Mechatronics_Session 3_ Position Sensors

8/17/2019 Mechatronics_Session 3_ Position Sensors

1/60

MECHATRONICS

Unit 1

Classification of Sensors & Transducers(Session-5

Mec!anical En"ineerin" #e$art%ent

' Uniersit)


2/60

2

'earnin" O*+ecties

In t!is lecture students ,ill learn• Classification of sensors• Classification of transducers

• #is$lace%ent transducers• Resistance transducers• Ca$acitie transducers• Inductance *ased transducers

• O$tical encoders


3/60

3

Classification of Sensors

1. Actie and .assie sensors

/0 Contact and non-contact sensors0 A*solute and relatie sensors

20 Ot!er sc!e%es


4/60

4

10 Actie and $assie sensors

.assie Sensor a sensor t!at re3uires e4ternal $o,er too$erate0

E4a%$les t!e car*on %icro$!one t!er%istors strain"au"es ca$acitie and inductie sensors etc0

Ot!er na%e $ara%etric sensors (out$ut is a function of a $ara%eter - li6e resistance

Actie Sensor "enerates its o,n electric si"nal and does

not re3uire a $o,er source0E4a%$les t!er%ocou$les %a"netic %icro$!ones $ie7oelectric sensors0

Ot!er na%e self-"eneratin" sensors


5/60

5

/0 Contact and noncontact sensors

Contact sensor a sensor t!at re3uires $!)sical

contact ,it! t!e sti%ulus0

E4a%$les strain "au"es %ost te%$erature sensors

Non-contact sensor re3uires no $!)sical contact0E4a%$les %ost o$tical and %a"netic sensors

infrared t!er%o%eters etc0


6/60

6

0 A*solute and relatie sensors

A*solute sensor a sensor t!at reacts to a sti%ulus on

an a*solute scale

E4a%$les T!er%istors strain "au"es etc0

(t!er%istor ,ill al,a)s read t!e a*solute te%$erature

Relatie sensor T!e sti%ulus is sensed relatie to a

fi4ed or aria*le reference0

E4a%$les T!er%ocou$le %easures t!e te%$erature

difference $ressure is often %easured relatie to

at%os$!eric $ressure0


7/60

7

20 Ot!er sc!e%es

Classification *) *road area of detection10Electric sensors

/0Ma"netic

0Electro%a"netic

20Acoustic50C!e%ical

80O$tical

90Heat Te%$erature

:0Mec!anical

;0Radiation

1


8/60

8

20 Ot!er sc!e%es (cont0

Classification *) $!)sical la,

10.!otoelectric/0Ma"neto electric

0T!er%oelectric

20.!otoconductie

50Ma"nitostrictie80Electrostrictie

90.!oto%a"netic

:0T!er%oelastic

;0T!er%o%a"netic1


9/60

9

20 Ot!er sc!e%es (cont0Classification *) s$ecifications

10Accurac)

/0Sensitiit)0Sta*ilit)

20Res$onse ti%e

50H)steresis

80>re3uenc) res$onse90In$ut (sti%ulus ran"e

:0Resolution

;0'inearit)

1


10/60

10

20 Ot!er sc!e%es (cont0Classification *) area of a$$lication

10Consu%er $roducts 1/0 Scientific

/0Militar) a$$lications

0Infrastructure

20Ener")

50Heat

80Manufacturin"

90Trans$ortation

:0Auto%otie

;0Aionic

1


11/60

11

Classification of transducers10 =ased on $rinci$le of transduction

(a T!er%o electric

(* Ma"neto resistie

(c Electro 6inetic

(d O$tical

/0 Actie & $assie

0 Analo" & di"ital20 Inerse transducer


12/60

12

.assie transducer #eice ,!ic! derie $o,er re3uired for

transduction fro% au4iliar) $o,er source - e4ternall) $o,ered

E4a%$le resistie inductie ca$acitie

?it!out $o,er t!e) ,ill not ,or6 Actie transducer

No e4tra $o,er re3uired to $roduce I@$

Self "eneratin" #ra, $o,er fro% in$ut a$$lied


13/60

13

Analo" transducer conert I@$ 3uantit) into an analo" o@$

Analo" o@$- a continuous fn0 Of ti%eE"0 Strain "au"e ' #T t!er%ocou$le

#i"ital transducer

Conerts I@$ into an electrical O@$ in t!e for% of $ulses

Inerse transducer

?!ic! conerts electrical si"nal to $!)sical 3uantit)


14/60

1405/03/16 09:05 AM


15/60

1505/03/16 09:05 AM


16/60

1605/03/16 09:05 AM


17/60

1705/03/16 09:05 AM


18/60

1805/03/16 09:05 AM


19/60

19


20/60

20


21/60

21

Inductie Transducers

T!ere is a ariet) of transducers ,!ose o$eration isinductie0

B >or %otion %easure%ent a$$lications a c!an"e in t!e

3uantit) to *e %easured %ust *e conerted into a c!an"e in

inductance (and t!en to olta"e usin" a circuit0

• ?e first reie, inductanceDD *riefl)0


22/60

22

Inductance

• A %a"netic field can *e isuali7ed *) lines of %a"netic

force0 T!e entire "rou$ of %a"netic field lines is called

%a"netic flu40

B Ma"netic field lines are $racticall) unaffected *)

non%a"netic %aterial suc! as air acuu% $a$er "lass,ood and $lastics0 Ho,eer ,!en a %a"netic su*stance

li6e iron is $laced in t!e field t!e %a"netic field lines

*eco%e concentrated0

B T!is a*ilit) of a su*stance to concentrate %a"netic flu4 iscalled $er%ea*ilit)0 A %a"netic field can *e created *) a

$er%anent %a"net or an electro%a"net ,!ic! is a loo$ed

coil of conductin" %aterial ,ound on a core %an) ti%es0


23/60

23

Inductance

T!e (self inductance ' is an indication of t!e a*ilit) of a

coil to o$$ose an) c!an"e in current flo,in" t!rou"! t!e

coil0 T!e inductance ' of a c)lindrical coil is "ien *)

?!ere ' is t!e inductance Henr) HF

G is t!e $er%ea*ilit) of t!e core H@%F

n is t!e nu%*er of turns of coil A is t!e cross sectional area of core %/F

l is t!e len"t! of core %F


24/60

24

Inductie transducers

Inductie transducers are t!ose in ,!ic! SE'>

IN#UCTANCE of a coil or t!e MUTUA' IN#UCTANCE

of a $air of coil is altered due to ariation in t!e

%easurand0 C!an"e in inductance ' is %easured0 T!e self inductance of a coil refers to t!e flu4 lin6a"e

,it!in t!e coil due to current in t!e sa%e coil0

Mutual inductance refers to t!e flu4 lin6a"es in a coil

due to current in ad+acent coil0


25/60

25


T!e self inductance of a coil refers to t!e flu4 lin6a"e

,it!in t!e coil due to current in t!e sa%e coil0


26/60

26


Mutual inductance refers to t!e flu4 lin6a"es in a coil

due to current in ad+acent coil0


27/60

27


• Consider a set of t,o coils s!arin" t!e sa%e core i0e0 a

transfor%er *asicall)0 Note t!at one of t!e coil ($ri%ar)coil is drien *) a $o,er source ,!ile t!e ot!er

(secondar) coil $roduces a olta"e induced fro% t!e

$ri%ar) coil0

B T!e olta"e on t!e secondar) coil de$ends on %utual

inductance *et,een t!e t,o coils0 If t!e core is %ade

%oa*le in res$onse to t!e dis$lace%ent of a tar"et o*+ect

t!e %utual inductance ,ill c!an"e resultin" in a olta"e

c!an"e in t!e secondar) coil0

• Usin" t!is $rinci$le t!e '#T and R#T ,or6s0


28/60

28


• In t!e %a"netic circuits reluctance is e3uialent to resistance

and de$ends on

Nu%*er of turns

Area of cross section of ,ire .er%ea*ilit) of t!e %ediu%

• Air !as %uc! lo,er $er%ea*ilit) t!an a ferro%a"netic

%aterial0

• Introducin" air "a$ is li6e introducin" !i"! resistance0


29/60

29


• In t!e %a"netic circuits reluctance is e3uialent to resistance

and de$ends on

Nu%*er of turns

Area of cross section of ,ire

.er%ea*ilit) of t!e %ediu%

• Air !as %uc! lo,er $er%ea*ilit) t!an a ferro%a"netic

%aterial0

• Introducin" air "a$ is li6e introducin" !i"! resistance0


30/60

30


• Air Cored Coils

Can *e o$erated at !i"!er

fre3uencies *ecause t!ereare no edd) current losses

in air core0


31/60

31


• Iron cored coils

Inductance de$ends on

t!e alue of current0

At !i"! fre3uencies

edd) current losses are

!i"!0

Si7e %uc! s%aller t!an

air cored0


32/60

32

Linear Variable-Differential Transformer(LVDT)

• T!e t,o secondar) coils are connected in t!e o$$osite

$!ase0• ?!en t!e core is in t!e %iddle t!ere is no out$ut olta"e0

• Moin" t!e core fro% t!e central $osition un*alances t!esecondar)Js deelo$in" an out$ut0


33/60

33

Linear Variable-Differential Transformer(LVDT)

Applications: To %easure linear dis$lace%ent e0"0 for%easurin" tu*e len"t!s in a steel $lant a$$lied in linearsero%ec!anis%s etc0


34/60

'inear aria*le-#ifferential

Transfor%er ('#T

-x

Vo=V1-V2

Vi

V1 V2

V1 > V2 Vi

Vo

'#Ts are deices to %easure

dis$lace%ent *) %odif)in" s$atialdistri*ution of an alternatin"

%a"netic field0

Oscillating excitation voltage-5 !" to 25 #!"


35/60

'inear aria*le-#ifferential Transfor%er

('#T

$=

Vo=V1-V2

Vi

V1 V2

V2 = V1

Vi

Vo


36/60

'inear aria*le-#ifferential Transfor%er

('#T

%x

Vo=V1-V2

Vi

V1 V2

V2 > V1

Vi

Vo

&o' te irection of is*lacement can be etermine from te relative *ase of te

signal+


37/60

Linear Variable Diferential

Trans!r"er #LVDT$


38/60


39/60

• T!e s$an ran"es fro%


40/60

40

A rotar) aria*le differential transfor%er(R#T

A rotar) aria*le differential transfor%er (R#T isfor %easurin" an"ular dis$lace%ents and

o$erates in t!e sa%e %anner as a '#T0


41/60

, ca*acitor is an electrical com*onent ic

essentiall. consists of to *lates se*arate

b. an ins/lator+Te *ro*ert. of a ca*acitor to store an

electric carge en its *lates are at ifferent

*otential is referre to as ca*acitance+

CA.ACITIE TRANS#UCERS

05/03/16 09:05 AM

0f te ca*acitance is large more carge is


42/60

d

AC

r <εε

=

+

0f te ca*acitance is large' more carge is

neee to establis a given voltage ifference+

Te ca*acitance beteen to *arallel metallic

*lates of area

×= −

m

F 1/<

1


43/60

05/03/16 09:05 AM


44/60

44


45/60

45


46/60

05/03/16 09:05 AM


47/60

05/03/16 09:05 AM


48/60

48


49/60

49


50/60

50


51/60

51

10 Circular %otion %easure%ent• Aaila*le in arious si7es and resolutions

• Used in co%$uter %ouse rollers

/0 Co%$onents• Circular dis6 ,it! slots

• #iode and $!oto sensor

• #i"ital circuitr) to $rocess $ulses

Incre%ental O$tical Encoders


52/60

%!r&in' (rin)i(le

Ligt so/rce' ioe

*oto sensor

•1 f/ll *inc is e/ivalent to one f/ll c.clemae b. te trans*arent an o*a/e

inos

05/03/16 09:05 AM &al*an

t,


53/60

+)!nt,.

oto sensor

ioe

oto sensor

ioe

•3otating is#

blocking ligt

•oto sensor as a

low logic o/t*/t

•3otating is#

allowing ligt tro/g

•oto sensor as a

high logic o/t*/t

•4ontin/o/s train of */lses forme as te *oto sensor traverses

beteen logic ig an logic lo in res*onse to te rotation of te is#

Logical Logical 1

05/03/16 09:05 AM &al*an


54/60

10 O$tical incre%ental encoder is used to %easure

10 .osition

/0 elocit)

0 #irection of rotation/0 No need for ot!er A@# circuits

10 Out$uts can *e directl) fed to

%icro$rocessor@%icrocontroller

05/03/16 09:05 AM &al*an

Absolute Optical Encoder working


55/60

Absolute Optical Encoder working

• A disc or a $late containin"o$a3ue and trans$arent se"%ents $asses *et,een a li"!t source(suc! an 'E# and detector tointerru$t a li"!t *ea%0

• T!e electronic si"nals t!at are"enerated are t!en fed into t!econtroller ,!ere $osition and

elocit) infor%ation iscalculated *ased u$on t!e si"nalsreceied

05/03/16 09:05 AM &al*an


56/60

56


57/60

57

A*solute O$tical Encoder


58/60

A*solute O$tical Encoder

• In t!e fi" ,ord si7e of data is 2*its0

• Outer%ost Ele%ent is 'S=0• Inner%ost Ele%ent is MS=0• T!e An"ular $osition is "ien as8


59/60

'inear Encoder Codes


60/60

Reca$

To$ics dealt ,it! in t!is class• Classification of transducers• #is$lace%ent transducers

• resistance *ased transducers $otentio%eter

• Inductie transducers '#T• Ca$acitie transducers• Non contact $osition sensors O$tical Encoders

Mechatronics_Session 3_ Position Sensors

Documents

Transcript of Mechatronics_Session 3_ Position Sensors