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A Method for Verifying Traceability in Effective Area for High Pressure Oil Piston-Cylinders

A Method for Verifying Traceability in Effective Area for High Pressure Oil Piston-Cylinders. Michael Bair Director of Metrology-Pressure Fluke Calibration . Introduction. Traceability in pressure, like temperature, cannot be “built up” by measuring in parallel.

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A Method for Verifying Traceability in Effective Area for High Pressure Oil Piston-Cylinders

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  1. A Method for Verifying Traceability in Effective Area for High Pressure Oil Piston-Cylinders Michael Bair Director of Metrology-Pressure Fluke Calibration

  2. Introduction • Traceability in pressure, like temperature, cannot be “built up” by measuring in parallel. • Traceability in pressure is dependent upon effective area and the elastic properties of piston-cylinders used with pressure balances (piston gauges). • Fluke Calibration’s reference (method) for effective area/ pressure is the Piston-Cylinder Pressure Calibration Chain. • With this Fluke Calibration’s uncertainty in pressure is ±0.0028% at 200 MPa (30,000 psi) which is very low when reviewing NMI’s CMC uncertainties for that range. • Because there is extrapolation of the effective area and elastic deformation coefficient verification is required at high pressure. • Calibration chain was re-characterized in 2010. This paper shows 3 methods of verification, one being an attempt to use the Dadson single piston method. 2011 NCSL International Workshop & Symposium

  3. One Minute Piston Gauge Primer Mass x Gravity Masses are rotated Effective Area Effective Area Changes with Pressure EQUILIBIUM! Pressure x Area Pressure = (Mass x Gravity)/ Effective Area

  4. Calibration Chain • Primary standard for effective area from 5 kPa to 500 MPa (<1 psi to 72500 psi). • Re-characterized in 2009/2010. 4th modern re-characterization. • Original traceability is defined using dimensional measurements and the Dadson method on a 50 mm diameter piston-cylinder. • Traceability is transferred to higher pressures/ smaller effective areas using the “Base Ratio” crossfloat. • Each level has some portion of the range that extrapolates elastic deformation to support the next higher range. • Uncertainties increase as pressure gets higher. 2011 NCSL International Workshop & Symposium

  5. PTB Comparison/ Dimensional Characterization 5 kPa/kg 1161 Gas - controlled clearance: 5 to 500 kPa 5 kPa/kg 450 407 Gas - controlled clearance: 5 to 175 kPa 10 kPa/kg 154 335 Gas - free deformation: 13 to 1000 kPa 50 kPa/kg 117 118 Gas - negative free deformation: 50 to 5000 kPa 100 kPa/kg 572 624 Gas/Oil - negative free deformation: 0.1 to 10 MPa 200 kPa/kg 512D 20D Hydraulic - free deformation: 0.2 to 20 MPa 500 kPa/kg 22D 23D Hydraulic - free deformation: 0.5 to 50 MPa 1 MPa/kg 24D 25D Hydraulic - free deformation: 1 to 100 MPa 2 MPa/kg 397 742 Hydraulic - free deformation: 2 to 200 MPa 5 MPa/kg 468 405 Hydraulic - free deformation: 5 to 500 MPa 2 MPa/kg 1488 and 27D Hydraulic – Controlled Clearance (1488) And free deformation (27D) Lines between piston-cylinders are the average of at least two measured ratios between the two piston-cylinders. Calibration Chain 2011 NCSL International Workshop & Symposium

  6. Calibration Chain Verification • Comparison with Houston facility primary to 280 MPa (40,000 psi) • Comparison with SN 27D, an old/dormant 200 MPa range piston-cylinder with original traceability with NIST and LNE (France). • A alternate method based on a basic principal discussed by Dadson called the single piston method. 2011 NCSL International Workshop & Symposium

  7. Calibration Chain Verification • Comparison with Houston facility primary to 280 MPa (40,000 psi) 2011 NCSL International Workshop & Symposium

  8. Calibration Chain Verification • Comparison with SN 27D, an old/dormant 200 MPa range piston-cylinder with original traceability to NIST and LNE (France). 2011 NCSL International Workshop & Symposium

  9. Calibration Chain Verification • A alternate method based on a basic principal discussed by Dadson called the single piston method. • Not used this time as a complete characterization of the pressure balance but just as a verification tool for the results of the CalChain. • Attractive because of the equation used for an incompressible fluid to determine average gap and the fact a known viscosity characterization existed for the test fluid (Vergne). 2011 NCSL International Workshop & Symposium

  10. Single Piston Method Procedure • Determine the effective area of SN 1488 controlled clearance piston gauge using the calibration chain and base ratio method. • Dimensionally characterize SN 1488 2.5 mm piston at NIST. • Perform drop rate tests to determine the average gaps at various pressures. • Using the zero pressure gap and dimensioned piston, calculate the effective area at zero pressure and 20˚C and compare to what was determined from the crossfloats. 2011 NCSL International Workshop & Symposium

  11. Single Piston Method 2011 NCSL International Workshop & Symposium

  12. Single Piston Method • Two pistons were sent to NIST for dimensioning, one was for SN 1488, the other a slightly smaller piston for future use. • Two different orthogonal planes • ±16.5 mm to cover float range • 24 total diameter measurements 2011 NCSL International Workshop & Symposium

  13. Single Piston Method Average diameter = 2.4980883 mm 2011 NCSL International Workshop & Symposium

  14. Single Piston Method - Gap Determination • Performed gap determinations for three different controlled clearance pressures, 0, 25 and 50% of measured pressure. • For each CCP performed drop rates for at least 5 pressures. • Tried to get 5 drop rates for each CCP/measured pressure combination. Performed 92 drop rate tests. • Calculated gap for each drop rate test. • Plotted gap to get zero pressure gap to be used with the diameter. 2011 NCSLI Workshop & Symposium

  15. Single Piston Method - Gap Determination • Where • h = average gap between piston and cylinder. • L = engagement length of piston cylinder • R = radius of the piston • Vfl = volume flow calculated by piston drop rate • Pgauge = gauge pressure of the fluid 2011 NCSLI Workshop & Symposium

  16. Single Piston Method - Gap Determination 2011 NCSLI Workshop & Symposium

  17. Single Piston Method - Gap Determination • Keys to performing the drop rate tests. • Started with high end industrial drop indicator. • Kept getting stuck. • Contact reduced rotation times. • Found out that the internal non-contact position sensor performed very well if calibrated every day – 2 minute procedure. • It was essential to perform the tests from approximately +1.5 to -1.5 mm to match the dimensional tests on the piston. • Could not have ANY air in the system, went through extensive purge procedure. • Temperature had to be very stable. Used piston-cylinder temperature for the temperature of the media. • Isolated pressure directly outside the piston gauge to reduce environmental temperature influences on the fluid. (changes were usually less than 0.02 deg for each test) • Leveled as best as possible for each test. 2011 NCSLI Workshop & Symposium

  18. Single Piston Method - Gap Determination Using the average piston radius and the average of the gaps at zero pressure, the result effective area at 20˚C and zero pressure is 4.9033956 mm2. +1.4 ppm from CalChain Determination 2011 NCSLI Workshop & Symposium

  19. Single Piston Method - Gap Determination • Result was actually much better than the uncertainty analysis. 2011 NCSLI Workshop & Symposium

  20. Conclusion • Results are good due to the keys described earlier. • All methods of validation show that the CalChain to 200 MPa is within stated uncertainties. • Would like to move forward with FEM analysis, Heydemann and Welch model and also verify using a smaller piston in the same cylinder. • The 100 – 500 MPa part of the CalChain will be re-characterized at the end of 2012. Will attempt to repeat this process. • Thanks to Ken Kolb and NIST. 2011 NCSLI Workshop & Symposium

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