IEC 60051-1:2016

IEC 60051-1 ®
Edition 6.0 2016-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Direct acting indicating analogue electrical measuring instruments and their
accessories –
Part 1: Definitions and general requirements common to all parts

Appareils de mesure électriques indicateurs analogiques à action directe et
leurs accessoires –
Partie 1: Définitions et exigences générales communes à toutes les parties

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IEC 60051-1 ®
Edition 6.0 2016-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Direct acting indicating analogue electrical measuring instruments and their

accessories –
Part 1: Definitions and general requirements common to all parts

Appareils de mesure électriques indicateurs analogiques à action directe et

leurs accessoires –
Partie 1: Définitions et exigences générales communes à toutes les parties

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20 ISBN 978-2-8322-3162-3

– 2 – IEC 60051-1:2016 © IEC 2016
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references. 8
3 Terms and definitions . 9
3.1 General terms . 9
3.2 Description of instruments according to their method of operation . 13
3.3 Constructional features of instruments . 14
3.4 Characteristic features of instruments . 16
3.5 Characteristic values . 17
3.6 Influence quantity, reference conditions, nominal range of use and
preconditioning . 17
3.7 Uncertainty and variations . 19
3.8 Accuracy, accuracy class and class index . 21
3.9 Test . 21
4 Description, classification and compliance . 22
4.1 Description. 22
4.1.1 Description according to methods of operation or nature . 22
4.1.2 Description according to environmental conditions . 22
4.1.3 Description according to mechanical conditions . 22
4.1.4 Description according to degrees of protection . 22
4.2 Classification . 22
4.3 Compliance with the requirements of this standard . 23
5 Requirements . 23
5.1 Reference conditions . 23
5.2 Limits of intrinsic uncertainty, fiducial value . 23
5.2.1 Limits of intrinsic uncertainty . 23
5.2.2 Correspondence between intrinsic uncertainty and accuracy class . 23
5.2.3 Fiducial value. 23
5.3 Nominal range of use and variations . 25
5.3.1 Nominal range of use . 25
5.3.2 Limits of variations . 27
5.3.3 Conditions for the determination of variations . 28
5.4 Operating uncertainty, overall system uncertainty and variations . 28
5.5 Electrical requirements . 28
5.5.1 Electrical safety requirements . 28
5.5.2 Self-heating . 28
5.5.3 Permissible overloads . 29
5.5.4 Limiting range of temperature . 29
5.5.5 Deviation from zero . 29
5.5.6 Electromagnetic compatibility (EMC) . 29
5.6 Constructional requirements . 30
5.6.1 General constructional requirements . 30
5.6.2 Damping . 30
5.6.3 Sealing to prevent access . 30
5.6.4 Scales . 31

5.6.5 Stopper . 32
5.6.6 Preferred values . 32
5.6.7 Adjusters, mechanical and/or electrical . 32
5.6.8 Effects of vibration and shock . 33
5.6.9 Degrees of protection provided by enclosure . 33
5.6.10 Terminals . 34
6 Information, markings and symbols . 34
6.1 Information. 34
6.2 Markings, symbols and their locations . 35
6.3 Markings relating to the reference values and nominal ranges of use of
influence quantities . 36
6.4 The symbols for marking instruments and accessories . 36
6.5 Markings and symbols for terminals . 45
6.5.1 Requirements for markings . 45
6.5.2 Earthing (grounding) terminals . 45
6.5.3 Measuring circuit terminals . 45
6.5.4 Special markings for terminals . 45
6.6 Instructions for use . 45
7 Package . 46
8 Test rules . 46
8.1 Type of test . 46
8.2 Type tests . 46
8.3 Routine tests . 46
8.4 Recurrent tests . 46
8.5 Nonconformity classification . 47
8.6 Judgement of test results . 47
Annex A (normative) Limits of intrinsic uncertainty and variations . 48
Annex B (informative) Relationship between ambient temperature and relative
humidity. 51
Annex C (informative) Estimation of uncertainties . 52
C.1 Uncertainties in this standard . 52
C.2 Operating uncertainty . 52
C.2.1 General . 52
C.2.2 Estimating absolute operating uncertainty according to type test results . 52
C.2.3 Estimating absolute operating uncertainty according to limit of intrinsic
uncertainty and limit of variations due to every influence specified by
this standard . 53
C.3 Overall system uncertainty . 54
C.4 Fiducial operating uncertainty . 54
Annex D (normative) Routine Tests . 55
Bibliography . 56

Figure 1 – Measuring range 10 A to 50 A . 31
Figure 2 – Measuring range 80 V to 110 V . 32
Figure 3 – Measuring ranges 0,06 MΩ to 0,4 M Ω and 0,1 MΩ to 2 MΩ . 32
Figure A.1 – Effect of temperature . 48
Figure A.2 – Effect of temperature . 49
Figure B.1 – Relationship between ambient temperature and relative humidity . 51

– 4 – IEC 60051-1:2016 © IEC 2016
Figure C.1 – Different kinds of uncertainty . 52

Table 1 – Minimum IP requirements . 22
Table 2 – Reference conditions and tolerances for testing purposes relating to the
influence quantities . 24
Table 3 – Limits of the nominal range of use and permissible variations . 26
Table 4 – The diameters of conductive screw and the diameters or the area of contact
surface . 34
Table 5 – Units, quantities and SI prefixes . 37
Table 6 – Symbols for marking instruments and accessories . 38

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DIRECT ACTING INDICATING ANALOGUE ELECTRICAL
MEASURING INSTRUMENTS AND THEIR ACCESSORIES –

Part 1: Definitions and general requirements common to all parts

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of 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, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). 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. 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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60051-1 has been prepared by IEC technical committee 85:
Measuring equipment for electrical and electromagnetic quantities.
This sixth edition cancels and replaces the fifth edition published in 1997. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– adding the EMC requirements;
– updating the safety symbols and requirements according to new IEC 61010 series;
– replacing the concept of “error” to the concept of “uncertainty”;
– adding service environment classification and classification by method of operation,
mechanical condition and the degrees of protection;

– 6 – IEC 60051-1:2016 © IEC 2016
– adding the requirements for transport and storage of instruments and accessories
according to IEC 60359;
– updating the Annexes to provide more information.
The text of this standard is based on the following documents:
FDIS Report on voting
85/521/FDIS 85/536/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 publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60051 series, published under the general title Direct acting
indicating analogue electrical measuring instruments and their accessories, can be found on
the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
IEC 60051 is published in separate parts according to the following structure and under the
general title Direct acting indicating analogue electrical measuring instruments and their
accessories.
Part 1: Definitions and General Requirements Common to all Parts.
Part 2: Special Requirements for Ammeters and Voltmeters.
Part 3: Special Requirements for Wattmeters and Varmeters.
Part 4: Special Requirements for Frequency Meters.
Part 5: Special Requirements for Phase Meters, Power Factor Meters and Synchroscopes.
Part 6: Special Requirements for Ohmmeters (Impedance Meters) and Conductance Meters.
Part 7: Special Requirements for Multi-function Instruments.
Part 8: Special Requirements for Accessories.
Part 9: Recommended Test Methods.
Parts 2 to 9 are not complete in themselves and shall be read in conjunction with this Part 1.
All of these parts are arranged in the same format and a standard relationship between
subject and clause number is maintained throughout. This re-arrangement will assist the
reader of IEC 60051 to distinguish information relating to the different types of instruments.

– 8 – IEC 60051-1:2016 © IEC 2016
DIRECT ACTING INDICATING ANALOGUE ELECTRICAL
MEASURING INSTRUMENTS AND THEIR ACCESSORIES –

Part 1: Definitions and general requirements common to all parts

1 Scope
This part of IEC 60051 specifies definitions and general requirements for direct acting
indicating analogue electrical measuring instruments and their accessories.
This part applies to direct acting indicating analogue electrical measuring instruments, such
as:
• ammeters and voltmeters;
• wattmeters and varmeters;
• frequency meters of pointer and vibrating-reed types;
• phasemeters, power-factor meters and synchroscopes;
• ohmmeters(impedance meters) and conductance meters;
• multi-function instruments of the above types.
It also applies to:
• certain accessories used with these instruments, such as:
– shunts;
– series resistors and impedance elements;
• combination of the instruments and the accessories provided that the adjustments have
been made for the combination;
• direct acting indicating electrical measuring instrument whose scale marks do not
correspond directly to its electrical input quantity, provided that the relationship between
them is known;
• instruments and accessories having electronic devices in their measuring and/or auxiliary
circuits.
These series standards do not apply to:
• special purpose instruments which are covered by their own IEC standards;
• special purpose devices which are covered by their own IEC standards when they are
used as accessories.
This standard does not specify requirements concerning dimensions of instruments or
accessories (for the former, see IEC 60473).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60051-9, Direct acting indicating analogue electrical measuring instruments and their
accessories – Part 9: Recommended Test Methods
IEC 60359:2001, Electrical and electronic measurement equipment – Expression of
performance
IEC 60529:2013, Degrees of protection provided by enclosures (IP Code)
IEC 60721-3-3:1994, Classification of environmental conditions – Part 3: Classification of
groups of environmental parameters and their severities – Section 3: Stationary use at
weatherprotected locations
IEC 60721-3-3/AMD1:1995
IEC 60721-3-3/AMD2:1996
IEC 60721-3-7:1995, Classification of environmental conditions – Part 3: Classification of
groups of environmental parameters and their severities – Section 7: Portable and non-
stationary use
IEC 60721-3-7/AMD1:1996
IEC 61010-1:2010, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 1: General requirements
IEC 61010-2-030:2010, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 2-030: Particular requirements for testing and measuring circuits
IEC 61326-1:2012, Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 1: General requirements
IEC 61326-2-1:2012, Electrical equipment for measurement, control and laboratory use –
EMC requirements – Part 2-1: Particular requirements – Test configurations, operational
conditions and performance criteria for sensitive test and measurement equipment for EMC
unprotected applications
ISO 780:1997, Packaging – Pictorial marking for handling of goods
3 Terms and definitions
For the purpose of this standard, the terms and definitions given in IEC 60359 as well as the
following, apply.
3.1 General terms
3.1.1
electrical measuring instrument
measuring instrument intended to measure an electrical or non-electrical quantity using
electrical or electronic means
[SOURCE: IEC 60359:2001, 3.2.4]
3.1.2
analogue display instrument
measuring instrument intended to present or display the output information as a continuous
function of the measured quantity
________________
To be published.
– 10 – IEC 60051-1:2016 © IEC 2016
Note 1 to entry: An instrument in which a change of the indication occurs by small discrete steps, but which does
not have a digital display, is considered to be an analogue display instrument.
3.1.3
indicating instrument
measuring instrument which displays at any time the value of the measured quantity without
recording it
Note 1 to entry: The indicated value may be different from the value of the quantity measured by the instrument
and may be in units of a different quantity.
3.1.4
direct acting indicating instrument
instrument in which the indicating device is mechanically connected to and actuated by the
moving element
3.1.5
multi-function instrument
instrument having a single means of indication intended for the measurement of more than
one kind of quantity (e.g. an instrument measuring current, voltage and resistance)
3.1.6
fixed instrument
measuring instrument designed to be permanently mounted and which is intended to be
connected by means of permanently installed conductors
[SOURCE: IEC 60050-300:2001, 312-02-17]
3.1.7
portable instrument
instrument specifically designed to be carried by hand
Note 1 to entry: The instrument is intended to be connected and disconnected by the user.
3.1.8
hand-held instrument
instrument intended to be held by one hand during normal use
3.1.9
panel mounted instrument
fixed installed instrument intended to be mounted in a cut out of a panel or a chassis
[SOURCE: IEC 62586-1:2013, 3.1.6]
3.1.10
polyphase instrument
instrument for measurement in a polyphase system and arranged for connection to more than
one phase of the system
3.1.11
astatic instrument
measuring instrument in which the measuring element is, by design, unaffected by uniform
magnetic fields of external origin
[SOURCE: IEC 60050-300:2001, 312-02-05]
3.1.12
ammeter
instrument intended to measure the value of a current

[SOURCE: IEC 60050-300:2001, 313-01-01]
3.1.13
voltmeter
instrument intended to measure the value of a voltage
[SOURCE: IEC 60050-300:2001, 313-01-03]
3.1.14
ohmmeter
resistance meter
instrument intended to measure electrical resistance
[SOURCE: IEC 60050-300:2001, 313-01-09]
3.1.15
wattmeter
instrument intended to measure active power
[SOURCE: IEC 60050-300:2001, 313-01-06]
3.1.16
varmeter
instrument intended to measure reactive power
[SOURCE: IEC 60050-300:2001, 313-01-07]
3.1.17
phase meter
instrument which indicates the phase angle between two electrical input quantities of the
same frequency and of similar waveform
Note 1 to entry: Such an instrument measures:
– the phase angle between a voltage and another voltage or between a current and another current,
or
– the phase angle between a voltage and a current.
3.1.18
power factor meter
instrument intended to measure the ratio of the active to the apparent power in an electrical
circuit
[SOURCE: IEC 60050-300:2001, 313-01-14]
3.1.19
synchroscope
instrument intended to indicate that two alternating voltages or polyphase voltage systems
have the same frequency and are in phase
[SOURCE: IEC 60050-300:2001, 313-01-22]
3.1.20
accessory
element, group of elements or device associated with the measuring circuit of a measuring
instrument in order to confer specified characteristics to the measuring instrument

– 12 – IEC 60051-1:2016 © IEC 2016
3.1.21
interchangeable accessory
accessory having its own properties and accuracy, these being independent of those of the
instrument with which it may be associated
Note 1 to entry: An accessory is considered to be interchangeable when its rated characteristics are known and
marked and are sufficient to enable its errors and variations to be determined without using the associated
instrument. A shunt whose adjustment takes into account an instrument current which is not negligible and which is
known, is considered to be interchangeable.
3.1.22
accessory of limited interchangeability
accessory having its own properties and accuracy, which can only be associated with
measuring instruments for which certain characteristics are within specified limits
3.1.23
non-interchangeable accessory
accessory adjusted to take into account the electrical characteristics of a specific measuring
instrument
3.1.24
shunt
resistor connected in parallel with a measuring circuit of a measuring instrument
Note 1 to entry: A shunt is generally intended to provide a voltage proportional to a current to be measured.
3.1.25
series resistor (impedance)
resistor (impedance) connected in series with a measuring circuit of a measuring instrument
Note 1 to entry: A series resistor (impedance) is generally intended to extend the voltage measuring range of an
instrument.
3.1.26
instrument lead
lead comprising one or more conductors, specially designed for interconnecting measuring
instruments to external circuits or to accessories
3.1.27
calibrated instrument lead
instrument lead whose resistance has a specified value
Note 1 to entry: A calibrated instrument lead is considered as being an interchangeable accessory of a measuring
instrument.
3.1.28
distortion factor (total harmonic distortion factor) (of a quantity)
ratio of the r.m.s. value of the harmonic content to the r.m.s. value of the non-sinusoidal
quantity
3.1.29
ripple content of a quantity
ratio of the r.m.s. value of the fluctuating component to the value of the d.c. component
3.1.30
peak factor
ratio of the peak value to the r.m.s. value of a periodic quantity

3.2 Description of instruments according to their method of operation
3.2.1
permanent-magnet moving-coil instrument
instrument which operates by the interaction of the magnetic field due to a current in a
movable coil with the field of a fixed permanent magnet
Note 1 to entry: The instrument can have more than one coil, measuring the sum or ratio of the currents in them.
3.2.2
moving-magnet instrument
instrument which operates by the interaction of the field of a movable permanent magnet with
the magnetic field due to a current in a fixed coil
Note 1 to entry: The instrument can have more than one coil.
3.2.3
moving-iron instrument
instrument which operates by the attraction between a movable piece of soft magnetic
material and the field due to a current in a fixed coil or by the repulsion (and attraction)
between one (or more) fixed piece(s) of soft magnetic material and a movable piece of soft
magnetic material, both (all) magnetized by a current in a fixed coil
3.2.4
polarized moving-iron instrument
instrument comprising a movable piece of soft magnetic material polarized by a fixed
permanent magnet and magnetically excited by a current in a fixed coil
3.2.5
electrodynamic instrument
instrument which operates by the interaction of the magnetic field due to a current in a
movable coil with the magnetic field due to a current in one or more fixed coils
3.2.6
ferrodynamic instrument (iron-cored electrodynamic instrument)
electrodynamic instrument in which the electrodynamic effect is modified by the presence of
soft magnetic material in the magnetic circuit
3.2.7
induction instrument
instrument which operates by the interaction of the magnetic field(s) of (a) fixed a.c.
electromagnet(s) with the magnetic field(s) due to currents which they induce in (a) movable
conductive element(s)
3.2.8
thermal instrument (electrothermal instrument)
instrument which operates by the heating effect(s) of (a) current(s) on it(s) conductor(s)
3.2.8.1
bimetallic instrument
thermal instrument in which the deformation of a bimetallic element (the materials having
different rates of expansion due to a change in temperature), heated directly or indirectly by a
current, produces the indication
3.2.8.2
thermocouple instrument
thermal instrument making use of the e.m.f. of one or more thermocouples heated by the
current to be measured
Note 1 to entry: The e.m.f. is often measured using a permanent-magnet moving-coil instrument.

– 14 – IEC 60051-1:2016 © IEC 2016
3.2.9
rectifier instrument
instrument which is the combination of a measuring instrument sensitive to direct current and
a rectifying device whereby alternating currents or voltages may be measured
3.2.10
electrostatic instrument
instrument the operation of which depends on the effects of electrostatic forces between fixed
and movable electrodes
3.2.11
pointer-type frequency meter
instrument which indicates the measured frequency by the relationship between an index and
a scale
3.2.12
vibrating-reed frequency meter
instrument intended to measure frequency, comprising a set of tuned vibrating reeds, one or a
few of which resonate under the action of an alternating current of the relevant frequency
flowing through one or more fixed coils
3.2.13
ratiometer (quotientmeter)
instrument for measuring the ratio (quotient) of two quantities
3.2.14
R.M.S.-responding instrument
instrument which, over a specified frequency range, provides an indication which is designed
to be proportional to the root-mean-square value of the measured quantity, even when it is not
sinusoidal or containing a d.c. part
3.2.15
mean value-responding instrument
instrument with scale of R.M.S value but which, over a specified frequency range, provides an
indication which is designed to be proportional to the mean value of the measured quantity
Note 1 to entry: These instruments do not reflect R.M.S. value of a measurand when the measurand is not
sinusoidal or containing a d.c. part.
3.3 Constructional features of instruments
3.3.1
measuring circuit (of an instrument)
part of the electrical circuit internal to the instrument and its accessories, together with the
interconnecting leads, if any, which is energized by a voltage or a current, one or both of
these quantities being a prime factor in determining the indication of the measured quantity
(one of these quantities may be the measured quantity itself)
3.3.1.1
current circuit
measuring circuit through which flows a current which is a prime factor in determining the
indication of the measured quantity
Note 1 to entry: It may be the current directly involved in the measurement or a proportional current supplied by
an external current transformer or derived from an external shunt.
3.3.1.2
voltage circuit
measuring circuit to which is applied a voltage which is a prime factor in determining the
indication of a measured quantity

Note 1 to entry: It may be the voltage directly involved in the measurement or a proportional voltage supplied by
an external voltage transformer or an external voltage divider or derived by means of an external series resistor
(impedance).
3.3.2
external measuring circuit
part of the electrical circuit external to the instrument from which a measured value is
obtained
3.3.3
auxiliary circuit
circuit, other than a measuring circuit, required for the operation of the instrument
3.3.4
auxiliary supply
auxiliary circuit which provides electrical energy
3.3.5
measuring element
assembly of those parts of a measuring instrument which are acted upon by a measured
quantity, resulting in a movement of the moving element related to that quantity
3.3.6
moving element
moving part of a measuring element
3.3.7
indicating device
part of a measuring instrument which displays values of the measured quantity
3.3.8
index
means which, in conjunction with the scale, indicates the position of the moving element of an
instrument
3.3.9
scale
series of marks and numbers from which, in conjunction with the index, the value of the
measured quantity is obtained
3.3.10
scale marks
marks on the dial for the purpose of dividing it into suitable intervals so that the position of the
index may be determined
3.3.11
zero scale mark
mark on the dial associated with the figure zero
3.3.12
scale division
distance between any two consecutive scale marks
3.3.13
scale numbers
series of numbers which are associated with the scale marks

– 16 – IEC 60051-1:2016 © IEC 2016
3.3.14
dial
surface which carries the scale and other marks and symbols
3.3.15
mechanical zero
equilibrium position which the index will approach when the measuring element (if
mechanically controlled) is de-energized.
Note 1 to entry: This may or may not coincide with the zero scale mark.
Note 2 to entry: In mechanically suppressed zero instruments, the mechanical zero does not correspond to a
scale mark.
Note 3 to entry: In instruments without restoring torque the mechanical zero is indeterminate.
3.3.15.1
mechanical zero adjuster
mechanism by means of which the instrument may be adjusted so that the mechanical zero
coincides with the appropriate scale mark
3.3.15.2
mechanical span adjuster
mechanism by means of which the instrument may be adjusted so that the lower/upper limit of
the measuring range coincides with the appropriate scale mark
3.3.16
electrical zero
equilibrium position which the index will approach when the measured electrical quantity is
either zero or a set value and the control circuit (if any), producing a restoring torque, is
energized
3.3.16.1
electrical zero adjuster
for an instrument which needs an auxiliary supply, the mechanism by means of which the
instrument may be adjusted so that the electrical zero coincides with the appropriate scale
mark
3.3.16.2
electrical span adjuster
for an instrument which needs an auxiliary supply, the mechanism by means of which the
instrument may be adjusted so that the lower/upper limit of the measuring range coincides
with the appropriate scale mark
3.4 Characteristic features of instruments
3.4.1
scale length
length of the line (curved or straight) which passes through the centres of all the shortest
scale marks contained between the first and the last scale marks
Note 1 to entry: It is expressed in units of length.
Note 2 to entry: If an instrument has more than one scale, each scale may have its own scale length. For
convenience, the scale length of the instrument is taken to be that of the major scale.
3.4.2
span
algebraic difference between the upper and lower limits of the measuring range
Note 1 to entry: It is expressed in units of the measured quantity.

3.4.3
measuring range (effective range)
range defined by two values of the measured quan
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