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Components of Uncertainty in the Force Calibration of Universal Brake Testers
Paula Solano Sánchez
NCSLI Measure | Vol. 9 No. 1 (2014) | 10.1080/19315775.2014.11721673
Publisher NCSL International | Published 3/1/2014 | Pages 46-51
Abstract: Universal brake testers are measuring instruments used to measure the effectiveness of heavy vehicle braking and, occasionally, the braking of light vehicles. These brake testers are calibrated by comparing an indication of
the brake tester with a force standard. This paper addresses the uncertainty components related to this process.
Direct Traceability for Ultra-Pure Water Conductivity
Carsten Thirstrup, Hans Jensen
NCSLI Measure | Vol. 9 No. 1 (2014) | 10.1080/19315775.2014.11721676
Publisher NCSL International | Published 3/1/2014 | Pages 68-72
Abstract: Danish Fundamental Metrology (DFM) has established a calibration setup with direct International System (SI) traceability for conductivity sensors and measurement systems for conductivity of pure to ultra-pure water. Electrolytic
conductivity is a widely used parameter for the characterization of purity of water, due to its high sensitivity to ionic content e.g. from contaminants. The Pharmacopoeias (US, EU, etc.) specify (traceable) conductivity measurements as the method
for documenting compliance with requirements of Water for Injection (WFI), and other regulations on pure water quality also rely on conductivity as the quality parameter. Conductivity sensors are presently calibrated either using reference materials
with conductivity many orders of magnitude different from the level of measurement, and/or in a matrix different (sometimes very different) from pure water. Some users rely on indirect properties such as the conductivity temperature coefficient of
water as a quality control parameter. DFM has developed a geometrically characterized measurement cell, hence a primary standard, relevant for pure water conductivity. Combined with a bulk resistance derived from impedance spectroscopy, also traceable
to international standards, it allows direct measurement of low conductivity (less than 2 mS/m). A calibration setup with comparison to the primary cell establishes direct traceability to the SI, without the need for assumptions on scaling properties
of conductivity cells or insignificant matrix effects. The setup has been validated through an international measurement comparison at the national metrology institute (NMI) level.
How to Weigh Everything from Atoms to Apples Using the Revised SI
Jon Pratt
NCSLI Measure | Vol. 9 No. 1 (2014) | 10.1080/19315775.2014.11721671
Publisher NCSL International | Published 3/1/2014 | Pages 26-38
Abstract: The fact that the unit of mass might soon be derived from the Planck constant, rather than from an artifact standard, can seem daunting and downright baffling when viewed from the vantage point of our day to day perception of
mass. After all, at measurement levels that register with our human senses, the connection between the quantum mechanics of Planck (atoms) and the engineering mechanics of Newton (apples) is less than obvious. However, as the physicist Richard Feynman
famously observed, “there is plenty of room at the bottom”, and our need to quantify the mass of objects isn't always limited to the familiar quantities we encounter in the produce section of our grocery store. Here, I explore the connection between
mass and the Planck constant and suggest that a benefit of deriving the unit of mass from a fundamental constant is that it is inherently more scalable than the present artifact. For example, scientists and engineers working at the forefront of measurement
science are increasingly pushing the boundary on what we consider a measurement of mass. In fact, a group now claims to have measured the mass of a cesium atom to within well below a yoctogram, which is below the mass of a single proton. This unit
of mass is a submultiple of our present artifact kilogram so small that it requires 27 zeros after the decimal point before it even registers as a significant digit! How are such things possible? Why would you try? Can we even conceive of a traceable
yoctogram? To begin grappling with these questions, I will attempt to guide you through the physics of Newton and Planck and, I hope, shed some light on how we can weigh everything from atoms to apples in a revised SI based on fundamental constants.
Implementing a Shock Calibration System Using a Vibration Exciter and Pendulum
Christiaan Veldman
NCSLI Measure | Vol. 9 No. 1 (2014) | 10.1080/19315775.2014.11721672
Publisher NCSL International | Published 3/1/2014 | Pages 40-45
Abstract: As the custodian of the National Measurement Standards (NMS), the vibration laboratory of the National Metrology Institute of South Africa (NMISA) has developed a mechanical shock calibration system in response to the requirements
of industry. This project was an extension of the recently implemented dynamic force calibration system. This paper discusses the measurement system and its components, as well as the calibration procedure to be followed. The determination of the
peak acceleration as a result of the generation of the shock pulse is discussed, indicating the chain of traceability to the International System of units (SI). The paper concludes with a discussion of the calibration results and an overview of the
measurement uncertainty.
New Technologies to Improve AC-DC Difference Measurements at NIST
Yi-Hua Tang, June Sims, Joseph Kinard, Thomas Lipe
NCSLI Measure | Vol. 9 No. 1 (2014) | 10.1080/19315775.2014.11721674
Publisher NCSL International | Published 3/1/2014 | Pages 52-58
Abstract: Determination of ac-dc difference of thermal voltage converters has traditionally been done by range-to-range scaling techniques, beginning at the voltage level and optimal frequencies of the primary standards, and continuing
until the parameter space has been completed. Range-to-range scaling propagates uncertainties of the measurement process at each step, so that the uncertainties become larger at values away from the primary standards, with the magnitude determined
largely from the number of scaling steps. At the National Institute of Standards and Technology (NIST), we have recently fabricated multijunction thermal converters with exceptional properties over a large range of voltages and frequencies. Coupled
with the use of an ac voltage standard based on quantum effects, we have reevaluated the NIST uncertainty matrix for ac-dc voltage transfer difference, and have made significant reductions in the uncertainties at all voltage and frequency levels.
The International Temperature Scale: Past, Present, and Future
Alan G. Steele, Kenneth D. Hill
NCSLI Measure | Vol. 9 No. 1 (2014) | 10.1080/19315775.2014.11721675
Publisher NCSL International | Published 3/1/2014 | Pages 60-67
Abstract: Since its inception in 1927, the International Temperature Scale (ITS) has changed to meet the needs of the time. The ITS protocol specifies phase transitions with assigned temperatures (the defining fixed points), defining
instruments (thermometers), and interpolating (or extrapolating) equations. Since 1927, the selection of fixed points and their assigned temperatures have changed, defining instruments have been added and deleted, and the equations have become more
complex. Since its introduction in 1990, the ITS-90 has served its user community well. However, its departure from thermodynamic temperature is more than is desirable for the most demanding applications. One approach is to continue making measurements
on the ITS-90 (T90), and then correct the temperatures for better accord with thermodynamic temperature (T) using the Consultative Committee for Thermometry's best estimates of (T – T90). Alternatively, these shortcomings can be addressed by an evolutionary
change that maintains the familiar mathematical structure of the ITS-90, but updates the coefficients of the reference functions and the temperatures of the defining fixed points. The impact on embedded instrumentation is minimal – requiring only
an updating of the coefficients of the reference functions and not a complete reworking of the mathematics.
Advanced Thermal Sensors for Broadband AC Voltage Metrology
June Sims, Joseph Kinard, Donald Novotny, Thomas Lipe
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721687
Publisher NCSL International | Published 6/1/2014 | Pages 74-78
Abstract: We report on the development and application of a new generation of multijunction thermal converters (MJTCs). These devices, fabricated on fused silica substrates, show exceptional performance over the frequency range from 10
Hz to 100 MHz over input voltages ranging from 1 V to 30 V, depending on design. We anticipate that these devices will form the future basis for ac voltage metrology at the National Institute of Standards and Technology (NIST).
New Generation of AC-DC Voltage Transfer Standards at Inmetro
Gean Marcos Geronymo, Andre Poletaeff, Renato Afonso, Jr, Renata T. de Barros e Vasconcellos
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721686
Publisher NCSL International | Published 6/1/2014 | Pages 66-73
Abstract: This paper describes the new reference standard for ac-dc voltage transfer at Inmetro, the national metrology institute of Brazil. The reference standards are based on Planar Multijunction Thermal Converters (PMJTCs), and are
used over the voltage range from 300 mV to 1000 V. The ac-dc voltage scale is described in detail, including the measurement uncertainty analysis. The results of an international comparison between Inmetro and Laboratoire National de Metrologie et
d'Essais (LNE), the national metrology institute of France, are provided for 1.5 V and 1000 V.
Supercontinuum Generation in Photonic Crystal Fibers by use of an Ultrashort Pulse Laser with a Cr:LiSAF Crystal
Minerva Robles-Agudo, Hector A. Castillo-Matadamas, Eric M. Rivera-Muñoz , Miguel A. Ocampo-Mortera, Rafael Quintero-Torres
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721685
Publisher NCSL International | Published 6/1/2014 | Pages 60-64
Abstract: We present the generation of two supercontinuum spectrums, in wavelength intervals of 580 to 950 nm and of 450 to 950 nm. These spectrums were obtained in two different photonic crystal fibers using an ultrashort pulse laser
with low repetition of 41 MHz developed with a Cr:LiSAF crystal. With the results obtained, tunable low cost sources and applications in the field of frequency combs as calibration references for standard lasers can be developed.
Technical Diagnostics: Principles, Methods, and Applications
Horst Czichos
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721681
Publisher NCSL International | Published 6/1/2014 | Pages 32-40
Abstract: The term diagnostics originates from the medical field and refers to the identification of the nature of a health problem and its classification by examination and evaluation. Technical Diagnostics has adopted this term and
deals with the “health” of technical objects. This paper provides an overview of Technical Diagnostics. It reviews the physics of failure and describes principles and methods of fault and failure examination, including structural health monitoring
and nondestructive evaluation. The role of metrological parameters as indicators of technical diagnostics is analyzed, and a methodology to monitor the functional performance and structural integrity of technical objects is outlined. Technical diagnostics
can be applied in nearly all areas of technology and industry in order to ensure functionality, quality, and, most importantly, safety and reliability of products, technical structures and systems.
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721682
Publisher NCSL International | Published 6/1/2014 | Pages 42-50
Abstract: Accreditation is an additional layer of assurance in a complex quality infrastructure. The role of accreditation has received very little attention from economists. This study contributes to filling this gap in two ways, by
outlining a theoretical framework that positions accreditation within the wider quality system, and by measuring benefits from accreditation to businesses in the United Kingdom (UK). Key information comes from a survey of stakeholders of the UK Accreditation
Services collected by the authors, which is used with data on the financial benefits to customers of the UK National Physical Laboratory (NPL). We conclude by suggesting that the value added by accreditation is likely to be of the order of several
hundred million pounds, rather than of the order of tens of millions or billions.
Use of Effective Emissivity of the Ear Canal on the Design of Cavities for Verification and Calibration of Ear Thermometers
Daniel Cárdenas-García
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721683
Publisher NCSL International | Published 6/1/2014 | Pages 52-54
Abstract: In some applications, radiation thermometers measure the temperature of radiators that have effective emissivities very close to one. For example, the ear canal is a natural cavity whose emissivity approaches that of a blackbody,
due to the high emissivity of human skin and tissue in the working wavelength range of ear thermometers. There are several designs for cavities to verify and calibrate ear thermometers, but in all of them there is a design error due to the difference
between the effective emissivities of the ear canal and the manufactured cavity. This work presents a method that utilizes the effective emissivity of the ear canal as a design parameter to manufacture a cavity with an effective emissivity equal to
that of the ear canal, thus minimizing the design error. The method presented can be used for other applications that require reducing the design error for radiant cavities that model high emissivity radiant sources.
Wavelength Independent Method for the Calibration of Radiation Thermometers with Fixed Emissivity of Less than One
David Cywiak-Córdova, Daniel Cárdenas-García, Hugo Rodríguez-Arteaga
NCSLI Measure | Vol. 9 No. 2 (2014) | 10.1080/19315775.2014.11721684
Publisher NCSL International | Published 6/1/2014 | Pages 56-58
Abstract: The increasing use of infrared thermometers operating at a fixed emissivity of less than one has made it necessary to develop new methods for their calibration. There are several possible solutions for this purpose. Unfortunately,
many of these solutions depend on the range of operating wavelength of the thermometer involved. This paper presents a method to calibrate radiation thermometers that can be used regardless of the working wavelength range of the thermometer. The method
is based on the use of a blackbody source and an optical chopper disk with a transmittance (mark-to-space ratio) that matches the fixed emissivity of the thermometer to be calibrated. The experimental set-up and the contributions to the measurement
uncertainty that are due to the transmittance of the chopper disk are described.
A 40 GHz Air-Dielectric Cavity Oscillator with Low Phase Modulation Noise
Archita Haiti, David A. Howe, Bill Riddle, Craig W. Nelson
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721695
Publisher NCSL International | Published 9/1/2014 | Pages 48-54
Abstract: We describe a 40 GHz cavity stabilized oscillator (CSO) that uses an air-dielectric cavity resonator as a frequency discriminator to reduce the phase modulation (PM) noise of a commercial 10 GHz dielectric resonator oscillator
(DRO) frequency multiplied by four. Low PM noise and small size were the main design goals. Single sideband (SSB) PM noise equal to −128 dBc/Hz at a 10 kHz offset from the carrier frequency is achieved for the CSO. In addition, we report on the PM
noise of several Ka-band components.
A Calibration System for Reference Radiosondes that Meets GRUAN Uncertainty Requirements
Martti Heinonen, Richard Högström , Heikki Kajastie, Hannu Sairanen, Antti Lakka
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721696
Publisher NCSL International | Published 9/1/2014 | Pages 56-60
Abstract: A new International System (SI) traceable calibration set-up for reference radiosondes is presented here with a preliminary uncertainty analysis. By meeting the GRUAN requirements, this development fulfils the needs of the meteorological
community for disseminating SI traceability to upper air humidity measurements with reduced uncertainty. The set-up was designed for calibrations from laboratory temperature down to 183 K and in terms of dew-point temperature from 193 K to 283 K.
To enable rapid changes in humidity and to shorten the time needed for a single calibration, the set-up utilizes a hybrid humidity generator method in which two air flows with known water vapor concentrations are mixed. According to a preliminary
uncertainty analysis, the relative expanded uncertainty (k = 2) of the set-up is less than 2 % expressed in terms of mixing ratio.
An Uncertainty Model and Analyzer for a Space Environmental Test Facility
Mihaela Fulop
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721698
Publisher NCSL International | Published 9/1/2014 | Pages 70-79
Abstract: This paper introduces a measurement uncertainty model and analyzer tool being developed for one of the world's largest space environmental test facilities, the Spacecraft Propulsion Research Facility (B–2) located at NASA Glenn
Research Center's Plum Brook Station near Sandusky, Ohio. The B–2 is the world's only facility capable of testing full-scale upper-stage launch vehicles and rocket engines under simulated high-altitude conditions. Developing an uncertainty tool for
the data acquisition of a test facility of this scale presents unique metrology challenges. Not only must the uncertainty analyzer tool be versatile enough to accommodate a wide range of disciplines and measurement requirements (such as temperature,
pressure, strain, vacuum, and acceleration), but it must provide a user-interactive platform for evaluating system measurement uncertainty based on customer-chosen measurement scenarios ranging from the most simplistic tests to the most complex ones.
The uncertainty analyzer tool, which was developed in Microsoft's Visual Basic for Applications (VBA) in Excel, will serve multiple purposes, including aiding in the optimal selection of measuring and test equipment, communicating capabilities to
customers, and supporting all decisions based on measurements. Although the analysis tool was developed for the data acquisition system in B–2, it can be easily sized to fit other data acquisition systems at the site utilizing similar measurement
methods. This paper outlines the methodology followed, the features of this tool, and how the tool can be applied to the measurement processes of different facilities.
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721697
Publisher NCSL International | Published 9/1/2014 | Pages 62-69
Abstract: A calibration system for ultrasonic flaw detectors has been developed at the Government of the Hong Kong Special Administrative Region Standards and Calibration Laboratory (SCL) in accordance with the international standard
EN12668-1:2010. The calibration covers all the periodic and repair tests (the Group 2 tests) required in the standard for checking the performance of ultrasonic instruments, including their stability, transmitter pulse parameters, receiver response
parameters, and time-base linearity. During the calibration, the ultrasonic flaw detector's transmitter is connected to a combination of a delay generator and function generator which simulates a delayed version of the transmitted signal as the reflected
signal. The simulated reflected signal is then fed to the receiver of the ultrasonic flaw detector. The stabilities over time and voltage variation of the received waves are measured and the receiver frequency response is obtained. Other performance
parameters of the receiver such as gain accuracy and linearity are calibrated by comparing gain steps with step attenuators. Lastly, a burst of pulse waves are generated by the arbitrary waveform generator to simulate a burst of reflected waves to
check the linearity of the time base.
Electrical Units in the New SI: Saying Goodbye to the 1990 Values
Nick Fletcher , Gert Rietveld ,
James Olthoff, Ilya Budovsky, Martin Milton
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721692
Publisher NCSL International | Published 9/1/2014 | Pages 30-35
Abstract: The proposed redefinition of several International System (SI) base units is a topic that has been on the metrology agenda for the last decade. Recent progress on several determinations of the fundamental constants means that
we now have a good idea of the defined numerical values that will be given in the new system to the Planck constant, h, and the elementary charge, e. This is especially relevant to electrical metrology as new numerical values for the von Klitzing
and Josephson constants, given by the relations RK = h/e2 and KJ = 2e/h, will replace the existing 1990 ‘conventional’ values, RK-90 and KJ-90. The implementation of the new system cannot be done without introducing small step changes into sizes of
the electrical units that are disseminated using Josephson and quantum Hall intrinsic standards. At the time of writing it looks likely that the relative change from KJ-90 to KJ will be of the order 1 × 10−7, and that from RK-90 to RK will be approximately
2 × 10−8. This paper discusses the practical impact of these changes on electrical metrology and highlights the long term benefits that will come from the updated system. The CCEM (Consultative Committee for Electricity and Magnetism) of the International
Committee for Weights and Measures is now taking the first steps to ensure a smooth implementation, most probably in 2018.
Evaluation of Proficiency Testing Results with a Drifting Artifact
Chen-Yun Hung, Chen-Yen Fang, Pin-Hao Wang
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721694
Publisher NCSL International | Published 9/1/2014 | Pages 42-46
Abstract: Proficiency testing (PT) is an evaluation of participant's performance against pre-established criteria by means of interlaboratory comparisons. The normalized error, En, is the most widely used performance statistic for determining
the measurement capability of a calibration laboratory. One of the variables in the En equation is Uref, which is the expanded uncertainty of the reference laboratory's assigned value. To evaluate a participant's performance effectively, if any effects
of the PT scheme are significant, the additional uncertainties should be combined with the reference laboratory's reported expanded uncertainty to estimate Uref. Among such uncertainties, the stability of artifacts is an important uncertainty component
in the PT scheme, especially for a calibration laboratory. Based on practical PT experience, most artifacts can be regarded as sufficiently stable if the difference between three reference laboratory measurements is small. In such cases, the median
of the three measurements is usually chosen as the assigned value, and its reported expanded uncertainty is used as the Uref value. However, some artifacts, such as standard resistors, drift over time. This leads to questions about how to accurately
determine the assigned values and expanded uncertainties of these artifacts. This paper presents a PT scheme for standard resistors that demonstrates the evaluation of PT results with a drifting artifact.
Realization and Dissemination of the International Temperature Scale of 1990 (ITS-90) above 962 °C
Andrew D.W. Todd ,Donald J. Woods
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721693
Publisher NCSL International | Published 9/1/2014 | Pages 36-40
Abstract: Above 962 °C, the ITS-90 is realized at the National Research Council (NRC) of Canada by a standard radiation thermometer with a known spectral responsivity and a silver freezing-point blackbody. Together with Planck's law,
the temperature scale can be extrapolated to temperatures in excess of 2500 °C, albeit with uncertainties that increase with higher temperatures. This realization can then be disseminated to other radiation thermometers via a variable-temperature
blackbody for use in, for example, calibration laboratories. In the future, it is expected that new high-temperature fixed points with transition temperatures exceeding 3000 °C will allow an interpolated high-temperature realization and lower uncertainties.
Software Analysis and Protection for Smart Metering
Cristiano G. de Castro, Charles B. do Prado , Renato Oliveira, Sérgio M. Câmara, Luci Pirmez, Lucia M.S. Bento, Raphael C.S. Machado,
Rafael O. Costa, Luiz F.R. da Costa Carmo , Tiago M. do Nascimento, Davidson R. Boccardo
NCSLI Measure | Vol. 9 No. 3 (2014) | 10.1080/19315775.2014.11721691
Publisher NCSL International | Published 9/1/2014 | Pages 22-29
Abstract: Smart meters are devices equipped with embedded software that are capable of processing complex digital data. These devices are now a reality in most areas of metrology. They enable a number of new applications, but they also
introduce new challenges with regards to their validation. This paper describes initiatives developed by Inmetro, the national metrology institute of Brazil, and Eletrobrás, a Brazilian power utility company, that are designed to support the validation
of smart electricity meters.
A Comparison of Primary Gas Flow Standards Spanning the Range from 10 sccm N2 to 10 slm N2
Michael Bair, Casey Rombouts, Jean Barbe, Rainer Kramer, Zdenek Krajicek, John Wright
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721705
Publisher NCSL International | Published 12/1/2014 | Pages 46-54
Abstract: We describe an international comparison of gas flow standards spanning the range from 2.1 × 10−4 g/s (10 sccm) of nitrogen to 0.21 g/s (10 slm) of nitrogen. For each of the participating laboratories, |En| < 0.78, where En
is the difference between the participant 's result and the comparison reference value divided by the uncertainty of this difference. The k = 2 uncertainties (corresponding to 95 % confidence level) of the comparison reference values range from 0.036
% to 0.052 %. These comparison uncertainties include a contribution of 0.042 % from the uncertainty of the three laminar flow elements used as transfer standards. The participating laboratories were: Laboratoire National de Métrologie et d'Essais
(LNE), National Institute of Standards and Technology (NIST), Fluke Primary Pressure and Flow Laboratory, Phoenix Arizona USA (FCP), Český Metrologický Institut (CMI), and Physikalisch-Technische Bundesanstalt (PTB).
In-situ Temperature Calibration Capability for Dimensional Metrology
Steve Phillips, Bala Muralikrishnan, Gregory Strouse, Prem Rachakonda, Daniel Sawyer, Chris Blackburn, Craig Shakarji
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721704
Publisher NCSL International | Published 12/1/2014 | Pages 40-45
Abstract: The Dimensional Metrology Group (DMG) at the National Institute of Standards and Technology (NIST) has developed a new in-situ temperature calibration system. This paper discusses the system components, an in-situ calibration
procedure, and the uncertainty sources involved in the calibration process. It also presents an uncertainty budget, and examines it with a Monte Carlo simulation. This system enables the DMG to perform quicker in-situ temperature calibration, at frequent
intervals with minimal downtime, and provides lower uncertainties for the dimensional measurements.
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721702
Publisher NCSL International | Published 12/1/2014 | Pages 24-35
Abstract: Demands for quality assured measurement are increasing, not only from sectors such as health care, services and safety, where the human factor is obvious, but also from manufacturers of traditional technical products of all
kinds who realize the need to assure the quality of their products as perceived by the customer. The metrology of human-based observations is, however, in its infancy. This article reviews how this can be tackled with a measurement system analysis
approach, particularly where Man acts as a measurement instrument. Connecting decision risks when handling qualitative observations with information theory, perceptive choice and generalized linear modelling – through the Rasch invariant measure approach
– enables a proper treatment of ordinal data and a clear separation of person and item attribute estimates. This leads in turn to opportunities for establishing measurement references, and the metrological quality assurance that is urgently needed
in many contemporary applications.
Maximizing Machine Volumetric Performance by Minimizing Plane Squareness Error
Michael Fink
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721708
Publisher NCSL International | Published 12/1/2014 | Pages 68-75
Abstract: In a three-axis orthogonal machine frame, there are 21 parametric error sources: three sources related to linear positioning, six to straightness, nine to angular, and three to plane squareness. Of all the sources of error,
the squareness errors can most easily dominate the volumetric performance of the machine. In industry, the existing traditional methods of evaluating squareness errors typically do a poor job. This paper describes a simple robust method for evaluating
plane squareness error by effectively averaging multiple squareness measurements using linear laser interferometer measurements and the law of cosines for data evaluation. This process also prevents any errors of length within the plane from influencing
the squareness error determination. The net effect has been an improvement of volumetric performance on every machine where this process has been implemented.
Measuring the Flashing Time Interval of LED Lights in Toys
Henry C.K. Ma, Aaron Y.K. Yan, Samuel C.K. Ko
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721703
Publisher NCSL International | Published 12/1/2014 | Pages 36-39
Abstract: We have developed two methods to measure the light flashing time interval in toys. One method uses high speed video recording and a synchronous counter. The method starts by taking a short video clip of the flashing Light Emitting
Diodes (LEDs) under test, together with the reading of an in-house designed synchronous counter which is phase locked to a cesium frequency standard. The flashing time interval is obtained by viewing the recorded video to search frame-by-frame for
the time interval between two successive LED state changes. This method has a measurement uncertainty (k = 2) of less than 2 ms. The second method is a direct measurement with a time interval counter. A circuit with a photo-transistor converts the
light signal to an electrical signal. A variable resistor is connected in series with the photo-transistor to tune the detection sensitivity such that it can work well in low illuminance conditions. The output signal is then amplified and fed to a
time interval counter that is phase locked to a cesium frequency standard. The time interval measurement range is 1 Hz to 10 Hz and the measurement uncertainty (k = 2) is less than 2 μs. A soft opaque silicon tube is used as a mask to select which
LED is to be measured when there are multiple LEDs used in a toy.
Moisture Measurement Setup for Wood Based Materials
Hannu Sairanen, Heikki Kajastie, Martti Heinonen, Maija Ojanen , Kari Riski
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721706
Publisher NCSL International | Published 12/1/2014 | Pages 56-60
Abstract: We are developing a novel gravimetric moisture measurement system for wood based materials. The measurement principle is based on combining the Loss on Drying (LoD) method with complementary water loss detection systems. In
our setup, air flows through a sample container containing sample material from 5 g to 400 g. The sample container is placed in a thermally controlled enclosure, which can be heated up to 200 °C. The mass loss of water is studied by weighing the sample
before and after heating, and by monitoring the humidity of the air exiting the sample container with a capacitive sensor. The amount of evaporated water is also studied by trapping the water from the through-passed air in a separately weighed cold
trap. The material samples can be exposed to different heating cycles in order to study different binding degrees of the water. This paper presents the measurement concept and the setup.
Selecting the Appropriate Type of Measurement Control Chart
Paul Kam-Wa Lui, Gwo-Sheng Peng, Chen-Yun Hung
NCSLI Measure | Vol. 9 No. 4 (2014) | 10.1080/19315775.2014.11721707
Publisher NCSL International | Published 12/1/2014 | Pages 61-67
Abstract: According to Section 5.9 of ISO/IEC 17025:2005 [1], laboratories shall have quality control procedures for monitoring the validity of tests and calibrations. The resulting data shall be recorded in such a way that trends are
detectable and, where practicable, statistical techniques shall be applied to the review of the results. In order to meet these requirements, control charts are commonly used to monitor the variation of measurement systems. However, the inappropriate
selection of process parameters or control charts may result in a failure to detect changes in the central tendency of measurement systems. This paper describes how to select the appropriate types of control charts in metrology, including situations
where the process parameters are characterized by a trend or have low resolution. In addition, some patterns are provided to help laboratory staff immediately evaluate measurement systems.
