Some applications of inductive transducers with magnetic liquids

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Sensors and Actuam~ A 59 (It)97) 107 21}0

Some applications of inductive transducers with magnetic liquids N.C. Popa, I. Potencz, L Bro~tean, L V6k~is * "Pl.litl'hnit'a' ~hzit'ersit), Of Timi~o+lra. R~'searlh Center f~Jr I~vdro~lvnamit',~. ('uri++ni,m and ,tlagnerir Flnid~, B~ndetard Mihai rirea:u! I, R- 19¢~0 T#ni~alra. Romania

Abstract

The paper presents the main constructive and functional characteristics of a leakage flow detector for degree of porosity control or aluminum cylinder heads and of transducers for two-axes inclination angle and air velocity, designed for wind turbine applications, f) 1997 Elsevier Science S.A. Keyw+u'd~: Inductivetr~lnsducers; Magneticliquids; Pre~,:;uredifl~rence:Inclinationmcasllrement;Gd'; flOW

I, Introduction Fluid and magnetic properties brought together by magnetic liquids confer to these synthetic materials wduable new features, which are at the origin of various engineering and biomedical applications [1]. A particularly interesting domain is that of the inductive sensors with magnetic liquid as basic component [2-.6]. The principle of functioning of an inductive magnetic liquid sensor (MLS) is illustruted in Fig. 1. A differential pressure sensor (L~, L:) and ~.r. inclination angle sensor (L'~, L'.,) are rigidly coupled and electrically cennected to an ac bridge, as it is shown sehematicaUy in Fig. 2. The electric signal measured between P~ and P" depends only on the pressure difference Pt - P., = Ap:

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IIZ;I Z,l l ~ Fig. 2. Electricconneclitm~chcmeof flowrate sensor. ,~'lk,magnetic liquid column: R~d~,~ariableresistor for null point adjustment. small magnetic liquid level differences produced by unwanted inclinations or accelerations of the system are compensated due to the inclination angle sensor (L~, L3). In the particular case presented in Fig. 1 the sensor is used to measure the volumic flow rate Q ~ AP of a gas in laminar flow through a measuring tube [7], one of the promising applications of these sensors, Using various laminar measuring elements such as sire. ple cylindrical tubes and laminarization structures or complex flow transducers with the sensitive magnetic liquid sensor in by-pass, the measuring domains easily cover a wide range from ~ 1 cm ~ rain- ~ to ~ 10 m ~ rain x [8]. Various basic aspects of '.he calculus and design of the inductive sensors with magnetic liquids are thoroughly discussed in [4,9,10]. In what follows some special applications of these devices will be presented.

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The concrete problem solved was related to aluminum cylinder heads of clirs, manulhctured by casting under pressure and workcd out by mechlmical cutting, An automatic manufacturing line was provided by a pneumatic quulity control system of cylinder's degree of porosity. Each cylinder, whose approximate shape is given in Fig. 3, wits supposed to a pr,;ssure difference of I atm. To ensure the rcquired quality, the leakage flow through the walls of the cylinder had to be below 511 cm ~ rain J. The pneumatic control system is sketched in Fig. 4, while the time sequence of electric valt,es and the variation of pressure and temperature in the controlled cylinder and the porosity fi'cc cylinder of equivalent volume are presented in Fig. 5. At the moment t,,, when all the valves arc closed, a~ cylinder C to be cram'oiled is automatically inserted in the pneumatic system. At h the electric valves I'~, I', and V', are opened and the pressurized air from the source PS liils up the cylinder C and the equivalent volume leakage free cylinder, EV. Alter the time intervul r~ the system pressure is stabilized at P~, wtlve I.'~ is closed and during time interval r., thermal stabilization is also fidlilled. In this period, valve I~'~is opened in order to introduce the magnetic liquid trunsducer in the pneumatic system. At the moment l+ the valves V+and

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l", arc dosed and tluring litne interval r,, a certuin quantity of air from C is lOSt lhretigh its porous walls. To equalize the pressures from C anti EV, one half part of the air lost is completed from EV through the MLS. The volume of C EV and pneumatic circuit is mud1 larger than the lost uir vo]unl¢, therefore practically P~ is constant in the whole period r: + r~. The MLS may be for differential pressure or Ibr volumic flow rate. There were experimented both type of transducers with good rcsuhs, ,aking inlo uccount their high rcsolution. ~ I pm I-I:O and ~ 10 cms h ~respectively. Due to some una~oidublc pressure vitriations associated with the operation of valves I',. I", and because or the relatively long measuring time (rs) needed by the differentiul pressure sensor, the final eqnipment used a magnetofluidic leakage flow detector manufuctured in cooperation with AEM S.A. Timi:~oara
3, "hvo-axes inclination and rdneit) measurements in wind energetic Fig. ,t Scheme o1' Ihc pneumatic sy,,tcm for controlling leakage tlo',s through porosities: C, c~',li.der heud to hc comrolled: EV. cqui',alcnt ,~olume cylinder: MLS. magnetic liquid sensor: V~,,electric ,,ul,,es: PS (Pll, pressurized air suuruu.

A two-axes inductive inclination sensor with mLtgnetie liquid consists, hi essence, of t','~,,) U-shaped sensors us in Fig. I, however both should be closed and

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mounted along two orthogonal axes: N - S and £ - V. The eleclronic system has tv,o it|dcpcndcnt ways to treat the sign.ds provided by the Bvo orthogon:d sensors, The sensor, its electronic unit and power supply, were constructed in cooperation with AEM S.A, Timi~oara tM:tgnetic fluid transdnccrs. Products ClttltIoguc, 1991) for a measuring domain of .~ 3° to + 30 :md a precision of __.+ "~%, The churactcristic curves for the axes N - S and E - V arc practically superposed and show good linearity [Fig. 6). A robust and portable device of this type was used In control the correct position of supports for wind generators assetnblcd in Semenic mountains. An other application in this lield of tile magnetic liquid differential pressure sensors is a wind selocity sensor pre~medschematically in Fig. 7 cxpcrir~cnted in htboratory conditions. "l'ae laminariz'.ttion structure ensures good linearity of the air velocity volhlge difference curve. Various differentM pressure sensors with magnetic liquid are currendy used in ktbor.ttory aerodynamic measurements [I]

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Fig. 7. Air ',elodtv sensor: I, external ,.:ylindcr;2. sen~r body; 3. metallic sie',,~J,. laminarizationslruelure: 5. pressuretalg.'s6. dit'fcrential pressure seamy;:ilh magnelicliquid.

Aeknowledgemenls 4. Conelusiotts

Magnetic fluids proved to be a very efficient component lor design and construction of it wide variety of sensors, illustrated by mmc special applications presented in this paper. Tile leakage flow detector, twoaxes inclination angle transducer and the air velocymeter are constructively simple and their functional characteristics were easil~ tailored to the requirements of ;m automatic porosity control system and of a wind energy station respectively

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References

[I] I, .',.nton. L De Sabata and L. V,3k~is,Application orientated r¢~'archcson magneticfluid:
50 Deg

This research was supported by the Romanian Ministry of Research and Technology.

[hI L Potea¢/, Nl', Pgpa. L. '¢¢kfs. E. Suciu and A. Melinte. [rausdtlc#r for Ihc measnrt2nlenlof small pressuredifferences.

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RotHiotntO Pdtt'tH ~ . 9.q431 1959.

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-18{} -200 -I(}O 0 100 Calibrated inlclinafion (deg.) Fig. 6. Calibration cur,.c of uu~-axc:,indiaatioa seasor.

17l N.C. Popa. I. P~uenczand L. V~kfs. Magneticfluid tiny. meter Ibr gases. IEEE 77ae~. Iht,~n, 30119941936 935. ISl I. Polcnct lind L. Bro~tean, Experimental in',rc,~,tigationsOff ",olumit:Ihw, trmlsdu,:ers.Romwfitm Rep Phl's.. 47 ( 19961493 5UL lttl X C Po~,. I De Sahata and R. Potenez. Tile calculus or the htdnctance for a coil of real current loops. '~ertieaflyand partially immcBc,.Iin ntagnctic liquid. Roma,uoz Rt?. Phys. 47 11995) 455 472. till I N.C Popa, L. De .~abata and R. Poleutcz.The calculus of the indudanee Ibr :t coil of lilit'om'kcurrent loops, verticallyand partiall) ilnmerscdin magneti,.:liquid. ~lllHlalhlPi Rt'/L Phys., 47 Ih19q 473 492.

N.C, Ptqmet al. Sensors m~d Actuators A 59 (19971 197-200

Biographies losif Potencz was born in 1935. He received his degree in electromechanical engineer in 1958 from the University "Politehniea" Timi~oara. From !967 to 1990 he was a ~enior researcher at the Laboratory of Hydraulic Machines and since 1991 at the Research Center for Hydrodynamics, Cavitation and Magnetic Fluids of the University "Politehnica' Timi~oara. His current fields of interest include engineering applications of magnetic fluids (sensors, rotating seals, magnetogravimetric separators, bearing,~, dampers} and cavitational phenomena.

physics degree in 1968 from the West University Timi~oara and his Doctorat in physics in 1983 from the University 'A.I, Cuza' l~l~i). From 1977 to 1990 lie was a senior researcher at the Laboratory of Hydraulic Machines and since 1991 at the Research Center for Hydrodynamics, Cavitation and Magnetic Fluids in the University 'Politehnica' Timi~oara, Since 1996. he has been Director of the Condensed Matter Research Institute Timiwara and also has been a member of the International Steering Comm,tee of Magnetic Fluids since 1993. His current fields of interest include physicochemistry of magnetic fluids, magnetohydrodynamics, phase transitions, nanoscale physics.

La-6r Bro~tean was born in 1940. He received his mechanical engineering degree in 1966 from the University 'Politehnica' Timi~oara. From 1966 to 1980, he worked as a design engineer and from 1980 to 1990 he was a senior researcher at the Laboratory of Hydraulic Machines and at the Research Center for Hydrodynamics, Cavitation and Magnetic Fluids (I 99 [ - 1996) of the University 'Politehnica' Timi~oara. He died on 9 October, 1996. His research fields include hydraulic engineering and applications of magnetic fluids, Ladi~lau V~kds was born in 1945. He received his

Nicokte C Popa was born in 1955. He received his degree in electronic engineering in 1980 from the University 'Politehnica' Timi~oara. From 1980 to 1986, lie worked as a design engineer in industrial activities, from 1986 to 1990 as a design engineer at the Laboratory of Hydraulic Machines. Since 1990, he has been a senior researcher at the Research Center for Hydrodynamics, Cavitation and Magnetic Fluids in the University 'Politehniea" Timid;data. His current fields of interest include engineering applications of magnetic fluids (sensors and actuators) and electronics.