Vacuum Standards

Characterization of Gas Operated Piston Gauge against UIM, the Nation Primary Standard:

We have evaluated of measurement uncertainty using:

(a) Method of Effective Area Estimation of Piston-Cylinder assembly

Preparation of Uncertainty Budget

Determination of Coverage Factor for the required confidence level

Estimation of expanded uncertainty

Q(0.05 Pa, 0.000828 % of reading) at k=2.

(b) Method of Direct Comparison

Preparation of Uncertainty Budget

Determination of Coverage Factor for the required confidence level

Estimation of expanded uncertainty

Q(0.05 Pa, 0.0008 % of reading) at k = 2.

Bilateral Comparison between NIST, USA and NPL, India

The Artefact came from NIST, USA consisted of four numbers of Resonant Silicon Gauges – (RSGs) housed in IGLOU. These four RSGs are : RSG # A : Range: 0 to 10 kPa (abs); RSG # B : Range: 0 to 10 kPa (abs); RSG # C : Range: 0 to 130 kPa (abs) and RSG # D : Range: 0 to 130 kPa (abs). We have collected the data as per the protocol which is agreed upon by both the laboratories. The precise measurements included the collection of minimum ten zero data initially for each set, eight pressure points (RSG # A and RSG # B) in the range 0 to 10 kPa (abs), five data points in each Pressure points, twelve Pressure points (RSG # C and RSG # D) in the range 0 to 130 kPa (abs), five data points in each Pressure points and ten sets of data collection over a period of three months (Jan – Mar, 2008) and finally, five sets required for each RSG (4 Nos). The compilation of collected data and analysis is in progress.

In-house calibration of reference standards

A large numbers of reference standards namely SRGs (NPL-0, NPL-1, NPL-5), CDGs (100 torr abs (2 nos.), 10 torr abs, 10 torr diff, 0.1 torr (abs.)), Resonant silicon gauges, Digital pressure indicator have been carried out for use on our primary standards and for customer gauge calibration. Resuming of calibration service of Standard Leaks for industry. We have fabricated an Igloo package capable of housing our reference gauges at NIST, USA. This package has been given by NIST, USA as a free gift to NPLI.

Studies on the binding energy of H2O and H2 on SS surfaces.

Two methods were adopted for this purpose: in the first method, TPD studies were conducted while in the second, actual desorption species of gas evolved during bakeout of a UHV system were monitored at NIST, USA.

Pressure standards

Draft report of key comparison APMP.M.P-K6

The regional key comparison APMP.M.PK6 for pressure measurements in gas media and in gauge mode from 20 kPa to 105 kPa was piloted by the Pressure and Vacuum Standards of NPLI, New Delhi. The transfer standard was a pressure-balance with a piston–cylinder assembly with nominal effective area 335.7 mm2 (TL-391). Nine laboratories from the APMP region; namely KRISS (Korea), NMI (Australia), NMI (Japan), MSL (New Zealand), SPRING (Singapore), NML-SIRIM (Malaysia), SCL (Hong Kong) and NMI (South Africa) with one specially invited laboratory from the EURAMET region, namely Physikalisch-Technische Bundesanstalt (PTB), Germany, participated in this comparison. The obtained data were compiled and processed under the same program as per the Consultative Committee for Mass and Related Quantities (CCM)/BIPM guidelines and establish a link with CCM.P-K6 through the link laboratory PTB (Germany). Figure 1 shows the degree of equivalence between CCM.P-K6 key comparison participants, namely NMi-VSL(The Neither land), METAS (Sweden), PTB (Germany), NIST (USA), NIM(China), NPL(UK) and NRC(Canada) with the APMP participants mentioned above. These results show an excellent agreement of all participating laboratories within the estimated expanded uncertainties using a coverage factor k = 2 (Fig.1.8).

Fig. 1.8 : Summary of results for the degree of equivalence for each NMI with respect to the key comparison reference value for CCM.PK6 ( red mark) and APMP.M.P-K6 (green mark).

The effect of pressure transmitting fluids in the characterization of a controlled clearance piston gauge up to 1.0 GPa

The studies were carried out on the effect of different pressure-transmitting fluids (PTFs) on the systematic characterization of an oil-operated controlled clearance piston gauge (CCPG) (nominal diameter of the piston, 2.5 mm) in the pressure range up to 1000 MPa (1GPa). Pure and mixtures of different PTFs are studied and four will be discussed here; namely, (a) pure normal hydraulic oil (J-13), (b) mixture of J-13 and aviation turbine fuel (ATF), (JATF), (c) pure di-ethyl-hexyl-sebacate oil (BIS) and (d) the mixture of white gasoline (G), J-13 and sebacate (GJBIS).

The characterization is the measurement of the fall-rate of the piston as a function of applied jacket pressure (pj) with various PTFs using the method of Heydemann and Welch (HW model). The analysis of the results is the determination of the cube root of the piston fall-rate (v1/3) with pj at different loads or measured pressures (pm). The linear portion of this v1/3 – pj curve is extrapolated towards the null value of fall-rate, and the stall jacket pressure (pz) at different pm is obtained. It is observed that reasonably good fall-rate data could be obtained for J-13, JATF and BIS up to maximum pressures of 500 MPa, 700 MPa and 650 MPa, respectively. For GJBIS, this fall-rate data can be obtained up to a maximum pressure of 1 GPa. From the values of pz at different pm and also the values of jacket pressure coefficient (d) along with other characteristic parameters in the HW model, we have determined the relative standard uncertainties in the effective area (u(Ae)/Ae) for GJBIS up to 1 GPa for pj = 0 (free deformation mode) and pj /pm = 0.3. It is interesting to note that for pj = 0, at a pm of 100 MPa, u(Ae)/Ae is 74 x 10–6 while at a pm of 1 GPa, u (Ae)/Ae is 248 x 10–6. However, for pj /pm = 0.3, at a pm of 100 MPa, u(Ae)/ Ae is 67 x 10–6, while at a pm of 1 GPa, u(Ae)/Ae is 125 x 10–6. A comparative study of u(Ae)/Ae has been elaborated with the four PTFs investigated. We have shown that at a pm of 100 MPa, u(Ae)/Ae is 202 x 10–6, 114 x 10–6, 66 x 10–6 and 67 x 10–6, for J-13, JATF, BIS and GJBIS, respectively, while at a pm of 500 MPa, u(Ae)/Ae is seen to be 97 x 10–6, 57 x 10–6, 46 x 10–6 and 56 x 10–6 for J13, JATF, BIS and GJBIS, respectively. Our measurements show that GJBIS is a convenient PTF for working up to 1 GPa. Finally, the results of the characterization are compared with the NPLI pressure scale through calibration of a NPLI secondary standard which is traceable to the LNE (France) pressure scale though direct comparison and participation in a recently concluded bilateral comparison with NIST (USA).

Characterization of a hydraulic Piston Gauge up to 50 MPa

We have evaluated of measurement uncertainty of a newly acquired Piston gauge from 0.1 MPa to 50 MPa using the method of crossfloat with reference to the national secondary standard and determine effective Area of the Piston-Cylinder assembly. Evaluation of measurement uncertainty shows that the relative expanded uncertainty is < 43 x 10-6 at k = 2.

Coordinated and completed three proficiency testing

NABL-Pressure-PT005: This PT is organized for the laboratories having measurement capabilities better than 0.25 % and coarse than 0.05% of full scale using digital pressure calibrator as an artifact in the pressure range 7 – 70 MPa. The second phase of the PT is already completed during March 2007. There are total 23 participating laboratories. All the laboratories have performed measurement during and the results are being compiled.

NABL-Pressure-PT006: This PT is already completed. It was organized for the laboratories having measurement capabilities coarse than 0.25 % of full scale using pressure dial gauge as an artifact in the pressure range 10 – 70 MPa. There were total 17 participating laboratories. During the period under report, final report is prepared and submitted to NABL. Out of the total 159 measurement results reported, 135 (84.91 %) measurement results are found in good agreement with the results of the reference laboratory, NPLI, New Delhi, in the present case.

NABL-Pressure-PT007: This PT is also completed. It was also organized for the laboratories having measurement capabilities coarse than 0.25 % of full scale using pressure dial gauge as an artifact in the pressure range 6 – 60 MPa. There were total 17 participating laboratories. During the period under report, final report is prepared and submitted to NABL. Out of the total 117 measurement results reported, 95 (81.2%) measurement results are found in good agreement. Overall, the results are considered to be reasonably good, being the first proficiency testing for most of the participating laboratories.

High pressure pneumatic controller installed and tested to 250 bar

For the upgradation of pneumatic pressure facility a pneumatic pressure intensifier along with a high pressure gas controller/calibrator were successfully installed and tested upto 250 bar. These along with our newly procured high pressure piston cylinder assembly would enhance our pneumatic capability.

Basics of ANSYS simulation software utilization

Preliminary ANSYS analysis was carried out for pneumatic piston cylinder assembly wherein Finite Element Meshing was employed to simulate the stress/ strain on the piston cylinder assembly and also the distortion in the cylinder under the influence of pressure upto 8 GPa. Our results showed a close agreement with the effective area calculation when calculated using ANSYS software and simulation method. Further work in underway.

Development of Window-based Software for the calibration of hydraulic pressure measuring instruments

Work for developing the above software started. The starting point was the presently used DOS-based software in Quick Basic, which is monolithic (non-modular) and makes use of files to store data. The new software would be modular, which makes it easier to maintain and upgrade and it also uses RDBMS tables to store data. Moreover, it will have well designed interface screens for user interaction. Software Engineering Methodology of Structured Analysis and Design will be applied for developing the software.

DST sponsored project entitled “High Pressure Raman studies of rare earth sesquioxides”

We have carried out Raman spectroscopic studies on Y2O3, Gd2O3 and Sm2O3 under high pressures in a diamond anvil cell. The results are very interesting and submitted for publication. Presently we are in the process of carrying out high pressure work on other rare earth sesquioxides. Apart from these we have also been collaborating with various institutes for Raman analysis under ambient conditions and have carried out Raman spectroscopy work for Delhi University- Carbon nanotubes, SN Bose Institute- Mg and Cd doped ZnO, and Jamia Millia Islamia- Si etched GaAs samples