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Measure Articles 2008 (22)

 
Picture of the productA Guard-Band Strategy for Managing False-Accept Risk
Michael Dobbert
When performing a calibration, the risk of incorrectly declaring a device as in-tolerance (false-accept risk) is dependent upon several factors. Those factors include the specified tolerance limit, guard-band, the calibration process uncertainty and the a priori probability that the device is in-tolerance. A good estimate of the a priori probability may be difficult to obtain. Historical or device population information for estimating the a priori probability may not be readily available and may not represent the specific device under test. A common strategy for managing measurement decision risk is to choose a guard-band that results in the desired false-accept risk given the tolerance limit, the calibration process uncertainty and the a priori probability. This paper presents a guard-band strategy for managing false-accept risk with only limited knowledge of the a priori probability that a device is in-tolerance and with minimal increase in false-reject risk.


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MS08_04_DOBBERT
Picture of the productAn Alternative Approach to Standard Decade Series Linear
D. Dikken, C. Geppert and S.M. Lee
A brief review of current practices in dissemination of the unit of mass is discussed focusing on the strengths and weakness of current practice. Based on improved mass comparators and advances in data collection/analysis systems, an opportunity exists to employ an alternative method of calculation which uses a Weighted Least Squares Regression on measured observations to better predict a solution to the selected mass comparison design matrix. Mathematical equations employing a Weighted Least Squares Regression approach are derived as a generalized solution for any valid mass calibration design. While this approach may be employed with demonstrated benefit over a traditional decade series approach, it also opens up an alternative for eliminating the necessity for single restraints to be passed from decade series to decade series. Etc…


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MS08_03_DIKKEN
Picture of the productAre Gas Pumps Measuring Up? The Mexican Experience
Heinz Luchsinger, Cesar Cajica, Manuel Maldonado and Ismael Castelazo
Advances in measurement and electronics technology have allowed manufactures to produce improved fuel dispensers that offer the consumer fair and convenient transactions at the gas station. However, authorities are having a difficult time developing reliable conformity assessment procedures that assure the consumer that the same sophisticated technology is not working against them. This paper describes the experience of CENAM in assessing the conformity of fuel dispensers sold in Mexico to the new, more stringent regulations issued in the last two years. The issues discussed include a comparison of the measurement capabilities of modern dispensers with the tolerance accepted by the standard and the difficulties involved in verifying the software and electronic components that compute and display the total sale amount.


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MS08_02_LUCHSIN
Picture of the productCalculation of Effective Area and Uncertainty
Michael Bair and Rob Haines
Dimensional measurements of piston­cylinders for the purpose of defining effective area have improved to a level that allows laboratories to use them as primary references for pressure. Because of their relatively large size and uniform cylindrical geometry, 50 mm tungsten carbide piston­cylinders are frequently utilized as primary standards in pressure based on a dimensionally characterized effective area. Because of the very low uncertainties in diameter, roundness and straightness measurements, it is essential to properly model the piston­cylinder annular space based on those dimensional measurements. This paper describes a model for calculating the effective area from dimensional measurements and also provides a method for calculating the uncertainty in the resultant effective area and final uncertainty in pressure.


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MS08_03_BAIR
Picture of the productComparing and Contrasting Studies of Metrology Education
Georgia Harris and Leslie R. Pendrill
This paper compares and contrasts two studies of the status of metrology education and training completed within NCSL International (NCSLI) and Implementing the Metrology European Research Area (iMERA). The current formulation by NCSLI and its partners of a strategic roadmap for metrology education and training and a survey of accreditation body assessors are presented. In addition, a corresponding iMERA study in Europe of metrology knowledge transfer has been initiated in preparation for the new European Metrology Research Program. This paper compares and contrasts the approaches and the formulations of these project and concludes with suggestions for future cooperation. Both the NCSLI and iMERA studies have shown a coordinated forum is needed to ensure that metrology staffing requirements are met at all levels i.e., competent personnel and the necessary resources to support them.


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MS08_02_HARRIS
Picture of the productComparison Between Melting and Freezing Points of Indium
R. Ding, M. J. Zhao, D. Cabana and D. Chen
In the interest of improving convenience and plateau duration, the use of melting points instead of freezing points for temperature fixed points in temperature calibration is considered. The question is whether adequately low uncertainties can be achieved with melting plateaus. Experimental research was carried out to compare the melting and freezing points of indium and zinc by using the inter­comparison method with standard platinum resistance thermometers (SPRTs). The influence of the furnace maintenance temperature on the performance of melting plateaus of indium and zinc was investigated and discussed. Differences in results between the melting points and the freezing points are shown. Uncertainty budget analysis of the melting points is presented. The experimental results show that because of the small differences between the freezing points and melting points using the optimal methods of realization, it is possible to replace the …


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MS08_01_DING
Picture of the productComparison of Results of the Volume Determination of Mass
Jorge Nava-Martinez and Luis M. Peña-Pérez
Two methods for the volume determination of mass standards are compared. The conventional hydrostatic weighing method where the mass standards are immersed in water and weighings in air where the mass standards are subjected to a variation in air density of ± 10% or less. The balance is installed in an air-tight chamber. Two kilogram masses were used and uncertainty analysis is compared. The En value was used in order to quantify the degree of agreement among the two methods. The results are within the expanded uncertainty of the measurements.


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MS08_04_NAVA
Picture of the productDesign of an Electro-Optic Device for In-Situ Measurement
Beverly J. Klemme and A. Roderick Mahoney
Design of a Pockels cell based electro­optic device is described. The device is designed to measure the amplitude of high voltage pulses in our new Pulsed High Voltage Measurement System (PHVMS) with a very high signal to noise ratio allowing a measurement precision of better than 0.5 %. However, the ultimate measurement uncertainty is limited by the uncertainty of currently available pulse high voltage standards. The PHVMS is capable of generating voltage pulses ranging from 2 kV to 320 kV in amplitude, with pulse durations from 2.5 µs to 25 µs. The Primary Standards Laboratory's AC Project at Sandia National Laboratories is in the process of validating the PHVMS for calibrat­ing resistive and capacitive voltage dividers. Single voltage pulses are difficult to measure with uncertainties less than 1%(k = 2) because of the high bandwidth involved (> 10 MHz) and their non­repetitive nature which rules out standard AC measurement and signal averaging techniques in our system…


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MS08_02_KLEMME
Picture of the productEvaluation of Dual Quartz Resonant Pressure Transducers
John Ball
The Army is considering the use of transfer standards rather than traditional, hierarchical methods to support high accuracy calibration requirements in tactical environments. Such schemes have the potential to improve accuracy, reduce cost, shrink logistical overhead, and eliminate the need to evacuate calibration equipment from the theater of operation. The Army recently selected a new set of tactical pressure calibration equipment with transfer calibration specifically in mind as the support concept of preference. The following presents an overview of the evolving Army transfer calibration system for pneumatic pressure and an evaluation of the expected performance of the quartz resonant transducer­based transport standards selected for this demanding application. Relevant data from commercial and government laboratories on quartz resonant pressure transducers, …


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MS08_01_BALL
Picture of the productExperiences with Novel Secondary Conductivity Sensors
Ulrich Breuel, Barbara Werner, Petra Spitzer and Hans D. Jensen
International efforts concentrate on the traceability of electrolytic conductivity at the field level having small associated measurement uncertainties. Although the measurement of conductivity at the primary level has been widely developed during the last decade, the dissemination of the small measurement uncertainty to the field level is lagging. There is a lack of easy to handle and reliable secondary calibration methods and transfer standards.This paper describes a procedure for determination of the electrolytic conductivity on the secondary level appropriate for calibration lab­oratories. The procedure was developed within a joint project of the German calibration laboratory (ZMK ANALYTIK GmbH, DKD­K­06901) together with the Physikalisch­Technische Bundesanstalt and the Danish Metrology Institute. Altogether a chain of five measuring cells has been used so that it is possible to measure the conductivity over a wide range from 2 µS/cm up to 100 mS/cm…


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MS08_02_BREUEL
Picture of the productImproved Measurements in Contact Thermometry at High Temp.
R. Morice, P. Ridoux and J.R. Filtz
The development of High Temperature Fixed Points (HTFPs) based on metal­carbon eutectics, as well as improvements of contact sensors, such as platinum­palladium thermocouples, has opened new perspectives for accurate temperature measurements in processes requiring good control at high temperature. Recently three major Euro­pean laboratories, LNE, NPL and PTB, have decided to join their research efforts with the aim of developing robust HTFPs to reduce current calibration uncertainties of noble metal thermocouples up to 1554 °C. HTFPs have also been successfully investigated at LNE for the study of tungsten­rhenium alloy thermocouples. This paper first presents general results in the development of metal­carbon fixed points and then discusses prospects in the near future through a description of some current research activities.


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MS08_01_MORICE
Picture of the productImprovements in High Temperature Metrology
Graham Machin
The accurate measurement and control of temperatures above 1100 °C is essential for the success of many industrial processes. However these measurements are generally difficult, leading to wide uncertainty margins, particularly at very high temperatures above 1800 °C. Recent developments in high temperature metrology mean that there will be a step change improvement in this field in the next few years, particularly due to the advent of high temperature fixed­points and improved thermocouple types, such as Pt/Pd. This paper reviews international developments in these areas that could ultimately lead to an improved way of realising ITS­90 above the Ag point, reduced thermocou­ple calibration uncertainties by factors of two or more, and improved dissemination and measurement of high temperatures to industry.


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MS08_01_MACHIN
Picture of the productInfluence of Pre-Weighing Conditions
Shih Mean Lee and David, Lee Kwee Lim
In the measurement of mass standards, thermal gradients can have an adverse influence on the uncertainty of measurement. OIML R111­1: 2004 has specific guidelines on the maximum allowable temperature changes during calibration and the thermal stabilisation time required for different classes of mass standards. However, thermal stability is disturbed during the measurement process due to the presence of various heat sources. Further thermal conditioning can be accomplished by performing pre­weighing operations, which simulate the actual measurement configurations. Dif­ferent pre­weighing conditions, including the number of pre­weighing cycles, the sequence of pre­weighing operations, size of mass standards, and loading positions of the standards, were investigated and were found to have varying influences on the repeatability of the measurement results. It was found that the Pre­Weighing' (PW) sequence improved overall repeatability etc…


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MS08_03_LEE
Picture of the productParametric Optimization of an Automated Weighing Comp.
S. Lee, J. W. Chung, K. P. Kim and H. W. Song
Manual mass comparison encumbers essentially a measurement or calibration with frequent interventions. To overcome this problem and ensure concretely the traceability of national standard, an MT­a5 automatic comparator (for the range of 1 mg to 5 g) from Mettler­Toledo (MT) has been recently introduced to Korea Research Institute of Standards and Science. In order to find the shortest operation time and lowest measurement repeatability, the stabilization time, the integration time, and the number of measurements are selected as time optimization parameters. The repeatability is obtained based on more than 350 measurements. From the viewpoint of the uncertainty, one preference condition (stabilization time = 20 s; integration time = 20 s; and number of measurements = 3) is found from the independent repeatability result, but its repeatability (0.24 µg) is within the manufacturer's repeatability specification (0.4 µg for 5 g). etc...


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MS08_02_LEE
Picture of the productPower Loading Effects in Precision 1 Ω Resistors
George R. Jones and Randolph E. Elmquist
Five manganin alloy Thomas-type 1 Ω resistors serve as primary working standards at the National Institute of Standards and Technology (NIST) in the precision potentiometer direct current comparator (DCC) system used for special 1 Ω customer calibrations. To maintain and predict the values of these resistors, the value of this bank is compared to the quantized Hall resistance (QHR) standard at NIST approximately twice a year. This is accomplished through the use of several precision 1 Ω resistors manufactured from 1975 through 1992 by the Australian National Measurement Laboratory, using the resistance alloy Evanohm. Over many years of careful monitoring, the relative values of these transfer resistors were seen to have discrepancies that were not related to the drift in the value of the primary working standards and exceeded the Type A (statistically derived) uncertainty in the measurement systems. Some of these variations were believed to be due to power loading in the transfer resistors. Recent experiments have demonstrated that conditions of power dissipation within the precision 1 Ω resistors and the duty cycle of the power applied to the resistors can change the value of a resistor measured at 100 mA in the NIST precision 1 Ω measurement system by as much as 0.06 μΩ/Ω. This paper describes the experimental results and measurement uncertainty due to these power loading effects. Generally, the power loading effects in the Thomas-type resistors appear to be dependent on the first order temperature coefficient, i.e., the larger the coefficient, the larger the change in the resistance value. However, there appears to be no similar relationship between the power loading effects and the first order temperature coefficient in the various Evanohm resistors that were tested. Known temperature coefficient gradient contributions to the changes of resistance can explain the results observed in these measurements.


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MS08_04_JONES
Picture of the productProposed Changes to the SI and Their Impact on Electrical
Barry Wood
Recent proposals to fundamentally change the SI system of units have generated considerable debate and are now being seriously considered by international committees. These proposals all have a common theme: to exactly fix the values of a set of fundamental physical constants and then to define the SI units with respect to the values of these invariants. The proposed changes and the ways in which national standards institutes would typically realize the SI units are outlined. The expected benefits and drawbacks of these changes are reviewed as they pertain to measurement science, to fundamental constants and in particular to electrical metrology. The positions of the Consultative Committee for Units, the Consultative Committee for Electricity and Magnetism and the Committee on Data for Science and Technology (CODATA) Task Group for Fundamental Constants …


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MS08_01_WOOD
Picture of the productRadiation Thermometry Capabilities of the PTB up to 3200
Klaus Anhalt, Juergen Hartmann and Joerg Hollandt
The accuracy of the high temperature part of the International Temperature Scale of 1990 (ITS­90) was for a long time limited by the lack of appropriate fixed points above the freezing temperature of copper at 1084.6 °C. Recently novel high temperature fixed points have been developed for temperatures up to 3200 K. Using blackbody radiators immersed in metal­carbon (M­C) or metal­carbide­carbon (MC­C) eutectic materials results in fixed points which can be used as reference sources for radiation thermometry, radiometry and photometry. Currently, implementation of these novel MC­C eutectics in an improved international high temperature scale is the topic of a worldwide cooperation of several national metrology institutes (NMI). Within this cooperation PTB determines by radiation thermometry and radiometry based on Planck's law.


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MS08_01_ANHALT
Picture of the productRatio Calibration of a Digital Voltmeter for Force Measure
Yi-hua Tang, Thomas W. Bartel and June E. Sims
Ratio calibration of a digital voltmeter (DVM) is critical for applications such as load cell response for force measurement. The National Institute of Standards and Technology (NIST) DVM ratio service provides ratio voltage measurements that are traceable to the Josephson Voltage Standard (JVS). Previously, the service was supported by NIST JVS systems using manual measurements. The NIST JVS uses a conventional Josephson junction array which often experiences a spontaneous step transition, caused by electromagnetic interference, during its operation. An adjustment is required to obtain a stable voltage step for the ratio calibration. The programmable JVS (PJVS), developed in the last decade, uses an array with non­hysteretic steps to provide a stable voltage. The PJVS was implemented in the DVM ratio calibration service to improve the efficiency and reliability of the service. The new protocol can be executed automatically to reduce the labor cost of the calibration service.


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MS08_02_TANG
Picture of the productThe Use of GPS Disciplined Oscillators as Primary Freq.
Michael A. Lombardi
An increasing number of calibration and metrology laboratories now employ a Global Positioning System disciplined oscillator (GPSDO) as their primary standard for frequency. GPSDOs have the advantage of costing much less than cesium standards, and they serve as “self­calibrating” standards that should not require adjustment or calibration. These attributes make them an attractive choice for many laboratories. However, a few of their characteristics can make a GPSDO less suitable than a cesium standard for some applications. This paper explores the use of GPSDOs in calibration laboratories. It discusses how GPSDOs work, how measurement traceability can be established with a GPSDO, and how their performance can vary significantly from model to model. It also discusses possible GPSDO failure modes, and why a calibration laboratory must be able to verify whether or not a GPSDO is working properly.


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MS08_03_LOMBARD
Picture of the productTowards the New Kelvin
Wolfgang Buck, Bernd Fellmuth and Joachim Fischer
Since 1954, the kelvin has been defined by the temperature distance between absolute zero and the triple point of water, with an assigned temperature value of exactly 273.16 K. Hence, the base unit of temperature depends on the limited stability and reproducibility of a certain material sample. A new definition of the kelvin not based on a special material should be aspired similar to the second or the metre, where a fixed value is assigned to an atomic transition or a fundamental constant. Following this road, the kelvin can be related to the thermal energy, kT, with the Boltz­mann constant, k, as a fixed conversion factor. In order to determine a reliable value of k, currently several methods are investigated by different research institutes. The methods with the lowest expected uncertainties are the acoustic gas thermometer and the dielectric constant gas thermometer. Other methods include Doppler­broadening thermometry and radiation thermometry.


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MS08_01_BUCK
Picture of the productUncertainty Est. for the Outdoor Cal. of Solar Pyranometers
Ibrahim Reda, Daryl Myers and Tom Stoffel
Pyranometers are used outdoors to measure solar irradiance. By design, this of radiometer can measure the total hemispheric (global) or diffuse (sky) irradiance when the detector is unshaded or shaded from the sun disk, respectively. These measurements are used in a variety of applications including solar energy conversion, atmospheric studies, agriculture, and materials science. Proper calibration of pyranometers is essential to ensure measurement quality. This paper describes a step-by-step method for calculating and reporting the uncertainty of the calibration, using the guidelines of the ISO "Guide to the Expression of Uncertainty in Measurement" or GUM, that is applied to the pyranometer calibration procedures used at the National Renewable Energy Laboratory (NREL). The NREL technique characterizes a responsivity function of a pyranometer as a function of the zenith angle, as well as reporting a single calibration responsivity value for a zenith angle of 45°. The uncertainty analysis shows that a lower uncertainty can be achieved by using the response function of a pyranometer determined as a function of zenith angle, in lieu of just using the average value at 45°. By presenting the contribution of each uncertainty source to the total uncertainty; users will be able to troubleshoot and improve their calibration process. The uncertainty analysis method can also be used to determine the uncertainty of different calibration techniques and applications, such as deriving the uncertainty of field measurements.


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MS08_04_REDA
Picture of the productUncertainty of Gauge Block Calibration by Mechanical Comp.
Jennifer E. Decker, Anthony Ulrich and James R. Pekelsky
This paper presents a detailed measurement uncertainty analysis for the calibration of gauge blocks made from like materials using a mechanical comparator consisting of opposing styli and a digital readout. After discussing the influence parameters affecting the calibration process, a mathematical model is developed that leads to a measurement equation relating the length of the client’s gauge block to measurements of the standard gauge block and associated temperature corrections. Following the ISO “Guide to the Expression of Uncertainty in Measurement,” all of the uncertainty components and their sensitivity components are calculated. These components include factors related to the calibration of the standard, the measured difference between the client’s gauge and the standard gauges, and various temperature differences. After discussing a specific measurement process in a typical laboratory environment,all of the uncertainty omponents are quantified and then combined in quadrature. The resulting expanded uncertainty for the calibration of a client gauge against a working standard is given by and a coverage factor of k = 2 is used. While the detailed characterization of any system and its associated measurement uncertainties will be unique to a given set of conditions, by providing all the details at each step, this paper is intended to be used as a guide for other similar situations.


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MS08_04_DECKER