Sensing, Computing, Actuating

Transcription

1 Sensing, Computing, Actuating Sande Stuij Depatment of Electical Engineeing Electonic Systems

2 SENSING TEMPEATUE, SELF-HEATING (Chapte.,., 5.)

3 3 Engine coolant tempeatue senso

4 Applications dischage ai tempeatue (NTC themisto) fuel tempeatue (NTC themisto) actie in-ca tempeatue (NTC themisto) outside ai tempeatue (NTC themisto) cylinde head tempeatue (themocouple) intae ai tempeatue (NTC themisto) ehaust gas ecycle Tempeatue (TD)

5 5 Applications

6 6 Tempeatue sensos placement ecitation physical effect mateial themal senso contact passie themal epansion metal bimetal contact actie esistie effect metal TD contact actie esistie effect semiconducto silicon esistie contact actie esistie effect polyme o ceamic themisto contact passie themoelectic effect conducto themocouple contact actie PN junction semiconducto non-contact passie pyoelectic effect pyoelectic pyoelectic non-contact actie ultasound piezoelectic acoustic thee ae many othe classification citeia: constuction, lineaity, efeence point,...

7 7 Tempeatue sensos tempeatue sensos ae deceptiely simple esistie senso a conducto connected to a oltage souce themocouple any two dissimila mateials welded togethe at one end and connected to a mico-oltmete tempeatue sensos can be used to measue othe quantities, e.g., S e n s o t y p e Quantity Acceleation / ibation Flow ate / Point elocity Foce esistie Mass-sping + stain gage Themisto Stain gage Self-geneating Mass-sping + piezoelectic senso Themal tanspot + themocouple Piezoelectic senso comple sensos fo adiation, pessue, position, leel, and chemical eactions can be constucted on the basis of tempeatue o tempeatue-diffeence sensos

8 8 Tempeatue sensos placement ecitation physical effect mateial themal senso contact passie themal epansion metal bimetal contact actie esistie effect metal TD contact actie esistie effect semiconducto silicon esistie contact actie esistie effect polyme o ceamic themisto contact passie themoelectic effect conducto themocouple contact actie PN junction semiconducto non-contact passie pyoelectic effect pyoelectic pyoelectic non-contact actie ultasound - acoustic

9 9 esistance esistance of a mateial is defined as i l esistance depends on geometical factos a length of wie (l) coss-sectional aea (a) esistance depends on tempeatue numbe of fee electons (n) mean time between collisions (τ) l a m l ne a changing dimensions affect esistance (piezoesistie effect) changing tempeatue affect esistance (themoesistie effect) esistie senso can be used to sense changes in these quantities only one quantity should be measued othe quantity should be ept constant o coected fo

10 Themoesistie effect specific esistiity of a mateial m ne tempeatue dependency though numbe of fee electons (n) in semiconductos NTC behaio: T n ρ mean time between collisions (τ) in conductos PTC behaio: T τ ρ semiconducto (silicon) conducto (wolfam)

11 esistance tempeatue detectos (TDs) TD is a tempeatue senso build fom metal (conducto) specific esistiity of metal depends on time between collisions positie tempeatue coefficient (PTC) inceasing tempeatue leads to inceasing esistiity elation between tempeatue and esistance n T T T T... T T T ] [ n T efeence tempeatue PT TD esistance at T coefficients can be found using calibation eample PT TD α /K, α /K, α /K 3 almost linea elation between tempeatue and esistance

12 Tempeatue coefficient of esistance assume linea tempeatue/esistance elation fo an TD senso T T ] [ T α T is called the tempeatue coefficient of esistance (TC) T T ( T T ) T TC indicates elatie change in esistance pe unit tempeatue (between tempeatue T and a efeence tempeatue T ) TC is often called elatie sensitiity PTC deices: TC deceases when tempeatue incease (why?) factional incease in esistance deceases with inceasing tempeatue limits usability of PTC deices at highe tempeatues

13 3 Tempeatue coefficient of esistance eample PT senso = Ω, α =.389 (Ω/Ω)/K at C, T = [+ α (T-T )] what is the sensitiity of this senso? what ae TC at 5 C and 5 C? (use C as efeence) A).389 Ω/K,.389 /K,.389 /K B).389 Ω/K,.355 /K,.36 /K C).389 Ω/K,.36 /K,.355 /K D).355 Ω/K,.355 /K,.36 /K

14 Tempeatue coefficient of esistance eample PT senso = Ω, α =.389 (Ω/Ω)/K at C, T = [+ α (T-T )] what is the sensitiity of this senso? sensitiity is the slope of the esistance-tempeatue cue esistance-tempeatue cue is staight line sensitiity S.389( / ) / K.389 what ae TC at 5 C and 5 C? (use C as efeence) TC (at 5 C) [ (5 C C)] (5 C).389( / ) / K.389 / K(5 C).355( / ) / K / K TC (at 5 C) (5 5 ) / o C).36( / K TC deceases fo inceasing tempeatue

15 5 Self-heating in TDs cuent must be passed though senso to measue esistance powe will be dissipated in the TD ceating heat (self-heating) P D = I I effect of self-heating educed by themal dissipation to enionment heat dissipation facto δ (W/K) depends on suounding fluid elocity of the fluid tempeatue eo gien by PD I T self-heating eo can be limited by dimensioning the cuent I

16 6 Self-heating in TDs eample PT senso (T)= [+ α (T-T )] = Ω, α =.389 (Ω/Ω)/K at C δ = 6mW/K (in ai), δ = mw/k (in still wate) senso used in ange [ C, + C] what is the maimal cuent though the senso to eep the self-heating eo below. C when emeged in ai? I poide a numeical answe

17 7 Self-heating in TDs eample PT senso (T)= [+ α (T-T )] = Ω, α =.389 (Ω/Ω)/K at C δ = 6mW/K (in ai), δ = mw/k (in still wate) senso used in ange [ C, + C] what is the maimal cuent though the senso to eep the self-heating eo below. C when emeged in ai? I tempeatue PT aboe enionment T PD I self-heating eo maimal when esistance is maimal maimal self-heating at + C esistance ( C) = Ω[ +.389/ C C] = 39 Ω

18 8 Self-heating in TDs eample PT senso (T)= [+ α (T-T )] = Ω, α =.389 (Ω/Ω)/K at C δ = 6mW/K (in ai), δ = mw/k (in still wate) senso used in ange [ C, + C] what is the maimal cuent though the senso to eep the self-heating eo below. C when emeged in ai? I tempeatue PT aboe enionment T PD I elation between cuent and tempeatue I T ma cuent in ai ma cuent in wate I I o (. C) (.6W / K).mA 39 o (. C) (.W / K) 8.5mA 39

19 9 Self-heating in TDs eample PT senso (T)= [+ α (T-T )] = Ω, α =.389 (Ω/Ω)/K at C senso used in ange [ C, + C] δ = 6 mw/k (in ai), = 5, = Ω what is the maimal self-heating eo (esolution) of this senso? tempeatue PT aboe enionment T D cuent I depends on esistance and tempeatue T I T T maimal cuent when T = C, but minimal esistance tempeatue eo depends on powe dissipation maimal powe dissipation when T = C maimal self-heating eo occus when T = C o P I

20 Self-heating in TDs eample PT senso (T)= [+ α (T-T )] = Ω, α =.389 (Ω/Ω)/K at C senso used in ange [ C, + C] δ = 6 mw/k (in ai), = 5, = Ω what is the maimal self-heating eo (esolution) of this senso? tempeatue PT aboe enionment T D maimal self-heating eo occus when T = C o P I T 39 C T.5 C dominates when <<

21 Lead-wie esistance lead wies ae not pefect conductos (lead-wie esistance) esistance of the wies will affect measued oltage senso PT PT L L i out inteface cicuit tempeatue eo due to lead-wie esistance when inteface cicuit poides constant cuent i PT L L T S T S eample PT PT has esistance of 7.8Ω at C and S =.389Ω/K assume L = Ω ΔT = +5. C inteface cicuit measues tempeatue of 5 C measued tempeatue 5% aboe actual tempeatue L

22 Lead-wie esistance lead wies ae not pefect conductos (lead-wie esistance) esistance of the wies will affect measued oltage senso PT PT L L i out inteface cicuit out PT L i lead wie esistance can be cancelled with -wie sensing method inteface cicuit has high impedance senso L i L i= PT PT L i= out inteface cicuit cuent souce out PT L -wie sensing method equies stable cuent souce 6-wie sensing method can be used with stable oltage souce

23 3 Summay - esistie tempeatue detectos (TDs) tempeatue-esistance elation α T is called the tempeatue coefficient of esistance (TC) T dt dt T T ( T T ) TC indicates elatie change in esistance pe unit tempeatue (between two efeence tempeatues) TC is not equal to the sensitiity T T T ] [ T seeal eo souces influencing accuacy lead-wie esistance ( L ) self-heating ( T ) non-lineaity ( T ) senso loading effect ( m ) T PT L L inteface cicuit m

24 Inteface cicuits inteface cicuits can be used to incease senso sensitiity cancel lead-wie esistance lineaization of the senso output limit self-heating compensate fo eo souces (e.g. stain o tempeatue) set output oltage at efeence point amplify senso output fo use with AD-conete out

25 5 ESISTIE SENSOS (Ch.8)

26 6 esistie sensos esistance of esistie senso f() factional change in esistance (with f() = ) esistance of linea esistie senso ange of depends on type of senso [-, ] linea potentiomete [, ] TDs [.,.] stain gauges [, ] NTC themistos f ( [, ] switching PTC themistos ) equiements on signal conditiones fo esistie sensos electic oltage o cuent must be applied supply and output oltage/cuent ae limited by self-heating

27 7 esistie sensos cuent ecitation senso dien by cuent souce deflection measuement with cuent souce feedbac loop enfoces constant cuent I output of a linea senso o I choose = then output consists of offset and (small) fluctuation aound offset o I + - o

28 8 esistie sensos cuent ecitation eample cicuit fo tempeatue measuement [ C, C] measue tempeatue with. C esolution (self-heating <. C) PT senso ( =Ω and α=.389ω/ω/k at C) dissipation facto δ = mw/k in.m/s wate efeence oltage = 5 what esistance should hae to get a sensitiity of m/ C? poide a numeical answe I + - o

29 9 esistie sensos cuent ecitation eample cicuit fo tempeatue measuement [ C, C] measue tempeatue with. C esolution (self-heating <. C) PT senso ( =Ω and α=.389ω/ω/k at C) dissipation facto δ = mw/k in.m/s wate efeence oltage = 5 what esistance should hae to get a sensitiity of m/ C? tempeatue esolution limited by self-heating I T. C maimal dissipation at C, condition is thus (. C) 38.9 T T.389C 38.9 (mw / K) ( I + - C) o

30 3 esistie sensos cuent ecitation eample cicuit fo tempeatue measuement [ C, C] measue tempeatue with. C esolution (self-heating <. C) PT senso ( =Ω and α=.389ω/ω/k at C) dissipation facto δ = mw/k in.m/s wate efeence oltage = 5 what esistance should hae to get a sensitiity of m/ C? output oltage of the senso o T to get sensitiity of m/ C, should be I + - o S d dt o (5 )()(.389 / K) 95 S m / K senso output has also an offset (output not at C) 7. 8 offset 77m

31 3 Inteface cicuits esistance of linea esistie senso: () = (+) ange of depends on type of senso equiements on signal conditiones fo esistie sensos electic oltage o cuent must be applied supply and output oltage/cuent ae limited by self-heating oltage ecitation when does maimal self-heating eo occu? when is sensitiity maimal? when is non-lineaity eo minimized? o o

32 3 oltage diide self-heating eo senso dien by oltage souce senso: load esistance: when does maimal self-heating eo occu? powe consumption by senso maimal powe consumption occus when self-heating eo is maimal when = powe consumption is then equal to o P d dp P

33 33 oltage diide self-heating eo eample dimension oltage diide fo tempeatue measuement measue tempeatue fom C to C PT senso ( =Ω and α=.389ω/ω/k at C) maimal powe dissipation in senso is mw oltage souce = 5 what esistance must be used fo this oltage diide? poide a numeical answe o

34 3 oltage diide self-heating eo eample dimension oltage diide fo tempeatue measuement measue tempeatue fom C to C PT senso ( =Ω and α=.389ω/ω/k at C) maimal powe dissipation in senso is mw oltage souce = 5 what esistance must be used fo this oltage diide? powe dissipation in senso mw o maimal dissipation when = mw.w 5.W 6.5 senso ange is fom Ω to 39Ω always <, thus powe dissipation always below limit

35 35 oltage diide lineaity measue factional change in esistance senso: = (+) load esistance: = o output oltage of the cicuit o ( ) ( ) esponse becomes linea when >> (i.e. >> +)

36 36 oltage diide lineaity o / =. o = = = inceasing is good fo lineaity, but what about sensitiity?

37 37 oltage diide sensitiity measue factional change in esistance senso: = (+) load esistance: = sensitiity maimal sensitiity maimal sensitiity eached when = same situation as when self-heating eo is maimal maimal tansfe of powe (at = ) leads to maimal sensitiity and maimal self-heating d d S o ) ( ) ( ) ( ) ( d d d ds ) ( d d ) ( ) ( ) ( ) ( 3 o ) ( ) '( ) ( ) ( ) '( ) ( ) ( h h j h j h j d d use quotient ule

38 38 oltage diide sensitiity and lineaity S o = =. = = fo many sensos < sensitiity lagest fo = sensitiity may be consideed constant if maimal alue of <<

39 39 oltage diide output oltage maimal sensitiity when = output oltage o o offset oltage pesent in output

40 BIDGE CICUITS (Chapte.)

41 oltage diide disadantages of oltage diides may hae offset oltage at desied efeence point (e.g. tempeatue) o Wheatstone bidge offset oltage can be emoed at desied efeence tempeatue sign of output indicates diection of change with espect to efeence point (e.g. tempeatue) o 3 = (+)

42 Wheatstone bidge balance measuement balance o null measuement method adjusted till o = balance condition o 3 3 adantages of null measuement method insensitie to fluctuations senso may hae non-linea esistance-input elation fast auto balancing method fo is equied o 3 = (+)

43 3 Wheatstone bidge balance measuement ma input wod/output cuent of DAC I o ma () () I o DAC outputs two cuent souces I o cuent coesponding to digital input I o cuent coesponding to complement of digital input bidge imbalance eceeding compaato theshold changes counte change in counte alue change in cuent change in oltages on one am the oltage inceases on othe am the oltage deceases pocess of changing counte continues till balance is estoed

44 Wheatstone bidge deflection measuement deflection measuement method measue oltage diffeence on bidge ams measue cuent though a detecto between both ams deflection measuement is much faste than null measuement bidge output oltage 3 o 3 assume bidge balanced ( o = ) when = bidge is then balanced when what is o in tems of, and? o 3 = (+)

45 5 Wheatstone bidge deflection measuement bidge output oltage in tems of,, and o ) )( ( ) ( ) )( ( o 3 3 o 3 ) ( o o 3 = (+) o o ) )( (

46 6 Wheatstone bidge deflection measuement bidge output oltage ( )( ) o o / output popotional to when << + change in 3 () must be small compaed to / () ideal output eal output (=) sensitiity of the bidge S do d d d ( )( ) ( )( ) ( )( ) ( ) ( )( ) ( ) o 3 = (+)

47 7 Wheatstone bidge deflection measuement maimal sensitiity ds d d ( ) d ma sensitiity when = ( ) 3 = 3 bidge output oltage (=) o in denominato can be ignoed when << othewise moe adanced signal pocessing equied o 3 = (+)

48 8 Wheatstone bidge esus oltage diide o 3 = (+) = (+) o sensitiity ( ) S ma sensitiity when ( ) S =: = = = =: = output oltage (=) o bidge emoes DC offset o

49 9 Wheatstone bidge esus oltage diide 3 = (+) o = (+) o o / = =.,= o / = = =. sensitiity is equal, but DC offset maes esponse loo flat output of Wheatstone bidge can easily be boosted with amplifie

50 5 Wheatstone bidge esus oltage diide o 3 = (+) = (+) o output oltage (=) o esponse of bidge output to change in only half of esponse when using diide can we change the bidge to get the same esponse? use opeational amplifie (also amplifies non-lineaity eo) use an additional senso o

51 5 Wheatstone bidge incease sensitiity by adding senso on othe side of opposing am bidge output oltage = (+) 3 = (+) o o ) ( o 3 3 3, o 3 ) ( o o o

52 5 Wheatstone bidge measue diffeence by adding senso on same side of opposing am bidge output oltage = (+ ) 3 = (+ ) o o 3 3 o ) ( ), ( 3 o o o o o when, << +

53 53 Wheatstone bidge diffeent senso placements in Wheatstone bidge allow inceasing sensitiity ceate diffeential senso ceate aeaging senso compensate eo souces (stain, tempeatue,...) o o = (-) 3 = (+) (+ )/3 (+ )/3 (+ 3 )/3