This website uses cookies to store information on your computer. Some of these cookies are used for visitor analysis, others are essential to making our site function properly and improve the user experience. By using this site, you consent to the placement of these cookies. Click Accept to consent and dismiss this message or Deny to leave this website. Read our Privacy Statement for more.
Applying the Welch-Satterthwaite Formula to Correlated Errors
Mark Kuster
NCSLI Measure | Vol. 8 No. 1 (2013) | 10.1080/19315775.2013.11721629
Publisher NCSL International | Published 3/1/2013 | Pages 42-55
Abstract: The “Guide to the expression of uncertainty in measurement” (GUM) recommends the Welch-Satterthwaite (W-S) formula for effective degrees of freedom (DOF) estimates for an uncertainty composed of multiple components. However,
the formula does not apply strictly to measurement scenarios having correlated error sources. Correlations arise frequently in metrology, as does the question of how to compute DOF. Metrologists may resort to options such as acknowledging the potential
error and ignoring the correlation, adjusting the formula results, or modifying the formula itself. Such approaches introduce their own approximations. This paper describes and evaluates a technique that transforms any measurement scenario to one
involving only independent error sources, applies W-S, and transforms the results back to the original scenario. It also outlines matrix uncertainty formulations and recommends that uncertainty reports provide additional data to avoid information
loss in traceability chains.
Comparison of Flat Plate and Cavity Sources as Infrared Thermometry Calibration Standards
Frank Liebmann, Tom Kolat
NCSLI Measure | Vol. 8 No. 1 (2013) | 10.1080/19315775.2013.11721631
Publisher NCSL International | Published 3/1/2013 | Pages 66-71
Abstract: Flat plate and cavity sources have geometry designs that qualify both for use as calibration standards. Differences may arise, however, due to the emissivity of the source, the size of the source and the field of view. Additional
measurement parameters for infrared radiation thermometers, such as measuring distance, also warrant important consideration. This paper discusses the setup, process and results of a recent comparison between both source types. It demonstrates through
diagrams and gathered data how both sources were measured by a small sample of infrared radiation thermometers.
Establishing a Continuous Chain of Traceability for Pressure Measurements up to 40 Mpa
Jasveer Singh , A.K. Bandyopadhyay, D.R. Sharma, Ashok Kumar, D. Arun Vijayakumar, Nita Dilawar Sharma
NCSLI Measure | Vol. 8 No. 1 (2013) | 10.1080/19315775.2013.11721630
Publisher NCSL International | Published 3/1/2013 | Pages 56-65
Abstract: An Ultrasonic Interferometer Manometer (UIM) has been in use as the primary pressure standard at the National Physical Laboratory in India (NPLI) for absolute and gauge modes up to 130 kPa since 1982. However, the primary pneumatic
pressure standard in gauge mode up to 6 MPa was based on the performance of controlled clearance Piston Gauges (CCPG). The uncertainty of measurements in UIM and CCPG were of great concern in establishing the primary pneumatic pressure scale of NPLI.
To bridge the gap between the high vacuum, both in absolute and gauge modes, pneumatic pressure and hydraulic pressure up to 1 GPa, a conscientious attempt has been made to establish a uniform scale in the entire pressure range from 1 × 10−4 to 1
× 109 Pa that utilizes the UIM as the primary pressure standard. This paper presents the results of this entire systematic exercise up to a pressure of 40 MPa, in terms of the characterization of the piston gauges by the method of cross floating in
the overlapping pressure ranges, so that the measurement uncertainty in one range is transferred to the other range. We have evaluated the effective area (Ap) as a function of measured pressure (p) and estimated the zero pressure effective area (Ao)
and pressure distortion coefficient (λ) with an uncertainty statement, and then linked them to establish a new traceability chart which has superseded the old NPLI pressure scale. These established uncertainties are now included in the key comparison
database (KCDB) maintained by the Bureau International des Poids et Mesures (BIPM).
NCSLI Measure | Vol. 8 No. 1 (2013) | 10.1080/19315775.2013.11721628
Publisher NCSL International | Published 3/1/2013 | Pages 36-41
Abstract: This paper describes a technique for precisely measuring AC currents using a new patent pending design for a current transformer. This technique has been implemented in a new laboratory power analyzer. Tests of the existing
design have demonstrated Type A measurement uncertainties of less than 30 ppm (parts per million or parts in 106) for a field deployable instrument for both stationary and quasi-stationary AC current signals. Future modifications are being evaluated
for implementation into a non-portable laboratory instrument with the goal of achieving measurement uncertainties of less than 10 ppm (k = 2). These measurement techniques are applicable to AC ammeters and power analyzers. The associated fast asynchronous
sampling method and non-zero crossing calculations also materially improves the precision of both AC current and voltage measurements. In addition these techniques and the measurement circuitry can be adapted to provide the basis for determining phase
shifts between currents and voltages in single and multiple phase systems.
Proposed Guidelines for the Selection of Trapezoidal and Triangular Distributions for an Uncertainty Evaluation
Swanand Rishi
NCSLI Measure | Vol. 8 No. 1 (2018) | 10.1080/19315775.2013.11721632
Publisher NCSL International | Published 3/1/2018 | Pages 72-77
Abstract: Estimating measurement uncertainty involves categorizing sources of uncertainty into Type A and Type B components. Components evaluated as Type A are assumed to have a normal probability distribution based on a series of actual
observations, even when only a small number of observations are obtained. Under Type B evaluation, a rectangular distribution is the most common assumption. The rectangular distribution is also widely found in examples provided in standards documents,
particularly when the specifications are given with lower and upper bounds or containment limits. This paper discusses the views expressed in some standards about the validity of assuming a rectangular distribution. It includes a case study that demonstrates
that distributions other than the rectangular distribution can be used based on the analysis of data, resulting in reduced uncertainty. At present, the author has not found specific guidance regarding the assumption of trapezoidal and triangular distributions
with respect to the value of β. The paper proposes a criterion to select a trapezoidal or triangular distribution based on the value of β.
Standardized Specifications and Test Methods for Coordinate Measuring Machines with Imaging Probing Systems
Jim Salsbury
NCSLI Measure | Vol. 8 No. 1 (2013) | 10.1080/19315775.2013.11721627
Publisher NCSL International | Published 3/1/2013 | Pages 30-35
Abstract: ISO 10360-7:2011 is the first international standard to address the specification and testing of certain types of noncontacting dimensional measuring instruments. This important new standard was developed by a working group
within the International Organization for Standardization (ISO) technical committee 213, and addresses the need for common testing methods and specifications for coordinate measuring machines (CMMs) equipped with any type of imaging probing system,
such as video or vision systems. This paper provides an overview of this new standard along with some insight into the options available in the standard. It will also be shown how the tests in this standard can be used for the most modern three-dimensional
measuring systems while still providing testing methods to meet the needs of older systems.
A Survey of Time Transfer via a Bidirectional Fiber Link for Precise Calibration Services
Shinn-Yan Lin, Wen-Hung Tseng
NCSLI Measure | Vol. 8 No. 2 (2013) | 10.1080/19315775.2013.11721643
Publisher NCSL International | Published 6/1/2013 | Pages 70-77
Abstract: The aim of this survey is to prepare ourselves for the future need of precise time and frequency calibration services over fiber links. We study the accuracy requirements of some critical infrastructure timing applications,
and review the development of time and frequency transfer via fiber. We also present results from a preliminary experiment on two-way time transfer through a 25 km optical fiber link. The fiber link is based on a common-path configuration that provides
good reciprocity in both directions. Therefore, the propagation path delays in the fiber can be cancelled out almost entirely by employing the two-way method. The resulting data exhibit a time deviation of less than 7 ps for averaging periods ranging
from one second to one day. A frequency stability of 1 × 10−16 at one day has also been demonstrated. The time calibration and residual non-reciprocity of bidirectional fiber links are also discussed in this paper.
Automatic Calibration of DC Low Level Current Sources and Meters
Johnny C.Y. Poon, Dennis W.K. Lee, Y.C. Chau, Aaron Y.K. Yan, H.S. Lam
NCSLI Measure | Vol. 8 No. 2 (2013) | 10.1080/19315775.2013.11721638
Publisher NCSL International | Published 6/1/2013 | Pages 34-38
Abstract: An automated system has been developed at SCL for the calibration of low level dc current sources and meters, including electrometers and femtoammeters, from 100 picoamperes (pA) down to 100 femtoamperes (fA). The system is
comprised of in-house developed control software, ramping voltage generation circuitry, and a set of precision air capacitors. For measurement at the 100 pA level, expanded measurement uncertainties of 0.1 % and 0.3 % for generating test currents
and calibrating meters, respectively, can be achieved by this system.
Experimental and Simulation Study for a Time Transfer Service via a Commercial Geostationary Satellite
Jacqueline Walker, Marco Genova
NCSLI Measure | Vol. 8 No. 2 (2013) | 10.1080/19315775.2013.11721642
Publisher NCSL International | Published 6/1/2013 | Pages 62-69
Abstract: Time transfer over satellite links has been explored since the satellite era began. Currently, Two Way Satellite Time and Frequency Transfer (TWSTFT) is routinely used between national timing laboratories to align national timing
standards, and the Global Positioning System (GPS) provides accurate timing signals in addition to its more familiar navigation solution. This paper reports on a method for transferring time from a reference clock over commercial geostationary satellite
links with a specified low level of uncertainty at the receiving stations, using only the ephemeris information provided by the satellite operator. An initial experiment, reported here, showed that with one master station, measuring aggregate extraneous
delays and transmitting positioning and delay data plus a correction factor to the slave stations, allowed transfer of a 1 pps (pulse per second) timing signal with a standard deviation of 72 to 98 ns and peak-to-peak variations of 500 to 600 ns,
when measured against a GPS reference. Subsequent analysis of the experiment uncovered some issues with the implementation, suggesting that these results could be substantially improved upon. Furthermore, a simulation of the system that modeled the
extraneous delays produced results similar to those obtained in the experiment.
Implementation of an Accelerometer Transverse Sensitivity Measurement System
Christiaan Veldman
NCSLI Measure | Vol. 8 No. 2 (2013) | 10.1080/19315775.2013.11721639
Publisher NCSL International | Published 6/1/2013 | Pages 40-44
Abstract: The National Metrology Institute of South Africa (NMISA) has implemented a system to measure the transverse sensitivity of accelerometers. The system is in compliance with ISO 16063-31. As a mechanical device, the principle
sensing axis of an accelerometer is not 100 % perpendicular to the mounting axis. This gives rise to the effect that the accelerometer will produce an electrical output even when a mechanical input perpendicular to the principle measurement axis is
applied. The quantification of this “defect” parameter is of importance when high accuracy acceleration measurements are performed using accelerometers. This paper describes the system implemented by the NMISA to measure the transverse sensitivity
of vibration transducers.
NCSLI Measure | Vol. 8 No. 2 (2013) | 10.1080/19315775.2013.11721640
Publisher NCSL International | Published 6/1/2013 | Pages 46-51
Abstract: Integrating spheres are widely used for the photometric (or luminous flux) measurement of light sources. Their size and geometry influence the measurement uncertainty; including the baffle geometry inside the sphere, which avoids
the first incident light from the light source. Different set-up conditions of the directional light source, including the light emitting diode (LED) light-bar and surface light source, result in different luminous flux. We have simulated directional
light sources mounted at the center of sphere to advance the feasibility study of directional light sources in different mounting conditions. By varying the types of directional light sources, the geometry of the integrating sphere, the baffle condition,
the size of the sphere, and the absorptivity of the light source, we have found the optimal measurement conditions. This study provide knowledge about the limitations of an integrating sphere when measuring a directional light source, and this knowledge
can be applied to reduce the measurement uncertainty.
Two-Color One-Way Frequency Transfer in a Metropolitan Optical Fiber Data Network
Sven-Christian Edenhag, Per Olof Hedekvist , Kenneth Jaldehag
NCSLI Measure | Vol. 8 No. 2 (2013) | 10.1080/19315775.2013.11721641
Publisher NCSL International | Published 6/1/2013 | Pages 52-61
Abstract: Two-color one-way frequency transfer through one strand of optical fiber is an alternative method to two-way frequency transfer, and is useful if unknown asymmetries exist in the link due to different paths for each direction.
The term “two-color” refers to the ability to send signals at two different wavelengths utilizing the same fiber in one direction. The method is suitable for implementation in existing urban Single Mode Fiber networks, for instance in networks that
are utilized for data and television communication. It is therefore able to coexist with data channels in wavelength-division multiplexing (WDM) systems. It performs as a dynamical control of transit time and simultaneously enables a real-time phase
stabilized output signal. This paper presents results from a comparison of two cesium beam frequency standards separated by about 3 km over an optical fiber network located in a metropolitan area in Sweden. The cesium standards were simultaneously
compared to each other with a Global Positioning System (GPS) satellite link and over optical fibers, so that the optical fiber technique could be evaluated with respect to the GPS technique. The difference in frequency stability between the two methods
is shown to be about 3 × 10−15 over an averaging interval of 10,000 s.
An Examination of the Uncertainty of Industrial Deadweight Testers Used for Pressure Calibrations in Different Environments
Michael Bair
NCSLI Measure | Vol. 8 No. 3 (2013) | 10.1080/19315775.2013.11721649
Publisher NCSL International | Published 9/1/2013 | Pages 28-34
Abstract: The industrial deadweight tester (IDWT) is a dead weight pressure gauge that is designed, built, and calibrated to be used without having to make corrections or calculate pressure. In practice, the level of corrections ranges
from no corrections, or relying on the pressure value engraved on the weights, to using the full pressure equation to calculate a reference pressure. The environments in which IDWTs are used also differ. Some IDWTs are portable enough to be used in
an open environment, some are used on production floors, and some are used as references in laboratories with a controlled environment. It is not always clear what the uncertainty specifications are for the variety of levels of corrections and environments.
This paper carefully examines the levels of corrections made and applies them to an industrial environment, and provides the tools to be able to perform a valid uncertainty analysis in pressure.
Calibration of Industrial Weighing Systems by Use of a Coriolis Flowmeter
Pablo Canalejo Cabrera, Felipe González Rojas
NCSLI Measure | Vol. 8 No. 3 (2013) | 10.1080/19315775.2013.11721654
Publisher NCSL International | Published 9/1/2013 | Pages 70-77
Abstract: This paper presents the results of the calibration of a weighing system, composed of a tank mounted on load cells, by use of a Coriolis flowmeter. A model of calibration is proposed and discussed. The results are compared with
those obtained with reference mass standards, applying direct comparison and the substitution material methods. Common statistical tests were applied to evaluate the agreement of measurement results obtained with the various methods.
GWP® - The Science-Based Global Standard for Efficient Lifecycle Management of Weighing Instruments
Klaus Fritsch
NCSLI Measure | Vol. 8 No. 3 (2013) | 10.1080/19315775.2013.11721653
Publisher NCSL International | Published 9/1/2013 | Pages 60-69
Abstract: In the laboratory, weighing is only one step of a whole analysis chain in quality control; however it strongly influences the overall quality and integrity of the final result. In production, weighing is mandatory to achieve
batch uniformity and consistency in dispensing or formulation processes. In all industries, accurate weighing is essential to ensure continuous adherence to predefined process requirements and to avoid a frequent source of Out of Specification results
(OOS). This paper introduces GWP®, the science-based global standard for efficient lifecycle management of weighing instruments. Based primarily on the user's weighing requirements and prevailing weighing risks, it provides a state-of-the-art strategy
for reducing measurement errors and ensuring accurate weighing results. Besides addressing the instrument's metrological aspects as minimum weight, GWP® also establishes a specific routine testing scenario for the instrument. Applications with a high
risk of inaccurate weighings and stringent weighing accuracy requirements require frequent calibration and user tests to be carried out. However, for less risky and stringent applications, testing efforts can be reduced accordingly. Widespread misconceptions
– specifically with respect to the definition of test procedures and the selection of appropriate weights for periodic performance verification – are critically analyzed. Based on scientific principles, the user is guided on how to optimize his routine
testing procedures and how to avoid unnecessary or erroneous testing.
NCSLI Measure | Vol. 8 No. 3 (2013) | 10.1080/19315775.2013.11721652
Publisher NCSL International | Published 9/1/2013 | Pages
Abstract: A comprehensive calibration hinges upon selecting calibration test points that adequately cover the calibrated range of an instrument. ISO 17025 [1] addresses many factors that contribute to the quality of a calibration; however,
one aspect that it does not directly address is the selection of calibration points. The selection of calibration points can be viewed as a form of sampling with due risk resulting from insufficient points. The manufacturer of an instrument has unique
knowledge regarding the instrument's design. The calibration provider has insight into method constraints and perhaps into common modes of failure for a given measurement technology. The owner has unique knowledge regarding critical usage points.
Yet each of these three groups lacks some knowledge or expertise that may be important for assuring that calibration points are suitable. This paper surveys guidance documents related to the subject and discusses the need for further attention to
this important contribution to measurement quality.
Upgrade and Requalification of an Ultra-low Flow, Low Uncertainty Gas Leak Measurement System
Donavon Gerty
NCSLI Measure | Vol. 8 No. 3 (2013) | 10.1080/19315775.2013.11721651
Publisher NCSL International | Published 9/1/2013 | Pages 42-48
Abstract: The Accumulate Dump System (ADS) at Sandia National Laboratories is a high accuracy system designed to measure the volume flow rate of gas leak artifacts using fundamental quantities. One major advantage of this system is that
it can measure the flow rate of any gas species across several orders of magnitude (10−10 to 10−15 mol / s). This system determines the leak rate by comparing a known molar quantity of gas to that collected from the unknown over a measured period
of time. The known molar quantity is prepared by filling a known volume to a measured pressure at a specified temperature. Corrections are made for impurity of the gas, background signal, and equipment sensitivity. The ADS was brought online in the
1980's and used a magnetic sector to compare the ion currents of the two molar quantities. The ADS has been updated to now use a commercially purchased quadrupole system. Several components have been replaced allowing the system to be completely automated.
This led to several advantages but unfortunately increased the overall uncertainty of the system. The theory behind the leak rate calculation with the associated uncertainties will be discussed, as well as leak rate measurement results of a 3-Mass
species leak artifact.
Utilizing Size of Source Effect to Determine Minimum Sample Size in Radiation Measurement with a Fourier Transform Infrared Spectrometer
Daniel Cárdenas-García
NCSLI Measure | Vol. 8 No. 3 (2013) | 10.1080/19315775.2013.11721650
Publisher NCSL International | Published 9/1/2013 | Pages 36-40
Abstract: A Fourier transform infrared spectrometer (FTIRS) can be used to measure the emitted radiation of an opaque object. To perform the measurement correctly, most of the radiation getting into the FTIRS must come from the object
being measured. A size-of-source-effect (SSE) function, σ, can be defined for FTIRS in a similar way that it is defined for radiation thermometers. Then, σ can be used to establish a minimum diameter of the surface to be measured with the FTIRS. For
example, we can specify that a sample minimum diameter would be one for which σ ≥ 0.99. This would mean that at least 99 % of the radiation getting into the FTIRS comes from the sample. This work shows how σ is defined for FTIRS, and evaluates the
method with two experiments using different radiation sources. The first radiation source was a blackbody radiator with emissivity greater than 0.995, and the second radiation source was a heated graphite disk. It was found experimentally that a,
estimated according to the definition and within the estimated uncertainty, depended neither on the FTIRS working wavelengths, nor on the radiation source used. For this reason, it was concluded that the method to specify the sample minimum diameter
by using σ provides consistent results.
A Study of the Long Term Stability of Force Transducers
Harish Kumar
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721662
Publisher NCSL International | Published 12/1/2013 | Pages 40-44
Abstract: This paper discusses the long term stability, over a period of more than 10 years, of force transducers with capacities ranging from 10 kN to 500 kN. The force transducers have been calibrated using force standards machines
of various capacities, and are used to maintain the traceability of force measurements; from the force standard machines, to the force calibrating machines, and finally to industrial users. The study reveals that the deviation of the average values
of force transducers has been varying appreciably over time. The discussion that follows identifies the probable sources of the deviations.
An Automated Thermometer Calibration System Using Optical Character Recognition and Video Imaging Technology
Julian C.P. Cheung, Aaron Y.K. Yan
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721661
Publisher NCSL International | Published 12/1/2013 | Pages 32-38
Abstract: Thermometers under test are traditionally calibrated by comparison with reference thermometers, such as standard platinum resistance thermometers in liquid baths. The process is time consuming and costly, because an operator
is required to adjust the bath temperature and take the readings of the thermometers. The Government of the Hong Kong Special Administrative Region Standards and Calibration Laboratory (SCL) recently developed an automated calibration system for thermometer
calibration that requires only minimal attention from an operator. The system makes use of a computer to control the bath temperature and take the thermometer readings by using pattern recognition techniques. Optical Character Recognition (OCR) and
Liquid Level Recognition (LLR) techniques are employed to record the readings of the digital and liquid-in-glass thermometers, respectively. The reading process starts by taking pictures of the display of the thermometer under test by a smart video
camera. The images are analyzed with software to find the thermometer readings. The system can be trained to recognize various display formats of the thermometers under test. The images of the display readings are retained for proof checking when
a report is produced.
An Uncertainty Analysis of Fused-Quartz Bourdon Tube Pressure Instruments
Joshua Biggar
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721663
Publisher NCSL International | Published 12/1/2013 | Pages 45-51
Abstract: The forced-balanced fused-quartz Bourdon tube (QBT) technology is a proven pressure measurement method, which has been used in the metrology field for over 50 years. Fluke Calibration acquired Ruska Instrument Corporation from
General Electric's Sensing and Technologies division in the summer of 2010, which allowed it to add QBT pressure measurement technology to its family of pressure products. This paper explains the unique facets of QBT technology, its basis of operation,
and provides an uncertainty analysis for several different operational modes.
Industrial Metrology Engineering: An Educational Strategy to Fulfill the Needs of Industry and Society
Maria Guadalup López Granada, Luz Elena Narváez Hernández, Flora Mercader-Trejo , Raúl Herrera Basurto
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721660
Publisher NCSL International | Published 12/1/2013 | Pages 28-30
Abstract: The design and maintenance of controlled production processes in modern industry is largely based on measurements. Metrology, the science of measurement, is important not only in industry, but in every aspect of our daily lives.
Sound metrology practices would not be possible without the existence of qualified personnel in all fields of measurement, thus metrology education is essential for the development of science and technology in all countries. Aware of the needs for
professional training in the field of metrology, the Universidad Politécnica de Santa Rosa Jáuregui (UPSRJ), a public university located in the state of Querétaro in Mexico, conducted a survey on the relevance of opening a new educational program.
This new undergraduate program is an innovative and cutting edge educational option that was designed to satisfy the metrological needs of both industry and society.
Picometer Metrology for Precise Measurement of Refractive Index, Pressure, and Temperature
Jack Stone, Douglas A. Olson, Jacob R. Ricker, Gregory Strouse, Jay H. Hendricks, Donavon Gerty, Patrick Egan, G.E. Scace
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721666
Publisher NCSL International | Published 12/1/2013 | Pages 67-73
Abstract: Fabry-Perot interferometers can be used for very precise measurement of the refractive index of gasses. This can enable increased accuracy of interferometer-based length measurement. In addition, because the refractive index
of a gas depends on its pressure and temperature, measurements of refractive index can be used to monitor either one of these quantities if the second is known. Recently we have embarked on a project with a goal of measuring pressure with a relative
standard uncertainty below 1.4 × 10−6. Dimensional metrology with picometer uncertainties is the core of this technique and is the subject of this paper. Refractive index will be measured by comparing two precisely equal displacements (150 mm), where
one displacement is in vacuum and the second is in helium and will appear to be slightly longer due to the refractive index. The two displacements must be compared with < 3 pm uncertainty. Major challenges include many of the typical sources of
error in dimensional measurement, such as Abbe errors, alignment errors, material dimensional stability, etc. Careful consideration must be given to second-order effects that are not normally large enough to merit mention. The proposed experimental
design will minimize the major sources of error while providing additional metrology (including angle measurements with nanoradian precision) to correct residual errors.
Proficiency Testing for Pressure Calibration at the National Voluntary Laboratory Accreditation Program (NVLAP)
Douglas A. Olson, Gregory Driver, Thomas R. Hettenhouser
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721664
Publisher NCSL International | Published 12/1/2013 | Pages 52-58
Abstract: The National Voluntary Laboratory Accreditation Program (NVLAP) has initiated a proficiency testing program for calibration laboratories accredited for pressure, designated as NVLAP code 20/T05. This program involves measurements
by the laboratory on NVLAP-provided test artifacts at specific pressure points in gas, and then comparisons of the results to similar measurements by the NIST (National Institute of Standards and Technology) Thermodynamic Metrology Group. The statistical
test of the value of the En parameter is used to determine whether or not the laboratory shows proficiency at each pressure point, and the entire set of En values determines whether or not the laboratory demonstrates proficiency for their declared
scope in pressure. This proficiency test can evaluate both laboratories that primarily calibrate effective area of piston gauges, and laboratories that calibrate electronic pressure instruments. The test protocol, methods of data analysis, and some
results to date are presented. All NVLAP calibration laboratories currently accredited for effective area of piston gauges passed the proficiency test.
Summary of a LED Bulb Interlaboratory Comparison in Taiwan
Chen-Yun Hung, Chen-Yen Fang, Cheng-Hsien Chen, Paul Kam-Wa Lui, Pin-Hao Wang
NCSLI Measure | Vol. 8 No. 4 (2013) | 10.1080/19315775.2013.11721665
Publisher NCSL International | Published 12/1/2013 | Pages 60-66
Abstract: Interlaboratory comparisons (ILCs) organize, perform, and evaluate measurements or tests on the same or similar items by two or more laboratories in accordance with predetermined conditions. The results demonstrate the measurement
capability of each laboratory. In order to understand the light emitting diode (LED) bulb measurement capability of laboratories in Taiwan, the Center for Measurement Standards/Industrial Technology Research Institute (CMS/ITRI) conducted a LED bulb
ILC in accordance with ISO/IEC 17043:2010. Percent difference |D%| was chosen as the performance statistic to indicate the measurement capabilities of participants, and the measured values of the National Measurement Laboratory (NML), Republic of
China, were used as the assigned values. The analysis of this LED bulb ILC showed that the |D%| of most participants were less than 5 %, which implied that most of the LED bulb testing laboratories in Taiwan have good measurement competence.
