EN ISO 376:2011

SLOVENSKI STANDARD
01-februar-2012
1DGRPHãþD
SIST EN ISO 376:2005
Kovinski materiali - Umerjanje merilnikov sile, ki se uporabljajo za preverjanje
preskusnih strojev z enoosno obremenitvijo (ISO 376:2011)
Metallic material - Calibration of force-proving instruments used for the verification of
uniaxial testing machines (ISO 376:2011)
Metallische Werkstoffe - Kalibrierung der Kraftmessgeräte für die Prüfung von
Prüfmaschinen mit einachsiger Beanspruchung (ISO 376:2011)
Matériaux métalliques - Étalonnage des instruments de mesure de force utilisés pour la
vérification des machines d'essais uniaxiaux (ISO: 376:2011)
Ta slovenski standard je istoveten z: EN ISO 376:2011
ICS:
77.040.10 Mehansko preskušanje kovin Mechanical testing of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 376
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2011
ICS 77.040.10 Supersedes EN ISO 376:2004
English Version
Metallic materials - Calibration of force-proving instruments used
for the verification of uniaxial testing machines (ISO 376:2011)
Matériaux métalliques - Étalonnage des instruments de Metallische Werkstoffe - Kalibrierung der Kraftmessgeräte
mesure de force utilisés pour la vérification des machines für die Prüfung von Prüfmaschinen mit einachsiger
d'essais uniaxiaux (ISO 376:2011) Beanspruchung (ISO 376:2011)
This European Standard was approved by CEN on 4 June 2011.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same
status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 376:2011: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 376:2011) has been prepared by Technical Committee ISO/TC 164 "Mechanical
testing of metals" in collaboration with Technical Committee ECISS/TC 101 “Test methods for steel (other
than chemical analysis)” the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by December 2011, and conflicting national standards shall be withdrawn
at the latest by December 2011.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 376:2004.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 376:2011 has been approved by CEN as a EN ISO 376:2011 without any modification.

INTERNATIONAL ISO
STANDARD 376
Fourth edition
2011-06-15
Metallic materials — Calibration of force-
proving instruments used for the
verification of uniaxial testing machines
Matériaux métalliques — Étalonnage des instruments de mesure de
force utilisés pour la vérification des machines d'essais uniaxiaux

Reference number
ISO 376:2011(E)
©
ISO 2011
ISO 376:2011(E)
©  ISO 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2011 – All rights reserved

ISO 376:2011(E)
Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .1
4 Symbols and their designations .1
5 Principle.2
6 Characteristics of force-proving instruments .3
7 Calibration of the force-proving instrument.3
8 Classification of the force-proving instrument .8
9 Use of calibrated force-proving instruments.10
Annex A (informative) Example of dimensions of force transducers and corresponding loading
fittings.11
Annex B (informative) Additional information .18
Annex C (informative) Measurement uncertainty of the calibration and subsequent use of the
force-proving instrument.21
Bibliography.30

ISO 376:2011(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 376 was prepared by Technical Committee ISO/TC 164, Mechanical testing of metals, Subcommittee
SC 1, Uniaxial testing.
This fourth edition cancels and replaces the third edition (ISO 376:2004), which has been technically revised
(for details, see the introduction).
iv © ISO 2011 – All rights reserved

ISO 376:2011(E)
Introduction
An ISO/TC 164/SC 1 working group has developed procedures for determining the measurement uncertainty
of force-proving instruments, and these procedures have been added to this fourth edition as a new annex
(Annex C).
In addition, this fourth edition allows the calibration to be performed in two ways:
⎯ with reversible measurement for force-proving instruments which are going to be used with increasing
and decreasing forces;
⎯ without reversible measurement for force-proving instruments which are going to be used only with
increasing forces.
In the first case, i.e. when the force-proving instrument is going to be used for reversible measurements, the
calibration has to be performed with increasing and decreasing forces to determine the hysteresis of the force-
proving instrument. In this case, there is no need to perform a creep test.
In the second case, i.e. when the force-proving instrument is not going to be used for reversible
measurements, the calibration is performed with increasing forces only but, in addition, a creep test has to be
performed. In this case, there is no need to determine the hysteresis.

INTERNATIONAL STANDARD ISO 376:2011(E)

Metallic materials — Calibration of force-proving instruments
used for the verification of uniaxial testing machines
1 Scope
This International Standard specifies a method for the calibration of force-proving instruments used for the
static verification of uniaxial testing machines (e.g. tension/compression testing machines) and describes a
procedure for the classification of these instruments.
This International Standard is applicable to force-proving instruments in which the force is determined by
measuring the elastic deformation of a loaded member or a quantity which is proportional to it.
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.
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
force-proving instrument
whole assembly from the force transducer through to, and including, the indicator
4 Symbols and their designations
Symbols and their designations are given in Table 1.
ISO 376:2011(E)
Table 1 — Symbols and their designations
Symbol Unit Designation
b % Relative reproducibility error with rotation
b′ % Relative repeatability error without rotation
c % Relative creep error
F N Maximum capacity of the transducer
f
F N Maximum calibration force
N
f % Relative interpolation error
c
f % Relative zero error
a
i — Reading on the indicator after removal of force
f
a
i — Reading on the indicator before application of force
o
a
i — Reading on the indicator 30 s after application or removal of the maximum calibration force
a
i — Reading on the indicator 300 s after application or removal of the maximum calibration force
r N Resolution of the indicator
v % Relative reversibility error of the force-proving instrument
X — Deflection with increasing test force
X — Computed value of deflection
a
X ′ — Deflection with decreasing test force
X — Maximum deflection from runs 1, 3 and 5
max
X — Minimum deflection from runs 1, 3 and 5
min
X — Deflection corresponding to the maximum calibration force
N
X — Average value of the deflections with rotation
r
X — Average value of the deflections without rotation
wr
a
Reading value corresponding to the deflection.
5 Principle
Calibration consists of applying precisely known forces to the force transducer and recording the data from the
indicator, which is considered an integral part of the force-proving instrument.
When an electrical measurement is made, the indicator may be replaced by another indicator and the force-
proving instrument need not be recalibrated provided the following conditions are fulfilled.
a) The original and replacement indicators have calibration certificates, traceable to national standards,
which give the results of calibration in terms of electrical base units (volt, ampere). The replacement
indicator shall be calibrated over a range equal to or greater than the range for which it is used with the
force-proving instrument, and the resolution of the replacement indicator shall be at least equal to the
resolution of the original indicator when it is used with the force-proving instrument.
b) The units and excitation source of the replacement indicator should be respectively of the same quantity
(e.g. 5 V, 10 V) and type (e.g. AC or DC carrier frequency).
c) The uncertainty of each indicator (both the original and the replacement indicators) shall not significantly
influence the uncertainty of the whole force-proving instrument assembly. It is recommended that the
uncertainty of the replacement indicator be no greater than 1/3 of the uncertainty of the entire system
(see C.2.11).
2 © ISO 2011 – All rights reserved

ISO 376:2011(E)
6 Characteristics of force-proving instruments
6.1 Identification of the force-proving instrument
All the elements of the force-proving instrument (including the cables for electrical connection) shall be
individually and uniquely identified, e.g. by the name of the manufacturer, the model and the serial number.
For the force transducer, the maximum working force shall be indicated.
6.2 Application of force
The force transducer and its loading fittings shall be designed so as to ensure axial application of force,
whether in tension or compression.
Examples of loading fittings are given in Annex A.
6.3 Measurement of deflection
Measurement of the deflection of the loaded member of the force transducer may be carried out by
mechanical, electrical, optical or other means with adequate accuracy and stability.
The type and the quality of the deflection measuring system determine whether the force-proving instrument is
classified only for specific calibration forces or for interpolation (see Clause 7).
Generally, the use of force-proving instruments with dial gauges as a means of measuring the deflection is
limited to the forces for which the instruments have been calibrated. The dial gauge, if used over a long travel,
may contain large localized periodic errors which produce an uncertainty too great to permit interpolation
between calibration forces. The dial gauge may be used for interpolation if its periodic error has a negligible
influence on the interpolation error of the force-proving instrument.
7 Calibration of the force-proving instrument
7.1 General
7.1.1 Preliminary measures
Before undertaking the calibration of the force-proving instrument, ensure that this instrument is able to be
calibrated. This can be done by means of preliminary tests such as those defined below and given as
examples.
7.1.2 Overloading test
This optional test is described in Clause B.1.
7.1.3 Verification relating to application of forces
Ensure
⎯ that the attachment system of the force-proving instrument allows axial application of the force when the
instrument is used for tensile testing;
⎯ that there is no interaction between the force transducer and its support on the calibration machine when
the instrument is used for compression testing.
Clause B.2 gives an example of a method that can be used.
NOTE Other tests can be used, e.g. a test using a flat-based transducer with a spherical button or upper bearing
surface.
ISO 376:2011(E)
7.1.4 Variable voltage test
This test is left to the discretion of the calibration service. For force-proving instruments requiring an electrical
supply, verify that a variation of ±10 % of the line voltage has no significant effect. This verification can be
carried out by means of a force transducer simulator or by another appropriate method.
7.2 Resolution of the indicator
7.2.1 Analogue scale
The thickness of the graduation marks on the scale shall be uniform and the width of the pointer shall be
approximately equal to the width of a graduation mark.
The resolution, r, of the indicator shall be obtained from the ratio between the width of the pointer and the
centre-to-centre distance between two adjacent scale graduation marks (scale interval), the recommended
ratios being 1:2, 1:5 or 1:10, a spacing of 1,25 mm or greater being required for the estimation of a tenth of the
division on the scale.
A vernier scale of dimensions appropriate to the analogue scale may be used to allow direct fractional reading
of the instrument scale division.
7.2.2 Digital scale
The resolution is considered to be one increment of the last active number on the numerical indicator.
7.2.3 Variation of readings
If the readings fluctuate by more than the value previously calculated for the resolution (with no force applied
to the instrument), the resolution shall be deemed to be equal to half the range of fluctuation.
7.2.4 Units
The resolution, r, shall be converted to units of force.
7.3 Minimum force
Taking into consideration the accuracy with which the deflection of the instrument can be read during
calibration or during its subsequent use for verifying machines, the minimum force applied to a force-proving
instrument shall comply with the two following conditions:
a) the minimum force shall be greater than or equal to:
⎯ 4 000 × r for class 00;
⎯ 2 000 × r for class 0,5;
⎯ 1 000 × r for class 1;
⎯ 500 × r for class 2.
b) the minimum force shall be greater than or equal to 0,02 F .
f
4 © ISO 2011 – All rights reserved

ISO 376:2011(E)
7.4 Calibration procedure
7.4.1 Preloading
Before the calibration forces are applied, in a given mode (tension or compression), the maximum force shall
be applied to the instrument three times. The duration of the application of each preload shall be between 60 s
and 90 s.
7.4.2 Procedure
Carry out the calibration by applying two series of calibration forces to the force-proving instrument with
increasing values only, without disturbing the device.
Then apply at least two further series of increasing and, if the force-proving instrument is to be calibrated in an
incremental/decremental loading direction, decreasing values. Between each of the further series of forces,
rotate the force-proving instrument symmetrically on its axis to positions uniformly distributed over 360° (i.e. 0°,
120°, 240°). If this is not possible, it is permissible to adopt the following positions: 0°, 180° and 360° (see
Figure 1).
Figure 1 — Positions of the force-proving instrument
For the determination of the interpolation curve, the number of forces shall be not less than eight, and these
forces shall be distributed as uniformly as possible over the calibration range. The interpolation curve shall be
determined from the average values of the deflections with rotation, X , as defined in 7.5.1.
r
If a periodic error is suspected, it is recommended that intervals between the forces which correspond to the
periodicity of this error be avoided.
This procedure determines only a combined value of hysteresis of the device and of the calibration machine.
Accurate determination of the hysteresis of the device may be performed on dead-weight machines. For other
types of calibration machine, their hysteresis should be considered.
ISO 376:2011(E)
The force-proving instrument shall be preloaded three times to the maximum force in the direction in which the
subsequent forces are to be applied. When the direction of loading is changed, the maximum force shall be
applied three times in the new direction.
The readings corresponding to no force shall be noted after waiting at least 30 s after the force has been
totally removed.
There should be a wait of at least 3 min between subsequent measurement series.
Instruments with detachable parts shall be dismantled, as for packaging and transport, at least once during
calibration. In general, this dismantling shall be carried out between the second and third series of calibration
forces. The maximum force shall be applied to the force-proving instrument at least three times before the
next series of forces is applied.
Before starting the calibration of an electrical force-proving instrument, the zero signal may be noted (see
Clause B.3).
7.4.3 Loading conditions
The time interval between two successive loadings shall be as uniform as possible, and no reading shall be
taken within 30 s of the start of the force change. The calibration shall be performed at a temperature stable to
within ±1 °C. This temperature shall be within the range 18 °C to 28 °C and shall be recorded. Sufficient time
shall be allowed for the force-proving instrument to attain a stable temperature.
When it is known that the force-proving instrument is not temperature-compensated, care should be taken to
ensure that temperature variations do not affect the calibration.
Strain gauge transducers shall be energized for at least 30 min before calibration.
7.4.4 Creep test
If the force-proving instrument is to be calibrated in an incremental-only loading direction, record its output at
30 s and 300 s after application or removal of the maximum calibration force, in each mode of force
application, to enable its creep characteristics to be determined. If creep is measured at zero force, the
maximum calibration force shall be maintained for at least 60 s prior to its removal. The creep test may be
performed at any time after preloading during the calibration procedure.
The calibration certificate shall include the following information:
⎯ the method of creep measurement (creep at maximum force or after force removal);
⎯ when the creep measurement was performed (after preloading, after the last measurement series, etc.);
⎯ the length of time for which the force was applied prior to removal (for creep determined at zero force).
7.4.5 Determination of deflection
A deflection is defined as the difference between a reading under force and a reading without force. This
definition of deflection applies to output readings in electrical units as well as to output readings in length units.
6 © ISO 2011 – All rights reserved

ISO 376:2011(E)
7.5 Assessment of the force-proving instrument
7.5.1 Relative reproducibility and repeatability errors, b and b′
These errors are calculated for each calibration force and in both cases, i.e. with rotation of the force-proving
instrument (b) and without rotation (b′), using the following equations:
XX−
max min
b=×100 (1)
X
r
XX++X
13 5
where X = (2)
r
and
XX−
′
b=×100 (3)
X
wr
XX+
where X = (4)
wr
7.5.2 Relative interpolation error, f
c
This error is determined using a first-, second- or third-degree equation giving the deflection X as a function
r
of the calibration force.
The equation used shall be indicated in the calibration report. The relative interpolation error shall be
calculated from the equation:
XX−
r
a
f=×100 (5)
c
X
a
7.5.3 Relative zero error, f
The zero reading shall be recorded before and after each series of tests. The zero reading shall be taken
approximately 30 s after the force has been completely removed.
The relative zero error is calculated from the equation:
ii−
fo
f=×100 (6)
X
N
The maximum relative zero error evaluated should be considered.
7.5.4 Relative reversibility error, v
The relative reversibility error is determined at each calibration, by carrying out a verification with increasing
forces and then with decreasing forces.
The difference between the values obtained for both series with increasing forces and with decreasing forces
enables the relative reversibility error to be calculated using the following equations:
XX′ −
v=×100 (7)
X
ISO 376:2011(E)
′
XX−
v=×100 (8)
X
v is calculated as the mean value of v and v :
1 2
vv+
v = (9)
7.5.5 Relative creep error, c
Calculate the difference in outputs i obtained at 30 s and i obtained 300 s after the application or removal
30 300
of the maximum calibration force and express this difference as a percentage of maximum deflection:
ii−
300 30
c=×100 (10)
X
N
8 Classification of the force-proving instrument
8.1 Principle of classification
The range for which the force-proving instrument is classified is determined by considering each calibration
force, one after the other, starting with the maximum force and decreasing to the lowest calibration force. The
classification range ceases at the last force for which the classification requirements are satisfied.
The force-proving instrument can be classified either for specific forces or for interpolation, and for either
incremental-only or incremental/decremental loading directions.
8.2 Classification criteria
8.2.1 The range of classification of a force-proving instrument shall at least cover the range 50 % to 100 %
of F .
N
8.2.2 Case A: For instruments classified only for specific forces and incremental-only loading, the criteria
which shall be considered are:
⎯ the relative reproducibility, repeatability and zero errors;
⎯ the relative creep error.
8.2.3 Case B: For instruments classified only for specific forces and incremental/decremental loading, the
criteria which shall be considered are:
⎯ the relative reproducibility, repeatability and zero errors;
⎯ the relative reversibility error.
8.2.4 Case C: For instruments classified for interpolation and incremental-only loading, the criteria which
shall be considered are:
⎯ the relative reproducibility, repeatability and zero errors;
⎯ the relative interpolation error;
⎯ the relative creep error.
8 © ISO 2011 – All rights reserved

ISO 376:2011(E)
8.2.5 Case D: For instruments classified for interpolation and incremental/decremental loading, the criteria
which shall be considered are:
⎯ the relative reproducibility, repeatability and zero errors;
⎯ the relative interpolation error;
⎯ the relative reversibility error.
Table 2 gives the maximum allowable values of these parameters for each class of force-proving instrument
and the uncertainty of the calibration forces.
Table 2 — Characteristics of force-proving instruments
Expanded
uncertainty of
Relative error of the force-proving instrument applied
calibration force
Class (95 % level of
% confidence)
of reproducibility of repeatability of interpolation of zero of reversibility of creep %
b b′ f f v c
c 0
00 0,05 0,025 ±0,025 ±0,012 0,07 0,025 ±0,01
0,5 0,10 0,05 ±0,05 ±0,025 0,15 0,05 ±0,02
1 0,20 0,10 ±0,10 ±0,050 0,30 0,10 ±0,05
2 0,40 0,20 ±0,20 ±0,10 0,50 0,20 ±0,10
8.3 Calibration certificate and duration of validity
8.3.1 If a force-proving instrument has satisfied the requirements of this International Standard at the time
of calibration, the calibration authority shall draw up a certificate, in accordance with ISO/IEC 17025, stating at
least the following information:
a) the identity of all elements of the force-proving instrument and loading fittings and of the calibration
machine;
b) the mode of force application (tension/compression);
c) that the instrument is in accordance with the requirements of preliminary tests;
d) the class and the range (or forces) of validity and the loading direction (incremental-only or
incremental/decremental);
e) the date and results of the calibration and, when required, the interpolation equation;
f) the temperature at which the calibration was performed;
g) the uncertainty of the calibration results (one method of determining the uncertainty is given in Annex C);
h) details of the creep measurement, if performed (see 7.4.4).
8.3.2 For the purposes of this International Standard, the maximum period of validity of the certificate shall
not exceed 26 months.
A force-proving instrument shall be recalibrated when it sustains an overload higher than the test overload
(see Clause B.1) or after repair.
ISO 376:2011(E)
9 Use of calibrated force-proving instruments
Force-proving instruments shall be loaded in accordance with the conditions under which they were calibrated.
Precautions shall be taken to prevent the instrument from being subjected to forces greater than the maximum
calibration force.
Instruments classified only for specific forces shall be used only for these forces.
Instruments classified for incremental-only loading shall be used only for increasing forces. Instruments
classified for incremental/decremental loading may also be used to measure decreasing forces.
Instruments classified for interpolation may be used for any force in the interpolation range.
If a force-proving instrument is used at a temperature other than the calibration temperature, the deflection of
the instrument shall, if necessary, be corrected for any temperature variation (see Clause B.4).
NOTE A change of zero of the unloaded force transducer indicates plastic deformation due to overloading of the
force transducer. Permanent long-term drift indicates an influence of moisture on the strain gauge base or a bonding
defect of the strain gauges.
10 © ISO 2011 – All rights reserved

ISO 376:2011(E)
Annex A
(informative)
Example of dimensions of force transducers and corresponding
loading fittings
A.1 General
In order to calibrate force transducers in force standard machines and to enable easy axial installation in the
materials testing machines to be verified, the following design specifications and dimensions may be
considered.
A.2 Tensile force transducers
To aid assembly, it is recommended that the clamping heads on the face be machined down to the core
diameter over a length of about two threads. See Table A.1.
The centring bores used in the manufacture of the force transducer should be retained.
Table A.1 — Dimensions of tensile force transducers for nominal forces of not less than 10 kN
Maximum overall Size of external Minimum length Maximum width
Maximum (nominal)
b c
length thread of heads of thread or diameter
force of force-proving
a
instrument
mm mm mm
d
10 kN to 20 kN 500 M20 × 1,5 16 110
d
40 kN and 60 kN 500 M20 × 1,5 16 125
100 kN 500 M24 × 2 20 150
200 kN 500 M30 × 2 25 —
400 kN 600 M42 × 3 40 —
600 kN 650 M56 × 4 40 —
1 MN 750 M64 × 4 60 —
2 MN 950 M90 × 4 80 —
4 MN 1 300 M125 × 4 120 —
6 MN 1 500 M160 × 6 150 —
10 MN 1 700 M200 × 6 180 —
15 MN 2 000 M250 × 6 225 —
25 MN 2 500 M330 × 6 320 —
a
Dimensions of tensile force transducers for nominal forces of less than 10 kN are not standardized.
b
Length of tensile force transducer including any necessary thread adapters.
c
Of the tensile force transducer or of the thread adapters.
d
Pitch of 2 mm also permissible.
ISO 376:2011(E)
A.3 Compressive force transducers
To allow for the restricted mounting height in materials testing machines, compressive force transducers
should not exceed the overall heights given in Table A.2.
The overall height includes the height of the associated loading fittings.
Table A.2 — Overall height of compressive force transducers
a
Maximum overall height of devices for the verification of
Maximum (nominal)
materials testing machines
force of force-proving
mm
instrument
b b
class 1 class 2
≤40 kN 145 115
60 kN 170 145
100 kN 220 145
200 kN 220 190
400 kN 290 205
600 kN 310 205
1 MN 310 205
2 MN 310 205
3 MN 330 205
4 MN 410 205
5 MN 450 350
6 MN 450 400
10 MN 550 400
15 MN 670 —
a
The use of transducers having a greater overall height is permissible if the actual mounting
clearances of the materials testing machine make this possible.
b
In accordance with ISO 7500-1.
A.4 Loading fittings
A.4.1 General
Loading fittings should be designed in such a way that the line of force application is not distorted. As a rule,
tensile force transducers should be fitted with two ball nuts, two ball cups and, if necessary, with two
intermediate rings, while compressive force transducers should be fitted with one or two compression pads.
The dimensions recommended in A.4.2 to A.4.5 require the use of material with a yield strength of at least
350 N/mm .
A.4.2 Ball nuts and ball cups
Figure A.1 shows the shape of ball nuts and ball cups required for tensile force transducers. Their dimensions
should be in accordance with Table A.3.
Large ball cups and ball nuts for maximum (nominal) forces of 4 MN and greater should be provided with blind
holes distributed around the periphery as an aid to transportation and assembly. In the case of ball cups, two
pairs of opposite bores are sufficient, one of which should be made in the centre plane and the other in the
upper third of the top ball cup and in the lower third of the bottom ball cup (see Figure A.1).
12 © ISO 2011 – All rights reserved

ISO 376:2011(E)
In ball nuts, two opposite blind holes offset by 60° should be made in an upper plane, a mid plane and a lower
plane.
Key
1 ball nut
2 ball cup
3 tensile force measuring rod
a
Six bores.
b
Four bores.
Figure A.1 — Ball nut, ball cup and tensile force measuring rod
ISO 376:2011(E)
Table A.3 — Dimensions of ball nuts and ball cups for tensile force transducers
with a maximum force of not less than 10 kN
d d (c11) d h h r
Maximum (nominal) force 1 2 3 1 2
of force-proving instrument
mm mm mm mm mm mm
−0,120
From 10 kN to 40 kN 32 22 16 12 30
−0,280
−0,130
60 kN 43 45 27 18 15 30
−0,290
−0,130
100 kN 47 50 32 20 15 50
−0,290
−0,140
200 kN 60 64 44 25 15 50
−0,330
−0,170
400 kN and 600 kN 86 60 40 18 80
−0,390
−0,180
1 MN 115 120 74 60 25 100
−0,400
−0,230
2 MN 160 165 100 90 30 150
−0,480
−0,280
4 MN 225 150 120 40 250
−0,570
−0,300
6 MN 260 270 170 150 45 250
−0,620
−0,360
10 MN 335 220 180 55 300
−0,720
−0,440
15 MN 410 265 225 65 350
−0,840
−0,5
25 MN 550 345 310 85 500
−1,5
A.4.3 Intermediate rings
Wherever necessary, type A or type B intermediate rings as shown in Figure A.2 or A.3, respectively, and
specified in Table A.4 should be used for the verification of multi-range materials testing machines.
Intermediate rings should have a suitable holding fixture (e.g. threaded pins) for securing other mounting parts.

a
Chamfer.
b
Undercut (dimensions: 1,6 mm × 0,3 mm).
Figure A.2 — Type A intermediate ring
14 © ISO 2011 – All rights reserved

ISO 376:2011(E)
a
Chamfer.
b
Undercut (dimensions: 1,6 mm × 0,3 mm).
Figure A.3 — Type B intermediate ring
A.4.4 Adapters (extensions, reducer pieces, etc.)
If, owing to the design of the materials testing machine, adapters are required for mounting the force
transducer, they should be designed so as to ensure central loading of the force transducer.
A.4.5 Loading pads
Loading pads are used as the force introduction components of compressive force transducers. If a loading
pad has two flat surfaces for force transmission, they should be ground plane parallel.
In the verification of force-proving instruments used in a force calibration machine or a force standard machine,
the surface pressure on the compression platens of the machine should not be greater than 100 N/mm ; if
necessary, additional intermediate plates should be selected and installed (see Figure A.4) with a diameter, d ,
large enough to ensure that this condition is met.
Figure A.4 a) shows, by way of example, the shape of a loading pad for compressive force transducers having
a convex area of force introduction; its height, h , should be equal to or greater than d /2.
The height, h , and diameter, d , of all loading pads should, however, be adapted to the force introduction
8 10
components in such a way that the loading pad can be located both centrally and without lateral contact to the
force introduction component. The diameter, d , should therefore be 0,1 mm to 0,2 mm greater than the
diameter of the force introduction component.
Figure A.4 b) shows, by way of example, the shape of a loading pad for compressive force transducers having
a flat area of force introduction. The diameter, d , should be greater than or equal to the diameter of the force
introduction component.
ISO 376:2011(E)
Dimensions in millimetres
a)  Loading pad designed so as to reduce surface pressure for force transducers
having a convex area of force introduction

b)  Loading pad designed so as to reduce surface pressure for force transducers
having a flat area of force introduction
Figure A.4 — Loading pads
16 © ISO 2011 – All rights reserved

ISO 376:2011(E)
Table A.4 — Dimensions of intermediate rings
Maximum Maximum d d d d d h h h h
4 5 6 7 8 3 4 5 6
Type of
(nominal) force of force of
intermediate
materials testing force-proving H7 c11
ring
a
machine instrument mm mm mm mm mm mm mm mm mm
+ 0,025 −0,130
60 kN 40 kN A 24 — — 5 10 — —
35 45
−0,290
+ 0,025
40 kN A 35 24 — — 7 15 — —
−0,130
100 kN 50
−0,290
+ 0,025
60 kN A 29 — — 7 15 — —
+ 0,025
40 kN B 24 36 46 5 34 22 12
−0,140
+ 0,025
200 kN
60 kN A 45 29 64 — — 7 15 — —
−0,330
+ 0,025
100 kN A 34 — — 7 15 — —
+ 0,025
40 kN B 24 36 61 5 57 42 12
+ 0,025
60 kN B 29 46 61 7 57 42 12
400 kN and
−0,170
−0,390
600 kN
+ 0,025
100 kN B 50 34 51 61 7 57 42 15
+ 0,030
200 kN A 47 — — 12 20 — —
+ 0,025
60 kN B 29 46 77 7 60 45 15
+ 0,025
100 kN B 34 51 77 7 60 45 15
−0,180
1 MN 120
−0,400
+ 0,030
200 kN B 64 47 65 77 12 60 45 15
400 kN and
+ 0,035
A 65 — — 18 32 — —
600 kN
+ 0,030
200 kN B 47 67 103 12 87 60 15
400 kN and
−0,230
+ 0,035
2 MN A 65 165 — — 18 48 — —
−0,480
600 kN
+ 0,035
1 MN A 120 78 — — 25 50 — —
400 kN and
+ 0,035
B 90 65 92 158 18 130 95 35
600 kN
−0,280
+ 0,035
4 MN
1 MN B 78 122 158 25 130 95 45
120 −0,570
+ 0,040
2 MN A 105 — — 27 62 — —
400 kN and
+ 0,035
B 65 92 173 18 155 115 35
600 kN
+ 0,035
1 MN B 78 122 173 25 155 11545
−0,300
6 MN 270
−0,620
+ 0,040
2 MN A 105 — — 27 77 — —
+ 0,046
4 MN A 160 — — 35 60 — —
+ 0,035
1 MN B 120 78 122 223 25 200 15040
+ 0,040
2 MN B 165 105 167 223 27 200 15060
−0,360
10 MN
−0,720
+ 0,046
4 MN A 160 — — 35 90 — —
+ 0,052
6 MN A 185 — — 40 75 — —
a
Tensile testing machines for nominal forces greater than 10 MN are special versions for which any necessary intermediate rings
should be made by arrangement.
ISO 376:2011(E)
Annex B
(informative)
Additional information
B.1 Overloading test
The force-proving instrument is subjected, four times in succession, to an overload that should exceed the
maximum force by a minimum of 8 % and a maximum of 12 %. Overloading is maintained for a period of 60 s
to 90 s.
At least one overloading test should be done by the manufacturer before the instrument is released for
calibration or service.
B.2 Example of a method of verifying that there is no interaction between the force
transducer of an instrument used in compression and its support on the calibration
machine
The force-proving instrument is loaded by means of intermediate bearing pads having a cylindrical shape and
plane, convex and concave surfaces and which are in contact with the base of the device.
The concave and convex surfaces are considered as representing the limits of the absence of flatness and of
variations in hardness of the bearing pads on which the instrument could be used when in operation.
The intermediate bearing pads are made of steel having a hardness between 400 HV 30 and 650 HV 30. The
convexity and concavity of the surfaces are 1,0 ± 0,1 in 1 000 of the radius [(0,1 ± 0,01) % of the radius].
If a force-proving instrument is submitted for calibration with associated loading pads that will subsequently
always be used with that force-proving instrument, the test device is considered to be a combination of the
force-proving instrument plus the associated loading pads. This combination is loaded in turn through the
plane and convex and concave bearing pads.
Two test forces are applied to the force-proving instrument, the first being the maximum force of the
instrument and the second, the minimum calibration force for which deflection of the instrument is sufficient
from the point of view of repeatability.
The tests are repeated in order to have three force applications for each of the three types of intermediate
bearing pad. For each force, the difference be
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