ME6504
METROLOGY AND MEASUREMENTS
.BASICS OF METROLOGY Introduction to Metrology – Need – Elements – Work piece, Instruments – Persons – Env Environ ironme ment nt – thei theirr effe effect ct on Prec Precis isio ion n and and Accur ccurac acy y – Erro Errors rs – Erro Errors rs in Measurements – ypes – !ontrol – ypes of standards.
UNIT I
UNIT II
LINEAR EAR AND ANGU NGULAR LAR MEA MEAS SUREMENTS
"inear Measuring Instruments – Evolution – ypes – !lassification – "imit gauges – gauge design – terminology – procedure – concepts of interchange a#ility and selective assem#ly – Angular measuring instruments – ypes – $evel protractor clinometers angle gauges, spirit levels sine #ar – Angle alignment telescope – Autocollimator – Applications. Applications. UNIT III
ADVANCES IN METROLOGY
$asic concept of lasers Advantages Advantages of lasers – laser Interferometers Interferometers – types t ypes – %! and A! "asers interferometer – Applications Applications – &traightness &traightness – Alignment. Alignment. $asic concept of !MM – ypes of !MM – !onstructional features – Pro#es – Accessories – &oft'are – Applications Applications – $asic $asic concepts concepts of Machine (ision &ystem – Element – Applications. Applications. UNIT IV
FORM MEASUREMENT
Prin Princi cipl ples es and Meth Method ods s of stra straig ight htne ness ss – )lat )latne ness ss meas measur urem emen entt – hrea hread d meas measur urem emen ent, t, gear gear meas measur urem emen ent, t, surf surfac ace e fini finish sh meas measur urem emen ent, t, *oun *oundn dnes ess s measurement – Applications. UNI UNIT V
MEA MEASURE SUREME MENT NT OF POW POWER, ER, FLO FLOW AND TEMP EMPERA ERATURE URE
)orce, tor+ue, po'er mechanical , Pneumatic, -ydraulic and Electrical type. )lo' measurem measurement ent (entur (enturimet imeter er,, /rifice /rifice meter, meter, rotamete rotameter, r, pitot pitot tu#e – emperatur mperature e #imetall #imetallic ic strip, strip, thermoco thermocoupl uples, es, electric electrical al resistan resistance ce thermom thermometer eter – *elia#i *elia#ility lity and !ali#ration – *eada#ility and *elia#ility.
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UNIT-I BASICS OF METROLOGY 1.1. INTRODUCTION METROLOGY
Metrology: it is the name given to the science of pure measurement Engineering etrology: the measurement of lengths, angles, and other quantities that are expressed in linear or angular terms i! Unit e"#$reent ii! Error# e"#$reent iii! A%%$r"%y o& in#tr$ent# i'! In($#tri"l in#)e%tion
1.1.1.MET*OD OF MEASUREMENT OR CLASSIFICATION
1. Direct Direct method method of measurement measurement 2. Indire Indirect ct metho method d of measu measurem rement ent 3. Compar Comparati ative ve method method of measu measureme rement nt 4. Coinci Coinciden dence ce method method of measure measuremen mentt 5. Contact Contact and and contact contactless less method method of measureme measurement nt 6. efl eflec ecti tion on meth method od 1. Dire%t et+o( o& e"#$reent !his is a simple method of measurement, in "hich the value of the quantit# to $e measured is o$tained directl# "ithout an# calculations. %or example, measurements $# using scales, vernier calipers, micrometers, $evel protector etc. !his method is most "idel# used in production. !his method is not ver# accurate $ecause it depends on human insensitiveness in ma&ing 'udgment.
,. In(ire%t et+o( o& e"#$reent In indirect method the value of quantit# to $e measured is o$tained $# measuring other quantities "hich are functionall# related to the required value. (.g. )ngle measurement measurement $# sine $ar, $ar, measurement measurement of scre" pitch diameter diameter $# three three "ire method etc. etc.
. Co)"r"ti'e et+o( o& e"#$reent In this method the value of the quantit# to $e measured is compared "ith &no"n value of the same quantit# or other quantit# practicall# related to it. *o, in this method onl# the deviations from a master gauge are determined, e.g., dial indicators, or other comparators.
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UNIT-I BASICS OF METROLOGY 1.1. INTRODUCTION METROLOGY
Metrology: it is the name given to the science of pure measurement Engineering etrology: the measurement of lengths, angles, and other quantities that are expressed in linear or angular terms i! Unit e"#$reent ii! Error# e"#$reent iii! A%%$r"%y o& in#tr$ent# i'! In($#tri"l in#)e%tion
1.1.1.MET*OD OF MEASUREMENT OR CLASSIFICATION
1. Direct Direct method method of measurement measurement 2. Indire Indirect ct metho method d of measu measurem rement ent 3. Compar Comparati ative ve method method of measu measureme rement nt 4. Coinci Coinciden dence ce method method of measure measuremen mentt 5. Contact Contact and and contact contactless less method method of measureme measurement nt 6. efl eflec ecti tion on meth method od 1. Dire%t et+o( o& e"#$reent !his is a simple method of measurement, in "hich the value of the quantit# to $e measured is o$tained directl# "ithout an# calculations. %or example, measurements $# using scales, vernier calipers, micrometers, $evel protector etc. !his method is most "idel# used in production. !his method is not ver# accurate $ecause it depends on human insensitiveness in ma&ing 'udgment.
,. In(ire%t et+o( o& e"#$reent In indirect method the value of quantit# to $e measured is o$tained $# measuring other quantities "hich are functionall# related to the required value. (.g. )ngle measurement measurement $# sine $ar, $ar, measurement measurement of scre" pitch diameter diameter $# three three "ire method etc. etc.
. Co)"r"ti'e et+o( o& e"#$reent In this method the value of the quantit# to $e measured is compared "ith &no"n value of the same quantit# or other quantit# practicall# related to it. *o, in this method onl# the deviations from a master gauge are determined, e.g., dial indicators, or other comparators.
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. Coin%i(en%e et+o( o& e"#$reent It is a differential method of measurement in "hich a ver# small difference $et"een the value of the quantit# to $e measured and the reference is determined $# the o$servation of the coincidence of certain lines or signals. %or example, measurement measurement $# vernier calliper micrometer.
/. Cont"%t et+o( !he measuring tip of the instrument touches the 'o$ +or material. (g- vernier caliper, micrometer, dial indicator.
0. Cont"%tle## et+o( !he measuring tip of the instrument do not touches the 'o$ +or material. (g- !ool a&ers microscope
. De&le%tion et+o( In this method the value of the quantit# to $e measured is directl# indicated $# a deflection of a pointer on a cali$rated scale. (g- pressure measurement. measurement.
1.,.Nee( &or etrology 0 !o provide provide the required accurac# at minimum cost minimi/e the cost of inspection 0 !o minimi/e 0 !o ensure ensure the capa$ilit# of measuring instruments standardi/e the various measuring instruments 0 !o standardi/e 0 !o maintain maintain the accurac# of the instrument $# cali$rating them periodicall# design the gauges, fixtures and accessories. 0 !o design 1..ELEMENTS OF METROLOGY-GENERALISED MEASURING SYSTEM ) measuring s#stem exists to provide information a$out the ph#sical value of some varia$le $eing measured. In simple cases, the s#stem can consist of onl# a single unit that gives an output reading or signal according to the magnitude of the un&no"n varia$le applied to it. 0o"ever, in more complex measurement situations, a measuring s#stem consists of several separate elements as sho"n in %igure. !he follo"ing common element 0 rimar# sensing element 0 aria$le conversion element 0 aria$le manipulation element 0 ata transmission element 0 ata processing element 0 ata presentation element
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E2:FILLED T*ERMAL SYSTEM 3OR! BOURDON TUBE 4RESSURE GAUGE 0
It is the "idel# used pressure gauge.it "as inverted $# $ourdon.
Con#tr$%tion 0 ourdons gauge consists of an elastic $ron/e tu$e of elliptic cross section $ent into a circular arc. 0 ne end of the tu$e is fixed to the frame and other end is closed and is free to move. 0 !his end is fitted to a lever arrangement consisting of a lin&, sector, pinion and a pointer.
5OR6ING D"t" tr"n#i##ion eleentpressure +capillar# tu$e 7"ri"8le %on'er#ion eleent spiral $ourdon tu$e 7"ri"8le "ni)$l"tion eleent lin&age and gear D"t" )re#ent"tion eleent scale and pointer hen the fluid under pressure enters the $ourdon tu$e, elliptic cross section of tu$e tends to $ecome circular. ue to this, tu$e tends to straighten. !his elastic deflection of the tu$e causes the pinion to rotate through lever arrangement. !he pointer moves the dial and sho"s the reading.
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1..MEASURING INSTRUMENTS AND TY4ES. 1. 2. 3. 4.
eflection and null t#pe instrument )nalog and digital instrument )utomatic and manuall# operated Contacting and noncontacting instrument
1. De&le%tion "n( n$ll ty)e in#tr$ent It is mechanical device .the "eight of the o$'ect is indicated $# the deflection or movement of a pointer on a graduated scale.(g- spring $alance 7 $eam $alance
,.An"log "n( (igit"l in#tr$ent !he digital instrument gives the output "hich varies in discrete steps and can ta&e onl# finite num$er of values in given range. !he output of digital instrument is generall# displa#ed numericall# as digit. (g- galvanometer 7 ammeter.
. A$to"ti% "n( "n$"lly o)er"te( A$to"ti%: !hese instrument do not depend on the operators service.(g- automated null $alance instrument 7 C8C machines M"n$"lly: !hese instruments depend on the operator9s service. (g- :athe machine
1./.4RECISION AND ACCURACY 0
!hese terms are used in connection "ith the performance of an intrument.
A%%$r"%y )ccurac# is the degree to "hich the measured value of the qualit# characteristic agrees "ith the true value. !he difference $et"een the true value and the measured value is &no"n as error of measurement. It is practicall# difficult to measure exactl# the true value and therefore a set of o$servations is made "hose mean value is ta&en as the true value of the qualit# measured.
4re%i#ion !he terms precision and accurac# are used in connection "ith the performance of the instrument. recision is the repeata$ilit# of the measuring process. It refers to the group of measurements for the same characteristics ta&en under identical conditions. It indicates to "hat extent the identicall# performed measurements agree "ith each other. If the instrument is not precise it "ill give different +"idel# var#ing results for the same dimension "hen measured again and again. !he set of o$servations "ill scatter a$out the mean. !he scatter of these measurements is designated as ;, the standard deviation. It is used as an index of precision. !he less the scattering more precise is the instrument. !hus, lo"er, the value of ;, the more precise is the instrument.
1./.1.COM4ARISON OF ACCURACY AND 4RECISION. )ccurac# is ver# often confused "ith precision though much different. !he distinction $et"een the precision and accurac# "ill $ecome clear $# the follo"ing example. *everal measurements are made on a component $# different t#pes of instruments +), and C respectivel# and the results are plotted. In an# set of measurements, the individual measurements are scattered a$out the mean, and the precision signifies ho" "ell the various measurements performed $# same instrument on the same qualit# characteristic agree "ith each other.
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!he difference $et"een the mean of set of readings on the same qualit# characteristic and the true value is called as error. :ess the error more accurate is the instrument. %igure sho"s that the instrument ) is precise since the results of num$er of measurements are close to the average value. 0o"ever, there is a large difference +error $et"een the true value and the average value hence it is not accurate. !he readings ta&en $# the instruments are scattered much from the average value and hence it is not precise $ut accurate as there is a small difference $et"een the average value and true value.
1./.,.F"%tor# "&&e%ting t+e "%%$r"%y "n( )re%i#ion o& t+e Me"#$ring Sy#te !he $asic components of an accurac# evaluation are the five elements of a measuring s#stem such as1. %actors affecting the cali$ration standards. 2. %actors affecting the "or& piece. 3. %actors affecting the inherent characteristics of the instrument. 4. %actors affecting the person, "ho carries out the measurements, 5. %actors affecting the environment.
1. F"%tor# "&&e%ting t+e St"n("r( It ma# $e affected $#Coefficient of thermal expansion Cali$ration interval *ta$ilit# "ith time (lastic properties
,. F"%tor# "&&e%ting t+e 5or9 )ie%e !hese areCleanliness *urface finish, "aviness, scratch, surface defects etc., 0idden geometr# (lastic properties, adequate datum on the "or& piece )rrangement of supporting "or& piece !hermal equali/ation etc.
. F"%tor# "&&e%ting t+e in+erent %+"r"%teri#ti%# o& In#tr$ent )dequate amplification for accurac# o$'ective *cale error (ffect of friction, $ac&lash, h#steresis, /ero drift error eformation in handling or use, "hen heav# "or& pieces are measured
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Cali$ration errors echanical parts +slides, guide "a#s or moving elements =epeata$ilit# and reada$ilit# Contact geometr# for $oth "or& piece and standard.
. F"%tor# "&&e%ting )er#on: !raining, s&ill *ense of precision appreciation )$ilit# to select measuring instruments and standards *ensi$le appreciation of measuring cost )ttitude to"ards personal accurac# achievements lanning measurement techniques for minimum cost, consistent "ith precision requirements
5. F"%tor# "&&e%ting En'ironent !emperature, humidit# etc. Clean surrounding and minimum vi$ration enhance precision )dequate illumination !emperature equali/ation $et"een standard, "or& piece, and instrument !hermal expansion effects due to heat radiation from lights 0eating elements, sunlight and people anual handling ma# also introduce thermal expansion. 0igher accurac# can $e achieved onl# if, ail the sources of error due to the a$ove five elements in the measuring s#stem are anal#/ed and steps ta&en to eliminate them. !he a$ove anal#sis of five $asic metrolog# elements can $e composed into the acron#m
1.0.ERRORS IN MEASUREMENTS Error: the difference $et"een the measured value and the true value is called error. Error e"#$re( '"l$e ; tr$e '"l$e. !he error depends on the follo"ing factors S5I4E *tandard of cali$ration3S! or& piece 35! Instrument 3I! erson 34! (nvironment 3E!
1.0.1.TY4ES OF ERROR 1. *tatic error i (nvironmental errors ii Characteristic errors 2. =andom error 3. Cali$ration error 4. )m$ient error 5. )voida$le error
1. St"ti% error#: the static errors are due to the nature of the measuring s#stem. i!
En'ironent"l error# (ver# instrument is manufactured and cali$rated at one place and it is used in some other place "here the environmental conditions such as temperature, pressure etc. *o, the change in environment influences the reading of the instrument. !his change in environment is called environmental error. !hese result fromtheeffectofthefollo"ingsources.+!emperature,pressure,humidit#,vi$ration,radiation
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Control: this t#pe of environmental error can $e reduced $# controlling the a$ove sources as per the requirements. ii! C+"r"%teri#ti% error# !he deviation of the output of the measuring s#stem from the nominal performance specification is called characteristics error.
Control: it can $e reduced $# controlling the linearit#,h#sterisis,repeata$lit#,7 cali$ration error requirements.
,. R"n(o error !hese t#pes of errors occur randoml# and reason for this t#pe of error cannot $e specified. !he sources of random errors are as follo"s iariation in the position of setting the standard and the "or& piece ii isplacement of the levers +or 'oints of the measuring instruments. Control: it can $e reduced $# controlling the a$ove sources as per the requirements.
. C"li8r"tion error It is the process of determining and ad'usting an instruments to ma&e sure its accurac# is not "ithin the manufactures specification. Control: it can $e reduced $# controlling the a$ove sources as per the requirements.
. A8ient error !his is due to variation in atmospheric conditions normall# the instruments are cali$rated at particular pressure and temperature. Control: this t#pe of environmental error can $e reduced $# controlling the a$ove sources as per the requirements.
/. A'oi("8le error !his t#pe of error is due to nonalignment of "or&pice centers and improper location of measuring instrument. Control: it can $e reduced $# controlling the a$ove sources as per the requirements
UNITS Unit: to specif# and perform calculation "ith ph#sical quantities, the ph#sical quanties must $e defined $oth in &ind and magnitude. !he standard measuring of each &ind of ph#sical quantites is the unit. !he# are four s#stems of units i C.<.* units ii%..* unit iii .?.* units iv*.I units i C.<.* units- the fundamental units of length, mass and time are ta&en as centimeter, gram and second. ii %..* unit- footpoundsecond iii .?.* units- meter, &ilogram, second iv *.I units- s#stem of international units !he *.I unit divided into t"o t#pes i %undamental units ii erived units i %undamental units- length +m, ass +?g, time +sec, temperature +!. ii erived units- )rea +), olume +, densit# +@.
1..STANDARDS < TY4ES St"n("r(: an# s#stem of measurement must $e related to a &no"n standard.
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Ty)e# o& #t"n("r( 1 :ine standard 2 (nd standard 1! Line #t"n("r(: "hen the length is measured $et"een t"o lines it is called line standard. (g- !he protot#pe meter and imperial #ard are examples of line standard, as the distance is measured $et"een lines.
Intern"tion"l #t"n("r( eter 0
!his is a material standard esta$lished $# the ureau of "eights and measures and preserved in %rance. 0 )ccording to this standard, the length of one meter is defined as the distance $et"een the Centre portions of pure platinumiridium allo# of 1B2 cm, total length. 0 !he composition of the allo# is latinum DB Iridium 1B 0 !he graduation is on the upper surface of the "e$. !his coincides "ith neutral axis of the section. 0 !he sectional shape gives greater rigidit# 0 !he section offers economic use of the expensive platiniumirridium allo#. 0 !he international proto t#pe meter is &ept $#I +ureau international de poids et measures at *evres in %rance !he I is controlled $# the international committee of "eights and measures.
I)eri"l #t"n("r( y"r( 0 0 0 0 0
!he imperial standard #ard is ritish standard.it is made of 1 square cross section $ron/e $ar. !he composition of the $ron/e $ar Copper A2 !in 13 Einc 5 !he $ar has t"o holes of F diameters and F depths. (ach hole is fitted "ith a gold plug. !he top surface of the plug lies on the neutral axis of the $ron/e $ar. !his has the follo"ing advantages. 0 !he plug is protected from an# damage 0 !he neutral axis is unaffected due to $ending of the $eam 0 !hree lines are engraved on the gold plug as sho"n in the enlarged vie". 0 !he distance $et"een the t"o central lines on the golden plug is one #ard.it is equal to 36G "hen the temperature of the $ar is at 62% 0 !he total length of the $ron/e $ar is 3AG ,! En( #t"n("r(: "hen the distance +length is measured $et"een t"o surface +or faces it is called end standard. (g- *lip gauge.
SUBDI7ISION STANDARDS 1. rimar# standards 2. *econdar# standards 3. !ertiar# standards 4. or&ing standards 1. 4ri"ry #t"n("r(#: the material standard is preserved carefull# and used onl# at rare intervals +of 1B +or 2B #ears for comparison "ith secondar# standards it is called primar# standard (g protot#pe meter, imperial #ard. ,. Se%on("ry #t"n("r(#: these standards are &ept at num$er of places. !he# are used for comparison "ith tertiar# standards "henever required. . Terti"ry #t"n("r(#: the# are the first standard to $e used for reference purpose in la$oratories and "or& piece.
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. 5or9ing #t"n("r(#: these are used more frequentl# in la$oratories and "or&shop. !he# are made of lo" grade materials.
UNIT-II LINEAR AND ANGULAR MEASUREMENTS ,.1.Line"r e"#$reent: linear measurement refers to measurements of lengths, diameters, heights and thic&ness this ma# $e internal or e xternal. :inear measurement
Line"r e"#$reent EG: #%"le
en( e"#$reent Eg:#li) g"$ge
L=D= T+i%9= +eig+t#
t+e e"#$reent i# "(e 8et>een &l"t #$r&"%e#.
,.,.Line"r e"#$ring in#tr$ent ,.,.1.Dire%t et+o( 1. ernier calipers 2. icrometers 3. *lip gauge or gauge $loc& 4. Comparators 5. :imit gauges. ,.,.,.In(ire%t et+o( 1. !ool ma&ers microscope 2. Interferometr# 7 optical flat 1. 7ernier %"li)er# It is a precision instrument It has t"o scales, namel# the main scale and vernier scale. !he instrument has separate measuring tips for external dimensions and internal dimensions.
1B
Le"#t %o$nt o& 'ernier: it is defined as the difference $et"een the values of a main scale division and vernier scale division. :.C H 1*1* here, :.CHleast count, *Hmain scale division, *vernier scale division.
If 5B divisions on the vernier scale corresponds to 4Dmm !hen
1VSD =
49 50
mm
L. C =1−
49 50
=
50 −49 50
=
1 50
=0.02 mm
:east count can also calculated as 1 value of 1 MSD = =0.02 mm L. C = No of divisions on vernier scale 50 !he measured dimensionH*=+no.of vernier coincidence x :.C
Ty)e# o& 'ernier %"li)er: Ty)e A= B= C Ty)e A: ernier has 'a"s on $oth sides for external and internal measurements and a $lade for depth measurement.
Ty)e B: It is provided "ith 'a"s on one side for external and internal measurements.
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Ty)e C: It has 'a"s on $oth sides for ma&ing the measurement and for mar&ing operations
Error# in C"li)er#: !he degree of accurac# o$tained in measurement greatl# depends upon the condition of the 'a"s of the calipers and a special attention is needed $efore proceeding for the measurement. !he accurac# and natural "ear, and "arping of ernier caliper 'a"s should $e tested frequentl# $# closing them together tightl# and setting them to BB point of the main and ernier scales. !he external 7 internal measuring part is same $elo" i ernier height gauge ii vernier depth gauge. i! 7ernier +eig+t g"$ge it is a precision instrument used to measure and mar& vertical heights.it is also used to
measure difference in heights. !he $ase is massive in construction for rigidit# and sta$ilit# )ll the parts are made of stainless steel the vertical column is also called $eam or $ase. !he pro'ection of the 'a" should $e at least 25mm. !he auxiliar# head is attached to the $eam a$ove the sliding vernier head.it has fine ad'usting and clamping scre". !he method of measurement is ver# similar to the vernier caliper. !he measuring faces +of the $eam measuring 'a" and the scri$er should $e tested for straightness, squarness and parallelism.
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ii! 7ernier (e)t+ g"$ge. It is used to measure the depth of holes, slots etc. !he vertical $eam is perpendicular to the $ase. !he sliding head moves over the graduated
$eam. !he $ase is held firml# on the reference surface !he $eam is lo"ered into the holes until the $ottom surface is contacted. !he final ad'ustment is made $# fine ad'usting scre". !he clamping scre" of the sliding head is tighted. !he instrument is removed from the hole and reading is noted and the depth is calculated as per the vernier principle.
MICROMETERS It is also called scre" gauge. It is used for measurement of diameter and length 7 depth of small parts. Jshaped steel frame*leeve )nvil and spindlethim$le :oc&e nutratchet.
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Le"#t %o$nt: :east count of an instrument is the minimum distance that can $e measured accuratel# $# instrument.
pitch no fo thimbledivision here pitch of scre"HB.5mm
L. C =
8o of thim$le divisionH5B Ty)e# 1. 2. 3.
:.CH
0.5 50
0.01 mm
=
o& i%roeter utside micrometer !o measure external dimensions. Inside micrometer !o measure internal dimensions. epth micrometerto measure depth of holes 7 slots
1. utside micrometer It consists of t"o scales, main scale and thim$le scale. !he le"#t %o$nt of this micrometer is B.B1 mm.
!he micrometer requires the use of an accurate scre" thread as a means of o$taining a
measurement. !he scre" is attached to a spindle and is turned $# movement of a thim$le or ratchet at the
end. !he $arrel, "hich is attached to the frame, acts as a nut to engage the scre" threads, "hich are accuratel# made "ith a pitch of B.B5mm. (ach revolution of the thim$le advances the scre" B.B5mm. n the $arrel a datum line is graduated "ith t"o sets of division mar&s.
In#i(e i%roeter !he diameter of the $ore is measured approximatel# $# a scale (xtension rod is selected to the headrest dimensions !he micrometer head is held firml# inside the $ore and the contact surface is ad'usted !his is done $# moving the thim$le until the correct feel is sensed !he micrometer is then removed and the reading is noted. !he lengther of extensions and collar are added to the micrometer reading.
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De)t+ i%roeter It has a shoulder+$ase "hich acts as reference surface (xtension rods of different lengths can $e inserted these are availa$le in steps of 25mm !he measuring faces of the $ase and rods are hardened It should $e noted that the scale of depth micrometer is cali$rated in the reverse direction
SLI4 GAUGES !hese are rectangular $loc&s made of high grade steel or tungsten car$ide. *lip gauges are used as end standards and are also called gauge $loc&s.
!hese "ere introduced $# 'ohanson +s"eedish engineer and hence the# are also &no"n as 'ohanson gauges. !he "or&ing faces of slip gauge are made trul# flat and parallel.
Jse of slip gauges
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*lip gauges are "rung together $# hand. !his is done $ # a com$ined sliding and
t"isting motion. *lip gauges are used for direct precise measurement, for chec&ing the accurac# of
vernier calipers, micrometers, etc. !he# are also used for setting a specific dimension, or for angular setting along "ith sine $ar.
5ringing or Sli(ing is nothing $ut com$ining the faces of slip gauges one over the other. ue to adhesion propert# of slip gauges, the# "ill stic& together. !his is $ecause of ver# high degree of surface finish of the measuring faces.
Cl"##i&i%"tion o& Sli) G"$ge# *lip gauges are classified into various t#pes according to their use as follo"s1
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v. !o get the exact si/e of slip gauges, lapping operation is done. vi. Comparison is made "ith grand master sets. Sli) G"$ge# "%%e##orie# !he application slip gauges can $e increased $# providing accessories to the slip gauges. !he various accessories are easuring 'a" *cri$er and Centre point. 0older and $ase 1. Me"#$ring @">It is availa$le in t"o designs speciall# made for internal and external features. ,. S%ri8er "n( Centre )ointIt is mainl# formed for mar&ing purpose. . *ol(er "n( 8"#e0older is nothing $ut a holding device used to hold com$ination of slip gauges. ase in designed for mounting the holder rigidl# on its top surface. Co)"r"tor Comparator is a precision instrument and it is used to compare the component +dimension
"ith a "or&ing standard. *lip gauges are generall# used as "or&ing standards. It has the follo"ing three devices or s#stem.
i *ensing device ii magnification device or s#stem iii displa# s#stem i! Sen#ing (e'i%e: the sensing device commonl# used is a plunger "hich senses the change in the length or an# other dimensions ii! M"gni&i%"tion (e'i%e or #y#te: t+e magnification device is also called amplif#ing s#stem.it ma# $e mechanical, optical, pneumatics, electronic etc. iii! Di#)l"y #y#te: the displa# s#stem provides suita$le readout.) scale and pointer is generall# used as displa# s#stem. Ty)e# o& %o)"r"tor#: 1. echanical comparators 2. (lectrical comparators 3. ptical comparators 4. (lectronic comparators 5. neumatic comparators Me%+"ni%"l %o)"r"tor# !he method of magnif#ing small movement of the indicator in all mechanical comparators are effected $# means of levers, gear trains or a com$ination of these elements.
P p Hplunger movement
magnification =
here Hpointer movement Ty)e# o& e%+"ni%"l %o)"r"tor# i ial indicator ii =eed t#pe mechanical comparators
1. Di"l in(i%"tor: ) dial indicator or dial gauge is used as a mechanical comparator. !he essential parts of the instrument are li&e a small cloc& "ith a plunger pro'ecting at the $ottom as sho"n in fig.
1>
er# slight up"ard movement on the plunger moves it up"ard and the movement is indicated $# the dial pointer. !he dial is graduated into 1BB divisions. ) full revolution of the pointer a$out this scale corresponds to 1mm travel of the plunger. !hus, a turn of the pointer $ one scale division represents a plunger travel of B.B1mm. E)erient"l #et$): !he "hole setup consists of "or&ta$le, dial indicator and vertical post. !he dial indicator is fitted to vertical post $# on ad'usting scre" as sho"n in fig. !he vertical post is fitted on the "or& ta$leK the top surface of the "or&ta$le is finel# finished. !he dial gauge can $e ad'usted verticall# and loc&ed in position $# a scre".
4ro%e($re :et us assume that the required height of the component is 32.5mm. Initiall# this height is $uilt up "ith slip gauges. !he slip gauge $loc&s are placed under the stem of the dial gauge. !he pointer in the dial gauge is ad'usted to /ero. !he slip gauges are removed. 8o" the component to $e chec&ed is introduced under the stem of the dial gauge. If there is an# deviation in the height of the component, it "ill $e indicated $# the pointer. Me%+"ni# !he stem has rac& teeth. ) set of gears engage "ith the rac&. !he pointer is connected to a small pinion. !he small pinion is independentl# hinged. I.e. it is not connected to the stern. !he vertical movement of the stem is transmitted to the pointer through a set of gears. ) spring gives a constant do"n"ard pressure to the stem. ,. Re"( ty)e e%+"ni%"l %o)"r"tor In this t#pe of comparator, the linear movement of the plunger is specified $# means of read mechanism. !he mechanism of this t#pe is illustrated in fig. ) springloaded pointer is pivoted. Initiall#, the comparator is set "ith the help of a &no"n dimension eg. *et of slip gauges as sho"n in fig. !hen the indicator reading is ad'usted to /ero. hen the part to $e measured is &ept under the pointer, then the comparator displa#s the deviation of this dimension either in L orM side of the set dimension.
1A
A('"nt"ge# :1 It is usuall# ro$ust, compact and eas# to handle. 2 !here is no external suppl# such as electricit#, air required. 3 It has ver# simple mechanism and is cheaper "hen compared to other t#pes. 4 It is suita$le for ordinar# "or&shop and also easil# porta$le. Di#"('"nt"ge# 1 )ccurac# of the comparator mainl# depends on the accurac# of the rac& and pinion arrangement. )n# slac&ness "ill reduce accurac#. 2 It has more moving parts and hence friction is more and accurac# is less. 3 !he range of the instrument is limited since pointer is moving over a fixed scale. ELECTRICAL COM4ARATOR: )n electrical comparator consists of the follo"ing three ma'or part such as 1 !ransducer 2 ispla# device as meter 3 )mplifier Tr"n#($%er )n iron armature is provided in $et"een t"o coils held $# a lea spring at one end. !he other end is supported against a plunger. !he t"o coils act as t"o arms of an ).C. "heat stone $ridge circuit. A)li&ier !he amplifier is nothing $ut a device "hich amplifies the give input signal frequenc# into magnified output Di#)l"y (e'i%e or eter !he amplified input signal is displa#ed on some terminal stage instruments. 0ere, the terminal instrument is a meter.
5or9ing )rin%i)le If the armature is centrall# located $et"een the coils, the inductance of $oth coils "ill $e equal $ut in opposite direction "ith the sign change. ue to this, the $ridge circuit of
1D
).C. "heat stone $ridge is $alanced. !herefore, the meter "ill read /ero value. ut practicall#, it is not possi$le. In real cases, the armature ma# $e lifted up or lo"ered do"n $# the plunger during the measurement. !his "ould upset the $alance of the "heat stone $ridge circuit. ue to this effect, the change in current or potential "ill $e induced correspondingl#. n that time, the meter "ill indicate some value as displacement. !his indicated value ma# $e either for larger or smaller components. )s this induced current is too small, it should $e suita$l# amplified $efore $eing displa#ed in the meter. ELECTRONIC COM4ARATOR In electronic comparator, transducer induction or the principle of application of frequenc# modulation or radio oscillation is follo"ed.
Con#tr$%tion (et"il# In the electronic comparator, the follo"ing components are set as follo"s- i. !ransducer ii. scillator iii. )mplifier iv. emodulator v. eter 3i! Tr"n#($%er It converts the movement of the plunger into an electrical signal. It is connected "ith oscillator. 3ii! O#%ill"tor !he oscillator "hich receives electrical signal from the transducer and raises the amplitude of frequenc# "ave $# adding carrier frequenc# called as modulation. 3iii! A)li&ier )n amplifier is connected in $et"een oscillator and demodulator. !he signal coming out of the oscillator is amplified into a required level. 3i'! Deo($l"tor emodulator is nothing $ut a device "hich cuts off external carrier "ave frequenc#. i.e. It converts the modulated "ave into original "ave as electrical signal. 3'! Meter !his is nothing $ut a displa# device from "hich the output can $e o$tained as a linear measurement. 4rin%i)le o& o)er"tion !he "or& to $e measured is placed under the plunger of the electronic comparator. oth "or& and comparator are made to rest on the surface plate. !he linear movement of the plunger is converted into electrical signal $# a suita$le transducer. !hen it sent to an oscillator to modulate the electrical signal $# adding carrier frequenc# of "ave. )fter that the amplified signal is sent to demodulator in "hich the carrier "aves are cut off. %inall#, the demodulated signal is passed to the meter to convert the pro$e tip movement into linear measurement as an output signal. ) separate electrical suppl# of .C. is alread# given to actuate the meter. A('"nt"ge# o& Ele%tri%"l "n( Ele%troni% %o)"r"tor 1 It has less num$er of moving parts. 2 agnification o$tained is ver# high. 2 !"o or more magnifications are provided in the same instrument to use various ranges. 4 !he pointer is made ver# light so that it is more sensitive to vi$ration. 5 !he instrument is ver# compact.
2B
Di#"('"nt"ge# o& Ele%tri%"l "n( Ele%troni% %o)"r"tor 1 (xternal agenc# is required to meter for actuation. 2 ariation of voltage or frequenc# ma# affect the accurac# of output. 3 ue to heating coils, the accurac# decreases. 4 It is more expensive than mechanical comparator. O)ti%"l %o)"r"tor# Eeiss ultra optimeter-it is an optical comparators and it ma&es use of the enlarged image
principle. %or getting higher degree of maginification,the /eiss optimeters are used.$ecause of dou$le reflection of light gives higher degree of maginification
A('"nt"ge 0igh accurac# 0igh maginification 8o parallex error eightless optical lever Di#"('"nt"ge !he comparator is inconvenient for continuous use $ecause the scale is to $e vie"ed through
e#epiece It depends on external electrical po"er suppl# hen the scale is pro'ected on a screen the comparator is to $e used in dar& room.
4ne$"ti% %o)"r"tor# hen air is used to determine the variation of dimensions, the comparators is called pneumatic. Ty)e# i %lo" t#pe comparator +or velocit# t#pe comparators ii ac& pressure t#pe iii *olex air gauge
21
iv
ifferential comparators.
Flo> ty)e %o)"r"tor 3or! 'elo%ity ty)e %o)"r"tor# It consists of a compressor, filter, pressure regulator, float, glass column and the gauging head. !he air from the compressor passes through the filter and pressure regulator. !he air then passes through the tapered glass tu$e "ith a float and finall# to the measuring head. !he measuring head is also referred as gauging head. !he plug t#pe gauging head for chec&ing internal dimensions +holes
!he gauging head is provided "ith orifices for the escape of air into the atmosphere !he air flo" depends on the clearance $et"een the hole and the plug of the measuring head. !he velocit# or flo" of air is used to var# the position of the float. !he reading is indicated $# the float on a scale fixed $# the side of the glass tu$e !he scale can $e cali$rated to read the variation in the dimension +diameter.
B"%9 )re##$re ty)e !he t"o orifices are called Control rifice +C and easuring rifice +. !he pressure
+p inside the intermediate cham$er depends on the clearance +: $et"een the easuring rifice and the surface $eing chec&ed. 0ence, the change in dimension. !he magnification of this t#pe of comparator depends on the relative si/e of the orifices C and .
Sole Air G"$ge
It is a $ac& pressure t#pe of comparator. !his "as originall# introduced $# *olex )ir
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If the air pressure exceeds the desired pressure, the air escapes through the $ottom of the dip
tu$e. !he measuring head is designed for internal dimension, +It can $e used for external
dimensions, "ith suita$le modification. hen the measuring +or gauging head is applied, a $ac& pressure is developed $et"een the
control orifice and the gauging head. !he manometer indicates this $ac& pressure. !he manometer, "hen cali$rated, gives directl# the variation in the dimension to $e chec&ed.
Di&&erenti"l Co)"r"tor )ir at constant pressure is supplied to the t"o channels ) and . !he t"o Control rifices
are fixed. )ir flo"s through C1 and C2. %rom the control orifice C1, air flo"s through the measuring head. !he restriction of the
"or& piece causes a $ac& pressure. )ir also flo"s through the control orifice C2 and to the reference 'et +=. !he reference 'et is ad'usted for the standard or master "or& piece and the pressure indicating
device +p is set to read /ero. hen the actual "or& piece is chec&ed an# variation in dimension "ill cause a change in
$ac& pressure in channel N)9. !he pressure indicating device is directl# cali$rated to read the variation or change in dimension.
Coon &or "ll ty)e# o& 4ne$"ti% %o)"r"tor:
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A('"nt"ge#: It has fe" moving parts. !his is the $est method O*olex air gaugeP for chec&ing roundness and taperness of circular
+c#lindrical holes. !he measuring head + gauging head does not contact the surface $eing chec&ed hence the head is not su$'ected to "ear and tear. Di#"('"nt"ge# It is not porta$le. !he scale is generall# not uniform ifferent gauging heads are required for different dimensions !he range of the Instrument is less. ,.. LIMIT GAUGES ) limit gauge is not a measuring gauge. Qust the# are used as inspecting gauges. !he limit gauges are used in inspection $# methods of attri$utes. !his gives the information a$out the products "hich ma# $e either "ithin the prescri$ed limit
or not. # using limit gauges report, the control charts o f and C charts are dra"n to control
invariance of the products. !his procedure is mostl# performed $# the qualit# control department of each and ever#
industr#. :imit gauge are mainl# used for chec&ing for c#lindrical holes of identical components "ith a large num$ers in mass production.
4$r)o#e o& $#ing liit g"$ge# Components are manufactured as per the specified tolerance limits, upper limit and lo"er limit. !he dimension of each component should $e "ithin this upper and lo"er limit. If the dimensions are outside these limits, the components "ill $e re'ected. If "e use an# measuring instruments to chec& these dimensions, the process "ill consume more time. *till "e are not interested in &no"ing the amount of error in dimensions. It is 'ust enough "hether the si/e of the component is "ithin the prescri$ed limits or not. %or this purpose, "e can ma&e use of gauges &no"n as limit gauges. T+e %oon ty)e# "re "# &ollo>#1 lug gauges. 2 =ing gauges. 3 *nap gauges ,..1. 4LUG GAUGES !he ends are hardened and accuratel# finished $# grinding. ne end is the < end and the other end is 8< end. Jsuall#, the < end "ill $e equal to the lo"er limit si/e of the hole and the 8< end "ill $e equal to the upper limit si/e of the hole. If the si/e of the hole is "ithin the limits, the < end should go inside the hole and 8< end should not go. If the < end and does not go, the hole is under si/e and also if 8< end goes, the hole is o'er #ie. 0ence, the components are re'ected in $oth the cases.
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1. Do$8le en(e( )l$g g"$ge# In this t#pe, the < end and 8< end are arranged on $oth the ends of the plug. !his t#pe has the advantage of eas# handling.
,. 4rogre##i'e ty)e o& )l$g g"$ge# In this t#pe $oth the < end and 8< end are arranged in the same side of the plug. e can use the plug gauge ends progressivel# one after the other "hile chec&ing the hole. It saves time.
,..,. RING GAUGES =ing gauges are mainl# used for chec&ing the diameter of shafts having a central hole. !he hole is accuratel# finished $# grinding and lapping after ta&ing hardening process. !he peripher# of the ring is &nurled to give more grips "hile handling the gauges. e have to ma&e t"o ring gauges separatel# to chec& the shaft such as < ring gauge and 8< ring gauge. ut the hole of < ring gauge is made to the upper limit si/e of the shaft and 8< for the lo"er limit. hile chec&ing the shaft, the < ring gauge "ill pass through the shaft and 8< "ill not pass. !o identif# the 8< ring gauges easil#, a red mar& or a small groove cut on its peripher#.
,... SNA4 GAUGE *nap gauges are used for chec&ing external dimensions. !he# are also called as gap gauges. !he different t#pes of snap gauges are1. Do$8le En(e( Sn") G"$ge !his gauge is having t"o ends in the form of anvils. 0ere also, the < anvil is made to lo"er limit and 8< anvil is made to upper limit of the shaft. It is also &no"n as solid snap gauges
25
,. 4rogre##i'e Sn") G"$ge !his t#pe of snap gauge is also called caliper gauge. It is mainl# used for chec&ing large diameters up to 1BBmm. oth < and 8< anvils at the same end. !he < anvil should $e at the front and 8< anvil at the rear. *o, the diameter of the shaft is chec&ed progressivel# $# these t"o ends. !his t#pe of gauge is made of horse shoe shaped frame "ith I section to reduce the "eight of the snap gauges
. A(@$#t"8le Sn") G"$ge )d'usta$le snap gauges are used for chec&ing large si/e shafts made "ith horseshoe shaped frame of I section. It has one fixed anvil and t"o small ad'usta$le anvils. !he distance $et"een the t"o anvils is ad'usted $# ad'usting the ad'usta$le anvils $# means of setscre"s. !his ad'ustment can $e made "ith the help of slip gauges for specified limits of si/e.
,..G"$ge# "n( g"$ge (e#ign
form and relative positions of the surfaces of the parts.
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,..1.TAYLOR S 4RINCI4LE It states that < gauge should chec& all related dimensions. *imultaneousl# 8< gauge should chec& onl# one dimension at a time. St"teent 1:
St"teent ,:
limit of hole +mmc and the 8o
snap gauge must correspond to the high limit of the shaft+mmc and the 8o
cennoticed. In this case, onl# a pin gauge +8ot
E)l"n"tion o& St"teent ,: )s far as possi$le the
form.
gauge having a length equal to the length of hole. !he 8ot
(xample-
2>
If the
dimension is &no"n as interchangea$le part. !he operation of su$stituting the part for similar manufactured components of the same shape
and dimension is &no"n as interchangea$ilit#. 1. %ull interchangea$ilit# 2. *elective assem$l#.
,.0.Ang$l"r e"#$reent )ngular measurement are ta&ing ver# important role. ith the help of this measurement, the
ships and aeroplane are navigated "ithout the help of sight of the land. !he angle is defined as the opening $et"een t"o lines "hich meet at a point. If a circle is divided into 36B equal parts, each part is called as degree+B. (ach degree is divided into 6B minutes +N and each minute is divided into 6B seconds+R. !his is the method for (ngineering purposes .
!#pes of angular measuring instrument 1. evel protractor 2. Clinometer 3. )ngle gauge 4. *ine $ar 5. )ngle alignment telescope 6. )uto Collimator
,.0.1.BE7EL 4ROTRACTORS evel protractors are nothing $ut angular measuring instruments. Ty)e# o& 8e'el )rotr"%tor#- !he different t#pes of $evel protractors used are1 ernier $evel protractor 2 Jniversal protractor 3 ptical protractor 7ERNIER BE7EL 4ROTRACTOR 5or9ing )rin%i)le ) vernier $evel protractor is attached "ith acute angle attachment. !he $od# is designed its $ac& is flat and no pro'ections $e#ond its $ac&. !he $ase plate is attached to the main $od# and an ad'usta$le $lade is attached to the circular plate containing ernier scale. !he main scale is graduated
2A
in degrees from BS to DBS in $oth the directions. !he ad'usta$le can $e made to rotate freel# a$out the center of the main scale and it can $e loc&ed at an# position. %or measuring acute angle, a special attachment is provided. !he $ase plate is made fiat for measuring angles and can $e moved throughout its length. !he ends of the $lade are $eveled at angles of 45S and 6BS. !he main scale is graduated as one main scale division is 1S and ernier is graduated into 12 divisions on each side of /ero.
!herefore the least count is calculated as
!hus, the $evel protractor can $e used to measure to an accurac# of 5 minutes. Uni'er#"l Be'el 4rotr"%tor !his t#pe of protractor is same as that vernier evel protractor. In this, the $lade can $e rotated to measure an# angles in an# position $# means of providing a slot for the dial of protractor. !he accurac# of this protractor is 5 degrees.
O)ti%"l Be'el 4rotr"%tor
2D
!his is advanced level of vernier evel protractor "ith an accurac# of 2 minutes. !he readings are ta&en against a fixed index line or vernier $# means of optical magnif#ing s#stem "hich is intergral "ith the instrument. !he scale is graduated as a full circle mar&ed BDBBDB. !he /ero position is coincides "hen the $lade is parallel to the shoc&.
A))li%"tion# o& 8e'el )rotr"%tor !he $evel protractor can $e used in the follo"ing applications. 1. For %+e%9ing " 7 8lo%9:
,.0.,.Clinoeter Clinometer are used for the measurement of angle $et"een t"o surfaces. !he principle of
"or&ing is similar to a Nspirit level mounted on a rotata$le mem$er9 Clinometer is placed on the t"o surfaces in turn and readings are ta&en. !he angle $et"een the t"o surfaces can $e determined from the readings.
3B
Clinometer are also used for chec&ing the angular faces and relief angles on large cutting tools.
,.0..Angle g"$ge !hese gauges are developed $# r.!omlinson in 1D3D. It is a hardened steel $loc& of si/e
>5mm x 16m "hich has t"o lapped flat "or&ing faces l#ing at a ver# precise angle to each other. )ngle gauges are supplied in sets li&e slip gauges and can $e "rung together li&e slip gauges
to form required angles. e can measure "ith this gauges to an accurac# of 3 seconds.
,.0..SINE BAR *ine $ars are al"a#s used along "ith slip gauges as a device for the measurement of angles ver# precisel#. !he# are used to 1 easure angles ver# accuratel#. 2 :ocate the "or& piece to a given angle "ith ver# high precision.
31
5or9ing )rin%i)le o& #ine 8"r
!he "or&ing of sine $ar is $ased on trigonoetry )rin%i)le. !o measure the angle of a given specimen, one roller of the sine $ar is placed on the surface plate and another one roller is placed over the surface of slip gauges. 8o", Nh $e the height of the slip gauges and N:9 $e the distance $et"een roller centers, then the angle is calculated as
A))li%"tion o& #ine 8"r 1.locating an# "or& to a giving
32
,.%+e%9ing or e"#$ring $n9no>n "ngle# a "hen component is of small si/e 1 efore chec&ing the un&no"n angle of the specimen, first the angle +B of given specimen is found approximatel# $# $evel protractor. 2 !hen the sine $ar is set at angle of B and clamped on the angle plate. 3 8o", the "or& is placed on the sine $ar and the dial indicator set at one end of the "or& is moved across the "or& piece and deviation is noted. 4 *lip gauges are ad'usted so that the dial indicator reads /ero throughout the "or& surface.
$ "hen component is of large or heav# si/e the component is placed over a surface plate and the sine $ar is setup at approximate angle on the component so that its surface is nearl# parallel to the surface of the sine $ar to note the variation in parallelism.
33
De'elo)ent o& #ine 8"r
ecause of difficult# in mounting conicl "or& easil# on a conventional sine $ar, the sine $ar are modified as sine centres and sine ta$les. Sine Centre !he sine centres are consisting of a sine $ar hinged at one roller and mounted on its o"n datum surface. !he top surface of the $ar is provided "ith a pair of centres for holding "or&.
!he angle of inclination "ill $e half the included angle of the "or&.
So$r%e# o& error in #ine 8"r# !he different sources of errors are listed $elo"1 (rror in distance $et"een roller centers. 2 (rror in slip gauge com$ination. 3 (rror in chec&ing of parallelism. 4 (rror in parallelism of roller axes "ith each other. 5 (rror in flatness of the upper surface of sine $ar. ,.0./.Angle "lignent o& tele#%o)e
)lignment telescope is used for aligning of $ores, surfaces and chec&s squareness, straightness, flatness, parallelism, verticall# and level. ne of the important t#pe of alignment telescope is !a#lor0o$son alignment telescope. !his instrument can $e used to measure angular alignment as "ell as lateral displacement and for this purpose the sighting target is mounted in a collimating unit.
34
,..AUTO- COLLIMATOR )uto collimator is an optical instrument and a special form of telescope. )uto collimator is used to measure smaller angle of differences, changes, deflections and plane surface inspection. B"#i% )rin%i)le
If a light source is placed in the flo"s of a collimating lens, it is pro'ected as a parallel $eam of light. If this $eam is made to stri&e a plane reflector, &ept normal to the optical axis, it is reflected
35
$ac& along its o"n path and is $rought to the same focus. !he reflector is tilted through a small angle NB9. !hen the parallel $eam is deflected t"ice the angle and is $rought to focus in the same plane as the light source. !he distance of focus from the o$'ect is given
5OR6ING !here are three main parts in autocollimator. 1. icrometer microscope. 2. :ighting unit and 3. Collimating lens. %igure sho"s a line diagram of a modern autocollimator. ) target graticule is positioned perpendicular to the optical axis. hen the target graticule is illuminated $# a lamp, ra#s of light diverging from the intersection point reach the o$'ective lens via $eam splitter. %rom o$'ective, the light ra#s are pro'ected as a parallel ra#s to the reflector.
) flat reflector placed in front of the o$'ective and exactl# normal to the optical axis reflects the parallel ra#s of light $ac& along their original paths. !he# are then $rought to the target graticule and exactl# coincide "ith its intersection. ) portion of the returned light passes through the $eam splitter and is visi$le through the e#epiece. If the reflector is tilted through a small angle, the reflected $eam "ill $e changed its path at t"ice the angle. It can also $e $rought to target graticule $ut linearl# displaced from the actual target $# the amount 2T x f. linear displacement of the graticule image in the plane tilted angle of e#epiece is directl# proportional to the reflector. !his can $e measured $# optical micrometer. !he photoelectric auto collimator is particularl# suita$le for cali$rating pol#gons, for chec&ing angular indexing and for chec&ing small linear displacements. ,..A44LICATIONS OF AUTO-COLLIMATOR )utocollimators are used for 1 easuring the difference in height of length standards. 2 Chec&ing the flatness and straightness of surfaces. 3 Chec&ing square ness of t"o surfaces. 4 recise angular indexing in con'unction "ith pol#gons. 5 Chec&ing alignment or parallelism. 6 Comparative measurement using master angles. > easurement of small linear dimensions. A %or machine tool ad'ustment testing. ,..ANGLE DE66OR
36
!his is also a t#pe of autocollimator. !here is an illuminated scale in the focal plane of the collimating lens. !his illuminated scale is pro'ected as a parallel $eam $# the collimating lens "hich after stri&ing a reflector $elo" the instrument is refocused $# the lens in the filed of vie" of the e#epiece. In the field of vie" of microscope, there is another datum scale fixed across the center of screen. !he reflected image of the illuminated scale is received at right angle to the fixed scale as sho"n in fig. !hus the changes in angular position of the reflector in t"o planes are indicated $# changes in the point of intersection of the t"o scales. ne division on the scale is cali$rated to read 1 minute.
UNIT-III AD7ANCES IN METROLOGY .1.BASIC CONCE4T OF LASER 4rin%i)le o& L"#er# 0 Laser stands for light amplification $# stimulated emission of radiation 0 :asers for measurement are lo" po"er gas lasers that emit light in the visi$le range 0 :aser light $eam is – 0ighl# monochromatic the light has a single "ave length – 0ighl# collimated the light ra#s are parallel 0 !hese properties have motivated man# applications in measurement and inspection A('"nt"ge# o& L"#er# 1. The installation is easy
2. )ccurac# is high 3>
3. It has a long range optical path. 4. It has high repeata$ilit# of displacement measurement 5. !here is virtuall# no "ear and tear. 6. )s man# as six measurements can $e made simultaneousl# $# a single laser source. Di#"('"nt"ge# o& L"#er# 1. It is expensive 2. !he measurement is not in traditional units 3. Conversion instrumentation is required as the measurement is in terms of "avelength. .,.Inter&eroeter Interferometer is optical instruments used for measuring flatness and determining the lengths of slip gauges $# direct reference to the "avelength of light. .,.1.L"#er Inter&eroeter It is possi$le to maintain the qualit# of interference fringes over longer distance "hen lamp is replaced $# a laser source. :aser interferometer uses )C laser as the light source and the measurements to $e made over longer distance. :aser is a monochromatic optical energ#, "hich can $e collimated into a directional $eam )C. :aser interferometer. .,.,.L"#er Teleetri% #y#te !he laser s#stem of measurement is a noncontact s#stem. ) heliumneon laser $eam is ver# narro" and travels for greater distance "ithout an# deviation.it produces a red $eam of light and is visi$le on the screen. !he arrangement of laser telemetric s#stem is sho"n in fig. it mainl# consists of three main parts.
I !ransmitter ii =eceiver iii rocessor electronics.
!he transmitter contains a heliumneon gas laser, collimating lens, a h#steresis s#nchronous motor and protective "indo"s. !he receiver collects and senses the laser light transmitted past the o$'ect. !he output is availa$le in digital form.therfore this s#stem can $e applied on production machines to control them $# feed$ac& loops.
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!he processor electronics thus converts the received signal and displa#s the dimension $eing measured. A('"nt"ge#. 1. 0igh speed scanning is possi$le 2. nline gauging can $e done. 3. !he output is availa$le in digital form.
..AC LASER INTERFEROMETER
It is possi$le to maintain the qualit# of interference fringes over longer distance "hen lamp is replaced $# a laser source. :aser interferometer uses )C laser as the light source and the measurements to $e made over longer distance. :aser is a monochromatic optical energ#, "hich can $e collimated into a directional $eam )C. :aser interferometer +)C:I has the follo"ing advantages. 1. 0igh repeata$ilit# 2. 0igh accurac# 3.:ong range optical path 4.(as# installations ear and tear *chematic arrangement of laser interferometer is sho"n in fig. !"ofrequenc# /eeman laser generates light of t"o slightl# different frequencies "ith opposite circular polarisation. !hese $eams get split up $# $eam splitter ne part travels to"ards and from there to external cu$e corner here the displacement is to the measured. !his interferometer uses cu$e corner reflectors "hich reflect light parallel to its angle of incidence. eam splitter 2 opticall# separates the frequenc# Q "hich alone is sent to the mova$le cu$e corner reflector. !he second frequenc# from 2 is sent to a fixed reflector "hich then re'oins f1 at the $eam splitter 2 to produce alternate light and dar& interference flic&er at a$out 2 ega c#cles per second. 8o" if the mova$le reflector moves, then the returning $eam frequenc# opplershifted slightl# up or do"n $# Uf. !hus the light $eams moving to"ards photo detector 2 have frequencies f2 and +f1 L Uf1 and 2 changes these frequencies into electrical signal.
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hoto detector 2 receive signal from $eam splitter 2 and changes the reference $eam frequencies f1 and f2 into electrical signal. )n )C amplifier ) separates frequenc#. ifference signal f2 V f1 and )2 separates frequenc# difference signal. !he pulse converter extracts i. one c#cle per half "avelength of motion. !he updo"n pulses are counted electronicall# and displa#ed in analog or digital form. ..1.Mi%+el#on Inter&eroeter ichelson interferometer consists of a monochromatic light source a $eam splitter and t"o mirrors. !he schematic arrangement of ichelson interferometer is sho"n in fig. !he monochromatic light falls on a $eam splitter, "hich splits the light into t"o ra#s of equal intensit# at right angles. ne ra# is transmitted to mirror 1 and other is reflected through $eam splitter to mirror 2, from $oth these mirrors, the ra#s are reflected $ac& and these return at the semi reflecting surface from "here the# are transmitted to the e#e. irror 2 is fixed and mirror 1 is mova$le. If $oth the mirrors are at same distance from $eam splitter, then light "ill arrive in phase and o$server "ill see $right spot due to constructive interference. If mova$le mirror shifts $# quarter "avelength, then $eam "ill return to o$server 1ABB out of phase and dar&ness "ill $e o$served due to destructive interference
(ach half"ave length of mirror travel produces a change in the measured optical path of one "avelength and the reflected $eam from the moving mirror shifts through 36BS phase change. hen the reference $eam reflected from the fixed mirror and the $eam reflected from the moving mirror re'oin at the $eam splitter, the# alternatel# reinforce and cancel each other as the mirror moves. (ach
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c#cle of intensit# at the e#e represents lW2 of mirror travel. hen "hite light source is used then a compensator plate is introduced in each of the path of mirror 1 *o that exactl# the same amount of glass is introduced in each of the path. !o improve the ichelson interferometer 3i! Jse of laser the measurements can $e made over longer distances and highl# accurate measurements "hen compared to other monochromatic sources. 3ii! irrors are replaced $# cu$ecorner reflector "hich reflects light parallel to its angle of incidence. 3iii! hotocells are emplo#ed "hich convert light intensit# variation in voltage pulses to give the amount and direction of position change.
..,.A))li%"tion o& inter&eroeter 1. Linear measurement 2. Angular measurement
...U#e o& L"#er &or Alignent Te#ting !he alignment tests can $e carried out over greater distances and to a greater degree of accurac# using laser equipment. 1. :aser equipment produces real straight line, "hereas an alignment telescope provides an imaginar# line that cannot $e seen in space. 2. !his is important "hen it is necessar# to chec& num$er of components to a predetermined straight line. articularl# if the# are spaced relativel# long distances apart, as in aircraft production and in ship$uilding. . :aser equipment can also $e used for chec&ing flatness of machined surface $# direct displacement. # using are optical square in con'unction "ith laser equipment squareness can $e chec&ed "ith reference to the laser $ase line.
..CO-ORDINATE MEASURING MAC*INES
X
Coordinate metrolog# is concerned "ith the measurement of the actual shape and dimensions of an o$'ect and comparing these "ith the desired shape and dimensions. X In this connection, coordinate metrolog# consists of the evaluation of the location, orientation, dimensions, and geometry of the part or o$'ect. X A Coordinate Measuring Machine (CMM) is an electromechanical s#stem designed to perform coordinate metrolog#. ..1.Ty)e# o& Me"#$ring M"%+ine# 1. :ength $ar measuring machine. ,. 8e"ell measuring machine. . Jniversal measuring machine. . Coordinate measuring machine. /. Computer controlled coordinate measuring machine. ..,.Con#tr$%tion# o& CMM
) C consists of a constant pro$e that can $e positioned in 3 space relative to the surface of a "or& part, and the x, #, and / coordinates of the pro$e can $e accuratel# and precisel# recorded to o$tain dimensional data concerning the part geometr#. !hese measurements can $e made $# positioning the pro$e $# hand, or automaticall# in more expensive machines. ...Ty)e# o& CMM 1. Cantilever t#pe
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2. ridge t#pe1.moving 2.fixed 3. 0ori/ontal $oring t#pe 4. ertical $oring t#pe 3i! C"ntile'er ty)e: T+e cantilever t#pe is ver# eas# to load and unload, $ut mechanical error ta&es place $ecause of sag or deflection in Yaxis. 3ii! Bri(ge ty)e: ridge t#pe is more difficult to load $ut less sensitive to mechanical errors. 3iii! *oriont"l 8oring Mill ty)e: !his is $est suited for large heav# "or& pieces. i'! 7erti%"l 8oring ill ty)e: vertical $oring mill is highl# accurate $ut slo"er to operate.
5or9ing 4rin%i)le
C is used for measuring the distance $et"een t"o holes. !he "or& piece is clamped to the "or&ta$le and aligned for three measuring slides x, # and /. !he measuring head provides a taper pro$e tip "hich is seated in first datum hole and the position of pro$e digital read out is set to /ero. !he pro$e is then moved to successive holes, the read out represent the coordinate part print hole location "ith respect to the datum hole. )utomatic recording and data processing units are provided to carr# out complex geometric and statistical anal#sis. *pecial coordinate measuring machines are provided $oth linear and rotar# axes. !his can measure various features of parts li&e cone, c#linder and hemisphere. !he prime advantage of coordinate measuring machine is the quic&er inspection and accurate measurements.
...COM4UTER CONTROLLED CO-ORDINATE MEASURING MAC*INE
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!he measurements, inspection of parts for dimension form, surface characteristics and position of geometrical elements are done at the same time. echanical s#stem can $e divided into four $asic t#pes. !he selection "ill $e depends on the application. 1. Column t#pe. 2. ridge t#pe. 3. Cantilever t#pe. 4.
../.4er&or"n%e o& CMM
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1. Coordinate measuring machines find applications in automo$ile, machine tool, electronics, space and man# other large companies. 2. !hese machines are $est suited for the test and inspection of test equipment, gauges and tools. 3. %or aircraft and space vehicles, hundred percent inspections is carried out $# using C. C can $e used for determining dimensional accurac# of the components. 4. !hese are ideal for determination of shape and position, maximum metal condition, lin&age of results etc. "hich cannot do in conventional machines. 5. C can also $e used for sorting tas&s to achieve optimum pairing of components "ithin tolerance limits. 6. Cs are also $est for ensuring economic via$ilit# of 8C machines $# reducing their do"ntime for inspection results. !he# also help in reducing cost, re"or& cost at the appropriate time "ith a suita$le C. A('"nt"ge# 1. !he inspection rate is increased. ,. )ccurac# is more. . perators error can $e minimi/ed. . *&ill requirements of the operator is reduced /. =educed inspection fixturing and maintenancecost. 0. =eduction in calculating and recording time. . =eduction in set up time. . 8o need of separate go W no go gauges for each feature. . =eduction of scrap and good part re'ection. 1?. =eduction in off line anal#sis time. 11. *implification of inspection procedures, possi$ilit# of reduction of total inspection time through use of statistical and data anal#sis techniques. Di#"('"nt"ge# 1. !he la$le and pro$e ma# not $e in perfect alignment. ,. !he pro$e ma# have run out. . !he pro$e moving in Eaxis ma# have some perpendicular errors. . ro$e "hile moving in Z and Y direction ma# not $e square to each other. /. !here ma# $e errors in digital s#stem. ...CNC-CMM Con#tr$%tion !he main features of C8CC are sho"n in figure has stationar# granite measuring ta$le, :ength measuring s#stem. )ir $earingsK control unit and soft"are are the important parts of C8C 7 C.
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Control $nit the control unit allo"s manual measurement and programme. It is a microprocessor control. So&t>"re !he C, the computer and the soft"are represent one s#stemK the efficienc# and cost effectiveness depend on the soft"are. ...Fe"t$re# o& CMM So&t>"re 3i! easurement of diameter, center distance, length. 3ii! easurement of plane and spatial carvers. 3iii! inimum C8C programme. 3i'! ata communications. 3'! igital input and output command. 3'i! rogramme for the measurement of spur, helical, $evel9 and h#poid gears . 3'ii! Interface to C) soft"are. ) ne" soft"are for reverse engineering complex shaped o$'ects. !he component is digiti/ed using C8C C. !he digiti/ed data is converted into a computer model "hich is the true surface of the component. =ecent advances include the automatic "or& part alignment and to orient the coordinate s#stem. *avings in inspection time $# using C is 5 to 1B compared to manual inspection method. ...C"$#e# o& Error# in CMM 1 !he ta$le and pro$es are in imperfect alignment. !he pro$es ma# have a degree of run out and move up and do"n in the Eaxis ma# cause perpendicularit# errors. *o C should $e cali$rated "ith master plates $efore using the machine. 2 imensional errors of a C is influenced $# *traightness and perpendicularit# of the guide "a#s. *cale division and ad'ustment. ro$e length. ro$e s#stem cali$ration, repeata$ilit#, /ero point setting and reversal error. (rror due to digiti/ation. (nvironment 3 ther errors can $e controlled $# the manufacture and minimi/ed $# the measuring soft"are. !he length of the pro$e should $e minimum to reduce deflection. 4 !he "eight of the "or& piece ma# change the geometr# of the guide "a#s and therefore, the "or& piece must not exceed maximum "eight. 5 ariation in temperature of C, specimen and measuring la$ influence the uncertainl# of measurements. 6 !ranslation errors occur from error in the scale division and error in straightness perpendicular to the corresponding axis direction. > erpendicularit# error occurs if three axes are not orthogonal. ./.C"li8r"tion o& T+ree Co-Or(in"te Me"#$ring M"%+ine !he optical set up for the cali$ration is sho"n in figure !he laser head is mounted on the tripod stand and its height is ad'usted corresponding to the "or&ing ta$le of C. !he interferometer contains a polari/ed $eam splitter "hich reflects %1 component of the laser $eam and the %2 Component parts through. !he retro reflector is a polished trihedral glass prism. It reflects the laser $eam $ac& along a line parallel to the original $eam $# t"ice the distance. %or distance measurement the %1 and %2 $eams that leave the laser head are aimed at the interferometer "hich splits %1 and %2 via polari/ing $eaming splitter. Component %1 $ecomes the fixed distance path and %2 is sent to a target "hich reflects it $ac& to the interferometer. =elative motion $et"een the interferometer and the remote retro reflector causes a opper shift in the returned frequenc#. !herefore the laser head sees a frequenc# difference given $# %1%2 L U%2. !he %1%2 L U%2 signal that is returned from the external interferometer is compared in the measurement displa# unit to the reference signal. !he difference U%2 is related to the velocit#. !he longitudinal micrometer microscope of C is set at /ero and the
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laser displa# unit is also set at /ero. !he C microscope is then set at the follo"ing points and the displa# units are noted.1 to 1Bmm, ever# mm and 1B to 2BBmm, in steps of 1Bmm. !he accurac# of linear measurements is affected $# changes in air temperature, pressure and humidit#.
.0.M"%+ine 7i#ion
achine vision can $e defined as a means of simulating the image recognition and anal#sis capa$ilities of the human s#stem "ith electronic and electromechanical techniques. 7i#ion Sy#te !he schematic diagram of a t#pical vision s#stem is sho"n. !his s#stem involves image acquisitionK image processing )cquisition requires appropriate lighting. !he camera and store digital image processing involves manipulating the digital image to simplif# and reduce num$er of data points. easurements can $e carried out at an# angle along the three reference axes x # and / "ithout contacting the part. !he measured values are then compared "ith the specified tolerance "hich stores in the memor# of the computer.
!he main advantage of vision s#stem is reduction of tooling and fixture costs, elimination of need for precise part location for handling ro$ots and integrated automation of dimensional verification and defect detection.
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4rin%i)le Fo$r ty)e#3OR! Eleent# o& "%+ine 'i#ion #y#te and the schematic arrangement is sho"n 3i! Image formation. 3ii! rocessing of image in a form suita$le for anal#sis $# computer. 3iii! efining and anal#/ing the characteristic of image. 3i'! Interpretation of image and decisionma&ing.
!he surface of the o$'ect is to $e inspected $# using front lighting. %or inspecting three dimensional feature structured lighting is required. )n image sensor vidicon camera, CC camera is used to generate the electronic signal representing the image. !he image sensor collects light from the scene through a lens, using photosensitive target, converts into electronic signal. I"ge )ro%e##or: ) camera ma# form an image 3B times per sec at 33 m sec intervals. )t each time interval the entire image fro/en $# an image processor for processing. )n analog to digital converter is used to convert analog voltage of each detector in to digital value I"ge An"ly#i# !he distance of an o$'ect from a vision s#stem camera can $e determined $# tri"ng$l"tion te%+ni$e. !he o$'ect orientation can he determined $# the methods of e$i'"lent elli)#e. !he image can $e interpreted $# t"odimensional image. %or complex threedimensional o$'ects $oundar# locations are determined and the image is segmented into distinct region. I"ge Inter)ret"tion: T+i# involves identification of on o$'ect. In $inar# s#stem, the image is segmented on the $asis of "hite and $lac& pixels. !he complex images can he interpreted $# gre# scale technique and algorithms. !he most common image interpretation is template matching. .0.1.F$n%tion o& M"%+ine 7i#ion :ighting and presentation of o$'ect to evaluated. It has great compact on repeata$ilit#, relia$ilit# and accurac#. I.ighting source and pro'ection should $e chosen and give sharp contrast. Images sensor compressor ! camera ma# he vidicon or solid state. %or simple processing, analog comparator and a computer controller to convert the video information to a $inar# image is used. ata compactor emplo#s a high speed a"a# processor to provide high speed processing of the input image data. *#stem control computer communicates "ith the operator and ma&e decision a$out the part $eing inspected.
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!he output and peripheral devices operate the control of the s#stem. !he output ena$les the vision s#stem to either control a process or provide caution and orientation information t"o a ro$ot, etc. !hese operate under the control of the s#stem control of computer
.0.,.A))li%"tion# achine vision can he used to replace human vision fur "elding. achining and maintained relationship $et"een tool and "or& piece and assem$l# of parts to anal#/e the parts. !his is frequentl# used for printed circuit $oard inspection to ensure minimum conduction "idth and spacing $et"een conductors. !hese are used for "eld seam trac&ing, ro$ot guideness and control, inspection of microelectronic devices and tooling, on line inspection in machining operation, assem$lies monitoring highspeed pac&aging equipment etc. It gives recognition of an o$'ect from its image. !hese are designed to have strong geometric feature interpretation capa$ilities and pa handling equipment.
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UNIT-I7 FORM MEASUREMENT .1.4rin%i)le# o& #tr"ig+tne## . ) straightline ma# $e defined as the shortest distance $et"een t"o points. ) line is said to $e straight over a given length, if the variation of distance of its points from t"o planes perpendicular to each other. .1.1.Met+o(# o& Str"ig+tne## e"#$reent e can measure the straightness $# the follo"ing methods. 1. # using ?nife edge 7 dial indicator 2. # using autocollimator +li&e a telescope "ith a light $eam that $ounces 3. # using spirit level
1. By $#ing 6ni&e e(ge < (i"l in(i%"tor ) &nife edge7 dial indicator is a measuring instrument "hich consists of length of steel narro" and deep section and var#ing in length.it is made made in either steel or iron as per Indian standard. !he arrangement of testing is sho"n in fig.
!hen the &nife edge 7 dial indicator can $e inserted corresponding to each position and "ill ma&e contact "ith surfaces exactl# at mar&ed po sition. If there are errors in straightness of surface, the instrument ma# not fit exactl#. !heir corresponding mar&ed position "ill $e displaced one "a# or the other along the straight edge $# amounts proportional to the errors. By $#ing "$to%olli"tor )utocollimator is used to detect straightness accuratel# in "hich a light $eam $ounces $ac& from the o$'ect and measures small angular deviations. ptical means li&e laser $eams are used to align individual machine elements in the assem$l# of machine components. %or maintaining the reflected ra#s of light in the same vertical plane, the $loc& is moved along a straight edge, ma# $e clamped to the surface and the $loc& held against it.
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)n optical square ma# $e emplo#ed e mplo#ed so that the instrument can $e used in the hori/ontal position, "hen testing a vertical surface. By $#ing #)irit le'el ) sensitive sensitive level to the underside of "hich are fastened t"o feet at a convenient distance apart. !he spirit level is moved along the surface to $e tested in steps equal to the pitch of the feet and each position the reading of the one end of the $u$$le is noted. ariation ariation in the $u$$le $ u$$le position represent angular variations in the surface and test are converted into difference in height of the t"o feet. !hese $# steeping the level along the "hole length, the heights a$ove a$ov e or $elo", the acting point are determined and a graph can $e dra"n sho"ing the contour of the surface.
!he average of t"o reading for each position recorded.in this method onl# hori/ontal surfaces are tested. .,.Fl"tne## e"#$reent
rinciples of flatness. !he minimum distance $et"een t"o planes "hich cover all the irregularities of the surface. Fl"tne## te#ting !he easiest method of finding flatness of a surface is $ # comparing the surface "ith an accurate surface.one of the surface is mar&ed "ith russian $lue and the other surface ru$$ed over it. !he distri$ution of color over the other surface gives a rough idea of high and lo" points on the surface. !his method is meant for smaller plates onl#.
!hus the "hole of the surface is divided $# straight line. !he fig, sho"s the surface is divided $# straight line. line. !he end line line ) ) and ) ) etc are dra"n a"a# a"a# from the edges edges as the edges of the the
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surface are not flat $ut get "orn out $# use and can fall off little in accurac#. !he straightness of all these lines is determined and then those lines are related "ith each other in order to verif# "hether the# lie in the same plane or not. 4ro%e($re &or (eterining &l"tne## !he fig. sho"s the flatness testing procedure. +i Carr# out the straightness test and ta$ulate the reading up to the cumulative error column. +ii (nds of lines ), ) and are corrected to /ero and thus the height of the points ), and are /ero.
!he height of the point I is determined relative to the ar$itrar# plane ) H BBB. oint C is no" fixed relative to the ar$itrar# plane and points and are set at /ero, all intermediate intermediate points on C and C can $e corrected accordingl#. !he positions of 0 and <, ( and % are &no"n, so it is no" possi$le to fit in lines 0< and and (%. !his also provides provides a chec& on previous previous evaluations evaluations since the mid point of these lines lines should coincide coincide "ith the position of midpoint I. In this this "a#, "a#, the height height of all the points on the the surface relative to to the ar$itrar# plane plane ) ) is &no"n. &no"n. Anot+er et+o( &or &l"tne## e"#$reent
..T+re"( Me"#$reent 51
S%re> t+re"(: a scre" thread is a continuous helical groove of specified cross section produced on the external +or internal surface of a c#linder or cone. Ty)e# o& t+re"( a Internal thread $ (xternal thread Terinology o& #%re> t+re"( 3or! Noen%l"t$re o& #%re> t+re"(#
Etern"l t+re"(
Intern"l t+re"(
M"@or (i"eter: !ouch the crest of an (xternal thread +or roots of an internal thread it is called the external dia +or outside diameter. !ouch the roots of an external e xternal thread +or crests of an internal thread Minor (i"eter: !ouch E&&e%ti'e (i"eter: intersects the flan&s of the threads such that the "idths of the threads+metal and "idths of the space $et"een the thread are equal each $eing half the pitch. Cre#t: !op !op surface 'oining the t"o sides of thread. Root: =oot is the $ottom of the groove $et"een the sides of ad'acent threads. Fl"n9: the straight surface $et"een the crest and root is called flan&. 4it%+: the distance measured parallel to the axis from a point on a thread to the corresponding point on the next thread is called pitch of the thread. pe rpendicular to the thread axis is Fl"n9 "ngle: the angle made $# the flan& of a thread "ith the perpendicular called flan& angle. T+re"( "ngle: it is the angle included $et"een the flan&s +or slopes of a thread measured in an axial plane. T+re"( (e)t+: it is the distance $et"een the crest and root of the thread. Le"(: lead is the distance through "hich a scre" advances axiall# in one complete revolution. Error in T+re"( !he errors in scre" thread ma# arise during the manufacturing manufacturing or storage of threads. !he errors either ma# cause in follo"ing six main elements in the thread. 1 a'or diameter error 2 inor diameter error 3 (ffective diameter error 4 itch error 5 %lan& angles error
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6 Crest and root error 1! M"@or (i"eter error It ma# cause reduction in the flan& contact and interference "ith the matching threads. ,! Minor (i"eter error It ma# cause interference, reduction of flan& contact. ! E&&e%ti'e (i"eter error If the effective diameter is small the threads "ill $e thin on the external scre" and thic& on an internal scre". ! 4it%+ error# If error in pitch, the total length of thread engaged "ill $e either too high or too small. !he various pitch errors ma# classified into 1. rogressive error 2. eriodic error 3. run&en error 4. Irregular error 1! 4rogre##i'e error !he pitch of the thread is uniform $ut is longer or shorter its nominal value and this is called progressive. C"$#e# o& )rogre##i'e error: 1. Incorrect linear and angular velocit# ratio. 2. In correct gear train and lead scre". 3. *addle fault. 4. ariation in length due to hardening
4rogre##i'e Error
,! 4erio(i% error !hese are repeats itself at regular intervals along the thread C"$#e# o& )erio(i% error -
1. Un uniform tool wor velocity ratio. 2. !eeth error in gears. 3. :ead scre" error. 4. (ccentric mounting of the gears. ! Dr$n9en error run&en errors are repeated once per turn of the thread in a drun&en thread. In run&en thread the pitch measured parallel to the thread axis. If the thread is not cut to the true "ill helix the drun&en thread error form.
! Irreg$l"r error# It is var# irregular manner along the length of the thread.
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Irreg$l"r error %"$#e# 1. achine fault. 2. 8onuniformit# in the material. 3. Cutting action is not correct. 4. achining distur$ances. E&&e%t o& )it%+ error# Increase the effective diameter of the $olt and decreases the diameter of nut. !he functional diameter of the nut "ill $e less. =educe the clearance. Increase the interference $et"een mating threads ..1.Me"#$reent o& '"rio$# eleent# o& T+re"( !o find out the accurac# of a scre" thread it "ill $e necessar# to measure the follo"ing1. a'or diameter. 2. inor diameter. 3. (ffective or itch diameter. 4. itch 5. !hread angle and form 1. Me"#$reent o& "@or (i"eter: Etern"l t+re"( !he instruments "hich are used to find the ma'or diameter are $# rdinar# micrometer ench micrometer. Or(in"ry i%roeter !he ordinar# micrometer is quite suita$le for measuring the external ma'or diameter. It is first ad'usted for appropriate c#lindrical si/e +* having the same diameter +approximatel#.!his process is &no"n as Ngauge setting9. )fter ta&ing this reading N= the micrometer is set on the ma'or diameter of the thread, and the ne" reading is N=2.
Ben%+ i%roeter %or getting the greater accurac# the $ench micrometer is used for measuring the ma'or diameter. diameter. In this process the variation in measuring ressure, pitch errors are $eing neglected. !he fiducial indicator is used to ensure all the measurements are made at same pressure. !he instrument has a micrometer head "ith a vernier scale to read the accurac# of B.BB2mm. Cali$rated setting c#linder having the same diameter as the ma'or diameter of the thread to $e measured is used as setting standard. )fter setting the standard, the setting c#linder is held $et"een the anvils and the reading is ta&en. !hen the c#linder is replaced $# the threaded "or& piece and the ne" reading is ta&en.
a'or dia H += 2= 1 54
here diameter of the setting c#linder = 1 =eading micrometer on setting c#linder = 2 =eading of micrometer on scre" thread Me"#$reent o& t+e "@or (i"eter o& "n Intern"l t+re"(
1.En( #tyli et+o( the internal thread ma'or diameter is usuall# measured $ # thread comparator fitted "ith $all ended st#li.
Me"#$reent o& Minor (i"eter Etern"l t+re"( T>o 7 )ie%e et+o( !he minor diameter is measured $# a comparative method $# using floating carriage diameter measuring machine and small pieces "hich ma&e contact "ith the root of the thread. !hese pieces are made in several si/es, having suita$le radii at the edges. pieces are made of hardened steel. s teel. !he floating carriage diametermeasuring machine is a $ench micrometer mounted on a carriage.
Me"#$reent )ro%e##: !he threaded "or& piece is mounted $et"een the centers of the instrument and the pieces are placed on each side of the "or& piece and then the reading is noted. )fter ta&ing this reading the "or& piece is then replaced $# a standard reference c#lindrical setting gauge
Me"#$reent o& Minor (i"eter o& Intern"l t+re"(# !he inor diameter of Internal threads are measured $# 1. Jsing taper parallels 2. Jsing =ollers. 1. U#ing t")er )"r"llel#
55
%or diameters less than 2BBmm the use of !aper parallels and micrometer is ver# common. !he taper parallels are pairs of "edges "edges having reduced and parallel parallel outer edges. edges. !he diameter diameter across their outer outer edges can $e changed $# sliding them over each other.
,.U#ing roller# %or more than 2Bmm diameter this method is used. recision rollers are inserted inside the thread and proper slip gauge is inserted $et"een the rollers. !he minor diameter is then the length of slip gauges plus t"ice the diameter of roller.
Me"#$reent o& e&&e%ti'e (i"eter Etern"l t+re"( 1. T+re"( i%roeter et+o( !he anvils are then made to contact the thread to $e chec&ed and the reading is ta&en, "hich gives the pitch diameter +or effective diameter of thread.
(ffective diameter measurement is carried out $# follo"ing methods. 1. ne "ire, 2. !"o "ires, or 3. !hree "ires method. 4. icrometer method. "! One >ire et+o(
56
!he onl# one "ire is used in this method. !he "ire is placed $et"een t"o threads at one side and on the other side the anvil of the measuring micrometer contacts the crests. %irst the micrometer reading dl is noted on a standard gauge "hose dimension is approximatel# same to $e o$tained $# this method.
8! T>o >ire et+o( !"o"ire method of measuring the effective diameter of a scre" thread is given $elo". In this method "ires of suita$le si/e are placed $et"een the standard and the micrometer anvils. %irst the micrometer reading is ta&en and let it $e =. !hen the standard is replaced $# the scre" thread to $e measured and the ne" reading is ta&en.
5>
%! T+ree-5ire et+o( !he three"ire method is the accurate method. In this method three "ires of equal and precise diameter are placed in the groves at opposite sides of the scre". In this one "ire on one side and t"o on the other side are used. !he "ires either ma# held in hand or hung from a stand. !his method ensures the alignment of micrometer anvil faces parallel to the thread axis.
5A
. 4it%+ e"#$reent !he most commonl# used methods for measuring the pitch are 1. itch measuring machine 2. !ool ma&er9s microscope 3. *cre" pitch gauge 4it%+ e"#$ring "%+ine !he principle of the method of measurement is to move the st#lus along the screen parallel to the axis from one space to the next. !he pitchmeasuring machine provides a relativel# simple and accurate method of measuring the pitch. Initiall# the micrometer reading is near the /ero on the scale, the indicator is moved along to $ring the st#lus, next the indicator ad'usted radiall# until the st#lus engages $et"een the thread flan& and the pointer N?9 is opposite in the line :. !o $ring ! in opposite in its index mar& a small movement is necessar# in the micrometer and then the reading is ta&en next.
!he st#lus is moved along into the next space $# rotation of the micrometer and the second reading is ta&en. !he difference $et"een these t"omeasured readings is &no"n as the pitch of the thread. Tool "9er# i%ro#%o)e 5or9ing or&ta$le is placed on the $ase of the $ase of the instrument. !he optical head is mounted on a vertical column it can $e moved up and do"n. or& piece is mounted on a glass plate. ) light source provides hori/ontal $eam of light "hich is reflected from a mirror $# DBB up"ards to"ards the ta$le. Image of the outline contour of the "or& piece passes through the o$'ective of the optical head.
5D
!he image is pro'ected $# a s#stem of three prisms to a ground glass screen. !he measurements are made $# means of cross lines engraved on the ground glass screen. !he screen can $e rotated through 36BS. ifferent t#pes of graduated screens and e#epieces are used. A))li%"tion# o :inear measurements. o easurement of pitch of the scre". o easurement of pitch diameter. o easurement of thread angle. o Comparing thread forms. o Centre to center distance measurement. o !hread form and flan& angle measurement S%re> )it%+ g"$ge
T+re"( &or "n( &l"n9 "ngle e"#$reent !he optical pro'ections are used to chec& the thread form and angles in the thread. !he pro'ectors equipped "ith "or& holding fixtures, lamp, and lenses. !he light ra#s from the lens are directed into the ca$inet and prisons and mirrors. !he enlarged image of thread is dra"n. !he ideal and actual forms are compared for the measurement.
..GEAR MEASUREMENT
6B
evel
*eli%"l ge"r#: !hese gears used to transmit the po"er $et"een parallel shafts as "ell as nonparallel and nonintersecting shafts. It is a c#lindrical gear "hose tooth traces is straight line.
Be'el ge"r#- !he tooth traces are straightline generators of cone. !he teeth are cut on the conical surface. It is used to connect the shafts at right angles.
R"%9 "n( 4inion- =ac& gears are straight spur gears "ith infinite radius.
61
5or "n( 5or >+eel- It is used to connect the shafts "hose axes are nonparallel and non intersecting.
Ge"r terinology
0
B"#e %ir%le: it occurs onl# in involute gears and is the circle from "hich the involute curve of the tooth profile is generated. 0 4it%+ %ir%le: in ever# pair of gears in mesh, the t"o circles representing the t"o plain "heels in contact are al"a#s assumed to exist. (ach of these circle is called as pitch circle. Its diameter is the pitch circle. 0 A((en($ %ir%le: the circle "hich limits the top of the gear teeth and represents its maximum diameter. 0 De(en($ %ir%le: it is the circle "hich contains the $ottoms of the tooth spaces.it is also called as root circle. Its diameter is the root diameter. 0 A((en($: it is the radial height of tooth from the pitch circle to the tip of the tooth. 0 De(en($: it is the radial depth of tooth from the pitch circle to the root of the tooth. 0 Cle"r"n%e: the radial distance from the top of the tooth to the $ottom of the tooth space in the mating gears 0 Cir%$l"r )it%+: it is the distance measured along the pitch circle from a point on one tooth to a corresponding point on the ad'acent tooth. Ge"r error# 1. 4ro&ile error- !he maximum distance of an# point on the tooth profile form to the design profile. ,. 4it%+ error- ifference $et"een actual and design pitch . Cy%li% error- (rror occurs in each revolution of gear . R$n o$t- !otal range of reading of a fixed indicator "ith the contact points applied to a surface rotated, "ithout axial movement, a$out a fixed axis. /. E%%entri%ity- 0alf the radial run out Ge"r Me"#$reent !he Inspection of the gears consists of determine the follo"ing elements in "hich manufacturing error ma# $e present.
62
1. =unout. 2. itch 3. rofile 4. :ead 5. ac& lash 6. !ooth thic&ness >. Concentricit# A. )lignment 1. R$no$t- It means eccentricit# in the pitch circle. It "ill give periodic vi$ration during each revolution of the gear. !his "ill give the tooth failure in gears. !he run out is measured $# means of eccentricit# testers. In the testing the gears are placed in the mandrel and the dial indicator of the tester possesses special tip depending upon the module of the gear and the tips inserted $et"een the tooth spaces and the gears are rotated tooth $# tooth and the variation is noted from the dial indicator. ,. 4it%+ e"#$reent- !here are t"o "a#s for measuring the pitch. 1. oint to point measurement +i.e. ne tooth point to next toot point 2. irect angular measurement 1. Toot+ to Toot+ e"#$reent
!he instrument has three tips. ne is fixed measuring tip and the second is sensitive tip, "hose position can $e ad'usted $# a scre" and the third tip is ad'usta$le or guide stop. !he distance $et"een the fixed and sensitive tip is equivalent to $ase pitch of the gear. )ll the three tips are contact the tooth $# setting the instrument and the reading on the dial indicator is the error in the $ase pitch. ,. Dire%t Ang$l"r Me"#$reent It is the simplest method for measuring the error $# using set dial gauge against a tooth. in this method the position of a suita$le point on a tooth is measured after the gear has $een indexed $# a suita$le angle. If the gear is not indexed through the angular pitch the reading differs from the original reading. !he difference $et"een these is the cumulative pitch error. . 4ro&ile %+e%9ing !he methods used for profile chec&ing is 1. ptical pro'ection method. 2. Involute measuring machine. 1. O)ti%"l )ro@e%tion et+o(: !he profile of the gear pro'ected on the screen $# optical lens and then pro'ected value is compared "ith master profile. 2. In'ol$te e"#$ring "%+ine-
63
In this method the gear is held on a mandrel and circular disc of same diameter as the $ase circle of gear for the measurement is fixed on the mandrel. )fter fixing the gear in the mandrel, the straight edge of the instrument is $rought in contact "ith the $ase circle of the disc. 8o", the gear and disc are rotated and the edge moves over the disc "ithout sleep. !he st#lus moves over the tooth profile and the error is indicated on the dial gauge. . Le"( %+e%9ing- It is chec&ed $# lead chec&ing instruments. )ctuall# lead is the axial advance of a helix for one complete turn. !he lead chec&ing instruments are advances a pro$e along a tooth surface, parallel to the axis "hen the gear rotates. /. B"%9l"#+ %+e%9ing- ac&lash is the distance through "hich a gear can $e rotated to $ring its non"or&ing flan& in contact "ith the teeth of mating gear. 8umerical values of $ac&lash are measured at the tightest point of mesh on the pitch circle. Toot+ t+i%9ne## e"#$reent!ooth thic&ness is generall# measured at pitch circle and also in most cases the chordal thic&ness measurement is carried out i.e. the chord 'oining the intersection of the tooth profile "ith the pitch circle. !he methods "hich are used for measuring the gear tooth thic&ness is a
64
$ ase tangent method.
%! Con#t"nt %+or( et+o(. !he theoretical values of and d can $e found out $# considering one tooth in the gear and it can $e verified. In fig noted that " is a chord ) and tooth thic&ness is specified $# )(. !he distance d is noted and ad'usted on instrument and it is slightl# greater than addendum C(.
ernier method li&e the chordal thic&ness and chordal addendum are dependent upon the num$er of teeth. ue to this for measuring large num$er of gears different calculations are to $e made for each gear. *o these difficulties are avoided $# this constant chord method.
65
(! Me"#$reent o'er )in# or 8"ll#. ) ver# good and convenient method for measuring thic&ness of gear. In this method t"o or three different si/e rollers are used for chec&up the vi$rations at several places on the tooth. . Me"#$reent o& %on%entri%ity In setting of gears the centre a$out "hich the gear is mounded should $e coincident "ith the centre from "hich the gear is generated. It is eas# to chec& the concentricit# of the gear $# mounting the gear $et"een centres and measuring the variation in height of a roller placed $et"een the successive teeth. %inall# the variation in reading "ill $e a function of the eccentricit# present. . Alignent %+e%9ing It is done $# placing a parallel $ar $et"een the gear teeth and the gear $eing mounted $et"een centres. %inall# the readings are ta&en at the t"o ends of the $ar and difference in reading is the misalignment. 4"r9in#on ge"r te#ter 3Or! Rolling te#ter 3or! Gle"#on ge"r te#ting "%+ine 5or9ing )rin%i)le !he master gear is fixed on vertical spindle and the gear to $e tested is fixed on similar spindle "hich is mounted on a carriage. !he carriage "hich can slide either side of these gears are maintained in mesh $# spring pressure. hen the gears are rotated, the movement of sliding carriage is indicated $# a dial indicator and these variations arc is measure of an# irregularities. !he variation is recorded in a recorder "hich is fitted in the form of a "axed circular chart. In the gears are fitted on the mandrels and are free to rotate "ithout clearance and the left mandrel move along the ta$le and the right mandrel move along the springloaded carriage.
!he t"o spindles can $e ad'usted so that the axial distance is equal and a scale is attached to one side and vernier to the other, this ena$les center distance to $e measured to "ithin B.B25mm. If an# errors in the tooth form "hen gears are in close mesh, pitch or concentricit# of pitch line "ill cause a variation in center distance from this movement of carriage as indicated to the dial gauge "ill sho" the errors in the gear test. !he recorder also fitted in the form of circular or rectangular chart and the errors are recorded. :imitations of ar&inson gear tester1. )ccurac#LB.BB1mm 2. aximum gear diameter is 3BBmm 3. (rrors are not clearl# identified4. easurement dependent upon the master gear. 5. :o" friction in the movement of the floating carriage. ./.S$r&"%e &ini#+ e"#$reent hen "e are producing components $# various methods of manufacturing process it is not possi$le to produce perfectl# smooth surface and some irregularities are formed. !hese irregularities are causes some serious difficulties in using the components. *o it is ver# important to correct the surfaces $efore use. !he factors "hich are affecting surface roughness are
66
1. or& piece material 2. i$rations 3. achining t#pe 4. !ool and fixtures !he geometrical irregularities can $e classified as 1. %irst order 2. *econd order 3 !hird order 4. %ourth order 1. Fir#t or(er irreg$l"ritie# !hese are caused $# lac& of straightness of guide "a#s on "hich tool must move. ,. Se%on( or(er irreg$l"ritie# !hese are caused $# vi$rations . T+ir( or(er irreg$l"ritie# !hese are caused $# machining. . Fo$rt+ or(er irreg$l"ritie# !hese are caused $# improper handling machines and equipments. Eleent# o& #$r&"%e tet$re
S$r&"%e- it is confined $# the $oundar# "hich separates that part from another part Ro$g+ne##- %inel# spaced irregularities. It is also called primar# texture. 5"'ine##- *urface irregularities "hich are of greater spacing than roughness. 4ro&ile- Contour of an# section through a surface. L"y- irection of the Npredominate surface pattern9 Fl">#- *urface irregularities or imperfection, "hich occur at infrequent intervals. Sy8ol# t+"t In(i%"te Dire%tion o& L"y [[ arallel to $oundar# line of surface indicated $# s#m$ol \[\ erpendicular to $oundar# line of surface indicated $# s#m$ol Z )ngular in $oth directions on surface indicated $# s#m$ol ultidirectional C )pproximatel# circular to center of the surface indicated $# s#m$ol = )pproximatel# radial in relation to the center of surface indicated $# s#m$ol ./.1.An"ly#i# o& #$r&"%e &ini#+ a Centre line average +C:). $ =oot mean square +=* c !en point method ". C.L.A. et+o(: !he surface roughness is measured as the average deviation from the nominal surface
6>
8. R.M.S. et+o( !he roughness is measured as the average deviation from the nominal surface. :et, h1,h2, ... are the heights of the ordinates and : is the sampling length
%. Ten )oint +eig+t et+o( !he average difference $et"een five highest pea&s and five lo"est valle#s of surface is ta&en and irregularities are calculated $#
./.,.Met+o(# o& e"#$ring #$r&"%e &ini#+ !he methods used for measuring the surface finish is classified into 1. Inspection $# comparison 2. irect Instrument easurements 1. In#)e%tion 8y %o)"ri#on et+o(#- In these methods the surface texture is assessed $# o$servation of the surface. !he surface to $e tested is compared "ith &no"n value of roughness
6A
specimen and finished $# similar machining process. !he various methods "hich are used for comparison are 1. !ouch Inspection. 2. isual Inspection. 3. icroscopic Inspection. 4. *cratch Inspection. 5. icro Interferometer. 6. *urface photographs. >. =eflected :ight Intensit# A. allace surface #namometer. To$%+ In#)e%tion It is used "hen surface roughness is ver# high and in this method the fingertip is moved along the surface at a speed of 25mmWsecond and the irregularities as up to B.B125mm can $e detected 7i#$"l In#)e%tion In this method the surface is inspected $# na&ed e#e and this measurement is limited to rough surfaces. Mi%ro#%o)i% In#)e%tion In this method finished surface is placed under the microscopic and compared "ith the surface under inspection. !he light $eam also used to chec& the finished surface $# pro'ecting the light a$out 6BS to the "or&. S%r"t%+ In#)e%tion: !he materials li&e lead, plastics ru$$ed on surface are inspected $# this method. !he impression of this scratches on the surface produced is then visuali/ed. Mi%ro-Inter&eroeter ptical flat is placed on the surface to $e inspected and illuminated $# a monochromatic source of light. S$r&"%e 4+otogr")+# agnified photographs of the surface are ta&en "ith different t#pes of illumination. !he defects li&e irregularities are appear as dar& spots and flat portion of the surface appears as $right. Re&le%te( lig+t Inten#ity ) $eam of light is pro'ected on the surface to $e inspected and the light intensit# variation on the surface is measured $# a photocell and this measured value is cali$rated 5"ll"%e #$r&"%e Dyn"oeter- It consists of a pendulum in "hich the testing shoes are clamped to a $earing surface and a predetermined spring pressure can $e applied and then, !he pendulum is lifted to its initial starting position and allo"ed to s"ing over the surface to $e tested. ,. Dire%t in#tr$ent e"#$reent# irect methods ena$le to determine a numerical value of the surface finish of an# surface. !hese methods are quantitative anal#sis methods and the output is used to operate recording or indicating instrument. irect Instruments are operated $# electrical principles. !hese instruments are classified into t"o t#pes according to the operating principle. In this is operated $# carrier modulating principle and the other is operated $# voltagegenerating principle, and in the $oth t#pes the output is amplified. *ome of the direct measurement instruments are 1. *t#lus pro$e instruments. 2. rofilometer. 3. !omlinson surface meter. 4. !a#lor0o$son !al#surf 1. Styl$# )ro8e ty)e in#tr$ent 4rin%i)le hen the st#lus is moved over the surface "hich is to $e measured, the irregularities in the surface texture are measured and it is used to assess the surface finish of the "or& piece.
6D
5or9ing !he st#lus t#pe instruments consist of s&id, st#lus, amplif#ing device and recording device. !he s&id is slo"l# moved over the surface $# hand or $# motor drive. !he s&id follo"s the irregularities of the surface and the st#lus moves along "ith s&id. hen the st#lus moves verticall# up and do"n and the st#lus movements are magnified, amplified and recorded to produce a trace. !hen it is anal#/ed $# automatic device. A('"nt"ge )n# desired roughness parameter can $e recorded. Di#"('"nt"ge# 1. %ragile material cannot $e measured. 2. 0igh Initial cost. 3. *&illed operators are needed to operate. 4ro&iloeter It is an indicating and recording instrument to measure roughness in microns. !he main parts of the instrument are tracer and an amplifier. !he st#lus is mounted in the pic&up and it consists of induction oil located in the magnet. hen the st#lus is moved on the surface to $e tested, it is displaced up and do"n due to irregularities in the surface. !his movement induces the induction coil to move in the direction of permanent magnet and produces a voltage. !his is amplified and recorded.
Tolin#on S$r&"%e eter !his instrument uses mechanicalcumoptical means for magnification. Con#tr$%tion In this the diamond st#lus on the surface finish recorder is held $# spring pressure against the surface of a lapped c#linder. !he lapped c#linder is supported one side $# pro$e and other side $# rollers. !he st#lus is also attached to the $od# of the instrument $# a leaf spring and its height is ad'usta$le to ena$le the diamond to $e positioned and the light spring steel arm is attached to the lapped c#linder. !he spring arm has a diamond scri$er at the end and smo&ed glass is rest on the arm.
>B
hen measuring surface finish the $od# of the instrument is moved across the surface $# a scre" rotation. !he vertical movement of the pro$e caused $# the surface irregularities ma&es the hori/ontal lapped c#linder to roll. !his rolling of lapped c#linder causes the movement of the arm. *o this movement is induces the diamond scri$er on smo&ed glass. %inall# the movement of scri$er together "ith hori/ontal movement produces a trace on the smo&ed glass plate and this trace is magnified $# an optical pro'ector. T"lyor-*o8#on-T"ly#$r& It is "or&ing a carrier modulating principle and it is an accurate method comparing "ith the other methods. !he main parts of this instrument is diamond st#lus +B.BB2mm radius and s&id 4rin%i)le !he irregularities of the surface are traced $# the st#lus and the movement of the st#lus is converted into changes in electric current.
5or9ing n t"o legs of the (shaped stamping there are coils for carr#ing an ).C. current and these coils form an oscillator. )s the armature is pivoted a$out the central leg the movement of the st#lus causes the air gap to var# and thus the amplitude is modulated. !his modulation is again demodulated for the vertical displacement of the st#lus. *o this demodulated output is move the pen recorder to produce a numerical record and to ma&e a direct numerical assessment. .0.Ro$n(ne## e"#$reent =oundness is defined as a condition of a surface of revolution. here all points of the surface intersected $# an# plane perpendicular to a common axis in case of c#linder and cone. De'i%e# $#e( &or e"#$reent o& ro$n(ne## 1 iametral gauge. 2 Circumferential conferring gauge H] a shaft is confined in a ring gauge and rotated against a set indicator pro$e. 3 =otating on center 4 loc& 5 !hreepoint pro$e. 6 )ccurate spindle.
>1
1. Di"etr"l et+o( !he measuring plungers are located 1ABS a part and the diameter is measured at several places. !his method is suita$le onl# "hen the specimen is elliptical or has an even num$er of lo$es. iametral chec& does not necessaril# disclose effective si/e or roundness. !his method is unrelia$le in determining roundness.
,. Cir%$&erenti"l %on&ining g"$ge %ig. sho"s the principle of this method. It is useful for inspection of roundness in production. !his method requires highl# accurate master for each si/e part to $e measured. !he clearance $et"een part and gauge is critical to relia$ilit#. !his technique does not allo" for the measurement of other related geometric characteristics, such as concentricit#, flatness of shoulders etc.
2. Rotating on centers The shaft is inspected for roundness while mounted on center. In this case! relia"ility is dependent on many factors lie angle of centers! alignment of centres! roundness and surface condition of the centres and centre holes and run out of piece. #ut of straightness of the part will cause a dou"ling run out e$ect and appear to "e roundness error.
. 7-Blo%9 !he set up emplo#ed for assessing the circularit# error $# using loc& is sho"n in fig. !he $loc& is placed on surface plate and the "or& to $e chec&ed is placed upon it. ) diameter indicator
>2
is fixed in a stand and its feeler made to rest against the surface of the "or&. !he "or& is rotated to measure the rise on fall of the "or&piece. %or determining the num$er of lo$es on the "or& piece, the "or& piece is first tested in a 6BS loc& and then in a DBS loc&. !he num$er of lo$es is then equal to the num$er of times the indicator pointer deflects through 36BS rotation of the "or& piece. Liit"tion# a !he circularit# error is greatl# $# affected $# the follo"ing factors. +i If the circularit# error is i^e, then it is possi$le that the indicator sho"s no variation. +ii osition of the instrument i.e. "hether measured from top or $ottom. +iii 8um$er of lo$es on the rotating part. $ !he instrument position should $e in the same vertical plane as the point of contact of the part "ith the $loc&. c ) leaf spring should al"a#s $e &ept $elo" the indicator plunger and the surface of the part.
/. T+ree )oint )ro8e !he fig. sho"s three pro$es "ith 12BS spacing is ver#, useful for determining effective si/e the# perform li&e a 6BS $loc&. 6BS $loc& "ill sho" no error for 5 a > lo$es magnif# the error for 3lo$ed parts sho" partial error for randoml# spaced lo$es.
O$t-o&-Ro$n(ne## E'"l$"tion Fo$r A##e##ent Met+o(#
>3
UNIT-7 MEASUREMENT OF 4O5ER=FLO5 AND TEM4ERATURE /.1.MEASUREMENT OF FORCE !he mechanical quantit# "hich changes or tends to change the motion or shape of a $od# to "hich it is applied is called force. %orce is a $asic engineering parameter, the measurement of "hich can $e done in man# "a#s as follo"s irect methods Indirect methods irect methods- It involves a direct comparison "ith a &no"n gravitational force on a standard mass, sa# $# a $alance. Indirect methods- It involves the measurement of effect of force on a $od#, such as acceleration of a $od# of &no"n mass su$'ected to force. /.1.1.De'i%e# to e"#$re For%e 1.*cale and $alances a. (qual arm $alance $. Jnequal arm $alance c. endulum scale 2. (lastic force meter +roving ring 3. :oad cells a. *train gauge load cell $. 0#draulic load cell c. neumatic load cell S%"le "n( 8"l"n%e# ". E$"l "r 8"l"n%e )n equal arm $alance "or&s on the principle of moment comparison. !he $eam of the equal arm $alance is in equili$rium position "hen, Cloc&"ise rotating moment H )nticloc&"ise rotating moment 2:2 H 1:1 !hat is, the un&no"n force is $alanced against the &no"n gravitational force. De#%ri)tion !he main parts of the arrangement are a follo"s ) $eam "hose center is pivoted and rests on the fulcrum of a &nife edge. (ither side of the $eam is equal in length "ith respect to the fulcrum
>4
) pointer is attached to the center of the $eam. !his pointer "ill point verticall# do"n"ards "hen the $eam is in equili$rium. ) rovision to place masses at either end of the $eam. O)er"tion
) &no"n standard mass +m1 is placed at one end of the $eam and an un&no"n mass +m 2 is placed at its other end. (quili$rium condition exists "hen, cloc&"ise rotating moment H )nticloc&"ise rotating moment oreover at a given location, the earth9s attraction "ill act equall# on $oth the masses +m1 and m2 and hence at equili$rium condition. 1H2. !hat is, the un&no"n force +"eight "ill $e equal to the &no"n force +"eight. 8. Une$"l "r 8"l"n%e )n unequal arm $alance "or&s on the principle of moment comparison. !he $eam of the unequal arm $alance is in equili$rium position "hen, Cloc&"ise rotating moment H )nticloc&"ise rotating moment % x :2 H %xx :1 De#%ri)tion !he main parts of the arrangements are as follo"s ) graduated $eam pivoted to a &nife edge RYG ) leveling pointer is attached to the $eam ) &no"n mass RmG is attached to the right side of the $eam. !his creates an un&no"n force R%G. !his mass RmG can slide on the right side of the $eam. rovisions are made to appl# an un&no"n force R%xG on the left side of the $eam. peration )n un&no"n force R%xG is applied on the left side of the $eam through &nife edge REG as sho"n 8o" the position of mass RmG on the right side of the $eam is ad'usted until the leveling pointer reads null $alance position. hen the leveling pointer is in null $alance position, the $eam is in equili$rium. Cloc& "ise rotating moment H )nticloc& "ise rotating moment %x.:1 H %. :2 %xH g.:2W:1 !hus the un&no"n force R% xG is proportional to the distance R:2G of the mass RmG from the &nife edge RYG !he right hand side of the $eam "hich is graduated is cali$rated to get a direct measure of R% xG %. 4en($l$ S%"le3M$lti-le'er Ty)e! It is a moment comparison device. !he un&no"n force is converted to torque "hich is then $alanced $# the torque of a fixed standard mass arranged as a pendulum. De#%ri)tion !he scale9s frames carr# support ri$$ons. !hese support ri$$ons are attached to the sectors. !he loading ri$$ons are attached to the
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sectors and the load rod a sho"n. !he load rod is inturn attached to the "eighing platform. !he t"o sectors are connected on either side of an equali/er $eam. !he sectors carr# counter "eighs. !o the center of the equali/er $eam is attached a rac& and pinion arrangement. ) pointer is attached to the pinion "hich s"eeps over a "eight +force cali$rated scale. O)er"tion !he un&no"n force is applied to the load rod. ue to this force, the loading tapes are pulled do"n"ards. 0ence the loading tapes rotate the sectors. )s the sectors rotate a$out the pivots, it moves the counter "eights out"ards, !his movements increases the counter "eight effective moment until the torque produced $# the force applied to the load rod and the moment produced $# the counter "eight $alance each other, there$# esta$lishing an equili$rium. uring the process of esta$lishing equili$rium, the equali/er $eam "ould $e displaced do"n"ards. )s the rac& is attached to the equali/er $eam, the rac& also is displaced do"n"ards rotating the pinion. )s the pointer is attached to the pinion, the rotation of the pinion ma&es the pointer to assume a ne" position on the scale. !he scale is cali$rated to read the "eight directl#. !hus the force applied on the load rod is measured. El"#ti% &or%e eter 34ro'ing Ring! hen a steel ring is su$'ected to a force across its diameter, it deflects. !his deflection is proportional to the applied force "hen cali$rated. De#%ri)tion ) steel ring attached "ith external $osses to appl# force. ) precision micrometer "ith one of its ends mounted on a vi$rating reed. O)er"tion !he force to $e measured is applied to the external $osses of the proving ring. ue to the applied force, the ring changes in diameter. !his deflection of the ring is proportional to the applied force.
)t this stage, the reed is pluc&ed to o$tain a vi$rating motion. hen the reed is vi$rating, the micrometer "heel is turned until the micrometer contact moves for"ard and ma&es a noticea$le damping of the vi$rating reed. 8o" the micrometer reading is noted "hich a measure of deflection of the ring is. !he device is cali$rated to get a measure of force in terms of deflection of the proving ring. Lo"( %ell# ". Str"in g"$ge lo"( %ell
hen a steel c#linder is su$'ected to a force, it !ends to change in dimension. n this c#linder if *train gauges are $onded, the strain gauge also is *tretched or compressed, causing a change in its
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:ength and diameter. this change in dimension of the strain gauge causes its resistance to change. !his change in resistance of the strain gauge $ecomes a measure of the applied force. De#%ri)tion ) c#linder made of steel on "hich four identical strain gauges are mounted. ut of the four strain gauges, t"o of them +=1 and =4 are mounted along the direction of the applied load+ertical gauges !he other to" strain gauges +=2 and =3 hori/ontal gauges are mounted circumferentiall# at right angles to gauges =1 and =4. !he four gauges are connected to the four lim$s of "heat stone $ridge. peration hen there is no load on the steel c#linder, all the four gauges "ill have the same resistance. )s the terminals 8 and are at the same potential, the "heat stone $ridge is $alanced and hence the output voltage "ill $e /ero. 8o" the force to $e measured is applied on the steel c#linder. ue to this, the vertical gauges =1 and =4 "ill under go compression and hence there "ill $e a decrease in resistance. )t the same time, the hori/ontal gauges =2 and =3 "ill undergo tension and there "ill $e an increase in resistance. !hus "hen strained, the resistance of the various gauges change. 8o" the terminals 8 and "ill $e at different potential and the change in output voltage due to the applied load $ecomes a measure of the applied load "hen cali$rated. 8. *y(r"$li% Lo"( Cell hen a force is applied on liquid medium contained in a confined space, the pressure of the liquid increases. !his increase in pressure of the liquid is proportional to the applied force. 0ence a measure of the increase in pressure of the liquid $ecomes a measure of the applied force "hen cali$rated. !he force to $e measure is applied to the piston !he applied force moves the piston do"n "ards and deflects the diaphragm and this deflection of the diaphragm increase the pressure in the liquid medium. !his increase in pressure of the liquid medium is proportional to the applied force. !his increase in pressure is measured $# the pressure gauge "hich is connected to the liquid medium. !he pressure is cali$rated in force units and hence the indication in the pressure gauge $ecomes a measure of the force applied on the piston.
%. 4ne$"ti% lo"( %ell# If a force is applied to one side of a diaphragm and an air pressure is applied to the other side, some particular value of pressure "ill $e necessar# to exactl# $alance the force. !his pressure is proportional to the applied force. !he force to $e measured is applied to the top side of the diaphragm. ue to this force, the diaphragm deflects and causes the flapper to shutoff the no//le opening. )ir suppl# is provided at the $ottom of the diaphragm. )s the flapper closes the no//le opening, a $ac& pressure results underneath the diaphragm
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!his $ac& pressure acts on the diaphragm producing an up"ard force. )ir pressure is regulated until the diaphragm returns to the preloaded position "hich is indicated $# air "hich comes out of the no//le. )t this stage, the corresponding pressure indicated $# the pressure gauge $ecomes a measure of the applied force "hen cali$rated.
/.,.TORHUE MEASUREMENT easurement of applied torques is of fundamental importance in all rotating $odies to ensure that the design of the rotating element is adequate to prevent failure under shear stresses. !orque measurement is also a necessar# part of measuring the po"er transmitted $# rotating shafts. !he four methods of measuring torque consist of easuring the strain produced in a rotating $od# due to an applied torque )n optical method easuring the reaction force in cradled shaft $earings Jsing equipment &no"n as the ron# $ra&e. Me"#$reent o& In($%e( Str"in easuring the strain induced in a shaft due to an applied torque has $een the most common method used for torque measurement in recent #ears. !he method involves $onding four strain gauges onto a shaft as sho"n in %igure, "here the strain gauges are arranged in a d.c. $ridge circuit. !he output from the $ridge circuit is a function of the strain in the shaft and hence of the torque applied. It is ver# important that positioning of the strain gauges on the shaft is precise, and the difficult# in achieving this ma&es the instrument relativel# expensive. !his technique is ideal for measuring the stalled torque in a shaft $efore rotation commences. 0o"ever, a pro$lem is encountered in the case of rotating shafts $ecause a suita$le method then has to $e found for ma&ing the electrical connections to the strain gauges. ne solution to this pro$lem found in man# commercial instruments is to use a s#stem of slip rings and $rushes for this, although this increases the cost of the instrument still further.
O)ti%"l Tor$e Me"#$reent
ptical techniques for torque measurement have $ecome availa$le recentl# "ith the development of laser diodes and fi$eroptic light transmission s#stems. ne such s#stem is sho"n in %igure. !"o $lac&and"hite striped "heels are mounted at either end of the rotating shaft and are in alignment "hen no torque is applied to the shaft. :ight from a laser diode
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light source is directed $# a pair of fi$eroptic ca$les onto the "heels. !he rotation of the "heels causes pulses of reflected light, "hich are transmitted $ac& to a receiver $# a second pair of fi$eroptic ca$les. Jnder /ero torque conditions, the t"o pulse trains of reflected light are in phase "ith each other. If torque is no" applied to the shaft, the reflected light is modulated. easurement $# the receiver of the phase difference $et"een the reflected pulse trains therefore allo"s the magnitude of torque in the shaft to $e calculated. !he cost of such instruments is relativel# lo", and an additional advantage in man# applications is their small ph#sical si/e. Re"%tion For%e# in S+"&t Be"ring# )n# s#stem involving torque transmission through a shaft contains $oth a po"er source and a po"er a$sor$er "here the po"er is dissipated. !he magnitude of the transmitted torque can $e measured $# cradling either the po"er source or the po"er a$sor$er end of the shaft in $earings, and then measuring the reaction force, %, and the arm length, :, as sho"n in %igure. !he torque is then calculated as the simple product, %:. endulum scales are used ver# commonl# for measuring the reaction force. Inherent errors in the method are $earing friction and "indage torques. !his technique is no longer in common use.
4rony Br"9e
!he ron# $ra&e is another torquemeasuring s#stem that is no" uncommon. It is used to measure the torque in a rotating shaft and consists of a rope "ound round the shaft, as illustrated in %igure. ne end of the rope is attached to a spring $alance and the other end carries a load in the form of a standard mass, m. If the measured force in the spring $alance is %s, then the effective force, %e, exerted $# the rope on the shaft is given $# %e H mg %s If the radius of the shaft is =s and that of the rope is =r, then the effective radius, =e, of the rope and drum "ith respect to the axis of rotation of the shaft is given $# =e H = s = r !he torque in the shaft, !, can then $e calculated as !H %e= ehile this is a "ell&no"n method of measuring shaft torque, a lot of heat is generated $ecause of friction $et"een the rope and shaft, and "ater cooling is usuall# necessar#.
/..MEASUREMENT OF 4O5ER !orque is exerted along a rotating shaft. # measuring this torque "hich is exerted along a rotating shaft, the shaft po"er can $e determined. %or torque measurement d#namometers are used. ! H %.r H 2_8! here, ! V !orque, % V %orce at a &no"n radius r, V o"er !#pes of d#namometers 1. )$sorption d#namometers 2. riving d#namometers 3. !ransmission d#namometers A8#or)tion (yn"oeter#
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!he d#namometer a$sor$s the mechanical energ# "hen torque is measured. It dissipates mechanical energ# +heat due to friction "hen torque is measured. !herefore, d#namometers are used to measure torqueWpo"er of po"er sources li&e engine and motors. Me%+"ni%"l Dyn"oeter# In pron# $ra&e, mechanical energ# is converted into heat through dr# friction $et"een the "ooden $ra&e $loc&s and the fl#"heel +pulle# of the machine. ne $loc& carries a lever arm. )n arrangement is provided to tighten the rope "hich is connected to the arm. =ope is tightened so as to increase the frictional resistance $et"een the $loc&s and the pulle#. o"er dissipated, H 2_8!W6B !he capacit# of prone# $ra&e is limited due to "ear of "ooden $loc&s, friction coefficient varies. *o, it is unsuita$le for large po"ers "hen it is used for long periods.
E((y C$rrent Dyn"oeter
asicall# an electrical d#namometer of a$sorption t#pe, used to measure po"er from a source such as engine or a motor. hen a conducting material moves through a magnetic flux field, voltage is generated, "hich causes current to flo". If the conductor is a "ire forming, a part of a complete circuit current "ill $e caused to flo" through that circuit and "ith some form of commutating device a form of ).C or .C generator ma# result. )n edd# current d#namometer is sho"n a$ove. It consists of a metal disc or "heel "hich is rotated in the flux of a magnetic field. !he field if produced $# field elements or coils is excited $# an external source and attached to the d#namometer housing "hich is mounted in trunnion $earings. )s the disc turns, edd# currents are generated. Its reaction "ith the magnetic field tends to rotate the complete housing in the trunnion $earings. ater cooling is emplo#ed. *y(r"$li% or Fl$i( Fri%tion Dyn"oeter
) rotating dis& that is fixed to the driving shaft, *emi elliptical grooves are provided on the disc through "hich a stream of "ater flo"s. !here is a casting "hich is stationar# and the disc rotates in this casing. hen the driving shaft rotates, "ater flo" is in a helical path in the cham$er. ue to vortices and edd#currents setup in the "ater, the casting tends to rotate in the same direction as that of the driving shafts. # var#ing the amount of "ater, the $ra&ing action is provided. ra&ing can also $e provided $# var#ing the distance $et"een the rotating dis& and the casting.!he
AB
a$sor$ing element is constrained $# a forcemeasuring device placed at the end of the arm of radius r. /..FLO5 MEASUREMENTS !he flo" rate of a fluid flo"ing in a pipe under pressure is measured for a variet# of applications, such as monitoring of pipe flo" rate and control of industrial processes. ifferential pressure flo" meters, consisting of orifice, flo" no//le, and venturi meters, are "idel# used for pipe flo" measurement and are the topic of this course. )ll three of these meters use a constriction in the path of the pipe flo" and measure the difference in pressure $et"een the undistur$ed flo" and the flo" through the constriction. !hat pressure difference can then $e used to calculate the flo" rate. %lo" meter is a device that measures the rate of flo" or quantit# of a moving fluid in an open or closed conduit. %lo" measuring devices are generall# classified into four groups 7ent$ri Meter enturi tu$es are differential pressure producers, $ased on ernoulli9s !heorem.
Ori&i%e Flo> Meter )n rifice flo" meter is the most common head t#pe flo" measuring device. )n orifice plate is inserted in the pipeline and the differential pressure across it is measured.
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4rin%i)le o& O)er"tion !he orifice plate inserted in the pipeline causes an increase in flo" velocit# and a corresponding decrease in pressure. !he flo" pattern sho"s an effective decrease in cross section $e#ond the orifice plate, "ith a maximum velocit# and minimum pressure at the venacontracta. !he flo" pattern and the sharp leading edge of the orifice plate "hich produces it are of ma'or importance. !he sharp edge results in an almost pure line contact $et"een the plate and the effective flo", "ith the negligi$le fluidtometal friction drag at the $oundar#. Ty)e# o& Ori&i%e 4l"te# !he simplest form of orifice plate consists of a thin metal sheet, having in it a square edged or a sharp edged or round edged circular hole. !here are three t#pes of orifice plates namel# 1. Concentric 2.(ccentric and 3. *egmental t#pe !he concentric t#pe is used for clean fluids. In metering dirt# fluids, slurries and fluids containing solids, eccentric or segmental t#pe is used in such a "a# that its lo"er edge coincides "ith the inside $ottom of the pipe. !his allo"s the solids to flo" through "ithout an# o$struction. !he orifice plate is inserted into the main pipeline $et"een ad'acent flanges, the outside diameters of the plate $eing turned to fit "ithin the flange $olts. !he flanges are either scre"ed or "elded to the pipes. A('"nt"ge# 1. It is ver# cheap and eas# method to measure flo" rate 2. It has predicta$le characteristics and occupies less space 3. Can $e used to measure flo" rates in large pipes Liit"tion# 1. !he venacontracta length depends on the roughness of the inner "all of the pipe and sharpness of the orifice plate. In certain case it $ecomes difficult to tap the minimum pressure due the a$ove factor 2. ressure recover# at do"nstream is poor, that is, overall loss varies from 4B to DB of the differential pressure. 3. In the upstream straightening vanes are a must to o$tain laminar flo" conditions. 4. !he orifice plate gets corroded and due to this after sometime, inaccurac# occurs. !he coefficient of discharge is lo". Rot"eter !he orifice meter, enturimeter and flo" no//le "or& on the principle of constant area varia$le pressure drop. 0ere the area of o$struction is constant, and the pressure drop changes "ith flo" rate. n the other hand =otameter "or&s as a constant pressure drop varia$le area meter. It can $e onl# $e used in a vertical pipeline. Its it is simple in construction, read# to install and the flo" rate can $e directl# seen on a cali$rated scale, "ithout the help of an# other device, e.g. differential pressure sensor etc. oreover, it is useful for a "ide range of variation of flo" rates +1B-1. !he $asic construction of a rotameter is sho"n in figure. It consists of a vertical pipe, tapered do"n"ard. !he flo" passes from the $ottom to the top. !here is c#lindrical t#pe
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metallic float inside the tu$e. !he fluid flo"s up"ard through the gap $et"een the tu$e and the float. )s the float moves up or do"n there is a change in the gap, as a result changing the area of the orifice. In fact, the float settles do"n at a position, "here the pressure drop across the orifice "ill create an up"ard thrust that "ill $alance the do"n"ard force due to the gravit#. !he position of the float is cali$rated "ith the flo" rate.!he ma'or source of error in rotameter is due to the variation of densit# of the fluid. esides, the presence of viscous force ma# also provide an additional force to the float. A))li%"tion# 1. Can $e used to measure flo" rates of corrosive fluids 2. articularl# useful to measure lo" flo" rates A('"nt"ge# 1. %lo" conditions are visi$le 2. %lo" rate is a linear function +uniform flo" scales 3. Can $e used to measure flo" rates of liquids, gases and vapour 4. # changing the float, tapered tu$e or $oth, the capacit# of the rotameter can $e changed. Liit"tion# 1. !he# should $e installed verticall# 2.!he# cannot $e used for measurements in moving o$'ects 3. !he float "ill not $e visi$le "hen coloured fluids are used, that is, "hen opaque fluid are used. 4.%or high pressure and temperature fluid flo" measurements, the# are expensive 5.!he# cannot $e used for fluids containing high percentage of solids in suspension. 4itot t$8e )n o$struction t#pe primar# element used mainl# for fluid velocit# measurement is the itot tu$e. 4rin%i)le Consider %igure "hich sho"s flo" around a solid $od#. hen a solid $od# is held centrall# and stationar# in a pipeline "ith a fluid streaming do"n, due to the presence of the $od#, the fluid "hile approaching the o$'ect starts losing its velocit# till directl# in front of the $od#, "here the velocit# is /ero. !his point is &no"n as the stagnation point. )s the &inetic head is lost $# the fluid, it gains a static head. # measuring the difference of pressure $et"een that at normal flo" line and that at the stagnation point, the velocit# is found out. !his principle is used in pitot tu$e sensors. ) common industrial t#pe of pitot tu$e consists of a c#lindrical pro$e inserted into the air stream, as sho"n in %igure. %luid flo" velocit# at the upstream face of the pro$e is reduced su$stantiall# to /ero. elocit# head is converted to impact pressure, "hich is sensed through a small hole in the upstream face of the pro$e. ) corresponding
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) common industrial t#pe of pitot tu$e consists of a c#lindrical pro$e inserted into the air stream, as sho"n in %igure. %luid flo" velocit# at the upstream face of the pro$e is reduced su$stantiall# to /ero. elocit# head is converted to impact pressure, "hich is sensed through a small hole in the upstream face of the pro$e. ) corresponding *mall hole in the side of the pro$e senses static pressure. ) pressure instrument measures the differential pressure, "hich is proportional to the square of the stream velocit# in the vicinit# of the impact pressure sensing hole. !he velocit# equation for the pitot tu$e is given $# A('"nt"ge# 1. 8o pressure loss. 2. It is relativel# simple. 3. It is readil# adapted for flo" measurements made in ver# large pipes or ducts Di#"('"nt"ge# 1. oor accurac#. 2. 8ot suita$le for dirt# or stic&# fluids and fluids containing solid particles. 3. *ensitive to upstream distur$ances. /./.TEM4ERATURE MEASUREMENT !emperature is one of the most measured ph#sical parameters in science and technolog#K t#picall# for process thermal monitoring and control. !here are man# "a#s to measure temperature, using various principles. %our of the most common are echanical +$imetallic strips !hermo 'unctive +thermocouples (lectrical resistance thermometer Me%+"ni%"l Te)er"t$re Me"#$ring De'i%e# ) change in temperature causes some &ind of mechanical motion, t#picall# due to the fact that most materials expand "ith a rise in temperature. echanical thermometers can $e constructed that use liquids, solids, or even gases as the temperaturesensitive material. !he mechanical motion is read on a ph#sical scale to infer the temperature. Biet"lli% #tri) t+eroeter !"o dissimilar metals are $onded together into "hat is called a $imetallic strip, as s&etched to the right. *uppose metal ) has a smaller coefficient of thermal expansion than does metal . )s temperature increases, metal expands more than does metal ), causing the $imetallic strip to curl up"ards as s&etched. ne common application of $imetallic strips is in home thermostats, "here a $imetallic strip is used as the arm of a s"itch $et"een electrical contacts. )s the room temperature changes, the $imetallic strip $ends as discussed a$ove. hen the $imetallic strip $ends far enough, it ma&es contact "ith electrical leads that turn the heat or air conditioning on or off. )nother application is in circuit $rea&ers 0igh temperature indicates overcurrent, "hich shuts off the circuit. )nother common application is for use as oven, "ood $urner, or gas grill thermometers. !hese thermometers consist of a $imetallic strip "ound up in a spiral, attached to a dial that is cali$rated into a temperature scale. T*ERMOCOU4LES 3T+ero-@$n%ti'e te)er"t$re e"#$ring (e'i%e#! !homas Qohan *ee$ac& discovered in 1A21 that thermal energ# can produce electric current. hen t"o conductors made from dissimilar metals are connected forming t"o common 'unctions and the t"o 'unctions are exposed to t"o different temperatures, a net thermal emf is produced, the actual value $eing dependent on the materials used and the temperature difference $et"een hot and cold 'unctions. !he thermoelectric emf generated, in fact is due to the com$ination of t"o effects- eltier effect and !homson effect. ) t#pical thermocouple 'unction is sho"n in fig. 5. !he emf generated can $e approximatel# expressed $# the relationship-
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here, !1 and !2 are hot and cold 'unction temperatures in ?. C 1 and C2 are constants depending upon the materials. %or CopperW Constantan thermocouple, C 1H62.1 and C2HB.B45. !hermocouples are extensivel# used for measurement of temperature in industrial situations. !he ma'or reasons $ehind their popularit# are- +i !he# are rugged and readings are consistent +ii !he# can measure over a "ide range of temperature +iii !heir characteristics are almost linear "ith an accurac# of a$out B.B5. 0o"ever, the ma'or shortcoming of thermocouples is lo" sensitivit# compared to other temperature measuring devices +e.g. =!, !hermistor. T*ERMORESISTI7E TEM4ERATURE MEASURING DE7ICES OR Ele%tri%"l re#i#t"n%e t+eroeter
4rin%i)le o& o)er"tion ) change in temperature causes the electrical resistance of a material to change. !he resistance change is measured to infer the temperature change. !here are t"o t#pes of thermoresistive measuring devices- resistance temperature detectors and thermistors, $oth of "hich are descri$ed here. Re#i#t"n%e te)er"t$re (ete%tor# ) resistance temperature detector +a$$reviated =! is $asicall# either a long, small diameter metal "ire +usuall# platinum "ound in a coil or an etched grid on a su$strate, much li&e
4re##$re t+eroeter ) pressure thermometer, "hile still considered mechanical, operates $# the expansion of a gas instead of a liquid or solid. !here are also pressure thermometers that use a liquid instead of a gas *uppose the gas inside the $ul$ and tu$e can $e considered an ideal gas. !he ideal gas la" is H m=!, "here is the pressure, is the volume of the gas, m is the mass of the gas, = is the gas constant for the specific gas +not the universal gas constant, and ! is the a$solute temperature of the gas.
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*pecific gas constant = is a constant. !he $ul$ and tu$e are of constant volume, so is a constant. )lso, the mass m of gas in the sealed $ul$ and tu$e must $e constant +conservation of mass. ) pressure thermometer therefore measures temperature indirectl# $# measuring pressure. !he gage is a pressure gage, $ut is t#picall# cali$rated in units of temperature instead. ) common application of this t#pe of thermometer is measurement of outside temperature from the inside of a $uilding. !he $ul$ is placed outside, "ith the tu$e running through the "all into the inside. !he gauge is on the inside. )s T increases outside, the $ul$ temperature causes a corresponding increase in pressure, "hich is read as a temperature increase on the gauge. /.0.Reli"8ility: It is the a$ilit# of a s#stem to perform and maintain its function in routine circumstances. Consistenc# of a set of measurements or measuring instrument often used to descri$e a test. /..C"li8r"tion : Cali$ration is the process of determining and ad'usting an instruments accurac # to ma&e sure its accurac# is "ithin the manufacturer9s specifications. /..Re"("8ility: It is the ease "ith "hich the readings in an instrument can $e read. %ine and "idel# spaced graduations +lines improve the reada$ilit# of the instrument. ,-MAR6S HUESTION AND ANS5ER UNIT I 1. Di#ting$i#+ 8et>een line #t"n("r( "n( en( #t"n("r(.
s.no 1
,. .
.
/.
line #t"n("r( en( #t"n("r( hen the length is measured $et"een t"o hen the distance +length is measured $et"een t"o lines it is called line standard. surfaces +or faces it is called end standard. (g- !he protot#pe meter and imperial #ard (g- *lip gauge. , 5+"t yo$ e"n 8y #en#iti'e o& " e"#$ring in#tr$ent. !he ratio of the magnitude of output signal to the magnitude of input signal. De&ine #y#te error "n( %orre%tion Error: !he deviation $et"een the results of measured v alue to the actual value. Corre%tion: !he numerical value "hich should $e added to the measured value to get the Correct result. Di&&erenti"te 8et>een )re%i#ion "n( "%%$r"%y. A%%$r"%y !he maximum amount $# "hich the result differ from true value. 4re%i#ion egree of repetitiveness. If an instrument is not precise it "ill give d ifferent results for the same dimension for the repeated readings. 5+"t "re t+e i)ort"nt eleent# o& e"#$reent# I . easurand 2. =eference 3. Comparator
A6
0. 5+"t i# e"nt 8y noin"l #ie "n( toler"n%e Noin"l #ie: *i/e o$tained through measurement "ith permissi$le error. Toler"n%e: the difference $et"een allo"ed highest value into the allo"ed lo"est value . De&ine re"("8ility "n( re)e"t"8ility. Re"("8ility: it is the ease "ith "hich the readings in an instrument can $e read. Re)e"t"8ility: it is the a$ilit# of an instrument to repeat the same results for the same measurement . De&ine leg"l etrology. :egal metrolog# is part of etrolog# and it is directed $# a 8ational rgani/ation "hich is Called `8otional service of :egal etrolog#`. !he main o$ 'ective is to, maintain uniformit# of easurement in a particular countr#. . De&ine #t"ti% "n( (yn"i% re#)on#e. St"ti% re#)on#e: )n instrument "hich are used to measure an unvar#ing process conditions. Dyn"i% re#)on#e !he $ehavior of an instrument under such time var#ing inputoutput condition is called d#namic response of a instrument. 1?. Gi'e "ny &o$r et+o(# o& e"#$reent. 1. irect method. 2. Indirect method. 3. Comparison method. 4. Coincidence method. UNIT II 1. What are the various types of linear and angular measuring instruments? Line"r - i. ernier calipers ii. icrometers iii. *lip gauge or gauge $loc&s iv.Comparator Ang$l"r: +i )ngle gauges +ii *ine $ar "ith slip gauges +iii )utocollimator +iv )nglede&&or ,. 5+"t i# %o)"r"tor Comparators are one form of linear measurement device "hich is quic& and more convenient for Chec&ing large num$er of identical dimensions.
. 5+"t "re t+e So$r%e# o& error in #ine 8"r# 1 (rror in distance $et"een roller centers. 2 (rror in slip gauge com$ination. 3 (rror in chec&ing of parallelism. 4 (rror in parallelism of roller axes "ith each other.
. 5+"t i# e"nt 8y >ringing o& #li) g"$ge It is nothing $ut com$ining the faces of slip gauges one over the other. ue to adhesion propert# of slip gauges, the# "ill stic& together. !his is $ecause of ver# high degree of surface finish of the measuring faces.
/. 5+"t "re t+e liit g"$ge# 1. lug gauges. 2 =ing gauges. 3 *nap gauges 0. De&ine inter%+"nge "8ility. ) part "hich can $e su$stituted for the component manufactured to the same shape and dimension is &no"n as interchangea$le part. !he operation of su$stituting the part for similar manufactured components of the sa me shape and dimension is &no"n as interchangea$ilit#.
. *o> t+e e%+"ni%"l %o)"r"tor >or9# !he method of magnif#ing small movement of the indicator in all mechanical comparators is
A>
effected $# means of levers, gear trains or a com$ination of these elements.
. 5+"t "re t+e "('"nt"ge# o& e%+"ni%"l %o)"r"tor 1 It is usuall# ro$ust, compact and eas# to handle. 2 !here is no external suppl# such as electricit#, air required. 3 It has ver# simple mechanism and is cheaper "hen compared to other t#pes. 4 It is suita$le for ordinar# "or&shop and also easil# porta$le.
. 5+"t i# e"nt 8y le"#t %o$nt it is defined as the difference $et"een the values of a main scale division and vernier scale division. 1?. 5rite t+e le"#t %o$nt '"l$e o& 'ernier %"li)er= i%roeter= "n( (i"l g"$ge "n( 8e'el )rotr"%tor. 7ernier %"li)er: B.B2mm Mi%roeter: B.B1mm Di"l g"$ge: B.B1mm Be'el )rotr"%tor: 5 minute
UNIT III
1. State any two application of laser in machine tool metrology. i )ircraft production and ship$uilding ii to $e c hec&ed for predetermined straight line. iii !o $e chec&ed for flatness of machine surfaces 7 chec&ing squarness
,. Mention "ny &o$r "('"nt"ge# o& %ol$n ty)e CMM. i uic&er inspection ii )ccurate measurements iii (asier osition iv =eduction of good part re'ection.
. 5+"t "re t+e "('"nt"ge# o& l"#er inter&eroeter i It is ideall# suited for measuring linear positioning, straightness in t"o planes. ii :ong covering range and high sensitivit#. iii 8oncontact measurement is possi$le. iv Jse of single photo detector per measurement axis.
. 5+"t i# CNC -CMM !he computer numerical control +C8C s#stem is used "ith C for the measurement of complicated parts. !he inaccuracies are automaticall# corrected $ # the C8C
/. N"e t+e ty)e# o& "%%$r"%y #)e%i&i%"tion $#e( &or CMM i easurement accurac#- )xial length measuring 7 volumetric length measuring. ii )xial motion accurac#- :inear displacement, straightness, perpendicularit#, pitches etc.
0. 5+"t "re t+e %+"r"%teri#ti%# o& l"#er i onochromatic light source ii irectional possi$ilit# iii Coherent light ra#s
. Li#t "ny &o$r "))li%"tion# o& %o)$ter "i(e( in#)e%tion#. AA
i Chec&ing tool accurac# ii chec&ing tool "ear iii monitoring manufacturing process iv )ssisting qualit# engineers and machinist.
. De&ine M"%+ine 7i#ion. achine vision can $e defined as a means of simulating the image recognition and anal#sis capa$ilities of the human s#stem "ith electronic and electromechanical techniques. . 5rite t+e "))li%"tion o& inter&eroeter . i :inear measurement ii )ngular measurement
1?.5+"t (o yo$ e"nt 8y "lignent te#t on "%+ine tool !he alignment test is carried out to chec& the grade of manufacturing accurac# of the machine tool.
UNIT I7
1. 5+"t i# )rogre##i'e error in #%re> t+re"( !he pitch of the thread is uniform $ut it is longer +or shorter to its nominal value and this is called progressive error.
,. De&ine L"y. Mention "ny &o$r o& it# ty)e. :a#- irection of the bpredominate surface patternb i 0ori/ontal la# ii ertical la# iii =adial la# iv Circular la#
. 5+"t i# e"nt 8y 8e#t #ie >ire in #%re> t+re"( "n$&"%t$ring est si/e of "ire is a "ire of such diameter that it ma&es contact "ith the flan&s of the thread on the pitch line
. De&ine t+e ter %on#t"nt %+or( o& ge"r Constant chord is the chord 'oining those points, or opposite faces of the tooth.
/. De&ine (r$n9en t+re"( < 4erio(i% error. Dr$n9en t+re"(: !his is one, having erratic pitch, in "hich the advance f the helix is irregular in one complete revolution of thread. 4erio(i% error: !he periodic error repeats itself at equal intervals along the thread
0. St"te t+e et+o( $#e( &or %+e%9ing ge"r toot+ )ro&ile. i ptical pro'ection method ii involute measuring machine.
. 5+"t i# ge"r r$no$t !otal range of reading of a fixed indicate r "ith the contact points applied to a *urface AD
=otated, "ithout axial movement, a$out 3 fixed axis.
. 5+"t i# #e%on("ry tet$re o& #$r&"%e !he irregularities o$tained $# first and second order of irregularities are called secondar# texture.
. 5+"t i# e"nt 8y o($le oduleH pitch circle diameterW num$er of teeth
1?.De&ine Me"#$reent o& Str"ig+tne##= Fl"tne## < Ro$n(ne##. Str"ig+tne##: !he shortest distance $et"een t"o points. Fl"tne##: !he minimum distance $et"een t"o planes "hich cover all the irregularities of the surface. Ro$n(ne##: It is a surface of revolution "here all the surfaces intersected b$# an# plane perpendicular to a common axis in case of, c#linder and cone.
11. De&ine )it%+. !he distance measured parallel to the axis from a point, on a thread to the corresponding next point. UNIT-7 1. 5+"t "re lo"( %ell# )re devices for the measurement of force through indirect methods.
,. 5+"t i# >or9ing )rin%i)le o& t+ero%o$)le hen t"o metals are 'oined together it "ill create an emf and it is primaril# a function of the 'unction temperature. . Mention t+e )rin%i)le in'ol'e( in 8iet"lli% #tri). Is $ased on change in dimension . De&ine &or%e= tor$e < )o>er For%e: !he mechanical quantit# "hich changes or tends to change the motion or shape of a $od# to "hich it is applied Tor$e: !orque can $e defined as a measure of the tendenc# of a force to rotate the $od# on "hich it acts a$out an axis. 4o>er: %orce "ith respect to !ime /. Li#t t+e in#tr$ent# $#e( &or e"#$ring te)er"t$re
1. echanical +$imetallic strips 2.!hermo 'unctive +thermocouples 3.(lectrical resistance thermometer 0. 5+"t "re t+e (i&&eren%e 8et>een ori&i%e "n( 'ent$rieter #.no Ori&i%e eter 1 :oss of head is small 2 8o "ear and tear 3 Initial cost is more 4 =equires more space . St"te "ny &o$r in&erenti"l ty)e o& &lo> eter# enturi meter, orifice meter, rotameter, pitot tu$e. . St"te "ny t>o )rin%i)le o& &or%e e"#$reent
DB
'ent$rieter :oss of head is more ore "ear and tear :o" initial cost =equires less space as compared "ith venturimeter
