National Physical Laboratory Research Articles

Importance of Standards in Biomedical Device and Its Role in Strengthening the Healthcare Sector

Biomedical Metrology group of CSIR-NPL (Council of Scientific and Industrial Research—National Physical Laboratory), India is contributing significantly for establishing National Biomedical equipment standardswhich are traceable to primary standards to cater the quality control regulation in Health sector. This initiative has great impact on the health policy and Nation's economy as well. The laboratory has recently established biomedical equipment standard facility and disseminated the services to Industries, stake holders, hospitals and accredited laboratories. Although, the laboratory is successfully providing biomedical equipment calibration services for last 2 years, the sensitization of the information on the recently established metrological capabilities is required, which has great implications in implementation of India's New medical Device rule 2017 effectively. The present paper describes the summary on the significant achievements and role of National Physical Laboratory in supporting the Indian medical device regulations.

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.

Modeling the natural gas knocking behaviour using gas-phase infrared spectra and multivariate calibration

To assess the knocking properties of natural gas (NG) when it is used as fuel for vehicles is vital to optimize the design and functioning of their motors. Analytical efforts in this field are needed as the engines used to define it empirically are not available anymore, and existent mathematical algorithms yield different accuracy. The hybridization of gas-phase infrared spectrometry and partial least squares multivariate regression is presented first time to address the determination of the methane number (MN) of NG samples. It circumvents the need for the previous knowledge of the NG composition required to apply dedicated equations. The use of true NG samples to develop the models is also quite new in the field. Proof-of-concept studies were made with synthetic spectra and, then, a collection of liquefied NG samples for which MN values were computed by the National Physics Laboratory algorithm (NPL) from their sample composition were used to develop operative models. Additional validation was made with a collection of synthetic standard mixtures prepared for two European projects (EMRP LNG II and EMPIR LNG III) whose service methane numbers (SMN) were measured with an engine. The FTIR-PLS approach yielded statistically unbiased predictions with average standard errors around 0.4% MN when compared to the NPL-MN and SMN values, and standard deviations of the means ca. 1% MN. The approach is fast, cost effective as it involves standard instrumentation, and can be considered compliant with the green chemistry principles.

Comparability of calibration strategies for measuring mercury concentrations in gas emission sources and the atmosphere

Abstract. A primary mercury gas standard was developed at Van Swinden Laboratory (VSL) to establish an International System of Units (SI)-traceable reference point for mercury concentrations at emission and background levels in the atmosphere. The majority of mercury concentration measurements are currently made traceable to the empirically determined vapour pressure of mercury. The primary mercury gas standard can be used for the accurate and precise calibration of analytical systems used for measuring mercury concentrations in air. It has been especially developed to support measurements related to ambient air monitoring (1–2 ng m−3), indoor and workplace-related mercury concentration levels according to health standards (from 50 ng m−3 upwards) as well as stationary source emissions (from 1 µg m−3 upwards). The primary mercury gas standard is based on diffusion according to ISO 6154-8. Calibration gas mixtures are obtained by combining calibrated mass flows of nitrogen and air through a generator holding diffusion cells containing elemental mercury. In this paper, we present the results of comparisons between the primary gas standard and mercury calibration methods maintained by NPL (National Physical Laboratory in the United Kingdom), a National Metrology Institute (NMI), and the Jozef Stefan Institute (JSI), a Designated Institute (DI). The calibration methods currently used at NPL and JSI are based on the bell-jar calibration apparatus in combination with the Dumarey equation or a NIST (National Institute of Standards and Technology in the United States) reference material. For the comparisons, mercury was sampled on sorbent traps to obtain transfer standards with levels between 2 and 1000 ng with an expanded uncertainty not exceeding 3 % (k=2). The comparisons performed show that the results for the primary gas standard and the NIST reference material are comparable, whereas a difference of −8 % exists between results traceable to the primary gas standard and the Dumarey equation.

Results of an independent dosimetry audit for scanned proton beam therapy facilities

PurposeAn independent dosimetry audit based on end-to-end testing of the entire chain of radiation therapy delivery is highly recommended to ensure consistent treatments among proton therapy centers. This study presents an auditing methodology developed by the MedAustron Ion Beam Therapy Center (Austria) in collaboration with the National Physical Laboratory (UK) and audit results for five scanned proton beam therapy facilities in Europe. MethodsThe audit procedure used a homogeneous and an anthropomorphic head phantom. The phantoms were loaded either with an ionization chamber or with alanine pellets and radiochromic films. Homogeneously planned doses of 10Gy were delivered to a box-like target volume in the homogeneous phantom and to two clinical scenarios with increasing complexity in the head phantom. ResultsFor all tests the mean of the local differences of the absolute dose to water determined with the alanine pellets compared to the predicted dose from the treatment planning system installed at the audited institution was determined. The mean value taken over all tests performed was −0.1±1.0%. The measurements carried out with the ionization chamber were consistent with the dose determined by the alanine pellets with a mean deviation of −0.5±0.6%. ConclusionThe developed dosimetry audit method was successfully applied at five proton centers including various “turn-key” Cyclotron solutions by IBA, Varian and Mevion. This independent audit with extension to other tumour sites and use of the correspondent anthropomorphic phantoms may be proposed as part of a credentialing procedure for future clinical trials in proton beam therapy.

First Latin American and Caribbean interlaboratory comparison exercise for SSDLs on reference irradiation capabilities in personal dose equivalent

A comparison exercise of Latin American and Caribbean Secondary Standards Dosimetry Laboratories (SSDLs) was jointly organized by the International Atomic Energy Agency (IAEA) and the Ionizing Radiation Metrology Laboratory at the Federal University of Pernambuco (LMRI-DEN/UFPE). This exercise was organized during an IAEA regional meeting on the review and update of calibration capabilities in Latin America, held in Recife, during the period from 23 to 27 April 2018 under the technical cooperation project ME-RLA 9085-170572. Fifteen participating SSDLs were required to irradiate optically stimulated personal dosimeters in terms of the personal dose equivalent Hp(10) in 137Cs radiation quality. In addition, the IAEA Dosimetry Laboratory in Seibersdorf, Austria, and the National Physical Laboratory in Teddington, Middlesex, UK participated in this exercise as reference institutes. Each participant received 10 dosimeters that were hand-carried directly to the SSDL. Two nominal dose values of 2 mSv and 4 mSv were selected for this exercise. The participants irradiated the dosimeters using the setup and the procedures which are normally used in their standard laboratory for Hp(10) dosimeter irradiations. The dosimeters were evaluated as they were received by the coordinating laboratory, using a single BeOSL Reader. The results show that, except for one laboratory, the differences between the dosimeter reading and the assigned values were within 10%; this is consistent with the expanded uncertainty. The results indicate that most of the participant laboratories have a good capability to irradiate personal dosimeters in the quantity Hp(10).

The effects of constructed bivariate copulas on multivariate control charts effectiveness

AbstractThe average control chart monitors the shifts in the process. The familiar multivariate control charts are used to detect the mean vector of the process such as multivariate cumulative sum (MCUSUM) and Hotelling's T2 control charts. In this paper, the effects of constructing bivariate copulas on multivariate control charts, that is, MCUSUM and Hotelling's T2 control charts are intensively investigated when observations are drawn from the exponential distribution. Moreover, the dependence levels of observations are classified to be weak, moderate, and strong in both positive and negative values by Kendall's tau. The numerical results were obtained by Monte Carlo simulation to explore the average run length (ARL). The simulation results show that the performance of Hotelling's T2 control chart is superior to the MCUSUM control chart for all shifts in the mean vector of process. Furthermore, from applying the presented control chart to two sets of real data, data set of the strength of 1.5 cm glass fibers measured at the National Physical Laboratory, England and data set of the strength of glass of the aircraft window, it was found that for a small shift (), the MCUSUM control chart is better than Hotelling's T2 control chart.

Significance of Reference Materials for Calibration of Powder X-ray Diffractometer

The scientific research and new innovations are associated with the accurate and precise measurements which are crucial for operation of recent civilization. In order to maintain the precision and accuracy in analytical measurements, Reference Materials and Certified Reference Materials (CRMs) play a vital role for improving the measurement capability to obtain the property value close to its true value which in turn revamps the overall growth of country for better quality of life. Certified Reference Materials are basically used to assess the performance of analytical procedures and laboratory apparatus for authentic measurement data. In recent scientific world, many sophisticated instruments are emerging with their various facets of measurement capabilities to cater the need of high end research in the field of academia and industries. In recent years, powder X-ray diffraction (PXRD) has been shown as the most powerful characterization and non-destructive technique to explore the structural investigation in terms of phase identification, size of a unit cell, volume fraction of phases, site occupancy of different elemental component, anti-site defects in materials and having many more other applications. The identification of mentioned information from PXRD instrument is a basic need in material science, geology, polymer, forensic science and environment etc. This article focuses on the importance of CRMs for calibrating the instruments and validation of analytical methods. Also the article explicitly discuss about the importance and applications of PXRD technique together with the role of National Physical Laboratory, India the national institute of measurement NMI of India.

Characterisation of the NPL Thermal Conductivity Reference Material Inconel 600

Due to the depletion of the thermal conductivity reference materials, the National Physical Laboratory (NPL) has certified a new thermal conductivity reference material, NPL code 2I09 that is based on Inconel 600. This batch of material has been thermally and electrically characterised over the temperature range 100 °C to 500 °C. The primary thermal conductivity measurements used to generate the certified values were carried out in the NPL Axial Heat Flow apparatus, which is a UK national standard measurement facility. It is based on a steady-state absolute technique and is suitable for measuring specimens with thermal conductivities in the range 10 W·m−1·K−1 to 240 W·m−1·K−1. Comparisons were made between the reference thermal conductivity values and the derived thermal conductivity values obtained from two indirect methods based upon electrical resistivity and thermal diffusivity measurements, respectively. The reference thermal conductivity values of NPL 2I09 compare with those calculated from the measurements of electrical resistivity within 2 % and those calculated from the measurements of thermal diffusivity, specific heat capacity, density and thermal expansion better than 4 %. In addition, the certified thermal conductivity values of the new batch of Inconel 600, the NPL code 2I09, were compared with the representative reference thermal conductivity values of Inconel 600 reported by J Clark and R Tye, and the agreement is within 2 %. The new reference material NPL 2I09 is available from NPL and can be used to calibrate or check apparatus that provides measurements of thermal conductivity which includes the range 14 W·m−1·K−1 to 22 W·m−1·K−1 covering the temperature range from 100 °C to 500 °C. The overall uncertainty on the certified values is estimated to be within ± 4.8 %, based on a standard uncertainty multiplied by a coverage factor k = 2, providing a level of confidence of approximately 95 %.

Characterization of a Thermal Isolation Section of a Waveguide Microcalorimeter

The aim of this study is to examine the characterization of a thermal isolation section (TIS) for a waveguide microcalorimeter, used to characterize the effective efficiency of a thermistor power sensor (TPS). The power loss in the TIS has been analyzed for both the dielectric and conductor losses. Its effect on the thermopile output has been assessed using a foil short method through analysis of the heating ratio. This method involves a one-off measurement of the microcalorimeter system with the foil short before the unknown power sensor measurement and does not require additional S-parameters measurements of the isolation section. The estimated value of the heating ratio effect has been obtained between 1 for a fully reflected signal from the input of the unknown power sensor and 2 for a perfectly matched power sensor. The full analytical model and an estimated model for the heating ratios have been calculated for the National Physical Laboratory (NPL)'s WG25 (WR15) microcalorimeter and a commercial TPS. The analytical model has been applied to an effective efficiency measurement, and good agreement has been obtained when compared with the existing methodology used at NPL. This model can be applied to any metallic waveguide-type TIS in other bands. A rigorous uncertainty analysis of the analytical model for the heating ratio is also presented and shows an expanded uncertainty between 0.008 and 0.023 ( k = 2) for this microcalorimeter.

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.

Plans for neutron metrology at NPL

The National Physical Laboratory has provided industry and research with neutron fluence and dose standard neutron fields since the 1960’s. Sectors such as civil nuclear power, defence, radiation-protection and fusion generation rely on NPLs facilities to operate safely and ensure traceability back to an internationally recognised UK primary standard. A central part of the capability is the 3.5 MV Van de Graaff accelerator which, using light ions, generates monoenergetic fields of neutrons ranging from a few keV to 19 MeV and intense thermal neutron fields. This accelerator is reaching the end of its operational life and a project to replace it is underway.

Al Kα XPS reference spectra of polyethylene for all instrument geometries

This paper extends a previous description of XPS survey spectra from low density polyethylene (LDPE), which was specific for a single type of geometry, to all geometries. Instrument geometries are specified by two angles. The first angle, a, is between the sample-to-monochromator vector and the sample-to-analyzer vector. The second angle, b, is the dihedral angle between the anode-monochromator-sample plane and the monochromator-sample-analyzer plane. The second angle is important because of the polarization induced by the monochromator. We show, using theory, that the XPS spectrum can be decomposed into a “magic angle” reference spectrum, I1, and an anisotropy correction spectrum, f. The geometry for LDPE at which photoemission intensity is equivalent to isotropic emission is shown to be a function of a and b with extreme values for a of 64.6° (b = 0 or 180°) and 57.5° (b = 90°). The deviation of these angles from the “magic angle” a = 54.7° is due to a combination of x-ray polarization and nondipole effects in photoemission. Intensity-calibrated data from a number of instruments with two geometries with b = 180°, one set with a = 60° and the other set with a = 45° are used to determine I1 and f, and these are fitted with simple functions to allow the reproduction of LDPE reference spectra for any instrument geometry. The spectra are taken from the Versailles Project on Advanced Materials and Standards, Technical Working Area 2: Surface Chemical Analysis study A27 and are traceable to the National Physical Laboratory, UK intensity calibration spectra for argon ion sputter-cleaned gold. The functions in this paper may be used in the calibration of XPS instruments with quartz-crystal-monochromated Al Kα x-rays by the comparison of the calculated reference spectrum to data from clean LDPE.

Realization of Quantum Pascal Using Natural Fundamental Physical Constants

The acceptance of the redefinition of SI units on 20 May 2019, based on fundamental physical constants of nature led to significant changes in the field of metrology. The National Institute of Standards and Technology (NIST), USA has developed a quantum pressure standard, i.e. optical interferometer manometer (OIM), which is based on the change in the refractive index/polarizability/density of gas molecule that measures the pressure by calculating the change in fractional frequencies of monochromatic laser light passing through the medium compared to the vacuum. Theoretically, as per the ideal gas equation, pressure may be derived from fundamental physical constants either by Boltzmann’s constant or Avogadro number. The NIST, USA has developed fixed and variable-length optical cavity (FLOC and VLOC) OIM, which is based on the change in the resonance frequency of laser-molecule interaction depending on the pressure inside the cavity. Worldwide, most national metrology institutes (NMIs) have been working to realize the quantum Pascal based on the principle mentioned earlier; however, their design and configuration might differ. The national physical laboratory has also initiated the OIM project to realize the quantum Pascal in India. For that, we have reviewed the pressure standards based on the laser refractometer developed by NMIs.

IPEM code of practice for high-energy photon therapy dosimetry based on the NPL absorbed dose calibration service

The 1990 code of practice (COP), produced by the IPSM (now the Institute of Physics and Engineering in Medicine, IPEM) and the UK National Physical Laboratory (NPL), gave instructions for determining absorbed dose to water for megavoltage photon (MV) radiotherapy beams (Lillicrap et al ). The simplicity and clarity of the 1990 COP led to widespread uptake and high levels of consistency in external dosimetry audits. An addendum was published in 2014 to include the non-conventional conditions in Tomotherapy units. However, the 1990 COP lacked detailed recommendations for calibration conditions, and the corresponding nomenclature, to account for modern treatment units with different reference fields, including small fields as described in IAEA TRS483 (International Atomic Energy Agency (IAEA) , Vienna). This updated COP recommends the irradiation geometries, the choice of ionisation chambers, appropriate correction factors and the derivation of absorbed dose to water calibration coefficients, for carrying out reference dosimetry measurements on MV external beam radiotherapy machines. It also includes worked examples of application to different conditions. The strengths of the 1990 COP are retained: recommending the NPL2611 chamber type as secondary standard; the use of tissue phantom ratio (TPR) as the beam quality specifier; and NPL-provided direct calibration coefficients for the user’s chamber in a range of beam qualities similar to those in clinical use. In addition, the formalism is now extended to units that cannot achieve the standard reference field size of 10 cm × 10 cm, and recommendations are given for measuring dose in non-reference conditions. This COP is designed around the service that NPL provides and thus it does not require the range of different options presented in TRS483, such as generic correction factors for beam quality. This approach results in a significantly simpler, more concise and easier to follow protocol.

Performance of signal processing techniques for anomaly detection using a temperature-based measurement interpretation approach

This study investigates the effectiveness of four signal processing techniques in supporting a data-driven strategy for anomaly detection that relies on correlations between measurements of bridge response and temperature distributions. The strategy builds upon the regression-based thermal response prediction methodology which was developed by the authors to accurately predict thermal response from distributed temperature measurements. The four techniques that are investigated as part of the strategy are moving fast Fourier transform, moving principal component analysis, signal subtraction method and cointegration method. The techniques are compared on measurement time histories from a laboratory structure and a footbridge at the National Physical Laboratory. Results demonstrate that anomaly events can be detected successfully depending on the magnitude and duration of the event and the choice of an appropriate anomaly detection technique.

Serum zinc levels in children with upper respiratory tract infection in the age 2-12years in Pakistan.

Objectives: The persuasive evidence shows that proper Zinc (Zn) nutrition is important for human health. Hence an attempt was made to evaluate the serum Zn levels in children suffering from high respiratory infection in children aged 2-12years in Pakistan. Study Design: Case-control study. Setting: Jinnah Medical Teaching Hospital Peshawar with the collaboration of National Physical Standard Laboratory PCSIR Islamabad. Period: March 2017 to March 2019. Material & Methods: 60 children who were suffering from upper respiratory tract infection and were admitted in the Paediatric ward of Jinnah medical teaching hospital Peshawar. 60 normal controls of the same genders with an age range 2-12 years were selected for this study. Serum zinc levels were measured with atomic absorption spectrophotometer (AAS). Results: The serum zinc level was found to be low in 80% patients. Mean ±SD of serum zinc were 58.9 ±2.70µg/dl in diseased group and 100 ±2.22µg/dl in controls respectively. In patients serum zinc level was significantly lower than that of healthy controls (P<0.001). Conclusion: We may conclude that Zinc deficiency may play a role in the pathogenesis of upper tract respiratory infection since most diseased children have low serum Zn level.

Batteries and Hydrogen should be Seen as Partners Instead of Rivals

There has been a tendency for the automotive sector to view batteries and hydrogen as competing technologies when they are in fact highly complementary, says Dr Gareth Hinds, Science Area Leader in Electrochemistry at the National Physical Laboratory (NPL).

Trace moisture measurement in natural gas mixtures with a single calibration for nitrogen background gas

The measurement and control of trace moisture is an important procedure to maintain and secure the quality and safety of pipeline systems for natural gas. The natural gas mix typically comprises methane, ethane, propane, some higher hydrocarbons, carbon dioxide and nitrogen. It is too impractical to perform additional calibrations of trace moisture measurement every time the combination of gas components in the natural gas mix is changed. This paper proposes a method to separate and compensate for the effect of the background gas composition from the trace moisture measurement by using two different frequencies in a trace moisture analyzer utilizing a ball surface acoustic wave (SAW) sensor. The experiment was performed by connecting the ball SAW trace moisture sensor to supplies of trace moisture in multiple background gases from the National Physical Laboratory (NPL) Multi-gas, Multi-pressure Standard Humidity Generator, and changing the composition of the background gases including N2, air, CH4, 80% CH4/20% C2H6, and 50% CH4/50% C2H6. At the nominal humidity frost-point values of −70 °C, −50 °C, −40 °C and −30 °C, the deviations due to the change of the background gases were within 1 °C in frost point.

Cavitation-erosion measurements on engineering materials

The resistance of a material to cavitation erosion is assessed by measuring specimen weight change induced by the application of a high-power vibration horn close its surface. This paper describes a proof-of-concept study of a measurement technique for assessing the progression of cavitation erosion for commonly used engineering materials. UK National Physical Laboratory Cavitation Sensor enabled the generated acoustic signals produced by inertial cavitation collapse. Results suggest that acoustic emission monitoring shows promise as a tool which can be employed to quantitatively record the stability of the applied cavitation erosion stimulus.