Non-Intrusive Electrodynamic Characteristic Measurement for Circular Shape Electrode

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1 Intrnational Confrnc on Elctrical, Control and Computr Enginring Pahang, Malaysia, Jun 1-, 011 Non-Intrusiv Elctrodynamic Charactristic Masurmnt for Circular Shap Elctrod M. R. Ghazali, W. I. Ibrahim Faculty of Elctrical and Elctronic Enginring, Univrsiti Malaysia Pahang, 6600 Pkan, Pahang, Malaysia. M. F. Rahmat Dpartmnt of Control and Instrumntation Enginring, Faculty of Elctrical Enginring, Univrsiti Tknologi Malaysia, Skudai Johor, Malaysia. Abstract Th lctrostatic snsor was usd in procss industry bcaus of low cost and robust dsignd.thr typs of lctrod availabl in particular application such as pin shap, quartr ring shap and ring shap. Th papr was focusd on th invstigation of th pin shap structur and th charactristic of th circular shap by using diffrnt siz of structur. Noninstrusiv mthod with circular lctrod will b dsignd and applid to th shap.th snsitivity and spatial filtring ffct of snsor will b invstigatd by using diffrnt siz of lctrods.thn, th modl will b proposd and compard with xprimntal rsult. Kywords-lctrostatic, lctrodynamic, circular, mass flow, non intrusiv, snsitivity, spatial filtring ffct. I. INTRODUCTION Th flow of particl in piplin gnrats an lctrostatic charg. Elctrostatics charg can b dtctd using snsing dvic or lctrod and convrt into voltag by associatd lctronic or lctrodynamics transducr. Th masurmnt is basd on charg dtctd by th snsor as th chargd particls flow past it. Snsors gnrally consist of mtal or lctrod insulatd from th walls of th convyor. Th procss masurmnt of th ring lctrods ar widly usd and hav bn thoroughly invstigatd [3, 4]. Elctrostatic transducr ar robust and low cost application, so it has high th potntial to b applid for procss tomography. In procss tomography [5] svral idntical transducrs ar positiond around th vssl bing intrrogatd to provid masurmnts which ar usd to rconstruct dynamic imags of th movmnt of th matrial bing monitord.in larg numbrs of snsors th ring lctrod is no longr applicabl and small snsors as pin lctrod consisting of ithr rctangular or circular sction ar mor appropriat. Th applications whr th procss is varying rapidly, for xampl pnumatically convyd of solids particl, th masurmnt of th systm paramtrs should b known. This papr invstigats th rlationships btwn snsor siz of circular lctrod, snsor snsitivity and th frquncy bandwidth and trmd th spatial filtring ffct [6] of th transducd signals. Th principl of masurmnt tchniqus basd on lctrostatic phnomna in pnumatics piplins is contains information of vlocity and mass flow rat of particls. Th information of particl is dpnd on larg particl will carry highr charg on its surfac than a smallr on [1]. This charg lvl will b dtctd by using lctrostatic snsing and convrt it to voltag signal. Th charg lvl can b rprsntd by: whr, Vt () = α qt () (1) q =amount of lctronic charg carrid on ach particl α=constant dpnd th dsign of th charg amplifir circuit. V (t) =th rsulting voltag signal As mntion arlir, th fiction and collisions of particl in piplin ar ntirly random. So, th valu of V(t) is th rsult voltag of un dtrministic signal capturd by lctrostatic transducr and chang it to discrt tims squnc, V(n) at suitabl sampling frquncy whr n= 0,1, and so on. In th lctrostatic snsor dsign, th diffrnt trm was usd to dscrib th lctrostatic snsing tchnology, tri biolctric, lctrodynamics and lctrostatic. II. A. Th Elctrod Snsitivity THEORY Elctrods snsitivity is a chang output of th lctrodynamics transducr which is avrag voltag du to a chang in th mass flow rat. Mass flow rat of th pnumatic convying plant can b calculatd by doing th xprimnt on calibration in ordr to find rlation of mass flow rat with flow indicator. Th unit of snsitivity is volts/gram/scond /11/$ IEEE 1

2 Th lctrod snsitivity was modld basd on circular lctrod by considring th ffct of a singl chargd particl, q, as it movs vrtically downwards at th constant vlocity, v. Th assumptions is th point charg has travlling in an axial dirction paralll to th axis of th pip, th particl has a constant, finit amount of charg which is not dissipatd during th tim whn it travls through th snsing volum. Th surfac ara of th pin lctrod is small compard to th radius of th pip flow. Th charg acts as a point sourc and th lctrod not conducting with th pip. Singl chargd particl was assumd to b a point charg of valu q, which is th fild is uniformly radial [10]. q E= () 4πr ε Th point chargs can induc a potntial onto th small surfac of th flat lctrod. Th flat lctrod was usd to sns th changing of potntial at th non-conducting or dilctric pip wall. It was assumd, no othr intracting filds on th lctrod if no surfac chargs on th pip wall. Fig. 1 showd th surfac ara is which is considrd normal to th flux on particular dsignd. Th proportion of th flux passing through th snsor du to th chargd particl at th distanc i [10], is; πr (3) 4π r i i 0 dtctd. Th voltag also was amplifid, rctifid and avrag voltag was calculatd. B. Th Spatial Filtring Effct Th frquncy bandwidth charactristic or calld spatial filtring ffct invstigation arising from capacitanc lctrods was dscribd by Hammr and Grn [6]. This invstigation also was rlatd to th vlocity of flowing discontinuous matrial to th frquncy bandwidth of th snsd signal [8]. Th procss of tomography using lctrodynamic snsors gnrally us pin typ of lctrod which is circular or hmisphrical lctrods. Howvr, som applications mayb rquiring rctangular lctrods [7]. Th rsults from th rctangular lctrods can b compard with th masurmnts obtaind using capacitanc lctrods [6]. Th dsignd for circular lctrod nd to assum a singl chargd particl movs past to th diamtr of th snsor or lngth(a), th distanc (d), with a vlocity (v), can b considrd as a puls of charg q(t). This moving charg will b inducd into th snsor (Figur ). Th quantity of charg inducd into th snsor is qual; υ qt () δqi = k dt 0 a d (6) whr q(t) rprsnts th charg puls providd by th moving particl and k is th constant of proportionality with appropriat dimnsions. Whn th puls duration was short compard with a/v [6] it may b shown that th rspons is a 'sinc' function with th ffct of a and v on th modulus shown graphically in Fig.. Figur 1.Th rlationship btwn particl and snsor Charg inducd onto th lctrostatic snsor is proportional to q. Hnc, kqr Q = (4) Equation 4 show th amount of charg inducd onto th lctrod dpnds upon th radius of th lctrod squard or th ara of th lctrod. Th charg was stord at th capacitor and provids a voltag V givn by Q r i = CV (5) Th voltag was amplifid, rctifid, smoothd and th avrag was calculatd. Th snsitivity of th snsor is dfind as Q. This valu of snsitivity is difficult to dtrmin q i bcaus th lvl of th convyd charg, qi, cannot b control. In this papr, a sris of snsor diamtrs was compard simultanously as a rsultd th sam qi was Figur. Masurmnt amplitud frquncy rspons ( ω) h j ωa sin v = k ωa v Aftr drivation amplitud frquncy rspons quation 6 dscrib as [9], may b writtn quation 7 that produc sinc function. (7) 13

3 III. METHODOLOGY Th procss of masurmnt th static charg by lctrostatic snsor consist th dsign of th lctrod or snsing dvic in circular shap. Th svral sizs wr implmnting or assmbl to pnumatic convying plant of plastic bad. Th lctrical charg was dtctd from lctrod thn convrts to voltag by lctrodynamics transducr or associatd lctronic. Th calibration curv of gravity flow rig is important for calibration of pnumatic convying plant to masur th mass flow rat of th plastic bads at solid loading. Furthr procss can b prcding aftr find th flow rat. Th xprimnt of masurmnt using non-intrusiv lctrod circular can b stup by rading and convrting lctrodynamics transducr. Th systm was intrfacd by data acquisition systm. Furthr analyss wr carrid out using computr softwar. A. Elctrodynamic Snsor Th diagram of th lctrodynamic snsor (Fig. 3) consists of a plain mtal rod calld as lctrod. Th dsignd was isolatd from th mtal convying pip walls by th insulator such as glass or plastic. This lctrod has a capacitanc to arth. Th valu is vry small (fraction of a pico Farad) but th valus is diffrnt du to manufacturing tolrancs. A low valu of capasitor (svral pico farad) was connctd in paralll to minimis th ffct of capacitanc. Th rsistor was connctd in paralll with th capacitors to provid a charg/discharg path [10]. Th chargd particls in th pip flow th lctrod and producs inducing charg into th procss. Th currnt flow through th rsistor du to th induc charg caus voltag vary. Th voltag thn was buffrd by a unity gain non invrting amplifir. Th output provids a drivn guard for th input circuitry and was amplifid and conditiond by othrs circuitry. solid particl is vry difficult to quantify, howvr sinc th snsors ar valuatd at th sam tim thir outputs may b compard dirctly. Th small diamtr lctrod at ach nd of th array chcks that th flowing particl dos not chang its charactristics as it travrss th sction. Figur 4. Arrangmnt of circular lctrods for snsitivity masurmnts A sris of diffrnt particl flow rats was applid to th lctrods and th output was dtrmind. Rsults for th snsor snsitivity ( mm to 9 mm) diamtr lctrod wr collctd and th rsult of svral siz lctrod shown in Fig. 5 to Fig. 7. A linar rgrssion lin is fittd to th masurd valus. Th gradint of this lin provids th ovrall snsitivity of th snsor (V/gm/s) and summarizd in Tabl 1 and Fig. 8. Figur 5. Snsitivity for mm circular lctrod. Figur 6. Snsitivity for 6 mm circular lctrod. Figur 3. Th transducr circuit IV. RESULT AND DISCUSSION Th snsitivity can b dtrmind by using diffrnt siz of snsor. Th solid particl flows passing ach of th circular lctrods (Fig. 4). Th lvl of charg on th flowing Figur 7. Snsitivity for 9 mm circular lctrod. 14

4 TABLE I. ELECTRODE SENSITIVITY OF ELECTROSTATIC SENSOR Elctrod diamtr (mm) Elctrod ara (mm) Transducr snsitivity (mv/g/s) Elctronic gain Elctrod snsitivity (mv/g/s) x x x x x x x x 10 - Th rsults show th linar rlation btwn lctrod snsitivity and ara of circular lctrods. By incrasing th diamtr or siz of lctrod, th snsitivity of th snsor will b incrasd. Th diamtr mm and 3 mm show th bst fit or cofficint lin lss than 90 prcnt. That mans masurmnt of small diamtr isn t stabl and lss snsitivity for circular lctrod. Cut Off Frquncy= Hz Figur 9. Rctifid voltags in tim and frquncy domain for diamtr mm. Cut Off Frquncy= Hz Figur 10. Rctifid voltag in tim and frquncy domain for diamtr 4 mm. Cut Off Frquncy= Hz Figur 8. Plot showing snsitivity vrsus lctrod ara for circular snsors. For spatial filtring ffct analysis, rctifid voltag signal masurd by lctrodynamics transducr will b invrsd and convrtd into frquncy domain using Fourir transform analysis. Th rsult for circular lctrod on th frquncy spctrum is sinc function that follows th thory calculatd. Th frquncy spctrum can b obsrvd in trm of cut off frquncy. Th rsult of frquncy spctrum for circular lctrods with diamtr ranging from mm to 9 mm was shown in Fig. 9 until 11 with mass flow rat is g/s. At th right of th figur show th signal on tim domain which is non-invrting voltag and rctifid voltag signal. Th lft signal is frquncy domain signal which is frquncy spctrum of rctifid voltag. Figur 11. Rctifid voltag in tim and frquncy domain for diamtr 9 mm. Th rsult of frquncy rspons show that, for all frquncy spctrum ar in sam curv that givs from sinc function in Equation 7 in th diffrnt in cut off frquncy. Th charactristic of spatial filtring ffct will continu with th rlationship btwn cut off frquncy and lctrod lngth of lctrods and th rsult shown in Fig. 1. From this obsrvation, incrasing of diamtr circular lctrod will incras th cut off frquncy in linar proprtis of gradint Hz/mm. Th rsult of frquncy spctrum for circular lctrod diamtr mm to 9 mm collctd and rsult of svral siz lctrod shown in Fig. 9 to Fig. 11. Figur 1. Rlation btwn cut off frquncy with diamtr for circular lctrods. 15

5 ACKNOWLEDGMENT Th authors wish to thank for th support givn to this rsarch by Univrsiti Tknologi Malaysia (UTM), which mad this collaborativ work possibl. REFERENCES [1] A.M. Fathrston, R.G. Grn, M.E. Shacklton, "Yarn vlocity masurmnt." J Physics E: Sci Instrum, vol. 16, [] P.W. King, "Mass flow masurmnt of convyd solids, by monitoring of intrinsic lctrostatic nois lvls." nd. Int. Conf. on th Pnumatic Transport of Solids in Pips, Cranfild, [3] Shacklton ME, "Elctrodynamic snsors for procss masurmnt." Mphil Thsis, Univrsity of Bradford, [4] Y Yan, B Byrn, S Woodhad, J Coulthard, (1995), "Vlocity masurmnt of pnumatically convyd solids using lctrodynamic snsors." Mas. Sci. Tchnol. 6, [5] Procss Tomography: Principls, Tchniqus and Applications, Ed R.A.Williams and M.S.Bck, Buttrworth-Hinmann, 1995, [6] E.A.Hammr, R.G.Grn, (198) "Th spatial filtring ffct of capacitanc transducr lctrods". J.Phys.E:Sci. Instrum., 16, No. 5, [7] Machida, M., Scarltt, B., Procss Tomography Systm by Elctrical Charg Carid by Particl, IEEE Snsors Journal. Vol. 5, No.,, April 005, p5-59. [8] Yang, W.Q, Lihui Png, Rviw Articl : Imag rconstruction Alogrithms for Elctrical Capacitanc Tomography, Masurmnt Scinc and Tchnology, Institut of Physics Publiching 14 (003) p1- R13 [9] M. F. Rahmat, (1996). Instrumntation of Particl Convying Using Elctrical Charg Tomography. Doctor Philosophy, Shffild Hallam Univrsity, Unitd Kindom. [10] M. F. Rahmat and N.S. Kamaruddin,(009). An lctrodynamics snsor for lctrostatic charg masurmnt. Intrnational Journal on Smart Snsing and Intllignt Systms, Vol., No., Jun [11] M. D. Isa, M. F. Fua ad, K. Jusoff, T. A. R. Hussin (009). Validation Procss for Elctrical Charg Tomography Systm Using Digital Imaging Tchniqu. Applid Physics Rsarch, Vol. 1 No., Novmbr. [1] M. F. Rahmat, M. D. Isa, R. A. Rahim, T. A. R. Hussin (009). Elctrodynamics Snsor for th Imag Rconstruction Procss in an Elctrical Charg Tomography Systm. Snsor, 9, ; doi: /s