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The International Space Science Institute — E— Glossaries and Acronyms E.1 Glossary of Metrology This section is intended to provide the readers with the definitions of certain terms often used in the calibration of instruments. The definitions were taken from the Swedish National Testing and Research Institute (http://www.sp.se/metrology/eng/ terminology.htm), the Guide to the Measurement of Pressure and Vacuum, National Physics Laboratory and Institute of Measurement & Control, London, 1998 and VIM, International Vocabulary of Basic and General Terms in Metrology, 2nd Ed., ISO, Geneva, 1993. Accuracy The closeness of the agreement between a test result and the accepted reference value [ISO 5725]. See also precision and trueness. Adjustment Operation of bringing a measuring instrument into a state of performance suitable for its use. Bias The difference between the expectation of the test results and an accepted reference value [ISO 5725]. Calibration A set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument (or values repre- sented by a material measure) and the corresponding values realized by standards. The result of a calibration may be recorded in a document, e.g. a calibration certifi- cate. The result can be expressed as corrections with respect to the indications of the instrument. Calibration in itself does not necessarily mean that an instrument is performing in accordance with its specification. Certification A process performed by a third party that confirms that a defined product, process or service conforms with, for example, a standard. Confirmation Metrological confirmation is a set of operations required to ensure that an item of measuring equipment is in a state of compliance with requirements for its intended use. Metrological confirmation normally includes, for example, calibra- tion, any necessary adjustment or repair and subsequent recalibration, as well as any required sealing and labeling. Corrected result Result of a measurement after correction for systematic error. Correction The value which, added algebraically to the uncorrected result of a measure- ment, compensates for an assumed systematic error. The correction is equal to the assumed systematic error, but of the opposite sign. Since the systematic error can not be known exactly, the correction is subject to uncertainty. 519 520 E. GLOSSARIES AND ACRONYMS Dead band Maximum interval through which a stimulus may be changed in both direc- tions without producing a change in response of a measuring instrument [VIM 5.13]. Detector Device or substance that indicates the presence of a phenomenon, body, or sub- stance when a threshold value of an associated quantity is exceeded. NOTES: 1) In some fields the term ”detector” is used for the concept of sensor. 2) In chemistry the term ”indicator” is frequently used for this concept. Device Any artifactual object designed to perform an action or process, with or without an operator in attendance. Drift A slow change of a metrological characteristic of a measuring instrument. Error ((of indication) of a measuring instrument) The indication of a measuring instru- ment minus a ’true’ value of the corresponding input quantity, i.e. it has a sign. Expectation (of the measurable quantity) The mean of a specified population of mea- surements. Fiducial error (of a measuring instrument) Error of a measuring instrument divided by a (fiducial) value specified for the instrument [VIM 5.28]. Fiducial value Can be the span or upper limit of nominal range of measuring instrument. Group standard A set of standards of chosen values that, individually or in combination, provides a series of values of quantities of the same kind. Inspection Involves measurement, investigation or testing of one or more characteristics of a product, and includes a comparison of the results with specified requirements in order to determine whether the requirements have been fulfilled. Instrument constant Coefficient by which the direct indication of a measuring instru- ment must be multiplied to give the indicated value of the measurand or of a quantity to be used to calculate the value of the measurand [VIM 5.8]. Kind, quantities of the same Quantities that can be placed in order of magnitude relative to one another [VIM 1.1]. Laboratory bias The difference between the expectation of the test results from a partic- ular laboratory and an accepted reference value [ISO 5725]. Limiting conditions Extreme conditions that a measuring instrument is required to with- stand without damage, and without degradation of specified metrological character- istics when it is subsequently operated under its rated operating conditions [VIM 5.6]. (Measurable) quantity Attribute of a phenomenon, body or substance that may be dis- tinguished qualitatively and determined quantitatively [VIM 1.1]. Measurand Particular quantity subject to measurement [VIM 2.6]. Measurement Set of operations having the object of determining a value of a quantity [VIM 2.1]. E.1. Glossary of Metrology 521 Measurement procedure Set of operations, described specifically, used in the perfor- mance of particular measurements according to a given method [VIM 2.5]. Measurement signal Quantity that represents the measurand and which is functionally related to it [VIM 2.8]. Measurement standard, Etalon Material measure, measuring instrument, reference mate- rial or measuring system intended to define, realize, conserve or reproduce a unit or one or more values of a quantity to serve as a reference [VIM 6.1]. Measuring chain Series of elements of a measuring instrument or system that constitutes the path of the measurement signal from the input to the output [VIM 4.4]. Measuring range Set of values of measurands for which the error of a measuring instru- ment in intended to lie within specified limits [VIM 5.4]. Measuring system Set of measuring instruments and other devices or substances assem- bled and adapted to the measurement of quantities of specified kinds within specified intervals of values. Measuring instrument A device or combination of devices designed for measurement of quantities. Measuring transducer Device that provides at its output a quantity having a determined relation to the quantity at its input. Metrology The science of measurement. National (measurement) standard Standard recognized by a national decision to serve, in a country, as the basis for assigning values to other standards of the quantity concerned. Nominal range Range of indications obtainable with a particular setting of the controls of a measuring instrument [VIM 5.1]. Nominal value Rounded or approximate value of a characteristic of a measuring instru- ment that provides a guide to its use [VIM 5.3]. Precision The closeness of agreement between independent test results obtained under stipulated conditions [ISO 5725]. Quality Relates to all the characteristics that meet an expressed or implied need. Reference Accepted value that serves as an agreed-on reference for comparison, and which is derived from a theoretical or established value, based upon scientific princi- ples, or from an assigned or certified value, based upon experimental work of some national or international organization, or from a consensus or certified value based upon collaborative experimental work under the auspices of a scientific or engi- neering group. When these are not available, the reference value is taken to be the expectation of the measurable quantity. Reference conditions Conditions of use prescribed for testing the performance of a mea- suring instrument or for intercomparison of results of measurements [VIM 5.6]. 522 E. GLOSSARIES AND ACRONYMS Relative error Error of measurement divided by a true value of the measurand [VIM 3.12]. Repeatability Precision under repeatability conditions. Repeatability conditions Conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time [ISO 5725]. Reproducibility Precision under reproducibility conditions. Reproducibility conditions Conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment. Resolution Smallest change of measured quantity which changes the indication of an measuring instrument. Result of a measurement Value attributed to a measurand, obtained by measurement [VIM 3.1]. Response characteristic Relationship between a stimulus and the corresponding response, for defined conditions [VIM 5.9]. Response time Time interval between the instant when a stimulus is subjected to a spec- ified abrupt change and the instant when the response reaches and remains within specified limits around its final steady value [VIM 5.17]. Sensitivity Change in the response of a measuring instrument divided by the correspond- ing change in the stimulus. Sensor Element of a measuring system that is directly affected by the phenomenon, body, or substance carrying the quantity to be measured. Note in some fields the term ’detector is used for this concept. Span Modulus of the difference between the two limits of a nominal range [VIM 5.2]. Stability Refers to the ability of a measuring instrument to maintain constant its metro- logical characteristics with time. Standard, national Standard recognized by a national decision to serve, in a country, as the basis for assigning values to other standards of the quantity concerned (see National standard).
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