Error
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Error Wolfgang Knapp IWF, ETH Zurich, Schleitheim, Switzerland
Synonyms Error of measurement; Measurement error
Definition Measured quantity value minus a reference quantity value NOTE 1 The concept of “measurement error” can be used both (a) When there is a single reference quantity value to refer to, which occurs if a calibration is made by means of a measurement standard with a measured quantity value having a negligible measurement uncertainty or if a conventional quantity value is given, in which case the measurement error is known, and (b) If a measurand is supposed to be represented by a unique true quantity value or a set of true quantity values of negligible range, in which case the measurement error is not known
NOTE 2 Measurement error should not be confused with production error or mistake. (ISO Guide 99:2007, Definition 2.16)
Theory and Application Let’s start discussing the term “error” with the well-accepted definition of (ISO 99:2007), the International Vocabulary of Metrology (VIM), see “Definition.” In Note 1, we recognize two concepts: – Reference quantity value is known. – Reference quantity value is not known. In the introduction of (ISO 99:2007), the VIM, these two concepts are named and explained in more detail: – Error approach (or traditional approach or true value approach) and – ▶ Uncertainty approach In the error approach, where the reference quantity value is known, the aim of the measurement is to determine an estimate of the true value that is as close as possible to that single true value. The deviations from the true value consist of random
# CIRP 2016 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_6580-4
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Error
Error, Fig. 1 Measurement errors in the error approach. E error, MPE maximum permissible measurement error, R random measurement error, S systematic measurement error
and systematic errors that have to be treated differently. There are no rules, how systematic and random errors combine to form the total error of any measurement result. Usually the total error is estimated as an upper limit of the absolute value. This upper limit is sometimes loosely named “uncertainty.” In the uncertainty approach, where the reference quantity value is not known, the aim of the measurement is not to determine a true value as closely as possible but to assign an interval of reasonable values to the measurand, based on the assumption that no mistakes have been made in performing the measurement. In this approach, the interval of reasonable values assigned to the measurand cannot be reduced to zero, because of the definitional uncertainty, which is due to the finite amount of detail in the definition of the measurand. Figure 1 illustrates the error approach. Measured quantity values show an error E to a reference quantity value, the error might change for each measurement, due to the fact that we have a random measurement error component R and a systematic measurement error component S. Errors,
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