Measurement of gas flow rate from helium standard leaks

Helium standard leaks are widely used to check and calibrate mass spectrometer leak detectors. Precisely known gas flows are required for measurement of quantities of standard leak rates. A fundamental task of the constructed and presented calibration apparatus is precise measurement of gas leak rate. Thus a primary standard for calibration helium standard leaks in the range from 10⁻¹⁰ to 10⁻⁵ Pa m³/s has been completed at the Laboratory of Vacuum Measurements in Tele & Radio Research Institute.     

Accurate conductance measurements of a pinhole orifice using a constant-pressure flowmeter

A pinhole orifice with a known conductance can be used as a secondary flow standard. Commercially available laser-drilled pinhole orifices with diameters ranging from 1.0 μm to 50 μm can have molecular-flow conductances ranging from about 0.1 μL/s to 200 μL/s for N₂ at 23 °C. Gas flows of 10⁻¹¹–10⁻⁶ mol/s can easily be produced by applying an upstream pressure in the range of 1–10⁵ Pa. Accurate measurements of the orifice conductance as a function of pressure are required to use the pinhole orifice as a basis of a flowmeter. We use a constant-pressure flowmeter to make accurate measurements of the conductance of a 20 μm orifice as a function of pressure for gas flows of Ar and N₂ into vacuum. We present results of these conductance measurements for an orifice with a nominal diameter of 20 μm. The N₂ conductance of this orifice ranged from 30 μL/s to 60 μL/s over the range of pressures investigated, and was measured with an uncertainty of better than 0.2% (k = 2) for upstream pressures greater than 10 Pa.     

Metrological characterization of the new 1 MN force standard machine of NPL India

Since November 2010, NPL India’s force scale has been complemented in the range from 10 kN to 1 MN by a further force standard machine. This automatically working 1 MN force standard machine utilizes a lever amplification of a 100 kN mass stack and enables low relative expanded uncertainties of smaller than 9 × 10⁻⁵ on the lever, and 2 × 10⁻⁵ on the deadweight side. In this paper, the constructional design of the machine is described. According to the new EURAMET Calibration Guide, a model for the uncertainties is developed.Supplementary to this, results from comparison measurements of the new NPL India machine with PTB´s force standard machines are presented.     

Improved system for the automatic calibration of standard resistors in the meg-ohm range

An automated measuring system has been developed to improve the calibration of high value standard resistors in the meg-ohm range at the National Institute for Standards (NIS), Egypt. This system is suitable for the calibration of the standard resistors from 100 kΩ to 100 MΩ using the DMM-based method by the substitution technique where the unknown resistor and the standard resistor are indirectly compared in the same position using a dummy resistor as a short-term reference standard. The system operation is automatically controlled by using a Lab VIEW program which is especially developed for this purpose. The uncertainty for the high value standard resistors measurement of this system is estimated. The performance of this system is also evaluated by comparing the measurement results obtained from this technique with those obtained by the direct comparison DMM-based method. It is found that the measurement uncertainty of with this method spans from 4.1 × 10⁻⁶ to 27 × 10⁻⁶, while it spans from 40 × 10⁻⁶ to 110 × 10⁻⁶ for the direct comparison method. The relative differences of the deviation from nominal values of the working standards resistors measured by the two methods are found to be within their expanded uncertainties.     

Distributed amplified ultra-stable signal quartz oscillator based

The aim of this communication is to present the performances of 5 MHz distributed ultra-stable system, based on ultra-stable Boitiers à Vieillissement Amélioré (BVA) oscillator. We demonstrated flicker frequency modulation (FFM) floor better than 4.5 × 10⁻¹⁴ ± 2.5 × 10⁻¹⁵ at 12 s with an intrinsic noise floor about 6 × 10⁻¹⁵ at 1 s with a τ^−1/2 time integration dependence slope.     

Hamon 10 × 100 MΩ resistor based traceable source for calibration of picoammeters in the range 100 pA–100 nA

This paper describes a measurement method developed at National Institute of metrological Research (INRIM) to calibrate picoammeters in dc current from 100 pA to 100 nA. The current source is based on a traceable to the dc resistance national standard 10 × 100 MΩ Hamon resistor developed at INRIM and on a traceable to the dc voltage national standard high precision dc voltage calibrator. The expanded uncertainties of the method for the calibration of picoammeters span from 9.4 × 10⁻⁴ for the gain of a picoammeter at 100 pA to 4.0 × 10⁻⁴ for the gain at 100 nA. A detailed uncertainties budget at 10 nA level and the results of a comparison with a different technique are also reported.     

Use of a higher order Heydemann–Welch model to characterize a controlled clearance piston gauge

We present a new method for characterizing a controlled-clearance piston gauge as a primary pressure standard. This method requires operating the piston gauge to jacket pressures of over 80% of the system pressure. We present measurements on a hydraulic piston gauge with a 290 MPa maximum pressure and a nominal piston diameter of 3.27 mm. Measurements showed that the cylinder becomes stiffer as the jacket pressure increases, and that non-linear models of the Heydemann–Welch parameters improve the determination of the effective area. The relative standard uncertainty in the effective area of the piston gauge ranges from 16.0 × 10⁻⁶ to 17.6 × 10⁻⁶, and the agreement to the present NIST pressure scale is within the standard uncertainty.     

A traceable technique to calibrate dc current shunts and resistors in the range from 10 μΩ to 10 mΩ

A traceable to dc resistance and dc voltage National Standards measurement technique to calibrate dc current shunts and resistors in the range from 10 μΩ to 10 mΩ has been developed at National Institute of Metrological Research (INRIM) in addition to the primary reference system for low value resistors calibration. This technique is applicable in secondary and industrial metrological laboratories. It is based on a volt-amperometric method, to compare an unknown shunt with a standard one in 1:1 or 1:10 ratios. In the setup are involved: a dc current calibrator and a current generator to supply currents respectively up to 100 A and up to 1200 A, with a switch to reverse the current, two 7 1/2 digit nanovoltmeters (nVs) for the acquisition of the voltage on the standard and under calibration shunts and two Tinsley 100 μΩ and 1 mΩ standard shunts kept in mineral oil and with a cooling system. An optional variation in the procedure that can reduce the measurement uncertainties is discussed. The 2σ relative capabilities of the technique span from 6.0 × 10⁻⁶to 4.6 × 10⁻⁴. Compatibility results with the INRIM reference measurement system for low value resistors calibration are also given.     

Study on carrier mobility measurement using electroluminescence in frequency domain and electrochemical impedance spectroscopy

In this paper, the two methods, electroluminescence in frequency domain and electrochemical impedance spectroscopy, have been applied to investigate the carrier mobility in single layer polymer light-emitting diode employing the polymer MEH-PPV (Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) as the light-emitting layer. The carrier mobility μ is 1.64 × 10⁻⁶ cm²/V s under the electric field 8.3 × 10⁵ V/cm measured by the method of electroluminescence in frequency domain. The electrochemical impedance spectroscopy results indicate that the carrier mobility μ is 1.08 × 10⁻⁶ cm²/V s under the electric field 7.5 × 10⁵ V/cm. A significant advantage of the two methods is that both of them can be applied to measure the carrier mobility in the thin film.     

Measurement uncertainty estimation of health risk from exposure to natural radionuclides in soil

Cancer mortality risk were estimated due to external exposure to ⁴⁰K in soil. Uncertainty estimation was performed for the risk considered as a measurand. It was presented uncertainty estimation using two methods. One method is based on the Guide to the Expression of Uncertainty in Measurement Framework (GUF) and other represents Monte Carlo method. For the Monte Carlo method, the mean of the obtained distribution that represents mortality cancer risk estimation, due to one year exposure to ⁴⁰K with mean activity concentration of 708 Bq/kg in soil, is 12.9 × 10⁻⁶ with 90% confidential interval (k ≈ 1.64) of (4.7–25.5) × 10⁻⁶. According to GUF the mean value is estimated as 10.9 × 10⁻⁶, with 90% confidential interval of (0.9–20.8) × 10⁻⁶. Uncertainty of assessed risk obtained by numerical simulation is slightly different with asymmetrical boundaries related to the mean value, comparing to the uncertainty estimated using GUF.     

1–15,000 Pa Absolute mode comparisons between the NIST ultrasonic interferometer manometers and non-rotating force-balanced piston gauges

The National Institute of Standards and Technology (NIST) Low Pressure Manometry Project maintains and operates primary standard ultrasonic interferometer manometers (UIMs) over the pressure range of 1 mPa to 360 kPa. Over the past decade a new type of customer gauge, the non-rotating force-balanced piston gauge or FPG (model 8601, DH Instruments, a Fluke Company¹) has been introduced to the standards community that covers the range of ≈1–15,000 Pa and is capable of both absolute and differential measurement modes. Since 2002, NIST customers² have requested that four different FPG units be compared to the NIST primary pressure ultrasonic interferometer manometer standards (UIMs). The results of the comparisons were that all four FPG units were within manufacturers stated uncertainty (0.008 Pa + 30 × 10⁻⁶ × P for absolute mode) when compared against the NIST UIMs at pressures between 10 Pa and 15,000 Pa (absolute mode). At pressures between 5 Pa and 10 Pa, the results were generally within manufacturer’s specifications. Below 5 Pa some of the FPG units were outside of manufacturer’s uncertainty specifications. The use of an isolating capacitance diaphragm gauge (CDG) was necessary during the comparisons to prevent humidified gas from the FPG from entering the NIST 160 kPa mercury UIM primary pressure standard. The results of these four different comparison tests will be discussed in detail, along with test conditions, equipment set-up, and test uncertainty analysis.     

FEA calculation of pressure distortion coefficients of gas-operated pressure balances – EURAMET project 1039

Finite element analysis methods were developed and applied to gas piston–cylinder units (PCUs) of piston- and cylinder-floating configuration (2, 5, 10 and 20) cm² nominal effective area, operated in gauge and absolute mode at pressures (0.06–7.5) MPa to determine their zero pressure and pressure-dependent effective areas, as well as pressure distortion coefficients (λ) with associated uncertainties. Real dimensional properties of the PCUs were used. λ were found to be independent of gas (ideal, N₂, He) within the viscous flow model, but strongly dependent on the gap shape, operation mode and elastic properties. Results demonstrate good agreement for λ, with its uncertainty for different PCUs varying between (0.03 and 0.21) × 10⁻⁶ MPa⁻¹ corresponding to maximum relative uncertainties in pressure of (0.07–0.34) × 10⁻⁶.     

Thermal diffusivity measurement of Au nanofluids of very low concentration by using photoflash technique

In this paper, the application of photoflash technique to measuring the thermal diffusivity of gold nanofluids of very low concentration at room temperature was presented. The nanofluid samples were prepared from the pulse laser ablation procedure. The thermal diffusivity was obtained by fitting the theoretical temperature signal to the experimental data, and it was found to increase linearly from 1.47 × 10⁻³ cm² s⁻¹ to 1.68 × 10⁻³ cm² s⁻¹ as the concentration increased from 1.11 mg/L to 3.18 mg/L. The increase in thermal diffusivity in these multidispersed nanofluids was attributed to the higher nanoparticle concentration as well as to the increasing presence of the smaller size nanoparticles.     

Charge compensation by in-situ heating for insulating ceramics in scanning electron microscope

With a steady temperature increase under high vacuum (HV) in an environmental scanning electronic microscope, we observed charge-free characterization and fine secondary electron (SE) images in focus for insulating ceramics (alumina (Al₂O₃), aluminum nitride (AlN), pure magnesium silicate (Mg₂SiO₄)). The sample current I_sc increased from −8.18×10⁻¹³ to 2.76×10⁻⁷ A for Al₂O₃ and −9.28×10⁻¹² to 2.77×10⁻⁶ A for AlN with the temperature increased from 298 to 633 K. The surface conductance σ increased from 5.6×10⁻¹³ to 5.0×10⁻¹¹/Ω for Al₂O₃ and 1.1×10⁻¹² to 1.0×10⁻⁷/Ω for AlN with the temperature increased from 363 to 593 K. The SE image contrast obtained via heating approach in high vacuum with an Everhart–Thornley SE-detector was better than that via conventional approach of electron–ion neutralization in low vacuum (LV) with a gaseous SE-detector. The differences of compensation temperatures for charge effects indicate dielectric and thermal properties, and band structures of insulators. The charge compensation mechanisms of heating approach mainly relate to accelerated release of trapped electrons on insulating surface and to increase of electron emission yield by heating.     

A Josephson voltage-traceable DC high-voltage divider evaluation using the binary step-up method

An evaluation technique and traceability for a DC-resistive high-voltage divider was established based on 1 kV, which was traceable to a Josephson voltage standard at the Korea Research Institute of Standards and Science. To do this, the binary step-up method was used to evaluate the voltage-dividing ratio and the voltage coefficient of the divider up to 100 kV. The expanded relative uncertainty for the dividing ratio up to 100 kV was 16 × 10⁻⁶ level. To confirm the validity of the method, the ratio at 1 kV was compared with the resistance ratio of the divider, and the two results agreed to within 5.3 × 10⁻⁶.     

Influence of Cr content on tribological properties of Ni3Al matrix high temperature self-lubricating composites

High temperature self-lubricating composites Ni₃Al-BaF₂-CaF₂-Ag-Cr were fabricated by powder metallurgy technique. In this paper the effect of Cr content on tribological properties at a wide temperature range starting from room temperature to 1000 °C was investigated. It was found that Ni₃Al matrix composite with 20 wt% Cr exhibited low friction coefficient of 0.24-0.37 and a wear rate of 0.52-2.32×10⁻⁴ mm³ N⁻¹ m⁻¹. Especially at 800 °C it showed the lowest friction coefficient of 0.24 and a favorable wear rate of 0.71×10⁻⁴ mm³ N⁻¹ m⁻¹. This implied that 20 wt% Cr was the optimal Cr content and its excellent tribological performance could be attributed to the balance between strength and lubricity.     

Evaluation of moment arm length and fulcrum sensitivity limit in a 10 N·m dead weight torque standard machine

Many torque tools, such as torque wrenches and torque screwdrivers, as well as torque measuring devices (TMDs) with a rated capacity of less than 5 N·m are being widely used in industry. Thus, a small-rated-capacity torque standard has to be established as soon as possible. A 10 N·m dead weight torque standard machine (10 N·m DWTSM) has been under development since 2006 at the National Metrology Institute of Japan (NMIJ), part of the National Institute of Advanced Industrial Science and Technology (AIST). Characteristically, the main parts of the moment arm are made of low thermal-expansion alloy (Super INVAR), and an aerostatic bearing is employed as the fulcrum supporting the moment arm to minimize rotational friction. The moment arm was evaluated with regard to the coefficient of thermal expansion (CTE), the lengths measured by a 3D coordinate measurement machine (CMM), and temperature correction realized by measuring the moment arm temperature. The sensitivity limit of the fulcrum in the 10 N·m DWTSM was also estimated. As a result, the apparent overall CTE of the moment arm was 1.06 × 10⁻⁶ K⁻¹, and the expanded uncertainty was 2.24 × 10⁻⁹ K⁻¹ (k = 2). The results of the CMM measurement were a right-hand side length of 510.2773 mm and a left-hand side length of 510.2657 mm, with a relative expanded uncertainty of 4.0 × 10⁻⁵ (k = 2). The moment arm temperature increased by approximately 0.6 K during the ordinary calibration process. The corresponding change in the lengths of the moment arm was estimated to be approximately 0.3 μm, which is considered to be sufficiently small compared with the expanded uncertainty of the lengths of the moment arm. The fulcrum of the 10 N·m DWTSM was found to have sufficient sensitivity under three conditions: without the weight loading components, with the weight loading components, and with loaded weights. In particular, the fulcrum had sufficient sensitivity of at least 0.5 mg when weights of 100 g were loaded on both 5th stages in the weight loading components to generate a radial load equivalent to 1 N·m.     

Electroanalysis of ascorbic acid using poly(bromocresol purple) film modified glassy carbon electrode

We report a simple method for determination of ascorbic acid (AA) by using a glassy carbon electrode (GCE) modified with poly(bromocresol purple) (poly(BCP)/GCE). Compared with a bare GCE, the poly(BCP) film exhibited the obvious electrocatalytic effect towards ascorbic acid oxidation, which reduced the oxidation overpotential about 240 mV with obviously increased current response. Under the optimized conditions, the catalytic current increased linearly with the concentration of AA in the range of 2.0 × 10⁻⁵–7.0 × 10⁻⁴ M with the detection limit of 6.5 × 10⁻⁶ M (S/N = 3) in 0.1 M phosphate buffer solution (pH 6.5). The interferences from different species and the repeatability of the poly(BCP)/GCE for the determination of AA were also investigated. The proposed method has been successfully applied to the determination of AA in vitamin C injection and tablet with satisfactory results.     

Polypyrrole-NiO hybrid nanocomposite: Structural,morphological, optical and electrical transport studies

Polypyrrole (PPy)-nickel oxide (NiO) hybrid nanocomposite thin films have been prepared by spin coating method. The PPy–NiO hybrid nanocomposites were characterized for structural, morphological, optical and electrical analysis, and the results were compared with the pure PPy films. The structural and optoelectronic properties of PPy–NiO hybrid nanocomposites are quite different from those of pure PPy and NiO nanoparticles, which were attributed to the strong interaction between the PPy and NiO nanoparticles. The XRD pattern shows that broad peak of PPy becoming weaker on increasing the content of NiO nanoparticles in the PPy–NiO hybrid nanocomposites. Also the diffraction peaks of NiO nanoparticles in PPy–NiO (10–50 wt%) nanocomposites were found to shift to lower 2θ values. The morphological studies revealed that the transformation of granular morphology of PPy to the nanospheres and clusters in the PPy–NiO hybrid nanocomposites. FTIR spectra of PPy–NiO hybrid nanocomposites, revealed that the main absorption at 1204 cm⁻¹ and 1559 cm⁻¹ are affected by the presence of NiO nanoparticle in pure PPy and get shifted to 1216 cm⁻¹ and 1570 cm⁻¹ respectively indicates, insertion of NiO nanoparticles in the PPy–NiO hybrid nanocomposite. UV–vis absorption spectrum of PPy corresponding to λ_max = 442 nm is blue shifted to λ_max = 375 nm in the PPy–NiO hybrid nanocomposites, reveals strong interaction between PPy and NiO nanoparticles. The room temperature dc electrical conductivity is increased from 8.66 × 10⁻⁹ to 4.08 × 10⁻⁷ (Ω/cm)⁻¹ as the content of NiO nanoparticles increased from 10 to 50 in wt% in the PPy–NiO hybrid nanocomposites.