chapter 2 electrical power sec 2

8/20/2019 Chapter 2 Electrical Power Sec 2

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SENSORS ,SIGNAL PROCESSING

& DATA PRESENTATION


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Transducers /sensors

Takes input information about the phs!ca"

#ar!ab"e to be $easured and convert it into a

suitable form

S.No Physical variable Output

1 Change intemperature

Change inelectricalvoltage

2 Pressure Resistance3 Flow of liquid Capacitanc

e

4 Level of liquid Inductance

!isplacement


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"#$IC %&P'$

• Active transducer (does not requiree)ternal stimulation to wor*+

Examples( %hermocouples,Pie-oelectric accelerometers+

• Passive transducer (requirese)ternal suppl. to wor*+

Examples( %hermistor, Resistancetemperature detector,$traingauges+


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Tpes o% transducers based on app"!cat!ons

D!sp"ace$ent sensor

Speed sensor

"u!d %"o' sensor

"u!d pressure sensor

L!(u!d "e#e" sensor

Te$perature sensor


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!isplacement sensors

• %.pes (

1.Contact type( have direct contactwith the o/0ect

2.Non contact type ( use laser/eam or ultrasonic /eam fordetection+


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)* Potent!o$eter

Supply voltage = VS +o"ts-*

Output voltage = V0 = V

S x (R

! " R# +o"ts- .bet'een ter$!na"s & )0*

R = $otal Resistance.

R !

= Resistance bet%een terminals ! & .

1ence, output voltage !s d!rect" proport!ona" to the input linear 'isplacement of the sli'er.

)*N+, -N -N,*R /-SP*,,N$ 1 )*N+, -N VO$*+,*


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* Stra!n 2au2e e"e$ent

S$R*-N = 2 = (hange in ength# " (Original ength#

esistance change is directly proportional to strain

+3 is constant of proportionality terme' as gauge factor*

3eta" '!re stra!n 2au2e has 2au2e %actors o% order4*5*

∆R = R !.

Strain +auge 1 stretche' 1 Resistance increases.

Strain +auge 1 compresse' 1 Resistance 'ecreases.


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L!near #ar!ab"e d!%%erent!a" trans%or$er

' PRI#R& CIL and %56 $'C!#R&CIL$,' CR'


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E3 !nduced !n secondar co!" )6E) E3 !nduced !n secondar co!" 6E

Net output #o"ta2e 6 E)4E

3AGNETIC CORE7 -//,4,N$,R POS-$-ON , ,=,!.

N,$ O5P5$ VO$*+, o% secondar co!"s 6 (,4,!# = 0 Volts.

3AGNETIC CORE 1 5P POS-$-ON -N,*R /-SP*,N$6 , 7 ,!.

N,$ O5P5$ VO$*+, o% secondar co!"s = (,4,!# = (8V,#.

3AGNETIC CORE 1/O9N POS-$-ON -N,*R /-SP*,N$6 ,! ",N,$ O5P5$ VO$*+, o% secondar co!"s = (,4,!# = (4V,#.

inear variable 'ifferential transformer


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$peed sensor

ptical method7linear speed8

• %achogenerator7#ngular speed8

C#ANE $N AN%&AR 'PEE() C#ANE $N *+&,AE'peed = distance -time


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Fluid pressure sensor


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Fluid 9ow sensor

• Rotameter

• %ur/ine meter


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Liquid level sensor

• Potentiometer 9oatgauge

• Load cell

CHANGE IN LEVEL → CHANGE IN WEIGHT

→ CHANGE IN LOAD

→CHANGE IN RESISTANCE OF

STRAIN GAUGE


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%emperature sensors

sense temperature and gives a proportional output+ %he output ma. /e a resistance change or voltage or current signal

,ypes o temperature sensors

1+ :lass thermometer

2+ Resistance thermometer 7R%! 83+ %hermistor

4+ %hermocouples


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1+:lass thermometer

ercur. ( ;3 o C to > o C

#lcohol ( ;?> o C to o CPentane ( ;2>> o C to o C

!isadvantages Fragile 7easil.

/ro*en8 $low reacting

#dvantages ( Cheap Reasona/le

accurac.

Asa/le range B ;3 o C to > o C

#ccurac. B 1 D

&i/uid inside the tu0eexpands hen it sense

temperature


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*Res!stance te$perature detector

-)+ t R R ot α +=

metal ire used are

→ Resistance of metal wie at tem!eat"e t# $%C&

→ Resistance of metal wie at ' $%C&

→ Constant ( Tem!eat"e Coefficient of Resistance)

PL#%IA, ICE'L, R CPP'R #LL&

$ense the temperature and gives a resistance change as output

Resistance varies linearl. with temperature


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$:P, $,P,R*$5R,O,;;--,N$ 4 < (" #

R*N+,

P*$-N5 0.00>? " 4!00 to @A0 N-B, 0.00CD " 4@0 to >00

OPP,R 0.00>@ " 4!00 v to !A0

CHANGE IN TE*+ERATURE → CHANGE IN RESISTANCE


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3+%hermistor• semiconductor temperature sensor made

from mixture o metal oxides.

• etal;)ides used( CRIA, C"#L%, IR,#:#'$' G ICE'L+

an,e( #-.' /C to 01.' /C with

acc"ac2 ( ')34)


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4+%hermocouple

When two different metals are joined together, a potential

difference occurs across the junction. The potential differenceacross the junction 5e!en5s on the two metals used and the

temperature of the junction

"oth at same temperature ;;;;;no '++Fone 6"nction $Col5 7"nction& is

8e!t at ' $%C&

E*F depends on the tem!eat"e

$%C& of ot9e 6"nction $Hot

7"nction&)

,


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E

S,NS-$-V-$:EV"

R*N+, ( # *$,R-* $:P,

89 0 to ?@0 )RO,4ONS$*N$*N ,

:9 4@0 to DC0 -RON4ONS$*N$*N F

;) 4@0 to !C0 ),O,4*5, B

8 0 to DA0 P*$-N54P*$-N5"R)O/-5 >G

R

;9 4@0to >D0 OPP,R4ONS$*N$*N $

TA:LE#THER*OCOU+LES

E4 54 6 7 ,

3 Cheap4&ess 'ta0le4'mall &ie4

Accuracy=1.8 to 9.8

:.

Rore 'ta0le&ong3lie4;ast Response4

Accuracy = 1:.


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$ignal processor conditioner classiJcations

• %a*es signal from the sensor and convert itinto a form suita/le for displa. ortransmission to other places+

Examples

• $mall signal K ampliJed K"igger signal+

• Resistance change K Current or oltage

change+• #nalogue signal to !igital signal+


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$ignal processore)amples (

1+Resistance to voltage converter potential divider circuits+

When the esistance of t9e

T9emiste $RT& c9an,es the o"t!"t

;olta,e of +otential 5i;i5e c9an,es)

'ource *oltage = *'


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5heatstone /ridge converter

In /alanced condition , output voltage is -ero+if R1 changes ,it /ecomes un/alanced +

The voltage drop in across AB =

The voltage drop in across A =

o"t!"t ;olta,e ( VO is!


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#nalog to digital converter

process o converting theanalogue signals rom thesensors to digital orm is calledAnalogue to (igital Conversion


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A(C stagesB

$tage 1;;;;;; sampling$tage 2+;;;;;; #nalog todigital

conversion

The minim"m c9an,e in in!"t that can "e 5etecte5 #T9e Resol"tion$,

.

Resol"tion


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Pro/lems related to #!C

1+ 5ith an #! converter having a wordlength of 1> /its and the ma)imumanalogue signal input range 1>, what

will /e the resolutionN2+ # thermocouple gives an output of >+4mv

for each degree change in temperature+5hat will /e the word length required

when its output passes through an #! iftemperatures from > to 2>>OC are to /emeasured with a resolution of >+OCN


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#!C techniques

• $ingle slope #!C

• !ual slope #!C

•$uccessive appro)imation #!C• Flash t.pe #!C


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!igital to analog conversion

1+ "inar. weighted resistor !#C

2+ R2R ladder !#C


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Pro/lems related to !#C

1+ # microprocessor gives an output ofan ?;/it word+ %his is fed through an?;/it !# converter to a control

valve, which requires =+> to /efull. open+ If the full. open state isto /e indicated /. the output of the

digital word 7111111118 what will /ethe change in output to the valvewhen there is a change of 1 /itN


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• %he output voltage will /e dividedinto 2intervals+

• utput B = +

• a change of 1/it is a change in theoutput voltage of =+> B>+>23 +

chapter 2 electrical power sec 2

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