calibration procedure kriss

Download Calibration Procedure Kriss

Post on 18-Apr-2015

53 views

Category:

Documents

3 download

Embed Size (px)

TRANSCRIPT

Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 1 /10 Contents 1. Scope --------------------------------------------------------------------------------------- 2/10 2. References --------------------------------------------------------------------------- 2/10 3. Terminology --------------------------------------------------------------------------- 2/10 4. Calibration Item -------------------------------------------------------------------------- 2/10 5. Preparation ----------------------------------------------------------------------------------- 2/10 6. Calibration ----------------------------------------------------------------------------------- 3/10 7. Uncertainty Evaluation -------------------------------------------------------------------- 5/10 8 Records ----------------------------------------------------------------------------------- 7/10 9.Calibration Certificate ------------------------------------------------------------------ 7/10 AMENDMENT RECORD Amended Item (or Section) Version Date Contents 1(E) 2001/6/15 English version of C-09-1-0022-2000 Drafted by Reviewed by Authorized by Woo, Sam-Yong - - - Han, Seung-Woong Chung, Kwang-Hwa Director Division of Physical Metrology Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 2 /10 1. Scope This procedure describes the calibration and uncertainty evaluation method of pressure balances used for the calibration of various kinds of pressure gauges. This procedure includes for the calibration of oil pressure balances in gauge mode. 2. References Guide to the Expression of Uncertainty in Measurement, ISO(1993). Heydemann and Welch, Experimental Thermodynamics, Vol.2, ch.4, Butterworth, London(1975) Deadweight Pressure Gauges, NCSL RISP-4(1998) Pressure Balance, OIML R 110(1994) Recommended procedure for the calculation and expression of pressure balance measurement uncertainties, NPL Report MOM 122 Recommended contents for pressure balance calibration certificates, NPL Report MOM 123 3. Terminology Pressure balance : generally consists of following main parts: a) piston-cylinder assembly with weight carrier b) set of weights c) pressure fitting for connecting another pressure gauge. 4. Calibration Item Pressure 5. Preparation 5.1 Cleaning Oil pressure balance will usually operate satisfactorily under most conditions, but damage can result if particles of dirt become lodged between the piston and cylinder. Oil pressure balance should be cleaned with solvents whenever a change is made from oil to another. To obtain the highest performance one method is simply to use neutral soap and warm water. The piston and cylinder should be scrubbed thoroughly, rinsed with warm water, air blasted to remove the water droplets and finally polished with lens tissue. Before assembling Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 3 /10 the piston and cylinder clean nitrogen is used to remove lint particles. To evaporate water rapidly, vacuum pump can be used. 5.2 Installation Pressure balance should be placed on a table that is strong enough not to tilt under a varying load. Table tops should be non-magnetic. When connections are made, care should be taken to install the properly rated tubing, fittings, valves, etc. Plumbing material should be chosen to be fully compatible with pressure fluid and be cleaned to remove particles. Lines are kept short and internal diameters should be as large as is practicable. Leak check should be done at maximum pressure. Leave the gages for several hours until temperature equilibrium reaches. 6. Calibration 6.1 Cross-float calibration technique Both pressure balances are connected to a common pressure line along with an appropriate pressure generator. The effective area of the test gauge is P F Ae/ = (1) where p is the pressure generated at the reference level of the test gauge by the standard gauge and F is the force exerted on the piston of the test gauge which is ) )( ( 1)] / ( 1 [r c pm a iT TC g MF + + + = o o (2) where iM are the masses of the piston, weight hanger and weights corresponding to P, a is the density of the ambient air, m is the density of the material from which the weights are made, g is the local acceleration due to gravity, is the surface tension of the pressurizing fluid, C is the circumference of the piston in the test gauge, Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 4 /10 c p o o , are the linear thermal expansion coefficients of the piston and cylinder. For simplicity, the temperature correction of the area has been included with the force. The two gauges are brought into pressure equilibrium by adjusting F and then Ae is calculated by equation (1). Values of Ae are determined over the entire operating pressure range of the test gauge. The effective area at atmospheric pressure, Ao, and the coefficient can be obtained by fitting ) 1 ( p A A o e + = (3) to the Ae(p) data obtained from the cross-float measurements. 6.2 Experimental Arrangement Measure the reference level difference of standard and DUT. Set up the weights corresponding to the measuring pressure respectively. Both pistons are raised above their operating level with the help of the screw After closing the isolating valve which is placed between two pressure balances, measure the fall rates of both pistons using x-t recorder. Open the isolating valve. Add or remove small mass onto the piston to make balance state. At this state both pistons must have the same natural fall rate as . When balance is attained, the applied loads and the piston temperatures are recorded. Repeat the procedures from to at next pressure point. The time interval between two successive loadings shall be as uniform as possible, and no reading shall be taken at least 15 min after the start of the pressure change. 6.3 Data evaluation Calibration curve of pressure balance is calculated from the following equation (3). At low pressures, the pressure coefficient is usually insignificant. The computer program used for these Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 5 /10 calculations provides pressure coefficients and standard deviation of residuals. A plot of the effective area as a function of pressure will show which equation is appropriate. 1) The pressure p at the reference level of the test gauge is determined by the KRISS standard pressure gauge. The temperature corrected force F on the test gauge are calculated using the expression ) )( ( 1)] / ( 1 [r c pm aT TC g MF + + + = o o (4) 2) The area of the test gauge at each pressure is calculated using the expression P F Ae/ = 3) To obtain an expression for calculating the area at any pressure, the P and eA data have been fitted to the following equations P A F0= (5) P P A F ) 1 (0 + = (6) 0A is the extrapolated area at zero applied pressure and reference temperature, is the linear pressure coefficients for the area. 7. Uncertainty evaluation 7.1 Type A uncertainty, Au A graph is plotted of the effective area against pressure. It is often sufficient to use the method of Gauss to fit a straight line to the results: the gradient gives the distortion coefficient and the intercept with the abscissa gives the effective area extrapolated to zero applied pressure. The method gives the experimental standard deviation of the estimated mean value of eA (i.e. at the centroid) and the experimental standard deviation of the gradient. The uncertainty of eA is a minimum at the centroid and increases as one moves to higher or to lower pressures. Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 6 /10 7.2 Type B uncertainty 1) Relative uncertainty in downward force acting on p/c of test gauge is given by 2)1( iittFt dxxFFucc= (7) where ix is the influence quantity. ix Value itt xFF cc 1 Value idx (1o ) 2)1( iittdxxFF cc m m / 1 g 1/g a m / 1 m 2ma gm C / C gm / c p o o + rt t rt t c p o o + u u tan Total 2) Relative uncertainty in downward force acting on p/c of standard gauge is given by 2)1( iissFs dxxFFucc= (8) ix Value itt xFF cc 1 Value idx (1o ) 2)1( iittdxxFF cc m m / 1 g 1/g a m / 1 Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 7 /10 m 2ma gm C / C gm / c p o o + rt t rt t c p o o + u u tan h m A a f/ ) (0 f m h A /0 Total 3) Relative uncertainty of effective area of standard gauge, Asu 2)1( iissAs dxxAAucc= (9) ix Value iss xAA cc 1 Value idx (1o ) 2)1( iissdxxAA cc 0A 0/ 1 A 1 0/ A Fs Total 7.3 Relative combined uncertainty, cu 2 2 2 2As Fs Ft A c u u u u u + + + = (10) 7.4 Expanded relative uncertainty, U cu k U = (11) 8. Records Completely fill out the Data Record Format without any vacancies in the attached sample. Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE Version 1(E) Oil Pressure Balance Page 8 /10 9. Calibration Certificate and Cal

Recommended

View more >