National Physical Laboratory India Research Articles

Comparison of four-terminal-pair 1 pF, 10 pF, 100 pF and 1000 pF capacitance standards at frequencies of 10 kHz, 100 kHz, 1 MHz and 10 MHz (APMP.EM-S15)

Main textIn order to calibrate an LCR meter, metrological traceability of capacitance above 10 kHz becomes more and more important. For this reason, NIM (National Institute of Metrology, China)，NPLI (National Physical Laboratory, India) and NIMT (National Institute of Metrology, Thailand) have carried out research on capacitance metrology from 10 kHz to 10 MHz.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Evaluation of effective area of air piston gauge with limitations in piston–cylinder dimension measurements

The air piston gauge (APG) has been established at the National Physical Laboratory, India (NPLI) for Pascal realization since 2002. The APG at NPLI has been considered a transfer pressure standard because it has been calibrated against the primary pressure standard, i.e. ultrasonic interferometer manometer. As per existing international protocol, the APG establishment as a primary standard, the effective area (A e) of piston–cylinder (p–c) assembly and masses must be directly traceable to SI units. We have calculated A e and associated uncertainty of p–c assembly using the theory of rarefaction gas dynamics, which is based on dimension measurements. The value of A e is obtained for varying temperatures and radii of piston and cylinder in their respective uncertainty limits. The variation of the cylinder's inner radius within its uncertainty limit of 0.7 µm includes the expected effective area, i.e. 3.356 775 (5) cm2. The effective area’s expected values are obtained for the cylinder’s radius of 10.338 00 (2) mm, which is approximately 0.65 µm away from the value obtained from dimensional measurements and well within the uncertainty limit. Therefore, to get the effective area of 3.356 775 (5) cm2, the uncertainty of the cylinder’s radius should be at least one order less (similar to piston’s radius) than that of the present value. The precision in dimension measurement of the cylinder's internal radius is the critical parameter for effective area calculation of p–c assembly.

Characterization of spinning rotor gauge-3 using orific flow system and static expansion system

This article elucidates the calibration of newly procured spinning rotor gauge (SRG 3) from MKS Instruments, USA using primary vacuum standards: Orifice flow system (OFS) and Static expansion system (SES) established at National Physical Laboratory, India (NPLI) in the range of 10<sup>-4</sup> Pa to 1 Pa and further compared with manufacturer reported value which was calibrated by transfer standard of National Institute of Standards & Technology (NIST). The key parameters to calculate the pressure measured by SRG is the accommodation coefficients. The accommodation coefficients for N<sub>2</sub> gas obtained using OFS, SES, and calibration report form NIST USA (SRG2) are 0.957, 0.961, and 0.954 respectively.

Uncertainty evaluation and phase variation of ultrasonic interferometer manometer: A primary pressure and vacuum standard

The ultrasonic interferometer manometer (UIM) is an apex level primary pressure standard for Pascal realization established at National Physical Laboratory India (NPLI). The performance of UIM has been evaluated from time to time by participation in key comparisons, calibration and measurement capabilities (CMC) and publications in reputed international metrology journals. The pressure is measured using time of flight technique at 44 different frequencies in ultrasonic range and the phase measurement. The phase measurement combined with the time of flight measurement using the exact fractional algorithm provides highly accurate column length hence respective pressure values. The combined process helps in lowering the uncertainty in real experimental conditions. Recently, we have also changed UIM software from tbasic to window based program with the same algorithm which provides a column length measurement study. A detailed study was carried out for variation of fringe counts or oscillations with varying pressure. Experimental and theoretical calculation for both resolution and pressure dependent part has been carried out for uncertainties involves the physical parameters. The uncertainties in lower pressure range, i.e., between 1 Pa and 1000 Pa were varying equal or sometimes higher than the theoretical resolution value 0.0092 Pa (k = 2) because of environmental conditions like vibration, temperature, atmospheric pressure, and humidity whereas for higher pressure range, i.e., 1000 Pa to 130 kPa the uncertainties were either close or smaller than the pressure dependent theoretical uncertainty value, i.e. 7.2 × 10−6 of the reading.

Realization of 2.4 mm coaxial microcalorimeter system as national standard of microwave power from 1 MHz to 50 GHz

A 2.4 mm coaxial microcalorimeter system based on thermoelectric principle has been realized as a national standard of microwave power at National Physical Laboratory India (NPLI). The design is based on two symmetrical and thermally isolated transmission lines, one connected to power standard and the other connected to an identical power standard used as a thermal reference. The main function of the system is to determine the temperature variation between the two power standards, which is of the order of few milli-Kelvin, using a specially designed thermopile. The coaxial microcalorimeter along with the thermocouple power sensor will provide traceable measurements from 1 MHz to 50 GHz. An interlaboratory measurement comparison of microwave power for the validation of the 2.4 mm coaxial microcalorimeter system has been carried out between NPLI and Laboratoire National de Métrologie et d'Essais (LNE) France. The difference between the effective efficiency evaluated by the two laboratories was less than 0.5% at all frequency points. The normalized error value of NPLI for effective efficiency varies between −0.23 and +0.09 with respect to LNE. The result shows good agreement in assigning the effective efficiency to power sensor among the two labs within their claimed expanded uncertainty. It proves the degree of equivalence in measurements between two national metrology institutes (NMIs).

Realization of Four-Terminal-Pair Capacitors as Reference Standards of Impedance at High Frequency Using Impedance-Matrix Method

The four-terminal-pair air capacitors of nominal values 1000 and 100 pF have been realized as reference standards of impedance upto 10 MHz using impedance-matrix method. The reported work has been successfully practically implemented at the National Physical Laboratory India (NPLI) in the direction of establishing metrological traceability of capacitance standards at high frequency (HF). The realization procedure is based on the determination of effective capacitance of each capacitor as a function of frequency upto 10 MHz. It involves single-port-impedance measurements at HF using RF impedance analyzer and capacitance measurements at 1 kHz using ultraprecision capacitance bridge. The least squares data approximation method is thereafter used to extrapolate the resistive and inductive components of the measured HF single-port-impedances to lower frequencies down to 1 kHz. The measurement automation program has been developed to measure the single-port impedances at set of frequencies between 40 and 100 MHz using impedance analyzer. The air capacitors characterized using impedance-matrix will be used as reference standards of impedance at NPLI to calibrate impedance bridges, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCR</i> meters, and impedance analyzers upto 10 MHz.

Validation of Software Used for Calibration of Angle Block at CSIR-NPL, India

In the field of dimensional metrology, angle blocks are calibrated using a precision indexed rotary table in conjunction with an autocollimator. Only few national metrology institutes (NMI) of developed counties has sophisticated automatic setup of indexed table, autocollimator. NMIs use individual analytical model for angle block calibration. Based on the analytical model, NMIs has exclusively written software to generate calibration results. Some NMIs of developing economics manually operate indexed rotary table, autocollimator for angle calibration. The readings of indexed table, autocollimator are recorded manually. The results are calculated manually or on excel sheets. Frequently, operator commits mistakes in determining the sign of angular deviation. At National Physical Laboratory-India, a generic analytical mathematical model is devised for angle block calibration. Software entitled “Calibration of angle gauge” is developed. The software takes readings of indexed table, autocollimator to calculate the angular deviation of angle block. Instead of direct coding the generic analytical mathematic model, the software is written with logical basis of the generic analytical mathematic model. A set of measurement readings of angle blocks are used as reference data to validate the software and analytical model.

Development of automatic intercomparison system for generation of time scale ensembling several atomic clocks

National physical laboratory India (NPLI) has five commercial cesium atomic clocks. Till recently one of these clocks had been used to maintain coordinated universal time (UTC) of NPLI. To utilize all these clocks in an ensemble manner to generate a smoother time scale, it has been essential to inter-compare them very precisely. This has been achieved with an automatic measurement system with well-conceived software. Though few laboratories have developed such automatic measurement system by themselves based on the respective requirements; but they are not reported. So keeping in mind of the specific requirement of the time scale generation, a new system has been developed by NPLI. The design has taken into account of the associated infrastructure that exists and would be used. The performance of the new system has also been studied. It has been found to be quite satisfactory to serve the purpose. The system is being utilized for the generation of time scale of NPLI.

Research Output on Biosensor Literature in India during 1988-2014: A Scientometric Study

The study presents the research output on biosensor literature in India during 1988-2014. A total of 1444 papers were found in the Scopus database. Starting with one research paper has been published on biosensor literature in India in the year 1998 and a maximum of 231 papers were published in the Scopus indexed journals in 2013. The National Physical Laboratory India has contributed the highest number of papers followed by Maharshi Dayanand University. Number of papers in the area of Biochemistry, Genetics, Molecular Biology, and Chemistry are being increased in the research output on Biosensor in India for the past five years.

Evaluation of Measurement Uncertainty for Absolute Flatness Measurement by Using Fizeau Interferometer with Phase-Shifting Capability

It is important to precisely measure flatness of the optical flats, as many industries use these as reference standards to ensure the quality of precision measurements and fabricated components. This paper describes identification of sources of error and measurement uncertainty evaluation for three flat test. Three flat test is used for absolute flatness measurement of optical flats, with the help of Fizeau interferometer (VerifireXP/D, with phase shift interferometry) established recently at National Physical Laboratory, India (NPL-I). The absolute profile of reference flat with higher accuracy can be determined using liquid level reference but liquid flat reference is more difficult to realize practically. Therefore three flat test is frequently adopted in standard interferometric measurements and traceability of this test can also be established by using a traceable laser head. This paper describes three flat method in detail along with observations and evaluation of measurement uncertainty as per ISO GUM is also done. Factors contributing to uncertainty of measurement of surface flatness have been indentified and detailed evaluation of uncertainty in measurements has been reported here.

Atomic clocks: A brief history and current status of research in India

Frequency corresponding to the energy difference between designated levels of an atom provides precise reference for making a universally accurate clock. Since the middle of the 20th century till now, there have been tremendous efforts in the field of atomic clocks making time the most accurately measured physical quantity. National Physical Laboratory India (NPLI) is the nation’s timekeeper and is developing an atomic fountain clock which will be a primary frequency standard. The fountain is currently operational and is at the stage of complete frequency evaluation. In this paper, a brief review on atomic time along with some of the recent results from the fountain clock will be discussed.

NPLI Cesium Atomic Fountain Frequency Standard: Preliminary Results

National Physical Laboratory India has developed a cesium atomic fountain frequency standard. The fountain has now become operational and is ready for complete frequency evaluation. In this paper, we report for the first time, the preliminary results obtained with this fountain, which include Ramsey fringes, frequency stability analysis, with an H-maser, and magnetic field mapping in the atomic flight region.

ESTABLISHMENT OF TRACEABILITY OF REFERENCE GRADE HYDROMETERS AT NATIONAL PHYSICAL LABORATORY, INDIA (NPLI)

The present paper discusses the establishment of traceability of reference grade hydrometers at National Physical Laboratory, India (NPLI). The reference grade hydrometers are calibrated and traceable to the primary solid density standard. The calibration has been done according to standard procedure based on Cuckow's Method and the reference grade hydrometers calibrated covers a wide range. The uncertainty of the reference grade hydrometers has been computed and corrections are also calculated for the scale readings, at which observations are taken.

Final report on APMP.M.M-K2.1: Bilateral comparison of four stainless steel mass standards (500 g, 20 g, 2 g and 100 mg) between KRISS and NPLI

This report describes a bilateral comparison of 500 g, 20 g, 2 g and 100 mg stainless steel mass standards between Korea Research Institute of Standards and Science (KRISS) and National Physical Laboratory, India (NPLI), which is registered in the KCDB as APMP.M.M-K2.1. These nominal values were chosen as they followed the nominal values of CCM.M-K2. This bilateral comparison was piloted by KRISS. The Measurement Standard Laboratory (MSL), New Zealand has provided a linkage analysis of this bilateral comparison to CCM.M-K2. The set of four weights was circulated between KRISS and NPLI laboratories in June 2010 and received back from the last participant in July 2010. NPLI has tried to improve their calibration and measurement capabilities (CMCs) for mass below 1 kg. KRISS participated in both this comparison and CCM.M-K2, providing the link between the NPLI results and the key comparison reference value of CCM.M-K2.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Co-author Pairs’ frequencies of the National Physical Laboratory India

Special collaboration structures (Gestalts) are studied on the basis of the publications data on papers published by the National Physical Laboratory, India, during 1997–2008. The corresponding three-dimensional distribution of the co-author pairs’ frequencies is compared with the distribution of the National Physical Laboratory, UK, as well as with distributions of two journals. The regularities for these four three-dimensional distributions are described by the same mathematical model (Social Gestalts). The varying shapes of these distributions are probably caused by the different research conditions. These new empirical results should initiate future research about the corresponding theoretical background followed by further empirical studies.

Validation of RF power standard in the frequency range of 100 MHz to 18 GHz by an inter laboratory data comparison

Radio frequency (RF) power is one of the most important quantities in RF metrology. An inter laboratory data comparison of RF power for the validation of a coaxial microcalorimeter has been carried out between Physikalisch-Technische Bundesanstalt (PTB-Germany) and National Physical Laboratory India (NPLI). A coaxial thermistor mount equipped with type N connector is used for this intercomparison. The results show good agreement in measuring the effective efficiency of the coaxial thermistor mount between the two laboratories within their claimed expanded uncertainty. It confirms the equivalence of national standards for RF power in the frequency range of 100 MHz to 18 GHz.

Static expansion primary vacuum standard — Part 1: Determination of the volume ratio of the expansion stage

Measurement of volume ratio forms an essential part of the characterization of a static expansion system (SES) for the generation of pressures in the medium and high vacuum region. Because of the complexity of the vacuum chambers, it is not possible to determine the absolute volumes of the chambers involved. Hence an expansion process is resorted to, in which the gas enclosed in the small volume at a known pressure is allowed to expand, under isothermal conditions, into the large volume. The accuracy of the volume ratio thus determined depends on the stability of the vacuum gauges used for the measurement of initial and the final pressures and the ambient temperature. High accuracy resonant silicon gauges (RSGs) of two different ranges, one 130 kPa full scale and the other 1 kPa full scale for measurement of the initial and final pressures are found to be useful. This paper reports the results obtained with these RSGs for the measurement of the volume ratio of the National Physical Laboratory, India (NPLI) SES which is nominally 2820. With the use of the RSGs, and calibrated platinum resistance thermometers (PRTs) mounted inside the vacuum chambers, it has been possible to measure the volume ratio within the relative expanded uncertainty (k = 2) of 0.0014. The results of the volume ratio determination exercise are given in this paper while the Part 2 of this paper will discuss the procedure for the calibration of spinning rotor gauges on the Static expansion primary standard.

Static expansion primary vacuum standard — Part 2: Characterization of two spinning rotor gauges

The Part 1 of this paper discussed the determination of the volume ratio of the Static Expansion Primary Vacuum Standard (SES). Part 2 of the paper discusses in detail the use of the SES thus characterized for generating primary pressures. This standard has been used to calibrate Spinning Rotor Gauges (SRGs) at a number of pressures in the range 0.1 Pa to 1 Pa in steps of 0.1 Pa. The Gauge Coefficient at each of these pressures, defined as equal to the ratio of the indicated pressure to the true pressure is then plotted against the true pressure. The resulting straight line plot has a negative slope and its intercept equals the gauge coefficient. Two SRGs, NPL-0 and NPL-2 thus calibrated are used (i) as a device for measuring the pressure rise in the flowmeter of the National Physical Laboratory, India (NPLI) orifice flow system and (ii) as a secondary standard for the calibration of the user gauges.

AC power &amp; energy standard — NPLI measurement, calibration &amp; testing

AC power & energy standard of National Physical Laboratory, India (NPLI) is responsible for maintenance of national measurement standard of ac power & energy and international traceability through intercomparisons. It serves as the basis for dissemination of traceability in measurement through high level calibration and measurement services to the various user organizations in the country. It also supports and helps the industries in improving the measurement assurance systems through interlaboratory proficiency testing (PT) program and in solving actual field problems. Power measurement at zero power factors using zero power factor standards is described as it is used in intercomparison. The performance of energy meters under the various influence quantities is described as a service to the industries.

Time scale of NPLI: current status and future plan of improvement

The National Physical Laboratory, India (NPLI), is responsible for maintenance and development of the Indian Standard Time (IST) and also contributes through the GPS network to the generation of UTC coordinated by BIPM. Recently NPLI has made some special efforts to improve the uncertainty of UTC(NPLI) with respect to UTC. One basic clock ensemble algorithm is implemented to make the time scale of UTC(NPLI) by combining the intercomparison data of five caesium clocks. Some initial tests have been carried out to check the validity of this algorithm. The recent UTC − UTC(NPLI) values (shown in Circular T) and the corresponding frequency offset with respect to UTC have exhibited significant improvements. This paper describes these studies and presents the analysis of these observations.