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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
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.
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
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.
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.