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Doc. No. C-09-1-0022-2000 (E) CALIBRATION PROCEDURE

Version 1(E) Oil Pressure Balance /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



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 ① 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. ② 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



the piston and cylinder clean nitrogen is used to remove lint particles. To evaporate water rapidly, vacuum pump can be used.

5.2 Installation ① 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. ② 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.

③ Lines are kept short and internal diameters should be as large as is practicable. ④ Leak check should be done at maximum pressure. ⑤ 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

PFAe / (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[

rcp

mai

TTCgM

F

(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,



cp , 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( pAA oe (3)

to the Ae(p) data obtained from the cross-float measurements.

6.2 Experimental Arrangement ① Measure the reference level difference of standard and DUT. ② Set up the weights corresponding to the measuring pressure respectively. ③ Both pistons are raised above their operating level with the help of the screw ④ After closing the isolating valve which is placed between two pressure balances, measure the

fall rates of both pistons using x-t recorder. ⑤ Open the isolating valve. ⑥ 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 ④. ⑦ When balance is attained, the applied loads and the piston temperatures are recorded. ⑧ Repeat the procedures from ② to ⑦ 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



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[

rcp

ma

TTCgM

F

(4)

2) The area of the test gauge at each pressure is calculated using the expression PFAe /

3) To obtain an expression for calculating the area at any pressure, the P and eA data have been

fitted to the following equations

PAF 0 (5)

PPAF )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.



7.2 Type B uncertainty 1) Relative uncertainty in downward force acting on p/c of test gauge is given by

2)1( ii

t

tFt dx

xF

Fu

(7)

where ix is the influence quantity.

ix Value

i

t

t xF

F 1

Value idx

(1 ) 2)1( i

i

t

t

dxxF

F

m m/1

g 1/g

a m/1

m 2m

a

gmC /

C gm/

cp rtt

rtt cp

tan

Total

2) Relative uncertainty in downward force acting on p/c of standard gauge is given by

2)1( ii

s

sFs dx

xF

Fu

(8)

ix Value

i

t

t xF

F 1

Value idx

(1 ) 2)1( i

i

t

t

dxxF

F

m m/1

g 1/g

a m/1



m

2m

a

gmC /

C gm/

cp rtt

rtt cp

tan

h mA af /)(0

f mhA /0

Total

3) Relative uncertainty of effective area of standard gauge, Asu

2)1( ii

s

sAs dx

xA

Au

(9)

ix Value

i

s

s xA

A 1

Value idx

(1 ) 2)1( i

i

s

s

dxxA

A

0A 0/1 A

1 0/ AFs

Total

7.3 Relative combined uncertainty, cu

2222AsFsFtAc uuuuu (10)

7.4 Expanded relative uncertainty, U

cukU (11)

8. Records

Completely fill out the ‘Data Record Format” without any vacancies in the attached sample.



9. Calibration Certificate and Calibration Results See the attached samples.



Data Record Format

Requested by Measurement No. Date Ref. Level Ht differ. STD PG Base Unit Test PG Base Unit STD PG P/C No. Test PG P/C No. STD PG Mass No. Test PG Mass No.

Room Atmosphere Weight combinations P/C Temp. Press. T(C) P(hPa) RH(%

) STD TEST

No.

(Unit)

Time

Mass # EA

Add (g)

Mass # EA

Add (g)

STD TEST Remark

1

2

3

4

5

6

7

8

9

10



Certificate of Calibration (1) Page of (2) Pages

① 의뢰기관 Applicant O O O ② 교정번호

Certificate No. 01-03589-001

품 명 Description Oil deadweight tester (유압분동식압력계)

③ 측정기 Calibration Item

제작회사 및 형식 Manufacturer & Model OOO 기기번호

Serial No. 7384

④접수일자 Date of receipt 2001.03.13

⑤ 교정일자 Date of cal.

2001.04. 02 ⑥ 교정장소 Calibration Site

고정표준실 이동교정실 현장

⑦ 교정환경 Environment

온 도 Temperature (23 ± 1) ℃ 상대습도

Relative Humidity 55 % 이하

⑧ 교정방법 Cal.ibration Method

유압분동식압력계의 표준교정절차서(KRISS C-09-004 ) Calibration procedure of oil pressure balance (KRISS C-09-004)

⑨ 교정에 사용한

표준기의 소급성 Calibration Traceability

상기 기기는 다음의 압력계를 표준기로 사용하여 비교 교정 하였다. The above test gauge was calibrated by the following standard gauge.

* 사용한 표준기 : 유압분동식압력계 Standard gauge : Oil Pressure Balance (Ruska, Model No. : 2450-601-14900, Ser. No. : 25616) * 표준기 불확도 : 별첨 “교정 결과” 참조 Uncertainty of standard gauge : See attached sheet

권장차기교정일(Recommended Next Calibration Date): 2003.04.02

(자체규정에서 교정주기를 정한 경우는 그에 따름)

⑩ 교정결과

Calibration Results 별첨 “교정 결과” 참조

See attached sheet

⑫ 불 확 도 Uncertainty

별첨 “교정 결과” 참조 See attached sheet

⑪ 담당자 Calibrated by

(042) 868-5119, Kim, Boo-Shik

위의 교정결과는 국가표준기본법 제13조 규정에 의거 국가측정표준과 소급성이 확립된 측정기로 교정한 성적서 임을 증명합니다. (We certify that this certificate is based on the calibration by the measurement standards traceable to the national measurement standards being held and operated by the Korea Research Institute of Standards and Science in accordance with the provision of Article 13 of the Framework Act on the National Standards.)

2001 년 04 월 03 일

교정책임자(Approved by) ; 직 책(급) Principal Researcher , 성 명 000 , 서 명 국가측정표준대표기관 National Metrology Institute

한 국 표 준 과 학 연 구 원 장 Korea Research Institute of Standards and Science Seal of the President 대전광역시 유성구 도룡동 1번지, Tel: 042) 868-5403, Fax: 042)868-5555

(주의) 이 성적서는 상기 교정기기에 한하여 유효하며, 한국표준과학연구원장 승인 없이 수정 또는 재 발행 할 수 없습니다.

P-22-01(A)/03 개정 ’01.3.



CALIBRATION RESULTS ===================== Cal. No. :01-01664-002 (2) Page of (2) Pages

SUBMITTED BY : OOO Co.

DATE : 2001. 1.04

MAKER : NAGANO

MODEL NO. : NONE

SERIAL NO. : 1516

PISTON NO. : NONE

CYLINDER NO. : NONE

UNIT : kgf/cm2

* EFFECTIVE AREA OF PISTON/CYLINDER

A0(23;atm) = 4.999221D-05 m^2

* PRESSURE DISTORTION COEFF. = 6.187D-11 /Pa

= 6.067D-06 /kgf/cm2

* STANDARD UNCERTAINTY OF THE EFFECTIVE AREA = 2.2 D-09 m^2

* EXPANDED UNCERTAINTY = 0.0088% OF READING

1.THIS UNCERTAINTY IS CALCULATED FROM THE RSS OF THE

A-TYPE UNCERTAINTY OF EFFECTIVE AREAS OF THE TEST

PISTON GAUGE AND B-TYPE UNCERTAINTIES OF FORCES ACTING

ON STANDARD & TEST PISTON GAUGE AND B-TYPE UNCERTAINTY

OF EFFECTIVE AREAS OF STANDARD PISTON GAUGE.

2.COMBINED STANDARD UNCERTAINTY : 0.0044% AT MAX.P

3.CONFIDENCE LEVEL = 95 %

4.COVERAGE FACTOR = 2

5.UNCERTAINTY OF STANDARD GAUGE: 0.0061% OF READING

(COVERAGE FACTOR k=2, 95% CONF. LEVEL)

Note) The long term stability of test gauge is not included in the above uncertainties.

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