitance and load resistance respectively. As long

as the load resistor is large enough so that this time constant is much longer

than the time of one ripple cycle, the above configuration will produce a

well smoothed *9 voltage across the load resistance. /n some designs, a

series resistor at the load side of the capacitor is added. 1he smoothing can

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then be improved by adding additional stages of capacitorresistor pairs,

often done only for subsupplies to critical highgain circuits that tend to be

sensitive to supply voltage noise.

>oltage *egulators

A 6oltage regulator is an electrical regulator designed to automatically

maintain a constant voltage level. /t may use an electromechanical

mechanism, or passive or active electronic components. *epending on the

design, it may be used to regulate one or more A9 or *9 voltages. With the

exception of shunt regulators, all voltage regulators operate by comparing

the actual output voltage to some internal fixed reference voltage. Any

difference is amplified and used to control the regulation element. 1his

forms a negative feedback servo control loop. /f the output voltage is toolow, the regulation element is commanded to produce a higher voltage. 3or

some regulators if the output voltage is too high, the regulation element is

commanded to produce a lower voltageD however, many ust stop sourcing

current and depend on the current draw of whatever it is driving to pull the

voltage back down. /n this way, the output voltage is held roughly constant.

1he control loop must be carefully designed to produce the desired tradeoff

between stability and speed of response.

LMA$ (8'Terminal ,i2e/ >oltage *egulator"

1he <9%Y<%Y<9%A series of three terminal positive

regulators are available in the

17$$'Y*2A+ package and with several fixed output voltages, making

them useful in a wide range of applications. ach type employs internal

current limiting, thermal shut down and safe operating area protection,

making it essentially indestructible. /f adeEuate heat sinking is provided,

they can deliver over #A output current. Although designed primarily as

fixed voltage regulators, these devices can be used with external components

to obtain adustable voltages and currents.

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,igure %1 +nternal :loc5 Diagram

,igure % 1 ,i2e/ utput *egulator '

,eatures

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7utput 9urrent up to #A

7utput ?oltages of ), -, %, @, #', #$, #), #%, $&?

1hermal 7verload 2rotection

Short 9ircuit 2rotection

7utput 1ransistor Safe 7perating Area 2rotection

%%.$ *EL)?0 '

A relay is an electrically operated

switch. 9urrent flowing through

the coil of the relay creates a magnetic

field, which attracts a lever and changes

the switch contacts. 1he coil current

ircuit symbol for a

relay

Relays

2hotographs j "apid lectronics

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can be on or off so relays have two switch positions and they are double

throw BchangeoverC switches.

"elays allow one circuit to switch a second circuit that can be completely

separate from the first. 3or example a low voltage battery circuit can use a

relay to switch a $('? A9 mains circuit. 1here is no electrical connectioninside the relay between the two circuits, the link is magnetic and

mechanical.

1he coil of a relay passes a relatively large current, typically ('mA for a

#$? relay, but it can be as much as #''mA for relays designed to operate

from lower voltages. <ost /9s BchipsC cannot provide this current and a

transistor is usually used to amplify the small /9 current to the larger value

reEuired for the relay coil. 1he maximum output current for the popular )))

timer /9 is $''mA so these devices can supply relay coils directly without

amplification.

"elays are usually S2*1 or *2*1 but they can have many more sets

of switch contacts, for example relays with & sets of changeover contacts are

readily available. 3or further information about switch contacts and the

terms used to describe them please see the page on switches.

<ost relays are designed for 290 mounting but you can solder wires

directly to the pins providing you take care to avoid melting the plastic case

of the relay.

1he supplierVs catalogue should show you the relayVs connections. 1he coil

will be obvious and it may be connected either way round. "elay coils

produce brief high voltage VspikesV when they are switched off and this can

destroy transistors and /9s in the circuit. 1o prevent damage you must

connect a protection diode across the relay coil.

1he animated picture shows a working relay with its coil and switch

contacts. 4ou can see a lever on the left being attracted by magnetism when

the coil is switched on. 1his lever moves the switch contacts. 1here is one

set of contacts BS2*1C in the foreground and another behind them, makingthe relay *2*1.

1he relayVs switch connections are usually labeled 97<, N9 and N7:

• 97< 9ommon, always connect to this, it is the moving part of the switch.

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• N9 Normally 9losed, 97< is connected to this when the relay coil is off.

• N7 Normally 7pen, 97< is connected to this when the relay coil is on.

• 9onnect to 97< and N7 if you want the switched circuit to be on when the

relay coil is on.

• 9onnect to 97< and N9 if you want the switched circuit to be on when the

relay coil is off.

%#.$ C*?0T)L 0C+LL)T* -

/t is often reEuired to produce a signal whose freEuency or pulse rate is very

stable and exactly known. 1his is important in any application where

anything to do with time or exact measurement is

crucial. /t is relatively simple to make an oscillator that produces some sort

of a signal, but another matter to produce one of relatively precise freEuency

and stability. A< radio stations must have a carrier freEuency accurate

within #'56 of its assigned freEuency, which may be from )(' to ##' k56.

SS0 radio systems used in the 53 range B$(' <56C must be within )' 56

of channel freEuency for acceptable voice Euality, and within #' 56 for best

results. Some digital modes used in weak signal communication may reEuire

freEuency stability of less than # 56 within a period of several minutes. 1he

carrier freEuency must be known to fractions of a hert6 in some cases. An

ordinary Euart6 watch must have an oscillator accurate to better than a few parts per million. 7ne part per million will result in an error of slightly less

than one half second a day, which would be about ( minutes a year. 1his

might not sound like much, but an error of #' parts per million would result

in an error of about a half an hour per year. A clock such as this would need

resetting about once a month, and more often if you are the punctual type. A

programmed ?9" with a clock this far off could miss the recording of part

of a 1? show. Narrow band SS0 communications at ?53 and 853

freEuencies still need )' 56 freEuency accuracy. At &&' <56, this is slightly

more than '.# part per million.

7rdinary 9 oscillators using conventional inductors and capacitors can

achieve typically '.'# to '.# percent freEuency stability, about #'' to #'''

56 at # <56. 1his is 7+ for A< and 3< broadcast receiver applications

and in other lowend analog receivers not reEuiring high tuning accuracy. 0y

careful design and component selection, and with rugged mechanical

construction, .'# to '.''#, or even better B.''')C stability can be

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achieved. 1he better figures will undoubtedly employ temperature

compensation components and regulated power supplies, together with

environmental control Bgood ventilation and ambient temperature regulationC

and battleship mechanical construction. 1his has been done in some

communications receivers used by the military and commercial 53

communication receivers built in the #@)'#@-) era, before the widespread

use of digital freEuency synthesis. 0ut these receivers were extremely

expensive, large, and heavy. <any modern consumer grade A<, 3<, and

shortwave receivers employing crystal controlled digital freEuency synthesis

will do as well or better from a freEuency stability standpoint.

An oscillator is basically an amplifier and a freEuency selective feedback

network B3ig #C. When, at a particular freEuency, the loop gain is unity or

more, and the total phaseshift at this freEuency is 6ero, or some multiple of

(-' degrees, the condition for oscillation is satisfied, and the circuit will produce a periodic waveform of this freEuency. 1his is usually a sine wave,

or sEuare wave, but triangles, impulses, or other waveforms can be

produced. /n fact, several different waveforms often are simultaneously

produced by the same circuit, at different points. /t is also possible to have

several freEuencies produced as well, although this is generally undesirable.

#(.' C)P)C+T*'

A capacitor or con/enser is a passive electronic component consisting of a pair of conductors separated by a dielectric BinsulatorC. When a potential

difference BvoltageC exists across the conductors, an electric field is present

in the dielectric. 1his field stores energy and produces a mechanical force

between the conductors. 1he effect is greatest when there is a narrow

separation between large areas of conductor, hence capacitor conductors are

often called plates.

An ideal capacitor is characteri6ed by a single constant value, capacitance,

which is measured in farads. 1his is the ratio of the electric charge on each

conductor to the potential difference between them. /n practice, the dielectric between the plates passes a small amount of leakage current. 1he conductors

and leads introduce an eEuivalent series resistance and the dielectric has an

electric field strength limit resulting in a breakdown voltage.

9apacitors are widely used in electronic circuits to block the flow of direct

current while allowing alternating current to pass, to filter out interference,

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to smooth the output of power supplies, and for many other purposes. 1hey

are used in resonant circuits in radio freEuency eEuipment to select particular

freEuencies from a signal with many freEuencies.

157"4 73 72"A1/7N

<ain article: 9apacitance

9harge separation in a parallelplate capacitor causes an internal electric

field. A dielectric BorangeC reduces the field and increases the capacitance.

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A simple demonstration of a parallelplate capacitor

A capacitor consists of two conductors separated by a nonconductive

region.1he nonconductive substance is called the dielectric medium,although this may also mean a vacuum or a semiconductor depletion region

chemically identical to the conductors. A capacitor is assumed to be self

contained and isolated, with no net electric charge and no influence from an

external electric field. 1he conductors thus contain eEual and opposite

charges on their facing surfaces, and the dielectric contains an electric field.

1he capacitor is a reasonably general model for electric fields within electric

circuits.

An ideal capacitor is wholly characteri6ed by a constant capacitance & ,

defined as the ratio of charge 3 on each conductor to the voltage 8 betweenthem

Sometimes charge buildup affects the mechanics of the capacitor, causing

the capacitance to vary. /n this case, capacitance is defined in terms of

incremental changes:

/n S/ units, a capacitance of one farad means that one coulomb of charge on

each conductor causes a voltage of one volt across the device.

E "ER!Y STORA!E

Work must be done by an external influence to move charge between the

conductors in a capacitor. When the external influence is removed, the

charge separation persists and energy is stored in the electric field. /f charge

is later allowed to return to its eEuilibrium position, the energy is released.

1he work done in establishing the electric field, and hence the amount of

energy stored, is given by:

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%&.$ *E0+0T* '

"esistors are used to limit the value of current in a circuit. "esistors offer

opposition to the flow of current. 1hey are expressed in ohms for which the

symbol is FΩH. "esistors are broadly classified as

B#C 3ixed "esistors

B$C ?ariable "esistors

,i2e/ *esistors 1

1he most common of low wattage, fixed type resistors is the moldedcarbon

composition resistor. 1he resistive material is of carbon clay composition.

1he leads are made of tinned copper. "esistors of this type are readilyavailable in value ranging from few ohms to about $'<Ω, having a

tolerance range of ) to $'. 1hey are Euite inexpensive. 1he relative si6e of

all fixed resistors changes with the wattage rating.

Another variety of carbon composition resistors is the metali6ed

type. /t is made by deposition a homogeneous film of pure carbon over a

glass, ceramic or other insulating core. 1his type of filmresistor is

sometimes called the precision type, since it can be obtained with an

accuracy of ±#.

ead 1inned 9opper <aterial

9olour 9oding <olded 9arbon 9lay 9omposition

3ixed "esistor

) !ire !oun/ *esistor 1

/t uses a length of resistance wire, such as nichrome. 1his wire is wounded

on to a round hollow porcelain core. 1he ends of the winding are attached to

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these metal pieces inserted in the core. 1inned copper wire leads are attached

to these metal pieces. 1his assembly is coated with an enamel coating

powdered glass. 1his coating is very smooth and gives mechanical

protection to winding. 9ommonly available wire wound resistors have

resistance values ranging from #Ω

to #''+ Ω

, and wattage rating up to about$''W.

Co/ing f *esistor 1

Some resistors are large enough in si6e to have their resistance printed on

the body. 5owever there are some resistors that are too small in si6e to have

numbers printed on them. 1herefore, a system of colour coding is used to

indicate their values. 3or fixed, moulded composition resistor four colour

bands are printed on one end of the outer casing. 1he colour bands arealways read left to right from the end that has the bands closest to it. 1he

first and second band represents the first and second significant digits, of the

resistance value. 1he third band is for the number of 6eros that follow the

second digit. /n case the third band is gold or silver, it represents a

multiplying factor of '.#to '.'#. 1he fourth band represents the

manufactureHs tolerance.

RESISTOR COLOUR CHART

&or e2ample, if a resistor has a colour band seEuence: yellow, violet,

orange and gold

green

9 blac

1 brown

2 red

* orange

+ yellow

- blue

. purple

sil!er

8 white

9 blac

1 brown

2 red

* orange

+ yellow

- blue

. purple

sil!er

8 white

green green

9 blac

1 brown

2 red

* orange

+ yellow

- blue

. purple

sil!er

8 white

green

9 blac

1 brown

2 red

* orange

+ yellow

- blue

. purple

sil!er

8 white

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T!" #$% &'"(! )#** +!,

4ellow&, violet, orange#'Z, gold) &+ ) $.()+

Most resistors ha6e & :an/s1

• 1he first band gives the first digit.

• 1he second band gives the second digit.

• 1he third band indicates the number of 6eros.

• 1he fourth band is used to show the tolerance BprecisionC of the resistor.

1his resistor has red B$C, violet BC, yellow B& 6erosC and gold bands.

So its value is $'''' $' k .

1he standard colour code cannot show values of less than #' . 1o show

these small values two special colours are used for the third band: gold,

which means '.# and silver which means '.'#. 1he first and second

bands represent the digits as normal.

,or e2ample1

red, violet, gold bands represent $ '.# $.

blue, green, silver bands represent )- '.'# '.)-

1he fourth band of the colour code shows the tolerance of a resistor.

1olerance is the precision of the resistor and it is given as a percentage. 3or

example a (@' resistor with a tolerance of #' will have a value within

#' of (@' , between (@' (@ ()# and (@' G (@ &$@ B(@ is #' of

(@'C.

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A special colour code is used for the fourth band tolerance:

silver #', gold ), red $, brown #.

/f no fourth band is shown the tolerance is $'.

>)*+)BLE *E0+0T*1

/n electronic circuits, sometimes it becomes necessary to adust the values of

currents and voltages. 3or n example it is often desired to change the volume

of sound, the brightness of a television picture etc. Such adustments can be

done by using variable resistors.

)lthough the 6aria:le resistors are usually calle/ rheostats in

other applications7 the smaller 6aria:le resistors commonly use/ in

electronic circuits are calle/ potentiometers.

%.$ T*)N0+0T*0 '

A transistor is an active device. /t consists of two 2N unctions formed by

sandwiching either ptype or ntype semiconductor between a pair of

opposite types.

1here are two types of transistor:

#. npn transistor

$. pnp transistor

An npn transistor is composed of two ntype semiconductors

separated by a thin section of ptype. 5owever a pnp type semiconductor is

formed by two psections separated by a thin section of ntype.

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1ransistor has two pn unctions one unction is forward biased and

other is reversed biased. 1he forward unction has a low resistance path

whereas a reverse biased unction has a high resistance path.

1he weak signal is introduced in the low resistance circuit and output

is taken from the high resistance circuit. 1herefore a transistor transfers asignal from a low resistance to high resistance.

1ransistor has three sections of doped semiconductors. 1he section on

one side is emitter and section on the opposite side is collector. 1he middle

section is base.

Emitter 1 1he section on one side that supplies charge carriers is called

emitter. 1he emitter is always forward biased w.r.t. base.

Collector 1 1he section on the other side that collects the charge is called

collector. 1he collector is always reversed biased.

Base 1 1he middle section which forms two pnunctions between the

emitter and collector is called base.

A transistor raises the strength of a weak signal and thus acts as an

amplifier. 1he weak signal is applied between emitterbase unction and

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output is taken across the load "c connected in the collector circuit. 1he

collector current flowing through a high load resistance "c produces a large

voltage across it. 1hus a weak signal applied in the input appears in the

amplified form in the collector circuit.

%@.$ CNNECT*0 '

9onnectors are basically used for interface between two. 5ere we use

connectors for having interface between 290 and %')# <icroprocessor +it.

1here are two types of connectors they are male and female. 1he one,

which is with pins inside, is female and other is male.

1hese connectors are having bus wires with them for connection.

3or high freEuency operation the average circumference of a coaxial cable

must be limited to about one wavelength, in order to reduce multimodal

propagation and eliminate erratic reflection coefficients, power losses, and

signal distortion. 1he standardi6ation of coaxial connectors during World

War // was mandatory for microwave operation to maintain a low reflection

coefficient or a low voltage standing wave ratio.

0e6en types of micro<a6e coa2ial connectors are as follo<s1

1%AP=*%

2%AP=.

*%$4

+%6'A

%6'

-%T4

.%Type 4

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'I'LIOGRAP()

• www%datasheets%com

• www%technowa!e%co%in

•

www%microtutorials%com

• www%o!erclocers%com