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5.1 The test method is effective for the following test objectives:5.1.1 To determine whether a perceptible difference results or a perceptible difference does not result, for example, when a change is made in ingredients, processing, packaging, handling, or storage; or5.1.2 To select, train, and monitor assessors.5.2 The test method itself does not change whether the purpose of the test is to determine that the products are perceptibly different versus that the products are sufficiently similar to be used interchangeably. Only the selected values of α, β, and δ or Pd change. If the objective of the test is to determine if there is a perceptible difference between two products, then initially the products are assumed to be indistinguishable (for example, HO: δ or Pd = 0) and the data are examined to determine if the assumption can be rejected (that is, conclude that the products are perceptively different). If the objective is to determine if the two products are sufficiently similar to be used interchangeably, then initially the products are assumed to be meaningfully different (for example, HO: δ or Pd > the value chosen to represent a meaningful difference) and the data are examined to determine if the assumption can be rejected (that is, conclude that the samples are sufficiently similar to be used interchangeably).5.3 The tetrad method involves the evaluation of four samples. When the products being tested cause excessive sensory fatigue, carryover, or adaptation, methods that involve the evaluation of fewer samples (same-different, triangle test, etc.) may be preferred.1.1 This test method covers a procedure for determining whether a perceptible sensory difference exists between samples of two products or to estimate the magnitude of the perceptible difference.1.2 This test method applies whether a difference may exist in a single sensory attribute or in several.1.3 This test method is applicable when the nature of the difference between the samples is unknown. The attribute(s) responsible for the difference are not identified.1.4 The tetrad test is more efficient statistically than the triangle test (Test Method E1885) or the duo-trio test (Test Method E2610).1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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3.1 Corrosion test results often show more scatter than many other types of tests because of a variety of factors, including the fact that minor impurities often play a decisive role in controlling corrosion rates. Statistical analysis can be very helpful in allowing investigators to interpret such results, especially in determining when test results differ from one another significantly. This can be a difficult task when a variety of materials are under test, but statistical methods provide a rational approach to this problem.3.2 Modern data reduction programs in combination with computers have allowed sophisticated statistical analyses on data sets with relative ease. This capability permits investigators to determine if associations exist between many variables and, if so, to develop quantitative expressions relating the variables.3.3 Statistical evaluation is a necessary step in the analysis of results from any procedure which provides quantitative information. This analysis allows confidence intervals to be estimated from the measured results.1.1 This guide covers and presents briefly some generally accepted methods of statistical analyses which are useful in the interpretation of corrosion test results.1.2 This guide does not cover detailed calculations and methods, but rather covers a range of approaches which have found application in corrosion testing.1.3 Only those statistical methods that have found wide acceptance in corrosion testing have been considered in this guide.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

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