Instruments-flow and Temperature Sensors

8/16/2019 Instruments-flow and Temperature Sensors

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SENSORS

(FLOW AND TEMPERATURE)


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• Most Common industrial sensors: – Pressure

– Flo

– Tem!erature – Le"el


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FLOW SENSORS


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Flo

• En#ineerin# units o$

– "olumetri% &orate: $t's m'*r #!m

– Mass &orate: +#*r l,min

– -elo%it.: ms $ts

• Flo is usuall. measured indire%tl. ,. /rstmeasurin# a di0erential !ressure or t*e&uid "elo%it.1 T*is measurement is t*enrelated to t*e "olume rate ele%troni%all.1


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Ori/%e meter

2 &at dis+ it* a ma%*ined *ole

– T*e dis+ is inserted in t*e !ro%ess line

!er!endi%ular to t*e &uid motion it* t*e intentionto !rodu%e a !ressure dro! 3P

Flo sensor


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• 4 T*e ta! u!stream t*e ori/%e is %alled t*e *i#*!ressure ta!

• 4 T*e ta! donstream t*e ori/%e is %alled t*e lo!ressure ta!

• 4 a di0erential !ressure sensor is used to measure t*e!ressure dro! a%ross t*e ori/%e

• 4 t*e out!ut si#nal $rom t*e ori/%e is t*e !ressure dro!not t*e &o


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• 4 T*e !ressure dro! a%ross t*e ori/%e isa nonlinear $un%tion o$ t*e "olumetri%&o rate t*rou#* t*e ori/%e

• W*ere

• $ 5 "olumetri% &o rate• 3 po 5!ressure dro! %ross ori/%e

• Ao 5area o$ ori/%e

• Co 5ori/%e %oe6%ient• ρ 5 &uid densit.

• Β 5 dimensionless ratio o$ t*e diameter o$ t*eori/%e d to t*e diameter o$ t*e !i!e D


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T*e e7uation deri"es $rom t*e a!!li%ation and ame%*ani%al ener#. ,alan%e (8ernoulli)1

T*e e7uation s*os t*at t*e !ressure dro! isrelated to t*e s7uare o$ t*e "olumetri% &o rate

3!o 9f

;nstall a s7uare root e


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• Most ori/%e diameter "ar. ,eteen => to ?@ o$

t*e !i!e diameter >1= B B >1?@

• t*e !ressure dro! %ross t*e ori/%e is measuredit* ta!s:

– Flan#e ta!s 4 line ta!s

– Radius ta!s 4 "ena %ontra%ta ta!s

– Corner ta!s


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4 Se"eral %ondition ma. !re"ent use o$ ori/%esensor:

4 Not enou#* a"aila,le !ressure dro! e1# #ra"it. &o

4 Flo o$ %orrosi"e &uid4 Fluids it* sus!ended solids 2!lu# t*e ori/%e

4 Fluid t*at %lose to t*eir saturated "a!or !ressure 2ma. &as* *en su,e%ted to a dro! in !ressure


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• Ma#neti% &o

– O!eratin# !rin%i!le o$ t*is element is Farada.s la – A %ondu%ti"e material (a &uid e1# ater t*at

%ontains ion) mo"es at ri#*t an#les t*rou#* ama#neti% /eld and indu%es a "olta#e

– T*e "olta#e %reated is !ro!ortional to t*e intensit.o$ t*e ma#neti% /eld and t*e "elo%it. o$ t*e &uid1

– ;$ t*e intensit. o$ t*e ma#neti% /eld is %onstantt*en t*e "olta#e is !ro!ortional to t*e "elo%it. o$t*e &uid


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• t*e "elo%it. measured is t*e a"era#e "elo%it.

• t*is sensor %an ,e used $or tur,ulent andlaminar &o

• T*is sensor is suita,le to measure #ra"it. &oslurr. &o and &o o$ &uids %lose to t*eir"a!or &o

• oe"er t*e &uid must *a" a minimumre7uired %ondu%ti"it. o$ a,out => Go*m%m: 1

Not suita,le $or #ases and *.dro%ar,on li7uids(non%ondu%ti"e)1


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• Tur,ine meter

• 4 most a%%urate and %ommer%iall. a"aila,le &ometers1• 4 t*e or+in# !rin%i!le : %onsists o$ a rotor t*at t*e &uid

"elo%it. %auses to s!in1

• 4t*e rotation o$ t*e ,lades is dete%ted ,. a ma#neti%!i%+u! %oil t*at emits !ulses t*e $re7uen%. o$ *i%* is

!ro!ortional to t*e "olumetri% &o rate1• 4 !ulse is e7uall. %on"erted to a H to > mA

• 4!ro,lem: ,earin# re7uire %lean &uids it* somelu,ri%atin# !ro!erties


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Coriolis e0e%t• 4 mass &orate measurement o$

li7uids

T* C i li & t t i i l i , d


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T*e Coriolis mass &o meter measurement !rin%i!le is ,asedon NetonIs Se%ond La o$ Motion: For%e 5 Mass <A%%eleration (F 5 M < A)1

;nside t*e meter &o is di"erted into to !arallel tu,es t*at"i,rate at *i#* $re7uen%. "ia an ele%troma#neti% dri"e %oil1

T*e tu,e loo!s *a"e "aried s*a!es sometimes $or%in# t*e&uid t*rou#* se"eral J>K turns ,e$ore reoinin# t*e &o line1

U!ard and donard $or%es are e


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• t*e measurement a%%ura%. usin# t*is e0e%t isuna0e%ted ,. %*an#es in t*e &uids tem!eraturedensit. !ressure "is%osit. or ,. %*an#es in"elo%it. !ro/le1

• ,e%ause t*e measurement ,ased on mass &oon%e t*e %ali,ration o$ t*e &ometer *as ,eenesta,lis*ed it* a %on"entional &uid as ater ita!!lied e7uall. to ot*er &uids1

• ma1=@


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TEMPERATURE SENSORS


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Tem!erature sensor

• one o$ t*e most $re7uent measured"aria,le in t*e !ro%ess industries1

• "er. $e !*.si%al !*enomena are nota0e%ted ,. tem!erature

• tem!erature is also o$ten used toin$er ot*er !ro%ess "aria,les1

• En#ineerin# units: oC oF R


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o!u ar sensors ortem!erature measurement

• E

– Solid4e

– Filled4s.stem t*ermometers (!ressure t*ermometers)• as4/lled

• Li7uid4/lled

• -a!or4/lled

• Resistan%e4sensiti"e de"i%es – Resistan%e t*ermometers

– T*ermistor elements

• T*ermo%ou!les


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• Li7uid in #lass termometer

• 4 indi%ate tem!erature %*an#e %aused ,. di0eren%e,eteen t*e tem!erature %oe6%ient o$ e

#lass and t*e li7uid em!lo.ed1• 4 mer%ur. and al%o*ol are t*e most idel. used li7uids

• 4 mer%ur. in #lass t*ermometer made $rom ordinar.#lass are use$ul ,eteen 4'@ and >> oF

• 4 loer limit :due to $reein# !oint o$ mer%ur.• 4 u!!er limit: due to ,oilin# !oint o$ mer%ur.

• 4 u!!er limit %an ,e e


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• For tem!erature ,elo t*e $reein# !ointo$ mer%ur. (4'Q oF) anot*er li7uid must ,eem!lo.ed1

• Al%o*ol is idel. used $or tem!eraturesdon 4Q> oF

• Pentane $or tem!eratures don 4>> oF

• Toluene $or tem!eratures don 4'> o

F

meta % str !


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meta % str !t*ermometer

• 4t*e or+in# !rin%i!le ,ased on $a%tst*at:

– t*e metal e

– t*e e

• T*e tem!erature sensiti"e element is a

%om!osite o$ to di0erent metals$astened to#et*er into a stri!1

• One metal *as a *i#* t*ermal e

• One *as lo t*ermal e


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• 4 %ommon %om,ination – Ni%+el4iron *i%* *as lo %oe6%ient and anot*er

ni+el4iron allo. it* *i#* %oe6%ient

–Usuall. t*e e

– T*e s!iral is atta%*ed to a dial t*at indi%atestem!erature


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Filled s.stem t*ermometer

• Tem!erature "ariations %ause t*ee

• T*e e

sensed ,. 8ourdon s!rin# andtransmitted to an indi%ator


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Resistan%e Tem!eratureDe"i%es (RTD)

• or+in# !rin%i!le : t*e ele%tri%al resistan%eo$ !ure metals in%reases it* in%rease intem!erature1

T R• T*e RTDs are %*ara%teried ,. a linear

%*an#e in resistan%e it* res!e%t totem!erature1

• A *eatstone ,rid#e is usuall. to measuret*e resistan%e1

• RTD: metal i1e Pt Ni Co!!er


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• Relation ,eteen resistan%e it*tem!erature

• Rt ()5Ro (=t(oC)t:)

• Measurement:

• Rt ()5Ro (=t(oC))


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T*ermistor elements

• Dete%t "er. sensiti"e tem!erature %*an#es1

• Made o$ sintered %om,ination o$

– Cerami% material

– Semi%ondu%tin# metalli% o


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T*ermo%ou!le

– Dis%o"ered ,. T1V1 Seed,a%+

– Seed,a%+ states t*at an ele%tri% %urrent&os in a %ir%uit o$ to dissimilar metals

i$ t*e to un%tions are at di0erenttem!eratures1

– Prin%i!le o$ measurement: measuret*ermo%ou!le "olta#es m- to #ettem!erature

• - (T!4Tr) – is seed,a%+ %oe6%ient in X-oC or m-oC


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• Tr must ,e +non and %onstant1 Normall. Tr5>oC

• Termo%ou!le : – C*romel4 alumel – ;ron4%onstantan

– Co!!er4%onstantan

Instruments-flow and Temperature Sensors

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