1. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico A 36 MPa PRESSURE BALANCE IN LIQUID MEDIUM: EXPERIMENTAL RESULTS AND FEM ANALYSIS M. Caravaggio 1, G. Molinar Min Beciet 2, P. De Maria 2, G. Buonanno 3 1.Scandura & FEM, Milano, Italy, marcello.caravaggio@scandura.itmarcello.caravaggio@scandura.it 2. Istituto Nazionale di Ricerca Metrologica (i.N.Ri.M.), Torino, Italy, g.molinar@inrim.itg.molinar@inrim.it 3. University of Cassino, Cassino, Italy, buonanno@unicas.itbuonanno@unicas.it

2. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico The main purpose of this work is the presentation of the experimental results for a new 36 MPa piston/cylinder unit operating in liquid media. A baseline for a FEM analysis of this unit will be also shown. This analysis has already started and the results will be presented soon. This assembly in one of the four available for the MPA series pressure balance (12 MPa, 36 MPa, 60 MPa, 120 MPa). Aims of the work M. Caravaggio

3. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Peculiarities design suitable for industrial use easily transportable, mass rotation, fully accessories mass values by code, pressure calculation in real time use M. Caravaggio

4. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Oil lubricated pressure balance Different full scale (12, 36, 60 and 120 MPa) Weight set up to 50 kg Nominal effective area A 0  13 mm 2 Piston-Cylinder in tungsten carbide Free deformation piston-cylinder (P 3) Radial clearance in the central part of the piston- cylinder engagement length < 1 µm M. Caravaggio

5. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Oil lubricated pressure balance Different full scale (12, 36, 60 and 120 MPa) Weight set up to 50 kg Nominal effective area A 0  13 mm 2 Piston-Cylinder in tungsten carbide Free deformation piston-cylinder (P 3) Radial clearance in the central part of the piston- cylinder engagement length < 1 µm M. Caravaggio

6. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Oil lubricated pressure balance Different full scale (12, 36, 60 and 120 MPa) Weight set up to 50 kg Nominal effective area A 0  13 mm 2 Piston-Cylinder in tungsten carbide Free deformation piston-cylinder (P 3) Radial clearance in the central part of the piston- cylinder engagement length < 1 µm M. Caravaggio

7. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Oil lubricated pressure balance Different full scale (12, 36, 60 and 120 MPa) Weight set up to 50 kg Nominal effective area A 0  13 mm 2 Piston-Cylinder in tungsten carbide Free deformation piston-cylinder (P 3) Radial clearance in the central part of the piston- cylinder engagement length < 1 µm M. Caravaggio

8. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Oil lubricated pressure balance Different full scale (12, 36, 60 and 120 MPa) Weight set up to 50 kg Nominal effective area A 0  13 mm 2 Piston-Cylinder in tungsten carbide Free deformation piston-cylinder (P 3) Radial clearance in the central part of the piston- cylinder engagement length < 1 µm M. Caravaggio

9. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Motor drive system: 1-motor, 2-eccentric system, 3-wheel with gears, 4-driving belt and 5-proximity sensor Automatic piston rotation A particular system drives the piston rotation. This system drags the piston only when it is in its lower position and keep it free when it is in the floating position. In this way there are very small influences due to the motor drive on pressure measurements. M. Caravaggio

10. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Mass corrections with small spheres (1 mm in diameter corresponding to about 4 Pa for the 36 MPa unit); possibility to adapt at nominal value and g L values M. Caravaggio

11. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Description of MPA 36 MPa pressure balance Errors electronic compensation integration of the sensors used to compensate the effects of the main influence variables like: ● piston-cylinder assembly temperature, ● floating level of the piston, and correction to refer measurements at the reference level, ● ambient temperature, barometric pressure, relative humidity for determination of air density used to calculate the generated pressures. An electronic card with a microprocessor manages all the information M. Caravaggio

12. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Experimental characteristics (P 3 piston-cylinder unit) Dimensional measurements of piston and cylinder Radial clearance as a function of engagement length U ( r ) = U ( R ) = 50 nm z = 0 bottom of p-c engag. lengthz = 22 mm top of p-c engag. length From 2.5 to 18.5 mm rad. clearance < 1  m M. Caravaggio

13. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Experimental characteristics (P 3 piston-cylinder unit) Reduction of rotation speed as a function of time, p =8,06 MPa, t mean = 23.22 °C, p atm = 97300 Pa, RH = 11 % M. Caravaggio

14. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Experimental characteristics (P 3 piston-cylinder unit) Reduction of rotation speed as a function of time, p =34,23 MPa, t mean = 23.18 °C, p atm = 97169 Pa, RH = 12 % M. Caravaggio

15. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Experimental characteristics (P 3 piston-cylinder unit) M. Caravaggio Piston fall rate versus pressure: - free rotation - CW rotation between 30 rpm and 50 rpm

16. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Experimental characteristics (P 3 piston-cylinder unit) Influence of speed rotation on the piston fall rate @ 8 MPa: 1.27  m s -1 @ 46 rpm 1.52  m s -1 @ 19 rpm Influence of speed rotation on the piston fall rate @ 8 MPa: 1.27  m s -1 @ 46 rpm 1.52  m s -1 @ 19 rpm Piston fall rate versus pressure: - free rotation - CW rotation between 30 rpm and 50 rpm M. Caravaggio

17. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Experimental characteristics (P 3 piston-cylinder unit) Effective area as a function of pressure The effective area of piston-cylinder assembly P3 has been determined from pressure cross-floating with one of I.N.Ri.M. pressure national standard and taking into account each influence quantity during the experimental cross-floating. - Sensitivity smaller than 7 ppm -A 0 (p atm, 20 °C) = 13.611 mm 2 - U(A 0 ) = 32 ppm - = 1.3 10 -6 MPa -1 - U( M. Caravaggio

18. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico FEM analysis M. Caravaggio A FEM analysis of the 36 MPa piston-cylinder unit (P3) is in progress in these days The Baseline model for the P 3 (36 MPa, Liquid) Piston – Cylinder unit has already been done As soon as the calculation will be over the data regarding: the distortion coefficient, the effective area, the piston fall rate, the verticality effects, etc., will be available.

19. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Baseline model Cylinder boundary conditions Piston boundary conditions p c = p in clearance p a = atm p p m = measuring p w = axial displacement M. Caravaggio

20. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Material and fluid properties PropertyValue Measurement range / MPaFrom 0.4 to 36 Piston Young modulus (tungsten carbide) / GPa590 ± 59 Cylinder Young modulus (tungsten carbide) / GPa590 ± 59 Piston and cylinder Poisson ratio0.22 ± 0.022 Working fluiddi-ethyl-hexyl-sebacate Density / kg m -3 at 20°C and pressures p up to 36 MPa Dynamic viscosity / Pa·s at 20°C and pressures p up to 36 MPa The numerical solutions through FEM will be achieved by using the multipurpose finite element software FEMLAB 2.3 ®, by running the FEM models from the Matlab ® prompt. As regards the iterative procedure, home made Matlab subroutines where developed by the authors. M. Caravaggio

21. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Conclusions the piston fall rate, measured at the pressure of about 34 MPa, using as pressurized medium the di-ethyl-hexyl sebacate is about 7  ms -1 ; the quality of the piston-cylinder assembly is confirmed by a quite regular behaviors of rotatio speed as a function of time; the rotation time is always long enough to ensure a good use of the pressure balance at every pressure point; the behaviors of effective area as a function of pressure is linear as expected for a free deformation piston-cylinder unit, its expanded uncertainty ranges from 32 ppm at atmospheric pressure to 40 ppm at the maximum pressure of 36 MPa; the pressure sensitivity, derived from cross-floating against a national standard was found to be better than 7 ppm in all pressure range from 2.4 MPa to 36 MPa. M. Caravaggio

22. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico Next Steps the production of the pressure balances in liquid media has already been started for all the piston-cylinder assemblies; the complete metrological characteristic for the 12 MPa and 60 MPa units will be shown soon. a series of pressure balance in gas media will be designed soon. M. Caravaggio

23. IMEKO TC 16 (Pressure) International Conference Cultivating metrological knowledge November, 27 – 30, 2007, Merida, Mexico M. Caravaggio Thank you for your attention ! marcello.caravaggio@scandura.it