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Description of ASTM-E1791 2008ASTM E1791 - 96(2008)e1Standard Practice for Transfer Standards for Reflectance Factor for Near-Infrared Instruments Using Hemispherical GeometryActive Standard ASTM E1791 | Developed by Subcommittee: E13.03 Book of Standards Volume: 03.06 ASTM E1791Significance and Use Most commercial reflectometers and spectrophotometers with reflectance capability measure relative reflectance. The instrument reading is the ratio of the measured radiation reflected from the reference specimen to the measured radiation reflected by the test specimen. That ratio is dependent on specific instrument parameters. National standardizing laboratories and some research laboratories measure reflectance on instruments calibrated from basic principles, thereby establishing a scale of absolute reflectance as described in CIE Publication No. 44 (5) . These measurements are sufficiently difficult and of prohibitive cost that they are usually left to laboratories that specialize in them. A standard that has been measured on an absolute scale could be used to transfer that scale to a reflectometer. While such procedures exist, the constraints placed on the mechanical properties restrict the suitability of some of the optical properties, especially those properties related to the geometric distribution of reflected radiation. Thus, reflectance factor standards that are sufficiently rugged or cleanable to use as permanent transfer standards, with the exception of the sintered PTFE standards, depart considerably from the perfect diffuser in the geometric distribution of reflected radiation. The geometric distribution of reflected radiance from such standards is sufficiently diffuse that such a standard can provide a dependable calibration of a directional-hemispherical or certain directional-directional reflectometers. Although pressed powder standards are subject to contamination and breakage, the reflectance factor of pressed powder can be sufficiently reproducible from specimen to specimen from a given lot of powder to allow the assignment of absolute reflectance factor values to all of the powder in a lot. Sintered PTFE materials exhibit sufficient reproducibility from within the same specimen after resurfacing or cleaning the specimen to allow the assignment of absolute reflectance factor values. Preparation of packed powder reflectance standards is covered in Practice E 259 . This practice describes the spectral and physical properties of these materials and of the sintered PTFE materials. 1. Scope 1.1 This practice covers procedures for the preparation and use of acceptable transfer standards for NIR spectrophotometers. Procedures for calibrating the reflectance factor of materials on an absolute basis are contained in CIE Publication No. 44 ( 9 ). Both the pressed powder samples and the sintered PTFE materials are used as transfer standards for such calibrations because they have very stable reflectance factors that are nearly constant with wavelength and because the distribution of flux resembles closely that from the perfect reflecting diffuser. 1.2 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. 1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
ASTM Standards E131 Terminology Relating to Molecular Spectroscopy E259 Practice for Preparation of Pressed Powder White Reflectance Factor Transfer Standards for Hemispherical and Bi-Directional Geometries E284 Terminology of Appearance Keywords hemispherical optical measurement system; integrating sphere; materials standards; reflectance and reflectivity; transfer standards; Geometric analysis; Hemispherical geometry; Infrared (IR) analysis--metals/alloys; Integrating sphere reflectometer; Near-infrared analysis/instruments; Reflectance and reflectivity--metals/alloys; Spectralon; Transfer standards; ICS Code ICS Number Code 37.020 (Optical equipment) DOI: 10.1520/E1791-96R08E01 ASTM International is a member of CrossRef. ASTM E1791This book also exists in the following packages...Subscription InformationMADCAD.com ASTM Standards subscriptions are annual and access is unlimited concurrency based (number of people that can access the subscription at any given time) from single office location. For pricing on multiple office location ASTM Standards Subscriptions, please contact us at info@madcad.com or +1 800.798.9296.
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