Newly Established Hydrometer Calibration Set Up at UM. Ümit Y. AKÇADAĞ, S. Eren SAN TÜBİTAK, Ulusal Metroloji Enstitüsü (UME) Gebze Kocaeli, Turkey

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1 Proceedins of the 7 th Interntionl Conference on Force, Mss, Torque nd Pressure Mesurements, IMEKO TC3, 7- Sept. 00, Istnbul, Turkey Newly Estblished Hydrometer Clibrtion Set Up t UM Ümit Y. AKÇADAĞ, S. Eren SAN TÜBİTAK, Ulusl Metroloji Enstitüsü (UME) Gebze Koceli, Turkey Abstrct Hydrometer clibrtion could be performed by Cuckow Method in which just sinle liquid is sufficient for the clibrtion of the whole scle. Hydrometers re weihed first in ir nd then in reference liquid in this method. The density of the reference liquid is well known nd it is possible to determine the ssocited density vlue of the rdution mrk by mkin use of weihin vlues nd the density vlue of liquid in relted formuls. The entire scle of Hydrometer cn be clibrted in this wy by immersin the hydrometer to the interested scle mrks. In this pper, hydrometer clibrtion set up of UME is introduced nd obtined mesurement results from this set up re iven for smple hydrometer.. Introduction Hydrometers ply n importnt role in the ccurte nd relible density mesurements of liquids. This equipment is desined in such wy tht the density vlue of the liquid corresponds to the scle mrk t which hydrometer flots freely. They must be clibrted nd trceble so tht their pplictions become stisfctory. A enerl view of this lss equipment is shown in Fiure. Fiure. Hydrometer In the process of clibrtion; severl liquids were used s reference until Cuckow, who introduced method llowin the use of 87

2 Proceedins of the 7 th Interntionl Conference on Force, Mss, Torque nd Pressure Mesurements, IMEKO TC3, 7- Sept. 00, Istnbul, Turkey sinle reference liquid for the clibrtion of different scle mrks. This method sves time nd decreses the expense of the clibrtion procedure by reducin the reference demnd to just one liquid whose density is well known [].. Method nd Theory The method is bsed on weihin of the hydrometer when it hs been flotin t the scle mrk, which is supposed to be clibrted. Density of the liquid must be previously mesured. Hydrometer experiences n upthrust equl to its weiht when it is immersed up to the scle mrk nd order of upthrust is proportionl to the mount of immersion. If we weih the body immersed to interested extent in two medi of known density it would be possible to determine the density correspondin to interested extent which is supposed to be scle mrk. Appliction of this procedure requires specil pprtus nd specil desins for sensitive immersion. Theory of the method is bsed on the fct tht, if we weih solid body t point in between two medi whose densities re known we my find the density of the medium in which the upthrust on the immersed portion would be equl to the weiht of the body. One cn exploit this principle in such wy tht hydrometers re firstly weihed in ir nd then in reference liquid of known density, which is used s reference. The weihin vlue is mesured while the hydrometers were immersed up to different levels nd the correspondin density vlues of different immersion levels could be determined by liner extrpoltion [,,3]. Theoreticl nlyses strts from the weihin equtions. If hydrometer freely flots in liquid we cn write, m. V v () In the cse of weihin in ir below eqution holds, W m V v () Hvin completed the process of weihin in ir, it is strted to crry out mesurements while the hydrometer is prtly immersed into the liquid of density m. W V v 3 (3) Used nottion, throuhout the pper, is presented ltoether for simplicity, m = Mss of the hydrometer, D = Stem dimeter t meniscus level, = Surfce tension of the liquid durin the free flotin, = Surfce tension of the liquid durin the immersed flotin (here in tridecne), = Grvittionl ccelertion, 88

3 Proceedins of the 7 th Interntionl Conference on Force, Mss, Torque nd Pressure Mesurements, IMEKO TC3, 7- Sept. 00, Istnbul, Turkey V = Volume of the hydrometer under the liquid t 0 o C, v = Volume of the hydrometer bove the liquid t 0 o C, Density of tridecne durin the mesurement, T Tridecne density obtined by usin Sinker t certin temperture, = iquid density correspondin to scle mrk of hydrometer, = Air density durin the free flotin, = Air density durin the weihin in ir, 3 = Air density durin the weihin in liquid of density W = Weihin vlue of hydrometer while it is weihed in ir, W = Weihin vlue while the hydrometer is prtly immersed up to certin level, t =Temperture vlue durin the mesurement, t R = Reference temperture, v = Therml volume expnsion coefficient of hydrometer, N = Nominl density vlue of hydrometer, m s = Mss of the sinker, V S = Volume of the sinker, V N =Volume of reference msses, = Density of weihts of the blnce (usully: =8000 k/m 3 ), w = Difference in the weihin vlue, In order to be ble to ssume the equlity of ir density vlue we crry out mesurements in ir nd in liquid one fter the other in short periods nd lettin the equtions (), () nd (3) re trnsformed to the followin forms,. m V v (4) m W V v (5). m W V v (6) Eqution (5) is substrcted from eqution (4),. V W V 0 (7) Eqution (6) is substrcted from eqution (5),. W V W V 0 (8) V is eliminted from eqution (7) s,. V { W } (9) ( ) Hvin inserted V into (8) nd performin lebric mnipultions it yields, m N = Reference msses equivlent to mss of sinker, 89

4 Proceedins of the 7 th Interntionl Conference on Force, Mss, Torque nd Pressure Mesurements, IMEKO TC3, 7- Sept. 00, Istnbul, Turkey. ( )( W ). W W ( ) (0) If we eliminte which denotes the density vlue of scle mrk of the hydrometer,. ( ){ W } (). W W Hvin concerned with coefficient of cubicl expnsion ( v ) of the mteril of hydrometer, eqution () turns out to the followin form so tht it could be used t reference temperture []. ( t R. ( ){ W } ) [ V ( t t R )]. W W () 3. Mesurement Firstly mesurements re crried out in ir medium with blnce hvin 0. m redbility (Mettler, AT 400). Clibrted weihts re used in substitution method nd ir density is clculted by usin mbient conditions so tht ir buoyncy correction would be concerned in weihin vlue. Riht fter weihin hydrometers in ir, it is importnt to mesure stem dimeters t the interested scle mrks of hydrometer, nd reference surfce tensions of the liquid, where 0 the hydrometer is supposed to be used, re determined from relted tbles. Surfce tension of the clibrtion liquid (tridecne) is lredy known. Second ste is to perform hydrosttic Cuckow weihin. In this process; the blnce (Mettler, AT 400) is locted t the top of the system nd it hs the bility to perform mesurements inside the liquid vi n pprtus, which connects the blnce into the liquid. Thermostticlly controlled bth (TAMSON, TV 7000) is used for temperture stbiliztion. Actully, temperture is the mjor effect for the density of liquid in which the weihin tkes plce. Ambient conditions re monitored durin the weihin in liquid. The desin of the system, llowin the immersion of hydrometer t different immersion extent, is criticl durin the mesurements. Density of tridecne is determined by usin sinker whose density nd mss re known [4]. Substitution method is pplied with below formul for liquid density determintion. m s mn VN w( ) T (3) V S Density of tridecne could be obtined by usin eqution (4) t 0 o C 0,75.( t 0) (4) o 0 C T 90

5 Proceedins of the 7 th Interntionl Conference on Force, Mss, Torque nd Pressure Mesurements, IMEKO TC3, 7- Sept. 00, Istnbul, Turkey Temperture of tridecne is determined with pltinum sensin element hvin 0.00 o C resolution durin the mesurements. The evlution of meniscus effect is importnt in the weihin vlue. For this evlution; surfce tension of tridecne is tken s =5,9 mn/m nd stem dimeter of ech scle is mesured by compss before the mesurements. Hydrosttic weihin system, used in our mesurements for hydrometer clibrtions, is shown in Fiure. 4. Results nd Conclusion A smple hydrometer in the rne of k/m 3 hvin 0, k/m 3 redbility is clibrted in terms of Cuckow method. This hydrometer hs been bein used for density determintion of minerl oils whose surfce tension is considered in the evlution of mesurement results. Clibrtion process is crried out in the newly estblished set up of UME nd mbient conditions of lbrotory re controlled durin the mesurement. Temperture dependency of liquid is criticlly concerned nd iquid temperture is specificlly mesured t ll mesurement steps by lss thermometer. Density informtion of tridecne is iven in the followin tble. Tble. Density of Tridecne iquid Density (0 o C) C 3 H 8 756,378 k/m 3 Use of density stndrd known s sinker stisfies the density determintion of tridecne durin the mesurements. Results of mesurements, theoreticlly obtined from eqution (), re iven in Tble. Fiure. Hydrometer clibrtion system 9

6 Proceedins of the 7 th Interntionl Conference on Force, Mss, Torque nd Pressure Mesurements, IMEKO TC3, 7- Sept. 00, Istnbul, Turkey Tble. Mesurement results N D W t R t W Correction [k/m 3 ] [k/m 3 ] [mm] [mn/m] [] [k/m 3 ] [ o C] [mn/m] [ o C] [] [k/m 3 ] [k/m 3 ] ,344 6,640 8,00 47,386,58 0 5,9 0,047 7, ,988-0, ,344 6,645 8,0 47,386,58 0 5,9 0,047 8, ,04 0, ,344 6,650 8,0 47,386,58 0 5,9 0,047 8, ,088 0, ,344 6,635 8,30 47,386,58 0 5,9 0,047 8,66 866,08 0, ,344 6,635 8,40 47,386,58 0 5,9 0,047 8, ,033 0, ,344 6,635 8,50 47,386,58 0 5,9 0,047 9, ,998-0, ,343 6,640 8,60 47,386,58 0 5,9 0,049 9,550 87,043 0, ,343 6,635 8,70 47,386,58 0 5,9 0,049 9, ,04 0, ,340 6,65 8,80 47,386,58 0 5,9 0,053 0,67 875,995-0, ,340 6,630 8,90 47,386,58 0 5,9 0,053 0, ,994-0, ,339 6,630 9,00 47,386,58 0 5,9 0,055 0, ,970-0,030 Clculted uncertinty is /5 th of density vlue for ech scle mrk. It is shown tht mesurement uncertinty is t resonble level for the relible dissemintion pplictions of liquid density scle for industry. 5. References []. Cuckow F. W., A new method of hih ccurcy for the clibrtion of reference stndrd hydrometers, Journl of the Society of Chemicl Industry, 949, 68, pp []. orefice S., Heinonen M. nd Mdec T., Bilterl comprisons of hydrometer clibrtions between the IMGC-NE nd the IMGC-MIKES, Metroloi, 000, 37, 4-47 [3]. Spiweck F., & Bettin H., Solid nd iquid Density Determintion, Technisches Messen 59, 99 [4]. orefice S., IMGC fcility for reference liquids in density mesurements, IMEKO-XV World Conress. Contct Person for pper: Ümit AKÇADAĞ Address: TUBITAK-Ulusl Metroloji Enstitüsü P.O.Box: 4470 Gebze-Koceli-TURKEY Fx: , Tel: e-mil : kcd@ume.tubitk.ov.tr 9