SIST IEC 60359:1995

SLOVENSKI STANDARD
01-avgust-1995
Expression of the performance of electrical and electronic measuring equipment
Electrical and electronic measurement equipment - Expression of performance
Appareils de mesure électriques et électroniques - Expression des performances
Ta slovenski standard je istoveten z: IEC 60359
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

NORME CEI
INTERNATIONALE IEC
INTERNATIONAL
Troisième édition
STANDARD
Third edition
2001-12
Appareils de mesure électriques
et électroniques –
Expression des performances
Electrical and electronic measurement
equipment –
Expression of performance
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60359 © IEC:2001 – 3 –
CONTENTS
FOREWORD.5
INTRODUCTION.9
1 Scope and object.11
2 Normative references .11
3 Definitions .13
4 Specification of values and ranges .31
5 Requirements for IEC standards related to the equipment .33
6 Specification of limits of uncertainty.33
7 Specification of influence quantities.49
8 General rules for compliance testing.53
Annex A (informative) Conceptual and terminological evolution from "error" to
"uncertainty" .55
Annex B (informative) Steps in the specification of performance .63
Bibliography.67
Figure 1 – Calibration diagram.35
Figure 2 – Calibration diagram with scale marks in units of measurement .37
Figure 3 – Calibration diagram in different operating conditions .41
Figure 4 – Calibration diagram for extended operating conditions .43
Figure B.1 – Steps in the specification of performance.63

60359 © IEC:2001 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL AND ELECTRONIC MEASUREMENT EQUIPMENT –
EXPRESSION OF PERFORMANCE
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International
Organization for Standardization (ISO) in accordance with conditions determined by agreement between the
two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use published in the form of
standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60359 has been prepared by IEC technical committee 85:
Measuring equipment for electrical and electromagnetic quantities.
This third edition cancels and replaces the second edition published in 1987 and its
amendment 1 (1991), of which it constitutes a technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
85/219/FDIS 85/220/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This International Standard was prepared by IEC TC 85 following its resolution 85/45/AC of
1994-12-16 “to revise the IEC 60359, taking into account the "Guide to the Expression of
Uncertainty in Measurement" (GUM) published by ISO in 1993”.
The main technical changes from the previous edition of this International Standard consist in
adapting the requirements on the instrument performance to the approach on uncertainty
taken by the GUM, adapting the terminology to the new edition of the IEV, and offering a
wider and more correct choice of options in specifying the limits of uncertainty.

60359 © IEC:2001 – 7 –
Annexes A and B are for information only.
The committee has decided that the contents of this publication will remain unchanged until
2005-12. At this date, the publication will be:
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60359 © IEC:2001 – 9 –
INTRODUCTION
With the appearance of the interorganizational Guide to the expression of uncertainty in
measurement (GUM) that embodied the suggestions of CIPM Recommendation CI-1981, it
became clear that the classical approach to the precision and accuracy of measurement in
terms of true value and error is being superseded by the approach in terms of uncertainty.
The intrinsic pitfalls of the concept of true value (hence of error) had indeed led the operative
measurement world to rely increasingly on the concept of uncertainty, notwithstanding that the
main body of standards concerning the performance of measuring instruments was still written
in terms of the traditional approach. The widening gap between the best practice in metrology
and the wording of the standards prompted the normative organizations to invite their
Technical Committees to update these publications.
This new edition of the International Standard IEC 60359 was prepared in order to bring it into
agreement with the GUM. During the procedure for its approval the chapters on measurement
of the new edition of the International Electrotechnical Vocabulary (IEV) were published, and
the opportunity was taken to bring the standard into agreement with the terms used in the
IEV.
The main performance characteristics of an instrument are those related to the uncertainty of
the results obtained by using the instrument. The GUM provides a general terminology and a
computational framework for combining uncertainties of different origin, but it substantially
deals with the issue of evaluating uncertainty in the measurement of a quantity defined as a
function of other measured quantities, and does not address the issue of evaluating
instrumental uncertainty, i.e. the uncertainty of the results of the single direct measurements
carried out by the instruments. The GUM treats it as a component of uncertainty of category B,
known from information supplied by the manufacturer or calibrator of the instrument, in the
form of an expanded uncertainty with a stated coverage factor. It is therefore up to this
standard to provide indications for expressing and evaluating instrumental uncertainty in a
way consistent with the philosophy of the GUM. This means stating the requirements on
performance of the instruments in terms of limits of uncertainty instead of limits of error, which
implies a careful distinction between the indication of the instrument and the set of values
assigned to describe the measurand (see Annex A for the conceptual evolution from the
notion of error to the notion of uncertainty).
To this purpose, this standard systematically uses (in agreement with the IEV) the notion of
calibration diagram, which is also quite helpful in describing the interplay between intrinsic
uncertainty, variations, and operating uncertainty. Distinctions of this kind are essential, by
the way, for the new measuring systems, based on microprocessors with internal software or
using more than one input (multisensorial systems), that need to address the issue in general
terms without restrictive hypotheses on the instrumental hardware. They also allow a wider
choice of options in specifying performance characteristics.
For many people, of course, the passage from time-honored traditional terms and notions to
the ones evolved by modern metrology will require some mental adjustment, which is
altogether necessary, as current instrumentation has made giant steps from the times of
index-on-scale instruments. However, no particular difficulty is expected in translating into
terms consistent with this standard the bulk of existing technical specifications, most of which
are written in terms of "limits of error", often with ambiguities about whether or not suggested
corrections for influence quantities are included. When such ambiguities are removed, the old
specifications are easily harmonized to this standard by substituting the "limits of error" with
the "limits of instrumental uncertainty" expounded in clause 5, provided the contextual
indications (if any) on the means of evaluating these limits are adjusted to satisfy the
definitions given in this standard.
———————
Comité International des Poids et Mesures (CIPM)

60359 © IEC:2001 – 11 –
ELECTRICAL AND ELECTRONIC MEASUREMENT EQUIPMENT —
EXPRESSION OF PERFORMANCE
1 Scope and object
This International Standard applies to the specification of performance, with primary reference
to industrial applications, of the following kinds of electrical and electronic equipment:
– indicating and recording instruments which measure electrical quantities;
– material measures which supply electrical quantities;
– instruments which measure non-electrical quantities using electrical means, for all parts of
the measuring chain which present electrical output signals.
This standard applies to the specification of performance of instruments operating in steady-
state conditions (see 3.1.15), usual in industrial applications.
It is based on the methods expounded in GUM for expressing and evaluating the uncertainty
of measurement, and refers to GUM for the statistical procedures to be used in determining
the intervals assigned to represent uncertainty (including the way to account for non-
negligible uncertainties in the traceability chain).
This standard does not address the propagation of uncertainty beyond the instrument (or the
measuring equipment) whose performance is considered and which may undergo compliance
testing.
The object is to provide methods for ensuring uniformity in the specification and determination
of uncertainties of equipment within its scope. All other necessary requirements have been
reserved for dependent IEC product standards pertaining to particular types of equipment
which fall within the scope of this standard.
For example: the selection of metrological characteristics and their ranges, and of influence
quantities and their specified operating ranges, is reserved for IEC product standards.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-300:2001, International Electrotechnical Vocabulary (IEV) – Electrical and
electronic measurements and measuring instruments – Part 311: General terms relating to
measurements – Part 312: General terms relating to electrical measurements – Part 313:
Types of electrical measuring instrument – Part 314: Specific terms according to the type of
instrument
ISO/IEC GUIDE EXPRES:1995, Guide to the Expression of Uncertainty in Measurement

60359 © IEC:2001 – 13 –
3 Definitions
For the purposes of this International Standard, the following definitions apply.
A word between brackets in the title of a definition is a qualifier that may be skipped if there is
no danger of confusion with a similar term. When two terms may be used interchangeably with
the same definition, these are separated by "or". Terms in italics in a note are new terms
defined by the context.
Most definitions are taken or adapted, together with their notes, from Part 311 of IEC 60050-300
(International Electrotechnical Vocabulary – IEV). As only terms pertaining to the "uncertainty
approach" are used, IEV notes stating that the term is used in this approach were omitted.
Where such definitions are simultaneously drawn from the International Vocabulary of Basic
and General Terms in Metrology (VIM), this has been indicated. In some cases, notes have
been added for the purposes of this standard.
3.1 Basic definitions
3.1.1
measurand
quantity subjected to measurement, evaluated in the state assumed by the measured system
during the measurement itself
NOTE 1  The value assumed by a quantity subjected to measurement when it is not interacting with the measuring
instrument may be called unperturbed value of the quantity.
NOTE 2  The unperturbed value and its associated uncertainty can only be computed through a model of the
measured system and of the measurement interaction with the knowledge of the appropriate metrological
characteristics of the instrument, that may be called instrumental load.
3.1.2
(result of a) measurement
set of values attributed to a measurand, including a value, the corresponding uncertainty and
the unit of measurement
[IEV 311-01-01, modified]
NOTE 1  The mid-value of the interval is called the value (see 3.1.3) of the measurand and its half-width the
uncertainty (see 3.1.4) [IEV modified].
NOTE 2  The measurement is related to the indication (see 3.1.5) given by the instrument and to the values of
correction obtained by calibration [IEV modified].
NOTE 3  The interval can be considered as representing the measurand provided that it is compatible with all
other measurements of the same measurand [IEV modified].
NOTE 4  The width of the interval, and hence the uncertainty, can only be given with a stated level of confidence
(see 3.1.4, NOTE 1) [IEV modified].
3.1.3
(measure-) value
mid element of the set assigned to represent the measurand
NOTE The measure-value is no more representative of the measurand than any other element of the set. It is
singled out merely for the convenience of expressing the set in the format V ± U, where V is the mid element and U
the half-width of the set, rather than by its extremes. The qualifier "measure-" is used when deemed necessary to
avoid confusion with the reading-value or the indicated value.
3.1.4
uncertainty (of measurement)
parameter, associated with the result of a measurement, that characterizes the dispersion of
the values that could reasonably be attributed to the measurand
[IEV 311-01-02, VIM 3.9]
NOTE 1  The parameter can be, for example, a standard deviation (or a given multiple of it), or a half-width of an
interval having a stated level of confidence [IEV, VIM].

60359 © IEC:2001 – 15 –
NOTE 2  Uncertainty of measurement comprises, in general, many components. Some of these components can
be evaluated from the statistical distribution of the results of a series of measurements and can be characterized
by experimental standard deviations. The other components, which can also be characterized by standard
deviations, are evaluated from the assumed probability distributions based on experience or other information [IEV,
VIM].
NOTE 3  It is understood that the result of the measurement is the best estimate of the value of the measurand,
and that all components of uncertainty, including those arising from systematic effects, such as components
associated with corrections and reference standards, contribute to the dispersion [IEV, VIM].
NOTE 4  The definition and notes 1 and 2 are from GUM, clause B.2.18. The option used in this standard is to
express the uncertainty as the half-width of an interval with the GUM procedures with a coverage factor of 2. This
choice corresponds to the practice now adopted by many national standards laboratories. With the normal
distribution a coverage factor of 2 corresponds to a level of confidence of 95 %. Otherwise statistical elaborations
are necessary to establish the correspondence between the coverage factor and the level of confidence. As the
data for such elaborations are not always available, it is deemed preferable to state the coverage factor. This
interval can be "reasonably" assigned to describe the measurand, in the sense of the GUM definition, as in most
usual cases it ensures compatibility with all other results of measurements of the same measurand assigned in the
same way at a sufficiently high confidence level.
NOTE 5  Following CIPM document INC-1 and GUM, the components of uncertainty that are evaluated by
statistical methods are referred to as components of category A, and those evaluated with the help of other
methods as components of category B.
3.1.5
indication or reading-value
output signal of the instrument
[IEV 311-01-07, modified]
NOTE 1  The indicated value can be derived from the indication by means of the calibration curve [IEV].
NOTE 2  For a material measure, the indication is its nominal or stated value [IEV].
NOTE 3  The indication depends on the output format of the instrument:
– for analogue outputs it is a number tied to the appropriate unit of the display;
– for digital outputs it is the displayed digitized number;
– for code outputs it is the identification of the code pattern.
NOTE 4  For analogue outputs meant to be read by a human observer (as in the index-on-scale instruments) the
unit of output is the unit of scale numbering; for analogue outputs meant to be read by another instrument (as in
calibrated transducers) the unit of output is the unit of measurement of the quantity supporting the output signal.
3.1.6
calibration
set of operations which establishes the relationship which exists, under specified conditions,
between the indication and the result of a measurement by reference to standards
[IEV 311-01-09]
NOTE 1  The relationship between the indications and the results of measurement can be expressed, in principle,
by a calibration diagram [IEV].
NOTE 2  The calibration must be performed under well defined operating conditions for the instrument. The
calibration diagram representing its result is not valid if the instrument is operated under conditions outside the
range used for the calibration.
NOTE 3  Quite often, specially for instruments whose metrological characteristics are sufficiently known from past
experience, it is convenient to predefine a simplified calibration diagram and perform only a verification of
calibration (see 3.2.12) to check whether the response of the instrument stays within its limits. The simplified
diagram is of course wider than the diagram that would be defined by the full calibration of the instrument, and the
uncertainty assigned to the results of measurements is consequently larger.
3.1.7
calibration diagram
portion of the co-ordinate plane, defined by the axis of indication and the axis of results of
measurement, which represents the response of the instrument to differing values of the
measurand
[IEV 311-01-10]
60359 © IEC:2001 – 17 –
3.1.8
calibration curve
curve which gives the relationship between the indication and the value of the measurand
[IEV 311-01-11]
NOTE 1  The calibration curve is the curve bisecting the width of the calibration diagram parallel to the axis of
results of measurement, thus joining the points representing the values of the measurand (see 6.1 and Figure 1).
NOTE 2  When the calibration curve is a straight line passing through zero, it is convenient to refer to the slope
which is known as the instrument constant [IEV].
3.1.9
indicated value
value given by an indicating instrument on the basis of its calibration curve
[IEV 311-01-08]
NOTE The indicated value is the measure-value of the measurand when the instrument is used in a direct
measurement (see 3.2.7) under all the operating conditions for which the calibration diagram is valid.
3.1.10
(measurement) compatibility
property satisfied by all the results of measurement of the same measurand, characterized by
an adequate overlap of their intervals
[IEV 311-01-14]
NOTE 1  The compatibility of any result of a measurement with all the other ones that represent the same
measurand can be asserted only at some level of confidence, as it depends on statistical inference, a level that
should be indicated, at least by implicit convention or through a coverage factor.
NOTE 2  The compatibility of the results of measurements obtained with different instruments and methods is
ensured by the traceability (see 3.1.16) to a common primary standard (see 3.2.6) of the standards used for the
calibration of the several instruments (and of course by the correctness of the calibration and operation
procedures).
NOTE 3  When two results of a measurement are not compatible one must decide by independent means whether
one or both results are wrong (perhaps because the uncertainty is too narrow), or whether the measurand is not
the same.
NOTE 4  Measurements carried out with wider uncertainty yield results which are compatible on a wider range,
because they discriminate less among different measurands allowing to classify them with simpler models; with
narrower uncertainties the compatibility calls for more detailed models of the measured systems.
3.1.11
intrinsic uncertainty of the measurand
minimum uncertainty that can be assigned in the description of a measured quantity
NOTE 1  No quantity can be measured with narrower and narrower uncertainty, inasmuch as any given quantity is
defined or identified at a given level of detail. If one tries to measure a given quantity with uncertainty lower than
its own intrinsic uncertainty one is compelled to redefine it with higher detail, so that one is actually measuring
another quantity. See also GUM D.1.1.
NOTE 2  The result of a measurement carried out with the intrinsic uncertainty of the measurand may be called the
best measurement of the quantity in question.
3.1.12
(absolute) instrumental uncertainty
uncertainty of the result of a direct measurement of a measurand having negligible intrinsic
uncertainty
NOTE 1  Unless explicitly stated otherwise, the instrumental uncertainty is expressed as an interval with coverage
factor 2.
NOTE 2  In single-reading direct measurements of measurands having intrinsic uncertainty small with respect to
the instrumental uncertainty, the uncertainty of the measurement coincides, by definition, with the instrumental
uncertainty. Otherwise the instrumental uncertainty is to be treated as a component of category B in evaluating the
uncertainty of the measurement on the basis of the model connecting the several direct measurements involved.

60359 © IEC:2001 – 19 –
NOTE 3  The instrumental uncertainty automatically includes, by definition, the effects due to the quantization of
the reading-values (minimum evaluable fraction of the scale interval in analogic outputs, unit of the last stable digit
in digital outputs).
NOTE 4  For material measures the instrumental uncertainty is the uncertainty that should be associated to the
value of the quantity reproduced by the material measure in order to ensure the compatibility of the results of its
measurements.
NOTE 5  When possible and convenient the uncertainty may be expressed in the relative form (see 3.3.3) or in
the fiducial form (see 3.3.4). The relative uncertainty is the ratio U/V of the absolute uncertainty U to the
measure value V, and the fiducial uncertainty the ratio U/V of the absolute uncertainty U to a conventionally
f
chosen value V .
f
3.1.13
conventional value
measure-value of a standard used in a calibration operation and known with uncertainty
negligible with respect to the uncertainty of the instrument to be calibrated
NOTE This definition is adapted to the object of this standard from the definition of "conventional true value (of a
quantity)": value attributed to a particular quantity and accepted, sometimes by convention, as having an
uncertainty appropriate for a given purpose [IEV 311-01-06, VIM 1.20]
3.1.14
influence quantity
quantity which is not the subject of the measurement and whose change affects the
relationship between the indication and the result of the measurement
[IEV 311-06-01]
NOTE 1  Influence quantities can originate from the measured system, the measuring equipment or the
environment [IEV].
NOTE 2  As the calibration diagram depends on the influence quantities, in order to assign the result of a
measurement it is necessary to know whether the relevant influence quantities lie within the specified range [IEV].
NOTE 3  An influence quantity is said to lie within a range C' to C" when the results of its measurement satisfy the
relationship: C' ≤ V – U < V + U ≤ C".
3.1.15
steady-state conditions
operating conditions of a measuring device in which the variation of the measurand with the
time is such that the relation between the input and output signals of the instruments does not
suffer a significant change with respect to the relation obtaining when the measurand is
constant in time
3.1.16
traceability
property of the result of a measurement or of the value of a standard such that it can be
related to stated references, usually national or international standards, through an unbroken
chain of comparisons all having stated uncertainties
[IEV 311-01-15, VIM 6.10]
NOTE 1  The concept is often expressed by the adjective traceable [IEV, VIM].
NOTE 2  The unbroken chain of comparisons is called a traceability chain [IEV, VIM].
NOTE 3  The traceability implies that a metrological organization be established with a hierarchy of standards
(instruments and material measures) of increasing intrinsic uncertainty. The chain of comparisons from the primary
standard to the calibrated device adds indeed new uncertainty at each step.
NOTE 4  Traceability is ensured only within a given uncertainty, that should be specified.
3.2 Definitions of devices and operations
3.2.1
(measuring) instrument
device intended to be used to make measurements, alone or in conjunction with sup-
plementary devices
[IEV 311-03-01, VIM 4.1]
NOTE The term "(measuring) instruments" includes both the indicating instruments and the material measures.

60359 © IEC:2001 – 21 –
3.2.2
indicating (measuring) instrument
measuring instrument which displays an indication
[IEV 311-03-02, VIM 4.6]
NOTE 1  The display can be analogue (continuous or discontinuous), digital or coded [IEV].
NOTE 2  Values of more than one quantity can be displayed simultaneously [IEV].
NOTE 3  A displaying measuring instrument can also provide a record [IEV].
NOTE 4  The display can consist of an output signal not directly readable by a human observer, but able to be
interpreted by suitable devices [IEV].
NOTE 5  An indicating instrument may consist of a chain of transducers with the possible addition of other process
devices, or it may consist of one transducer.
NOTE 6  The interaction between the indicating instrument, the measured system and the environment generates
a signal in the first stage of the instrument (called sensor). This signal is elaborated inside the instrument into an
output signal which carries the information on the measurand. The description of the output signal in a suitable
output format is the indication supplied by the instrument.
NOTE 7  A chain of instruments is treated as a single indicating instrument when a single calibration diagram is
available that connects the measurand to the output of the last element of the chain. In this case the influence
quantities must be defined for the whole chain.
3.2.3
material measure
device intended to reproduce or supply, in a permanent manner during its use, one or more
known values of a given quantity
[IEV 311-03-03, VIM 4.2]
NOTE 1  The quantity concerned may be called the supplied quantity [IEV].
NOTE 2  The definition covers also those devices, such as signal generators and standard voltage or current
generators, often referred to as supply instruments.
NOTE 3  The identification of the value and uncertainty of the supplied quantity is given by a number tied to a unit
of measurement or a code term, called the nominal value or marked value of the material measure.
3.2.4
electrical measuring instrument
measuring instrument intended to measure an electrical or non-electrical quantity using
electrical or electronic means
[IEV 311-03-04]
3.2.5
transducer
technical device which performs a given elaboration on an input signal, transforming it into an
output signal
NOTE All indicating instruments contain transducers and they may consist of one transducer. When the signals
are elaborated by a chain of transducers, the input and output signals of each transducer are not always directly
and univocally accessible.
3.2.6
primary standard
standard that is designated or widely acknowledged as having the highest metrological
qualities and whose value is accepted without reference to other standards of the same
quantity
[IEV 311-04-02, VIM 6.4]
NOTE 1  The concept of a primary standard is equally valid for base quantities and derived quantities [IEV].
NOTE 2  A primary standard is never used directly for measurement other than for comparison with duplicate
standards or reference standards [IEV].

60359 © IEC:2001 – 23 –
3.2.7
direct (method of) measurement
method of measurement in which the value of a measurand is obtained directly, without the
necessity for supplementary calculations based on a functional relationship between the
measurand and other quantities actually measured
[IEV 311-02-01]
NOTE 1  The value of the measurand is considered to be obtained directly even when the scale of a measuring
instrument has values which are linked to corresponding values of the measurand by means of a table or a graph
[IEV].
NOTE 2  The method of measurement remains direct even if it is necessary to make supplementary measurements
to determine the values of influence quantities in order to make corrections [IEV].
NOTE 3  The definitions of the metrological characteristics of the instruments refer implicitly to their use in direct
measurements.
3.2.8
indirect (method of) measurement
method of measurement in which the value of a quantity is obtained from measurements
made by direct methods of measurement of other quantities linked to the measurand by a
known relationship
[IEV 311-02-02]
NOTE 1  In order to apply an indirect method of measurement one needs a model able to supply the relationship,
fully explicitated, between the measurand and the parameters that are measured by direct measurement.
NOTE 2  The computations must be carried out on both values and uncertainties, and therefore require accepted
rules for the propagation of the uncertainty as provided by the GUM.
3.2.9
(method of) measurement by repeated observations
method of measurement by which the result of the measurement is assigned on the basis of a
statistical analysis on the distribution of the data obtained by several observations repeated
under nominally equal conditions
NOTE 1  One should resort to a statistical analysis when the instrumental uncertainty is too small to ensure the
measurement compatibility. This may happen in two quite different sets of circumstances:
a) when the measurand is a quantity subjected to intrinsic statistical fluctuations (e.g. in measurements involving
nuclear decay). In this case the actual measurand is the statistical distribution of the states of the measured
quantity, to be described by its statistical parameters (mean and standard deviation). The statistical analysis is
carried out on a population of results of measurement, each with its own value and uncertainty, as each
observation correctly describes one particular state of the measured quantity. The situation may be considered a
particular case of indirect measurement.
b) when the noise associated with the transmission of signals affects the reading-value more than in the operating
conditions used for the calibration, contributing to the uncertainty of the measurement to an extent comparable with
the instrumental uncertainty or higher (e.g. in the field use of surveyor instruments). In this case the statistical
analysis is carried out on a population of reading-values with the purpose of separating the information on the
measurand from the noise. The situation may be considered as a new calibration of the instrument for a set of
operating conditions outside their rated range.
NOTE 2  One cannot presume to obtain by means of repeated observation an uncertainty lower than the
instrumental uncertainty assigned by the calibration or the class of precision of the instrument. Indeed if the results
of the repeated measurements are compatible with each other within the instrumental uncertainty, the latter is the
valid datum for the uncertainty of the measurement and several observations do not bring more information than
one; if on the other hand they are not compatible within the instrumental uncertainty, the final result of the
measurement should be expressed with a larger uncertainty in order to make all results compatible as they should
be by definition.
NOTE 3  For instruments that exhibit non-negligible hysteresis a straightforward statistical analysis of repeated
observations is misleading. Appropriate test procedures for such instruments should be expounded in their
particular standards.
3.2.10
intrinsic (instrumental) uncertainty
uncertainty of a measuring instrument when used under reference conditions
[IEV 311-03-09]
60359 © IEC:2001 – 25 –
3.2.11
operating instrumental uncertainty
instrumental uncertainty under the rated operating conditions
NOTE The operating instrumental uncertainty, like the intrinsic one, is not evaluated by the user of the instrument,
but is stated by its manufacturer or calibrator. The statement may be expressed by means of an algebraic relation
involving the intrinsic instrumental uncertainty and the values of one or several influence quantities, but such a
relation is just a convenient means of expressing a set of operating instrumental uncertainties under different
operating conditions, not a functional relation to be used for evaluating the propagation of uncertainty inside the
instrument.
3.2.12
verification (of calibration)
set of operations which is used to check whether the indications, under specified conditions,
correspond with a given set of known measurands within the limits of a predetermined
calibration diagram
[IEV 311-01-13]
NOTE 1  The known uncertainty of the measurand used for verification will generally be negligible with respect to
the uncertainty assigned to the instrument in the calibration diagram [IEV].
NOTE 2  The verification of calibration of a material measure consists in checking whether the result of a
measurement of the supplied quantity is compatible with the interval given by the calibration diagram.
3.2.13
adjustment (of a measuring instrument)
set of operations carried out on an instrument in order that it provides given indications
corresponding to given values of the measurand
[IEV 311-03-16]
NOTE When the instrument is made to give a null indication corresponding to a null value of the measurand, the
set of operations is called zero adjustment [IEV].
3.2.14
user adjustment (of a measuring instrument)
adjustment, employing only the means at the disposal of the user, specified by the
manufacturer
[IEV 311-03-17, VIM 4.31]
3.2.15
deviation (for the verification of calibration)
difference between the indication of an instrument undergoing verification of calibration and
the indication of the reference instrument, under equivalent operating conditions
[IEV 311-01-20]
NOTE 1  The comparison of the indications may be carried out by simultaneous measurement or by substitution. In
principle the comparison ought to be carried out on the same measurand in the same measuring conditions, but
this is impossible because the measurand can never be rigorously the same. Only the metrological expertise of the
operator can warranty that the difference in the measurement conditions of the two instruments is negligible for the
comparison purposes.
NOTE 2  If one of the instruments is a material measure, its nominal value is taken as the assigned measure-
value.
NOTE 3  The term is used only in operations of verification of calibration where the uncertainty of the reference
instrument is negligible by definition.
3.3 Definitions on manners of expression
3.3.1
metrological characteristics
data concerning the relations between the readings of a measuring instrument and the
measurements of the quantities interacting with it

60359 © IEC:2001 – 27 –
3.3.2
range
domain of values of a quantity included between a lower and an upper limit
NOTE 1  The term "range" is usually used with a modifier. It may apply to a performance characteristic, to an
influence quantity, etc.
NOTE 2  When one of the limits of a range is zero or infinity, the other finite limit is called a threshold.
NOTE 3  No uncertainty is associated with the values of range limits or thresholds as they are not themselves
results of measurements but a priori statements about conditions to be met by results of measurements. If the
result of a measurement has to lay within a rated range, it is understood that the whole interval V ± U representing
it must lay within the values of the range limits or beyond the threshold value, unless otherwise specified by
relevant standards or by explicit agreements.
NOTE 4  A range may be expressed by stating the values of its lower and upper limits, or by stating its mid value
and its half-width.
3.3.3
relative form of expression
expression of a metrological characteristic, or of other data, by means of its ratio to the
measure value of the quantity under consideration
NOTE 1  Expression in relative form is possible when the quantity under consideration allows the ratio relationship
and its value is not zero.
NOTE 2  Uncertainties and limits of uncertainty are expressed in relative form by dividing their absolute value by
the value of the measurand, ranges of influence quantities by dividing the halved range by the mid value of the
domain, etc.
3.3.4
fiducial form of expression
expression of a metrological characteristic, or of other data, by means of its ratio to a
conventionally chosen value of the quantity under consideration
NOTE 1  Expression in fiducial form is possible when the quantity under consideration allows the ratio
relationship.
NOTE 2  The value to which reference is made in order to define the fiducial error is called fiducial value.
3.3.5
variation (due to an influence quantity)
difference between the indicated values for the same value of the measurand of an indicating
instrument, or the values of a material measure, when an influence quantity assumes,
successively, two different values
[IEV 311-07-03]
NOTE 1  The uncertainty associated with the different measure values of the influence quantity for which the
variation is evaluated should not be wider than the width of the reference range for the same influence quantity.
The other performance characteristics and the other influence quantities should stay within the ranges specified for
the reference conditions.
NOTE 2  The variation is a meaningful parameter when it is greater than the intrinsic instrumental uncertainty.
3.3.6
limit of uncertainty
limiting value of the instrumental uncertainty for equipment operating under specified
conditions
NOTE 1  A limit of uncertainty may be assigned by the manufacturer of the instrument, who states that under the
specified conditions the instrumental uncertainty is never higher than this limit, or may be defined by standards,
that prescribe that under specified conditions the instrumental uncertainty should not be larger than this limit for
the instrument to belong to a given accuracy class.
NOTE 2  A limit of uncertainty may be expressed in absolute terms or in the relative or fiducial forms.

60359 © IEC:2001 – 29 –
3.3.7
accuracy class
class of measuring instruments, all of which are intended to comply with a set of
specifications regarding uncertainty
[IEV 311-06-09]
NOTE 1  An accuracy class always specifies a limit of uncertainty (for a given range of influence quantities),
whatever other metrological characteristics it specifies.
NOTE 2  An instrument may be assigned to different accuracy classes for different rated operating conditions.
NOTE 3  Unless otherwise specified, the limit of uncertainty defining an accuracy class is meant as an interval
with coverage factor 2.
3.3.8
rated value
quantity value assigned by a manufacturer for a specified operating condition of the
equipment or instrument
NOTE A rated value V assigned with an uncertainty U is actually a range V ± U and should be handled as such
(see 3.3.2, note 4)
3.3.9
(specified) measuri
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