Sensors and Actuators Introduction to sensors

Transcription

1 Snsrs and Actuatrs Intrductin t snsrs Sandr Stuijk (s.stuijk@tu.nl) Dpartmnt f Elctrical Enginring Elctrnic Systms

2 APAITIVE IUITS (haptr., 7., 9., 0.6,.,.)

3 apaciti snsr capacitanc dpnds n physical prprtis r 0 A ε 0 dilctric cnstant fr acuum (8.85 pf/m) ε r rlati dilctric cnstant dic usabl as snsr changing A,, ε r changs capacitanc chang in capacitanc can b snsd signals studid s far tmpratur humidity displacmnt / ll / rtatin all ths signals can b snsd with rsisti snsrs

4 apaciti snsr adantags lading rrr f capaciti displacmnt snsr is minimal ngligibl frc ndd t m plat nrgy strd n a capacitr E V frc rquird t m plat r distanc F E ampl (V = 0V, A = 0cm, = cm) n hating ffct r 0A V 8.85pF / m 0cm F cm 0V. nn rslutin f capaciti snsr nly limitd by nis ll fast rspns tim bcaus f lw inrtia (lightwight plats)

5 5 apaciti snsr masurmnt ptins masur impdanc (ltag drp) V j I snsr rquirs cnstant currnt surc linar whn changing nnlinar whn changing ε r r A masur admittanc (masur currnt) I jv snsr rquirs cnstant ltag surc linar whn changing ε r r A nnlinar whn changing

6 6 Signal prcssing d d capaciti ll snsr h ε 0 0 r 0 ln( d / d ) H h H h ε circuit fr linar admittanc changs (ε r r A) prids bias currnt path utput ltag L 0 linar rlatin btwn utput ltag and input signal ffst ltag prsnt in utput circuit knwn as charg amplifir V rspns largr cmpard t masuring ltag drp r

7 7 Signal prcssing d d ampl capaciti ll snsr capacitanc: min =.6 pf, ma = pf H h ε placd in circuit as capacitr ltag surc: = 0 sin(ωt) h ε rsistrs: = rsistr usd t bias p amp dsign and t btain 0V whn tank is mpty and V (pak) whn tank is full (ignr ffct f bias rsistr ) L

8 8 Signal prcssing ampl capaciti ll snsr utput ltag null utput n mpty tank implis using = w find utput ltag is thn qual t p n n n j j j min min min

9 9 Signal prcssing ampl capaciti ll snsr utput ltag utput V (pak) n full tank implis using =, min =.6 pf, and ma = pf w find hnc 0V 0V.6pF 8pF 69. 5pF min min ma min ma min 0V 8. 05pF ma

10 0 Signal prcssing stray capacitanc influncs utput signal utput ltag (ignring stray capacitanc) stray capacitanc s and s d nt affct utput ltag s in paralll with bth nds f s at sam ltag utput ltag (cnsidring stray capacitanc) s s stray capacitrs shilding rducs s V s s

11 utput ltag (V) Masuring admittanc whil arying distanc admittanc Y, utput ltag (V) impdanc d d V V V r

12 Vltag diidr singl snsr with linar impdanc chang utput ltag f th ltag diidr utput ltag is nnlinar 0 0 () utput ltag diffrntial snsr () utput ltag is linar utput ltag has ffst ltag 0 ()

13 Vltag diidr intrfrnc (chang in dilctric cnstant) causd by tmpratur humidity capacitanc f snsr impdanc f snsr utput ltag diffrntial snsr A 0 r y 0 d 0 0 y 0 y y y 0 diffrntial ltag diidr rms intrfrnc y 0 ()/(y) 0 ()/(y)

14 = 0 () A bridg rm ffst ltag using bridg singl snsr with linar impdanc chang utput ltag f th bridg ( 0 = = = ) utput ltag nnlinar with dirctin f lst whn cnsidring amplitud /

15 5 A bridg rm ffst ltag using bridg diffrntial snsr with linar impdanc chang utput ltag f th bridg ( 0 = = ) / = 0 () = 0 () utput ltag linar with dirctin f lst whn cnsidring amplitud

16 6 apaciti bridg analg linariatin psudbridg circuit with singl snsr what is th utput ltag f th circuit? singl plat capacitr as snsr plac at whn changing plac at whn changing A r ε r and can b rsistrs linar with rspct t masurd signal V p n n n A r 0

17 7 apaciti bridg analg linariatin psudbridg circuit with diffrntial snsr utput ltag and frm diffrntial capacitr if masurand changs ε r r A and frm diffrntial capacitr if masurand changs includ rsistrs t bias p amps matchd rsistrs d nt affct utput V

18 8 Instrumntatin amplifir ampl capaciti rtatin snsr capacitanc prprtinal t angl r 0 d r 0 d capacitrs in bridg circuit s utput ltag prprtinal t angl rtr plats d statr plats insulatr gap s

19 9 Instrumntatin amplifir ampl capaciti rtatin snsr bridg utput ltag s signal can b amplifid using instrumntatin amplifir s rtr plats d statr plats insulatr gap a s b