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Measure Articles 2013 (23)

 
Picture of the productA Study of the Long Term Stability of Force Transducers
Harish Kumar
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.


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MS13_04_KUMAR
Picture of the productA Survey of Time Transfer via a Bidirectional Fiber Link
Wen-Hung Tseng and Shinn-Yan Lin
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.


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MS13_02_TSENG
Picture of the productAn Automated Thermometer Calibration System Using Optical
Julian C. P. Cheung and Aaron Y. K. Yan
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.


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MS13_04_CHEUN
Picture of the productAn Examination of the Uncertainty of IDWT
Michael Bair
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.


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MS13_03_BAIR
Picture of the productAn Uncertainty Analysis of Fused-Quartz Bourdon Tube
Joshua Biggar
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.


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MS13_04_BIGG
Picture of the productApplying the Welch-Satterthwaite Formula to Correlated Error
Mark Kuster
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.


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MS13_01_KUSTER
Picture of the productAutomatic Calibration of DC Low Level Current Sources
Dennis W. K. Lee, Y. C. Chau, Aaron Y. K. Yan, H. S. Lam, and Johnny C. Y. Poon
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.


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MS13_02_LEE
Picture of the productCalibration of Industrial Weighing Systems
Pablo Canalejo Cabrera and Felipe González Rojas
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.


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MS13_03_CABR
Picture of the productComparison of Flat Plate and Cavity Sources as Infrared
Tom Kolat and Frank Liebmann
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.


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MS13_01_KOLAT
Picture of the productEstablishing a Continuous Chain of Traceability for Pressure
Nita Dilawar Sharma, D. Arun Vijayakumar, Jasveer Singh, Ashok Kumar, D. R. Sharma, and A. K. Bandyopadhyay
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 X 104 to 1 X 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 (Aρ) as a function of measured pressure (ρ) and estimated the zero pressure effective area (Aρ) 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).


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MS13_01_SHARMA
Picture of the productExperimental and Simulation Study for a Time Transfer Ser.
Jacqueline Walker and Marco Genova
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.


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MS13_02_WALK
Picture of the productGWP® - The Science-Based Global Standard for Lifecycle Man.
Klaus Fritsch
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. 1. Out of Specification Results and Their Consequences Out of Specification (OOS) results have had a significant impact in the pharmaceutical industry for many years, but especially since the Barr Labs court ruling in 1993 [1]. In this case, the court ruled in favor of Barr Labs, upholding their view that an OOS result does not necessarily constitute a batch failure, but it should be investigated if there are other causes such as a laboratory error. In October 2006, the Food and Drug Administration (FDA) revamped their guidance concerning how to handle OOS results and how to perform a proper investigation [2]. Since then, the FDA has issued a significant number of 483 observations concerning poor investigations. It seems that some seven years after the FDA guidance and 20 years after the Barr ruling, we still have a lot of work to do in this area. A recent three-part article concerning OOS investigations begins by saying: “Out of Specification. It’s a term that brings the fear of the gods to the laboratory. It causes


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MS13_03_FRITS
Picture of the productImplementation of an Accelerometer Transverse Sensitivity
Christiaan S. Veldman
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.


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MS13_02_VELD
Picture of the productIndustrial Metrology Engineering: An Educational Strategy
Flora Mercader-Trejo, Luz Elena Narváez Hernández, Maria Guadalupe López Granada, and Raúl Herrera Basurto
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.


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MS13_04_MERC
Picture of the productLamp Orientation Dependence of an Integrating Sphere Res.
Cheng-Hsien Chen, Bao-Jen Pong, Yuh-Der Jiaan, and Hsiu-Lin Lin
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.


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MS13_02_CHEN
Picture of the productPicometer Metrology for Precise Measurement
Jack Stone, Patrick Egan, Donavon Gerty, Jay Hendricks, Douglas Olson, Jacob Ricker, Gregory Scace, and Gregory Strouse
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.


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MS13_04_STONE
Picture of the productPrecision AC Current Measurement Technique
Richard Timmons and Tom Barczyk
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.


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MS13_01_TIMMONS
Picture of the productPrinciples for Calibration Point Selection
Joseph W. Petersen
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.


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MS13_03_PETER
Picture of the productProficiency Testing for Pressure Calibration at NVLAP
Douglas A. Olson, Thomas R. Hettenhouser, and R. Gregory Driver
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.


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MS13_04_OLSO
Picture of the productProposed Guidelines for the Selection of Trapezoidal
Swanand Rishi
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.


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MS13_01_RISHI
Picture of the productStandardized Specifications and Test Methods for CMMs
James G. Salsbury
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.


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MS13_01_SALSBUR
Picture of the productSummary of a LED Bulb Interlaboratory Comparison in Taiwan
Chen-Yun Hung, Cheng-Yen Fang, Pin-Hao Wang, Paul Kam-Wa Lui, and Cheng-Hsien Chen
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.


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MS13_04_HUNG
Picture of the productTwo-Color One-Way Frequency Transfer in a Metropolitan Optic
Sven-Christian Ebenhag, Per Olof Hedekvist, and Kenneth Jaldehag
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 “twocolor” 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.


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MS13_02_EBEN
Picture of the productUltra-low Flow, Low Uncertainty Gas Leak Measurement System
Donavon Gerty
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.


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MS13_03_GERT
Picture of the productUtilizing Size of Source Effect to Determine Minimum Sample
Daniel Cárdenas-García
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 σ, 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.


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MS13_03_CARD